ABSTRACT Mechanical recycling of plastics is the most common process, but mixed polymer chain lengths make molecular weight effects unclear. By blending high and low molecular weight ( M w ) Polyethylene terephthalate (PET), we want to investigate the changes in molecular weight distribution in the extrusion process and the properties regarding processability and performance. Bottle‐grade PET (high M w ) and fiber‐grade PET (low M w ) were used. The aim of the study was to understand the structure–property relationship relevant to mechanical recycling for PET. We focused on melt viscosity, degree of crystallinity, tensile strength, and elongation at break, all strongly dependent on molecular weight. Different blend ratios were extruded and tested for molecular weight, thermal, rheological, and mechanical behavior. The results show that blending enables precise tuning of properties. GPC and rheology confirm chain scission and extension during extrusion, leading to convergence of molecular weight distributions. Thermal analysis shows a reduced degree of crystallinity and melting temperature with higher M w . Mechanical tests reveal that higher M w improves tensile strength and elongation up to a threshold. All blends show similar molecular weight distribution, ensuring consistent properties and wider processing options for recycled PET.
Stephan et al. (2026) studied this question.