Dissertations / Theses on the topic 'Smolder'

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 63-67). Also available in electronic version. Access restricted to campus users.

This research investigated the potential of smouldering combustion to be employed as a remediation approach for soil contaminated by non-aqueous phase liquids (NAPLs). Small-scale (~15 cm), proof-of-concept experiments were the first to demonstrate that organic liquids embedded within an inert soil matrix can be successfully smouldered. Intermediate-scale (~30 cm) column experiments examined in detail the behaviour of the combustion process including its relationship to mass and energy balance and the evolution of temperature profiles. In addition, detailed evaluations of environmental parameters (e.g., soil concentrations, gas emissions) were conducted. For the first time, it was demonstrated that NAPL smouldering combustion can be self-sustaining (i.e., propagation of the smouldering front after termination of the igniter) and self-terminating (i.e., natural extinction of the reaction after all of the NAPL is destroyed). More than 30 column sensitivity experiments quantified the broad range of process parameters - including contaminant type, contaminant mass, soil type, and oxidizer flow rates - within which the process was self-sustaining and essentially complete remediation was achieved (i.e. contaminant mass removal in excess of 99.5%). Maximum burning temperatures were observed in the range 600-1100 C. Average propagation velocities varied between 0.7e-4 and 1.2e-4 m/s. Intensity and velocity of the process were shown to be controlled by the rate at which oxidizer is delivered. Contaminant type and mass was observed to affect peak temperatures and propagation velocity by influencing the energy balance at the reaction front. Moreover, mass and energy balance models were demonstrated to provide reasonable predictions of the observed propagation velocities. Overall, this research introduced an entirely new approach to the remediation of NAPL-contaminated soils and, further, advanced the understanding of the mechanisms that control the underlying process of smouldering combustion of liquids.

Sintetisane su klasične alkidne smole polazeći od ricinolne kiseline, anhidrida ftalnekiseline i tri poliola (glicerina, trimetilolpropana i etoksilovanog pentaeritritola), kao ihiperrazgranati alkidi na osnovu ditrimetilolpropana, dimetilolpropionske kiseline iricinolne kiseline. Smole su karakterisane određivanjem hidroksilnog i kiselinskog broja,viskoznosti, srednjih molskih masa i njihove raspodele. Struktura sintetisanih smola jepotvrđena infracrvenom spektroskopijom sa Furijeovom transformacijom (FTIR).Sintetisani alkidi imaju veliki sadržaj hidroksilnih grupa, a mali kiselinski broj. Prisustvohidroksilnih grupa, kao krajnjih funkcionalnih grupa, omogućuje modifikaciju alkidnihsmola i dobijanje materijala različitih svojstava. Sintetisani alkidi su umrežavani satriizobutoksimetil i heksametoksimetil melaminskom smolom u cilju dobijanja umreženog materijala željene strukture i svojstava za primenu u premazima. Umrežavanje smeša smola praćeno je FTIR spektroskopijom, dinamičko skanirajućom kalorimetrijom (DSC), reometrijom, kao i određivanjem sadržaja gela. Ispitivana su toplotna svojstva, dinamičkomehaničko ponašanje, fizičko-mehaničke karakteristike i hemijska otpornost filmova premaza. Umrežavanje smeša smola teče uglavnom preko hidroksilnih i karboksilnih grupa alkida sa izobutoksimetil i metoksimetil grupama u melaminskim smolama. Sintetisane klasične alkidne smole u smeši sa melaminskim smolama umrežavaju u temperaturnom opsegu od 90 do 170 ⁰C, a hiperrazgranati alkidi od 80 do 170 ⁰C, što su uobičajene temperature u tehnologiji lakova koji umrežavaju “pečenjem“. Umreženi filmovi premaza su toplotno veoma stabilni, budući da početak razgradnje premaza započinje na temperaturama od 281 do 330 ⁰C. Potvrđeno je da postoji linearna zavisnost između modula izgubljene energije na 25 ⁰C, koji je mera viskoznog odgovora materijala, i tvrdoće premaza određene metodom klatna. Svi projektovani premazi, bez obzira na nesavršenost nastale polimerne mreže, su pokazali zadovoljavajuća svojstva. Najbolja svojstva od klasičnih alkidnih premaza ima onaj na osnovu smeše alkida sa etoksilovanim pentaeritritolom i heksametoksimetil melaminske smole. Korišćenje hiperrazgranatih alkidnih smola kao veziva u ekološki prihvatljivim premazima ima prednost zbog manjeg sadržaja organskih rastvarača i manje viskoznosti u odnosu na klasične smole. Pretpostavljeno je da bi smeše sintetisanih klasičnih i hiperrazgranatih alkida sa melaminskim smolama (maseni odnos 70:30) bile pogodne za primenu u industriji boja i lakova. Potvrđeno je da su sistemi alkid/melaminska smola veoma složeni. Dobijeni rezultati omogućuju da se objasni uticaj građe prekursora na strukturu nastale polimerne mreže, a time i na svojstva premaza.
Conventional alkyd resins based on ricinoleic acid, phthalic anhydride and three polyols (glycerin, trimethylolpropane or ethoxylated pentaerythritol), as well as hyperbranched alkyds based on ditrimethylolpropane, dimethylol propionic acid and ricinoleic acid were synthesized. Prepared alkyds were characterized by the determination of hydroxyl and acid numbers, viscosity, average molecular masses and molecular masses distribution. The structure of synthesized resins is confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Obtained alkyd resins have high content of hydroxyl groups and low acid number. The presence of hydroxyl groups as functional end groups opens up a high potential for further chemical modifications and for obtaining materials with different properties. Synthesized alkyds were cured by triisobutoxymethyl- and hexamethoxymethyl melamine resins, in order to obtain crosslinked material with desired structure and properties for coating applications. Curing of the resin mixtures were examined by FTIR spectroscopy, dynamic scanning calorimety (DSC), rheometry and by the determination of gel content. Thermal properties, dynamic mechanical behavior, physico-mechanical characteristics and chemical resistance of coated films were determined. Curing of the resin mixtures proceeds via the reactions between hydroxyl and carboxyl groups of alkyds with isobutoxymethyl and metoxymethyl groups in melamine resins. Synthesized alkyd/melamine resin mixtures became cured in the temperature range from 80 to 170 0C, which is the usual temperature range employed in the baking enamel technology. Cured films are thermally very stable since the onset of films degradation starts at high temperatures (from 281 to 330 0C). It is confirmed that there is a linear dependence between the loss modulus at 25 0C, which is the measure of the material viscosity response, and the coating hardness determined by pendulum method. All projected coatings, despite of defects in the resulting polymer networks, show satisfying properties. Among the conventional systems coating based on mixture of alkyd with ethoxylated pentaerythritol and hexamethoxymethyl melamine resin show the best properties. Application of hyperbranched alkyd resins, as binders in environment friendly coatings has an advantage due to less content of organic solvent and lower viscosity, compared to conventional alkyd resins. It is supposed that the combination of synthesized conventional and hyperbranched alkyds with melamine resins (weight ratio of 70:30 based on dried mass) could be employed as new materials for the industrial preparation of baking enamels. It is confirmed that alkyd/melamine resin systems are very complex. Results obtained enable to explain the effect of precursor type on the structure of resulting polymer network, and thus, on the coating properties.

U ovoj doktorskoj disertaciji je ispitan uticaj montmorilonita itermoplastičnih segmentiranih poliuretana na kinetiku reakcijaumrežavanja, strukturu i svojstva funkcionalnih hibridnihmaterijala na osnovu epoksidnih smola. Pripremljene su dveserije uzoraka hibridnih materijala: prva na osnovu epoksidnesmole sa različitim sadržajem organski modifikovanogmontmorilonita (0, 1, 3, 5 i 10 mas.%) umrežene saumreživačem Jeffamine D-230; druga serija je sintetisana naosnovu epoksidne smole, sa različitim sadržajem (10, 15 i 20mas.%) termoplastičnog poliuretanskog elastomera sarazličitim sadržajem tvrdih segmenata (20, 25 i 30 mas.%)sintetisanih na osnovu alifatičnog polikarbonatnog diola iheksametilendiizocijanata i produživača lanca butandiola, kaoi katalizatora dibutiltin dilaurata; kao i bez dodatog elastomeraumrežene sa diaminom Jeffamine D-2000. Umrežavanjereaktivnih sistema sa projektovanim sirovinskim sastavom jepraćeno diferencijalnom skenirajućom kalorimetrijom (DSC).Modeli izokonverzije primenjeni su da se ustanovi da lidodatak punila utiče na reakciju umrežavanja hibridnihmaterijala. Sintetisani materijali su analizirani dinamičkomehaničkomanalizom (DMA), mikroskopijom atomskih sila(AFM), kao i TG-DSC i TG-MS metodama i određena sumehanička svojstva (zatezna čvrstoća, prekidno izduženje itvrdoća po Šoru A). Epoksidni materijal sa 10 mas.% organskimodifikovanog montmorilonita ima značajno niže vrednostienergija aktivacije za definisane stepene reagovanja, čime jepotvrđen katalitički efekat gline sa slojevitom strukturom kadaje prisutna u reakcionoj smeši u dovoljnoj količini. Uticajotežane difuzije pri kraju reakcije je izraženiji u prisustvumontmorilonita, čime je pokazano da njegovo prisustvo utičena ceo mehanizam umrežavanja. Utvrđeno je da na vrednostiG', pored udela montmorilonita, utiče i stepen dispergovanjačestica unutar polimerne matrice. Zaključeno je da dodatakpunila do 3 mas. % utiče povoljno na ispitana mehaničkasvojstva, dok pri sadržaju od 5 i 10 mas. % dolazi doaglomeracije čestica punila, što negativno utiče na ispitanasvojstva, osim tvrdoće, koja se povećava linearno sa dodatkompunila montmorilonita. Na osnovu rezultata TG analizezaključeno je da je sa porastom udela montmorilonita uepoksidnoj matrici termička stabilnost uzoraka ispitivanih uatmosferi vazduha neznatno poboljšana, dok u inertnojatmosferi nema uticaja na termičku stabilnost, niti namehanizam raspada hibridnih materijala na osnovu epoksidnihsmola sa različitim udelima montmorilonita. Kod sistema kodkojih je dodavan termoplastični poliuretanski elastomer,zaključeno je da pri većem sadržaju segmentiranih poliuretanau epoksidnoj matrici (10 i 15 mas.%) proces umrežavanjazapočinje na nižim temperaturama i maksimalna brzina seostvaruje na nižim temperaturama, a najveća vrednostpromena ukupne entalpije reakcije umrežavanja je određena zahibridni materijal sa poliuretanom koji u svojoj strukturi ima30 mas.% tvrdih segmenata. Zatezna čvrstoća hibridnihmaterijala raste sa porastom udela tvrdih segmenata u strukturipoliuretana, kao i sa porastom masenog udela poliuretanskogelastomera u epoksidnoj matrici. Dodatkom termoplastičnihsegmentiranih poliuretana značajno je povećano prekidnoizduženje epoksidnih smola. Sa porastom udela tvrdihsegmenata kod poliuretana dodatih u istom masenom procentuu epoksidnu matricu, tvrdoća raste. Ustanovljeno je da nakonačna svojstva hibridnih materijala utiče izbor polaznihkomponenti, način umešavanja punila u matricu i uslovi prikojima se vrši umrežavanje. Zaključeno je da je dobropoznavanje kinetičkih parametara reakcije umrežavanja važnoza pravilan odabir optimalnih uslova za proizvodnju i preraduhibridnih materijala u industrijskim uslovima.
In this thesis the influence of clay fillers and thermoplasticsegmented polyurethanes on the curing kinetics, structure andproperties of functional hybrid materials based on epoxy resinswas assessed. Two sets of hybrid material samples wereprepared. First type of samples was based on epoxy resin witha different content of organically modified montmorillonite (0,1, 3, 5 and 10 wt. %) and crosslinking with hardener JeffamineD-230. Second type of samples was based on epoxy resin,having different content (10, 15 and 20 wt. %) of thermoplasticsegmented polyurethane with different content of hardsegments (20, 25 and 30 wt. %) based on aliphaticpolycarbonate macrodiols and hexamethylene diisocyanate,with chain extender 1,4-butanediol and the catalyst, dibutyltindilaurate, and also a sample without added elastomericpolyurethane and crosslinking with hardener Jeffamine D-2000. The curing of the hybrid materials based on epoxy resinssystems were investigated by non-isothermal differentialscanning calorimetry (DSC). The kinetic study byisoconversion models has been carried out using data fromDSC. The synthesized materials were analyzed by dynamicmechanicalanalysis (DMA), atomic force microscopy (AFM)as well as TG-DSC and TG-MS methods and mechanicalproperties (tensile strength, elongation and hardness at ShoreA) were determined. Epoxy based hybrid material with 10 wt.% of the organically modified montmorillonite hassignificantly lower activation energy values for the definedreaction rates, thereby confirming the catalytic effect of theclay with the layered structure when present in the reactionmixture in sufficient quantity. The diffusion effects at the endof the reaction are more pronounced in the presence ofmontmorillonite, which indicates that its presence affects theentire curing mechanism. It was found that G', along withmontmorillonite content, is affected by the degree of particledispersion inside the polymer matrix. It was concluded that theaddition of montmorillonite up to 3 wt. % improvesinvestigated mechanical properties, while the samples with 5and 10 wt. % of montmorillonite resulted in agglomeration ofthe filler particles, which negatively influenced theinvestigated properties, except for the hardness whichincreases linearly with the addition of montmorillonite. TGanalysis shows that the increase of montmorillonite content inthe epoxy matrix slightly improves the thermal stability in theair, while in the inert atmosphere there is no influence on thethermal stability nor on the mechanism of the decompositionof epoxy based hybrid materials. In the system with athermoplastic polyurethane filler, it was concluded that hybridmaterials with a higher content of segmented polyurethane (10and 15 wt. %), curing process starts at lower temperatures andthe maximum speed is achieved at lower temperatures and thehighest value of changes in total enthalpy of the crosslinkingreaction is determined for the epoxy hybrid material withpolyurethanes containing 30 wt. % of hard segments. Tensilestrength of hybrid materials increases with the increase of hardsegments content in the polyurethane elastomer as well as withthe increase of polyurethane content in the epoxy matrix. Theaddition of thermoplastic segmented polyurethanessignificantly increased the elongation at break of preparedepoxy resins hybrid materials. The increase of the hardsegments content in polyurethane, in the same ratio, improveshardness of epoxy based hybrid material. It was concluded thatthe final properties of hybrid materials are influenced by theselection of initial compounds, methods of processing and thecuring conditions. It was concluded, as well that knowing thekinetic parameters of curing reaction is important for theproper selection of optimal parameters for production andprocessing of hybrid materials in industrial conditions.

Uvođenje nanočestica u stomatološke kompozitne materijale predstavlja pokušaj da se odgovori univerzalnim zahtevima za kvalitetom direktnog zubnog ispuna, i da se stvori materijal koji kombinuje visoku mehaničku otpornost sa dobrim estetskim karakteristikama i zadovoljavajućim kvalitetom poliranja. Cilj sprovedene studije je bio da se ispita uticaj nanočestica, i soft-start metode svetlosne indukcije polimerizacije na mehanička i površinska svojstva savremenih stomatoloških nanokompozita, dostupnih na tržištu. Ispitana su četiri stomatološka nanostrukturisana kompozitna materijala na bazi smola i jedan univerzalni mikrohibridni kompozit, kao referentni materijal (Filtek Z250, 3M ESPE). Korišćena su po dva reprezentativna materijala iz dve podgrupe nanokompozita: nanopunjenih (Filtek Ultimate Body, 3M ESPE i Filtek Ultimate Translucent, 3M ESPE) i nanohibridnih kompozita (Filtek Z550, 3M ESPE i Tetric EvoCeram, Ivoclar Vivadent - TEC). Uzorci su polimerizovani nakon svetlosne aktivacije polimerizacije, uz korišćenje dva svetlosna režima: konvencionalnog i soft start režima. Pritisna i zatezna čvrstoća (dobijena poprečnim sabijanjem valjka, engl. diametral tensile strength) testirane su na Univerzalnoj mašini, kidalici. Tvrdoća uzoraka merena je testom za određivanje tvrdoće po Vickersu. Površinska tekstura i parametri hrapavosti određeni su skeniranjem površine mikroskopom atomskih sila. Uopšteno, TEC je pokazao najniže vrednosti pritisne i zatezne čvrstoće, i tvrdoće, i statistićki je značajno bio slabiji od drugih testiranih materijala kroz sve mehaničke testove. Suprotno, TEC je imao najniže vrednosti parametara hrapavosti među testiranim materijalima. Spoj prepolimerizovanog punioca i polimerne baze u ovom materijalu pokazao se kao njegova slaba tačka. Navedeni materijal je iz tog razloga pokazao značajno slabiju otpornost od ostalih na razvijene napone izazvane dejstvom mehaničkih sila. Čestice nanodimenzija u sastavu stomatoloških polimernih kompozita, samostalno, nisu imale značajan uticaj na poboljšanje mehaničkih i površinskih svojstava testiranih kompozita. Zaključeno je i da se procentualna zastupljenost neorganskih čestica u polimernoj bazi ne može smatrati apsolutnim kriterijumom kvaliteta kompozita, u pogledu njihovih mehaničkih svojstava. Samo srodni materijali, izrađeni istim tehnološkim postupkom, koji imaju veoma sličan ili isti hemijski sastav, pokazali su se kao mehanički superiorniji ukoliko su sadržali veći procenat neorganske komponente u svom sastavu. Nano prefiks u nazivu klase materijala ne garantuje sigurnu prednost stomatoloških nanokompozita nad univerzalnim mikrohibridnim kompozitima.
The introduction of nanoparticles in dental composite materials was an attempt to respond to the universal quality requirements for a direct dental restoration, and to create a material that meets the needs of high mechanical resistance, good aesthetic characteristics and surface properties of tooth restoratives. The aim of this study was to investigate the effect of nanoparticles in materials composition, and the soft start photoactivation method on the mechanical and surface properties of contemporary dental nanocomposites, available in the market. Four dental resin based nanostructured composites were tested along with a universal microhybrid one, as reference material (Filtek Z250, 3M ESPE). Two representative materials from the two classification subgroups were tested, nanofilled (Filtek Ultimate Body, 3M ESPE and Filtek Ultimate Translucent, 3M ESPE) and nanohybrid composites (Filtek Z550, 3M ESPE and Tetric EvoCeram, Ivoclar Vivadent, TEC). Polymerization of the samples was light activated using two light modes: conventional and soft start. Compressive and diametral tensile strength were tested on the Universal testing machine. The Vickers hardness was also determined. Surface texture and roughness parameters were examined by atomic force microscopy. Generally, TEC showed the lowest values of compression, tensile strength and hardness, and was statistically different from the other tested materials throughout all mechanical tests. In contrast, TEC had the lowest values of roughness parameters among the tested materials. In this material, contact zone of prepolimeryzed filler and polymer matrix appeared to be a weak point. For this reason, this material showed significantly lower resistance than the others on mechanically developed stresses. Nanosized particles within the dental polymer composites, individually, did not have a significant influence on improving the mechanical and surface properties of tested composites. It is concluded that the inorganic volume fraction in composites cannot be considered as an absolute criterion of their quality, regarding their mechanical properties. Only similar materials, made using the same technological process, which have very similar or the same chemical composition, and similar technological method of synthesis and optimization of organic and inorganic components, showed improved mechanical strength, if they contained a higher percentage of inorganic components in their composition. Nano prefix in the name of material’s class does not guarantee the pure advantage of dental nanocomposites in comparison with the universal microhybrid composites.

Uobičajeni pristup i testiranju biološkog ponašanja materijala je da se počne sa jednostavnim in vitro testovima baziranim na ćelijskim kulturama. In vitro testovi citotoksičnosti su danas jedan od osnovnih načina za procenu biološkog odgovora na materijal jer su brži, lakši za ponavljanje, ocenjivanje i jeftiniji u odnosu na eksperimente koji se izvode na životinjama i ljudima. Koriste se kao neka vrsta skrining testova za procenu biološke sigurnosti materijala. Za razliku od ćelijskih kultura, istraživanja koja uključuju eksperimentalne životinje pružaju bolji uvid u biokompatibilnost materijala, zbog mogućnosti praćenja kompleksnog imunološkog odgovora živog organizma. Smatraju se neophodnim za ocenu biloških odgovora na novi materijal, pre nego što se on upotrebi na ljudima. Mnogi aspekti biološkog odgovora ne mogu biti reprodukovani in vitro testovima uključujući krvne interakcije, zarastanje rana, reakcije preosetljivosti, karcinogenezu, hroničnu inflamaciju. Eksperimenti na životinjama pružaju informacije o ovim tipovima efekata bez izlaganja ljudi riziku. Cilj ovog istraživanja bio je da se oceni biokompatibilnost objekata od polimera na bazi epoksi smole Accura® ClearVue™ (hemijski sastav: 4,4’- izopropilidendicikloheksanol, produkti oligomerne reakcije sa 1-hlor-2,3- epoksipropanom(40-65%), smešа triaril-sulfonijum soli (50% propilen-karbonata i 50% triaril-sulfonijum heksafluoroantimonatnih soli) (1-10%) i 3-etil-3hidroksimetil-oksetan(10-20%). U oceni citotoksičnosti materijala Accura® ClearVue™ korišćeni su agar diguzioni i MTT test. Oba testa rađena sun a ćelijskim kulturama L929 (mišiji fibroblasti) i MRC-5 (humani fibroblasti). Ocena biokompatibilnosti testiranog materijala vršena je na osnovu urađenog testa iritacije oralne mukoze na modelu bukalne kesice hrčka, što je definisano standardom ISO 10993-10:2010. Biokompatibilnost materijala ispitana je i implantacijom uzoraka u potkožno tkivo dorzuma pacova soja Wistar.
Uobičajeni pristup i testiranju biološkog ponašanja materijala je da se počne sa jednostavnim in vitro testovima baziranim na ćelijskim kulturama. In vitro testovi citotoksičnosti su danas jedan od osnovnih načina za procenu biološkog odgovora na materijal jer su brži, lakši za ponavljanje, ocenjivanje i jeftiniji u odnosu na eksperimente koji se izvode na životinjama i ljudima. Koriste se kao neka vrsta skrining testova za procenu biološke sigurnosti materijala. Za razliku od ćelijskih kultura, istraživanja koja uključuju eksperimentalne životinje pružaju bolji uvid u biokompatibilnost materijala, zbog mogućnosti praćenja kompleksnog imunološkog odgovora živog organizma. Smatraju se neophodnim za ocenu biloških odgovora na novi materijal, pre nego što se on upotrebi na ljudima. Mnogi aspekti biološkog odgovora ne mogu biti reprodukovani in vitro testovima uključujući krvne interakcije, zarastanje rana, reakcije preosetljivosti, karcinogenezu, hroničnu inflamaciju. Eksperimenti na životinjama pružaju informacije o ovim tipovima efekata bez izlaganja ljudi riziku. Cilj ovog istraživanja bio je da se oceni biokompatibilnost objekata od polimera na bazi epoksi smole Accura® ClearVue™ (hemijski sastav: 4,4’- izopropilidendicikloheksanol, produkti oligomerne reakcije sa 1-hlor-2,3- epoksipropanom(40-65%), smeša triaril-sulfonijum soli (50% propilen-karbonata i 50% triaril-sulfonijum heksafluoroantimonatnih soli) (1-10%) i 3-etil-3hidroksimetil-oksetan(10-20%). U oceni citotoksičnosti materijala Accura® ClearVue™ korišćeni su agar diguzioni i MTT test. Oba testa rađena sun a ćelijskim kulturama L929 (mišiji fibroblasti) i MRC-5 (humani fibroblasti). Ocena biokompatibilnosti testiranog materijala vršena je na osnovu urađenog testa iritacije oralne mukoze na modelu bukalne kesice hrčka, što je definisano standardom ISO 10993-10:2010. Biokompatibilnost materijala ispitana je i implantacijom uzoraka u potkožno tkivo dorzuma pacova soja Wistar.
The usual approach in testing biological behavior of materials is to start with simple in vitro tests based on cell cultures. In vitro cytotoxicity tests are one of the basic methods of assessing the biological response to material because they are faster, cheaper, easier for repeating and evaluating compared to experiments carried out on animals and humans. They are used as a kind of screening test for evaluating the biosafety of materials. Unlike cell culture, studies involving experimental animals provide better insight into the biocompatibility of materials due to the possibility of monitoring the complex immune response of a living organism. They are considered necessary for assessing the biological response to new material before it is used on humans. Many aspects of a biological response cannot be reproduced with in vitro tests, including blood interaction, wound healing, hypersensitivity reactions, carcinogenesis, chronic inflammation. Animal experiments provide information about these types of effects without exposing humans to risk.  The aim of this study was to evaluate the biocompatibility of polymer objects on the basis of epoxy resins Accura® ClearVue ™ (chemical composition: 4.4' Isopropylidenedicyclohexanol, oligomeric reaction products with 1-chloro-2.3-epoxypropane (40-65%), a mixture of triaryl sulfonium salt (50% propylene carbonate and 50% of a triarylsulfonium hexafluoroantimonate salt) (1- 10%) and 3-ethyl-3-hydroxymethyl-oxetane (10-20%). In the assessment of the cytotoxicity of materials Accura® ClearVue ™ agar diffusion and MTT tests were used. Both tests were conducted on cell cultures L929 (mouse fibroblasts) and MRC-5 (human fibroblasts). An assessment of the biocompatibility of the tested material was done on the basis of an oral mucosa irritation test on a hamster cheek pouch as defined by ISO 10993-10: 2010. The biocompatibility of the material was also tested with the implantation of a samples into the dorsal subcutaneous tissue of a Wistar rats. The subcutaneous implantation test, as one of the most reliable methods for assessing the biocompatibility of dental materials, is defined by ISO 10993-6: 2010. The study was conducted on 30 rats which were sacrificed in groups

This report is a study on the smoldering combustion of natural sawdust from untreated woods. The objective was to develop and test an experimental technique to study the fundamental behavior of sawdust smolder. The experimental setup was an annulus cookstove packed with sawdust between the inner and outer radii creating a central hollow core. The sawdust was ignited by a heating coil wrapped around the inner radius. Thermocouples were embedded in the sawdust bed fanning out in the radial direction, and temperature was recorded throughout the smolder process. Consistent with the literature, the experimental results indicate that wood smolder consists of three pathways, 1) sawdust to char, 2) sawdust to volatiles, and 3) char to ash. Pathways 1 and 3 can be clearly characterized by the temperature profile of the smolder; however, pathway 2 often involves flaming of the sawdust and is beyond the scope of this study. Pathway 1, sawdust to char, is an endothermic reaction that results in a clearly defined char front that propagates across the sawdust bed in the radial direction. As smolder proceeds, the char continues to oxidize and breaks down into non-volatile products such as water vapor and carbon dioxide (CO₂) in further exothermic reactions. Pathway 2, char to ash, is an exothermic reaction that can lead to glowing combustion when exposed to sufficient amounts of oxygen and results in spikes in temperature. In contrast to the clearly defined char front, the ashing zone traces cracks in the sawdust where air can penetrate through, and has no discernible front. Section 1 discusses the motivation behind the study of sawdust cookstoves in third world countries, in particular Ghana, to replace wood with sawdust as a cheap alternative for household fuel. Section 2 details the experimental setup of the cookstove rig and the methodology of the experiments conducted. Section 3 reports the results of the experiments and analyzes the temperature profiles in relation to the three types of chemical reactions as noted above. Section 4 concludes with a summary of the results and discusses efforts in measuring emissions from the smolder and future work to be done.
text

This dissertation critically examines why mid-Victorian fiction often dismisses or complicates monetary transactions and monetary charity, even as it negatively portrays differences in social status and wealth. I argue that the novel uses representations of failed charity to reconstruct, however briefly, a non- monetary and non-economic source of value. Further, I examine how the novel uses techniques of both genre and style to predict, form, and critique alternate, non-economic, social models. While tension surrounding the practice of charity arises in the late eighteenth century, the increasing dominance of political economy in public discourse forced Victorian literature to take a strong stance, for reasons of both ethics and genre. This stance is complicated by the eighteenth-century legacy that sees charity as a kind of luxury. If giving to the poor makes us feel good, this logic suggests, surely it isn’t moral. Thus, while much eighteenth- and nineteenth-century literature remains dedicated to the ethics of charity, the practice becomes immensely complex. By discussing the works of Tobias Smollett, Charles Dickens, Elizabeth Barrett Browning, and George Eliot, this project exposes a wide variety of responses to this deep cultural anxiety. These authors are, ultimately, strongly invested in redefining the meaning of benevolence as a valid form of social action by moving that benevolence away from monetary gifts and toward abstractly correct moral feelings, though their individual solutions vary widely.
text