THE FUNDAMENTAL MATERIAL PARAMETERS THAT GOVERN SLOW CRACK-GROWTH IN LINEAR POLYETHYLENES

The effect of stress, notch depth, and temperature on slow crack growth are generally the same for all linear polyethylenes. The great difference in the rate of slow crack growth resides in the material parameters such as molecular weight distribution and branch density. Branch sequence and the placing of branches on the high molecular weight molecules make a contribution. The effects of varying the morphology by varying the thermal history are presented. The importance of the density of tie molecules is emphasized. The density of the tie molecules depends on the molecular weight and the spacing of the branches. Suggestions are made for producing a resin with a maximum resistance to slow crack growth.