GB2326115A - Water resistant fibrous material - Google Patents

Abstract

A method of providing a water resistant treatment on a fibrous cellulosic material includes the steps of coating the cellulosic material with a waterproofing globular protein such as ovalbumen, whey, bovine serum albumen or soy protein in water, heating the coated material to 120-200‹C to bring protein into stable chemical contact with the cellulose and allowing to cool. The process is applicable to paper and cotton materials and it allows good waterproofing from a water-based treatment.

Description

WATER RESISTANT FIBROUS MATERIAL This invention relates to a water resistant fibrous material. It relates particularly to a cellulose fibrous material such as a paper sheet and it concerns means for and a method of achieving a water resistant effect in the material.

A cellulosic material such as a sheet of paper or card has a tendency to absorb moisture whether this is present as liquid water or as a constituent of a humid atmosphere.

The effect of the moisture is to soften the sheet, to weaken it and frequently to cause the sheet to disintegrate. For some purposes, a paper is required to retain its strength when it is wet and to achieve this it is sometimes impregnated with a waterproofing agent from solution in an organic solvent.

This technique is considered to give a better result than using a water-based solvent although for many reasons it would be advantageous if a satisfactory result could be achieved with an aqueous solvent.

I have now discovered means for achieving a good level of water resistance in a cellulose fibrous material where the solvent or a dispersion medium is water.

According to the invention, there is provided a water resistant treatment for a fibrous cellulosic material, the method comprising the steps of coating the cellulosic material with a waterproofing globular protein in aqueous suspension or solution, heating the resulting material to a temperature within the range of 1200 to 2000C for a period sufficient to bring the protein into a stable chemical contact with the cellulose, and allowing the resulting cellulosic material to cool. Preferably, the cellulosic material is in a dry state prior to coating it with the globular protein.

The waterproofing globular protein may be ovalbumen, whey, bovine serum albumen or soy protein. The globular protein may be destabilised in aqueous suspension before it is applied to the cellulosic material.

The heating temperature may be within the range of 1700 to 2)00C. The heating time may be within the range of from to 40 minutes.

The cellulosic material may be a non-woven material such as paper or fibres of cotton, hemp or flax. Alternatively, the material could be of woven fibres such as a cotton fabric.

The invention also includes a fibrous cellulosic material one it has been given a water resistant treatment as just described.

By way of example, some particular embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a graph showing te proportion of protein stabilisation effected at different heating temperatures, Figure 2 is a graph showing water uptake occurring after heating the treated material to different temperatures.

Figure 3 depicts four graphs indicating respectively, wet strength, Cobb Test measurement for water absorption, bend stiffness and tear resistance, against different temperature and time variables, for a white paper specimen, Figure 4 shows a similar four graphs obtained from corresponding tests on a brown paper specimen, and, Figure 5 shows paper and fabric samples having been given the water resistance treatment of the invention.

One significant principle upon which the present invention depends is believed to be that a water proofing globular protein such as ovalbumen when raised to a suitably high temperature becomes insoluble in water and thus can act as a water proofing agent.

In a first experiment, a sheet of paper in an untreated condition was painted liberally with a solution of ovalbumen.

The ovalbumen solution had been prepared from a standard chemical laboratory preparation of ovalbumen commercially available from the supplier, Sigma. The solution strength was 10 by weight in water and the deposited material amounted to 2g on an A4 size area of the paper sheet. This was equivalent to a deposit of 0.25g ovalbumen per gram weight of the paper.

The paper was then heated in a domestic oven to temperatures in the range of 1200 to 2000C for different periods of time. After the heating stage, the paper samples were removed from the oven and tested for their water uptake in units of grams of water per gram of paper.

The results of some of these tests are shown in Figure 1 which depicts on a vertical axis Albumen Lost (AL) in grams per gram weight of paper against Water Uptake (WU) in grams per gram of paper. The dot symbols apply to heating temperatures below or equal to 1650C whilst the asterisk symbols apply to a heating temperature of 18O0C. It will be seen that at the temperatures up to or equal to 1650C there is a water uptake of over one gram per gram of paper and some loss of albumen has occurred. At the temperature of 18O0C, there is less than one gram of water uptake and there is no significant loss of albumen. When the temperature is reduced to only 1200 as marked on the graph, there is a high water uptake and a high loss of albumen. It was found that at the lower temperatures, the maximum fixation of the protein occurred only slowly, a period of five minutes being hardly sufficient to achieve the maximum fixation. However, at 1800C, a five minute period for the fixation was adequate. A temperature lower than 1800 can result in an inadequate stabilisation of the protein, leading to its later dissolution in water and a reduced capacity for the protein waterproofing of the paper.

In further experiments, the paper was treated as already described then heated to temperatures ranging from 1200 to 1800C for periods of 5, 10, 20 or 40 minutes. The paper was then weighed, soaked in distilled water for twentyfour hours, weighed, dried and weighed again. It became apparent that the waterproofing effect relies on rendering the ovalbumen insoluble as a result of the heat treatment.

In these experiments, it appeared that the intrinsic strength and stiffness of the dry paper had been increased.

The degree of waterproofing was such that, after soaking for two or more hours in pure water, the paper retained less than its own weight of water and tended to tear in a brittle fashion. The water was found not to have penetrated into the centre of the paper sheet.

In general, the relevant chemical experiments already published in scientific and general literature have been performed in relatively dilute solution whereas it is very likely that the main reaction required here occurs in the solid or highly concentrated state. It is therefore believed to be more akin to a melting process rather than to dissolution due to heat. Melting is perceived to denature the protein and allow it to spread over the cellulose fibres in the paper, thus bringing it into a closer and more stable chemical contact with the cellulose.

This condition leads to insolubility and a more effective waterproofing.

The temperature for the reaction can be reduced if the protein is destabilised (that is, denatured or unravelled) before being applied to the paper. This can be achieved by boiling it in a strong detergent, a breaker of S-S bonds or other stabilising interactions, for example sodium lauryl sulphate or mercaptoethanol. If the ovalbumen is applied in more dilute solution, that is in smalier amounts, the degree of waterproofing apparent after the heat treatment appears to be reduced.

Further experiments were done by using a Differential Scanning Calorimetry technique which is a means of measuring the energies of a chemical reaction. If an energy exchange can be measured then it is deduced that a physical or chemical reaction has occurred. If the energy exchange is irreversible, as observed in the present series of experiments, then the reaction can be considered to be a chemical one.

Figure 2, on one vertical axis shows water uptake (I2U) in grams per grail of paper occurring after heating the treated material to different temperatures between 1200 and 1800C.

On a second vertical axis, Differential Scanning Calorimetry (DSC) results are plotted against a heating temperature ranee between 1200 to over 3000C. It will be seen that the ovalbumen protein on its own (Curve OA) tends to fall from a zero point then rises to a maximum at a heating temperature of 2900C.

when the protein is in a close contact wit the cellulose, the DSC measurement (Curve PC) shows a definite maximum at the temperature of 1800C indicating that a chemical reaction has occurred at this temperature.

Figure 3 shows a series of graphs that were obtained from waterproofing tests on a white paper specimen. The graphs were all obtained using heating temperatures (TOC.) within the range from 1400 to 2000C. On vertical axes, the graphs show respectively values for Wet Strength (WS) as a percentage of dry strength, a Cobb Test (CT) measurement for water absorption in units of grams per square metre, Bend Stiffness (BS) in units of Newton metres, and Tear Resistance (TR) in units of Newtons. The graphs show different oven heating durations, where D1 represents a duration of ten minutes, D2 a duration of twenty minutes and D3 a duration of thirty minutes.

As already mentioned, the Cobb Test (CT) measurement gives water absorption in the paper sample. In practice, most of the paper sizing compositions used normally for waterproofing purposes serve to completely block the pores of the paper so that there is no capillary absorption. By contrast, the method of the present invention has been found to leave the paper pores unblocked so that the Cobb Test reading is unexpectedly poor despite the fact that the paper is waterproofed.

Figure 4 shows a series of graphs similar to those of Figure 3 but where the tests were carried out on a brown paper specimen.

As indicated in the graphs of Figures 3 and 4, the various tests show that in general the wet strength of the paper increases (especially for a heating temperature above 1800C) but the tear resistance is reduced, that is the paper becomes more brittle, because the fibres become adhesively secured to one another. This is a characteristic which can be reduced by applying the protein at an earlier stage.

Measurement of the paper porosity has shown that the porosity is not much affected by the process.

Figure 5 shows examples of paper and fabric samples that have been given the water resistance treatment of the invention. On the left, a paper sample is depicted whilst to the right there is a cotton fabric that has been shown to retain the water resistance through a washing operation.

The method of the invention has been found, in practice, to provide a simple process whereby a paper or fabric cellulosic material can be given a water resistant treatment.

The type of cellulose material can be a cotton, hemp, flax, nettle, for example, so long as the fibre is 'pure' and chemically exposed. This means that the fibre strands should not be masked for example by lignins or other natural or non-natural chemicals. When ovalbumen is used as the protein, this is present in the solution in a partly extended, partly globular form. The degree of solubility depends on the balance between these two states, in turn dependent on the chemistry of the protein.

The invention is not of course restricted to the use of ovalbumen or the other proteins specifically mentioned.

Other molecules which have a hydrophobic interior and a hydrophilic exterior will bond onto cellulose in a condensation reaction. Such a mechanism would also tend to give water resistance to the cellulose fibre.

Use of the invention has been proposed as a water resistant sheet for food packaging which would be a possible alternative to a plastics sheet. Since the protein and cellulose ingredients are natural ones, the resulting sheet will be entirely biocompatible, biodegradable and edible.

No extended testing period should be needed before the treated sheet could be accepted for food use. A woven cotton fabric has also been made water resistant by the method of the invention, the water resistance was retained through a washing process so that the production of waterproofed clothing is a further possibility.

The foregoing description of embodiments of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, the protein material can be applied to a paper base at any one of a number of stages in its manufacture.

It could be applied to the paper after it had been laid down on the web of the paper-making machine or be included in the finish before it goes to the web. It could be sprayed on the paper on the web itself. The method of heating can employ microwaves or any other suitable method of raising the temperature of the ovalbumen. It is likely that a shorter period of heating would be possible if the temperature was higher, so long as the total energy absorbed by the protein is above the minimum required to melt it and cause it to react with the cellulose. In the spinning of cotton, the ovalbumen could be added to the cotton fibre at an early stage before the fibre was made up into a thread. The protein can be obtained in any one of a number of ways, for example, the albumen can be fresh or commercial egg white, from whole eggs, or from fresh, dried, powdered or reconstituted eggs.

Claims (10)

CLADS

1 A method of providing a water resistant treatment on a fibrous cellulosic material, the method comprising the steps of coating the cellulosic material with a waterproofing globular protein in aqueous suspension or solution, heating the resulting material to a temperature within the range of 1200 to 2000C for a period sufficient to bring the protein into a stable chemical contact with the cellulose, and allowing the resulting cellulosic material to cool.

2 A method as claimed in Claim 1, in which the globular protein is ovalbumen, whey, bovine serum albumen or soy protein.

3 A method as claimed in Claim i or 2, including the further step of destabilising the globular protein in aqueous suspension before applying it to the cellulosic material.

4 A method as claimed in any one of Claims l to 3, in which the heating temperature is within the range of 1700 to 1800C.

5 A method as claimed in any one of Claims 1 to 4, in which the heating time is within the range of 2 to 40 minutes.

6 A method as claimed in any one of Claims 1 to 5, in which the protein suspension is coated on the cellulosic material by a painting or imersion process.

7 A metnod as claimed in any one of Claims 1 to 6, in which the cellulosic material is a paper or fabric.

8 A method as claimed in any one of Claims 1 to 6, in which the cellulosic material is cotton.

9 A method of providing a water resistant treatment on a fibrous cellulosic material substantially as hereinbefore described with reference to any one of the accompanying drawings.

10 A water resistant cellulosic material when having been treated by a method as claimed in any one of Claims i to 9.