DRAWING BEHAVIOR OF LINEAR POLYETHYLENE .1. RATE OF DRAWING AS A FUNCTION OF POLYMER MOLECULAR-WEIGHT AND INITIAL THERMAL-TREATMENT

In the reported experiments the drawing behavior of a series of HDPE with weight-average molecular weight (M//w) ranging from 67,800 to 3,500,000 and variable distribution (M//w/M//n equals 5. 1 - 20. 9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (120 degree C) followed by quenching into cold water. When the samples (2 cm long) were drawn in air at 75 degree C using a crosshead speed of 10 cm/min it was found that for low M//w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M//w such effects are negligible. It is shown how some of the structural features of the initial materials can be interpreted in terms of the mol. wt and MWD of the polymers. Although crystallization and morphology can be important at low M//w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of mol. wt.