SLOW CRACK-GROWTH IN BLENDS OF HDPE AND MODEL COPOLYMERS

The resistance to slow crack growth (SCG) was measured in binary blend s of high density polyethylene (HDPE) and 5-10% concentrations of mode l ethylene-butene random copolymers by measuring the time to failure ( t(f)) under a constant stress intensity. An increase of ti with the ad dition of the copolymer if the copolymer could crystallize and the inc rease was greater the higher branch density. The copolymer with 117 br anches/1000C could not crystallize and therefore its blend had a ti th at was less than that of the HDPE. The fracture energies of the blends as determined by their resistance to SCG were compared with the energ y by rapid fracture, J(c), as previously measured by Rhee and Crist. I t is concluded that SCG is more sensitive to variations in the microst ructure than is rapid fracture and that the differences in SCG behavio r can be qualitatively explained in terms of the differences in micros tructure of the blends. (C) 1995 John Wiley & Sons, Inc.