The influence of nucleation density and cooling rate on crystallization of polyethylene from the melt

Different samples of high‐density polyethylene provided different nucleation densities which were assessed by optical microscopy and light scattering. Crystallizations were carried out under controlled cooling rates using a microscope hot stage and DSC from which crystallization temperatures were obtained. It is shown that the effective crystallization temperature is a function of the nucleation density, and a quantitative fit is found with theoretical predictions based on crystallization kinetics. The melting point was, in turn, found to be dependent on nucleation density, through the agency of lamellar thickness as assessed by low‐frequency Raman spectroscopy. The effect of cooling rate on melting point is also explained in terms of variation of supercooling. The implications of these effects together with considerations of surface and interior nucleation and sample size are discussed for the industrial processing of polyethylene.