Influence of Black Alder Bark Extractives as Integral Building Blocks on the Susceptibility to Biodegradation of Resilient Polyether Polyurethanes ^†

In response to the increasing demand for environmentally friendly materials and the necessity of effective end-of-life management [1], this study investigates the susceptibility of innovative polyurethanes (PUs) that incorporate plant extractives to biodegradation. The PUs were synthesized using polymeric methylene diphenyl diisocyanate, polyol PEG 400, and tetrahydrofuran as a solvent, with NCO/OH ratios of 1.0, 0.8, and 0.5 [2]. Partial or complete substitution of the conventional PEG 400 polyol with black alder bark extracts as bio-polyols was performed. Degradation tests were conducted in sewage water and compost-enriched soil [3,4]. The susceptibility to biodegradation was assessed through weight loss measurements, FTIR spectroscopy, and biological oxygen demand (BOD) analysis [5,6,7]. After 2 months, conventional PUs exhibited weight losses of 9.6% in soil and 12.4% in water. Complete replacement of PEG 400 with bark-sourced polyol increased weight loss to 15.6% in soil and 15.7% in water. The reference biodegradable polylactic acid (PLA) film displayed weight losses of 35.6% in soil and 15.0% in water. BOD measurements indicated that PUs, particularly those containing bio-based building blocks, supported microbial metabolism, corroborating previous findings [8]. The incorporation of bark extractives significantly enhanced the susceptibility of PUs to biodegradation, resulting in a reduction of up to 45% in the intensity of FTIR spectral peaks associated with the urethane functional group (-NHC(=O)-O-), compared to a maximum reduction of 11% for conventional PUs. Moreover, it displayed increased peak intensities for O-H and N-H stretches after biodegradation, exhibiting a notable negative correlation with changes in peak intensities for N-CO-O, C-O-C, and C-N vibrations following PU biodegradation. This indicates the formation of hydroxyl and amino groups resulting from the hydrolysis of various chemical bonds within the polyurethane network, facilitated by the integration of bark extractives. This work emphasizes the potential of bark-derived building blocks in the design of PU materials suitable for biological recycling while recognizing the need for further investigation into the optimal agents and conditions for the biological conversion of the latter.