Efficient Depolymerization and Recycling of Poly(trimethylene terephthalate) Using 1,3-Propanediol as Reaction Media

Abstract The chemical depolymerization of poly(trimethylene terephthalate) (PTT) in 1,3- propanediol (1,3-PDO) was investigated in this study. After depolymerization, the bis-(3-hydroxypropyl terephthalate) (BHPT) was recovered, which can be directly utilized as monomer in the synthesis of PTT. Zinc acetate (Zn(OAc) 2 ) was found to be the most suitable catalyst in the depolymerization of PTT in 1,3-PDO since a high monomer yield was achieved and no side reactions were triggered during the depolymerization process. The reaction parameters for depolymerization in the presence of Zn(OAc) 2 catalyst was optimized. Under the optimized depolymerization conditions: reaction temperature of 220 °C, catalyst concentration of 0.2 wt% and a ratio of 1,3-PDO to PTT of 8:1, the recovered BHPT monomer yield was 83 mol% within 45 min. Then, the recovered BHPT monomer was directly regenerated into PTT though a single polycondensation process. Comparing with PTT synthesized from virgin dimethyl terephthalate (DMT), the regenerated PTT shows a better quality in terms of color.