The impact of new crystalline lamellae formation during annealing on the properties of polypropylene based films and membranes

• Published in: Polymer (Guilford) 2014-06, Vol.55 (14), p.3156-3167
• Main Authors: Saffar, Amir, Ajji, Abdellah, Carreau, Pierre J., Kamal, Musa R.
• Format: Article
• Language: English
• Subjects: Annealing; Applied sciences; Correlation; Crystalline lamellar morphology; Endothermic reactions; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Membranes; Polymer industry, paints, wood; Polypropylene based films; Polypropylenes; Porosity; Technology of polymers; Tensile deformation; Yield point
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2014.05.017

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. [Display omitted]