Beyond processing methods: the impact of the drying technique on PET performance

Abstract

Plastic materials are essential in modern societies, and their recycling is a very important step in the transition towards acircular economy. PET (polyethylene terephthalate) is currently considered one of the plastics with the greatest potentialfor recycling due to its good properties and ability to be processed by industrial methods. However, those processes maydeteriorate PET properties, since they involve high temperatures and shear stresses that together with the presence ofmoisture (due to the strong hydrophilic nature of PET) can provoke hydrolysis of the polymer with a corresponding lossin molecular weight. When working with recycled PET the excess moisture contained in the material may be higher. Itis evident the huge importance of the drying stage in the processing of this resin. However, it has not been yet studiedthe infuence of diferent techniques on the fnal mechanical properties of processed parts and on the processing cycle(time/costs). In this work, two drying techniques were applied: a convection oven—widely used in the industry—andan infrared oven. The aim was to study the infuence of this part of the processing cycle on the fnal mechanical properties of PET parts obtained from both virgin material and waste soda bottles. Results confrmed that drying by infraredtechnology reduces drying time by 80% which implies a drastic reduction in total processing time for both types of PET(virgin and recycled). Even though no signifcant diferences were found in the conventional and non-conventionalmechanical properties, diferences in the propagation mode under fracture were noticeable. These were found to be dueto unintentional esterifcation reactions induced by IR radiation in thick materials, probably due to heat concentration,that should be taken into account when this drying technique is intended to be used.