Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Materials

Background:

• Growing demand for sustainable and eco-friendly adhesive solutions.
• Need for utilizing wood waste streams in high-value applications.
• Polyurethane adhesives offer versatile bonding properties.

Purpose of the Study:

• To synthesize and characterize polyurethane (PU) adhesives using bio-polyols derived from wood sawdust.
• To investigate the effect of varying isocyanate to hydroxyl (NCO:OH) molar ratios on adhesive properties.
• To evaluate the performance of these bio-based PU adhesives through shear strength and thermal analysis.

Main Methods:

• Acid-catalyzed liquefaction of wood sawdust to produce crude (CLW) and purified (PLW) bio-polyols.
• Synthesis of PU adhesives (CLWPU and PLWPU) by reacting bio-polyols with polymeric diphenylmethane diisocyanate (pMDI) at different NCO:OH ratios (0.5:1 to 2:1).
• Characterization using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA).
• Performance evaluation via single-lap joint shear tests (EN 302-1:2003) and adhesive penetration tests.

Main Results:

• High yield (99.7%) of bio-polyols achieved through liquefaction.
• Optimal shear strength of 4.82 N/mm² (CLWPU) and 4.80 N/mm² (PLWPU) obtained at an NCO:OH ratio of 1.5:1.
• NCO:OH molar ratio significantly influenced the chemical structure and thermal properties of the cured PU adhesives.

Conclusions:

• Wood sawdust can be effectively converted into bio-polyols for synthesizing high-performance polyurethane adhesives.
• The developed bio-based PU adhesives exhibit promising mechanical strength, comparable to conventional adhesives.
• The study highlights a sustainable pathway for wood waste valorization in the adhesive industry.