Features of foaming of melts of mixtures of polyethylene and polypropylene

One of the promising areas of recycling polyethylene and polypropylene is the production of foam materials for heat-insulation, sound-insulation, and packaging. This work focuses on the study of the technology of their foaming process. The authors conducted research on the kinetics of foaming of molten mixtures of linear low-density polyethylene and block copolymer of propylene and ethylene of various compositions using azodicarbonamide. The obtained experimental results were mathematically processed using the proposed exponential model of this process, which allowed for a quantitative assessment of the kinetics of melt foaming. Rheological studies were conducted to assess the effect of the viscosity of mixtures on the rate of foaming, and the highest Newtonian viscosities of the mixtures’ melts were determined. In a wide range of temperatures and compositions, a regular («asymptotic») pattern of the generalized dependence of the foaming rate of mixtures on the viscosity of their melts was observed. It is shown that the increased shape stability of foamed mixtures and their porous structure is due to the appearance during their cooling of a reinforcing polypropylene phase with a higher crystallization temperature in a foaming polymer melt with a lower crystallization temperature.