Effect of addition of glycolysis products of poly(ethyleneterephthalate) wastes to urea-formaldehyde resin on its adhesion performance to wood substrates and formaldehyde emission

摘要

Recycling of poly(ethyleneterephthalate) waste was achieved through glycolysis using diethyleneglycol (DEG) and poly(ethyleneglycol) (PEG 400), which yielded different fractions that exhibited hydroxyl numbers of 174.41 and 54.86 mg of KOH/g, respectively, whereas GPC profiles revealed bimodality in both cases corresponding to M_n values equivalent to 534 and 1648. The products of glycolysis from both cases were individually incorporated as modifiers during the synthesis of urea-formaldehyde resins from both the basic as well as acidic stages, respectively. It was found that the free formaldehyde level was remarkably decreased for the modified resins while the gel time was slightly affected indicating some activation of the resins. In addition, the adhesion strength of wood joints bonded with the modified resins improved markedly in the dry state while the moisture resistance was significantly fortified with respect to the comparable joints formulated from unmodified resins where instant failure took place within few hours after immersion in water. The shelf life of the resins did not prolong and lasted maximum for about 2 months which was ascribed to the presence of reasonable amount of carboxyl terminal groups at the ends of a minor portion of the glycolyzed products that could actively act to self-catalyze the polycondensation and crosslinking reactions during storage leading eventually to vitrification of the resin and shortening of shelf life.