It is convenient to remark that several studies have reported that raw material flakes produced by the size reduction of PET waste should have certain minimum requirements in order to achieve a satisfactory PET recycling process [12- 15]. This is because there is a loss of molecular weight in PET extrusion process due to hydrolytic [16,17] and thermal- mechanical degradation during melting process [18]. Degradation also causes non uniformity in the flow of fused material generating negative effects in subsequent processes and the properties of final product are also affected [4].
Gurudatt et al. [19] obtained chips from PET waste for the filament extrusion process. Virgin PET and waste PET from bottles were used in mixtures of different compositions. These authors analyzed the extrusion and stretching stages of the spinning process and found that the variations of molecular orientation is very important for determining the properties, efficiency and production of final fiber. Abbasi et al. [20] showed that the crystallinity of recycled materials was higher than those obtained for virgin materials. Consequently, the tenacity of samples from used material was higher and the elongation was smaller. Herein, it is convenient to highlight that there are other scientific and industrial reports about the production of fibers from recycled PET [21-24]; unfortunately, the technical details are not described because of the industrial secrecy.
In this study, an analysis of the critical variables that impact on the flow uniformity of the melt polymer and the degradation of recycled PET using an extruder was performed. This study includes the following aspects: a) the design of the PET extrusion and spinning process for textile applications, b) the mathematical analysis of the operation curves in the extrusion process, c) experimental results and the material characterization in the extrusion and spinning stages, and finally, d) the validation of the operation curves using the experimental data.