Solvent-Stable Polymer Membranes via Crosslinking
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Solution Overview
Problem
Current methods for producing polymer membranes using polyacrylonitrile (PAN) are limited by solvent instability, requiring high-boiling solvents and lengthy processes, which result in membranes that are not suitable for high-pressure applications and composite membrane production.
Innovation Solution
A solution containing a copolymer based on (meth)acrylonitrile, a crosslinker with amino groups such as polyethyleneimine, and a solvent like dimethyl sulfoxide (DMSO) is used, which is cast or spun into a membrane and then crosslinked, achieving continuous crosslinking throughout the membrane for enhanced solvent stability and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase inversion process is used to produce membranes from high-boiling solvents, then membrane stability against solvents is improved, but the membranes become inherently unstable against the production solvents themselves
Solution Approach 1:
The patent applies parameter changes by modifying the chemical structure of polyacrylonitrile through copolymerization with functional monomers (acrylic acid, methacrylic acid, itaconic acid) to introduce reactive groups. This enables the membrane to undergo crosslinking reactions, fundamentally changing its chemical properties from solvent-unstable to solvent-stable, allowing it to withstand high-boiling solvents like NMP and DMF that were previously incompatible
Solution Approach 2:
The patent creates composite materials by combining polyacrylonitrile with crosslinking agents (polyethyleneimine, polyvinyl alcohol, or bifunctional crosslinkers) to form a crosslinked network structure. This composite approach transforms the membrane into a new material system with enhanced chemical stability while maintaining the desired pore structure and separation properties
2Reliability
If crosslinking is performed only on the surface of pre-fabricated membranes, then solvent stability is improved, but uncrosslinked inner areas remain causing swelling and loss of stability
Solution Approach 1:
The patent applies preliminary action by incorporating the crosslinking agent into the casting solution before membrane fabrication. This ensures that crosslinking sites are distributed uniformly throughout the membrane matrix from the beginning, enabling homogeneous crosslinking throughout the entire structure rather than just on the surface
Solution Approach 2:
The patent merges the membrane fabrication process with the crosslinking process by adding crosslinking agents to the casting solution. This combination ensures that crosslinking occurs uniformly throughout the membrane during or after formation, eliminating the distinction between crosslinked surface and uncrosslinked interior that plagues sequential approaches
3Reliability
If lengthy crosslinking processes at high temperatures are used, then solvent stability is achieved, but production time and complexity increase
Solution Approach 1:
The patent applies parameter changes by selecting crosslinking agents with optimal molecular weights and reactivities. Low-molecular-weight crosslinkers (e.g., PEI with Mw 25,000-750,000) provide rapid crosslinking at lower temperatures, while controlled parameter adjustments enable shorter crosslinking times compared to conventional high-temperature prolonged processes
Solution Approach 2:
The patent uses intermediary substances (crosslinking agents like polyethyleneimine, polyvinyl alcohol, or bifunctional crosslinkers) that facilitate crosslinking under milder conditions. These intermediaries enable the crosslinking reaction to proceed efficiently at lower temperatures and shorter times, bridging the gap between membrane formation and final stabilization
4Measurement precision
If pore-free membranes are used for gas separation, then separation selectivity is improved, but throughput capacity decreases
Solution Approach 1:
The patent applies local quality by creating membranes with spatially varying pore structures. The top side (feed side) can be pore-free or have very small pores for high selectivity, while the bottom side (permeate side) has larger pores for high throughput. This local differentiation allows each region to optimize for its specific function, achieving both high separation precision and high productivity
Solution Approach 2:
The patent employs asymmetric membrane structures with different pore configurations on opposite sides. This asymmetry enables the membrane to simultaneously achieve high separation selectivity (via the dense top layer) and high flux (via the porous bottom layer), resolving the trade-off between precision and productivity
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 membranes are mechanically stable, highly porous, and solvent-stable, suitable for both filtration and as a substrate for composite membranes, with improved resistance to high and low boiling solvents and consistent separation properties.
Implementation Method 1
The foam structure and the high porosity are presumably due to the use of DMSO as solvent and the subsequent phase inversion
Implementation Method 2
The solution contains a copolymer based on (meth)acrylonitrile... and a crosslinker for the polyacrylonitrile... The film is crosslinked... achieving continuous crosslinking throughout the membrane
Data Source
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AI summary
The invention relates to a method for producing a solvent-stable polymer membrane, wherein a solution containing poly(meth)acrylonitrile, which at the same time contains a cross-linking agent, is used. The solution can be cast as a film, and the film can be cross-linked. It is also possible to spin a hollow yarn membrane from the solution and subsequently cross-linking the same. The polymer membrane thus obtained based on poly(meth)acrylonitrile, that is, copolymers derived therefrom, is characterized by a continuously formed cross-linking. The invention further relates to a solution containing a solvent and a poly(meth)acrylonitrile dissolved therein, that is, a copolymer derived therefrom, and a cross-linking agent for the polyacrylonitrile suitable for the method according to the invention for producing polymer membranes according to the invention.