Dissertations / Theses on the topic 'Degradace materiálu'

The thesis deals with the use of hydrophilic mineral wool in green roof structures. In the first part of the thesis, based on current legislation, there are summarized relevant technical properties of the hydrophilic wool. Specific demands on the green roof parts were classified and the work was consequently updated by the research of available products from the national market. A large part of the thesis consists of the extended documentation of technical properties of new products and also the changes that are associated with ageing after the material incorporation into the structure. Not only the laboratory properties of the material itself, but also properties of the material embedded in green roof structure were measured, for example an acoustic capabilities. Water accumulation properties of the mineral wool were documented on the real roof models too. Various impacts were observed by using mineral wool in comparison with substrate assemblies. Additional experiments were applied on using different types of mineral wool for an assessment of specific green roof vegetation adaptation. The environmental product declarations for each mineral wool product were calculated with the specific software using LCA methodology. In this way, the environmental impacts of mineral wool could be compared with other materials, such as artificial substrates, foils, etc. As a conclusion of the research results were summarized and reported demands for the hydrophilic mineral wool use in the green roof structures.

This diploma thesis deals with the influence of long term thermal load on the stability of high-viscous resins used for dental composites matrix. The process of polymerization was also investigated in connection with type and ratio of monomer units, mass content of the initiator system and the presence of nanosilica filler. Prepared resins were characterized by differential compensation photocalorimetry (DPC) and dynamic mechanical analysis (DMA). The dependence of the heat flow on time was measured by DPC. Based on the experimental data, the dependence of conversion on time and the dependence of polymerization rate on conversion were determined. Viscoelastic properties of the cured resins were determined by DMA. Experimentally measured data implies that by the influence of elevated temperature both the degree of conversion and the polymerization rate decreased. With a higher content of the initiator system incorporated in resin the decrease was more significant. Therefore, we can conclude that when the resin was exposed to the elevated temperature one of the components of the initiator system was inactivated. For the photopolymerized resins presence of two glass transition temperatures is typical due to the inhomogenous morphology of the cured resin. There are two types of domains with varying relative composition. However, after the degradation only one glass transition temperature was detected. That was caused by reducing the resin viscosity due to the increased temperature. Higher mobility of the initiator system molecules and monomers itself resulted in more homogenous structure of the cured resin. In case of elevated temperature exposed resins more significant decrease of the elastic modulus was observed. The curing process is considerably influenced by the type and ratio of the monomer units and by the presence of filler.

The work is devoted to the influence of dust particles on the operation of rotating machines with sliding contact. In the work are described and characterized dust particles from environment of selected machines. Their influence on sliding contact and influence on the insulation system of these machines is investigated.

Yttria-stabilized zirconia-based thermal barrier coating systems are the most widely used commercial coatings in the industry, with practical applications in aircraft engines and land-based power turbines. The purpose of thermal barriers is primarily to protect the substrate from high temperatures and also to increase its oxidation resistance. Currently, concerning the relatively frequent volcanic eruptions and increasing air traffic intensity in desert areas, increased attention is being paid to the development of new thermal and environmental coatings that will withstand the so-called CMAS attack and still successfully meeting the strictest requirements of the aerospace industry. Two newly developed experimental coatings consisting of three successive layers have been developed for this work. The upper two layers are thermal insulating ceramic coatings, where two different uppermost coatings were deposited. The first uppermost layer of the coating is a mixture of mullite and hexacelsian in a ratio of 70/30 wt. %. The second upper most type of coating consists of Al6Si2O13 + MgAl2O4 + BaCO3 in a ratio of 6:3:1 wt. %. The interlayer is made of the commercially utilized yttria-stabilized zirconia. The metallic CoNiCrAlY coating, which is directly deposited on the nickel-based superalloy MAR-M247, fulfils a compensatory function between the mechanical properties of the nickel superalloy and the ceramic coating. The thermal and environmental barrier system was deposited using air plasma spraying (APS) technology. The main objective of this work was to evaluate the effect of the newly developed thermal and environmental barrier coating, which has a high potential for the protection of component surfaces in an aggressive environment, on isothermical and thermomechanical fatigue behaviour of nickel-based superalloy MAR-M247. Low cycle fatigue tests were performed in strain control mode with constant strain amplitude on both uncoated and TEBC coated superalloy. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves in the representation of total strain amplitude, plastic strain amplitude and stress amplitude on the number of cycles to failure were obtained. Microstructural analysis of MAR-M247 superalloy and a newly developed experimental coating was performed in a scanning electron microscope. The fatigue crack initiation sites were identified and the process of fatigue crack propagation was described. The dislocation arrangement after fatigue loading of MAR-M247 was investigated in a transmission electron microscope. The findings of isothermical and thermomechanical low cycle fatigue behaviour of uncoated and TEBC coated MAR-M247 superalloy and identification of damage mechanisms presented in this dissertation will improve the estimation of safe-life that is particularly relevant to aircraft engines components.

Diplomová práce se zabývá vlivem nutričních a aeračních faktorů na produkci lipáz bakterií Bacillus subtilis (CCM 1999). Produkce lipáz byla studována zejména z hlediska katalytického působení lipáz při degradaci polyesterových řetězců. Mezi studované parametry patřily: růst bakterií, lipolytická aktivita, pH optimum, teplotní optimum, tepelná stabilita, proteolytická aktivita, množství bílkovin, atd. a to v různých typech živných medií zaočkovaných Bacillus subtilis. Jedna série vzorků kultivačních médií pro BS na bázi: pepton a kvasničný extrakt (NB), pepton, kvasničný extrakt s 2% přídavkem (w/v) glukózy (NBG) a minerální médium s kvasničným extraktem (MS-YE) obsahovala jeden PCL vzorek o definovaných rozměrech (Mn = 10 kDa, = 1.4). Experimenty probíhaly po dobu 21 dnů pří rychlosti třepání 160 a 200 rpm. Přítomnost PCL způsobila v obou typech médií (NB, NBG) inokulovaných BS zvýšení lipolytické aktivity, což naznačuje, uvolnění a následné uplatnění se nízko-molekulekulárních řetězců PCL jako substrátů pro BS. BS kultivovaný v MS-YE medium vykazoval ve srovnání s NB a NBG médii nízké hodnoty lipolytické aktivity a to i v přítomnost PCL. Během experimentů se hodnota pH posunula z neutrální (pH 7.0) do alkalické (pH 8.5-9.3) oblasti a to ve všech typech médií s i bez přítomnosti PCL vzorku v důsledku metabolických pochodů BS využívajících různé substráty. Lipolytické enzymy stanovené v supernatanech bez bakteriálních buněk vykazují dvě pH optima v přítomnosti PCL, pH 7 a 9. V nepřítomnosti polymeru vykazují pouze jedno pH optimum při pH 7. Na základě měření tepelné stability bylo prokázáno, že extracelulární lipázy jsou relativně termostabilní enzymy, zejména v nepřítomnosti polymeru. Dále byla provedena základní proteomická analýza lipáz produkovaných bakterií Bacillus subtilis v NBG médiu pomocí metody peptidového mapování (PMF). Byla ověřena přítomnost proteinů s molární hmotnosti (19.3 kDa) pomocí FPLC. SDS-PAGE a IEF-PAGE prokázaly přítomnost těchto proteinů v obou studovaných mediích inokulovaných BS (NBG vs. NBG/PCL). Zásadní rozdíly proteinového složení v přítomnosti PCL nebyly potvrzeny a identifikace pomoci MALDI-TOF hmotnostní spektrometrie nestanovila žádnou lipázu. Proces degradace v PCL vzorcích byl vyhodnocen také na základě hmotnostních úbytků, které byly zjištěny ve všech typech médií inokulovaných BS pravděpodobně v důsledku synergického účinku enzymaticky-katalyzované a biotické hydrolýzy v alkalickém prostředí. . Modelová degradační studie PCL a jeho kompozitu s oxidem grafenu (2.7 hm.%, GO) byla provedena v přítomnosti bakterie Bacillus subtilis v NBG při 30 °C a počátečním pH 7 po dobu tří týdnů. Hmotností úbytky PCL filmů se postupně zvyšovaly během celého degradačního testu až ke 12 hm%. Degradace PLC/GO kompozitu probíhala pomaleji, což je prokázáno maximální hmotnostním úbytkem 5 hm%. Podobný charakter elučních křivek PCL a jeho kompozitu stanovený pomocí SEC potvrzoval snížení molární hmotnosti po degradaci.

Biodegradable metallic materials for medical applications have received considerable attention in recent years. The main reason is that they provide high potential for fabrication of temporal orthopedic implants such as bone fixation devices. Magnesium is an excellent candidate for fabrication of biodegradable implants due to its biocompatibility, mechanical properties similar to human bone and relevance for biological body functions. The fast degradation rate of magnesium and its biodegradable alloys in physiological environment limits its clinical application. Another attractive material in the field of biodegradable materials is zinc, which is among the essential elements in human body. Zinc exhibits an excellent corrosion resistance, and inferior biocompatibility compared to with magnesium. Hence, surface modification to form a hard, dense/porous, biocompatible and corrosion resistant modified layer has become an interesting topic in magnesium base biomaterials. Since hydroxyapatite is well tolerated by living organisms and in addition, improves the bone growth, it appears to be excellent candidate for such coatings on surface of biodegradable materials (e.g. Mg, Zn). This thesis is focused on comparison of corrosion behavior of pure non ferrous metals (Mg, Zn) and metals coated with hydroxyapatite, in simulated body fluids. The present approach is the use of modified atmospheric plasma spray technology to produce the hydroxyapatite coatings – suspension spraying. Composition and structure of the coatings and corrosion products were studied by light microscopy, scanning electron microscopy equipped with energy dispersive microanalyzer and X-ray diffraction. Corrosion of Mg and Zn samples was monitored by weight loss and determined by X ray and micro-tomography. The application of the HA coating resulted in decrease of corrosion rate of pure Mg. The corrosion rate of coated Mg samples was lower by 27,3 % in comparison with the corrosion rate of pure non coated Mg. Corrosion degradation of uncoated and coated Zn samples was minimal. The aplication of HA on the non ferrous surface appears to be a very promising method to improve corrosion and biological properties of these biodegradable materials.

This master’s thesis is focused on the study of chemical and physical properties of dielectric materials with main focus on epoxy resins. It includes possible processes that can influence the properties of epoxy resins, both processes that improve polymer properties and processes that cause material degradation. Next part of the thesis is a description of diagnostic methods suitable for measurement of basic electrical quantities of material and design of a suitable method for measuring properties of epoxy resins with different additives, influencing the samples by solar radiation. At the end, the work includes an experiment dedicated to the degradation of epoxy resins with various additives by solar radiation and the evaluation of the experiment.

The plant cell wall consists of several layers: cellulose, hemicellulose, lignin and pectin. These biopolymers are degraded by many microorganisms. Extracellular enzymes are used for biodegradation by microorganisms. This thesis was focused on studying the impact of cultivation conditions on the production of extracellular enzymes at carboxymethyl cellulase and pectin when a mixed thermophilic culture containing Bacillus and Thermus microorganisms is used. The cultivation was carried out in flasks on a shaking machine with a shaking speed of 99 min-1 at a temperature of 60°C. The monitoring covered cellulolytic and polygalacturonase activities, protein concentration by the Biuret method, concentration of reducing substances by the Somogyi and Nelson methods, and the temperature optimum.

Nedbrytbara metaller utgör en ny klass av biomaterial med potential attersätta permanenta material i tillfälliga applikationer. Detta för att minskarisken för långvariga biverkningar. I den pågående forskningen för att utvecklanya nedbrytbara metaller är screening av nya material genom in vitro testmetoderett attraktivt alternativ för att undvika onödiga, tidskrävande ochdyrbara djurstudier.Denna avhandling fokuserar på in vitro-testning av zink- och magnesiumbaserademetaller. Inverkan av faktorer såsom sammansättningen av testlösningen,buffersystemet, belastning samt mikrostruktur hos legeringar undersöktes.Genom att använda elektrokemiska in situ tekniker såsom impedansspektroskopi(EIS) är det möjligt att studera gränssnittet mellan metall ochlösning och karakterisera egenskaperna hos den korroderande ytan. Ex situytkaraktäriseringstekniker som svepelektronmikroskopi och infraröd spektroskopianvändes sedan för att komplettera resultaten av de elektrokemiskamätningarna.Korrosionen av zink i Ringer’s lösning fanns vara närmare in vivo korrosionän korrosionen i fosfatbuffrad saltlösning (PBS). Ringers lösning är därför denföredragna testmiljön för långsiktig utvärdering av zinkbaserade metallerDet biologiska buffersystemet (CO2/H2CO3) bör företrädesvis användasför att stabilisera pH-värdet på testlösningen vid magnesiumnedbrytning. NärHEPES användes för att stabilisera pH ökade korrosionshastigheten på grundav bildning av mindre skyddande skikt av korrosionsproduktMöjligheten att använda helblod och plasma som mer kliniskt relevantatestmiljöer utvärderades och befanns producera reproducerbara resultat.Bildning av ett korrosionsskikt bestående av både organiskt och oorganisktmaterial detekterades på zink i både plasma och helblod.När zink prover i helbod utsattes för belastning förhindrade korrosionsskiktetbildningen av mikrosprickor och förtidigt brott av provet. Det varvidare möjligt att detektera tidig sprickbildning på grund av belastning avMagnesium AZ61-legering med EIS.Adsorption av organiska species på zinkytan under anodisk polariseringökar yttäckningen av Zn-joner i helblod. Den ökade yttäckningen leder sedantill utfällningen av ett skyddande skikt av zinkfosfater och en minskadkorrosionshastighet vid högre potentialer.Korrosion av Zn-Mg och Zn-Ag legeringar i Ringers lösning befanns skevia selektiv upplösning. Lokal utfällning av korrosionsprodukter och bildningav ett poröst, mindre skyddande skikt av korrosionsprodukter hittades påZn-Mg legeringar. Den selektiva upplösningen av Zn-Ag legering orsakade enanrikning av AgZn3 vilket kan påverka biokompatibiliteten av ett implantatmed tiden.<br>Degradable metallic implants are a new class of biomaterials with potentialto replace permanent materials in temporary applications to reduce therisk of long term adverse effects.This thesis focuses on in vitro testing of zinc and magnesium based metals.As new degradable metals are developed screening of new materials within vitro test methods is an attractive option to avoid unnecessary, time consumingand expensive animal studies. The influence of factors such as ioniccomposition of the test solution, buffer system, strain and alloy compositionwas investigated. By employing electrochemical in situ techniques such asimpedance spectroscopy it is possible to study the metal-solution interfaceand determine the properties of the corroding surface. Ex situ surface characterizationtechniques such as scanning electron microscopy and infraredspectroscopy were then used to complement the results of the electrochemicalmeasurements.The importance of appropriate selection of the test solution is highlightedin this work. Zinc was found to corrode in Ringer’s solution by a mechanismcloser to in vivo corrosion than in a phosphate buffered saline solution(PBS).Ringer’s solution is therefore the more appropriate test environment for longterm evaluation of zinc based metals.When evaluating the corrosion of Zn-Mg and Zn-Ag alloys in Ringer’ssolution selective dissolution was found to occur for both types of alloys. Localprecipitation and formation of a porous, less protective, layer of corrosionproducts was found for Zn-Mg alloys. The selective dissolution of Zn-Agalloy caused an enrichment of AgZn3 on the surface which may affect thebiocompatibility of the alloy.The use of HEPES to maintain the pH of the test solution increasedthe corrosion rate of magnesium due to formation of a less protective layerof corrosion products. Magnesium corrosion should therefore preferably bestudied in solutions where the pH is maintained by the biological buffer systemCO2/H2CO3.In addition to saline solutions human whole blood and plasma were evaluatedas more clinically relevant in vitro environments. They were found toproduce reproducible results and to be suitable for short term experiments.Formation of a corrosion product layer comprised of both organic and inorganicmaterial was detected on zinc in both plasma and whole blood.During anodic polarization the adsorption of organic species on the zincsurface was found to increase the surface coverage of Zn ions in whole blood.The increased surface coverage then allowed for precipitation of a protectivelayer of Zn5(PO4)3 and a subsequent decrease in corrosion rate at higherpotentials.When subjecting zinc samples to strain the organic/inorganic corrosionproduct formed in whole blood was observed by impedance spectroscopy toprevent micro cracking and premature failure.The cracking of magnesium alloy samples under applied strain was alsocharacterized by impedance. Changes in surface properties due to crack initiation<br><p>QC 20171019</p>

Target of this thesis is analyse problems of dielectric materials ageing and environment characteristic applied by ageing process. Types of electric stress are comparing in this work, when and how they are working and how to eleminate them. Next aim is design the high voltage sinus transformer as source for measuring of electric stress and ageing dielectric materials. There is discuss about computer control and collecting of the output datas. In the end is source testing by practical measurement of some dielectric samples.

The field of Tissue Engineering has developed in response to the shortcomings associated to the replacement of tissues lost to disease or trauma: donor tissue rejection, chronic inflammation, and donor tissue shortages. The driving force behind Tissue Engineering is to avoid these problems by creating biological substitutes capable of replacing the damaged tissue. This is done by combining scaffolds, cells and signals in order to create living, physiological, three-dimensional tissues.<br/>Scaffolds are porous biodegradable structures that are meant to be colonised by cells and degrade in time with tissue generation. Scaffold design and development is mainly an engineering challenge, and is the goal of this PhD thesis.<br/>The main aim of this thesis is to develop and characterise scaffolds for Tissue Engineering applications. Specifically, its objectives are: <br/>1. To study, optimise and characterise two scaffold processing methods: Solvent Casting and Phase Separation. This is done by experiment design analysis. <br/>2. To characterise the degradation, surface properties, and cellular behaviour of the scaffolds produced. <br/>The scaffolds are made of a composite of polylactic acid polymer and a calcium phosphate soluble glass. The comparison of the two processing methods reveals that in general, the solvent cast scaffolds have higher porosities and lower mechanical properties than the phase-separated ones. Two compositions containing 20 weight % and 50 weight % of glass particles were chosen for further characterisations including degradation, surface properties and cellular behaviour. <br/>The degradation of the scaffolds was studied for a period of 10 weeks. The evolution of various parameters such as: morphology, weight loss, mechanical properties, thermal transitions and porosity, was monitored. Scaffolds produced via solvent casting were found to be more severely affected by degradation than phase-separated ones. <br/>The surface properties of the scaffolds were measured by modelling the scaffold pore walls as thin composite films. The morphology, topography, surface energy and protein adsorption of the films was characterised thoroughly. Again, the processing method was critical in determining scaffold properties. Films made via phase-separation processing had markedly different properties due to extensive coating of the glass particles by the polymer. This made the surfaces rougher and more hydrophobic. When the glass particles are not completely coated with polymer, they increase the material's hydrophilic and protein adsorption properties, thus confirming the potential biological benefits of the inclusion of the calcium phosphate glass.<br/>The biological behaviour of the scaffolds was characterised by means of in vitro cell cultures with primary osteoblast stem cells and cells from a stable cell line, under static and dynamic conditions. Their morphology, proliferation and differentiation were monitored. Both types of scaffolds sustained osteblastic cell growth. The solvent cast scaffolds were easily colonised by cells which migrated throughout their structure. The cells on the phase-separated scaffolds, however, tended to form thick layers on the scaffold surface. <br/>Finally, an alternative characterisation technique was explored applying Synchrotron X-Ray Microtomography and in-situ micromechanical testing. These experiments allowed for the qualitative and quantitative analysis of the microstructure of the scaffolds both at rest and under strain. A finite element model of the solvent cast scaffolds was developed and a preliminary analysis was performed. This technique could be used to complement and overcome some of the limitations of traditional mechanical characterisation of these highly porous materials.

The aim of this project was to develop injectable materials to repair damaged bone and, to simultaneously release antibacterial drugs and genes in a controllable manner. Fluid poly (propylene glycol -co- lactide) dimethacrylate (PGLA-DMA) was first synthesised and then filled with varying levels of β- tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM) to fabricate composite materials. For all formulations (including polymer and composites), full methacrylate conversion was found to occur within 200 s of exposure to blue light. The initial dry polymer modulus was enhanced three-fold by increasing total filler content to 70%. After composite immersion in water, β-TCP and MCPM was found to react and re-precipitate within the set materials as dicalcium phosphate (DCP, i.e. brushite and monetite). At higher MCPM levels there was an increase in DCP formation, composite degradation rate, release of both calcium and phosphate ions and buffering of acidic polymer degradation products. Additionally, bone-like MG-63 cells were found to attach, spread and proliferate on both the polymer and the composite surfaces and, composites implanted into chick embryo femurs demonstrated close apposition to the host tissue. To examine the potential value for drug delivery, both the polymer and the composites were prepared containing 10% of the antibacterial chlorhexidine (CHX). The drug was found to be released from material via diffusion, which increased along with antibacterial activity when the filler content was raised. PGLA-DMA polymer was additionally prepared containing complexes of the commercial cationic lipid MetafecteneTM Pro and green fluorescent protein plasmid DNA. Initial studies demonstrated that the components released from the materials were capable of gene transfection into human bone-forming mesenchymal stem cells in vitro. These studies thus demonstrate that the injectable, rapidly settable PGLADMA materials produced here might have clinical potential as both bone adhesives and drug delivery devices.

Bioengineering<br>Ph.D.<br>Current degradable orthopedic fixation devices do not typically facilitate tissue integration during healing. Proposed here is a novel combination of processing methods to enhance the tissue integration capability of degradable thermoplastics used in temporary orthopedic fixation devices. The provision of open pores in devices used to affix reconstructed hard tissues would allow for local cells to infiltrate during the healing process. Any openly porous structure is inherently weakened in comparison to its monolithic peers (i.e. decreased relative bulk modulus), such that the matrix materials must be made more resilient in keep the device from becoming friable. These processing methods aim to improve degradable surgical fixation devices at multiple levels of design: both through the inclusion of porous morphology, processing changes, and additives to regain mechanical integrity. Biomimetic pores are added for cellular infiltration by dissolving a porogen’s interpenetrating polymer network. The addition of open pores significantly reduces the bulk stiffness. More uniform phase separation has led to better pores, but the objects still need more resilience. Carbon nanomaterials are used to improve on the mechanics and surface chemistry of the polymer matrix material, composites of polylactide/nanodiamond are produced through cryogenic milling and solid state polycondensation. The addition of minute amounts of functionalized nanodiamond has remedied the brittle failure of the material, by cryogenic milling and solid state polycondensation of poly((D,L)lactide-co-glycolide) and hydroxyl functionalized detonation nanodiamonds. This composite has also demonstrated increased cytocompatability with 7F2 osteoblasts, as analyzed by cellular adhesion through fluorescence microscopy and alamar blue assay.<br>Temple University--Theses

The research carried out in this thesis focusses on the development of novel functional and degradable materials for use in Microstereolithography (μSL), a type of additive manufacturing (AM) technology. Chapter 1 provides a background into the μSL technology with regards to key developments and the current state-of -the-art for the μSL apparatus itself in addition to providing an overview of the various types of commercially or non-commercially available materials currently developed for μSL. Chapter 2 describes the current state-of-the-art in terms of four-dimensional (4D) printing materials used within the μSL technology and subsequently focusses on expanding the limited scope of materials currently developed. The previously described poly(ethylene glycol) di-ortho-nitrobenzyl (PEG-oNB) ester molecule is successfully synthesised. Upon optimisation of a PEG-oNB containing resin, the material was found to be capable of solidifying to a defined two dimensional (2D) shape utilising one wavelength of light in the μSL apparatus and subsequently able to undergo photodegradation upon controlled exposure by a secondary wavelength of light thereby exemplifying a fourth dimension. In chapter 3, a library of previously described and novel malate based monomers with various functionality are synthesised and subsequently polymerised by step-growth polymerisation either in bulk or in solution to form short chain homopolymers. Copolymerisations carried out in bulk are shown to form polymers with the desired alkene bearing functionality required for cross-linking via radical thiol-ene coupling and the Poly(EtMa-co-BuMa) copolymer is successfully functionalised using dodecanethiol demonstrating its potential for use as a material within μSL. Chapter 4 describes the successful application of Poly(EtMa-co-BuMa), as synthesised in chapter 3, within a novel resin composition, containing dibutenyl succinate (DBS) as reactive diluent, that is capable of printing complex 3D architectures within the μSL process. The materials produced demonstrate exemplar degradation via the surface erosion mechanism and consequently exhibit near-zero order release kinetics upon encapsulation of a model small molecule. Furthermore, small alterations of the resin composition allowed for the rate of degradation and release to be tuned whilst applying multiple materials within the same device allows for controlled, temporal release. Chapter 5 concludes the most significant findings of Chapters 2-4 whilst Chapter 6 lists all the experimental protocols and methods used in this thesis.

The first part of the master’s thesis deals with sandwich materials. Starting with composition of parts which the sandwich panel is made of. The thesis continues with loading distribution and testing of entire sandwich panel. The impact of environment is considered as well. The second part is its goal – determine degradation of the properties of sandwich panels with metal sheets and core after 15 years aging in the common atmosphere and aging in moistheat and salt environment by experiment.

This document includes methods of testing and measuring of the protective layers used in solar panels with crystallic solar cells. The main emphasis here is placed on the degradation of these materials due to exposure to strong electric field. Main point of diploma thesis is evovle an experimental workplace for electric aging of dielectric materials and monitor changes of material properties. Final knowledges are then analysed with the climate degradation tests. Tested samples were prepared in cooperation with Solartec s.r.o.

Leather is a natural material that can be used in different environments and often under aggressive environmental conditions that may cause premature ageing. Since upholstery leather is considered a very high-tech product, a long service life is expected by the costumer. According to different studies carried out on historical/ancient leathers by leather conservation centers and museums, leather also is strongly affected by these three main environmental parameters: temperature, relative humidity, and UV radiation. The aim of this work is to study the effect of the environment exposure, to identify the most important variables affecting this weathering process and to check for interactions among the three factors on the degradation and leather ageing on wet-blue and wet-white upholstery leather, applying the leather to natural weathering, tropical environmental exposure and finally a combination of the three critical factors. The tests were carried out on Spanish pickled cattle hides. Two types of tanned leather were tested: on the one hand, chrome tanned leather and on the other hand, wet-white tanned leather using tetrakishydroxymethylphosphonium sulphate (THPS) and silicate-phenolic synthetic and retanned with protein-amide polymer. Both types of leathers were finished using common industrial formulation. Firstly, the work was undertaken to better understand the effect of degradation of chrome tanned leather and wet-white leather and the physical and chemical processes occurring during long-term exposure to outdoor conditions. The samples were tested before and after 20, 40, 80, 120 and 180 days of exposure. Increasing the levels of the three critical weathering variables, the leathers were exposed to tropical environment using a climatic chamber at 70ºC and 95% relative humidity during 7, 14 and 21 days. Additionally half of the leathers were exposed to UV radiation for 4 days. Finally, the leathers were exposed to accelerating ageing test using a multilevel centralized factorial experimental design and an analysis of variance (ANOVA) with 3 variables and 2 levels (23). The evaluation of the leathers was carried out with physical, fastness, chemical and organoleptic properties of the leathers. With the natural weathering studies, wet-white leather and chrome-tanned leather show a different behavior to leather ageing. The loss in properties in chrome-tanned leather increases steadily until 40 days exposure, and after this point the leather stabilizes and no longer degrades. In wet-white leather, however, there is a progressive loss in properties but stabilization does not occur until a period of exposure of 80-120 days. Tropical environmental exposure causes physical and chemical degradation of both types of tanned leather. In chrome-tanned leather, the loss of all properties occurs progressively over time, in wet-white leather it occurs only after 7 days exposure, and is followed by carbonization of the leathers after 14 days exposure. Additionally, when wet-white samples are exposed for long periods at high relative humidity are attacked by fungi. Resistance and dimensional stability of wet-white leather both in accelerated ageing tests and natural weathering exposure is higher than that of chrome-tanned leather. However, these leathers have the disadvantage of not resisting simultaneous exposure to high temperatures and high relative humidity, that's to say, tropical environmental conditions. Results from experimental designs prove again that chrome-tanned leather and wet-white leather have a different ageing behavior. Whereas chrome-tanned leathers are strongly affected by UV radiation, wet-white leathers are strongly affected by relative humidity. Additionally, no correlation has been found between ageing caused by natural weathering and that caused under controlled conditions in the laboratory.<br>La pell és un material natural que pot ser utilitzat en diferents ambients i molt sovint pot ser sotmès a condicions ambientals agressives provocant el seu envelliment prematur. Segons diferents estudis portats a terme en pells històriques procedents de centres de conservació de la pell i museus, la pell es veu afectada pels tres paràmetres ambientals principals: temperatura, humitat relativa i radiació UV. L’objectiu d’aquest treball és estudiar l’efecte de l’exposició ambiental, identificar les variables més importants que afecten al procés d’envelliment i buscar les interaccions entre els tres factors, en la degradació i envelliment de la pell adobada al crom i pell adobada wet-white per tapisseria, sotmetent la pell a exposició directa a la intempèrie, exposició a ambient tropical artificial i finalment a una combinació dels tres factors crítics. Els assajos es porten a terme amb pell vacuna piquelada, es preparen dos tipus de pell: pell adobada al crom, i pell adobada wer-white utilitzant sulfat de tetrakishidroximetilfosfoni (THPS) i sintètic silicat-fenòlic readobat amb polímer de proteína-amida. Les pells s’acaben utilitzant una formulació industrial estàndard. Inicialment el treball pretén entendre millor l’efecte de la degradació de la pell adobada al crom i pell adobada wet-white, i els processos físics i químics que ocorren durant una exposició prolongada a les condicions ambientals exteriors. Les mostres s’analitzen abans i després de 20, 40, 80, 120 i 180 dies d’exposició. Incrementant els nivells de les tres variables crítiques d’envelliment, les pells s’exposen a un ambient tropical utilitzant una cambra climàtica a 70ºC i 95% d’humitat relativa durant 7, 14 i 21 dies d’exposició. Addicionalment la meitat de les pells s’exposen a radiació UV durant 4 dies. Finalment, les pells s’exposen a un test d’envelliment accelerat utilitzant un disseny experimental factorial centralitzat, com a eina estadística per estimar els efectes dels paràmetres es treballa amb un anàlisis de variància (ANOVA) amb 3 variables i 2 nivells cadascun. L’avaluació de les pell es porta a terme a través de l’anàlisi de propietats físiques, químiques i organolèptiques de les pells. En els estudis d’exposició natural les pells adobades al crom i les pells adobades wet-white mostren un comportament diferent a l’envelliment. Mentre que per la pell adobada al crom la pèrdua de propietats físiques es produeix als 40 dies d’exposició i després d’aquest punt la pell s’estabilitza i no es degrada més, en el cas de la pell adobada wet-white es produeix una pèrdua progressiva de les propietats però l’estabilització no es produeix fins als 80-120 dies. L’exposició a un ambient tropical artificial causa una degradació física i química en els dos tipus de pells. En la pell adobada al crom, la pèrdua de propietats ocorre progressivament en el temps, mentre que en la pell adobada wet-white això només succeeix després de 7 dies d’exposició, seguit d’una carbonització després de 14 dies d’exposició. A més, quan la pell adobada wet-white s’exposa a períodes llargs d’humitat relativa alta és atacada per fongs. La resistència i l’estabilitat dimensional de la pell adobada wet-white, tant en l’assaig d’envelliment accelerat com en l’exposició ambiental natural, és molt superior a la de la pell adobada al crom. Tanmateix, aquesta pell té la desavantatge de no resistir simultàniament l’exposició a elevada temperatura i elevada humitat relativa, condicions de l’ambient tropical. Els resultats dels dissenys experimentals demostren una altra vegada que la pell adobada al crom i la pell adobada wet-white tenen un comportament a l’envelliment molt diferent. Mentre que la pell adobada al crom es veu molt afectada per la radiació UV, la pell adobada wet-white està afecta per la humitat relativa. Addicionalment, no es troba cap correlació entre l’envelliment causat per exposició ambiental natural i el causat sota condicions controlades al laboratori.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 111-131).<br>Degradable polymeric materials provide opportunities for the development of improved vaccines and immunotherapies by acting as platforms that facilitate the delivery of molecules to appropriate tissue and cellular locations to achieve therapeutic outcomes. To this end, we have designed and characterized nano-films and particles employing a hydrolytically degradable polymer for the delivery of vaccine antigens and immunotherapeutics. We first describe protein- and oligonucleotide-loaded layer-by-layer (LbL)-assembled multilayer thin films constructed based on electrostatic interactions between a cationic poly(p-amino ester) (PBAE, denoted Poly-1) with a model protein antigen, ovalbumin (OVA), and/or immunostimulatory CpG oligonucleotides for transcutaneous delivery. Linear growth of nanoscale Poly-1/OVA bilayers was observed. Dried OVA protein-loaded films rapidly deconstructed when rehydrated in saline solutions, releasing OVA as non-aggregated/non-degraded protein, suggesting that the structure of biomolecules integrated into these multilayer films are preserved during release. Using confocal fluorescence microscopy and an in vivo murine ear skin model, we demonstrated delivery of OVA from LbL films into barrier-disrupted skin, uptake of the protein by skin-resident antigen-presenting cells (Langerhans cells), and transport of the antigen to the skin-draining lymph nodes. Dual incorporation of OVA and CpG oligonucleotides into the nanolayers of LbL films enabled dual release of the antigen and adjuvant with distinct kinetics for each component; OVA was rapidly released while CpG was released in a relatively sustained manner. Applied as skin patches, these films delivered OVA and CpG to Langerhans Cells in the skin. To our knowledge, this is the first demonstration of LbL films applied for the delivery of biomolecules into skin. This approach provides a new route for storage of vaccines and other immunotherapeutics in a solid-state thin film for subsequent delivery into the immunologically-rich milieu of the skin. In parallel, we also developed biodegradable core-shell nanoparticles with a PBAE core enveloped by a phospholipid bilayer shell for cytosolic delivery, with a view towards delivery of messenger RNA (mRNA)-based vaccines. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. mRNA was efficiently adsorbed via electrostatic interactions onto the surface of these net positively charged nanoparticles. In vitro, mRNA-loaded particle uptake by dendritic cells led to mRNA delivery into the cytosol with low cytotoxicity, followed by translation of the encoded protein in these difficult-to-transfect cells at a frequency of -30%. Particles also promoted cytosolic uptake of co-delivered anti-tumor toxins in tumor cells resulting in synergistic killing, demonstrating potential for cancer therapy. In vivo, particles loaded with mRNA administered intranasally or intratracheally in mice led to the enhanced expression of the reporter protein luciferase compared to naked mRNA. This system may thus be promising for noninvasive delivery of mRNA-based vaccines.<br>by Xingfang Su.<br>Ph.D.

This diploma thesis deals with evaluation of the conditions for laboratory testing of composite profiles with fiber-reinforced polymer (FRP). Theoretical part describes the main material properties of FRP profiles and method of manufacturing by pultrusion. Experimental part evaluates imposition of the test samples in alkaline environment and their subsequent changes in physical properties. Next part contains evaluation of cuts FRP profiles by electron microscopy in combination with element analysis. The outcome of this work is the method of evaluation of accelerated durability FRP profiles.

This thesis deals with monitoring the durability of FRP reinforcement in different types of environments which cause degradation. The theoretical part of the thesis describes reinforcing fibers, matrix materials, manufacturing technology of composite reinforcements by pultrusion and durability of FRP materials in environmental degradation. In the experimental part of this thesis was carried storing samples reinforcements in alkaline environment with various temperatures. As suitable were selected temperatures of 20 °C, 40 °C and 60 °C. Subsequently are described changes in physical properties of the reinforcements and tracking optical microscope.

La difusión de los materiales cerámicos en muchos campos de la industria es amplia y está en fuerte expansión, debido a las excelentes propiedades de estos materiales, ya sean mecánicas, térmicas, tribológicas o biológicas. Sin embargo, su fragilidad intrínseca y falta de fiabilidad limitan una mayor difusión en esas aplicaciones donde se precisa alta resistencia estructural. La producción de composites multilaminares es un camino prometedor para aumentar la fiabilidad de los cerámicos. Los cerámicos multicapa permiten que las propiedades mecánicas sean mejores que las de los componentes, debido a la presencia en la superficie de tensiones residuales de compresión provocadas diferencias de expansión térmica entre las capas.<br/>Las aplicaciones óptimas de estos materiales son las que están relacionadas con las propiedades superficiales; por eso la respuesta a las cargas por contacto son especialmente importantes para caracterizar las propiedades mecánicas y para mejorar el diseño de cerámicos composites avanzados.<br/>Las técnicas de indentación Hertziana son herramientas muy útiles para estudiar este tipo de carga, que por otro lado es difícil de caracterizar por ensayos mecánico tradicionales. El daño por contacto en materiales frágiles aparece principalmente como grietas anillo en la superficie, que pueden desarrollarse como grietas cono, características de este tipo de carga. Este agrietamiento es perjudicial para la funcionalidad del material, y puede llevar al fallo de la pieza. Las cerámicas tenaces, por otro lado, pueden presentar un daño, cuasi-plástico, que se genera debajo la superficie en forma de microagrietamento, y que es causa de deformación inelástica.<br/>En esta tesis, se caracteriza la resistencia al daño por contacto materiales cerámicos en base alúmina, incluyendo todos los aspectos de ese daño, desde la aparición de fisuras superficiales, a la propagación de grietas frágiles en la primera capa y su influencia sobre la resistencia del material, hasta el fallo inducido por carga de contacto. Se comparan medidas experimentales con análisis a los Elementos Finitos de los parámetros involucrados en cada caso, lo que permite formular pautas para una correcta caracterización y diseño de cerámicas multicapas avanzados.<br/>Se vio que la presencia de tensiones residuales es efectiva en mejorar la resistencia a la formación de grieta anillo, sea generada por cargas monotónicas, cíclicas o estáticas.<br/>La alta resistencia frente a este último tipo de carga revela que existen mecanismos de puenteo intergranular que se oponen a la formación de grietas, lo que era inesperado por el tamaño de grano fino, y que se atribuye a un efecto de grieta corta, comparada con la microestructura. Ensayos cíclicos de larga duración mostraron, por otro lado, que en los materiales multicapas aparece daño superficial más severo que en los monolíticos, lo que sugiere un cambio del daño predominante hacía una degradación superficial producida por cuasi-plasticidad.<br/>Las tensiones residuales afectan tanto la longitud como el ángulo de la grieta cono. Se modeló el problema mediante Elementos Finitos y algoritmos de propagación de grieta, lo que permitió predecir el crecimiento de grieta en función tanto de las tensiones residuales, como de otros parámetros microestructurales, y determinar del ángulo de la grieta cono en materiales policristalinos.<br/>La respuesta a cargas remotas de materiales indentados, en otras palabras la degradación de la resistencia, se ve afectada por la geometría de la grieta cono, y por otros factores que son consecuencia de la estructura laminar, tales como las tensiones residuales y la redistribución de carga por el desajuste elástico entre capas. Asimismo, la resistencia por contacto, o sea la resistencia a compresión roma localizada, se ve mejorada en materiales laminares, como consecuencia de las tensiones residuales. Sin embargo, se evidenció que existe el riesgo de que se genere tensión elevada en las capas interiores bajo ambos tipos de carga, y se propusieron consideraciones generales sobre el diseño de materiales laminares.<br/>En definitiva, se consiguió una caracterización exhaustiva de las propiedades de contacto mecánico de los materiales estudiados, y se amplió y mejoró el conocimiento de la propagación de grieta en materiales frágiles policristalinos.<br>The use of ceramic materials in many industrial fields is spread and ever-increasing, for their excellent properties, either mechanical, thermal, tribological or biological. However, their intrinsic brittleness and lack of reliability are obstacles to further spreading these materials in applications where structural resistance is required. To build multilayered composite structures is a promising way which aims to increase the reliability of ceramics. As it is common in composite materials, layered materials allow the mechanical properties to be superior to those of the constituent materials, in the studied case due to the presence of compressive residual stress in the surface.<br/>The best applications for such materials are those related to the surface properties; for this reason the response to contact loading is especially important to characterize the mechanical properties and to assist in the design of advanced ceramic composites. Hertzian indentation techniques provide a powerful tool to study such type of loading, which is otherwise difficult to characterize with the traditional mechanical testing methodologies. <br/>Contact damage in brittle materials appears mainly as surface ring-cracks, which can develop in a characteristic cone crack. Such fissuration is detrimental to the functionality of the material, and can lead to the failure of the component. Tough ceramics often present another type of damage, the so-called quasi-plasticity, generated as subsurface microcracking and which is cause of inelastic deformation.<br/>In this thesis, alumina-based ceramic laminates were characterized in their resistance to contact damage in all its aspects, starting from the appearance of surface fissures, to the propagation of brittle cracks in the first layer and its influence on the material strength, to the contact loadinginduced failure. Experimental measurements were coupled with Finite Element analysis of the involved parameters, which assisted in formulating comprehensive guidelines for the correct characterization and the design of advanced multilayered ceramics. <br/>The presence of residual stress in ceramic laminates proved to be effective in improving the material resistance to the ring cracking, generated by monotonic, cyclic and longlasting tests.<br/>The better resistance to these latter revealed the existence of grain bridging hindering the crack formation, unexpected in fine-grained alumina and which was related to the small crack character of the ring crack. Longer lasting cyclic tests showed that more severe damage appears in the multilayered materials than in the monolithic one, suggesting a modification of the redominant damage mode to quasi-plastic-derived surface degradation.<br/>Propagation of long cone cracks is affected by residual stress in both the length and angle. An automatic Finite Element model of crack propagation allowed to predict crack growth as a function of both the extrinsic residual stresses and of microstructural parameters, which helped address the long-open question of the cone crack angle on polycrystalline materials.<br/>The response to remote loading of indented materials, in other words the strength degradation, is conditioned by the cone crack geometry, as well as by other factors deriving from the laminated structure, such as the presence of residual stress itself and the load redistribution due to the elastic mismatch between layers. Similarly, the contact strength, i.e. the resistance to local blunt compression, is improved in the composite materials as a consequence of the residual stresses. Nevertheless, the risk of high stress in the lower tensile layers was highlighted for both types of loading and general consideration on the design of laminated materials were proposed.<br/>In the overall, a comprehensive characterization of the contact properties of the studied materials was achieved, and the understanding of crack propagation on brittle polycrystalline materials was broadened and improved.

This thesis deals with monitoring of the durability of FRP reinforcements in alkaline environments with differing temperature exposures. The theoretical part of the thesis consists of a general description of the FRP composites, the manufacturing of these FRP reinforcements using pultrusion technology, the resistance of these composites in aggressive alkaline environments, and the influence of temperature on the speed and manner of degradation. In the experimental part of this thesis, the FRP reinforcements were placed in an alkaline environment tempered at different temperatures (20 °C, 40 °C, 60 °C). Subsequently, any optical physical changes of the reinforcements were described and evaluated by the use of optical microscopy and the destructive tests of these reinforcements.

Over 600,000 bone-grafting operations are performed each year in the United States. The majority of the bone used for these surgeries comes from autografts that are limited in quantity or allografts with high failure rates. Current synthetic bone grafting materials have poor mechanical properties, handling characteristics, and bioactivity. The goal of this dissertation was to develop a clinically translatable bone tissue engineering scaffold with improved handling characteristics, bioactivity, and smart delivery modalities. We hypothesized that this could be achieved through the rational selection of Food and Drug Administration (FDA) approved materials that blend favorably with hydroxyapatite (HA), the principle mineral component in bone. This dissertation describes the development of smart bone tissue engineering scaffolds composed of the biodegradable amphiphilic polymer poly(D,L-lactic acid-co-ethylene glycol-co- D,L-lactic acid) (PELA) and HA. Electrospun nanofibrous HA-PELA scaffolds exhibited improved handling characteristics and bioactivity over conventional HApoly( D,L-lactic acid) composites. Electrospun HA-PELA was hydrophilic, elastic, stiffened upon hydration, and supported the attachment and osteogenic differentiation of rat bone marrow stromal cells (MSCs). These in vitro properties translated into robust bone formation in vivo using a critical-size femoral defect model in rats. Spiral-wrapped HA-PELA scaffolds, loaded with MSCs or a lowdose of recombinant human bone morphogenetic protein-2, templated bone formation along the defect. As an alternate approach, PELA and HA-PELA were viii rapid prototyped into three-dimensional (3-D) macroporous scaffolds using a consumer-grade 3-D printer. These 3-D scaffolds have differential cell adhesion characteristics, swell and stiffen upon hydration, and exhibit hydration-induced self-fixation in a simulated confined defect. HA-PELA also exhibits thermal shape memory behavior, enabling the minimally invasive delivery and rapid (>3 sec) shape recovery of 3-D scaffolds at physiologically safe temperatures (~ 50ºC). Overall, this dissertation demonstrates how the rational selection of FDA approved materials with synergistic interactions results in smart biomaterials with high potential for clinical translation.

Over 600,000 bone-grafting operations are performed each year in the United States. The majority of the bone used for these surgeries comes from autografts that are limited in quantity or allografts with high failure rates. Current synthetic bone grafting materials have poor mechanical properties, handling characteristics, and bioactivity. The goal of this dissertation was to develop a clinically translatable bone tissue engineering scaffold with improved handling characteristics, bioactivity, and smart delivery modalities. We hypothesized that this could be achieved through the rational selection of Food and Drug Administration (FDA) approved materials that blend favorably with hydroxyapatite (HA), the principle mineral component in bone. This dissertation describes the development of smart bone tissue engineering scaffolds composed of the biodegradable amphiphilic polymer poly(D,L-lactic acid-co-ethylene glycol-co- D,L-lactic acid) (PELA) and HA. Electrospun nanofibrous HA-PELA scaffolds exhibited improved handling characteristics and bioactivity over conventional HApoly( D,L-lactic acid) composites. Electrospun HA-PELA was hydrophilic, elastic, stiffened upon hydration, and supported the attachment and osteogenic differentiation of rat bone marrow stromal cells (MSCs). These in vitro properties translated into robust bone formation in vivo using a critical-size femoral defect model in rats. Spiral-wrapped HA-PELA scaffolds, loaded with MSCs or a lowdose of recombinant human bone morphogenetic protein-2, templated bone formation along the defect. As an alternate approach, PELA and HA-PELA were viii rapid prototyped into three-dimensional (3-D) macroporous scaffolds using a consumer-grade 3-D printer. These 3-D scaffolds have differential cell adhesion characteristics, swell and stiffen upon hydration, and exhibit hydration-induced self-fixation in a simulated confined defect. HA-PELA also exhibits thermal shape memory behavior, enabling the minimally invasive delivery and rapid (>3 sec) shape recovery of 3-D scaffolds at physiologically safe temperatures (~ 50ºC). Overall, this dissertation demonstrates how the rational selection of FDA approved materials with synergistic interactions results in smart biomaterials with high potential for clinical translation.

This document describes the methods to test and measure the protective glasses used in solar panels. The next part of the dissertation covers the evolve summary for the norms of degradation tests. The purpose of this research is to scale the volume and surface electric resistivity of selected materials, as well as, specify the supposed durability of these materials. Evaluation of these features proceeds after enhanced aging by the use of dry heat. Samples of these materials were prepared with the cooperation of the company Solartec s.r.o

As all materials used for exterior construction, cement-bonded particleboards also subject to climatic effects, such as frost, chemicals (eg. sulphates) or UV rays. Degradation of theese effects is slightly increased by organic base. Increased susceptibility can be eliminated by a effective coating, which reduces direct contact with aggresive influences on the board and provides longer durability. Theoratical part of this thesis analyzes different types of negatice influences and their effect on durability. Practical part contains selection of specific types of coating and assessment of their mechanical and aesthetic properties including spectrophotometric analysis of color change for each degradation effect.

En aquesta tesi s'estudia la passivació del silici cristal·lí per a la producció de cèl·lules solars d'alta eficiència (> 20%) a baix preu.<br/>Actualment la indústria fotovoltaica empra capes de nitrur de silici crescut mitjançant la tècnica PECVD. Com a alternativa, es presenta el carbur de silici amorf (a-SiC), també crescut mitjançant PECVD. Resultats anteriors mostren que la passivacio del silici a partir de carbur de silici amorf son excel·lents quan el material és ric en silici i dopat amb fòsfor. L'alt contingut en silici provoca absorció de la llum a la capa, que no es tradueix en corrent elèctric, fent d'aquesta manera que el material sigui només útil quan s'aplica a la cara no il·luminada de la cèl·lula.<br/>L'objectiu d'aquesta tesi és millorar les propietats de passivació del carbur de silici afegint els requisits indispensables en cèl·lules solars: uniformitat, transparència i propietats antireflectants, estabilitat a llarg termini i enfront altes temperatures. A part de les aplicacions tecnològiques també es pretèn entendre millor les propietats fonamentals de passivació.<br/>Els principals resultats són: <br/>- La passivació millora a mesura que s'incrementa el gruix de la capa de a-SiC, fins arribar a una saturació a partir de 50 nm. El mecanisme responsable es una millor saturació dels defectes de la interficie amb hidrogen. Al contrari del que es pensava a priori, la càrrega el·lèctrica emmagatzemada a la capa es manté constant amb el gruix.<br/>- Experiments amb "corona charge" indiquen que l'origen de la càrrega el·lèctrica que produeix la passivació per efecte de camp es troba en la densitat d'estats a la interfície.<br/>- No ha estat possible trobar una capa tranparent (rica en carboni) amb bona passivació. La millor aproximació per combinar passivació més transparència és emprar dues capes, una molt prima rica en silici per passivar i l'altra rica en carboni per aconseguir les propietats antireflectants adequades. S'ha optimitzat el gruix de la capa rica en silici per aconseguir un compromís entre la pèrdua de corrent degut a l'absorció de la llum a la capa i les propietats de passivació. Aquesta combinació de doble capa s'ha fet servir per passivar bases tipus p i emissors tipus n amb resultats excel·lents. Finalment, amb la doble capa es va poder fabricar la primera cèl·lula passivada amb carbur de silici amb una eficiencia > 20%.<br/>- S'ha desenvolupat un material nou: l'al·leació de silici, carboni i nitrogen dopada amb fòsfor. Aquest material ha donat els millors resultats de passició fins ara obtingut dins el nostre grup en bases tipus p i tipus n i en emissors tipus n. La composició òptima és rica en silici i la combinació de capes dobles amb diferents composicions, com en el cas anterior, torna a donar bons resultats de passivació i transparència. <br/>- S'han desenvolupat experiments d'estrès tèrmic a alta temperatura. Les propietats de passivació es veuen fortament afectades desprès de l'estrès si les capes són riques en silici. D'altra banda, les dobles capes mostren una estabilitat molt més alta a l'estrès tèrmic.<br>The thesis focuses on the study of surface passivation of crystalline silicon to produce high efficiency solar cells (with conversion efficiencies > 20%) at reduced prices. The state of the art in surface passivation is done by thin films of amorphous silicon nitride grown by Plasma Enhanced Chemical Vapour Deposition (PECVD) and it is a very well established material in the photovoltaic field.<br/>In this thesis we offer an alternative that is based on amorphous silicon carbide (a-SiC), also grown by PECVD. The passivation properties of silicon carbide have been already studied in our group finding that excellent results can be obtained when the films are rich in silicon, especially for those doped with phosphorus to make a n-type material. Because this feature leads to undesirable absorption of solar light within the films that does not contribute to the photocurrent, silicon carbide would then be relegated to passivate only the rear side of the solar cell.<br/>The aim of this work is to improve surface passivation properties developed previously and add compulsory requisites for the application of crystalline solar cells. These requisites are: uniformity, transparency and antireflective properties, stability under long term operation and stability under high temperature steps (allowing screen printing processes). Also it is the willing to provide a better understanding of the fundamental properties.<br/>The main results achieved are enumerated hereafter:<br/>- Surface passivation improves with the film thickness and then saturates for films thicker than 50 nm. The mechanism responsible for this improvement is not an increase of the electric charge in the film, as in principle could be thought, but a better saturation of defects by the presence of hydrogen. The amount of charge density seems to be independent of the film. <br/>- Experiments of corona charge reveal some treats about the nature of the charge density to provide the field effect passivation. The origin of the charge seems to be a continuous density of states at the interface, rather a fixed charge allocated in the film.<br/>- None of the attempts using carbon rich films, which are transparent and with antireflective properties, resulted in excellent surface passivation. Such attempts included variation of the deposition parameters, use of remote plasma PECVD with high incorporation of hydrogen, and introduction of nitrogen of in the phosphorus doped a-SiC films. Therefore, up to now it becomes apparent that it is a fundamental property of silicon carbide films the necessity to be rich in silicon to perform surface passivation.<br/>- The way to combine surface passivation and antireflective properties was applying stacks of different a-SiC layers: one silicon rich and one carbon rich. The thickness of the silicon rich layer was optimized to reach a trade-off between level of passivation and lost of photocurrent due to the absorption in the film. The stacks were used to passivate p-type bases, with reasonably good results, and n+- type emitters, with very good results. The stacks provided the the first silicon solar a-SiC rear side passivated with efficiency above 20%.<br/>- A new material was tested: a ternary alloy of silicon, carbon and nitrogen doped with phosphorus. This material was applied to n- and p-type bases and n+-type emitters, presenting the best results in surface passivation achieved by our group, and comparable to surface passivation record achieved by amorphous silicon carbide. Best composition was rich in silicon, and again stacks of silicon rich and carbon rich films was combined successfully. <br/>- Stability against thermal processes was tested on different passivation schemes. After the treatment, the passivation is strongly reduced for single silicon rich films, which were offering good initial results. On the other hand, the stacks with a second carbon rich film maintain reasonably well the surface passivation properties.

In the rapidly changing scientific world, contributions of scientists and engineers are leading to major new solutions of significant medical problems. Biology and medicine are beginning to reduce the problems of disease to problems of molecular science, and are creating new opportunities for treating and curing disease. Such advances are coupled closely with advances in biomaterials and are leading to a variety of approaches for relieving suffering and prolonging life.<br/><br/>Of particular interest is the central position that materials especially biopolymers, have taken in the development of novel treatments over the last 30 years. Biopolymers are used in many biomedical and pharmaceutical preparations, they play a central role in extracorporeal devices; from contact lenses to kidney dialyzers, are essential components of implants; from vascular grafts to cardiac pacemakers, and are the basis of controlled drug delivery technology; from hydrogels to micro and nanoparticles.<br/><br/>In the last few years, novel synthetic techniques have been used to impart desirable chemical, physical, and biological properties to biomaterials. Materials have either been synthesized directly, so that desirable chain segments or functional groups are built into the material, or indirectly, by chemical modification of existing structures to add desirable segments or functional groups.<br/><br/>Polymeric biomaterials can be produced by copolymerizations of conventional monomers to achieve nearly monodisperse polymers. It is possible to produce polymers containing specific hydrophilic or hydrophobic entities or biodegradable repeating units.<br/><br/>One interesting strategy to develop multitalented biomaterials is the biosynthesis of polymers because these macromolecules have several advantages like: biological resorbability, hydrodegradability, absence of immunogenicity, and appropriately high molecular mass. The chemical derivatizability of these polymers allows the formation of several products with a wide range of properties.

A partir de polietilè d'alta densitat i de fibres lignocel·lulòsiques provinents del trèmol (Populus tremula) s'han obtingut uns materials amb propietats úniques denominats compòsits. Aquests compòsits, amb un màxim de 40% de fibres lignocel·lulòsiques han estat tractats i modificats amb diferents agents (silà A-174 i epolè C-18) per millorar la compatibilitat entre la matriu de polietilè i el reforç fibrós. <br/><br/>En una primera etapa les fibres lignocel·lulòsiques han estat pretractades amb cada un dels diferents tipus d'agents d'adhesió utilitzats i comentats prèviament, per seguidament barrejar aquestes fibres (en proporcions del 10, 20, 30 i 40%) amb la matriu d'HDPE. <br/><br/>Una vegada els dos components s'han homogeneïtzat, es sotmeten a un procés de mòlta per aconseguir, mitjançant compressió, les provetes corresponents. Finalment, el conjunt de provetes ha estat exposat a condicions climàtiques dràstiques (baixa temperatura i fatiga tèrmica, dues característiques significatives de l'hivern canadenc) durant períodes variables de temps (0, 15, 30, 60 i 90 dies).<br/><br/>Per tal d'avaluar tots i cada un dels paràmetres més significatius d'aquests compòsits, s'ha fet una caracterització orientada en dues vessants: estudi de la compatibilitat entre components del compòsit i estudi dels canvis estructurals que pateixen els compòsits degut a fenòmens d'envelliment provocats per exposició a les condicions climàtiques prèviament comentades.<br/><br/>L'estudi de compatibilitat es fonamenta en les possibles interaccions que s'originen entre els dos components en funció del tipus de tractament al que ha estat sotmès el compòsit (silà i epolè). Per valorar aquestes interaccions, s'han estudiat diferents propietats mecàniques, com ara la resistència a la tracció, el mòdul d'elasticitat, la deformació a trencament, la resiliència i la tenacitat, mitjançant una màquina universal d'assaigs. Tanmateix també s'ha fet una caracterització espectrefotomètrica FT-ir per comprovar els diferents mecanismes d'adhesió que actuen en la interfase fibra- matriu en funció del tipus de tractament i una caracterització morfològica, utilitzant la tècnica de microscòpia electrònica de rastreig (SEM). Amb els resultats obtinguts de la caracterització espectrefotomètrica, també s'ha realitzat un seguiment de la influència que cada component fa en la modificació del grau de cristal·linitat de l'altre.<br/><br/>L'estudi dels canvis estructurals que pateixen els compòsits degut a fenòmens d'envelliment s'ha fet partint de l'evolució de les propietats mecàniques bàsiques en funció dels diferents períodes d'exposició, on s'han caracteritzat els mateixos paràmetres definits anteriorment. Mitjançant valoració espectrefotomètrica s'han mesurat els canvis microestructurals (principalment de configuració), així com les modificacions en el grau de cristal·linitat que han tingut lloc sobre cada un dels diferents components del compòsit.<br/><br/>Cal afegir que les possibilitats que ofereix la tècnica espectrefotomètrica FT-ir ha permès dur a terme la realització d'aquesta tesi. L'estudi dels canvis en la microestructura dels compòsits esdevinguts a partir dels fenòmens prèviament esmentats no hauria pogut fer-se sense la possibilitat d'un processament adequat dels espectres, així com d'una subtracció espectral que permet la detecció de moltes bandes complexes i difícils de detectar mitjançant altres tècniques d'anàlisi.<br>Los materiales compuestos se han obtenido a partir de polietileno de alta densidad y fibras lignocelulósicas que provienen del alamo temblón. Estos materiales con un máximo del 40% de refuerzo lignocelulósico han sido tratadas y modificadas con distintos tipos de agentes de acoplamiento (Silano A-174 y epoleno C-18) para mejorar la compatibilidad entre la matriz y el refuerzo.<br/><br/>Las fibras tratadas previamente con cada uno de los distintos tipos de agentes de adhesión utilizados, se mezclan en distintas proporciones de las mismas (10,20,30 y 40%) con la matriz de HDPE.<br/> <br/>Una vez ambos componentes se han homogenizado se someten a un proceso de molturación para obtener probetas tipo halterio mediante compresión. Estas probetas se han sometido durante distintos períodos de tiempo (hasta 90 días) a condiciones de exposición drásticas (baja temperatura y fatiga térmica, características significativas del invierno canadiense).<br/><br/>Para evaluar los parámetros más significativos de estos materiales compuestos se ha caracterizado la compatibilidad entre la matriz y el refuerzo, asimismo también se han estudiado los cambios estructurales que sufren estos materiales debido a fenómenos de envejecimiento provocados por la exposición de los mismos a las condiciones climáticas previamente comentadas.<br/><br/>Els estudio de compatibilidad se centra en las posibles interacciones que se originen entre ambos componentes en función del tipo de tratamiento al que se ha sometido dicho material compuesto (silano y epoleno). Para valorar las interacciones que se generen entre ambos componentes, se ha ensayado distintas propiedades mecánicas (resistencia a tracción, módulo de elasticidad, deformación a rotura, resilencia y tenaciadad, utilizando la máquina universal de ensayos. Asimismo, también se ha caracterizado mediante espectroscopia de infrarrojo (FTIR) los posibles mecanismos de adhesión que tienen lugar entre la matriz y el refuerzo en función del tipo de tratamiento, asi como la caracterización morfológica utilizando la técnica de microscopía electrónica de barrido (SEM). A partir de los resultados obtenidos se ha podido seguir la influencia que tiene cada componente en la modificación de los respectivos grados de cristalinidad. <br/><br/>El estudio de los cambios estructurales a los que se han visto sometido los distintos materiales compuestos, debido a fenómenos de envejecimiento, se ha realizado mediante el seguimiento de la evolución de las propiedades mecánicas en función de los distintos períodos de exposición. Mediante valoración espectofotométrica se han medido los cambios micorestrucutrales (cambios de configuración), así como las modificaciones en el grado de cristalinidad sobre cada uno de los componentes de material compuesto.<br>Composite materials have been obtained from high density polyethylene (HDPE) and lignocellulosic fibers from aspen wood. These materials with a maximum of 40% of lignocellulosic reinforcement have been treated and modified with different types of coupling agents (Silane A-174 and epolene C-18) to improve the compatibility between the matrix and the reinforcement.<br/><br/>Four contents (10.20.30 and 40%) of fibers treated previously with each one of the different types of adhesion or coupling agents, are mixed with HDPE matrix. <br/><br/>The above mixture was compression-molded into dog-bone shaped tensile test specimens. The molding temperature was slowly raised to 150ºC and samples were held at this temperature for 20 min. Then the samples were slowly cooled to room temperature keeping constant pressure during cooling. These test specimens have been submitted during different periods of time (up to 90 days) to drastic conditions of exposition (low temperature and thermal stress, main characteristics of the Canadian winter).<br/><br/>In order to evaluate the most significant parameters of these composite materials, we have studied two ways: the compatibility between both components: matrix and reinforcement and the structural changes to composites due to phenomena of aging caused by the exposition of these materials to the drastic climatic conditions previously commented.<br/><br/>The study of compatibility has been centered in the possible interactions that are originated between both components as a function of lignocellulosic fiber pretreatment. In order to evaluate the interactions that are generated between both components, different mechanical test has been tested (tensile strength, elasticity modulus, deformation at break, resilence and toughness) by mean an Instron Testing Machine. Moreover, the possible mechanisms of adhesion that take place between the matrix and the reinforcement as a function of different pretreatments has been characterized by means infrared spectroscopy (FTIR), and by the morphologic characterization using the scanning electronic microscopy (SEM). From the obtained results it has been possible to follow the influence that has each component in the modification of the respective degrees of crystallinity.<br/><br/>The study of the structural changes of different composite materials, due to aging phenomena, has been analized by means of the pursuit of the evolution of the mechanical properties based on the different periods of exposure time. Furthermore the microstructural changes (basically configurational and crystallinity) has been evaluated by means of spectroscopy technique. <br/><br/>The obtained results indicate that the macroscopic properties of the composite materials must depend on the lignocellulosic fiber content and whether or not a coupling agent is used. SEM micrographs of fracture surfaces show that the addition of coupling agents enhances their dispersion in the continuous HDPE phase. They also show that the silane coupling agent facilitates the direct contact between the lignocellulosic fibers and HDPE matrix more than untreated and epolene treated composites do. The tensile strength depends on both the lignocellulosic fiber content and the type of coupling agent used. The other mechanical properties (elasticity modulus, elongation at break and toughness) mainly depend on the lignocellulosic fiber content and, to a lesser extent, on the presence of a coupling agent. Silane-treated composites show the best mechanical performance as a consequence of significant interactions at the interface between the HDPE matrix and the lignocellulosic fibers.<br/><br/>The differences observed between the various composites studied are explained by means of different adhesion mechanisms. Interdiffusion takes place in untreated composites; multiple mechanism of adsorption-wettability, interdiffusion and, to a lesser extent, chemical bonds take place in epolene treated composites, and finally, the adhesion in composites modified with silane is mainly a chemical mechanism of covalent bonds.

In questo studio è stata indagata l’efficacia di un nuovo consolidante inorganico a base di idrossiapatite (HAP) su due calcari porosi, la pietra leccese e il calcare globigerina, che sebbene considerati simili in letteratura differiscono per microstruttura e composizione. L’idrossiapatite può essere ottenuta per sintesi 'wet' facendo reagire un precursore fosfatico (DAP) con ioni calcio presenti nel substrato o aggiunti esternamente. Il trattamento ha già dato risultati promettenti su altri litotipi, ma per la pietra leccese l’efficacia del trattamento era ancora da indagare compiutamente, quindi sono state effettuate prove su campioni degradati termicamente, così da avere assenza di sali e degrado uniforme. Sono state considerate formulazioni con due diverse concentrazioni di DAP (3M e 0,1M) e diversa aggiunta di ioni calcio. Nella soluzione 0,1M è stato aggiunto etanolo per favorire la dissociazione in ioni PO43- che possono reagire e formare HAP. I risultati sono stati messi a confronto con quelli ottenuti dal trattamento tradizionale con silicato di etile (TEOS): sono stati valutati gli effetti del degrado, la variazione delle proprietà meccaniche, la formazione di fasi dopo il trattamento e un primo studio sulla durabilità. I risultati ottenuti sono buoni per entrambi i trattamenti, soprattutto per quello 3M: un buon aumento delle proprietà meccaniche, una buona profondità di penetrazione e l’assenza di fasi metastabili o sottoprodotti dannosi; i risultati sono confrontabili o superiori a quelli dati dal TEOS. Il trattamento 0,1M ha invece un’efficacia minore, forse a causa dell’elevata porosità dei substrati che richiedono un’alta quantità di HAP, pertanto la sua ottimizzazione è attualmente in corso. Inoltre per la prima volta il nuovo trattamento è stato applicato su supporti contaminati da sali, quasi sempre presenti in situ, indagando la possibile formazione di fasi metastabili solubili in grado di ridurre il successo del trattamento.

Percutaneous transluminal balloon angioplasty followed by drug-eluting stent implantation has been of great benefit in coronary applications, whereas in peripheral applications, success rates remain low. Analysis of healing patterns in successful deployments shows that six months after implantation the artery has reorganized itself to accommodate the increase in caliber and there is no purpose for the stent to remain, potentially provoking inflammation and foreign body reaction. Thus, a fully biodegradable polymeric stent that fulfills the mission and steps away is of great benefit. Biodegradable polymers have a widespread usage in the biomedical field, such as sutures, scaffolds and implants. Degradation refers to bond scission process that breaks polymeric chains down to oligomers and monomers. Extensive degradation leads to erosion, which is the process of mass loss from the polymer bulk. The prevailing mechanism of biodegradation of aliphatic polyesters (the main class of biodegradable polymers used in biomedical applications) is random scission by passive hydrolysis and results in molecular weight reduction and softening. In order to understand the applicability and efficacy of biodegradable polymers, a two pronged approach involving experiments and theory is necessary. A constitutive model involving degradation and its impact on mechanical properties was developed through an extension of a material which response depends on the history of the motion and on a scalar parameter reflecting the local extent of degradation and depreciates the mechanical properties. A rate equation describing the chain scission process confers characteristics of stress relaxation, creep and hysteresis to the material, arising due to the entropy-producing nature of degradation and markedly different from their viscoelastic counterparts. Several initial and boundary value problems such as inflation and extension of cylinders were solved and the impacts of the constitutive model analyzed. In vitro degradation of poly(L-lactic acid) fibers under tensile load was performed and degradation and reduction in mechanical properties was dependent on the mechanical environment. Mechanical testing of degraded fibers allowed the proper choice of constitutive model and its evolution. Analysis of real stent geometries was made possible with the constitutive model integration into finite element setting and stent deformation patterns in response to pressurization changed dramatically as degradation proceeded.

Cement bonded particleboards contain organic base and as they are set outside, extreme weather condition, such as frost, chemical defrosting substances or sulphates, cause their degradation. The presence of the organic base in the matrix of the material could be the reason why there is higher probability of degrading when compared with materials containing an inorganic base. It could be partially eliminated by an appropriate surface modification of the slab, which main goal is to weaken the impact of an aggressive environment and to extend the lifespan of the board. On the other hand, the surface modifications based on a polymer base are prone to degrade because of other unfavourable conditions such as UV radiation when compared with the cement bonded particleboard. The classification of the surface modifications and the way of their degradation caused by the aggressive environment in real applications are presented in the theoretical part of the thesis. In the experimental part, appropriate methodical ways of testing the resistance of cement bonded particleboard’s coating system were chosen. Then, the testing and comparing of the physical, mechanical and aesthetic properties of different types of coatings were done. Moreover, a spectrophotometric analysis of the colour shade changes for the different aggressive environment were carried out. Furthermore, microstructures of chosen surface modifications were assessed by using an optical and an electron microscope.

L'ingénierie tissulaire est une discipline récente aux enjeux ambitieux et prometteurs : la régénération de tissus ou d'organes lésés voire détruits en mettant à profit des connaissances et compétences dans différents domaines à l'interface de la chimie et de la biologie. Pour répondre à la demande d'alternatives aux techniques chirurgicales actuelles de réparation du ligament antérieur croisé, nous avons décidé d'appliquer l'ingénierie tissulaire à ce tissu en associant matrices en polymères dégradables et cellules souches mésenchymateuses (CSM). Dans un premier temps, nous avons donc travaillé à la synthèse de polymères adaptés à l'application en cherchant à mettre l'accent sur l'obtention de propriétés élastiques. De nouveaux élastomères dégradables obtenus par des approches originales de photoréticulation chimique de poly(lactide) (PLA) et de poly(ε-caprolactone) (PCL) par voie nitrène ou thiol-yne ont notamment été développés avec des résultats prometteurs. En parallèle, des copolymères thermoplastiques multiblocs à base de PLA et poloxamine ou poloxamère nous ont permis de mener une étude plus appliquée. Ces copolymères ont en effet montré, en particulier au cours d'une étude de dégradation in vitro de 7 semaines, des propriétés, notamment thermiques et mécaniques, qui en font d'eux des candidats intéressants pour le conception d'une matrice ligamentaire. C'est pourquoi ils ont été utilisés pour la conception de prototypes de matrices de régénération textiles dont les propriétés mécaniques se sont révélées être très proches de celles du ligament. Après avoir démontré l'excellente cytocompatibilité de ces matrices avec des CSM, nous avons finalement mené des expériences de différenciation in vitro de ces CSM et sommes parvenus à favoriser leur orientation vers un phénotype ligamentocytaire, notamment grâce à un procédé de stimulation mécanique cyclique des cellules ensemencées sur les matrices textiles.

This dissertation deals with the study of durability and degradation repair mortars for reinforced concrete structures. In its theoretical part, there are the research findings on the behavior of repair mortars exposed to corrosive environments with different exposure time and selected high temperatures. Processes occurring in repair mortars during their loading at high temperatures or when exposed to chemically aggressive environments are described, We can find recipes designed for cementitious binder based with a specific replacement using slag or fly ash in its practical part. The object of the research was to determine the durability of the proposed repair mortars, and determine their suitability for use on concrete structures, which may be exposed to a synergistic effect of chemically aggressive environments with high temperatures simulating fire.

The thesis discusses the degradation of metallic materials in the salt spray. The work is focused on material 42CrMo4. From this steel are prepared test specimens for laboratory measurements. In the first part of the thesis is a theoretical and research described heat treatment, oxidation, mechanical and dynamic material testing, to be carried out on laboratory machines. The second part of the thesis is focused on processing the material to the required dimensions. Furthermore, the thesis deals with marking and heat treatment of the prepared sample and subsequent insertion into the prepared salt chamber. In the third part of the thesis is an analysis of the results that were obtained for samples prepared using laboratory testing, which were dynamic and mechanical tests.

The aim of this paper is to analyse the process of wear and abrasive materials which are able to withstand wear and to prove these findings in experiments in both laboratory and operational conditions. The first section includes an analysis of a material of the worn parts of dies (mould tools) for the manufacture of technical ceramics and solutions to increase their lifespan. A more resistant ledeburitic tool steel for the manufacture of dies (mould tools) 19 573 (according to ČSN) was chosen. The second section comprises laboratory tests with chosen PVD coatings applied on selected steel. The most resistant nitride coating was chosen after laboratory tests done in an abrasive vessel and with an abrasive cloth. The third section describes the operational test of the dies (mould tools) with functional component parts on which there was applied a chosen coating. The last section of the work proves the possibility of a usage of tool steels for the manufacture of abrasively stressed components of a plough. Unalloyed structural steel samples with a different heat treatment and the abrasion-resistant material Hardox were tested together with the samples of tool steels. The wear resistance of these steels was also proven by the laboratory tests with the abrasive cloth and the Bond`s device. The results were statistically evaluated, compared and graphically displayed. The achieved results can be applied in technical practice and they enable us to determine the way of the future development.

碩士<br>國立勤益科技大學<br>化工與材料工程系<br>98<br>Degradable polymer materials were prepared by two method: the first one was blended thermoplastic polyurethane (TPU) with various contents of polylactic acid (PLA) and polycaprolactone (PCL) of high molecular weight respectively, and then the cellular material were prepared with constant content of microsphere. The second method was performed by prepolymer with various content of low molecular weight of PLA and PCL respectively and a few blowing agent. Besides, degradation rate and mechanism of all materials mentioned above after aging condition were investigated by Universal Testing Machine and ATR-FTIR. The test result with 90℃ and 100RH% condition in this research revealed: (I) TPU blended materials: TPU/PLA blended materials had higher degradation extent in alkaline and neutral condition; TPU/PCL blended materials had higher degradation extent in acidic and neutral condition. (II) Thermosetting PU cellular materials: the physical properties were decreased with PLA content, when the PLA of linear low molecular weight introducing into PU molecular chain of higher crosslinking degree; that the physical properties were increased with PCL content, and most of the tensile retention of samples after degradation condition was decreased to lower than 20% within 14 days. It was speeded up degradation rate due to the auto-catalytic effect, when both of PLA and PCL were introduced into PU molecular chain of lower corsslinking degree. Besides, the tensile retention of these samples after degradation condition was decreased to lower than 20% within 3 days, when PLA content above 10wt%. (III) Ester type TPU cellular materials: the physical properties were increased with the content of degradable materials, and tensile retention was decreasing to lower than 20% with in 7 days, whatever PLA, PCL or both them were introduced. (IV) Ether type TPU cellular materials: the tensile retention of pure TPU and introducing PLA, PCL, both of them after degradation condition for 56 days were decreased to 57%, 32%, 19% and 38% respectively. There are have higher hydrolysis stabilization and hydrophobic of ether type TPU due to non-carbonyl group in structure of itself.

This thesis is focused on biodegradable or compostable plastics. Focuses on their pro-perties and uses. The work also clarifies the concept of biodegradable and compostable plastic. The work also describes the process of composting and concepts associated with it. Finally, there are several chapters devoted to the normative environment that relates to biodegradable plastics in the thesis. There are connected researches concerning the verification of the degree of degra-dation of plastics known as compostable, biodegradable and 100% compostable, in the last few chapters. There were conducted simultaneously two experiments of disintegration selected samples of biodegradable plastics. The tests of disintegration in the laboratory and in real conditions of composting were founded in March 2014 for a period of three months. There was founded a phytotoxicity test after the expiry of the time allotted in the laboratory. In a real conditions the study time was increased to 12 months. After evaluating and comparing the results of both tests disintegration may be allowed the use of biodegradable plastics in composting under controlled condi-tions. Conversely, in real conditions of home composting these plastics can not be re-commended, does not decompose.

This dissertation focuses on the synthesis and characterization of an exciting new family of thermoresponsive polyacetal polymers with remarkable properties that are well suited for a myriad of applications. The new polyacetals are the first, intrinsically biodegradable polymers to exhibit a lower critical solution temperature (LCST). Their LCSTs are linearly dependent on the number of carbon and oxygen atoms in the repeat units, which can be easily adjusted over a wide range of temperatures. The LCSTs can be precisely and predictably tuned to any temperature ranging from 7-80°C by simply using mixtures of monomers during synthesis. The LCST transition of polyacetals is sharp and shows no hysteresis. These new materials have the potential to be used in a broad range of technologies that are important not only economically, but also affect the quality of life. In particular, they have the potential to be used as a drug delivery carrier for treatment of pancreatic cancer; an illness that has a dismal prognosis, for which other treatments have proven ineffective. Polyacetals are known to be chemically inert; the primary thesis objectives presented here are to develop frameworks for polyacetal functionalization for use in a variety of applications. Chapter 3 explores strategies to prepare water-soluble polyacetal-drug conjugates from three HIF-1 inhibitors; a highly hydrophobic class of cancer therapeutics. HIF-1 inhibitors explored in this chapter have simple structures containing di-hydroxy functionalities, which can be used for polyacetal main-chain attachment. Step-growth polymerization is used to prepare, for the first time, main-chain drug conjugates that are temperature responsive and pH degradable. Furthermore, the temperature response of main-chain polyacetal-drug conjugates is precisely tuned with the amount of the HIF-1 in the polymer backbone. The pH dependent backbone degradation of the drug conjugates show that pristine HIF-1 inhibitors evolve from the polymer at long degradation times, showing promise for use of this material as a drug delivery vehicle. Strategies outlined in Chapter 3 require specific di-hydroxy functionalities in the molecules of interest, without which, functionalization is not possible. Therefore, Chapter 4 considers polyacetal functionalization of molecules with mono- or poly- hydroxy functional groups, further expanding the scope of these new materials. Two strategies of functionalization are presented, namely, end group functionalization and pendent-chain polyacetal-conjugation using click chemistry. End group functionalization of polyacetal is achieved during step-growth polymerization, in situ, using mono-hydroxy functional molecules. Pendent-chain polyacetal-conjugates are prepared using backbone alkyne functional polyacetal with specialized heterobifunctional linkers that enable the use of orthogonal chemistries such as click-chemistry. Importantly, end group and pendent-chain functional polyacetals retain their temperature response and degradation properties. Both polyacetals evolve pristine mono- functional payloads at the onset of the degradation cycle in contrast to main-chain polyacetal-drug conjugates, which evolve the payload towards the end of the degradation cycle. Knowledge of both degradation mechanisms allows for precise control over the degradation profile of the resulting polyacetals. Chapter 5 further expands on the thesis objectives by the synthesis of ABA type polyacetal block co-polymers and micelles. Polyacetal block co-polymers encapsulate virtually any type of hydrophobic molecule of interest, significantly expanding the number of molecules that can be incorporated into polyacetals. For this purpose, click-functional polyacetal macromonomers are prepared and end-linked with the polymer. The resulting polyacetal micelles show remarkable temperature response, by a second-order θ collapse exhibited by base-polyacetals, and by coacervation of the individual micelles. The temperature response for polyacetal block co-polymers is sharp and reversible, with minimal hysteresis. Pyrene encapsulation studies conducted with polyacetal micelles show that, upon degradation, 99% the encapsulated pyrene is released, showing great promise for use of polyacetal block co-polymers as a delivery vehicle for a variety of applications. Using the methods outlined in Chapter 3-5, virtually any molecule of interest can be incorporated into the polyacetal chain. Lastly, the fundamental origins of the LCST behavior of PAs are explored using molecular dynamic simulations in Chapter 6. For this purpose, PA chains of 10,000 g/mol are accurately modeled using coarse-graining techniques. The experimental LCST transition is reproduced with an accuracy of ±20°C using the coarse grained model, which allows for precise prediction of the temperature response using simulations. The model is further expanded to obtain sequence transferability; that is, the LCST behavior of any sequence or architecture that consists of poly(ethylene oxide) and methylene units can be modeled with precision using this model. We also present sample conformations of the polyacetal during its coil-globule transition, which provides a degree of insight into the mechanism of the LCST.

Yes<br>Complex biological tissues are highly viscoelastic and dynamic. Efforts to repair or replace cartilage, tendon, muscle, and vasculature using materials that facilitate repair and regeneration have been ongoing for decades. However, materials that possess the mechanical, chemical and resorption characteristics necessary to recapitulate these tissues have been difficult to mimic using synthetic resorbable biomaterials. Herein, we report a series of resorbable elastomer-like materials that are compositionally identical and possess varying ratios of cis:trans double bonds in the backbone. These features afford concomitant control over the mechanical and surface eroding degradation properties of these materials. We show the materials can be functionalized post-polymerization with bioactive species and enhance cell adhesion. Furthermore, an in vivo rat model demonstrates that degradation and resorption are dependent on succinate stoichiometry in the elastomers and the results show limited inflammation highlighting their potential for use in soft tissue regeneration and drug delivery.