PVDF Liquid Separation Membrane via Composite Phase Inversion
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Solution Overview
Problem
Existing methods for producing polyvinylidene fluoride liquid separation membranes struggle to balance mechanical strength, permeability, and filtration accuracy, with thermally induced phase separation methods often resulting in membranes that are difficult to clean and have reduced permeability, while immersion precipitation methods enhance strength at the cost of permeability.
Innovation Solution
A method involving a thermally induced phase separation membrane as a substrate, soaked with water or a weak polar organic liquid, followed by coating with a polyvinylidene fluoride casting solution and rapid curing in a heated coagulating bath, to create a membrane with enhanced mechanical properties and high interception accuracy, avoiding solvent dissolution in the pore structure and ensuring membrane integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the membrane and sponge layer is increased to enhance mechanical strength, then the strength is improved, but the membrane permeability is reduced
Solution Approach 1:
The invention uses a composite structure consisting of a substrate membrane layer and a porous coating layer. The substrate membrane provides mechanical strength, while the porous coating layer maintains high permeability. This composite approach allows the membrane to have both high strength and high permeability simultaneously, resolving the contradiction between these two parameters.
2Strength
If the thermally induced phase separation method is used to improve mechanical properties, then the mechanical properties are improved, but the filtering accuracy and permeability cannot be balanced
Solution Approach 1:
The composite membrane structure combines the advantages of both thermally induced phase separation method (good mechanical properties) and immersion precipitation method (high filtering accuracy). The substrate membrane is prepared by thermal phase separation, and the porous coating layer is formed by immersion precipitation, achieving both high mechanical strength and high filtering accuracy.
Solution Approach 2:
Different layers of the membrane have different properties optimized for their specific functions. The substrate membrane layer has high mechanical strength, while the porous coating layer has high filtering accuracy and hydrophilicity. This local optimization allows each layer to perform its specific function excellently.
3Strength
If the thermally induced phase separation method is used, then the mechanical properties are improved, but the embedded pollutants are easily formed and difficult to remove
Solution Approach 1:
The porous coating layer is made homogeneous with high hydrophilicity through the immersion precipitation process, creating a uniform surface that prevents pollutant embedding. The homogeneous structure ensures consistent performance and easy cleaning, resolving the issue of embedded pollutants.
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 method produces membranes with improved mechanical strength, high filtration accuracy, and maintained permeability, suitable for applications like membrane bioreactors, with enhanced anti-backwashing performance and prolonged service life.
Implementation Method 1
soaking the substrate membrane with water or a weak polar organic liquid to make membrane pores of the substrate membrane filled with the liquid
Implementation Method 2
coating a casting solution of polyvinylidene fluoride on the surface of the soaked substrate membrane obtained in step (1), and quickly soaking the substrate membrane in a coagulating bath heated to a temperature of 60-100° C. for curing
Data Source
AI summary
A method for making a liquid separation membrane, including: (1) providing a polyvinylidene fluoride liquid separation membrane or polypropylene liquid separation membrane prepared by a thermally induced phase separation method as a substrate membrane, soaking the substrate membrane with water or a weak polar organic liquid to make membrane pores of the substrate membrane filled with the liquid, the soaking time being between 0.5 s and 1 min, and the weak polar organic liquid being indissolvable and compatible with the polyvinylidene fluoride liquid separation membrane or polypropylene liquid separation membrane; (2) coating a casting solution of polyvinylidene fluoride on the surface of the soaked substrate membrane obtained in step (1), and quickly soaking the substrate membrane in a coagulating bath heated to a temperature of 60-100° C. for curing to yield the liquid separation membrane.