Cellulose Nanomaterial Coating via Silane Crosslinking
Solution Overview
Problem
Current waterborne polyurethane coatings face challenges due to the moisture sensitivity of pristine cellulose nanocrystals, which limits their application and requires costly, time-consuming surface functionalization to overcome hygroscopicity, and traditional coatings rely on volatile organic solvents harmful to the environment.
Innovation Solution
A novel cellulose nanomaterial-based waterborne polyurethane coating is developed using pristine cellulose nanocrystals or nanofibrils combined with water-dispersible blocked polyisocyanates, where the cellulose nanomaterials contribute 40-90 wt% of the coating, and are crosslinked at elevated temperatures to enhance water resistance and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If pristine cellulose nanocrystals are used in waterborne coatings, then the coating achieves high cellulose content (40-90 wt%) and sustainability, but the coating suffers from high hygroscopicity and moisture sensitivity
Solution Approach 1:
Silane coupling agents (e.g., γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane) are used as intermediary substances to bridge the hydrophilic cellulose nanocrystals and the hydrophobic polyurethane matrix. The silane modifies the cellulose surface to be more compatible with the organic polymer, reducing moisture uptake while maintaining high cellulose content (40-90 wt%) in the waterborne coating.
Solution Approach 2:
The patent changes the chemical parameters of cellulose nanocrystals through silane grafting, transforming them from highly hygroscopic pristine state to modified state with improved hydrophobicity. This parameter change enables the coating to maintain high cellulose content while achieving acceptable moisture resistance for practical applications.
2Reliability
If surface functionalization is applied to reduce hygroscopicity, then moisture resistance improves, but the process becomes time-consuming and costly
Solution Approach 1:
The silane modification process allows cellulose nanocrystals to self-graft with silane agents during coating formulation and curing. This self-service approach eliminates the need for separate, complex surface functionalization steps, reducing processing time and cost while achieving the desired hydrophobicity improvement.
Solution Approach 2:
The silane coupling agents are pre-incorporated into the coating formulation, so the surface modification of cellulose nanocrystals occurs in advance during the coating application and curing process, rather than requiring separate pre-treatment steps. This preliminary action streamlines the overall manufacturing process.
3Reliability
If volatile organic solvents are used in traditional coatings, then coating performance is achieved, but environmental harm and health risks increase
Solution Approach 1:
The patent changes the solvent parameter from volatile organic solvents to water as the continuous phase, creating a waterborne polyurethane coating system. This parameter change maintains coating performance through proper formulation (using blocked isocyanates and silane-modified cellulose) while eliminating the harmful environmental and health effects of VOCs.
Solution Approach 2:
The patent converts the naturally hydrophilic nature of cellulose, which would normally cause moisture sensitivity problems, into a benefit by using silane modification to create a sustainable, water-based coating system that leverages the hydrophilicity for waterborne formulation while controlling moisture uptake through the crosslinked network.
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 coating achieves improved hydrophobicity, mechanical strength, and optical transparency, with reduced moisture uptake and hygroscopic strain, making it suitable for various applications including humidity sensors, while avoiding the use of harmful solvents.
Implementation Method 1
crosslinked at elevated temperatures to enhance water resistance and mechanical properties
Implementation Method 2
the polyurethane coating is a reacting product of a mixture comprising cellulose nanomaterials and at least one water dispersible blocked polyisocyanate
Implementation Method 3
aromatic protected isocyanates to can be unmasked to reveal diisocynates by shifting the equilibrium (between block and unblocked) via elevated temperatures (more than 100° C. for waterborne systems)
Implementation Method 4
where simple drying and heat curing leads to similar performance to solvent born (or neat) isocyanate coatings
Data Source
AI summary
The present disclosure relates to a novel cellulose nanomaterial (CN) based waterborne polyurethane coating, and to methods of making and using the novel cellulose nanomaterial (CN) based waterborne polyurethane coating.