Preparation, Characterization and Properties of Flame Retardant Unsaturated Polyester Resin Based on r-PET

A flame retardant unsaturated polyester resin (UPR) was prepared by methods of glycolysis of recycled polyethylene terephthalate (r-PET) via propylene glycol (PG) and diphenylsilanediol (DDS) as mixed glycolysis agent and esterification of the glycolyzed products with maleic anhydride (MA). The chemical structures of glycolyzed products and the resulted UPRs were characterized by fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H-NMR). The peaks at the range of 540–465 cm−1 and 1643 cm−1 on the FTIR spectrum indicated the introduction of Si–O into the main chain of UPR/Si and the reaction between glycolyzed product and MA, respectively). The different amounts of aluminum hydroxide (ATH) was added in the resulted UPRs to obtain UPR composites. The effects of DDS ratio on the flame retardancy, thermal stability, mechanical properties of the resulted UPRs and their composites were investigated. The result showed that the flame retardancy of UPR composites was further improved by addition of ATH to the UPR composites. Finally, the synergistic flame retardant mechanism between DDS and ATH was discussed based on scanning electronic microscopy (SEM) morphologies and FTIR spectra of the residual char after horizontal burning tests (UL-94). It suggested that r-PET can be glycolyzed successfully with PG and DDS as mixed glycolysis agent and the flame retardancy of the resulted UPR based on the glycolyzed products and their composites were improved due to incorporation of DDS in the main chain of UPR and the addition of ATH.