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ABSTRACT
The solidification kinetics of polyolefins (PO) under three cooling conditions were investigated using an in situ measurement of the temperature decay within the PO resins. The phase-change temperature range of high-density polyethylene (HDPE) was located between 110 and 120°C, and those of low-density polyethylene (LDPE) and polypropylene (PP) were 90–110°C and 100–120°C, respectively. The cooling rate of the liquid-state stage is larger than that of the crystallization stage, primarily owing to the release of the latent heat of crystallization as well as the reduced temperature difference between the sample and cooling medium; they jointly slow down the cooling rate to an extent. The time with respect to phase transformation and its lasting period have close relations to the materials' molecular characteristics (e.g., Mw, MWD, LCB, etc.). Three empirical equations were proposed, and found to be applicable for the cooling analysis of the PO molten materials at relatively low cooling rates prior to crystallization.
Funding
The authors are gratefully indebted to the National Natural Science Foundation of China (Nos. 51203002, 51273001), and the “211 Project” (ZLTS2015059, 201510357142, J01005113 and J18515262) of Anhui University. In addition, the financial supports from Institute of High Performance Rubber Materials & Products (Hefei) and Collaborative Innovation Center for Petrochemical New Materials (Anqing) were also acknowledged.