Deformation and entanglement in semicrystalline polymers

Abstract

Abstract Transmission electron microscopy (TEM) of amorphous and semicrystalline isotactic polystyrene (iPS) thin films deformed well below T g, suggests the same crazing mechanism to operate in both cases. Therefore, by analogy with the amorphous case, highly entangled semicrystalline polymers, such as poly(ether ether ketone) (PEEK) should craze less readily in the glassy-semicrystalline state than iPS, which has a low degree of entanglement. Since this is confirmed by observation, it is reasonable to extend this analogy, and invoke entanglement in order to account for the high fracture resistance of highly entangled semicrystalline polymers, such as polyoxymethylene, using models previously applied to glassy amorphous polymers. There are nevertheless often significant decreases in fracture toughness in polyoxymethylene as the crystallization temperature is raised and/or the molecular weight is reduced, which we attribute to entanglement loss during lamellar folding. Key Words: CrazingDeformationEntanglementFractureSemicrystalline polymers