Microhardness studies of chain-extended PE: II. Creep behaviour and temperature dependence

The variation of hardness with indentation time has been investigated for c hain-extended polyethylene (PE), other PE samples crystallised under differ ent conditions and paraffins. Hardness is shown to decrease with indentatio n time for all the samples investigated according to a power-law. Chain-ext ended PE, produced by high pressure crystallization or annealing, flows at the lowest rate under the indenter of all the PE samples considered. On the other hand, paraffins creep at the highest rate. Creep behaviour depends m arkedly on the crystal thickness of the material. The mechanical properties at long indentation times seem to be determined primarily by the deformati on modes of the crystals. The temperature dependence of hardness and that o f the creep behaviour has also been investigated. In chain-extended PE, the softening of the sample and the higher rate of creep with increasing tempe rature are discussed in terms of the thermal expansion of the unit cell. (C ) 2000 Kluwer Academic Publishers.