Modified resin from recycled PET: structural analysis and performance in glass fiber reinforced composite with adhesive study

Polymers play an indispensable role in modern society; however, their accumulation as waste poses serious environmental challenges. In the present study, polymer waste was valorized into high-value products via chemical recycling. Polyethylene terephthalate was depolymerized via glycolysis, and the resulting product was used to synthesize UPR through condensation polymerization with maleic anhydride and a dibasic acid. In parallel, a hexafunctional epoxy resin was synthesized by reacting bisphenol-A, formaldehyde, and epichlorohydrin. The glycolysis product, unsaturated polyester resin, and epoxy resin were systematically characterized using viscosity measurement, acid value determination, epoxy equivalent weight analysis, FTIR, 1 H NMR and GPC. The synthesized resins were subsequently used as matrix materials to fabricate glass fiber-reinforced composites and as adhesives for metal and wood substrates. The composites were prepared using the hand lay-up technique and evaluated for their chemical, thermal, morphological, and mechanical properties, including tensile and flexural strengths, thermogravimetric analysis, atomic force microscopy, Rockwell hardness, and chemical resistance. The composites exhibited less than 2.9% weight change upon chemical exposure and demonstrated activation energies in the range of 14.384–15.344 kcal/mol. Furthermore, adhesive performance studies revealed lap shear strength values between 1.356 and 1.921 MPa, confirming the potential of the synthesized resins for structural and adhesive applications.