Thermal, mechanical, and viscoelastic properties of recycled poly(ethylene terephthalate) fiber‐reinforced unsaturated polyester composites

Recycled polyethylene terephthalate (PET) fiber has been used as reinforcing filler for unsaturated polyester resin (UPR) in order to obtain UPR/PET fiber composites. Different loadings of PET fibers (5–18 phr—parts per hundred parts of resin) of different average lengths (2–3 to 20 mm) were added to the UPR. The mechanical properties of the UPR/PET fiber composites increased up to 8 phr PET fiber loading with a length lower than 5 mm, because of the high affinity between the UPR and the PET fiber surface and the good dispersion of the fiber into the matrix. However, higher PET fiber loading caused a decrease in the mechanical properties of the composites because of the agglomeration of the fibers. The UPR/PET fiber composites presented higher storage moduli than the UPR, and an increase of the glass transition temperature in the composites reinforced with 5–8 phr of short PET fiber was found; further, higher degree of crosslinking was reached. The addition of 5–8 phr PET fiber of short length improved the thermal stability of the composites and the post‐curing was produced at higher temperature with much reduced enthalpy