Polyurethane Adhesive Primer for Lignocellulosic Extractives
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Solution Overview
Problem
High levels of extractives in lignocellulosic materials like larch, particularly arabinogalactan, hinder the adhesion durability of polyurethane adhesive systems, leading to surface inactivation, poor wet adhesion, and reduced durability, which is a challenge in structural wood applications.
Innovation Solution
A primer composition comprising polyalkylene glycols or glycol ethers with a hydroxyl number of less than 30 mg KOH/g, applied to the lignocellulosic substrate before a moisture-curable one-component polyurethane adhesive, enhances adhesion strength and wet adhesion, meeting structural wood standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyurethane adhesive system is applied directly to lignocellulosic substrates with high extractive content, then the adhesive composition can be applied to the substrate, but the extractives migrate to the surface and cause inactivation of the substrate or react with the adhesive, leading to poor adhesion durability and wet adhesion
Solution Approach 1:
The patent applies a primer composition to the lignocellulosic substrate surface before applying the polyurethane adhesive. This preliminary treatment prevents extractive migration from occurring during the adhesive bonding process, thereby eliminating the harmful effects of extractives on adhesion durability and wet adhesion performance.
Solution Approach 2:
The primer composition acts as an intermediary layer between the lignocellulosic substrate and the polyurethane adhesive. This intermediate layer blocks the migration of extractives to the adhesive interface, preventing the harmful interactions that would otherwise occur between extractives and the adhesive system.
2Reliability
If a primer is used to treat the substrate surface before adhesive application, then adhesion durability is improved, but the process complexity increases with an additional treatment step
Solution Approach 1:
The patent combines the primer composition and polyurethane adhesive into a single integrated adhesive system. The primer is formulated to be compatible with and work synergistically with the polyurethane adhesive, allowing both components to function together as one unified bonding system rather than requiring separate, independent treatment steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The primer composition significantly improves the adhesion strength and durability of polyurethane adhesive systems on lignocellulosic materials, ensuring compliance with standards for structural wood products, including wet use requirements.
Implementation Method 1
the primer composition comprises: i) from 1 to 100% by weight of the composition of at least one compound having a hydroxyl number of less than or equal to 30 mg KOH/g
Implementation Method 2
the adhesive fails to wet the wood; the adhesive bonds to a thin layer of extractives at the wood surface
Data Source
AI summary
An adhesive system for preparing lignocellulosic composites comprising: a) a primer composition; and, b) a polyurethane adhesive composition, wherein said primer composition comprises: 1 to 100% by weight of the composition of at least one compound having a hydroxyl number of less than or equal to 30 mg KOH/g and being selected from the group consisting of polyalkylene glycols, polyalkylene glycol monoethers or polyalkylene glycol di-ethers; 0 to 99% by weight of the composition of solvent; and, 0 to 5% by weight of the composition of surfactant selected from the group consisting of water soluble surfactants, water emulsifiable surfactants and mixtures thereof. The adhesive system has particular applicability to wooden substrates characterized by high levels of water soluble extractives and, in particular, arabinogalactan.