Synthesis and characteristics of biobased copolyester for thermal shrinkage film

A series of poly(1,4-cyclohexanedimethyl-trimethylene glycol terephthalate), (PCTG), co-polyesters were synthesized using 1,3-propanediol (PDO) and 1,4-cyclohexanedimethanol (CHDM) via melt polymerization. The characteristic of having a high thermal shrinkage ratio at low processing temperature conditions and a suitable molecular weight for film manufacture, with Mn ranging from 20 000 to 25 000 g mol−1 and a polydispersity of 1.8–2.0, suggests the use of the biobased monomer, PDO, in the film industry. The composition of the PCTG samples was confirmed using 1H-NMR spectroscopy. 2D NMR analyses (correlation spectroscopy (COSY) and heteronuclear single quantum correlation spectroscopy (HSQC)) were performed to analyze detailed structural information for PCTG. Sequence distribution was used to reveal the effect of PDO dyads in the polyester chain and identify the structural effect. In the case of the transesterification time, under fixed esterification conditions, it decreased as the CHDM content increased due to the high reactivity of CHDM which has a higher boiling point. A thermal shrinkage ratio test was done with the temperature ranging from 70 °C to 100 °C. As the PDO content increased, the low temperature conditions showed a relatively higher thermal shrinkage ratio owing to the structural characteristics of CHDM and PDO. This result could induce advantageous energy savings in heat shrink processes at low temperatures.