Effect of blending high-pressure low-density polyethylene on the crystallization kinetics of linear low-density polyethylene

It is well known that the addition of a small amount of high-pressure low-density polyethylene (HPLDPE) to linear low-density polyethylene (LLDPE) can improve the optical properties of LLDPE, and LLDPE/HPLDPE blend is widely applied to various uses in the field of film. The optical haziness of polyethylene blown films, as a result of surface irregularities, is thought to be as a consequence of the different crystallization mechanisms. However, not much effort has been directed toward understanding the effect of HP-LDPE blending on the overall crystallization kinetics (k) of LLDPE including nucleation rate (n) and crystal lateral growth rate (v). In this study, we investigated the effect of blending 20% HP-LDPE on the crystallization kinetics of LLDPE polymerized by Ziegler-Natta catalyst with comonomer of 1-butene. Furthermore, by combining depolarized light intensity measurement (DLIM) and small-angle laser light scattering (SALLS), we have established a methodology to estimate the lateral growth rate at lower crystallization temperatures, in which direct measurement of lateral growth by polarized optical microscopy (POM) is impossible due to the formation of extremely small spherulites. This investigation revealed that HP-LDPE blending leads to enhanced nucleation rate, reduced crystal lateral growth rate, and a slight increase in the overall crystallization kinetics of pure LLDPE. From the estimated crystal lateral growth rate, it was found that the suppression in v from HP-LDPF blending is larger at lower temperatures than at higher temperatures. (c) 2007 Wiley Periodicals, Inc.