Beyond conventional processing methods: the impact of infrared drying on PET performance

Poly ethylene-terephthalate (PET) is currently considered one of the plastics with the greatest potential for recycling, and then a good candidate in the transition towards a circular economy. However, processing and re-processing may deteriorate PET properties, since they involve high temperatures and shear stresses that together with the presence of moisture (due to the strong hydrophilic nature of PET) can provoke hydrolysis of the polymer with a corresponding loss in molecular weight. It is evident the huge importance of the drying stage in the processing of this resin. However, it has not been yet studied the influence of different techniques on the final mechanical properties of processed parts and on the processing cycle (time/costs). In this work, two drying techniques were applied: a conventional one in an oven widely used in the industry, and a novel one that uses infrared rays. The aim was to study their influence on the processing cycle, and mainly on the final mechanical properties of PET parts obtained from both virgin material and waste soda bottles. It was found that drying by infrared technology reduces drying time by 80% which implies a drastic reduction in total processing time for both virgin and recycled PET. In addition, no significant differences were found in the conventional and non-conventional mechanical properties, but differences in the propagation mode under fracture were noticeable. These were found to be due to unintentional esterification reactions induced by IR radiation in thick materials, probably due to heat concentration, that can be avoided by using thinner materials.