Abstract
Several commercial grades of homo-polymer and its blends were selected to prepare microporous membranes through melt extrusion-annealing-uniaxial stretching technique (MEAUS). Branched or very fluid polypropylene was employed to modify the polymeric composition. In some blends, micro-sized calcium carbonate was added. We analysed the influence of sample composition, extrusion draw ratio, and we performed a deep study concerning the uniaxial strain rate, using in some cases extreme strain rates and strain extents. The crystalline features were studied by Differential Scanning Calorimetry (DSC), and the morphology of porous structure was analyzed through Scanning Electron Microscopy (SEM). Thermal stability and thermomechanical performance was measured by thermogravimetric analysis (TGA) and dynamic-mechanical-thermal (DTMA) study. A close relationship was found between crystalline characteristics, porous morphology and the trends registered for permeability.
Highlights
Polypropylene (PP) membranes have been studied by several authors due to their wide use for commercial separation processes
The exposition of the obtained results will be divided according to three main headings: composition of the samples, draw ratio applied in the production of precursor films, and the influence of the variation of crosshead speed and strain extent during the uniaxial strain stage
All the membranes discussed were obtained under the same processing conditions
Summary
Polypropylene (PP) membranes have been studied by several authors due to their wide use for commercial separation processes. Polypropylene is a good candidate for certain industrial applications such as gas separation, Li-ion batteries or medical applications, due to its outstanding properties such as high melting temperature, chemical resistance and good mechanical properties [2,3]. To avoid the use of solvents, due to their cost, environmental footprint and contamination risks, a dry process based on the stretching of extruded film with a specific structure called MEAUS (melt extrusion-annealing-uniaxial stretching) was developed in recent decades. This process is applicable to semi-crystalline polymers, and three consecutive stages are carried out: (a) fabrication of a precursor film with a row-nucleated lamellar structure;
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