Novel Applications Of Co Extruded Multilayer Polymeric Films

Download or read book Novel Applications of Co-Extruded Multilayer Polymeric Films written by Shannon Renee Armstrong and published by . This book was released on 2013 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multilayer co-extrusion, a highly flexible and unique process, has enabled the study of the permeation, mechanical, and optical properties of multilayer films. Gas separation membranes are strongly dependent upon the permeation of specific gases, which is controlled by the polymer structure and morphology. Poly(ether block amide) (PEBA) thermoplastic elastomers have an inherently high permeability and good selectivity for acid gases such as CO2. A series of PEBA copolymers containing poly(tetramethylene oxide) and polyamide-12 was studied to explore the influence of mechanically induced orientation and copolymer composition on gas permeability and morphology. Upon orientation, PEBA copolymers with high polyether content exhibited up to 3.5x reduction in permeation with increasing strain as a result of strain induced crystallization. To maintain high flux for membrane applications, elastic recovery and thermal treatment proved beneficial in reversing the effects of uniaxial orientation on PEBA copolymers. Gas separation membranes were produced through co-extrusion and subsequent orientation of films containing PEBA as the selective material and PP composites as the support, which are made porous through two methods: 1) inorganic fillers or 2) crystal phase transformation. Two membrane systems, PEBA/(PP + CaCO3) and PEBA/¿-PP, maintained a high CO2/O2 selectivity while exhibiting reduced permeability. Incorporation of an annealing step either before or after orientation improves the membrane gas flux by 50 to 100 %. The improvement in gas flux was a result of either elimination of strain induced crystallinity, which increases the selective layer permeability, or improvement of the PP crystal structure, which may increase pore size in the porous support layer. Forced assembly multilayer co-extrusion of commercially available polyurethane (PU) and polycaprolactone (PCL) polymers was used to create a continuous periodic alternating layer architecture that exhibits shape memory behavior. Similar shape memory properties were observed between PU/PCL layers and blends at 50/50 volume composition; however, offset compositions showed significantly different behavior. The layered structure was maintained across all compositions, as compared with blends that exhibit a composition dependent morphology. The difference in morphology was directly attributed to the difference in shape memory behavior observed between layered and blend films with domain sizes on the micro-scale. Additionally, films with layer thicknesses at the micro-scale and nano-scale were studied to determine the effects of scaling. For PU/PCL layered films, reduction in layer thicknesses lead to improved shape fixity as a result of increased levels of in-plane PCL crystal orientation. Layer multiplying melt co-extrusion is an attractive method for fabricating periodic structures with thousands of alternating polymer microlayers or nanolayers. Many advanced applications for periodic polymeric structures would be enabled by locating a photoactive dye in one or both layers. However, it is anticipated that due to the thinness of the individual layers and the relatively low molecular weight of the dye, a substantial fraction of the dye will diffuse from the doped layers into the undoped layers during melt co-extrusion. In the present study, we demonstrate two methods for confining the activity of a photoactive dye, lead phthalocyanine, to the doped layers. Polycarbonate containing lead phthalocyanine was co-extruded with undoped polyester. Using the absorption spectra, a high concentration of the monomer form was determined to persist in the polycarbonate layers, whereas the lead form was converted to the less active lead-free form in the polyester layers. In the second approach, the co-extrusion process was altered so that the alternating polycarbonate and polyester layers were separated by a thin layer of a barrier polymer. The barrier layer prevented diffusion of the dye during melt co-extrusion and the dye remained selectively in the polycarbonate layers.