This paper presents the results of research conducted on the influence of thermoplastic extrusion parameters (layer height per pass—Lh and the percentage fill density—Id) and heat treatment (annealing) on the compressive strength of specimens manufactured by thermoplastic extrusion of virgin and recycled polyethylene terephthalate glycol (PETG and rPETG) filaments. To support the study, using the parameters Lh = (0.10–0.20) mm and Id = (50–100)%, 90 compression test specimens were manufactured from PETG and rPETG (45 specimens for each material), which were subsequently subjected to heat treatment by annealing at a temperature of 75 °C for a period of 180 min. The results obtained highlight a significant correlation between the variable manufacturing parameters (Lh and Id) and the compressive strengths (Cs). The average compressive strengths of the 45 specimens made from PETG are 44.15% lower than the average compressive strengths of the specimens made from rPETG. The annealing heat treatment resulted in a 31.40% decrease in the average compressive strengths of the specimens made from PETG and a 0.63% increase in the average compressive strengths of the specimens made from rPETG. The specimens made from PETG exhibited increased thermal sensitivity, which led to molecular relaxation, while rPETG exhibited superior thermal stability acquired through recycling.
Zisopol et al. (Thu,) studied this question.