The shrinkage mechanism of polyethylene terephthalate fiber

The isothermal shrinkage kinetics of PET with higher crystallinity and higher orientation were studied in the. temperature range from 375 to 494K. All the curves of shrinkage vs. time were fitted by two exponential function, the form of which indicated this shrinkage could be divided into two different processes characterized by different relaxation time and the final shrinkage amount. The first process was a faster one and its main molecular mechanism was the disorientation of the extended tie molecules of chains in the noncrystalline region. The second process was resulted in the variation of the crystalline region. The contribution of the first process to the isothermal shrinkage was the main one, especially in the high temperature region. The restructuring of the crystalline region included the rapidly growth of the crystallites and the low speed process of formation of new paracrystals and the reorganization of existed crystals during the whole shrinkage process. The disorientation of molecules was restrained once the crystallinity structure had a large improvement.