US2168286A - Wettable material - Google Patents

Description

Patented Aug. 1, 1939 UNlTE WETTABLE MATERIAL chusetts No Drawing. Application October 10, 1936.

. Serial No. 105,080

2 Claims. (on. 91-68) The present invention relates to the treatmer t of cotton, wool, linen, silk or other fibres for the purpose of making such fibres, whether separateor organized for example as felts,

5 threads or fabrics, wettable by water, or to in-.

crease their wettability, so that aggregations of said fibres, or fabrics made therefrom, have the property of absorbing water. The invention also relates to the product of such treatment.

The phenomenon of absorption of water by a fabric or an aggregation of fibres, which we have herein for convenience termed capillary absorbency, involves the absorption and retention of water or water-like fluids between constituent fibres. This in turn involves wetting of the external surfaces of the fibres.

Fibrous bodies which lack the property of capillary absorbency are characterized by low wettability of the surfaces of constituent fibres. 20 By this invention the property of capillary absorbency may be imparted to fibrous bodies by treating the surfaces of constituent fibres so as to make them readily wet by water.

While, as just stated, the treatment is applicag5 ble to many other fibres, for illustrative purposes it will be described in connection with its application to cotton.

The water-wettability of a substance may be defined in terms of its wetting angle,-that is, 30 the angle formed at the juncture of the water with the surface of the material. If this angle is less than 90 degrees, water will in general tend to spread over the surface; if this angle is greater than 90 degrees, water will tend to retreat from $5 the material and collect into drops on the surface.

Although the pure cellulose constituent of cotton fibres is freely wettable by water, as cotton occurs in nature the cellulose contains or is coated 9 with natural waxes, oils, pectins, etc. These materials, in the form in which they occur on natural fibres, are substantially non-wettable by water and their presence imparts to the raw cotton fibre as a whole the property of being sub- 45 stantially non-wettable by water. Similar or other non-water wettable materials appear on raw wool, silk, etc. I

These non-wettable constituents may be removed, for example from cotton fibre, or at least 60 reduced in amount to such an extent that they no longer have any perceptible influence upon wettability of the fibre, by conventional boiling and bleaching treatments, involving cooking with caustic alkali, soaps and other preparations. 6; The conventional boil and bleach result in a loss retain water and water-like fiuids.

' raw material and a change in its character, the

boiled and bleached material being less springy and more prone to mat down than the raw fibre. Another effect of the conventional boil and bleach is the creation of a harsh and frequently undesirable feel, due to the removal or substantial reduction in the natural waxes, oils, etc. which provide lubrication in the natural fibres.

We have discovered that cotton and other fibres and materials may be made water wettable and absorbent, without removing the waxes, oils, etc., by a surface treatment of the fibre. I'he novel product. resulting from our treatment is adapted to a wide variety of uses, including use as an absorbent material in sanitary pads or surgical dressings, as a wiping cloth, etc.

Among various other uses, our treatment may,

is greatly increased, their natural appearance and feel are not perceptibly changed. Due to the fact that the natural springiness of the fibre may be retained through our treatment, it is possible to make a more flufiy, absorbent ma-' terial with larger capacity to hold water for a given weight of fibre.

In such materials as sanitary pads, surgical dressings, wiping cloths, mops, etc., the utility of the product lies in its ability to absorb and In this absorption the water or water-like fiuids are retained between the fibres, .where they are held by capillary forces due to the relatively high water wettability of the surfaces of the fibres. j The greater' the water wettability of the surfaces of the fibres, and the greater the total air space (within the limits of capillarity) between the fibres, the greater will be the capacity of the material for absorbing water and water-like materials. I

A further advantage of our novel product is that the natural springiness and softness of the material is retained, inasmuch as the natural lubricating materials already referred to, are not removed.

In accordance with our invention, non-wettable fibres may be made water. wettable, and fibres oflow wettability may have their wettability increased to a substantial extent, by applying over the solid.

, go into solution in the water, rather than adhersurfaces of the fibres a film or coating of a material which will form an interface between the natural non-wettable or diiilcultly wettable coating on the fibre, and water, and present a surface wettable by water. 7

In-selecting the material for this film or coating', certain principles should be borne in mind.

Whether a-liquid will wet or spread over a solid surface-to form a-continuous film, or whether it will'tend to collect intodrops, is determined bythe chemical nature of the liquid and solid involved. A liquid will spread if its work of surface cohesion is less, and will not spread if its work of surface cohesion is greater than, the work of surface adhesion with respect to the solid- In other words, if the attraction of the liquid for the solid is greater than the attraction increases the adhesion of the surface to water very markedly, and hence facilitates wetting and spreading of water over the surface so treated.

Because of this attraction for water, these groups also increase the solubility of non-polar compounds in water when they are substituted in the molecule of such compounds. If the coating substance is too solublein water, it will tend to ing to the surface of the fibre and promoting wettability thereof. In this connection, while in certain instances and for certain uses it'may be immaterial whether the water'wettable coating is removed from the fibrewhen the product is wetted by water. through solution of the coating in such water, in many instances this is undesir-- able because repeated use of the material is required. When this property of repeated wettability is desired, one should select substances which not only have polar groups to permit wetting by water, but also resist going into solution in water and tend to remain attached to the surface ofthe fibre. Such substances may be sparingly soluble in water, or have at least a slightly greater amn-.

ityfor the hydrophobic surface of the material to be treated than for water, or may form such closely-packed or coherent films that the wetting of the material or. fibrous mass only slowly dissolves or removes the wettable film.

One means or accomplishing this obiectiveof repeated .wettability is to -select a coating material which has a large hydrocarbon residue in the -molecule,- coupled with a highly polar solubilizing group, the net properties being determined by the relative effects of these two components. Substances, the molecule of which contains a chain of a considerable number of carbon atoms, say ten or more,- at one end of the structure, and a polar group at theother end, are advantageous.

Organic chain compounds, the molecules of which do not have; side chains except at the end of the molecules, are preferred for many uses. Organic compounds having a ring structure of carbon atoms, and containing a hydrophilic group, may

also be used, however.

aioaaee Molecules of sort are believed tend to orient themselves, for instance on-the surfacm of fibres to which they are applied, so that the hydrophobicend of the molecule is in contact with the hydrophobic content of the fibres, while the hydrophilic end remains free to present a.wettable surface. I t I Among specific examples of. coating'materials suitable for use-in our process, mention may be made of sulphated or sulphonated fatty alcohols, condensation products of fatty acids, substituted fatty acids, substituted alcohols, alkylated naphthalene sulphonic acids, sulphonated fatty'oils. sulph'onated fatty acids, and soaps.

Sulphonated-compounds having a long chain of carbon atoms in the molecule have been foun particularly well adapted to our purpose. a

Many suitable substances for use as coating materials are found in the group of commercial wetting agents. It should be borne in mind, however, that since the object is so totreat solid surfaces that they will be wettable even after drying, rather than to decrease the surface cohesion of a liquid, not all wetting agents are suitable for our purpose, and in selecting a coating, material, the considerations above discussed should be borne in mind.

In selecting a coating material, the nature; and

composition of the fibre treated,whether cotton, wool, silk or other material, whether dyed,

etc.,should also m considered. I

The .coating material may be applied to the fabric from a solution, for example a solution inwater, or alcohol, or water and alcohol. or other solvent, preferably a solvent which tends to have a greater attraction for the hydrophilic end of the molecule than for the hydrophobic end. The most advantageous concentration of the solution will depend on the wetting agentmsed and on the density of the material treated, lower concentrations of-solution being usable with higher count materials. Although preferred coating materials aresoluble in aqueous mixtures, it is not necessary that the coating material be so soluble. The

coating may be applied as a vapor or a spray, or

even as a solid, in which lastcase the application will preferably be followed by. heating to spread the coating. The important consideration in apsuch manner and in such amount to surfaces ofthe fibres that the fibres will be externally water wettable, as distinguished from water entering into the structure of the fibre itself.

As stated above, one methodof defining thewater-wettability of a substance-is in terms 0 its wetting angle. A more convenient test is observe the timer-equiredfora smallpadof material to sink beneath the surface of a water, under standard conditions. In this .one-haif square-yard of the material to be is folded into a padfour inches square. This pad is dropped from a height of two inches onto thesurface of a body of distilled water at 29-6.. and

I the time required for the indie pass th' surface of the water is noted. We have found materiaiswhich have asinking time greater 1 which may soi't, absorbent fibrous 9,: :1: than two minutes are not suitable for meet new requiring wettability. Materials which after treatment sink in thirty seconds or less are preferred. We have prepared quality products which sink in ten seconds or less.

The above test is based on the use of low count woven or knitted cotton materials (say up to 44 x count). 11 applied to heavier materials.

or to materials comprising substances having higher specific gravity than cotton, allowance must of course be made for this.

The following is an example .01 one treatment which gives very satisfactory raults: Gray cloth be Med with soap, although this step is optional) is immersed in 0.1% to 3.0% solution of sulphated or sulphonated fatty alcohol in water. The cloth, aiter immersion in the bath, issqueeaed to the point at which it retains in the neighborhood of by weight of the solution, as compared with the weight of the cloth. The cloth is then dried.

This treatment results in the deposit on the cloth of the interface material in amount from 0.1% to something more than 3% oi the Weight 01' the cloth. The amount actually left on the cloth may be greater than the amount calculated from the strength of the solution and the amount or solution left on the cloth alter squeefllng. because of selective adsorption from the solution.

-We claim:

1. As an article of manufacture, a rmilient. material 7 of an time, as herein defined, of less -zc oi fibres of the claw consistingoi natural fibres such which of themelves contain lent constituents to an extent rendering them dimcultly wettable by water, said fibres having on their surfaces a dried, adherent coating of a hrdrophllic wetting agent which also ineludm in the molecule a hyih-ophobic mun, said went bein: present in quantity suficient to import to the fibrous material the property of capillary abeorbency of water. said material having a slnmng than two minutes.

2. As an article of manuiact a resilient, soft, absorbent fibrous material consisting 0! an segrecation oi fibres oi the (time consisting of natural fibres such as cotton. wool. linen and silk, which at themaelvm contain natural water repellent. constituents to an extmt rendering them dimcultly wettabie by water, midilhres having on their surfaces a dried, adherent coating of a hydrophilicwetting agent which also includes in the molecule a hydrophobic group, said agent being selected from the group consisting oi aulphonated and sulphaten w a w a the molecule of which contalnsochalnoilatmsttencarbonatomamld agent being nrwent in quantity sumcient to render the material as a whole molly we'tteble by water. said material having a e t -5 herein defined, of not vmore than thirw seconds.

time, $8

as cotton, wool. linen and silk. natural water repel