Effect of size and loading of waste single-used plastic (SUP) aggregates on a bio-based high density polyurethane composite

Abstract The utilization of waste single-use plastic (SUP) as fillers by containment in a polyurethane matrix was investigated as an alternative solution to the detrimental disposal of these waste materials. High-density bio-based rigid polyurethane composites were prepared by adding polyol, isocyanate, and additives, along with densified SUP, which served as aggregate fillers to enhance the bulk density and flexural strength of rigid polyurethane while increasing the thermal conductivity. The aggregated SUPs were prepared using agglomeration-densification machine and exhibited size variations of 12.44 mm (A), 14.12 mm (B), and 15.56 mm (C). The resulting aggregates were added to the rigid polyurethane matrix at varied loadings of 40%, 50%, and 60% v/v. The green composites were cured in heated hydraulic press at constant temperature and pressure. Based on the obtained results, it was found that the formulation with a SUP size of C and a loading of 60% produced the composite of highest bulk density due to relatively high density of agglomerated SUP as the size enlarges. Additionally, the SUP size of A and a loading of 50% (50A) exhibited the highest flexural strength value. This behaviour was attributed to the increased filler-matrix interfacial area achieved with the smallest size aggregates. However, a further increase in aggregate loading resulted in a decrease in this property as common attribute for composite materials. On the other hand, it was revealed that increasing the loading of SUP aggregates provided a lesser insulating effect due to the increase in thermal conductivity resulting from the presence of filled pores within the polyurethane foam. The findings of this study contributed to understanding the effects of aggregate size and loading on the mechanical and thermal properties of the composite material, providing valuable insights for the development of energy-efficient and environmentally-friendly polyurethane structures.