On the Melting Behavior of Isothermally Crystallized 1-Octene Linear Low-Density Polyethylene Copolymers

摘要

The melting behavior of two l-octene linear low-density polyethylene (LL- DPE) copolymers is investigated. One made using Dow's INSITE constrained geometry catalyst technology (LLDPE-A} and the other using titanium-based Ziegler-Natta catalysts (LLDPE-B). Both have similar comonomer content as well as melt flow index. Differential scanning calorimetry (DSC) was used throughout the work. Isothermal crystallizations in the DSC for several times were carried out at various temperatures between 90 and loo°C for LLDPE-A and between 105 and 112.5°C for LLDPE-B. As a result of the isothermal crystallizations for both copolymers, multiple melting peaks are found in the DSC traces on subsequent heating. The melting behavior was alsoexam- ined as a function of heating rate ( 1, 2.5, 5, 10, and 20°C/min). The multiple melting behavior indicates that they are inhomogeneous. In addition, a melting-recrystalliza- tion process was shown to be responsible for the appearance of one of the melting peaks in LLDPE-B. A lowering in heating rate from the crystallization temperature favors the occurrence of me!ting-recrystallization during the dynamic experiment.