Friable Polyimide Powder for Composite Matrix Incorporation
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Solution Overview
Problem
High molecular weight polyimides, particularly polyetherimides, face challenges in incorporation into composite matrices due to high viscosity and glass transition temperature, which hinders their use in blends, composites, and coatings, necessitating the development of low molecular weight, highly friable polyimide powders that can be easily size-reduced by mechanical grinding.
Innovation Solution
A method involving melt blending high molecular weight polyimides with greater than 3.0 mole percent of an aromatic diamine to produce friable polyimide powders with a weight average molecular weight of less than or equal to 24,500 Daltons and a maximum particle size of 75 micrometers, enabling effective reduction in size through mechanical grinding and sieving, while maintaining reactive end group content and low polydispersity indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polyimides are used to achieve high strength and high temperature stability, then the mechanical properties and thermal resistance are improved, but the viscosity increases making incorporation into composite matrices difficult
Solution Approach 1:
The polyimide is processed into discrete powder particles with controlled size distribution (0.5-100 micrometers), dividing the material into small units that can be easily dispersed and incorporated into composite matrices while maintaining the desired molecular weight for strength
Solution Approach 2:
The patent controls the weight average molecular weight within a specific range (5,000-50,000 Daltons) and adjusts the polydispersity index to achieve optimal balance between mechanical strength and processability, allowing the material to be easily incorporated into composites while maintaining high strength properties
2Strength
If high molecular weight polyimides are used to achieve high toughness, then the mechanical toughness is improved, but the glass transition temperature increases hindering use in blends and coatings
Solution Approach 1:
The patent optimizes the molecular weight range (5,000-50,000 Daltons) and polydispersity index to achieve a balance where the glass transition temperature remains suitable for blend and coating applications while maintaining high toughness through adequate molecular weight
3Length of moving object
If particle size is reduced by jet milling to achieve fine particle size, then the particle size is reduced by interparticle collisions, but the process requires pressurized gas streams and complex equipment
Solution Approach 1:
The polyimide is synthesized directly as a friable powder with controlled molecular weight and particle size characteristics, preparing the material in advance with desirable properties that eliminate the need for complex post-processing milling operations
Solution Approach 2:
The patent controls the particle size distribution (0.5-100 micrometers) and molecular weight during synthesis to create inherently friable particles that can be easily size-reduced by simple mechanical grinding rather than requiring jet milling equipment
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 resulting friable polyimide powders exhibit improved dispersibility and chemical interaction with thermoset matrices, facilitating their incorporation and distribution within thermoset materials, reducing viscosity for enhanced flow and processing.
Implementation Method 1
cooling the melt blend product to form a friable polyimide powder
Data Source
Figure 1
AI summary
Disclosed herein is a friable polyimide powder having a weight average molecular weight, as determined by gel permeation chromatography (GPC) using polystyrene standards, of less than or equal to 24,500 Daltons and a reactive aromatic amine end group concentration greater than or equal to 3 mole percent, wherein 90 weight percent of the powder particles are reducible to less than or equal to 75 micrometers by mechanical grinding. Also disclosed is a method of making the friable polyimide powder, a processed polyimide resulting from the friable polyimide powder and compositions comprising the processed polyimide.