Use of a sequential extraction technique to determine the MWD of bulk UHMWPE

Abstract

SynopsisThe molecular weight distribution (MWD) of bulk ultrahigh molecular weight polyethylene (UHMWPE) was determined by an increasing temperature sequential extraction technique. Using decahydronapthalene (decalin) as the solvent, 5 g samples of UHMWPE were fractionated stepwise from room temperature to 190°C in 10Co increments. Results via high temperature capillary viscometry show that intrinsic viscosity ( [ q ] ) ranges from 12.0 to 37.0 dL/g or that the viscosity average molecular weight ( a o , r a n g e s from approximately 1.6 to 7.4 X lo6. When the integral distribution is plotted against M, on logarithmic probability graph paper, a straight line (i.e., a Wesslau distribution) results. Although the present methodology is tedious, many previous problems which have led to degradation are overcome by this technique.

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“…The shear force breaks long polymer chains; consequently, this method underestimates the true viscosity of UHMWPE [34,36,39]. Alternative methods for molecular weight determination, like gel permeation chromatography and sequential extraction, are also used for UHMWPE [39,40].…”