No description available.

A systematic study of the surface-initiated polymerisation kinetics of a relatively new type of atom transfer radical polymerisation (ATRP), activators regenerated by electron transfer (ARGET) ATRP, is first demonstrated in this report. Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(methyl methacrylate) (PMMA) were successfully grown from silicon surfaces at room temperature by surface-initiated ARGET ATRP using a "3rd generation" cationic macroinitiator. The polymer films were analysed by ellipsometry, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). With the initial experiment showing that water accelerated conventional ATRP but made it less controlled, the effect of solvent on ARGET ATRP was also evaluated. The living character of ARGET ATRP was demonstrated by successfully reinitiating PHEMA-grafted silicon wafers to grow a second block of PHEMA. Initiator density was shown to have a great effect on the growth rate of PHEMA film thickness on silicon surfaces by comparing the ARGET ATRP growth of PHEMA films using two different initiators, "1st generation" and "3rd generation" cationic macroinitiators, which have different ratios of initiating groups to positive charge. Another type of initiator for ATRP systems, an amide silane, was then investigated as an alternative to polyelectrolyte macroinitiators to avoid degrafting. The effects of solvent, 2, 2′ bipyridyl (bpy) ligand concentration and different types of reducing agent on the growth of PHEMA film from amide-initiator coated silicon wafers by ARGET ATRP were then explored at room temperature. However, it was found that the swings in the uncontrolled laboratory ambient temperature caused inter-sample and inter-experiment variability and so could make the evaluations inaccurate or even wrong. An investigation of temperature on ARGET ATRP showed a dramatic effect on the polymerisation rate. The higher the temperature, the faster the polymerisation proceeded. Therefore, the effects of solvent, ratio of bpy to Cu and reducing agent on the ARGET ATRP growth of PHEMA brushes from amide initiator-coated silicon wafers were re-evaluated at a constant temperature, 30 °C. The development of a polydopamine-based initiator, which was designed to be able to be immobilised on a wide range of surfaces, is then presented in this report. Polydopamine was first shown to be able to deposit on various types of material surfaces by oxidative polymerisation in aqueous solution. Bromoester initiating groups for ATRP systems were incorporated into polydopamine coatings by reacting a fraction of the dopamine monomer with 2-bromoisobutyryl bromide (BIBB) before polymerisation. The modified polydopamine initiator film grew at a comparable rate to unmodified polydopamine, with a 45 nm being grown in 24 hours. Successful incorporation of initiator groups was confirmed by XPS and FTIR, and by the growth of PMMA and PHEMA polymer brushes by ARGET ATRP from the polydopamine initiator coatings. A PMMA brush with a thickness of 239 nm was grown in 72 hours, indicating that the grafting density is sufficiently high to be in the brush regime. This initiator was demonstrated to be able to deposit on a range of substrates, such as metals (steel) and polymers (polystyrene), and successfully initiate polymer growth, demonstrating its broad applicability. The assessment of ARGET ATRP as a simple and effective tool for interfacial shear strength improvement in cellulose-based fibre reinforced thermoplastic composites is finally presented. It was demonstrated by control experiments that grafting polystyrene on glass fibre surfaces via ARGET ATRP greatly improved the interfacial adhesion between glass fibres and a high-impact polystyrene (HIPS) matrix, although a specific value of interfacial strength was not obtained due to failure of the modified glass fibre composite samples in areas other than the interface. It was then demonstrated that PMMA was successfully grown from the surfaces of polydopamine initiator coated cotton fibre and BIBB-modified cotton fibre by ARGET ATRP. Polydopamine initiator was shown to be a better initiator for cotton fibre than BIBB, possibly since the adsorbed water on cotton fibres can react with BIBB. The improvement of interfacial adhesion between cotton fibres and a PMMA matrix by grafting PMMA on the cotton surface was assessed by peel testing of cotton fibres pressed into PMMA sheets. There is a clear trend in the relationship between the peeling force and growth time of PMMA on the cotton fibre by ARGET ATRP, although the inter-sample reproducibility is not good.

It is an important issue for manufacturing and operation to formulate reliability about the effects of the moisture absorption and IR reflow parameters on IC packages. Two problems, the warpage of the thin IC package, and characterizing the adhesion features of IC package¡¦s interface, are studied in this dissertation. In a thin IC package, the CTE and CHE mismatch between materials are primarily attributed to the warpage which occurs when the package is being mounted on a PCB. The existence of defects in the corresponding interfaces can gradually degrade the interfacial adhesion when IC package is exposed to the high temperature and humidity. In this dissertation, the stability equations for the warpage in a thin IC package without the solder balls being subjected to hygrothermal loading, by modeling it as an initially perfect/imperfect composite plate, is developed. The analytical closed-form solutions are found and used to compute not only the critical moisture content but also the warpage occurrence before the critical loads are reached. The hygrothermal buckling phenomenon is checked by shadow moiré whole-field maps with different moisture content. The results indirectly indicate that the thin PBGA package has little imperfection. For characterizing the adhesion features of IC package¡¦s interface, the fuzzy controller is used to stabilize multiple performance characteristics, i.e., the moisture weight gain and adhesion strength, for the button shear test specimen. Parameters design, although based on the Taguchi method, can optimize the performance characteristic through the setting of process parameters and can reduce the sensitivity of the system performance to sources of variation. The control rules of the fuzzy controller were formed using the author¡¦s experience and knowledge of IC packaging process. The control parameters to be tuned were the membership functions. Therefore, the controller¡¦s performance depended on the membership functions. The fuzzy controller combined Taguchi parameter design, which makes the control performance insensitive to the operating condition change and noise, was used to determine the membership functions.

No description available.

No description available.

We studied PLA-microcrystalline cellulose composites, focusing on the effects of processing, particle size and surface modification. The thermal and mechanical properties of these PLA based composites were studied and the effect of cellulose addition on PLA degradation was analyzed. For our system, the degradation rate was found to depend on initial sample crystallinity, pH of the degradation media and cellulose content of the composite. Composites were prepared using solution processing and melt mixing methods. The processing methods influenced the polymer's ability to crystallize affecting the mechanical properties. Isothermal crystallization studies carried out to study the kinetics of crystallization showed melt processed samples to have lower half time for crystallization and higher value for the Avrami exponent. The crystallization rate of PLA was also found to depend on surface chemical composition of cellulose particles and the particle size. Influence of filler surface modification on the composite properties was studied via grafting of lactic acid and polylactic acid to cellulose particles and the effect of filler size was studied using hydrolyzed microcrystalline cellulose particles. A simple esterification reaction that required no external catalyst was used for surface modification of cellulose particles. Surface modification of cellulose particles enhanced the static and dynamic mechanical properties of the composite samples due to improvement in the PLA-cellulose compatibility that resulted in better interfacial interactions. The utility of cellulose, available from a renewable resource, as an effective reinforcement for PLA is demonstrated.

In present study, high energy electrons were used to modify blends based on RP and PP under two conditions: stationary and in-stationary conditions. Modification of blend under stationary condition is a process which is established in industrial application and where required absorbed dose is applied to form parts (after molding) at room temperature and in solid state. On the contrary, the modification of blend with high energy electrons under in-stationary condition is a new process (electron induced reactive processing) where required absorbed dose is applied to a molten state during melt mixing process. The modification of blend based on RP and PP under stationary condition resulted in slightly enhancement of tensile properties while the modification of this blend under in-stationary condition resulted in deterioration of tensile properties due to degradation of the PP matrix. Thus, special grafting agent (GA) is required for improving the tensile properties. The effect of different GAs on tensile, thermal, dynamic mechanical as well as morphological properties and melt flow properties of blends based on RP and PP were determined. The optimum absorbed dose for modification of blend based on RP and PP under both conditions was evaluated. In addition, the effect of treatment parameters of electron induced reactive processing was investigated.

La famille des élastomères silicones LSR (Liquid Silicone Rubber) de haute technicité est identifiée comme celle possédant les plus forts arguments de développement au cours des prochaines décennies en raison de leurs propriétés spécifiques et de leurs facilités de mise en forme en grande série. Notamment, le moulage par injection du LSR sur d’autres matières telles que les thermoplastiques ou les métaux est aujourd’hui possible, ce qui ouvre la possibilité d’obtenir des composants multi-matières, multi-couleurs et de nouvelles fonctionnalités. Cette thèse se concentre sur la transformation des élastomères silicones LSR dans le but de mieux appréhender les phénomènes impliqués, afin d’améliorer les procédés d’élaboration et d’optimiser les conditions de transformation des composants élastométriques mono ou bi-matières à géométrie et propriété fonctionnelle bien définie. Les comportements rhéologique, cinétique et thermique des élastomères silicones ont été étudiés et caractérisés sous des conditions réelles de mise en œuvre par différentes méthodes associées. Un modèle thermo-rhéo-cinétique a été développé et ensuite implémenté dans un code de calcul de remplissage Cadmould® pour simuler le moulage par injection des élastomères silicones LSR ou encore le surmoulage de thermoplastiques. Pour la validation des modèles choisis et des paramètres identifiés, les essais d’injection sur l’outillage industrielle instrumenté ont été réalisés et confrontés à des résultats numériques obtenus. Enfin, la caractérisation de l’adhésion et l’adhérence interfaciale entre les thermoplastiques et les élastomères silicones a été réalisé sous différentes sollicitations complexes. De plus, l’évolution d’adhérence interfaciale des assemblages collés au cours de la vulcanisation des élastomères silicones a été caractérisée par l’essai de traction en utilisant un rhéomètre rotatif sous différentes modes de chauffage. / The family of high technology silicone elastomers LSR (Liquid Silicone Rubber) is identified as having the strongest arguments for development in the coming decades due to their unique properties and easy forming in large series. In particular, the injection molding of LSR on other materials such as thermoplastics or metals is possible today, which opens the possibility of obtaining multi-material, multi-color and new features components. The work presented in this thesis focuses on the transformation of silicone elastomers in order to better understand the phenomena involved, as to improve production processes and optimize processing conditions for mono or bi-material components in geometry and property functional well defined. The rheological, curing kinetic and thermal behaviors of silicone elastomers have been studied and characterized under real conditions of production by different methods combined. A thermo-rheo-kinetic model was then developed and implemented in commercial computer software Cadmould® to simulate the injection molding process of LSR or the overmolding process of LSR on to thermoplastics. For the validation of the models chosen and the parameters identified, the injection molding tests on industrial instrumented tools were performed and compared to numerical results. Finally, the characterization of interfacial adhesion between the thermoplastic and silicone elastomers was carried out under various adhesion tests. Moreover, the evolution of interfacial adhesion in thermoplastic/silicone components during the vulcanization of silicone elastomers has been characterized by the tensile test using a rotating rheometer in different heating cycles

Polyethylene composites which contain low concentrations of metal-oxide nanoparticles e.g. ZnO and MgO are emerging materials for the use in insulations of extruded high-voltage direct-current (HVDC) cables. The challenge in the development of the composites with ultra-low electrical conductivity is to synthesize uniform and high-purity metal-oxide nanoparticles, which are functionalized with hydrophobic groups in order to make them compatible with polyethylene. The thesis reports different approaches to prepare this new generation of insulation materials. Different reaction parameters/conditions – zinc salt precursor, precursor concentrations and reaction temperature – were varied in order to tailor the size and morphology of the ZnO nanoparticles. It was shown that different particle sizes and particle morphologies could be obtained by using different zinc salt precursors (acetate, nitrate, chloride or sulphate). It was shown that 60 °C was a suitable reaction temperature in order to yield particles with different morphologies ranging from nano-prisms to flower-shaped superstructures. For removal of reaction residuals from the particles surfaces, a novel cleaning method based on ultrasonication was developed, which was more efficient than traditional water-replacement cleaning. After cleaning, the presence of one atomic layer of zinc-hydroxy-salt complex (ZHS) on the nanoparticle surfaces was suggested by thermogravimetry and infrared spectroscopy. A method involving three steps – silane coating, heat treatment and silica layer etching – was used to remove the last trace of the ZHS species from the nanoparticle surface while preserving its clean and active hydroxylated surface. The surface chemistry of these nanoparticles was further tailored from hydroxyl groups to hydrophobic alkyl groups with different lengths by reactions involving methyltrimethoxysilane (C1), octyltriethoxysilane (C8) and octadecyltrimethoxysilane (C18). MgO nanoparticles were prepared by aqueous precipitation of Mg(OH)2 followed by a partial transformation to MgO nanoparticles via heat treatment at 400 °C. The surface regions of the MgO nanoparticles convert into a hydroxide phase in humid media. A novel method to obtain large surface area MgO nanoparticles with a remarkable inertness to humidity was also presented. The method involved three steps:  (a) thermal decomposition of Mg(OH)2 at 400 °C; (b) silicone oxide coating of the nanoparticles to prevent inter-particle sintering and (c) a high temperature heat treatment at 1000 °C. These MgO nanoparticles showed essentially no sign of formed hydroxide phase even after extended exposure to humid air. The functionalized metal-oxide nanoparticles showed only a minor adsorption of phenolic antioxidant, which is important in order to obtain nanocomposites with an adequate long-term stability. Tensile testing and scanning electron microscopy revealed that the surface-modified metal-oxide nanoparticles showed improved dispersion and interfacial adhesion in the polyethylene matrix with reference to that of unmodified metal-oxide nanoparticles. The highly “efficient” interfacial surface area induced by these modified nanoparticles created the traps for charge carriers at the polymer/particle interface thus reducing the DC conductivity by more than 1 order of magnitude than that of the pristine polyethylene. / Polyetenkompositer med mycket låga halter av ZnO och MgO metalloxid nanopartiklar är en växande kategori material för användning som isolering av extruderade kablar avsedda för likriktad högspänning. En utmaning i utvecklingen av dessa material kan relateras till den praktiska kompositframställningen, vilken innefattar framställning av högrena metalloxid nanopartiklar som ytmodifieras med hydrofoba molekylstrukturer för att möjliggöra blandning med den hydrofoba polyetenplasten. Denna avhandling behandlar olika metoder för att framställa denna generation av isoleringsmaterial. Vid syntesen av de rena nanopartiklarna krävdes optimering av ett antal olika reaktionsparametrar för att uppnå tillfredställande slutresultat i form av partikelstorlekar och partikelmorfologier. Dessa inkluderade val av zinksalt, zinksaltkoncentration vid utfällning, samt reaktionstemperatur vid framställningen. Experimenten avslöjade att olika partikelstorlekar och partikelmorfologier kunde framställas som endast korrelerat mot källan av zinkjonerna, och berodde av vilka motjoner som zinkatomerna haft i zinksaltet (acetat, nitrat, klorid eller sulfat). Optimering av reaktionstemperaturen visade att ca 60 °C utgjorde en lämplig start för utvärdering av synteserna, som resulterade i olika partikelmorfologier i form av pyramidformade nanopartiklar till blomformationer. Utöver de specifika reaktionsparametrarna utvecklades även en ny ultrasonikeringsmetod för att rena ytorna hos partiklarna från motjoner relaterade till de valda specifika salterna. Metodiken som visade sig avsevärt mer effektiv än sedvanlig rening att utfällda nanopartiklar via repetitivt vattenutbyte, och skapade förutsättningar etablering av kolloidal stabilitet och fragmentering av aggregat i vattensuspensionerna. Efter ultrasonikeringsreningen beräknades de kvarvarande zinkhydroxidsalterna (ZHS) utgöra endast ett atomlager ZHS utifrån termogravimetriska data kompletterade med infraröd spektroskopi. En metod att eliminera de kvarvarande ZHS-komplexen från ytan av partiklarna tillämpades/utvecklades, inkluderade ytbeläggning av partiklarna med silan, följt av värmebehandling samt etsning av den resulterande kiseloxidytan, för att uppnå en ren hydroxylyta på partiklarna. Ytkemin hos dessa partiklar modifierades från att bestå av hydroxylgrupper till att utgöras av hydrofoba alkylgrupper med olika längder relaterade metyltrimetoxysilan (C1), oktyltrietoxysilan (C8), eller oktadekyltrimetoxysilan (C18). Även MgO nanopartiklar framställdes via vattenutfällning av Mg(OH)2 partiklar, vilka omvandlades till MgO nanopartiklar via en lågtemperatur värmebehandling vid 400°C. Ytan av dessa partiklar omvandlades dock till hydroxid i fuktig miljö. En ny metod att bibehålla den stora ytarean av MgO nanopartiklarna med anmärkningsvärd motståndskraft mot att omvandlas till hydroxid utvecklades således. Metoden består av (a) en låg temperatur omvandling av Mg(OH)2, (b) en kiseloxidytbehandling av nanopartiklarna för att undvika partikelsintring vid högre temperaturer och (c) en hög temperaturbehandling vid 1000 °C. De framställda partiklarna uppvisade ingen anmärkningsvärd känslighet mot luftfuktighet och bibehöll MgO sammansättningen efter exponering mot fukt. De modifierade metalloxid nanopartiklarna visade mycket liten adsorption av fenoliska antioxidanter, vilket medförde en långtidsstabilitet hos polyeten nanokompositerna. De ytmodifierade metalloxidpartiklarna visade även förbättrade möjligheter för dispergering och yt-kompatibilitet med/i polyetenmatrisen i jämförelse med omodifierade metalloxidpartiklar, utifrån mätningar baserade på dragprovning och svepelektronmikroskopi. Slutligen, de utvecklade ytorna på de modifierade nanopartiklarna skapade ett polymer/nanopartikel gränssnitt som kunder fungera som laddningsansamlingsområden i nanokompositerna, vilket resulterade i en storleksordning minskad ledningsförmåga hos kompositerna jämfört med den rena polyetenen. / <p>QC 20160829</p>

O interesse na utilização de fibras naturais com matrizes poliméricas para a preparação de compósitos espalhou-se rapidamente ao longo dos últimos anos. No entanto, a adesão interfacial entre a fibra e a matriz tem ainda de ser aperfeiçoada. Para melhorar a adesão entre os constituintes e, consequentemente as propriedades mecânicas e térmicas dos materiais, duas abordagens foram investigadas: a irradiação por feixe de elétrons e a mercerização. Este trabalho descreve a fabricação e caracterização de biocompósitos de polietileno de alta densidade e fibra do ouriço da castanha do Brasil que foram preparadas por duas metodologias diferentes: a primeira foi irradiar o compósito com 150 kGy e a segunda foi irradiar a matriz com 15 kGy e então produzir o compósito. Para ambas as metodologias foram utilizadas fibras naturais mercerizadas e não mercerizadas. O efeito dos tratamentos estudados para melhorar a adesão entre a fibra e a matriz polimérica foi avaliado através de caracterizações mecânica, química, térmica e morfológica. Com base neste estudo, observou-se que a fibra do ouriço da castanha do Brasil é um material tecnicamente viável para uso como reforço em compósitos poliméricos. Observou-se que o processo de irradiação da matriz seguida da produção dos compósitos é um método eficaz para melhorar as propriedades térmicas e mecânicas dos compósitos biopoliméricos e que, quando comparado com o processo de mercerização, esse método pode ser considerado mais ambientalmente correto (sem produtos químicos e sem geração de resíduo), mais barato e mais simples. / The interest in the use of natural fibres with polymeric matrix for the preparation of composite spread rapidly over the last years. However, the interfacial adhesion between the fiber and the matrix has to be improved. To improve the adhesion between the constituents and consequently the mechanical and thermal properties of materials, two approaches were investigated: electron beam irradiation and mercerization. This paper describes the fabrication and characterization of biocomposites compounds with high density polyethylene and fibre from Brazil nut pod that were prepared by two different methods: the first irradiating the composite with 150 kGy and the second was radiating matrix with 15 kGy and then produce the composite. For both methodologies, natural fibers, mercerized and non-mercerized were used. The effect of the treatments to improve adhesion between the fiber and the polymer matrix was evaluated through mechanical, chemical, thermal and morphology charcterization. Based on this study, it was observed that fibre from Brazil nut pod is a technically viable material for use as reinforcement in polymer composites. It was observed that the process of matrix irradiation followed by the composite fabrication is an effective method for improving the thermal and mechanical properties of the composites, when compared with mercerization process, this method can be considered more environmentally friendly (no chemicals, and without generating waste), cheaper and simpler.