Porous polymeric membrane comprising vinylidene fluoride
View Patent ↗A process for producing a porous polymeric structure which process comprises preparing a solution comprising a polymer which comprises vinylidene fluoride in a solvent/non-solvent mixture; holding the solution at an elevated temperature until the polymer is completely solvated; casting the solution to form a thin layer; and drying the thin layer to form a membrane. The polymer is dispersed in the non-solvent before addition of the solvent, when preparing the solution, to prevent microgel formation. The prolonged solvation at elevated temperature provides a stable solution, and enables membranes of controlled porosity to be formed.
1. A process for producing a porous polymeric membrane which process comprises:
a) preparing a solution comprising a polymer which comprises vinylidene fluoride in a solvent/non-solvent mixture in which the proportion of non-solvent is 2 to 30 wt % by dispersing the polymer in the non-solvent prior to addition of the solvent wherein the boiling point of the non-solvent is higher than that of the solvent;
b) holding the solution at an elevated temperature of at least 40° C. until the polymer is completely solvated;
c) casting the solution to form a thin layer; and
d) drying the thin layer to form a membrane.
2. Process according to claim 1 wherein the solution comprises polyvinylidene fluoride (PVdF).
3. Process according to claim 1 wherein the solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) or N-methyl-2-pyrrolidone (NMP).
4. Process according to claim 1 wherein the non-solvent is octanol, decanol, dodecanol or a mixture thereof.
5. Process according to claim 1 wherein the solution is solvated for up to 14 days.
6. Process according to claim 1 wherein mono-unsaturated carboxylic, sulphonic or phosphonic acid, ester or amide groups are grafted onto the vinylidene fluoride.