In response to growing environmental concerns and the need for sustainable resources, researchers worldwide are examining how to develop materials that are environmentally friendly and that can be effectively recycled as they reach the end of their useful life. Particularly interesting are polyurethanes (PUs), a broad class of synthetic polymers utilized in several applications. However, because of the high energy consumption and unwanted chemical side reactions, their chemical recycling is challenging. A possible method for recovering PU is biological recycling, which breaks down complex compounds using microbes and enzymes. The biodegradation susceptibility of novel PUs using tree bark extractives as building blocks is examined in this work. The PUs were synthesized with partial or complete substitution of conventional fossil-based polyol (PEG 400) with hydrophilic extractives from black alder bark. Biodegradation experiments in sewage water and compost-enriched soil were conducted over 60 days. Results indicate increased biodegradation in PUs containing bark-based polyols, showing weight losses of up to 15.7% and 15.6% in sewage water and soil, respectively, compared to 9.6% and 12.4% for fossil-based PU. Analytical pyrolysis and FTIR analysis revealed more significant structural changes in extractives-containing PU materials after biodegradation compared to fossil-based PU, indicating the cleavage of covalent bonds mainly in carbohydrate and aromatic constituents of biopolyol. But the urethane bonds revealed the highest stability towards biodegradation compared to others linkages in both fossil-based and bio-based PU. The study demonstrates the potential of using bark-derived polyols to design PU materials suitable for biological recycling, contributing to more environmentally friendly waste management strategies. Further investigations are needed to optimize the conditions for the biological conversion of PU materials synthesized with bark-based polyols.

The production of polyurethane films from bark-derived polyols requires the complete solubility of all components in the polyurethane synthesis media. In this study, a comprehensive investigation was conducted to achieve the copolymerization of black alder bark water extract-derived polyol with isocyanate for polyurethane film synthesis in THF solution. A fractionation approach using tetrahydrofuran (THF) as a solvent was employed to dissolve the extract, followed by filtration and removal of the solvent. The resulting THF-soluble fraction comprised 62±1% of the dry weight of the alder bark extract, mainly consisting of the xyloside form of the diarylheptanoid compound oregonin, along with oligomeric flavonoids and carbohydrates. The THF-insoluble fraction was the most enriched with carbohydrate compounds, followed by the crude extract and THF-soluble fraction. Another approach was aimed at obtaining bark extractives based liquid polyols suitable for producing rigid PU foams. For this purpose, oven-dried crude black alder bark water extract was liquefied with polyethylene glycol (PEG 400). The liquefaction of black alder bark and pine bark extractives was studied under different conditions, including varying temperature ranges (130-170⁰C), catalyst concentrations (0-1,5%), and bark extract content in the mixture (15-30%). The results showed that the use of sulphuric acid as a catalyst (1-1.5%) significantly improved the solubility of both extractives, enabling the attainment of extract concentrations up to 25% at 170⁰C. However, increasing the extract content beyond a certain threshold led to incomplete solubility. It was shown that the PEG-insoluble fractions consist mainly of carbohydrate components. To increase the content of biomass in liquid polyols, the effect of glycerol additions into the liquefaction agent is under study. The findings provide insights into tailoring bark-sourced polyols for polyurethane foam production through appropriate liquefaction conditions.

This publication investigates the potential application of bark extractives as a biopolyol and extracted bark residues as a filler for producing polyurethane materials. The aim is to enhance the properties of polymeric composites while reducing the environmental impact associated with the complex utilization of bark.The comprehensive study of compositions of extractives isolated from black alder (Alnus glutinosa) and Baltic pine (Pinus silvestris) barks was performed using microwave-assisted water extraction. The yield of the extracts obtained under different extraction conditions, as well as the total phenolic and monomeric carbohydrate content in the extractives, were studied. Furthermore, UHPLC-HRMS analysis was conducted to study the detailed composition of the bark extracts.The total content of hydroxyl groups and the relative portion of aliphatic and phenolic groups in the isolated extracts were determined depending on the extraction regimes and bark origination. The dominant compounds in black alder bark extracts isolated at 70-90⁰C were identified as diarylheptanoids and their derivatives bearing sugar units, with oregonin being the main compound. Pine bark extracts isolated at the same temperature were found to be rich in oligomeric proanthocyanidins. Extracts from both black alder and pine barks obtained at different times of isothermal heating between 130-150°C were rich in carbohydrates and showed an increased proportion of aliphatic OH groups.The study also focused on the composition of residual biomass. It was indicated by Py-GC/MS/FID and wet chemistry methods that residues of both black alder and pine bark are enriched with lignin in comparison with initial barks. Therefore, it can be proposed that extracted bark residues introduced into polyurethane compositions will act as a charcoal formation promoter, thus increasing the flame resistance of materials.Overall, the study provides valuable insights into the chemical composition of bark extractives and extracted bark residues for their potential application as biopolyol and fillers of polyurethane materials, contributing to a more sustainable approach in polymer composite production.