BAPB-Cured Epoxy Resin Solvent Resistance
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Solution Overview
Problem
Epoxy resins used in composite materials for aerospace applications face challenges in resisting crazing and cracking when exposed to solvents like methyl ethyl ketone (MEK), while attempts to enhance tensile strength and damage tolerance often compromise other desirable properties such as compression performance and solvent resistance.
Innovation Solution
The use of 4,4'-Bis(p-aminophenoxy) biphenyl (BAPB) as a curing agent for thermoplastic-toughened epoxy resins, combined with a mixture of tri and tetra-functional epoxy resins and thermoplastic components, enhances the solvent resistance and mechanical properties of the cured composites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoplastic materials are added to epoxy resins to enhance tensile strength and damage tolerance, then the tensile strength and damage tolerance are improved, but the resistance to solvent attack deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the epoxy resin system by introducing specific ratios of tri-functional and tetra-functional epoxy resins, along with controlled amounts of thermoplastic materials (5-20 wt%), to achieve optimal balance between tensile strength and solvent resistance. This parameter optimization allows the resin to maintain both mechanical properties and chemical resistance simultaneously.
Solution Approach 2:
The patent creates a composite resin system combining epoxy resins with thermoplastic materials (such as polyamide, polyester, or polyimide) to achieve synergistic effects. The thermoplastic components provide toughness and damage tolerance while the epoxy matrix maintains solvent resistance, creating a balanced composite material system.
2Reliability
If the resin viscosity is increased to improve damage tolerance, then the damage tolerance is improved, but the ease of manufacture deteriorates
Solution Approach 1:
The patent optimizes the viscosity parameter of the resin system by controlling the types and amounts of epoxy resins and thermoplastic materials used. The formulation maintains viscosity within a specific range (100-10,000 cP at 25°C) that enables both adequate damage tolerance and ease of impregnation into fiber reinforcements during prepreg manufacturing.
Solution Approach 2:
The patent applies different functional characteristics to different components of the resin system: the epoxy resins provide base properties and curing functionality, while the thermoplastic materials provide localized toughness and damage tolerance. This local functional differentiation allows the overall system to achieve both manufacturability and performance requirements.
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 BAPB-cured thermoplastic-toughened epoxy resins demonstrate significant resistance to solvent attack, maintaining high strength, damage tolerance, and interlaminar fracture toughness, with no visible cracking after 7 days of exposure to MEK at room temperature.
Implementation Method 1
4,4'-Bis(p-aminophenoxy) biphenyl (BAPB) as a curing agent for thermoplastic-toughened epoxy resins
Implementation Method 2
thermoplastic-toughened epoxy resins that are toughened with one or more thermoplastic materials
Implementation Method 3
resistance to the crazing and cracking that can occur when the cured epoxies are exposed to solvents, such as methyl ethyl ketone (MEK)
Data Source
Figure 1~2
AI summary
Thermoplastic toughened epoxy resin for use in making prepreg for aerospace applications. The resin includes an epoxy resin component comprising a tri functional epoxy resin and/or tetra functional epoxy, a thermoplastic component and 4, 4'- Bis ( p-aminophenoxy) biphenyl ( BAPB) as the curing agent. The use of BAPB as a curative was found to increase the resistance of the cured resin to attack by solvents.