GB2264724A - A method of increasing the shrink resistance of wool - Google Patents

Abstract

The method relates to a pre-treatment followed by treatment with a polymer. The pre-treatment includes treating the wool with peroxymonosulphuric acid or a salt thereof in an aqueous solution. The solution is adjusted to a pH of 2.0-5.0 with an oxidization resistant acid, preferably citric acid.

Description

A METHOD OF INCREASING THE SHRINK RESISTANCE OF WOOL The present invention relates to a method of increasing the shrink resistance of wool.

Woollen garments are susceptible to shrinkage, felting and pilling when washed. Consequently, it has been common practice to treat the wool during manufacture of the garments in order to reduce these effects, and especially to increase its resistance to shrinkage.

Traditionally, treatment processes for increasing the shrinkage resistance of wool have been adopted which use chlorine based agents. But, increased concern about the effects on the environment of the chlorinated waste products of these processes has led to the greater importance of non-chlorine based processes. The transition, however, to the use of existing non-chlorine based methods has been made less desirable because they are less effective than the traditional chlorine based methods.

The wool is treated in two steps either before or after dyeing in both chlorine and non-chlorine based processes.

The first step is a chemical pre-treatment which provides a key for a compatible polymer that is applied in the second step. Treatment with the polymer results in increased shrink resistance of the wool. The pre-treatment also produces an increase in the shrinkage resistance, but this is seldom sufficiently effective without the polymer treatment step. Suitable polymers include cationic reactive polymers eg proprietory polysiloxane polymers.

Chlorine based processes use chlorine based agents in the first step, whereas non-chlorine based processes use an unchlorinated pre-treatment agent A typical non-chlorine based process involves pre-treating the wool in the first step at a temperature of 15-250C with an alkali metal salt of peroxymonosulphuric acid (also known as permonosulphuric acid and Caro's acid) at pH 6 7.5. The salt is usually supplied commercially at a strength of approximately 45% of the salt in inactive diluents. An equivalent amount of the parent acid may also be calculated and used instead of the salt. The weight of agents such as the salt, used in the method is calculated as a percentage of the weight of wool to be treated, taking into account the presence of nylon or other materials with which the wool may be blended.Dipotassium peroxymonosulphate, which is available commercially under the Registered Trade Name 'Basolan 2448' is commonly used in the pre-treatment.

After the wool has been pre-treated for about 40 minutes, a reducing agent is added to the treatment bath. The reducing agent removes any free oxygen which may be present and could hinder the subsequent polymer treatment step or any later dyeing step. This reduction treatment is critical to the development of the full increase in the shrinkage resistance of the wool. Typically, 3-6% anhydrous sodium sulphite by weight of wool is added as the reducing agent. Treatment with the reducing agent is carried out for 10-20 minutes at 30-600C.

The present invention represents an improvement over existing non-chlorine based methods of increasing the shrinkage resistance of wool. The present invention, therefore, overcomes the low efficacy encountered with existing non-chlorine based processes and has an efficacy that is comparable with chlorine based processes. The present invention is also more effective than existing nonchlorine based processes in preserving the integrity of the wool, as shown by a reduced degree of pilling and felting.

According to the present invention there is provided a method of increasing the shrink resistance of wool comprising a pre-treatment followed by treatment with a reducing agent and then treatment with a polymer, wherein the pre-treatment includes treating the wool with peroxymonosulphuric acid or a salt thereof in an aqueous solution at a pH of 2.0 - 5.0.

Existing methods employ peroxymonosulphuric acid or one of its salts at a pH of 6.0 - 7.5. In the present invention the peroxymonosulphuric acid or salt thereof is adjusted to a pH of 2.0 - 5.0, and preferably pH 3.5, with an acid that is resistant to oxidation during the pre-treatment. Citric acid has been found to be particularly suitable as such a oxidization resistant acid.

Preferably 7% by weight of wool of the commercial salt of peroxymonosulphuric acid of or an equivalent amount the parent acid is used in the pre-treatment.

The salt of peroxymonosulphuric acid is provided as one or more of potassium hydrogenperoxymonosulphate, sodium hydrogenperoxymonosulphate, dipotassium peroxymonosulphate or disodium peroxymonosulphate.

The pre-treatment may take place at a temperature of 15 to 350C, and for 15 minutes to 1 hour, preferably 30 minutes.

The likelihood of an undesirable bleaching effect taking place, together with a reduction of the efficacy of the pre-treatment increases with the length of pre-treatment time. The parameters of the pH and the temperature of the pre-treatment should, therefore, be determined by experiment to achieve exhaustion of the peroxymonosulphuric acid or salt thereof in about 30 minutes. Exhaustion is judged to be complete when a starch-potassium iodide paper dipped in a sample of the treatment liquor shows no discolouration or a pale bluish tint only.

It is essential to treat the wool with a reducing agent, preferably sodium sulphite between the pre-treatment and treatment with a polymer in order to remove any free oxygen. In this way the hindrance of steps subsequent to the pre-treatment is obviated. Treatment with 3-108 by weight anhydrous sodium sulphite (preferably 68) and 2-8% by weight anhydrous sodium carbonate (preferably 5%) is particularly effective in removing free oxygen. The reducing treatment may be carried out at 30-400C for 15-20 minutes.

The wool may be rinsed and/or dyed following the pretreatment and any reducing treatment prior to treatment with the polymer. Rinsing is particularly desirable in order to remove any agents which may interfere with the polymer treatment. Any compatible polymer can be used in the polymer treatment. Cationic reactive polymers, eg, Polymer EC supplied by Precision Processes (Textiles) Ltd, are especially effective.

The wool may be pre-scoured with a detergent, preferably non-ionic, prior to the pre-treatment. An electrolyte such as Glaubers Salt (sodium sulphate decalhydrate) may also be utilised in this step. The pre-scour avoids the carry-over of agents, eg, anionic agents, which may interfere with the treatment of the wool.

EXAMPLE 1 Six practically identical socks constructed from a blend of 60% wool and 40% nylon were tested as follows in an established test for shrinkage resistance, after treatment to increase shrinkage resistance.

The treatment included pre-scouring the wool/nylon socks in a step using Glaubers Salt and a non-ionic detergent followed by a rinse at 400C. The socks were then pretreated at 300C for 30 minutes with 7% on the weight of wool of a commercial salt containing approximately 45% by weight of dipotassium peroxymonosulphate. This pretreatment was carried out in an aqueous medium adjusted to a pH of 3.5 with citric acid. At the end of the pretreatment time, 5% by weight of sodium carbonate and 6% by weight of sodium sulphite (both salts being anhydrous) were added to the treatment bath. Treatment was then allowed to proceed for a further 20 minutes. Finally, the socks were rinsed and treated with Polymer EC. The lateral stretch of each sock was determined using a Mathbirk testing apparatus and its volumetric fit and visual appearance noted.

Next, every sock was subjected to a severe wash that simulated the average washing conditions encountered by a sock during its lifetime. After washing the lateral stretch of each sock was once more determined and its visual appearance noted.

Table 1 shows the lateral stretch of each sock before and after washing. A comparison of the lateral stretch of each sock before and after washing was used to quantify the shrinkage resistance of each sock as shown by the shrinkage value in Table 1. A negative shrinkage value indicates that shrinkage has taken place during the washing step.

The results show that the lateral stretch of socks was practically the same before and after washing.

A comparison of the visual appearance of each sock before and after washing showed that the extent of pilling and felting after washing was very small.

TABLE 1 RESULTS OF A TEST FOR THE INCREASE IN THE SHRINKAGE RESISTANCE OF WOOL TREATED AS IN EXAMPLE 1 Sock Lateral Stretch Shrinkage Value Unwashed Washed 1 22.9 23.1 +0.2 2 22.5 22.7 +0.2 3 22.7 23.0 +0.3 4 22.6 23.1 +0.5 5 22.8 22.9 +0.1 6 22.4 22.6 +0.2 Mean shrinkage value +0.25 Standard deviation 0.138 Range 0.4 Upper 99.5% Quantile limit 0.606 Lower 99.5% Quantile limit -0.106 99.5 quantile range 0.711 The 99.5% quantile is calculated by the formula: Mean shrinkage value plus or minus 2.58 x standard deviation. The 99.5% indicates the limits within which 99.5% of a batch from which the sample was taken would fall.

EXAMPLE 2 A dozen practically identical socks were used as follows in an established comparative test for shrinkage resistance.

Half of the test socks were treated in accordance with the Example 1, while the other half were treated with an existing non-chlorine method as described below.

The socks were pre-scoured in a step using Glauber's salt and a non ionic detergent and then pre-treated at 250C for 40 minutes with 4% by weight of dipotassium peroxymonosulphate at an oxygen activity of 45%. The dipotassium peroxymonosulphate was present in an aqueous solution at a pH of 7.0. Next, 6% by weight of anhydrous sodium sulphite was added to the treatment bath. Treatment of the socks was then allowed to proceed at 450C for 15 minutes. Finally, the socks were rinsed and treated with a proprietory polysiloxane polymer. The lateral stretch of each sock was determined and its visual appearance noted.

Next, each sock was subjected to a severe wash as in Example 1. After washing the lateral stretch of each sock was once more determined and its visual appearance noted.

Table 2 shows the lateral stretch of each sock before and after washing together with the resulting shrinkage value.

The results show that the lateral stretch of socks treated with the existing non-chlorine method was reduced after washing.

The mean shrinkage values in Tables 1 and 2 show that the average shrinkage of socks treated the treatment according to the invention is much less than socks treated with the existing non-chlorine based method.

A comparison of the visual appearance of the socks before and after washing showed that socks treated in accordance with the present invention displayed a very small degree of pilling and felting, whereas socks treated with the existing non-chlorine based method displayed a considerably higher degree of pilling and felting.

TABLE 2 RESULTS OF A COMPARITIVE TEST FOR THE INCREASE IN THE SHRINKAGE RESISTANCE OF WOOL TREATED WITH AN EXISTING NON-CHLORINE BASED METHOD Sock Lateral Stretch Shinkage Value Unwashed Washed 1 23.1 22.6 - 0.5 2 22.6 22.1 -0.5 3 22.9 22.4 -0.5 4 22.6 22.0 -0.6 5 23.0 22.1 -0.9 6 23.1 22.1 -1.0 Mean shrinkage value - 0.667 Standard Deviation + 0.225 Range 0.500 Upper 99.5% Quantine limit - 0.086 Lower 99.5% Quantine limit - 1.247 99.5% Quantine range 1.161 The 99.5% quantile is calculated by the formula: Mean shrinkage value plus or minus 2.58 x standard deviation. The 99.5% quantine indicates the limits within which 99.5% of a batch from which the sample was taken would fall.

Claims (10)

CLAIMS:

1. A method of increasing the shrink resistance of wool comprising a pre-treatment followed by treatment with a reducing agent and then treatment with a polymer, wherein the pre-treatment includes treating the wool with peroxymonosulphuric acid or a salt thereof in an aqueous solution at a pH of 2.0 - 5.0.

2. A method according to Claim 1 wherein the reducing agent is anhydrous sodium sulphite.

3. A method according to any preceding claim wherein the solution is adjusted to a pH of 2.0 - 5.0 with an oxidization resistant acid.

4. A method according to any preceding claim wherein the oxidization resistant acid is citric acid.

5. A method according to any preceding claim wherein the solution is at a pH of 3.5.

6. A method according to any preceding claim wherein the salt of peroxymonosulphuric acid is provided as one or more of potassium hydrogenperoxymonosulphate, sodium hydrogenperoxymonosulphate, dipotassium peroxymonosulphate or disodium peroxymonosulphate.

7. A method according to any preceding claim wherein the temperature of the oxidizing composition is at 15 350C.

8. A composition for use in the method of claim 1 comprising an aqueous solution at a pH of 2.0 - 5.0 containing peroxysulphuric acid or a salt thereof and citric acid.

9. A composition according to claim 8 wherein the aqueous solution is at a pH of 3.5.

10. A composition according to claim 8 or 9 wherein the salt of peroxymonosulphuric acid is provided as one or more of potassium hydrogen peroxymonosulphate, sodium hydrogen peroxymonosulphate dipotassium peroxymonosulphate or disodium peroxymonosulphate.