Influence of heat-setting temperature on the properties of a stretched polypropylene microporous membrane

The influence of heat-setting temperature on the stress-strain curves, differential scanning calorimetry (DSC) curves and properties of a stretched polypropylene microporous membrane was studied. It was found that with an increase of heat-setting temperature, a plastic plateau region in the stress-strain curves and a melting endotherm plateau in the DSC curves became apparent. The permeability and porosity firstly increased with the temperature to 145 degrees C and then decreased. The pore structure arrangement showed similar changing trend. On the one hand, higher heat-setting temperature could decrease the shrinkage of the microporous membrane. On the other hand, the crystallization of some chains around separated lamellae during heat-setting was unfavorable to the properties of the microporous membrane. The occurrence of crystallization during heat-setting explained the origin of the plastic plateau. For the fabrication of microporous membranes based on the melt-stretching mechanism with good dimensional stability, heat-setting is necessary, but too high a heat-setting temperature can destroy the permeability. (c) 2013 Society of Chemical Industry