Polyurethane Adhesives Based on Oxyalkylated Kraft Lignin

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Polyurethane (PU) adhesives often rely on petroleum-derived polyols and isocyanates.
• Lignin, a byproduct of the paper industry, presents a potential renewable resource for chemical synthesis.

Purpose of the Study:

• To synthesize and characterize lignin-based polyols (LBPs) from eucalyptus kraft lignin.
• To develop and evaluate novel PU adhesives using LBPs for wood bonding applications.
• To compare the performance of lignin-based PU adhesives against commercial counterparts.

Main Methods:

• Lignin isolation using the Lignoboost® procedure.
• Oxyalkylation reaction with propylene carbonate to produce LBP.
• Preparation of PU adhesives by varying the NCO/OH ratio.
• Performance evaluation through wood adhesion tests.
• Characterization using Fourier transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA).

Main Results:

• Lignin-based PU adhesives exhibited increased lap shear strength and glass transition temperature with higher NCO/OH ratios (1.1-2.2).
• An NCO/OH ratio of 1.3 yielded superior chemical resistance and adhesion efficiency compared to a commercial PU adhesive (CPA).
• FTIR analysis suggested the CPA had a very high NCO/OH ratio, potentially impacting its performance.

Conclusions:

• Lignin-based PU adhesives demonstrate significant potential as sustainable alternatives in wood bonding.
• Optimizing the NCO/OH ratio is crucial for balancing adhesion, chemical resistance, and overall performance.
• This research highlights a viable pathway to reduce reliance on fossil fuels in adhesive production for industries like furniture manufacturing.