Surface response and photodegradation performance of bio-based polyurethane-forest derivatives foam composites

Rigid polyurethane (PU) foams are popular expanded polymers mostly due to their thermal and mechanical properties, although aesthetical features and photodegradation resistance are also of interest for certain applications. In this study, four different forest-based wastes (wood, bark, kraft lignin and paper sludge) were incorporated into rigid PU foams and their surface response and photodegradation resistance were investigated. The rigid foams were prepared via free rise pouring method and later aged by UV radiation. Their colour and specular gloss were evaluated according to the CIELab method. Contact angle measurements and morphological characterization by optical (OM) and scanning electron microscopy (SEM) were also carried out. The forest-based fillers induced different colour patterns on the rigid foams and their photodegradation yielded a decrease in L* and specular gloss and an increase in a* and b*, especially over the first 20 days of UV-exposure. These effects were accompanied by an increase in surface wettability and weakening of the foam structure. Also, the foams of darker colour (i.e. with bark and kraft lignin fillers) presented greater photodegradation resistance.