HIGH-STRENGTH ELASTIC POLYPROPYLENE

In the reported experiments, the transformation of a spun isotactic polypropylene fiber into a high strength elastic fiber has been followed structurally. By examining each stage of the transformation separately, it has been possible to identify the different structural mechanisms that occur as the process proceeds. The recognition of the important role the noncrystalline polymer plays in the process is a particularly significant result of the study. It is demonstrated that the minimum annealing temperature required to transform a moderately oriented spun polypropylene fiber into a hard elastic fiber is 130 degree C. The highest annealing temperature used in the study (150 degree C) yields hard elastic fibers with the best elastic recovery. The structural transformation from a spun fiber to a hard elastic fiber involves a decrease in the fraction of alpha prime -axis oriented crystals, an increase in the chain axis orientation of the crystals, and an increase in the orientation of the noncrystalline chains. These observations suggest the elastic character of the hard elastic fibers may be a consequence not only of the size and orientation of the crystal lamellae, but of the stiffness of the noncrystalline matrix as well.