SULFONATED POLYSTYRENE NONWOVEN

Abstract

Sulfonated polystyrene fibers having an average diameter from 450 nm to 2000 nm and a capacity from 0.05 meq/g to 2.0 meq/g.

Description

BACKGROUND

This invention relates generally to sulfonated polystyrene nonwovens and a method for their preparation.

Functionalization of polystyrene fibers via sulfonation is known. For example, Nitanan Todsapon, Tropical Journal of Pharmaceutical Research, 2014, 13(2), 191-197, discloses sulfonation of polystyrene fibers for use in controlled-release drug delivery. However, this reference does not disclose sulfonated fibers useful in forming non-woven mats for removal of metal ions.

STATEMENT OF INVENTION

The present invention is directed to a sulfonated polystyrene nonwoven having an average diameter from 450 nm to 2000 nm and a capacity from 0.05 meq/g to 2.0 meq/g.

DETAILED DESCRIPTION

All percentages are weight percentages (wt %), and all temperatures are in ° C., unless otherwise indicated. Averages are arithmetic averages unless indicated otherwise. All operations are performed at room temperature (from 18 to 25° C.) unless specified otherwise. Capacity is measured by first exchanging the acid sites with a 4.0 M NaNO₃ aqueous solution and then titrating the resulting acidified solution with 0.1M NaOH using a Mettler Toledo T90 Autotitrator or calculated by mass balance of the sulfonation reaction.

Preferably, the polystyrene used to make the fibers is a high heat crystalline polystyrene, preferably one that is acceptable in pharmaceutical processing.

Preferably, the average diameter of the fibers is at least 480 nm, preferably at least 500 nm, preferably at least 520 nm; preferably no greater than 1750 nm, preferably no greater than 1500 nm, preferably no greater than 1200 nm, preferably no greater than 1000 nm, preferably no greater than 800 nm, preferably no greater than 750 nm, preferably no greater than 700 nm.

Preferably, the fibers are produced by Hybrid Membrane Technology (HMT). This technology is described, e.g., in U.S. Pat. No. 7,618,579. Preferably, fibers are made from a solution of polystyrene in an aprotic solvent. Preferred solvents are those capable of dissolving polystyrene at room temperature, and include, e.g., N,N-dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone, dichloromethane and toluene. Preferably, the solution is processed via electroblowing under conditions which may be adjusted by known techniques to vary fiber properties, producing a nonwoven fiber mat. Preferably, the concentration of polystyrene in the solvent is from 15 to 30 wt %, preferably 18 to 27 wt %. Preferably, the solution is processed on a single hole or multi-hole electro-blowing unit. Preferably the fiber is spun onto a rotating drum.

Preferably, the fibers are treated with a crosslinking agent capable of crosslinking polystyrene prior to sulfonation. Preferred crosslinking agents are aldehydes and dialdehydes, preferably formaldehyde/sulfuric acid or glutaraldehyde/sulfuric acid, preferably formaldehyde/sulfuric acid. Preferably, at least 90 wt % of the polystyrene molecules contain crosslinks, preferably at least 94 wt %, preferably at least 96 wt %, preferably at least 98 wt %. The wt % of polystyrene molecules that are crosslinked may be determined by immersing the fibers in dichloroethane and weighing the insoluble material, which is the polystyrene molecules containing crosslinks. Preferably, fibers are treated with crosslinking agent at a temperature from 20 to 110° C., preferably at least 45° C., preferably at least 55° C.; preferably no more than 100° C., preferably no more than 95° C. Both time and temperature may be adjusted to produce the desired degree of crosslinking, however typical times preferably are in the range from 30 minutes to 6 hours, preferably 1 to 4 hours. Preferably, treatment with a crosslinking agent is done without a catalyst under the conditions given above. If a catalyst is used (e.g., Ag₂SO₄), times will be much shorter at a given temperature and can be adjusted to provide desired properties.

Preferably, the fibers resulting from treatment with a crosslinking agent are sulfonated by contacting them with a sulfonating agent, preferably at least 80 wt % (remainder at least 95 wt % water), preferably at least 90 wt %, preferably at least 94 wt %. Sulfonating agents are reagents capable of sulfonating aromatic rings. Preferred sulfonating agents include sulfuric acid, chlorosulfonic acid and oleum; preferably sulfuric acid. Preferably, sulfonation is performed at a temperature from 30 to 160° C., preferably at least 50° C., preferably at least 70° C.; preferably no more than 120° C., preferably no more than 110° C. Both time and temperature may be adjusted to produce the desired capacity, however typical times preferably are in the range from 30 minutes to 6 hours, preferably 1 to 4 hours. Preferably fibers are contacted with concentrated sulfuric acid for a time sufficient to produce sulfonated polystyrene fibers having a capacity from 0.4 meq/g to 2.0 meq/g or in any desired range therein contained. Preferably, sulfonation is done without a catalyst under the conditions given above. If a catalyst is used (e.g., Ag₂SO₄, acetic anhydride, trifluoroacetic anhydride), time will be much shorter at a given temperature and can be adjusted to provide desired properties Preferably, capacity of the sulfonated nonwoven is at least 0.2 meq/g, preferably at least 0.4 meq/g, preferably at least 0.45 meq/g, preferably at least 0.50 meq/g, preferably at least 0.55 meq/g, preferably at least 0.60 meq/g, preferably at least 0.65 meq/g; preferably no greater than 1.8 meq/g, preferably no greater than 1.6 meq/g, preferably no greater than 1.5 meq/g, preferably no greater than 1.4 meq/g, preferably no greater than 1.3 meq/g, preferably no greater than 1.2 meq/g, preferably no greater than 1.1 meq/g.

Examples

In these Examples a number followed by “C” (e.g., 30 C) is understood to be a temperature in ° C.

Fiber Preparation:

Polystyrene (PS) solutions were prepared using PS 685 D grade polystyrene obtained from Aldrich. The solvent was dimethylformamide (DMF). Solutions with concentrations in the range of 21 to 25 wt % were scouted. Sample solutions were spun on a single hole electro-blowing unit. The fiber was spun onto a rotating drum and the sample non-woven was collected from the drum after the run. Typical samples were prepared from a 21 wt % solution with 0.1 wt % salt added based on solution. The typical basis weight varied from 60 to 100 gsm. Typical distance between the spin pack and the drum collector was 33 cm. The typical applied voltage was 100 kV. The typical spin cell temperature was 30 C. The typical sample mean flow pour was 1 micron.

Treatment with Sulfuric Acid and Formalin

The nanofiber membrane (1700 nm average fiber diameter) is immersed into a bath containing a mixture of reagent grade concentrated sulfuric acid and formalin (37 wt % formaldehyde), typically 90:10 sulfuric acid: formalin (V/V). The bath is typically heated to 70 C for 3 h and gently shaken on an orbital shaker at 60-120 rpm. Next, the bath is cooled to <50 C, the reaction fluid is decanted, and membrane is slowly hydrated with 50% sulfuric acid, and the membrane is gradually diluted down to pure DI water.

Sulfonation

The nanofiber membrane after treatment with sulfuric acid/formalin is immersed in concentrated sulfuric acid (typically 96%), and then heated to 90 C for 0 to 8 h while shaking on an orbital. Next, the bath is cooled to <50C, the reaction fluid is decanted, and the membrane is slowly hydrated with 50% sulfuric acid, and then gradually diluted down to pure DI water.

			Mass			flexibility	brittleness	warping
Fiber	Initial		after	Meas.	Calc.	(1-5; 5 is	(1-5; 1 is	(1-5; 1 is
Size	Mass		reaction	Capacity	capacity	highly	highly	highly
(nm)	(g)	Conditions1	(g)	(meq/g)	(meq/g)	flexible)	brittle)	warped)
678	0.361	3 h, 70 C.	0.381			5	5	5
678	0.381	149 min, 90 C.	0.56		3.87	1	1	1
678	0.478	3 h, 70 C.	0.5			5	5	5
678	0.5	127 min, 90 C.	0.717	3.76		1	1	1
655	0.287	3 h, 70 C.	0.305			5	5	5
655	0.305	105 min, 90 C.	0.379	2.56		3	3	3
540	0.433	3 h, 70 C.	0.464			5	5	5
540	0.464	30 min, 90 C.	0.498		1.05	5	4	4
540	0.451	3 h, 70 C.	0.479			5	5	5
540	0.479	75 min, 90 C.	0.575		1.93	4	3	3
655	0.36	70 C., 10 min	0.361			5	5	5
655	0.361	70 C., 28 min	0.378	4.56		1	1	1
530	0.503	70 C., 10 min	n/a			5	5	5
530	n/a	70 C., 14 min	0.775	4.42		1	1	1
1718	0.483	0.5 h, 70 C.				5	5	5
1718		1 h, 90 C.	0.483	1.06		5	5	4
1718	0.576	3 h, 70 C.				5	5	5
1718		1 h, 90 C.	0.576	0.67		5	5	5
1200	0.302	210 min, 70 C.	0.313			5	5	5
1200	0.313	1 hr, 90 C.	0.322	0.49		4	3	5
1Conditions for sulfuric acid/formalin treatment in top cell, sulfonation in lower cell.
2. The results in the last two rows were obtained from fiber mat that had been compressed, which typically significantly degrades the properties measured here. The fact that acceptable properties were attained nevertheless shows that mats having capacities of 0.49, or even lower, would be acceptable.

Washing Metal residuals from PS Membranes and AmberTec™UP1400 ion exchange resin:

• • 47 mm disk nonwoven PS membrane (average fiber diameter: 1718 nm, capacity: 0.67 meq/g), UP1400 resin (strong acid cation exchange) (d=4 cm, h=6 cm)
  • Reagent: Low metal level HCl
  • Volumetric Flow rate: 6.9 ml/min for membrane, 5 ml/min for ion exchange resin.
  • Metal content of the nonwoven PS membrane is reduced to 9.76 ppb in 210 minutes, at which time the resin still had a metal content of 20.26 ppb.
  • After the HCl washing, the media is further rinsed with DI water to at least pH>5.
  • Removal of Metal from Spiked Solvent with PS membrane and ion exchange resin
  • Propylene glycol methyl ether acetate (PGMEA) spiked with 100 ppb each of
  • Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, K, Na, Sn, Ti, and Zn. was passed through a 4 cm×6 cm (D×h) column packed with the UP1400 resin and the 47 mm PS disk washed with HCl and DI water as described above. Volumetric Flow rate: 6.9 ml/min for membrane, 5 ml/min for ion exchange resin. Residence time in the resin bed is 15 min, while the residence time in the PS membrane disk is 3.5 seconds. Total metal content in the initial resin bed effluent was 512.7 ppb and total metal in the membrane disk effluent was 823.4 ppb. The membrane disk removes 96% of the initial metals at the first residence time of 3.5 seconds while ion exchange resin removes 94% of the initial metals at the first residence time of 15 min.

Claims

1. A sulfonated polystyrene nonwoven comprising fibers with an average diameter from 450 nm to 2000 nm and a capacity from 0.05 meq/g to 2.0 meq/g.

2. The nonwoven of claim 1 having a capacity from 0.4 to 1.5 meq/g.

3. The nonwoven of claim 2 in which the fibers have an average diameter from 450 nm to 1750 nm.

4. The nonwoven of claim 3 in which at least 90 wt % of the polystyrene molecules contain crosslinks.

5. A method for producing a sulfonated polystyrene nonwoven; said method comprising steps of: a) providing polystyrene nonwoven fibers having an average diameter from 450 nm to 2000 nm;b) contacting the polystyrene fibers with a crosslinking agent at a temperature from 30° C. to 150° C.; andc) contacting a product of step b) with at least 90 wt % sulfuric acid at a temperature from 30° C. to 150° C.

6. The method of claim 5 in which the fibers have an average diameter from 450 nm to 1750 nm.

7. The method of claim 6 in which step c) is carried out for a time sufficient to produce sulfonated polystyrene fibers having a capacity from 0.4 meq/g to 2.0 meq/g.

8. The method of claim 7 in which the crosslinking agent is sulfuric acid and an aldehyde or dialdehyde and in which step b) is carried out for a time sufficient to produce sulfonated polystyrene fibers, wherein at least 90 wt % of the fibers contain crosslinks.

9. The method of claim 8 in which step c) is carried out for a time sufficient to produce sulfonated polystyrene fibers having a capacity from 0.4 meq/g to 1.5 meq/g.

10. A method for removing metals from a liquid; said method comprising contacting said liquid with a polystyrene nonwoven comprising fibers with an average diameter from 450 nm to 2000 nm and a capacity from 0.05 meq/g to 2.0 meq/g.