THE DEPENDENCE OF BUTYL BRANCH DENSITY ON SLOW CRACK-GROWTH IN POLYETHYLENE - KINETICS

When the density of n‐butyl branches in an ethylene–hexene copolymer increases from 0 to 4.6 butyls/1000 C, the rate of slow crack growth decreases by a factor of 104 . The activation energy for the process is nearly independent of branch density and is about 120 kJ/mol. It is the number of tie molecules and whether they are pinned that control the rate of crack growth which involves the disentanglement of the fibrils in the craze. Branching increases the number of tie molecules by decreasing the lamella thickness, while the branches pin some of the tie molecules to prevent them from sliding through the crystal or other points of entanglement. Copyright © 1990 John Wiley & Sons, Inc.