KINETICS OF CHLOROSULFONATION AND OSO4 ATTACK IN THE INTERLAMELLAR REGIONS OF LOW AND HIGH-DENSITY POLYETHYLENE STUDIED BY MICROHARDNESS

The microhardness of low density polyethylene (LDPE) fractions and of high density polyethylene (HDPE) samples has been studied as a functio n of molecular weight in the range of about 2 x 10(4) up to 4 x 10(6). Details of the lamellar structure were determined by transmission ele ctron microscopy (TEM). The observed decrease of hardness with increas ing molecular weight is mainly due to the increase in thickness of the interlamellar layers (i.e. a decrease of crystallinity). After chemic al treatment with chlorosulfonic acid and with OsO4 the samples show a drastic hardness increase. The kinetics of OsO4 treatment as revealed by microhardness has been examined. The hardness increase is explaine d in terms of the large reduction in molecular mobility of the amorpho us, interlamellar layers. The strongest hardening effects arise in con sequence of the preferred reaction of these defect layers with increas ing molecular weight. (C) 1997 Elsevier Science Ltd.