Abstract
In this study, block and random copolymers of polypropylene–ethylene are selected to prepare porous membranes through the melt extrusion-annealing-uniaxial stretching technique (MEAUS), at a constant draw ratio. In some cases, these copolymers were blended with a homopolymer grade. The variation of temperature in the stages of extrusion, annealing and uniaxial strain was analysed. Several characterisation techniques were employed to study this influence. The crystalline orientation was analysed by polarised infrared spectroscopy (FT-IR), and crystalline features were studied by differential scanning calorimetry (DSC). The thermal stability of the membranes was checked by thermogravimetric analysis (TGA). Tensile tests were performed to ascertain the stiffness and ductility of the produced samples. The results were correlated with the porous morphology, global porosity, and permeability to air. A close relationship was found between crystalline characteristics, porous morphology and the trends registered. An improved pore distribution along the membrane surface was found when copolymers were employed.
Highlights
Polymeric microporous membranes are conventionally produced by two main techniques, one based on phase inversion process and the other is via melt processing extrusion, where a semi-crystalline polymer film with a specific structure is uniaxial stretched in order to create the porous morphology
This section will be divided into four main headings: (Section 3.1) Influence of extrusion and annealing temperature on neat resins; (Section 3.2) influence of annealing temperature on polymer blends; (Section 3.3) the effect of the hot temperature applied during the uniaxial stretching step; and (Section 3.4) the influence of polymer composition and annealing temperature on mechanical and thermal stability of membranes
In the first step of melt extrusion-annealing-uniaxial stretching technique (MEAUS) technique is possible to control some of the properties of precursor films, which will become membranes during subsequent stages
Summary
Polymeric microporous membranes are conventionally produced by two main techniques, one based on phase inversion process and the other is via melt processing extrusion, where a semi-crystalline polymer film with a specific structure is uniaxial stretched in order to create the porous morphology. Semi-crystalline homopolymers as polypropylene (PP) or polyethylene (PE) have been commonly employed to produce microporous membranes via MEAUS methodology The use of this stretching process facilitates the incorporation of mineral fillers to improve membrane performance [22,23,24,25]. Control of molecular weight and polymer architecture to create a suitable lamellar structure, influence of different annealing time and Polymers 2018, 10, 0854; doi:10.3390/polym10080854 www.mdpi.com/journal/polymers
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