ADSORBENT MATERIAL

Abstract

A flexible material is disclosed comprising a flexible substrate, a sorbent comprising zirconium hydroxide and a binder, wherein the solids weight ratio of the binder to the zirconium hydroxide is in the range 1:1 to 1:120. Also disclosed is a process for production of a fabric, comprising: providing a flexible material, providing at least one sorbent dispersion comprising zirconium hydroxide and a binder, applying the sorbent dispersion to the flexible material to produce a treated flexible material, squeezing the treated flexible material under pressure, and passing the pressed treated flexible material through a stenter.

Claims

1. A flexible material comprising a flexible substrate, a sorbent comprising zirconium hydroxide and a binder, wherein the solids weight ratio of the binder to the zirconium hydroxide is in the range 1:1 to 1:120.

2. A flexible material according to claim 1, wherein the sorbent comprises at least one further sorbent.

3. A flexible material according to claim 2, wherein further material is selected from one or more of a MOF, aluminium oxide, silicon-aluminium oxide, activated carbon, magnesium oxide and/or titanium dioxide.

4. A flexible material according to claim 1, wherein the zirconium hydroxide has a particle size in the range 0.05 μm to 100 μm.

5. A flexible material according to claim 1, wherein the flexible material comprises a textile.

6. A flexible material according to claim 5, wherein the textile is selected from the group consisting of a knitted textile, a woven textile and a non-woven textile.

7. A flexible material according to claim 6, wherein the textile is a knitted textile, optionally a pile knitted textile.

8. A flexible material according to claim 1, wherein the textile is texturised.

9. A flexible material according to claim 1, wherein the textile comprises a natural or synthetic textile or a combination of natural and synthetic textiles.

10. A flexible material according to claim 1, wherein the textile comprises elastane.

11. A process for production of a fabric, the process comprising: a) providing a flexible material, b) providing at least one sorbent dispersion comprising zirconium hydroxide and a binder, c) applying the sorbent dispersion to the flexible material to produce a treated flexible material, d) squeezing the treated flexible material under pressure, e) passing the pressed treated flexible material through a stenter, and f) optionally repeating any one of steps b), c), and e).

12. A process according to claim 11, wherein the flexible material is at least partially porous.

13. A process according to claim 11, wherein the sorbent dispersion further comprises a solvent, preferably water to provide a sorbent aqueous dispersion.

14. A process according to claim 11, wherein the impregnated flexible material is pressed at a predetermined pressure in the range 1 psi (6.9 kPa) to 150 psi (1 MPa).

15. A process according to claim 11, wherein the sorbent dispersion has a viscosity in the range 40 cps to 4000 cps.

16. A process according to claim 11, wherein the dispersion further comprises a polymeric thickener, a protective colloid, and/or a wetting agent.

17. A process according to claim 11, wherein the binder comprises a polymeric emulsion, optionally selected from an acrylic, a polyurethane, a natural rubber latex, chloroprene, styrene-butadiene rubber (SBR) and/or nitrile rubber, and optionally a colloid stabiliser and optionally a thickener.

18. A process according to claim 11, wherein the sorbent is loaded on the flexible material at 50 to 500 g/m.sup.2 dry weight.

19. A flexible material according to claim 1, wherein the flexible material is in the form of a protective garment.

20. A flexible material according to claim 1, wherein the flexible material is in the form of a decontamination wipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] Embodiments of the present invention will be described in more detail with reference to the accompanying FIGURE in which:

[0096] FIG. 1 shows schematically an embodiment of the method of applying adsorbents using an impregnation method and/or a coating method showing the combinations of products that may be produced.

DETAILED DESCRIPTION OF THE INVENTION

[0097] The present invention will now be described by way of example only with reference to the following non-limiting embodiments. Various options for applying the sorbent are illustrated, without limitation, in FIG. 1.

Impregnation (Dipping) of Adsorbent on Fabric

CBRN Clothing Application

[0098] For impregnation preferably any flexible material may be used providing it can hold a level of the applied finish. Flexible in this context is one which will easily be processed on an impregnation or coating production line.

[0099] Impregnation or coating may be carried out using an aqueous based application method as this is a more environmentally friendly as it limits or eliminates the of use of VOCs. The principle of impregnation is that a finish (formulation) is applied to a substrate where it is generally uniformly distributed throughout the textile as the substrate is fully immersed in the finish. To control the amount that is present on the fabric the soaked fabric may go through a mangle or nip. The wet fabric passes between the two rolls under pressure which causes excess finish to be squeezed out (running off back into the trough of finish) and leaving a set amount on the fabric. The amount of finish that is on the fabric is quantified as a wet pick up and is a percentage value based on the weight of finish on the fabric and the weight of the fabric. The wet pick up, for a given formulation/finish, is primarily dictated by the substrate structure and the pressure applied between the two bowls; to a lesser extent the viscosity of the finish can also influence this parameter. The resulting treated substrate is dried by going through a set of heating ovens—this is referred to as a stenter.

[0100] The concentration of the finish and the wet pick up determine the amount of overall solids that are applied in the process to the substrate. If there was insufficient adsorbent applied through a single pass, then then treated fabric can be put through the process again i.e. a second pass to apply more on. Carrying out a number of passes may be useful.

[0101] In a more complex process each pass may be different, and this results in a layered application. Determining the wet pick up and the applied solids allows an optimized formulation to be applied. Very high solids on a substrate cannot always be achieved in a single pass and so multiple passes may be required.

[0102] A starting formulation is provided which can be adjusted to accommodate various applications—see Formulation F1 in Tables 1 and 2.

[0103] The ratio of binder system to the adsorbent is important in controlling the rates of these sorption processes. In the starting formulation given for every 1 part by weight of binder 3.8 parts by weight of zirconium hydroxide is used. This provides a reasonable level of durability with very little or no shedding taking place.

[0104] Another factor is the particle size of the adsorbent. For the larger the particle size the ratio of surface area to volume is smaller than for a smaller particle. This means that for a given amount of material it is better to have bigger particle as less off the bulk of the material is affected by the binding system. There will be a compromise on particle size dependent upon the application technique being used and the nature of the adsorbent.

[0105] An important aspect when considering binder is that all the auxiliary components can influence the binder solids content. By this we mean that if a binder is used and e.g. a polymeric thickener then the polymer thickener solids will contribute towards the binding capacity.

[0106] Depending upon the nature of the adsorbent system and how prone it is to sedimentation then a thickening agent may be required, and this is to ensure that the adsorbent remains suspended for a sufficient length of time to prevent settling and so avoid inconsistent application.

[0107] The filling of the pores is an issue as it prevents or reduces the likelihood that other components enter and block the pores, thus a wetting agent may be used. The act of drying (during stentering) is important as it is believed that the evaporation of the water out of the pores helps breakthrough any film forming material to allow these pores to be accessible. The term wetting agent and dispersing agent are used interchangeably as it depends on the auxiliary used.

[0108] For some adsorbents, a wetting agent is not required as they will readily wet out in water as they are hydrophilic in nature. Generally, inorganics will tend to wet out relatively easily without the aid of a wetting agent. In the examples, zirconium hydroxide can be incorporated quite effectively without the use of a wetting agent as shown in the decontamination wipe formulation F6. The adsorbent may be of a particular particle size depending upon the application technique and also textile being used. Generally, for pad application the particle size may be less than 100 microns and preferably at or below 45 microns. Having smaller particle size than 45 microns is desirable from an application point of view but a comprise has to be reached as potentially pore volume properties will be compromised for certain adsorbents.

[0109] Smaller particle sizes will aid creating a good suspension as this is less likely to settle out. Adsorbents with high densities can be dispersed this way. The adsorbent can be supplied already as a ground powder which is ready for dispersing.

[0110] The first step is to incorporate the adsorbent in water; depending upon the nature of the adsorbent a wetting agent may be required to effectively incorporate it into the water. Generally inorganic adsorbents are readily dispersible in water as they are generally polar and hydrophilic in nature. The wetting agent can be selected from wide range that are generally available. Good wetting characteristics are achieved e.g. through the use of a sodium salt of a polymeric naphthalene sulphonate. These are particularly good at dispersing organic material which are generally hydrophobic in nature. Dispersing agent not only wet out but produce a charged system to reduce the propensity for agglomeration to take place.

[0111] The amount used will be enough to ensure the adsorbent can be effectively wetted and dispersed. Wetting agent could be fugitive in nature—small molecules such as IPA.

[0112] The choice of stirrer may affect incorporation of the adsorbent. A traditional propellor type stirrer may be used for mixing. The use of a high shear stirrer can be used. A high shear stirrer can be used to good effect to reduce the particle size if the starting material is too coarse for the application; the resulting reduced particle size adsorbent system then be used in a propellor mixing system for the remainder of the formulation.

[0113] High shearing for certain adsorbents can be advantageous in controlling the viscosity of the mix and in keeping the adsorbent suspended.

[0114] Protective colloids may be used. This may be useful where the adsorbent is particularly active. An example would be activated carbon where the surface is active and adsorbs organic molecules readily. If a binder was to be added directly to a dispersion of the activate carbon then coagulation/flocculation of the system may take place. Protective colloids are ideally large molecules which reduces the propensity for them entering the pores of the adsorbent but also provides steric hindrance to prevent agglomeration taking place. Examples of colloid stabilizers are carboxy methyl cellulose, methyl cellulose, hydroxy propyl methyl cellulose, Xanthan gum, polyvinyl alcohols, etc.

[0115] The ideal amount of the colloid stabilizer can be established by trial and error; generally adding a known amount and then checking to see if coagulation take place on addition of the binder system. The addition of the colloid stabilizer can help in controlling the viscosity; in this context it will help in maintain a low viscosity for ease of mixing. The amount of the protective colloid used, may help control the overall viscosity. After the addition of the colloid stabilizer it is generally desirable to leave stirring for a given length of time, for example 15 minutes, to ensure good stabilization.

[0116] As mentioned previously the end application can dictate the formulary components used and it is possible to just to use an adsorbent and the protective colloid as the latter will have film forming capabilities.

[0117] The binder can be added next slowly. The binders would typically be an emulsion polymer—be it synthetic or natural although a binding system based on a dispersion can also be used. The binder can be a variety of system, acrylic, polyurethane, natural rubber latex, nitrile etc. The function of the binder is to bind the adsorbent to the substrate. In general, the more durable the adsorbent needs to be adhered to the textile the more binder is required. If the durability is less of a concern then the amount of binder can be reduced.

[0118] The binder (and the protective colloid) can affect the handle of the material so a softer film forming emulsion would give a more conformable product. The pH of the emulsion may be taken into consideration in the formulation and adjustments may be required in terms of pH to allow it to be used.

[0119] Depending upon the particle size of the adsorbent used it may be that the resulting suspension is adequately stable with no sedimentation taking place in which case it is ready for application work. If the particles are coarse or the dispersed adsorbent has the propensity to settle then a thickener needs to be used. There are a variety of thickeners that can be used to thicken up water-based systems and those in the field will be aware of these. An alkali swellable thickener is particularly suitable. Ammonia may be added to the formulation to ensure an appropriate alkalinity and has the advantage that it is fugitive in nature when exposed to heat returning system to its original pH.

[0120] Sedimentation can be assessed—using a spatula to check if there is any sedimentation after a given length of time. The rate of sedimentation should reflect the process in which the system is to be used and so the viscosity and so the amount of thickener can be adjusted accordingly. Essentially no sedimentation should be observed for period that the formulation would be in the trough in a production process. Having no sedimentation for around 1 hr is a reasonable test.

[0121] By using a combination of viscosity control and additional production stirring/agitation one can prevent sedimentation taking place in the production environment. Once the dip is prepared it is ready to be applied to a textile substrate by impregnation. Different adsorbents can be applied in different passes—formulation F4 shows a carbon only adsorbent formulation that can be applied so a layered system can be generated. Formulation F5 & F7 represents a mixed adsorbent systems with activated carbon and zirconium hydroxide intimately mixed at different ratios i.e. blended application.

[0122] Some adsorbent systems, once dried, will become slightly hydrophobic in nature. This may cause a potential issue for any subsequent impregnation as the finished fabric may not absorb/wet out effectively when immersed in a formulation. In order to overcome this issue a wetting agent may be added in the adsorbent formulation to aid wetting of hydrophobic surface. Examples may be fugitive wetting agent such as IPA or other suitable materials for example alcohol polyglycol ether. Formulation F7 shows the use of such a system.

[0123] The textile may be more absorbent through the use of textured yarn and or through construction. Having a hydrophilic finish on the textile will also help with wetting out of the textile and improved absorption. Textiles could be a knitted, woven, or non-woven. A non-textile material such as foam could also be used as this a porous substrate.

[0124] A good example of a textile is a knitted pile fabric which has loops of yarn which create bulk. The textile may be of synthetic or natural yarns or mixed dependent upon the requirements of the end application. Double pile fabrics are particularly advantageous. Other textiles such as nonwovens can be used but application will be slow to build up solids but again it depends on the bulk and absorbency characteristic. Textiles or substrates can have stretch which will lead to more conformable material if required. Knitted structures containing elastane would be suitable although stretch can be introduced through construction and use of textured yarns alone; this can further be supplemented with the use of an elastane in the structure. Woven structures with textured yarns may be supplemented with the presence of an elastane to improve the stretch characteristics. The application of the dispersion results in a treated textile.

[0125] Application of up to around 500 gsm of solids formulation may be useful. The textile can be treated to provide appropriate wetting characteristics or/and repellence effects; where for example it may be desirable to prevent rapid absorption of the CWA agent in which case a repellence effect is desirable. In this situation a fluorochemical treatment can be applied as a separate treatment. Such treatment will provide oleophobic as well as hydrophobic effects. It may be desired that good wetting is required so that the CWA does not overwhelm the adsorbent but is distributed over a wider area of the treated textile; so a polar hydrophilic may be required. The nature of the wetting characteristics will depend upon the CWA that is likely to be used and whether the CWA is classed as being hydrophobic or hydrophilic (polar) in nature. If just a water-repellent effect is required then the finish can be tailored to provide this effect.

[0126] Examples of such finishes are silicones, hydrocarbon or structured effects i.e. nano finishes. The amount of finish to give this effect must be balanced with the fact that such finishes can cause reduced reactivity of the adsorbent system. It may be desirable to have hydrophilic effects and this can be achieved through the use of suitable polar hydrophilic finishes such as polyethylene glycol, polyvinyl alcohol etc.

Decontamination Wipes

[0127] For decontamination wipes advantageously zirconium hydroxide is used because it actively destroys many contaminants. The adsorbent does not have to be as robustly attached to the material as durability is not as important. A formulation that may be used may be e.g. Formulation F6.

[0128] A ratio of binder to adsorbent at approximately 1:40 (compared that with the CBRN clothing application where the binder to adsorbent ratio is around 1:4 respectively) may be used. The textile may be a single pile fabric e.g. a polyester knitted fabric. Other substrates and textiles can be used in conjunction with different fibre types. A double pile fabric is desirable as this will hold more formulation and either face would be effective in picking up CWA. It is anticipated that around 25 to 300 g/m.sup.2 solids loading may be effective where zirconium hydroxide is used as the adsorbent for a 10 g/m.sup.2 CWA challenge.

[0129] Mixed adsorbents (e.g. ZOH and activated carbon) can be used, and further functionalization to enhance the reactivity can be employed. A layered system can also be created where different adsorbents are applied at each pass.

EXAMPLES

[0130] Formulations F1 to F7 were prepared and applied to samples of a fabric. Table 1 describes the preparation of formulation F1 and the composition of each formulation is described in table 2, below. The fabric was a knitted pile fabric with the construction as follows:

TABLE-US-00001 Courses/ Wales/ thickness/ Weight/ Pile 10 cm 10 cm mm gsm height/mm Weft 100 to 130 95 to 125 0.85 to 1.05 100 to 120 1.09 to 1.21 Knitted Fabric Pile Fabric

[0131] In the formulations:

F1—Base starting formulation—Zirconium Hydroxide
F2—Thickened formulation to keep Zirconium Hydroxide suspended
F3—High Shear Slurry of Zirconium Hydroxide-Particle size reduced to D95 4 microns
F4—Standard formulation for activated carbon with D95 45 microns
F5—Thickened formulation containing a mixture of adsorbents—activated carbon & Zirconium Hydroxide
F6—Low binder system for Decontamination Wipe Application.
F7—Thickened formulation containing a mixture of adsorbents—activated carbon & zirconium hydroxide with inclusion of wetting agent.

TABLE-US-00002 TABLE 1 Preparation of formulation 1. Solids Content of Individual Components in Solids present in Sequence Supplied Product formulation for of Addition Component Nature Amount (g/100) (%) product (g) 1 Water Solvent 52.54 0 0 2 Polynaphthalene Dispersing Agent 1.84 20 0.4 Sulphonate, Sodium Salt 3 Zirconium Hydroxide Adsorbent 20 90 18 4 Carboxymethyl cellulose Colloid Stabiliser 17.12 3 0.5 sodium salt Solution 5 Self crosslinking acrylic Binder 8.5 50 4.3 polymer dispersion 100 23.2 Amount in Ratio Formulation (g) Zirconium Hydroxide 18 3.8 Binder System 4.8 1

TABLE-US-00003 TABLE 2 Composition of formulations F1 to F7 F1 F2 F3 F4 F5 F6 F7 Components (g/100) (g/100) (g/100) (g/100) (g/100) (g/100) (g/100) Water 52.54 51.81 52.54 52.54 51.81 78.2 51.01 ZOH (D95 4 micron) 20 ZOH, Mesh < 100, 15% moisture 20 ZOH, Mesh < 200, 15% moisture 15 ZOH, Mesh < 325, 11% moisture 20 Activated Carbon Powder, 20 5 8 Mesh < 325 ZOH, Mesh < 325, 10% Moisture 20 12 Dispersing Agent (20%) 1.84 1.84 1.84 1.84 1.84 1.84 Carboxy methyl cellulose Soln 17.12 17.12 17.12 17.12 17.12 17.12 (3%) Acrylic Dispersion 8.5 7.9 8.5 8.5 7.9 0.3 7.9 Ammonia (24%) 0 0.5 0 0 0.5 0.5 0.5 Alkali Swellable Acrylic 0 0.83 0 0 0.83 1 0.63 Thickener Alcohol, polyglycolether 0 0 0 0 0 0 1 Total 100 100 100 100 100 100 100 ZOH refers to zirconium hydroxide

[0132] All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.