Effects of Saturated Acids on Physical Properties of UPE Resins Prepared from Recycled PET Products

In this study, effects of saturated acids on physical properties, including hardness, impact strength, flexural properties and thermal properties, of unsaturated polyester or UPE resins prepared from recycled PET bottles and fabrics were investigated. PET was depolymerized by glycolysis reaction with the excess propylene glycol in the presence of zinc acetate as a catalyst. UPE resins were then synthesized by polyesterification of these glycolyzed products with maleic anhydride as an unsaturated diacid as well as succinic acid and adipic acid as a saturated diacid. With the addition of styrene monomer, UPEs were subsequently casted into specimens by crosslinking reaction using methyl ethyl ketone peroxide and cobalt octoate as an initiator and a catalyst, respectively. Physical properties of the cured specimens were then studied. The results showed that, when a saturated acid was incorporated, the hardness of the cured UPE resins decreased due to the decreasing amount of crosslinks. The extended distance between crosslinking sites on molecular chains facilitated load distribution, resulting in the significant improvement of impact strength. The flexural strength was also improved when the small amount of saturated acid was used. The onset thermal degradation temperatures and the glass transition temperatures of the prepared UPE resins were almost unchanged.