A NEUTRON-SCATTERING STUDY OF SLOWLY CRYSTALLIZED BULK POLYETHYLENE

Neutron scattering measurements on polyethylene slowly crystallized from the melt give similar results in the q range 0. 1-0. 4 A** minus **1, to melt-quenched material. The samples have been extensively characterized to assess the effects of slow crystallization (as opposed to quenching) and crosslinking, both separately and in combination. Slowly crystallized samples are similar whether crosslinked previously or not, the principal difference being changes in the way different lamellae stack together. In both cases the morphology is completely different from that of quenched material, as indicated by much larger lamellar thicknesses. Hence, in these experiments there is enough molecular mobility for stems (chain traverses of lamellae) to be much longer than in the case of quenching; the fold type (as assessed by stem separation) is however, similar to the quench case. This conclusion is discussed in the light of a new proposal for equilibrium roughness on the crystal growth surfaces.