Lignin-Based Phenolic Adhesives Without Premature Resin Gelation
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Solution Overview
Problem
Existing phenol-formaldehyde resins used in wood adhesives pose health concerns due to formaldehyde exposure during manufacturing, and lignin, despite its potential as a phenol substitute, faces challenges such as low reactivity, high molecular weight, and high polydispersity, leading to inefficient adhesive formation.
Innovation Solution
A controlled condensation reaction between lignin and aldehydes is conducted to prevent gelation, forming a non-crosslinked resin that is then cured, using biobased reactants to create a crosslinked adhesive, avoiding excessive crosslinking and maintaining reactant conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lignin is used as a phenol replacement in adhesive compositions, then health concerns associated with formaldehyde exposure are reduced, but the reactivity is low and molecular weight is high making effective phenolic resin formation difficult
Solution Approach 1:
The patent changes the reaction parameters by using a base catalyst (sodium hydroxide) to alter the pH and reaction conditions, enabling the condensation reaction between lignin and formaldehyde to proceed effectively. This parameter change overcomes the low reactivity of lignin while maintaining the health benefits of reduced formaldehyde exposure.
Solution Approach 2:
The patent creates a composite adhesive system by combining lignin (biobased phenol replacement) with formaldehyde in a controlled condensation reaction. This composite approach allows the adhesive to benefit from both the health safety of reduced formaldehyde and the effective bonding properties of phenolic resins.
2Quantity of substance
If lignin is used as a phenol replacement, then biobased content is increased, but molecular heterogeneity and high polydispersity complicate resin formation
Solution Approach 1:
The patent uses base catalyst to change the reaction parameters, creating optimal conditions for the condensation reaction to proceed despite the molecular heterogeneity of lignin. This parameter control simplifies the resin formation process while maintaining high biobased content.
Solution Approach 2:
The patent addresses the molecular heterogeneity of lignin by creating localized reaction conditions through base catalyst addition, allowing different regions of the lignin molecules to react effectively at different rates, thus simplifying the overall resin formation process.
3Productivity
If condensation reaction between lignin and aldehyde is promoted, then reactant conversion is improved, but gelation and premature crosslinking occur
Solution Approach 1:
The patent applies base catalyst preliminarily to the lignin before adding formaldehyde, preparing the lignin for optimal reaction. This preliminary action controls the reaction rate, improving reactant conversion while preventing premature gelation and maintaining composition stability.
Solution Approach 2:
The patent uses periodic or controlled addition of base catalyst and formaldehyde, allowing the condensation reaction to proceed in a controlled manner. This periodic action ensures complete reactant conversion while preventing runaway reactions that would cause gelation.
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 method produces an adhesive with similar dry adhesion strength to conventional PF adhesives while eliminating health risks associated with formaldehyde, utilizing lignin and aldehydes as sustainable alternatives.
Implementation Method 1
catalyzing a condensation reaction between the lignin and the aldehyde
Implementation Method 2
adding a base catalyst in a controlled manner to the aqueous reaction mixture, thereby catalyzing a condensation reaction
Data Source
AI summary
The disclosure relates to adhesive compositions, including non-crosslinked resins and crosslinked/cured adhesives joining substrates, as well as related methods for making the compositions and articles. Compared to a conventional phenol (P) and formaldehyde (F) resin, the disclosed methods and compositions use lignin (L) and higher aldehydes (A) as corresponding replacements to provide an analog to a conventional PF resin with biobased reactants. Due to the differing reactivity of the LA components compared to the PF components, the initial condensation reaction between ortho-reactive sites in the lignin and the aldehyde is controlled to prevent gelation of the aqueous reaction mixture while reacting substantially all of the LA reactants to provide a non-crosslinked resin reaction product. The resin reaction product can then be cured at high temperature/high pressure conditions to provide a crosslinked adhesive, for example joining two substrates.