Letteratura scientifica selezionata sul tema "Polyetherketoneketone"

Introduction: We assessed the effect of different available denture cleansers on the roughness and hardness of polyetherketoneketone, thermoinjection-molded polyamide, and polymethylmethacrylate. Materials and Methods: A total of 150 disc-shaped specimens were fabricated (10 mm × 2 mm) from these three denture base resins, and divided into five subgroups ( n = 10) according to immersion procedures. One of these groups subjected to distilled water served as control, whereas other groups were subjected to daily cleansing with four denture cleansers (Corega, Protefix, Curaprox, and Perlodent) for 8 h a day for 140 days. The surface roughness and hardness values of specimens were recorded by measuring twice at baseline, and again after application of chemical solutions. Topography alterations after treatments were assessed with scanning electron microscopy. The data were subjected to statistical analysis and comparison among groups was done using Kruskal Wallis and Wilcoxon Signed Ranks tests. P-value <0.05 was considered significant. Results: The surface roughness of polyetherketoneketone, polymethylmethacrylate, and polyamide dentures was increased significantly by chemical solutions of denture cleansers. While the hardness value of polyetherketoneketone was not affected significantly after immersion in denture cleansers, those of polymethylmethacrylate and polyamide decreased significantly. Compared with Curaprox, the effervescent tablets significantly altered the surface hardness and roughness of polyamide. Conclusion: Denture cleansers can considerably alter the surface roughness and hardness of denture base resins and should be used carefully depending on the material.

Objectives: The primary objective of this study is to investigate the resistance to fracture of Polyetherketoneketones PEKK, used as post and core by fabrication in different diameters in the canal, and comparing the test results for each group. Methods: Thirty extracted mandibular premolars were selected, endodontically treated and prepared to receive the post and cores milled from polyetherketoneketone disk. The specimens were randomly divided into five groups (n = 6) respectively: group 1 received pekk post with diameter = 0.70 mm, group 2 received pekk post with diameter = 0.90 mm, group 3 received pekk post with diameter = 1.10 mm, group 4 received pekk post with diameter = 1.50 mm, and group 5 received pekk post with diameter = 1.70 mm. All the posts were cemented using a self-adhesive resin cement. Fracture resistance was tested using a universal testing machine, failure patterns were then observed visually and radiographically. For the fracture resistance test, the Universal Testing machine employed the load cell of 10KN and the speed of the cross head of 1mm/min. Data was analyzed using Oneway analysis of variance (ANOVA) followed by Tukey post-hoc test in order to determine significant differences among groups and the materiality threshold was set at α = 0.05. Results: Statistical analysis revealed that the observed differences among the five groups were not significant. None of the PEKK posts caused any fracture in the root, and this observation was visually and radiographically confirmed across all groups. Conclusions: The dentist will be able to turn the diameter of the PEKK post and core as thin as 0.70mm till 1.70mm depending on the clinical requirement with no risk of root fracture, as specified by the guidelines of this research.

Osteoporotic fractures are prevalent in society, and their incidence appears to be increasing as the worldwide population ages. However, conventional bone repair materials hardly satisfy the requirements for the repair of pathological fractures. Here, we developed a biomimetic polyetherketoneketone scaffold with a functionalized strontium-doped nanohydroxyapatite coating for osteoporotic bone defect applications. The scaffold has a hierarchically porous architecture and mechanical strength similar to that of osteoporotic trabecular bone. In vitro and in vivo studies demonstrated that the scaffold could promote osteoporotic bone regeneration and delay adjacent bone loss via regulating both osteoblasts and osteoclasts. In addition, the correlations between multiple preimplantation and postimplantation parameters were evaluated to determine the potential predictors of in vivo performance of the material. The current work not only develops a promising candidate for osteoporotic bone repair but also provides a viable approach for designing other functional biomaterials and predicting their translational value.

Dental alloys, and later zirconia, have been used in dentistry as frameworks for many years in making crowns and bridges veneered with ceramic e.g. feldspathic porcelain. Such methods of restoring teeth have been extensively studied both in the laboratory and clinically. Although such substructures have excellent strength there remains a large properties mismatch between these materials and bone or dentine e.g. elasticity. Furthermore, other drawbacks have been documented such as possible allergies, colouring of alloy margins, veneer chipping and excessive wear to opposing natural dentition. Polyaryletherketone (PAEK) thermoplastic biomaterial polymers such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) have been successfully applied in different medical applications with the latter recently being introduced to dentistry as a restorative material. The material is called Pekkton® ivory (Cendres+Métaux, SA, Switzerland) and is proposed to be used for fabricating both monolithic and bi-layered structures veneered with indirect composite resin. The manufacturer recommends methods similar to well-established restorations such as alloy and ceramic based crowns which makes it a user friendly material for both dental clinics and laboratories. Furthermore, the material’s properties such as high strength, low elastic modulus close to that of dentine, high temperature, chemical, hydrolysis and wear resistance, makes it a promising material for the replacement of tooth material. There is little published data about this material and hence the aim of this research was to evaluate the manufacturing process, aesthetic properties, structural integrity and durability of bi-layered crowns made from PEKK based thermoplastic high performance polymer (Pekkton® ivory, Cendres+Métaux, SA) and veneered with indirect light cured composite (Vita VM LC, VITA Zahnfabrik H. Rauter GmbH & Co.KG, DE). The processing route for Pekkton® ivory is either via milling or hot-pressing and the procedures were compared. The polymer-based restoration was compared to equivalent zirconia and metal based bi-layered restoration systems veneered with either light cured composite resin or feldspathic porcelain. Optical properties of each crown system were compared using a UV and visible light spectrophotometer. Structural integrity was compared for each system by testing the fracture resistance of the crowns using a universal testing machine and durability was evaluated by testing the fatigue limit and fatigue life using a fatigue chewing apparatus. The research hypothesis is that the PEKK polymer as anunderlying substructure material will perform equivalently to metal and zirconia substructures when veneered with light cured composite in the aspects of optical properties, strength and durability. The outcome of the study established a pressing protocol for PEKK using a standard ceramic pressing furnace where the pressed samples showed no significant differences in the CIEL*a*b* colour values, hardness or biaxial flexural strength to those samples produced via milling. There was no significant optical difference between the systems compared, the study found no evidence of difference in the CIEL*a*b* colour value of PEKK, zirconia or metal based samples when veneered with the same composite veneer. However, zirconia based groups displayed greater translucency with the composite veneer and feldspathic porcelain veneer. The fracture resistance of the PEKK and metal composite veneered crowns showed to be comparable, whereas zirconia based crowns demonstrated significantly lower fracture resistance. The durability of the PEKK composite veneered crowns showed the highest fatigue limit in comparison to the zirconia and metal composite veneered crowns. Similarly they showed the highest survival rate in the fatigue life assessment under the same cyclic load. Furthermore, the fracture mode was significantly different than observed with the zirconia and metal based crowns. The conclusion was that this material is promising for use as a restorative material and that clinical evaluation should be undertaken.

Les matériaux thermoplastiques gagnent en popularité dans l'industrie aérospatiale en tant qu'alternatives aux métaux et aux thermodurcissables, offrant des avantages tels que la rapidité de fabrication, la réparabilité et la recyclabilité. Leur capacité à ramollir et à fondre sous l’effet de la chaleur leur permet d’être soudés sans avoir besoin d'incorporer de composants. De plus, certains thermoplastiques présentent une résistance aux environnements extrêmes, tels que des températures élevées et divers produits chimiques, ce qui les rend idéaux pour des applications exigeantes. Ces caractéristiques font des thermoplastiques des matériaux adaptés aux applications où la réduction du poids, les performances et la durabilité sont des critères essentiels. Dans ce contexte, le soudage par transmission laser (LTW) se révèle être une technique efficace pour le soudage des thermoplastiques en raison de sa simplicité, de sa précision et de sa capacité à produire des joints de haute qualité. Dans cette technique, un faisceau laser traverse une partie supérieure semi-transparente et est absorbé par une pièce inférieure absorbante, ce qui génère de la chaleur à l’interface pour faire fondre et fusionner les pièces. Le procédé LTW repose sur les propriétés thermochimiques et optiques des matériaux à souder. Le soudage laser de thermoplastiques semi-cristallins, tels que les polyaryléthercétone (PAEK), nécessite une attention particulière. Le polyéthercétonecétone (PEKK) a reçu moins d'attention que le PEEK en soudage laser. Cependant, le PEKK est un matériau encore plus prometteur pour le soudage laser par transmission en raison de sa cinétique de cristallisation modifiable par rapport au PEEK. Cette thèse doctorale étudie le procédé de soudage laser par transmission du PEKK, en se concentrant sur l'influence des propriétés du matériau et des paramètres de soudage sur la morphologie et les propriétés mécaniques du joint de soudure. La configuration d’assemblage consiste en un échantillon de PEKK quasi-amorphe sur une pièce de PEKK fortement cristallisée (PEKK-A/SC). Les propriétés thermophysiques et optiques des matériaux sont caractérisées afin de s’assurer qu'ils sont adaptés au LTW. Ensuite, les paramètres du procédé, tels que la puissance du laser et l’épaisseur de la pièce semi-transparente, sont systématiquement étudiés pour comprendre leur impact sur les propriétés du joint. Certains assemblages sont recuits à la température de cristallisation à froid du PEKK pour améliorer la qualité des joints soudés. La qualité des assemblages soudés et recuits est évaluée à l'aide d'essais mécaniques de cisaillement à simple recouvrement et de la microscopie. Le procédé LTW est modélisé à l'aide de la méthode des différences finies sous environnement MatLab, en incorporant le transfert de chaleur et la cinétique de cristallisation du PEKK. Cette modélisation a permis de comprendre l'histoire thermique des échantillons pendant le soudage et de prédire l'évolution de la cristallinité du joint de soudure en fonction des paramètres de soudage. Après avoir étudié et validé le procédé LTW pour le PEKK, la thèse étend l’étude LTW aux composites PEKK renforcés par des fibres courtes de carbone (PEKK-CF). Pour permettre le LTW des échantillons PEKK-CF, le PEKK quasi-amorphe est utilisé comme pièce supérieure pour l’assemblage. Cela représente un nouveau domaine de recherche, car aucune étude antérieure n'a été trouvée sur le soudage laser par transmission des composites PEKK-CF. Le soudage des échantillons de PEKK-CF est optimisé par des essais expérimentaux, et la qualité du joint de soudure est évaluée en faisant varier l’intensité de laser. Les résultats de cette thèse contribuent à une meilleure compréhension du procédé de soudage laser par transmission du PEKK et de ses composites, et fournissent des lignes directrices pour optimiser les paramètres de soudage et améliorer la résistance des joints dans les applications industrielles
Thermoplastic materials are gaining popularity in the aerospace industry as alternatives to metals and thermosets, providing benefits such as fast manufacturing, repairability, and recyclability. Their ability to soften and melt allows them to be welded without needing to incorporate external components. Additionally, high-performance thermoplastics exhibit resistance to harsh environments, such as high temperatures and various chemicals, making them ideal for high-demanding applications. These features make thermoplastics suitable for applications in which weight reduction, performance, and durability are essential. Laser transmission welding (LTW) has emerged as an effective technique for welding thermoplastics due to its simplicity, precision, and ability to produce high-quality joints. In LTW, a laser beam passes through a semi-transparent upper part and is absorbed by a lower absorbent sample, generating heat at the interface to assemble the parts. The LTW process relies on the thermo-chemical and optical properties of the materials to be welded. Careful consideration is needed when laser welding semi-crystalline thermoplastics, like polyaryletherketones (PAEK). Polyetherketoneketone (PEKK) has received less attention than PEEK in laser welding. However, PEKK is a more promising material for LTW due to its unique crystallization properties compared to PEEK. The crystallization kinetics of PEKK can be modified, which provides better control of its crystallinity by manipulating processing parameters. This PhD thesis investigates the laser transmission welding process of PEKK, focusing on the influence of material properties and process parameters on the weld joint morphology and mechanical properties. The overlapping configuration consists of a quasi-amorphous semi-transparent PEKK sample over a highly crystallized opaque PEKK one (PEKK-A/SC). Thermo-physical and optical properties of the PEKK samples are characterized to ensure their suitability for LTW. Then, process parameters for LTW, such as laser power and thickness of the upper part, are systematically studied to understand their impact on weld joint properties. After welding, some assemblies are annealed at the cold crystallization temperature of PEKK to enhance joint quality. The quality of the weld joints is assessed by mechanical tests and microscopic observations. Single lap-shear tests are employed to identify the failure type and mechanical strength of assemblies. Microscopy is used to analyze failure zones and the weld joint morphology on the cross-section along the welding path. A numerical simulation of the LTW process of PEKK parts was developed in MatLab using the finite differences method, incorporating heat transfer and the crystallization kinetics of PEKK. This model provided insights into the thermal history of the samples during welding and predicted the evolution of weld joint crystallinity as a function of welding parameters. The developed simulations offer insights into the complex thermal and crystallization behaviors observed during LTW of PEKK parts. Furthermore, after studying and validating the LTW process for PEKK polymer, this thesis extends the LTW study to PEKK composites reinforced with short carbon fibers (PEKK-CF). To enable LTW of PEKK-CF samples, the quasi-amorphous PEKK is used as the upper part for the overlapping configuration. That represents a novel area of research, with no prior studies found on LTW of PEKK-CF composites. The welding of PEKK-CF samples is optimized through experimental trials, and the weld joint quality is evaluated under varying laser intensities and the thickness of the upper part. The findings from this thesis contribute to a deeper understanding of the LTW process for PEKK and its composites, providing valuable guidelines for optimizing welding parameters and improving joint strength in industrial applications

There has been an enormous increase in using of carbon fiber reinforced thermoplastic (CFRTP) especially carbon fiber reinforce polyetherketoneketone (CF/PEKK) in automotive and aeronautical industries. However, fundamental material removal mechanism of such material has never been elucidated in the literature. In this work, finite-element (FE) method is deployed and microscale numerical model considering fiber, matrix and interface has been established to understand the mechanisms of chip formation in orthogonal cutting of unidirectional (UD) thermoplastic CF/PEKK composites. Chip formation and subsequent surface / subsurface damage with different fiber orientations (0°, 45°, 90°, 135°) are modelled and compared. Results suggest that, for CF/PEKK, the chip formation mechanism is significantly affected by the fiber orientation and the most severe subsurface damage can be seen at fiber orientation 135°, as a result of bending fracture below the ideal machined surface.

Abstract. This paper investigates a carbon fibre-reinforced polyetherketoneketone (CF-PEKK) thermoplastic composite used for low-temperature applications like hydrogen tank applications. The degree of crystallinity of the prepreg as received first and then consolidated after hot press has been investigated. The melting temperature and glass transition, as well as the melting enthalpy and degree of crystallinity, were also studied by DSC (differential scanning calorimetry). The fibre volume fraction and void content after consolidation have been measured by acid digestion and an optical microscopy image analysis. Thermomechanical analysis (TMA) was also used in order the coefficients of thermal expansion (CTE) to be determined. Tensile and compressive Dynamic Mechanical Analysis (DMA)test were performed. Storage modulus, loss modulus, and Tan δ relationship have thus been analysed. Multifrequency DMA experiments have been conducted in order to create the master curve thanks to the time-temperature superposition (TTS).

Abstract. Laser transmission welding (LTW) is a suitable process for assembling thermoplastic materials. This joining process is use to assembly most thermoplastics, but high-performance thermoplastics, such as polyetherketoneketone (PEKK), have received less attention until now. The present work deals with joining PEKK parts by LTW in amorphous over semi-crystalline state configuration. The optical properties of amorphous and semi-crystalline states were measured. The effect of the upper part thickness (2 or 4 mm) and those of the laser power reaching the interface was assessed through the determination of the heat affected zone (HAZ) dimensions and the mechanical resistance of the bonds. Single lap shear (SLS) tests were conducted to investigate the influence of the process parameters on the interfacial strength and to validate the weld quality. The highest LSS is obtained around 60 MPa. When increasing the laser power, the dimensions of the HAZ increase, and the mechanical strength decreases.

The development of high-temperature fused filament fabrication (FFF) 3D printers has enabled the additive manufacturing (AM) of polymers and composites with relatively high thermomechanical properties. Among them is polyetherketoneketone (PEKK) reinforced with short carbon fibers (CF-PEKK). PEKK is a high-performance thermoplastic that belongs to the polyaryletherketone (PAEK) polymer family with excellent mechanical properties. In particular, it offers a glass transition temperature of ~140°C, a relatively high modulus that can be readily enhanced by carbon fiber addition, and specific strength comparable to aluminum alloys. Therefore, there is a growing interest in using CF-PEKK to replace metal parts. Low dimensional accuracy and resolution, high porosity, and poor inter-layer strength [1-3] have limited FFF parts to rapid prototyping and non-structural applications. This paper aims to investigate extrusion rate, a printing parameter, and post-annealing as a potential solution to reducing porosity and enhancing inter-layer strength in CF-PEKK printed parts. A 5% increase in the theoretical extrusion multiplier (EM) resulted in a 1.6% reduction of void content accompanied by a 30% improvement in the inter-layer tensile strength of CFPEKK coupons. The impacts of extrusion rate and post-annealing (in a salt-packed container) on the printing quality of CF-PEKK parts are also determined. No significant structural or dimensional changes were detected with the higher extrusion rate or annealing in salt. This paper provides a new understanding of mechanical properties, processing, printability of CF-PEKK, and their AM challenges.

Abstract Polymer cold spray has yielded lower deposition efficiency (DE) and quality deposits compared to metal cold spray. The disparity stems from metals being studied far longer than polymers in cold spray; in addition, polymers exhibit richer thermo-mechanical behavior. An experimental study was conducted to examine the effects of polymer feedstock degree of crystallinity (D) on cold sprayed deposits of polyetherketoneketone (PEKK), a thermoplastic used in aerospace and other high-performance applications. As deposition relies on the plastic deformation of the impacting particle, polymers with high D may inhibit deposition, reducing deposit quality and efficiency. This study evaluates three PEKK grades produced using different ratios of terephthalic (T) to isophthalic (I) monomer moieties (T/I = 60/40, 70/30, 80/20). The ratios control D, with higher proportions of T monomers corresponding to higher crystallization rates and degrees of crystallinity. A parametric study was completed to evaluate functional process set points of system carrier gas temperature and powder mass flow rate. Using operational parameters common among the PEKK grades, spray cycles were completed for each material and quantitative responses to variation in crystallinity were evaluated through a suite of analyses. DE of the materials was assessed gravimetrically, deposit porosity was evaluated by scanning electron microscopy, and thermophysical changes to the feedstock during the spray cycle were determined by differential scanning calorimetry. Overall, we found that cold spray processing of powders of lower D formed less porous deposits with a higher DE than more crystalline powders sprayed at the same process conditions. PEKK grades with lower T/I ratios achieved DEs in the range of 60-75%, whereas the most T enriched grade only reached ~10% DE.

Thermoplastic composite (TPC) tapes can be consolidated in situ via automated fiber placement (AFP) at relatively high temperatures (>250°C) and local pressures (up to a few MPa). In situ consolidation of TPC parts requires special tooling and heated molds to prevent warping. Creating complex three-dimensional (3D) molds at a low cost and in a short time frame can facilitate TPC AFP adoption and entry into new markets requiring customized parts. The industry standard for mold manufacturing is milling or bending metal stock (typically invar, steel, or aluminum). This process can be costly and have lead times upwards of two months. Additive manufacturing can shorten the lead times significantly. Additively manufactured molds, to be used by TPC AFP, should withstand high temperatures and roller pressures. Current mold generation practices do not have a method of heating the mold surface necessary for dimensional accuracy of TPC tape-based parts. This paper investigates a process to create 3D molds via fused filament fabrication (FFF), a form of material extrusion additive manufacturing (AM), and high-performance materials that can withstand the temperatures and pressures of thermoplastic AFP application. FFF offers customized parts quickly and at a low cost. A laser-assisted AFP robot performed a layup over two heated FFF molds made of short carbon fiber reinforced polyetherketoneketone (CFPEKK), a flat plate and one with a one-axis curvature. These specimens performed well with no noticeable permanent deformation of the mold caused by either the roller or the laser demonstrating the viability of this mold generation process to create 3D molds usable with TPC AFP.

Semi-crystalline thermoplastic composites, such as carbon fiber-reinforced polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), are processed and consolidated while melted at high temperatures. During cool-down, polymer chains fold into lamellar structures at the nanoscale to form crystalline morphology. These lamellar structures radiate from a nucleus, creating spherulitic structures in bulk polymers, and transcrystallinity in fiber reinforced polymers. A certain amount of thermal degradation occurs when the thermoplastic matrix is melted, and the amount of degradation is a factor of several parameters such as melting temperature, time at melt, and whether the material is processed in an inert environment such as nitrogen. One form of degradation that occurs in the matrix is cross-linking and oxidation. In this case, the polymer chain breaks and new bonds form between chains or within the chain. Moreover, thermal degradation affects crystallization, the lamellar thickness and spacing, and overall degree of crystallinity. The spacing between lamellar structures can be measured through Small Angle X-ray Scattering (SAXS) at nanoscale, while the degree of crystallinity can be found using Wide Angle X-ray Scattering (WAXS). To study thermal degradation, the effect of melting temperature, environmental condition, and reprocessing was investigated on samples of neat PEEK, as well as carbon-fiber PEKK prepreg. Additionally, these samples were thermally cycled multiple times, and repeats were performed for each condition. Degree of crystallinity, spacing, and lamellar thickness were measured using an x-ray scattering system. To study underlying physics and correlations, a probabilistic Machine Learning (ML) framework was used for regression. Using this approach, different thermal degradation mechanisms for neat resin and prepreg samples were demonstrated at the nanoscale. The differences were explained in terms of crystallinity and nucleation around fibers in prepreg. This framework provides a unique holistic understanding of crystal formation and degradation, which affects the reprocessability and end-part properties of semicrystalline thermoplastic composites.