This PhD project investigated the effects of a co-continuous phase structure on the ductility of poly(lactic acid) (PLA) blends. An empirical model was used to predict the phase inversion point of the blends. The co-continuous phase morphology was first observed in polybutylene succinate(PBS)/PLA blends. With as little as 10 wt% of PBS, PBS/PLA blends achieved a dramatic improvement in ductility, over 250% elongation-to-break. Clay additives were incorporated in PBS/PLA blends. Clay was found out to affect the compatibility and co-continuous phase morphology of PBS/PLA blends. The clay dispersion was found to have an intercalated and exfoliated structure at a PBS/PLA composition ratio of 20/80. The clay particles increased the mixing conditions between the polymers by producing a finer structure, but also destroyed the co-continuous phase morphology, resulting in a substantial decrease in elongation-at-break. PLA was then blended with Poly(butylene adipate-co-terephthalate) (PBAT) to examine whether the co-continuous phase model could also be applied to other PLA-polymer blends. From the melt viscosity ratio of PLA and PBAT in the processing regime used in the study, the predicted phase inversion value was 19 wt% of PBAT. This value was verified by the results of mechanical properties, where results for elongation-to-break show a dramatic rise from around 10% up to 300% in the composition range between 10 and 20wt% of PBAT. Polyhydroxyalkanoate (PHA) was also blended with PLA and this project investigated how co-continuous phase morphology affects the blends of two brittle polymers. It was found that when PHA content ranged from 10 to 20wt%, the brittle-brittle polymer blends showed ductile behaviour due to a plane stress effect.

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.

The microstructure-property relationship for interpenetrating phase composites (IPCs) is currently poorly understood. In an attempt to improve this understanding this study focused on one particular part of this relationship: the effect of phase shape on the elastic and plastic behaviour. A review of previous research showed that investigations had linked phase shape to the elastic and plastic behaviour of various inclusion reinforced composites, but that no similar work had been completed for IPCs. <p> To study the complex response of the IPC microstructure under load, a numerical modelling analysis using the finite element method (FEM) was undertaken. Two three-dimensional models of IPCs were created, the first consisting of an interconnected spherical phase with the interstitial space forming the other interconnected phase, and the second replacing the spherical phase with an interconnected cylindrical phase. With the simulation of a uniaxial tension test under elastic and plastic conditions, these two models exhibited different responses based on the shape of the phases. <p> Results from an analysis of the macroscopic behaviour identified that the cylindrical model produced greater effective properties than the spherical model at the same volume fraction. The influence of phase shape was connected to the increased contiguity of the superior phase within the IPC for the cylindrical model, which allowed similar levels of long-range continuity with smaller amounts of the superior phase (compared to the spherical model). <p> An examination of microstructural stress distributions showed that preferential stress transfer occurred along paths of low compliance. This provided an explanation of how the improved contiguity of the stiffer (or stronger) phase could enhance the macroscopic effective properties of an IPC. Contiguity of the stronger phase was particularly important for plastic behaviour, where early yielding of the weaker phase requires the stronger phase to carry nearly all the load within itself.

The microstructure-property relationship for interpenetrating phase composites (IPCs) is currently poorly understood. In an attempt to improve this understanding this study focused on one particular part of this relationship: the effect of phase shape on the elastic and plastic behaviour. A review of previous research showed that investigations had linked phase shape to the elastic and plastic behaviour of various inclusion reinforced composites, but that no similar work had been completed for IPCs. <p> To study the complex response of the IPC microstructure under load, a numerical modelling analysis using the finite element method (FEM) was undertaken. Two three-dimensional models of IPCs were created, the first consisting of an interconnected spherical phase with the interstitial space forming the other interconnected phase, and the second replacing the spherical phase with an interconnected cylindrical phase. With the simulation of a uniaxial tension test under elastic and plastic conditions, these two models exhibited different responses based on the shape of the phases. <p> Results from an analysis of the macroscopic behaviour identified that the cylindrical model produced greater effective properties than the spherical model at the same volume fraction. The influence of phase shape was connected to the increased contiguity of the superior phase within the IPC for the cylindrical model, which allowed similar levels of long-range continuity with smaller amounts of the superior phase (compared to the spherical model). <p> An examination of microstructural stress distributions showed that preferential stress transfer occurred along paths of low compliance. This provided an explanation of how the improved contiguity of the stiffer (or stronger) phase could enhance the macroscopic effective properties of an IPC. Contiguity of the stronger phase was particularly important for plastic behaviour, where early yielding of the weaker phase requires the stronger phase to carry nearly all the load within itself.

Due to their large internal surface area, microporous materials have been widely used in applications where high surface activity is desired. Example applications are extracellular scaffolds for tissue engineering, porous substrates for catalytic reaction, and permeable media for membrane filtration, etc. To realize these potential applications, various techniques such as TIPS (thermal induced phase separation), particle leaching, and SFF (solid freeform fabrication) were proposed and investigated. Despite of being able to generate microporous for specific applications, these available fabrication techniques have limitations on controlling the inner porous structure and the outer geometry in a cost-effective manner. To address these technical challenges, a systematic study focusing on the generation of microporous structures using co-continuous polymer blend was conducted. Under this topic, five subtopics were explored: 1) generation of gradient porous structures; 2) geometrical confining effect in compression molding of co-continuous polymer blend; 3) microporous composite with high nanoparticle loading; 4) micropatterning of porous structure; 5) simulation strategy for kinetics of co-continuous polymer blend phase coarsening process.

Les matériaux thermodurcissables sont naturellement des isolants électriques, limitant leurs applications dans certains domaines comme l’électronique ou l'aéronautique. Ce travail de thèse consiste à développer un nouveau matériau composite thermodurcissable en présence de charges inorganiques conductrices pour apporter des propriétés électriques sans pour autant changer notablement la viscosité du système avant la polymérisation afin de permettre l'utilisation des technologies d'infusion de résine de l'aéronautique. La stratégie des travaux est basée sur la génération d'une séparation de phase au sein du matériau et la localisation des charges conductrices aux interfaces.Cette étude est scindée deux objectifs principaux. Le premier objectif consiste à étudier un système TP/TD (thermoplastique/thermodurcissable) afin d’obtenir et contrôler une morphologie interpénétrée, selon le processus de séparation de phase induite par la polymérisation. Le second objectif consiste à étudier la localisation des charges conductrices dans un système TP/TD. Deux procédés de mise en œuvre ont été développés. Le premier procédé dit « one shot » permet de localiser les charges préférentiellement et de manière homogène dans la phase thermodurcissable et apporte une conductivité uniquement à forte concentration en particules conductrices.Une seconde méthodologie a été élaborée permettant d’obtenir un matériau biphasique dans lequel les charges sont localisées préférentiellement à l’interface du système Epoxy/thermoplastique. Des conductivités, à faible taux de charges (5 % massique), de l’ordre 10-1 S/m ont pu être atteintes avec cette méthodologie. / Thermosetting materials suffer from a lack of electrical conductivity. In order to overcome this barrier, a natural strategy is to introduce conductive fillers above the percolation threshold. However, addition of fillers usually leads to an increase of viscosity of the formulation which precludes infusing the resin through the porous bed of carbon fibers. In order to solve this problem, we aim at creating a two phase material and locate the fillers at the interface in order to decrease the percolation at very low values.With this view, this study is divided into two parts. The first one concerns the control of multiphase composites in order to get a co-continuous morphology by a strategy called Reaction Induced Phase Separation (RIPS). Phase diagram and influence of parameters have been studied.The second part is the formulation of a composite material (thermoplastic/thermoset) in presence of inorganic fillers. We developed two differents processes which allowed us to control fillers localisation in the blend. A process called “one shot” allows to locate homogeneously inorganic particles in epoxy phase. A second process called “premix” would preferentially locate conductive fillers at the interface of the interpenetrating system.Diffusion of particles at the interface was observed in situ during the curing of a biphasic thermoset material permitting to open the road of conducting materials and a conductivity around 10-1 S/m has been reached using as low as 5 wt% carbon black. The concept of localization of filler has been valided on several systems.

No description available.