Polycarbonate (PC) is a glassy engineering thermoplastic that has been used for decades because of its superior mechanical properties such as high toughness and stiffness, and for its general thermal stability. However, the industrial demand for higher performance polymers with faster processing times has caused PC to be gradually replaced by different engineered polymer blends, such as polycarbonate/acyrlonitrile-butadiene-styrene (PC/ABS). Blends combine the advantages of the individual components but because they are a relatively new class of materials, their time-dependent behaviour is less well understood. The goal of the present work is to characterize two primary time-dependent processes in a commercial 75:25 PC:ABS blend that are known to affect the long-term mechanical properties of the individual components. The first is physical aging which is a result of non-equilibrium fast cooling of glassy or amorphous polymers. Physical aging is associated with structural relaxation due to enthalpic and volumetric recovery. The second process is hygrothermal conditioning which is the combined application of thermal aging and moisture absorption. Three sets of characterization tests were conducted using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The enthalpic relaxation results determined from DSC data for aging at nine different combinations of time and temperature showed that aging experiments are best conducted at temperatures between 80 and 90°C. This range is below the glass temperature of the ABS component. The activation energy for enthalpic relaxation for the unaged blend was found to fall between energies for PC and ABS relaxations, but not according to the rule-of-mixtures. The present study attempted to adopt the Tool–Narayanaswamy-Moynihan (TNM) phenomenological model to predict relaxation kinetics but was found to be complicated by multiple endothermic peaks. It was then concluded that the TNM model, although very useful for single polymer systems, is unsuitable for blends. A semi-empirical model was applied instead to fit the experimental data which provided a reasonable estimate of the relaxation behaviour. Aging at 80°C for the period investigated did not reach equilibrium and it is expected that aging times of upwards of 2 years will be necessary to minimize the errors associated with the data fitting to provide a better fit of the model. The FTIR studies revealed that thermal aging at 80°C in dry atmosphere results in oxidation of the butadiene component. However, the addition of moisture to the aging process appears to prevent, or at least impede, oxidation from occurring. The presence of moisture seems to trigger hydrogen bonding, which saturates regardless of the moisture content after approximately 80 days. The initial rate of moisture diffusion in PC/ABS appeared to depend predominantly on temperature while the ambient moisture concentration tends to only affect the final equilibrium content in the blend.

University, Diss., 2004--Münster (Westfalen).

Techn. University, Diss., 2004--Dresden.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14104号 / 工博第2968号 / 新制||工||1440(附属図書館) / 26392 / UT51-2008-L159 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 金谷 利治, 教授 伊藤 紳三郎, 教授 瀧川 敏算 / 学位規則第4条第1項該当

In this dissertation, new ways for controlling the internal structures of a system of polymer composites, polymer blends, and hydrogel composites by means of external electric or magnetic fields are presented. The first part of this study addresses the development of an anisotropic phase-separated morphology in polymer blends by using electrically pre-oriented clay particles. It was observed that electrically pre-oriented montmorillonite clay particles in a homogenous single-phase blend lead to anisotropic phase-separated morphology of the blends, undergoing demixing upon temperature shift to a two-phase regime. The initial co-continuous microstructure developed into a coarsened and directionally organized phase-separated morphology parallel to the direction of oriented clay particles (applied AC electric field direction) over the annealing time. It was also found that the degree of clay orientation under AC electric field was linearly proportional to the degree of polymer-phase orientation. The temporal morphological evolution was thoroughly analyzed by electron microscopy and X-ray diffraction studies. The second part of the study covers anisotropic hydrogel nanocomposites developed by orienting magnetically sensitive nontronite clay minerals under the strong magnetic fields. Anisotropic hydrogel nanocomposites were formed by magnetic-field assisted orientation of nontronite clays suspended in a hydrogel precursor solution followed by a gelation process. The degree of orientation of nontronite minerals was quantitively characterized by birefringence and small-angle X-ray scattering. The resultant hydrogels exhibited anisotropic optical, mechanical, and swelling properties along the direction of oriented clay minerals. Anisotropic water swelling behaviors can be particularly applied in medical dressing materials, where vertical wicking of fluid into the wound dressing is sought after for minimizing periwound maceration damage.

No description available.

Co-continuous structures generated from the phase separation of polymer blends present many opportunities for practical application. Due to the large interfacial area in such structures and the incompatibility between the components, such non-equilibrium structures tend to coarsen spontaneously into larger sizes and eventually form dispersed morphologies. Here, we utilize various strategies to kinetically stabilize the co-continuous structures in polymer blend systems at nano- to micro- size scales. In the partially miscible blend of polystyrene and poly(vinyl methyl ether), we took advantage of the spinodal decomposition (SD) process upon thermal quenching, and arrested the co-continuous micro-structures by the addition of nanoparticles. In this approach, the critical factor for structural stabilization is that the nanoparticles are preferentially segregated into one phase of a polymer mixture undergoing SD and form a percolated network (colloidal gel) beyond a critical loading of nanoparticles. Once formed, this network prevents further structural coarsening and thus arrests the co-continuous structure with a characteristic length scale of several microns. Our findings indicate that a key to arresting the co-continuous blend morphology at modest volume fractions of preferentially-wetted particles is to have attractive, rather than repulsive, interactions between particles. For the immiscible blend of polystyrene and poly(2-vinyl pyridine) (PS/P2VP), we presented a strategy to compatibilize the blend by using random copolymers of styrene and 2-vinylpyridine, controlling the degree of immiscibility between PS and P2VP. Based on such compatibilization, co-continuous structured membranes, having characteristic size down to tens of nanometers, were fabricated in a facile way, via the solvent-induced macrophase separation of polymer blend thin films. The feature size was controlled by controlling the film thickness and varying the molecular weight of the PS homopolymer and the random copolymers. As the processing method (solution casting) is simple and the structures are insensitive to the solvent or substrate choices, this approach shows great potential in the large scale fabrication of co-continuous nanoscopic templates on flexible substrates via roll-to-roll processes. Moreover, we proposed a quasi-binary blend system based on the PS/P2VP pair with the addition of a common solvent. An experimentally accessible phase mixing temperature was achieved, and the co-continuous morphologies were generated via thermally induced spinodal decomposition. The addition of solid particles significantly slowed down the coarsening kinetics and, in some cases, arrested the co-continuous structures at ~6 &mum for a short period of time. This study suggests an alternative means to achieve co-continuous structures in polymer solutions and also provides better understanding of the thermodynamics and kinetics of polymer blend phase separation. Our research demonstrates several means of kinetically trapping the non-equilibrium interconnected structures at sub-micron to tens-of-nanometer size scales that are germane to several functions including active layers of photovoltaic cells and polymer-based membranes.

Due to the wide range of properties of plastics (e.g. low density), more and more conventional materials are substituted by polymer materials. Complex requirement profiles on technical parts increase the demand for joining processes that enable the reliable joining of otherwise incompatible thermoplastics. In this case, material bonded connections are approaching their limits. In the following study two incompatible thermoplastic polymers were welded by using polymer blends that are compatible to both components. Industrially relevant thermoplastics polyethylene (PE) and polyamide 12 (PA12) were chosen to demonstrate the potential of an innovative joining technology.

Ce travail de recherche consiste à étudier les relations structure-propriétés de mélanges biopolymères à base de poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) et poly(butylène succinate) (PBS). Il est divisé en trois parties. La première partie est consacrée à l'étude des propriétés des mélanges PHBV/PBS préparés par voie fondue en fonction de la composition en termes de morphologie et de propriétés rhéologiques, mécaniques, thermiques et barrières. Les résultats obtenus ont été discutés par rapport aux polymères de base. La deuxième partie est consacrée à la compatibilisation des mélanges PHBV/PBS et l'amélioration des interactions à l'interface. Les effets de l'incorporation de la sépiolite à 5% en masse et du PHBV greffé par de l’anhydride maléique (PHBV-g-MA) à 5% en masse ont été étudiés en termes de changements morphologiques montrant un effet synergique entre le compatibilisant et la nanocharge sur les l’ensemble des propriétés des mélanges PHBV/PBS. Enfin, une étude sur le recyclage a été menée à travers une évaluation des effets du nombre de cycles d'extrusion sur les propriétés des matériaux. Elle révèle qu'après 6 cycles d'extrusion, la dégradation thermo-mécanique du PHBV est significativement réduite en présence du PBS. / The main objective of this work was to study the structure-properties relationships of biopolymerblends based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polybutylene succinate (PBS). The work was devised into three parts. The first part was devoted to the study of the properties of PHBV/PBS blends prepared by melt compounding at different weight ratio in terms of morphology and properties. The results obtained were discussed in terms of properties and compared with the neat polymers. The second part was devoted to the study of compatibility of PHBV/PBS blends aiming to improve the interactions at the interface between the two components. The effects of both sepiolite (5% wt.) and PHBV-g-MA (5% wt.) were studied in terms of properties. The results showed a synergistic effect between the compatibilizer PHBV-g-MA and the nanofiller sepiolite though an increase in thermal, mechanical and rheological properties. The last part dealing with the recyclability of PHBV/PBS through the study of the effects of repeated extrusion cycles on the properties of materials. The results showed that after 6 reprocessing cycles the thermo-mechanical degradation of PHBV is significantly reduced in the presence of PBS.

Copolymers are used to increase the interfacial strength of immiscible components and suppress recombination of the minor phase by steric hindrance. The experiments conducted in these studies are designed to investigate in situ polymer loop formation at soft interfaces and functionalized nanotube surfaces. Block copolymers are the most effective type of copolymer for compatibilization because they extend perpendicular to the interface, allowing good entanglement with the homopolymer chains. Multiblock copolymers are more effective than diblock copolymers for strengthening the interface because they can cross the interface multiple times, forming “loops” in each phase that provide entanglement points for the homopolymer. The first part of this dissertation focuses on understanding how telechelic variables influence their effectiveness to compatibilize an immiscible polystyrene (PS)/polyisoprene (PI) homopolymer blend. A fast reacting anhydride and amine telechelic pair (Anh-PS-Anh/NH2-PI-NH2) are compared with a slower reacting epoxy and carboxylic acid pair (Epoxy-PS-Epoxy/COOH-PI-COOH). Different molecular weight pairs are used to investigate the influence of end group concentrations and steric effects. We also investigate how the loading level affects the conversion of one telechelic pair. The PI telechelic has a fluorescent tag, which enables gel permeation chromatography (GPC) with fluorescence detection to be used for determining the amount of tagged PI converted and the molecular weight of the copolymer formed in situ as a function of mixing time. The effectiveness of these telechelic pairs as compatibilizers is quantified by annealing the samples and using scanning electron microscopy (SEM) to measure the domain size of the minor phase as a function of annealing time. The second part of this study investigates the grafting of polymer loops to carboxylated multiwall nanotube (COOH-MWNT) surfaces and determining the reaction rate. These polymer loops will improve the nanotube dispersion by steric hindrance and improve energy transfer by creation of polymer chain entanglements. Fourier transform infrared spectroscopy (FT-IR) is used as a novel technique to measure the quantity of Epoxy-PS-Epoxy grafted to the nanotube surface. In addition, we determined the fraction of telechelics that form loops by further reacting the grafted nanotubes with monocarboxy terminated poly(4-methylstryrene) (COOH-P4MS), which only reacts with unbound Epoxy-PS-Epoxy chain ends.