Aqueous Carbon Fiber Sizing With Stable Epoxy-Polyester Dispersion
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Solution Overview
Problem
Aqueous sizing compositions for carbon fibers face challenges such as poor stability and shelf life due to settling of dispersed resins and potential degradation or premature crosslinking, which can compromise the properties of composites and fibers.
Innovation Solution
The use of highly functionalized film-forming epoxy novolac phenolic resins in combination with highly functionalized sulfonated polyesters, which provides stability and long shelf life, and allows for reduced or eliminated small molecule dispersing aids, resulting in excellent film-forming characteristics and consistent coating coverage on carbon fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aqueous sizing compositions are used for carbon fibers, then safety and environmental aspects are improved (reduced toxicity and flammability), but stability and shelf life deteriorate due to settling of dispersed resins
Solution Approach 1:
The patent uses a composite resin system combining epoxy resin with polyester or polyurethane components. This composite approach creates a more stable dispersed phase in aqueous medium, preventing settling while maintaining the safety advantages of water-based formulations. The multi-component resin system provides both stability and performance.
Solution Approach 2:
The patent modifies the chemical parameters of the resin system by selecting specific epoxy equivalents, molecular weights, and resin compositions that optimize stability in aqueous medium. By carefully controlling these parameters, the formulation achieves long shelf life without compromising the safety benefits of aqueous-based sizing.
2Stability of the object's composition
If more emulsifiers or surfactants are added to improve stability, then stability is improved, but composite properties and fiber performance deteriorate due to co-reactivity and degradation
Solution Approach 1:
The patent extracts or eliminates the need for traditional small molecule emulsifiers and surfactants by using resin components themselves that provide adequate dispersibility. The epoxy-polyester or epoxy-polyurethane combination creates intrinsic stability without requiring additional surfactant chemistry, thereby avoiding co-reactivity issues.
Solution Approach 2:
The patent uses the resin components themselves as intermediaries that provide both structural integrity and dispersibility. Rather than adding separate emulsifier molecules, the resin system's own molecular structure acts as the mediating element that enables stable aqueous dispersion without compromising composite performance.
3Adaptability or versatility
If traditional epoxy resins are used in aqueous sizing, then compatibility with epoxy matrices is improved, but stability deteriorates due to premature crosslinking and degradation
Solution Approach 1:
The patent segments the epoxy functionality from the crosslinking reaction by using a multi-component system where epoxy resin is combined with polyester or polyurethane. This segmentation allows the epoxy groups to remain stable in aqueous storage while maintaining compatibility with epoxy matrices during composite processing, preventing premature crosslinking.
Solution Approach 2:
The patent performs preliminary formulation work by pre-combining epoxy resin with polyester or polyurethane components in a stable aqueous dispersion before application. This preliminary action ensures that the resin system is pre-stabilized and ready for use, preventing degradation and premature crosslinking during storage and handling.
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 solution maintains viscosity and particle size characteristics over extended periods, enhances interlaminar shear strength, and improves the thermal and chemical resistance of composites, while reducing the need for excessive emulsifiers, thus addressing stability and shelf life issues.
Implementation Method 1
aqueous sizing compositions including epoxy functional resins and sulfonated polyester resins
Implementation Method 2
maintains viscosity and particle size characteristics over extended periods
Implementation Method 3
highly functionalized film-forming epoxy novolac phenolic resins
Implementation Method 4
consistent coating coverage on carbon fibers
Implementation Method 5
the epoxy functionality has relatively high and favorable chemical reactivity toward a wide range of functional groups. This makes it easy to crosslink the size to enhance composite performance
Implementation Method 6
cured epoxy resins have high thermal and chemical stability
Data Source
AI summary
The present invention provides aqueous, epoxy-based sizing compositions for carbon fibers. The size composition incorporates highly functionalized film forming epoxy novolac phenolic resins in combination with highly functionalized sulfonated polyesters having high Tg characteristics, sulfonate equivalent weights in the range from 2000 to 20,000 and number average molecular weights in the range from about 1000 to about 100,000. The present invention also provides corresponding sized carbon fibers and fiber-reinforced matrices.