Polymer, Vol.167, 146-153, 2019
Large strain cavitation induced stress whitening in propylene-butene-1 copolymer during stretching
Large strain cavitation induced stress whitening was observed in propylene-butene-1 copolymer during stretching by means of ultra-small angle X-ray scattering technique. The critical stress for initiating this cavitation depended on the stretching temperature (T-s). A constant critical stress was found below T-s of 125 degrees C while the stress started to increase above 125 degrees C. This peculiar cavitation performance presented in propylene-butene-1 copolymer was supposed to be associated with the melting of unstable crystallites before deformation. Such unstable crystallites were normally composed of chains with co-units or short length. M the strain just before whitening, chains from those melted crystallites could recrystallize wholly into oriented crystallites as the copolymer was stretched below 125 degrees C while they remained molten when the sample was deformed above 125 degrees C. Thus, different highly oriented amorphous networks were created below and above 125 degrees C in copolymer, resulting in different critical stresses for large strain cavitation since this cavitation is determined by the fracture of such oriented amorphous network.