Cellulosic/polyamide composite

Abstract

Composite of polyamide layer solvent bonded to cellulosic substrate is formed by solution electrospinning deposit of polyamide on cellulosic substrate with the solution subjected to electrospinning containing as solvent for polyamide one that swells cellulosic fibers on contact therewith and/or by depositing very long polyamide fibers of low average diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of apparatus and method described in Working Example I.

FIG. 2 is a graph of pressure drop versus length of nylon fiber and shows results of Working Example II.

FIG. 3 is a graph of filtration efficiency of air filter media coated with electrospun nylon-6 fiber with average diameter of 120 nm at different coverage levels versus dust particle size of dust particles pulled into a tester and shows results of Working Example II.

FIG. 4 is a graph of filtration efficiency of air filter media coated with electrospun nylon-6 fiber with average diameter of 120 nm at coverage level of 0.1 g/m² with and without scratching of the nylon-6 fiber coating and shows results of Working Example II.

FIG. 5 is a graph of filtration efficiency of air filter media coated with electrospun nylon-6 fiber with average diameter of 300 nm at different coverage levels versus dust particle size of dust particles pulled into a tester and shows results of Working Example II.

FIG. 6 is a graph of filtration efficiency of air filter media coated with electrospun nylon-6 fibers with different fiber diameter at similar fiber lengths and shows results of Working Example II.

FIG. 7 is a graph of filtration efficiency of air filter media coated with nylon-6 fibers electrospun from a single or two electrospinning nozzle banks at the same weight coverage level, 0.1 g/m², showing effects of electrospinning nozzle spacing and shows results of Working Example II.

FIG. 8 is a bar graph of pore size distribution of uncoated air filter media and shows results for conventional air filter media for comparison purposes and shows results of Working Example II.

FIG. 9 is a bar graph of pore size distribution of air filter media coated with 120 nm nylon-6 electrospun fibers, at a weight coverage level of 0.1 g/m².

Claims

1. A composite comprising a cellulosic substrate comprising cellulosic fibers with a polyamide layer comprising polyamide fibers adhered thereto by an interrelation of fibers of the cellulosic substrate and fibers of the polyamide layer so that the cellulosic substrate and polyamide layer cannot be separated from each other by manually applied peeling force(s).

2. The composite of claim 1 where the cellulosic substrate has a caliper ranging from 0.010 inch to 0.020 inch and the polyamide fibers have average fiber diameter ranging from 50 to 700 nm, a coverage level to average diameter ratio ranging from 2×10−4 to 5×10−3 gms/m2/nm and a ratio of total length of polyamide fibers to the surface area of the cellulosic substrate ranging from 1×106 to 1×108 km polyamide fiber/square meter of cellulosic substrate surface area.

3. The composite of claim 2 where the polyamide fibers have average diameter ranging from 100 nm to 400 nm.

4. The composite of claim 1 which constitutes a filter medium and the cellulosic substrate contains filter grade cellulose fibers.

5. The composite of claim 4 where the filter medium has an inlet side and an outlet side and comprises: (a) substrate layer on the outlet side of the medium, said substrate layer having an inlet side and an outlet side, said substrate layer comprising media grade cellulose fibers, and having a caliper ranging from 0.010 inch to 0.020 inch, a basis weight ranging from 50 to 75 lbs/300 ft2, a Frazier permeability ranging from 12 to 20 CFM measured at 0.5 inch of water pressure drop and an initial fractional efficiency ranging from 5 to 15% for 0.3 μm particles;(b) polyamide layer having an inlet side and an outlet side, comprising the polyamide fibers;

6. The composite of claim 5 where the polyamide fibers have an average diameter ranging from 100 mm to 400 mm.

7. The composite of claim 5 where there is no cover layer on the inlet side of the polyamide layer.

8. Filter medium composite comprising a cellulosic substrate comprising cellulosic fibers and having a caliper ranging from 0.010 inch to 0.020 inch and polyamide layer comprising polyamide fibers having average diameter ranging from 100 to 150 nm with a coverage level being less than 0.1 gm/m2, said medium providing a ratio of increase in percent fractional efficiency compared to that for the cellulosic substrate to percent increase in pressure drop across medium compared to that for cellulosic substrate ranging from 3 to 15.

9. The medium of claim 8 wherein the coverage level of polyamide fibers on cellulosic substrate is less than 0.1 g/m2 and polyamide fiber length is at least 350 km and the layers are adhered to each other by solvent bonding so that the layers cannot be separated from each other by manually applied peeling forces.

10. The fiber medium composite of claim 8 wherein the coverage level of polyamide fibers on cellulosic substrate ranges from 0.01 to 0.08 gm/m2 and polyamide fiber length is at least 3.5×102 km.

11. A method for preparing a filter medium comprising the steps of: (a) dissolving polyamide in a solvent which swells cellulosic fibers during contact therewith, to form a polyamide solution,(b) moving the solution to a droplet forming zone,(c) forming droplets of the solution in the droplet forming zone,(d) providing an electric charge on the droplets to form jets of polyamide solution and provide unstable flow involving a plurality of electrically induced bending instabilities/whipping motions and flashing off of solvent and production of and elongation of polyamide fibers,(e) collecting the polyamide fibers on a surface of a moving substrate layer comprising cellulosic fibers to adhere a layer of polyamide fibers to substrate layer so as to prevent peeling apart of polyamide fiber layer and substrate layer.

12. The method of claim 8 where the solvent is aqueous formic acid.