The impact of new crystalline lamellae formation during annealing on the properties of polypropylene based films and membranes |
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| Authors: | Amir Saffar Abdellah Ajji Pierre J Carreau Musa R Kamal |
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| Affiliation: | 1. Research Center for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, Polytechnique Montreal, PO Box 6079, Stn Centre-Ville, Montreal, Quebec, Canada H3C 3A7;2. CREPEC, Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec, Canada H3A 2B2 |
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| Abstract: | Cast films, based on polypropylene (PP), were prepared via melt extrusion and, then, annealed below the melting temperature. The effect of annealing conditions on the properties of the films and the microporous membranes formed by stretching was investigated. It is shown that annealing is an effective method to improve the physical properties of semi-crystalline polymers by promoting chain rearrangement and creating secondary lamellae in the amorphous region. DSC results for annealed samples revealed the appearance of a shoulder endothermic peak and a new peak in the correlation function from the SAXS patterns was observed. The annealed films exhibited double yield points in the tensile deformation curves. A direct linear relationship was found between the strength of the second yield point and the fraction of the lamellae. From mercury porosimetry and SEM images of the membranes larger pore sizes and porosity were observed as the annealing time and temperature increased. |
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| Keywords: | Polypropylene based films Crystalline lamellar morphology Annealing |
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