Determination of molecular weight distribution and composition dependence of monomeric friction factors from the stress relaxation of ultrahigh molecular weight polyethylene gels

Abstract

The stress relaxation of ultrahigh molecular weight polyethylene (UHMWPE) gels in a broad composition range ( 0.025≤ϕP≤1.0) was studied within the framework of the reptation model. The molecular weight distribution (MWD) was determined at an optimum gel concentration ( ϕP=0.365) by regularization analysis of the stress relaxation data. The calculated relaxation moduli [ G(t)] by using MWD evaluated at a certain composition (UHMWPE gels, ϕP=0.365) were consistent with the experimental G(t) of other compositions in a broad range ( 0.218≤ϕP≤1.0). That is, the MWD (regularization method) was self-consistent within the framework of the reptation model. The composition dependence of the monomeric friction factor ( ζeff) of the UHMWPE gels was examined by use of the double reptation (DR) model with the determined MWD. The Ferry's free volume model of the molecular weight dependence of ζeff can be extended to the composition dependence of ζeff. In the low-concentration gels ( 0.025≤ϕP≤0.17), the experimental G(t) relaxed faster than G(t) expected by the DR model.