Two ternary blend systems of low-density polyethylene/poly­(ether-block-amide)/polyethylene terephthalate (LDPE/PEBA/PET) and LDPE/PEBA/polyvinylidene fluoride (PVDF) are prepared by melt blending to thermodynamically assemble the ionically conductive PEBA copolymer at the continuous interface. The LDPE/PEBA/PET blend demonstrates weak partial wetting and a novel morphology transition to complete wetting was observed as the PEBA composition increases from 3% to about 10%. The phenomena can be explained by a mechanism based on the competition between dewetting and coalescence of the PEBA phase at the interface. In the completely wet LDPE/PEBA/PVDF system, a minimum concentration is required to form intact PEBA layers with a thickness of ∼100 nm. Assembling PEBA at the interface of the ternary systems results in the formation of conductive pathways of very low percolation thresholds and thus leads to a significant reduction in the resistivity for both ternary systems as compared to binary blends with PEBA. A particularly sharp drop in resistivity is observed for the complete wetting morphology of LDPE/PEBA/PVDF.

Polypropylene/clay nanocomposites are attractive candidates for applications requiring good barrier properties because of the inherent features of the polymer matrix. To assess their potential, systematic research relating the barrier performance to the structural characteristics of polypropylene/montmorillonite samples has been conducted. The nanocomposites have been tested in the presence of helium, water vapor, toluene, and methanol, and the unmodified matrix has been found to exhibit better properties than its mixtures with the compatibilizer and/or clay. The method for the interpretation of the results proposed in this study considers the composition of the samples, the morphology of the semicrystalline polymer matrix, and the state of dispersion/exfoliation of the clay layers, along with the specific interactions between the solvent molecules and the system components. In this way, several points have been identified for understanding and improving the performance of the nanocomposites.

A study to evaluate the tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO 4 /SPEEK composite membranes has been carried out. It is aimed to give an assessment of these materials for applications in proton exchange membrane fuel cells. The stress-strain response of the membranes was measured as a function of the degree of sulfonation (DS) and the fillermatrix ratio. In addition, the effects of immersion in water at various temperatures were explored in situ by means of a homemade testing chamber fitted to the tensile analyzer. The results indicate that the DS has an important influence on the final mechanical behavior of the membranes. The introduction of the BPO 4 solid filler leads to deterioration in mechanical performance compared to unfilled SPEEK. A general picture of the microstructural features influencing the mechanical properties of SPEEK and BPO 4 /SPEEK membranes is proposed.

When a conductive polymer is blended with commodity polymers such as polyolefins and/or polystyrene (PS) as a ternary blend, it has a tendency to form the core phase due to its high interfacial tension with the other components. This can limit its capacity to reduce resistivity compared to situating it at the interface. In this work, starting with a ternary low-density polyethylene/polystyrene/poly(ether-block-amide) (LDPE/PS/ PEBA) blend, we examine the influence of the conductive PEBA concentration on morphology and resistivity when it exists as a core phase. Then, the hierarchical structuring of the PEBA phase will be modified through two strategies: by the addition of a fourth phase (polyethylene terephthalate (PET) or polyvinylidene fluoride (PVDF)) and by the addition of a copolymer interfacial modifier to the LDPE/PS/PEBA blend. Each of these approaches is shown to be capable of allowing the conductive PEBA to form a percolated structure assembled at the interface of two other continuous phases. The completely wet layered structuring of PEBA between PS and PVDF in the quaternary LDPE/PS/PEBA/PVDF blend leads to an exceptionally low percolation threshold of 0.37% compared to 9.7% in the initial LDPE/PS/PEBA blend where PEBA is the inside or core phase. To the best of our knowledge, this is the lowest value ever reported in the literature for a conductive polymer in melt blended systems.

ABSTRACT:In this work, virgin and sulfonated poly-(ether ether ketone) films (PEEK and SPEEK, respectively) have been studied by dynamic mechanical analysis, modulated differential scanning calorimetry, wide-angle X-ray diffraction, birefringence, and optical microscopy. The properties of the unmodified polymer have been addressed to assess the original morphological characteristics and the changes induced by sulfonation. In general, the introduction of ionic groups in the polymer backbone alters dramatically the intrinsic properties of the parent material. The particular thermomechanical response exhibited by PEEK and SPEEK samples, characterized by a hysteresis loop, can be explained by the reversible and irreversible relaxation-orientation of the microstructure, even in the sub-T g region. The results showed that the preparation conditions largely determine the nonequilibrium morphological features of both compression-molded PEEK films and solvent-cast SPEEK membranes.