Thermochemical Foaming of Mixed Single-Use Plastics Toward Flame Retardant Potential Foams

Abstract

Thermochemical foaming of polyolefin (PO) blends with ammonium polyphosphate (APP) is promising to directly convert polyethylene (PE) and polypropylene (PP) mixture into potential intumescent flame retardant (IFR) foams. However, this process has not been studied yet. Herein, thermochemical foaming behaviors of PO blends/APP were studied comparing with PP/ APP. PO blends have a fundamentally different foaming process comparing to that of PP. The results show that the porosity of PP/ APP blend follows the law of exponential growth. In contrast, the porosity of POs/APP blend follows the law of logarithmic growth. Generally, the tensile strength, elongation at break, and Young's modulus decrease with increasing porosity for both PP/APP blends and POs/APP blends. However, for PP/APP blends, a critical porosity exists. The limiting oxygen index (LOI) of the blends can be slightly increased with thermochemical foaming. The mechanism of the foaming processes was further revealed by the composition analysis of thermogravimetric analysis/infrared spectrometry (TG-IR) and Fourier transform infrared spectroscopy (FTIR). Finally, a demonstration of thermochemical foamed mixed postconsumer plastics is compared with an expanded polystyrene (EPS) foam. The results indicate the potential for a new avenue for waste PO conversion.