Study of the Crystallinity of Polyesters Derived from the Glycolysis of PET Gae ¨l Colomines, 1 Arie Van Der Lee, 2 Jean-Jacques Robin,* 3 Bernard Boutevin 1 1 Institut C. Gerhardt: Laboratory of Macromolecular Chemistry, UMR (CNRS) 5076, Ecole Nationale Supe ´rieure de Chimie de Montpellier, 8 rue Ecole Normale, 34296 Montpellier Cedex 5, France 2 Institut Europe ´en des Membranes, UMR (CNRS) 5635, Universite ´ de Montpellier II, C.C. 047, Place E. Bataillon, 34095 Montpellier Cedex 5, France 3 Institut C. Gerhardt: Laboratoire Organisation Mole ´culaire, Evolution, Mate ´riaux Fluore ´s, Groupe Polyme `res, Universite ´ Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France Fax: (33) 4 67 63 10 46; E-mail: Jean-Jacques.Robin@univ-montp2.fr Received: April 18, 2006; Revised: June 23, 2006; Accepted: June 26, 2006; DOI: 10.1002/macp.200600189 Keywords: glycolysis of PET; recycling; rheology; X-ray diffraction Introduction Poly(ethylene terephthalate) (PET) is a commodity polymer used in many areas such as packaging or textile industry. These different uses cause the formation of a continuously growing stream of waste, making PET a favorite candidate for different recycling techniques. Mechanical recycling consists in the reuse of PET after different purification steps such as grinding or washing. However, usual applications using recycled PET are saturated due to the continuous increase in the amounts of PET waste. Chemical recycling consists in the depolymerization of PET in order to obtain new intermediate products which can be used in various applications (e.g., polyurethane foams and unsaturated polyester resins). The main chemical recycling technique applied to PET scraps is glycolysis which can be des- cribed as a depolymerization process by ester inter- change between PET ester groups and a diol. [1–5] The most studied glycolysis reaction involves ethylene glycol (EG) in excess, [6–13] but the most significant problem for the resulting glycolysates is their high crystallinity which makes difficult their use after storage. This phenomenon has been studied extensively by DSC and diols other than EG have been tested [14–16] to decrease crystallization: diethyl- ene glycol (DEG), [17–23] propylene glycol, [24,25] or diol mixtures. [26–30] To limit the crystallization phenomenon, some authors proposed to polycondensate glycolysates with diacids having chemical structures different from the terephthalic acid, which is a constituent of the PET units. [17,31–35] Summary: The crystallinity of a glycolysate obtained by glycolysis of PET with diethylene glycol (DEG) was quali- tatively studied by optical microscopy using a polarizer and quantitatively by X-ray diffraction. Moreover, the rheolog- ical behavior of this glycolysate was also studied in relation with its crystallinity. New glycolysates obtained using oligo- esters of different chemical structures as reagents were studied under the same conditions and they show the total absence of crystallinity. According to the structure of the diol or of the oligoester used, the glycolysate crystallinity can be induced or not. DSC analyses of different glycolysates. Macromol. Chem. Phys. 2006, 207, 1461–1473 ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper DOI: 10.1002/macp.200600189 1461