Melting and Crystallization of High-Density Polyethylene Mixed with Organic Acids and Acid–Base Indicators after Plastic Deformation at High Pressures

Abstract

A study is performed of mixtures of ultra-high-molecular-weight high-density polyethylene (UHMWHDPE; T_m = 141°C; enthalpy of fusion, 180 J g⁻¹) with 90 wt % low molecular weight component (copper complex of phthalocyanine, anthracene, succinic acid, and spiropyran) in the presence of acid–base indicators (anthraquinone, phenolphthalein, phenol red, bromocresol purple, Congo red, methyl orange, and thymol blue), organic acids (succinic, fumaric, and aspartic), melamine, and cyanuric acid. The mixtures are subjected to plastic deformation at 1 GPa on an anvil-type high pressure apparatus and are analyzed with a DSC. Enthalpies of melting are determined for the polymer in the deformed mixtures (from 135 to 763 J g⁻¹). It is found that the enthalpy of fusion of UHMWHDPE in mixtures with organic acids grows along with the strength of the acid. The enthalpy of melting of the polymer is no more than 210 J g⁻¹ in mixtures with alkaline indicators, and is 664–763 J g⁻¹ in mixtures with acids. Endothermic peaks of small crystallite melting and the exothermic peaks of cold crystallization are observed on the thermograms of the deformed mixtures at temperatures T_m below those of the polymer. It is shown that the enthalpies of crystallization of the polymer in the deformed mixtures from melts are almost identical to those of the initial UHMWHDPE.