Tuning properties of sustainable castor oil based polyurethanes with bacterial biomass as fillers

A novel series of bio-based polyurethanes (bio-PUs) were synthesized from castor oil using hexamethylenediisocyanate (HMDI) as crosslinking agent by solvent casting method without any catalyst and further reinforced with bacterial biomass as bio-fillers. For the first time, biomasses from the biopolymer polyhydroxyalkanoate (PHA) production process, containing medium chain length biopolymer, mcl-PHA (F1) and residual bacterial biomass after the biopolymer extraction (F2), as well as bacterial biomass from the biopigment prodigiosin production process (F3) were applied as bio-fillers, resulting in PU-F1 to PU-F3 materials, respectively. The resulting functional bio-polyurethanes were characterized by various techniques including ATR-FTIR spectroscopy, SEM, X-ray diffraction, mechanical tests, transparency, water contact angle, but also cytotoxicity tests and shape memory ability were evaluated to open their applicative potential. The FTIR spectroscopy analysis confirmed the formation of polyurethane linkage. Bacterial biomass particles size and distribution reflected on the PUs properties suggesting that the type and the dispersion of the filler play an important role in the modulation of new PU materials. The water contact angle measurements revealed that PU-F1, containing mcl-PHA biopolymer exhibits higher hydrophobicity than other bio-PUs, that further reflected on better biofilm attachment in comparison to other bio-PUs. The addition of bacterial biomass containing biopigment resulted in purple dyed material of stable color over time and with the proved absence of toxicity (PU-F3). All synthesized bio-PUs appeared as non-toxic materials for human healthy fibroblast cell line MRC5. Shape memory ability was observed for the bio-PUs. The addition of variety of bacterial biomass into polyurethane matrix is a significant step towards the green conversion of resources and circular bio-economy for plastics.