Porous PTFE Membrane Structure for Balanced Orthogonal Strength
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Solution Overview
Problem
Existing porous polytetrafluoroethylene (PTFE) membranes have asymmetric strength properties, which are not suitable for applications requiring symmetric strength, such as fuel cells.
Innovation Solution
A porous PTFE membrane with a nonwoven web microstructure composed of substantially only microfibrils fused at crossover points, achieving a balance of orthogonal dimensions within 10%, and having tensile peak stresses in the machine and cross directions that are within 10% of each other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional porous PTFE membranes are used, then they provide filtration capability, but they exhibit asymmetric strength properties that are unsuitable for applications like fuel cells
Solution Approach 1:
The patent applies asymmetry in reverse - it deliberately creates a symmetric structure to eliminate the problematic asymmetry in conventional membranes. The nonwoven web is constructed with microfibrils arranged to provide substantially equal tensile peak stress in both machine and cross directions, achieving dimensional symmetry within 10% balance. This symmetric construction resolves the contradiction by making the membrane suitable for fuel cell applications that require uniform strength properties in all directions.
Solution Approach 2:
The patent changes the structural parameters of the PTFE membrane by using a nonwoven web of substantially only microfibrils fused at crossover points, without nodes. This parameter change in the microstructure enables the membrane to achieve both high tensile peak stress and dimensional symmetry, simultaneously improving strength and ease of operation for symmetric applications.
2Manufacturing precision
If pore size is reduced for better filtration, then filtration precision improves, but air and liquid permeability decreases
Solution Approach 1:
The patent utilizes a highly optimized porous structure consisting of a nonwoven web of microfibrils fused at crossover points. This porous material design maintains excellent air and liquid permeability even at reduced pore sizes (0.05-2 microns) because the interconnected microfibril structure creates efficient flow pathways. The porous architecture resolves the contradiction by allowing small pores for precise filtration while preserving high permeability for productivity.
Solution Approach 2:
The patent addresses the pore size-permeability contradiction by transitioning to a three-dimensional nonwoven web structure of microfibrils. This dimensional approach creates a complex spatial network where numerous interconnected pathways compensate for smaller individual pore sizes, maintaining high permeability while achieving precise filtration through the microfibril-scale pore dimensions.
Data Source
AI summary
A porous polytetrafluoroethylene (PTFE) membrane including a nonwoven web having a microstructure of substantially only microfibrils fused at crossover points, said membrane having a percent balance of orthogonal dimensions that is within 10%.