Exothermic Effects in Mixtures of Low-Density Polyethylene with 90 wt % of Low-Molecular-Weight Organic Compounds after Plastic Deformation under High Pressure

Mixtures of low-density polyethylene (Tm = 108°C, enthalpy of melting 80 J g–1) with 90 wt % indigo, lophine, bromcresol purple, spiropyran, phenol red, rhodamine, phenolphthalein, and fluorescein were subjected to plastic deformation under a pressure of 1 GPa on an anvils-type high-pressure apparatus. The study of deformed mixtures was carried out by the DSC method. The thermograms of heating the mixtures showed peaks of polymer melting with enthalpies, which varied from 25 to 170 J g–1. The thermograms below the polymer temperature showed either endotherm peaks of melting of fine crystallites with maxima at 44–57°С, the enthalpies of which varied within 20–120 J g–1, or exotherm peaks of crystallization of fine crystallites with maxima at 58–67°С and enthalpies from 20 up to 45 J g–1. In the range of 81–86°С, in some mixtures, the exotherm process of cold polymer crystallization took place, the enthalpy of which varied from 75 to 290 J g–1. At temperatures above the polymer Tm in the range 115–132°С, the heating thermograms showed exotherm peaks with enthalpies from 115 to 420 J g–1, while, in the range 137–164°С, they showed endotherm peaks with enthalpies of 520–540 J g–1. Crystallization of most mixtures from the melt was described by two peaks, one of which was always at 87°С, while the other could be at 48 or 112°С. The total enthalpies of crystallization varied from 40 to 82 J g–1.