Partially fluorinated proton exchange membranes based on PVDF\u2013SEBS blends compatibilized with methylmethacrylate block copolymers

This paper reports on a new route to prepare functional polymer blends for fuel cell\u2019s proton exchange membrane applications. Polyvinylidene fluoride (PVDF) and styrene-ethylene/butylene-styrene (SEBS) thermoplastic elastomer were melt blended and extruded into films. Interface modification using poly(methylmethacrylate-butylacrylate-methylmethacrylate) block copolymer (MAM), and two grades of poly(styrene-butadienemethylmethacrylate) block copolymer was used to optimize the blends performance. The films made out of these blends were grafted with sulfonic acid moieties to obtain ionic conductivity leading to semi-fluorinated proton exchange membranes. The effect of varying the nature and concentration of the compatibilizer on the morphology and properties of a 50/50 wt.% PVDF/SEBS blends was investigated. SEM analysis showed that the addition of the block copolymers to the blends affected the morphology significantly and in the best case, that as low as 1 wt.% block copolymer was sufficient to dramatically reduces the segregation scale and improves mechanical properties. The samples were characterized in terms of morphology, microstructure and thermo-mechanical properties and in terms of conductivity, ion exchange capacity (IEC) and water uptake to establish the blends morphology\u2013property relationships. Compatibilized blend membranes showed conductivities up to 3 710\u207b\ub2 S cm\u207b\ub9 at 100% relative humidity, and an IEC = 1.69 meq g\u207b\ub9. Water swelling decreased for compatibilized blend membranes.Peer reviewed: YesNRC publication: Ye

Biaxial orientation of polylactide/thermoplastic starch blends

The biaxial stretchability and film properties of polylactide/ thermoplastic starch blends were investigated. Polylactide (PLA) and thermoplastic starch (TPS) were blended in various proportions. Blends containing 27, 42 and 60 wt.% TPS were prepared via a twin-screw extrusion process. Interfacial modification was performed by grafting the PLA with maleic anhydride. These blends were subsequently cast into sheets and biaxially drawn using a laboratory biaxial stretcher. The morphology of extruded strands and cast sheets was investigated using scanning electron microscopy. The compatibilized blends exhibited a much finer morphology as well as preferential minor phase size orientation along the machine direction. The addition of starch did not affect significantly the biaxial stretchability of the pure PLA. Even at high starch content (60 wt.%), the biaxial draw ratio at which the sample breaks is very similar to that of the pure PLA. At higher temperatures, all blends could be stretched at significantly much higher biaxial draw ratio and very thin films could be obtained. The starch content and processing variables affected the tensile properties.Peer reviewed: YesNRC publication: Ye