Enhancement of thermo-mechanical and chemical resistance properties of polyurethane composite reinforced with hydrophobic nano-silica and scrape PET derived bis (2-hydroxyethyl terephthalate)

The study investigates the high-performance saturated polyurethane (SPU) composites based on the reinforcement of polymeric filler bis 2-hydroxyethyl terephthalate (BHET), hydrophobic nano-silica (NS), and fire retarding additives. The BHET was synthesized from scraped polyethylene terephthalate (PET). The thermal and morphological study of prepared SPU composites was analyzed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The fillers were analyzed by energy dispersive spectroscopy (EDX). Fourier transform infrared spectroscopy (FT-IR) was utilized to investigate the molecular functionality of filled SPU. The TGA, UL-94, Limiting oxygen index, smoke density were used to determine the thermal properties of filled SPU-A, SPU-A1 composite with (1:1) ratio of filler NS-BHET (0.5%, 1%, 1.5%, 2%) and non-halogenated fire-retarding additives ammonium polyphosphate-melamine (0%, 1%, 2%, 3%). The filler loading, at 1% the tensile strength increased to 42%, and the effect of the composites ruptured surface was supported by SEM analysis. Water contact angle, water absorptivity, gel content, and chemical exposure tests revealed that fabricated composites with varying filler percentages showed superior hydrophobicity with water, moisture, and first-rate resistance to chemical entities. The incombustibility of the composite is imparted by an enhanced thermal degradation temperature of filled SPU due to the thermic stability of terephthalic and sebacic acid utilized in synthesis revealed by TGA. Smoke density decreased from 85% to 45% after the fire, and smoke suppressing additives were introduced at A1 (0-3%). As a result, the LOI increased from 19 to 24. Ultimately, the thermo-mechanical, chemical, moisture resistance, and non-combustibility of the SPU composite improved.