Electrostatically charged porous nonwoven web, membrane and mask derived therefrom and methods for manufacture and cleaning
A nonwoven web obtained by electrospinning, suitable for the filtration of nano- and/or submicron aerosols, including a multiplicity of fibers of composition C 1 , the composition C 1 including at least 50% by weight of at least one polymer P 1 based on the repeat unit resulting from vinylidene fluoride (VDF), the fibers of composition C 1 having a degree of crystallinity in polar phase(s), preferentially in solely beta phase, of at least 65% by weight, with respect to their total weight. Also, a process for the manufacture of the web, to a membrane including the web and also to a process for the washing/sterilization of the web or of the membrane.
1 . A nonwoven web comprising a multiplicity of fibers of composition C 1 , the composition C 1 comprising at least 50% by weight of at least one polymer P 1 comprising a repeating unit of vinylidene fluoride (VDF),
said fibers of composition C 1 having a degree of crystallinity in polar phase(s), of at least 65% by weight, with respect to their total weight,
the web comprising less than 1% by number of fibers having a diameter strictly of less than 100 nm,
wherein the web is produced by a process comprising electrospinning,
wherein the web is configured for filtration of nano and/or submicron aerosols.
2 . The web as claimed in claim 1 , in which said fibers of composition C 1 have a degree of crystallinity in polar phase(s), of at least 75%, with respect to their total weight.
3 . The web as claimed in claim 1 , in which the polymer P 1 is chosen from the group consisting of: a homopolymer of VDF; a copolymer having a repeat unit resulting from VDF and at least one repeat unit resulting from a monomer other than VDF, the other monomer being chosen from the list consisting of: vinyl fluoride (VF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), a chlorofluoroethylene (CFE), a chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, a trichlorofluoroethylene, hexafluoropropylene (HFP), a trifluoropropene, a tetrafluoropropene, a chlorotrifluoropropene, hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkyl vinyl ether, ethylene, an acrylic monomer, a methacrylic monomer and their mixture; and a mixture of homopolymer(s) and copolymer(s).
4 . The web as claimed in claim 1 , in which the polymer P 1 is a PVDF, a P(VDF-HFP), a P(VDF-TFE), a P(VDF-TrFE) or their mixture.
5 . The web as claimed in claim 1 , in which said at least one polymer P 1 is a mixture consisting of:
a PVDF,
a copolymer chosen from: P(VDF-HFP), P(VDF-TFE) and P(VDF-TrFE);
the proportion by weight of PVDF, with respect to that of the copolymer, ranging from 1:99 to 99:1.
6 . The web as claimed in claim 1 , in which the polymer P 1 represents at least 60%, by weight, of the composition C 1 .
7 . The web as claimed in claim 1 , in which the composition C 1 additionally comprises at least one polymer P 1 ′ chosen from the list consisting of: a poly(methyl methacrylate) (PMMA), a poly(ethyl methacrylate) (PEMA), a poly(methyl acrylate) (PMA), a poly(ethyl acrylate) (PEA), a poly(vinyl acetate) (PVAc), a poly(vinyl methyl ketone) (PVMK), a thermoplastic polyurethane (TPU), and a thermoplastic starch.
8 . The web as claimed in claim 7 , in which the polymer P 1 consists of a PVDF and the polymer P 1 ′ consists of a PMMA, the proportion by weight of P 1 ′, with respect to the sum of the weights of the polymers P 1 and P 1 ′, being from 15% to 40%.
9 . The web as claimed in claim 1 , consisting of fibers of composition C 1 .
10 . The web as claimed in claim 1 , having a weight per unit area of 0.01 g/m 2 to 3 g/m 2 .
11 . The web as claimed in claim 1 , wherein the web is free of solvents from the list consisting of: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), tetramethylurea, trimethyl phosphate and N-methyl-2-pyrrolidone.
12 . A membrane suitable for the filtration of nano- and/or submicron aerosols comprising:
at least one web as claimed in claim 1 ,
a support layer supporting said web.
13 . The membrane as claimed in claim 12 , in which said support layer is a nonwoven set of fibers chosen from: polyolefins, polyesters, polyamides or copolyamides, a polyacrylonitrile (PAN), fluoropolymers, and their mixture.
14 . A process for the washing/sterilization of a web as claimed in claim 1 comprising a stage of heat treatment carried out at a temperature of 40° C. to 90° C.
15 . A process for the washing/sterilization of a membrane as claimed in claim 12 comprising a stage of heat treatment carried out at a temperature of 40° C. to 90° C.
16 . The web as claimed in claim 1 , comprising less than 0.5% by number of fibers having a diameter strictly of less than 100 nm.
17 . The web as claimed in claim 1 , comprising less than 0.1% by number of fibers having a diameter strictly of less than 100 nm.
18 . The web as claimed in claim 1 , wherein the polymer P 1 has a weight-average molecular weight ranging from 100,000 g/mol to 2,000,000 g/mol.
19 . The web as claimed in claim 1 , wherein the polymer P 1 has a weight-average molecular weight ranging from 400,000 g/mol to 700,000 g/mol.