M. Yasuniwa et al., LAMELLAR THICKENING OF POLYETHYLENE UNDER HIGH-PRESSURE, Journal of polymer science. Part B, Polymer physics, 35(4), 1997, pp. 535-543
Single crystal mat (SCM) samples of polyethylene (PE) were prepared fr
om dilute solution of p-xylen, then they were annealed at pressures of
200 and 500 MPa. Lamellar thickness of the original and annealed SCM
samples was measured by small-angle X-ray scattering method. Orientati
on of the molecular chain in those SCM samples was investigated by wid
e-angle X-ray diffraction pattern. From these X-ray measurements, anne
aling temperature dependence of the lamellar thickness, i.e., lamellar
thickening, under high pressure was obtained. Melting process of the
SCM samples was also investigated at 200 and 500 MPa by high pressure
differential thermal analysis. Then correspondence between the lamella
r thickening and the melting process was studied. The lamellar thickne
ss increases markedly with approaching to the melting temperature of t
he orthorhombic crystal even in the high pressure region where the hig
h pressure phase (hexagonal phase) appears. The annealing temperature
dependence curve of the lamellar thickness at 200 MPa can be superimpo
sed on the curve at 500 MPa by shifting the curve along the temperatur
e scale by 47 K. Large scale lamellar thickening occurs in the orthorh
ombic crystal phase in the high pressure region. The formation process
of extended-chain crystal is discussed. (C) 1997 John Wiley & Sons, I
nc.