Influence of crystallinity change on creep properties due to thermal history for polypropylene

Abstract

For crystalline polymers used as a matrix polymer at fiber-reinforced thermo-plastics, effects of crystallinity of polypropylene on creep characteristics were investigated. Measurements taken using DSC, DMA, SAXS, and WAXS elucidated crystallization behavior and crystallinity along with changes in the annealing temperature and annealing time. Although crystallinity increases with the annealing temperature and annealing time, a relation was found between the annealing temperature and time: crystallinity can be shifted by a shift factor. The time–temperature crystallinity superposition holds for crystalline polymers. Using this relation, creep time change caused by aging can be predicted. The relation between crystallinity and storage modulus \(E'\) was described using a Takayanagi type two-phase model. We proposed a mechanical model that extends the Takayanagi type two-phase model to express the phenomenon by which the creep time increases because of increased crystallinity together with a viscous element of a model implementing the Guth–Gold model. This model can express behaviors of increasing creep time caused by increased crystallinity.