Effect of distinct molecular structure of diols on the properties of bio-based wood adhesive

This study aimed to investigate the effect of different diol structures, both aliphatic and aromatic, on wood adhesives derived from renewable sources. Therefore, 1,3-propanediol (PRD), 1,5-pentanediol (PED), and hydroquinone (HQ) were used as crosslinkers with a non-edible oil-based polyol (castor oil (CO)). The HQ-based wood adhesive sample was anticipated to demonstrate higher mechanical strength due to its aromatic structure, which can impart rigidity and potentially lead to increased mechanical properties. Different weight percentages of diols relative to the bio-polyol were incorporated with the bio-polyol and isocyanate to prepare polyurethane (PU)-based wood adhesives, aiming to explore the effect of increasing diol concentrations on adhesive properties. All samples were cured at four different temperatures (room temperature, 50 °C, 75 °C, and 100 °C) to investigate thermal stability and mechanical strength. Unexpectedly, among all prepared adhesive samples, the PRD sample exhibited the highest mechanical strength (5.1 MPa). Gel and swell tests were conducted on all prepared samples to evaluate solubility, followed by FT-IR analysis to assess structural changes after these tests. No major changes were observed in the synthesized adhesive materials, indicating good crosslinking. The importance of bio-based materials in advanced wood adhesive applications is highlighted by our findings, which provide valuable insights into the design of sustainable PU adhesives with optimal characteristics.