Sizing compositions for carbon fibers
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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 resultant composites.
Innovation Solution
The use of highly functionalized film-forming epoxy novolac phenolic resins combined with sulfonated polyesters in an aqueous liquid carrier, providing a bimodal or log normal particle size distribution, reduces the need for small molecule dispersing aids and enhances stability and film-forming characteristics, leading to improved thermal and chemical resistance of composites.
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 resin settling and potential degradation
Solution Approach 1:
The patent combines epoxy resin with polyester resin to create a composite sizing composition. This hybrid system leverages the water solubility of polyester to enhance dispersion and stability in aqueous media, while epoxy provides the desired protective and adhesive properties. The synergistic interaction between the two resin types resolves the contradiction by maintaining safety benefits of aqueous systems while improving stability through composite material design.
Solution Approach 2:
The patent modifies the chemical composition parameters of the sizing agent by incorporating polyester resin with specific functional groups that enhance water compatibility and dispersion stability. This parameter change allows the aqueous system to maintain resin suspension without settling, thereby improving shelf life while preserving the safety advantages of water-based formulations.
2Stability of the object's composition
If emulsifiers or surfactants are added to improve stability of aqueous sizing compositions, then stability is improved, but composite properties deteriorate due to co-reactivity and premature crosslinking
Solution Approach 1:
The patent extracts or eliminates the need for traditional emulsifiers and surfactants by utilizing polyester resin that inherently provides water compatibility and dispersion stability through its molecular structure. This removal of problematic additives prevents co-reactivity and premature crosslinking, thereby maintaining both stability and composite properties without relying on harmful auxiliary chemicals.
Solution Approach 2:
The polyester resin component performs the stabilizing function that would otherwise require separate emulsifiers or surfactants. The molecular structure of polyester inherently provides water compatibility and prevents resin settling, making the system self-stabilizing without needing additional additives that could cause degradation or premature crosslinking.
3Ease of operation
If dispersed resins are used in aqueous sizing compositions, then ease of application is improved, but stability deteriorates due to settling over time
Solution Approach 1:
The patent creates a composite system where polyester resin and epoxy resin work together in aqueous dispersion. The polyester component provides inherent stability that prevents settling, while maintaining the dispersed state necessary for easy application. This composite approach resolves the contradiction by enabling both ease of application and long-term stability without requiring additional stabilizing additives.
Data Source
Figure 1
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.