Effect of crosslinking on the mechanical and thermal properties of poly(vinyl alcohol)

Poly(vinyl alcohol) was crosslinked with hexamethylene diisocyanate in solu tion. A broad range of degrees of crosslinking, from 1.7 up to 74 mol% of r eacted hydroxyl groups, was achieved. The variation of the thermal and mech anical properties of PVA with the crosslinking density show an initial decr ease due to the diminution of the crystallinity of the system, caused by th e crosslinking. After an abrupt rise at about 20%, the properties tend to l evel off independently on the increase of the crosslinking. This behaviour is explained as a result of the competitive action of at least three factor s during the crosslinking: (i) weakening of the existing physical network d ue to hydrogen bonding; (ii) formation of a chemical network; and (iii) int roduction of flexible moieties. The last factor is closely connected with t he specific chemical structure of the crosslinker itself. (C) 2000 Elsevier Science Ltd. All rights reserved.