SURFACE-INDUCED CRYSTALLIZATION IN ULTRAHIGH-MODULUS POLYETHYLENE FIBER REINFORCED POLYETHYLENE COMPOSITES

Surface-induced crystallization of a high-density polyethylene matrix on a gel-spun, ultrahighmodulus polyethylene fiber has been investigated both qualitatively and quantitatively. Under the microscope, the fiber exhibits a very good nucleation ability as seen from a uniform transcrystalline zone. As a first approach, heterogeneous nucleation is assumed. The free energy difference function DELTA-sigma, as it appears in the classical theory of heterogeneous nucleation, is then calculated. Because of the very high nucleation rate, which prevents the direct observation of individual spherulites at the interface, a new approach based on induction time is used to obtain an estimate of the free energy difference function DELTA-sigma, which is calculated to be DELTA-sigma = 0.3 erg/cm2. This very low value may be explained considering the similar lattice parameters for this polymer/substrate system. Crystallization by melt epitaxy rather than transcrystallization may be observed. A new way to qualify the nucleating ability of a substrate toward a polymer melt in relation to the expected morphology is also proposed.