GB2245605A

GB2245605A - Hydrogen peroxide bleach

Info

Publication number: GB2245605A
Application number: GB9113676A
Authority: GB
Inventors: Uwe Gunter Schulte; Sabine Dagmer Tandela
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1990-06-27
Filing date: 1991-06-25
Publication date: 1992-01-08
Also published as: GB9014348D0; GB9113676D0

Abstract

Aqueous alkaline solutions containing hydrogen peroxide are stabilised against decomposition by the inclusion of a synthetic hectorite clay. The clay may additionally serve to provide thickening of the composition, either on its own or in conjunction with some other means of thickening.

Description

BLEACHING COMPOSITION This invention relates to thickened liquid bleach compositions which may be suitable for sale and use as a domestic bleach. Pourable domestic bleach is frequently thickened by including one or more surfactants which, in the presence of electrolyte, act to thicken the solution rendering it more viscous than water. Thickening of a pourable domestic bleach helps the user to control dispensing of the composition and retards drainage from surfaces to which it is applied. This invention relates to pourable compositions which incorporate constituents serving to increase the viscosity.

A domestic bleach needs to be adequately stable so that a substantial proportion of the bleaching agent survives during storage between manufacture and use.

Prior to this invention commercial liquid bleach products have frequently utilised hypochlorite as bleaching agent.

It is well known that hydrogen peroxide is unstable unless stabilising agents are present. These counteract decomposition catalysed by transition metal ions. Hydrogen peroxide gives better bleaching action if used under alkaline conditions. However, stabilisation of hydrogen peroxide under alkaline conditions is difficult and in consequence commercial solutions of hydrogen peroxide have generally been acidic for the sake of stability. Certain phosphonates able to stabilise hydrogen peroxide alkaline solution are disclosed in EP-B-9839 (Unilever).

The presence of electrolyte tends to cause decomposition of alkaline hydrogen peroxide solution. For instance, we have found that a 4% by weight solution of hydrogen peroxide, made alkaline to pH 10 and containing 0.25% of ethylene diamine tetramethylene phosphonic acid as stabiliser (which is not as effective as the phosphonates in accordance with EP-B-9839) was found to retain 95% of its hydrogen peroxide after two weeks storage at 370C. By contrast, 85% or less of the hydrogen peroxide was retained if the solution also contained 1% by weight of sodium chloride, while only about 50% of the hydrogen peroxide was retained if the solution contained 10% by weight of sodium chloride. Similar results were observed using sodium tripolyphosphate rather than sodium chloride as the added electrolyte.Doubling the quantity of the phosphonate stabiliser had little effect on the rate of decomposition.

Thus, any attempt to make a surfactant-thickened, alkaline domestic liquid bleach product using hydrogen peroxide as the bleaching agent would encounter the potential problem that the thickening of the solution would require the presence of some electrolyte but that this electrolyte would serve to accelerate decomposition of the peroxide.

Our pending European application 89313623.4 (C3290) discloses an approach which makes it possible to formulate an aqueous alkaline solution of hydrogen peroxide with a low level of electrolyte. That application and our concurrent application 89313625.9 (C3348) also mention the need to counter decomposition catalysed by manganese. The phosphonate compounds disclosed in EP-B-9839 are effective to counter decomposition catalysed by iron but are less effective against manganese.

We have now found that synthetic hectorite clay is effective in addressing the problems referred to above.

Consequently, according to the present invention there is provided a pourable liquid bleaching composition comprising an aqueous alkaline solution containing hydrogen peroxide characterised in that synthetic hectorite clay is also present in the composition.

We have found that such clay functions as a stabilising agent countering the destabilising effect of manganese ions. Additionally, the clay may serve to provide thickening of a composition, either on its own or in conjunction with some other means of thickening.

More specifically, we have found that such clay provides stabilisation against the effect of manganese ions when the clay is used at levels which do not themselves give appreciable thickening of the composition.

If thickening is desired it may then be achieved by some other expedient, although in this latter case the clay may contribute to the thickening action.

The clay can provide thickening of a composition without any other expedient for thickening being present.

Such compositions may be somewhat thixotropic and may include surfactant which does not itself contribute to thickening.

an aqueous alkaline solution of hydrogen peroxide with a low level of electrolyte. That application and our concurrent application 89313625.9 (C3348) also mention the need to counter decomposition catalysed by manganese. The phosphonate compounds disclosed in EP-B-9839 are effective to counter decomposition catalysed by iron but are less effective against manganese.

manganese contamination will depend of course on the extent of contamination encountered. This may be low and in consequence the clay might be used at only low levels as a precaution against very low levels of manganese contamination. If the clay is the sole thickening agent a suitable quantity may well lie in the range from 0.5 to 3% by weight of the composition. Viscosity will be affected by the other materials present: the amount of the clay may lie in the higher ranges 1 to 3% or 1.5 to 3% by weight. If the clay is being used in conjunction with some other expedient for thickening, less than 1.0% by weight of the clay may be sufficient; indeed quantities less than 0.6% by weight may well be sufficient.

Surfactant included for the purpose of thickening may be selected from: a) Soap, especially sodium soap in which the carboxylate group contains 16 to 20 carbon atoms; b) Alkyl ether sulphate, eg. with Cg to C14 alkyl group and 1.5 to 4 ethylene oxide residues; c) a combination of a nonionic or amphoteric surfactant and an anionic surfactant which is either a C8 to C20 alkane sulphonate or a C8 to C20 alcohol sulphate.

Such a combination of surfactants is disclosed in our co-pending European application 89.313623.4 and is able to achieve thickening with a fairly low electrolyte concentration (and of course with clay absent). When used in conjunction with the synthetic hectorite clay they can provide a useful contribution to thickening without any deliberate inclusion of inorganic electrolyte. Thus they may give a useful contribution to thickening when the quantity of non-surfactant electrolyte present is less than 1% by weight quite possibly less than 0.7% by weight.

When a combination of surfactants in accordance with alternative (c) above is present, a preferred possibility for the nonionic/amphoteric surfactant is an amine oxide surfactant, preferably a trialkyl amine oxide with one long chain alkyl of 8 to 20 carbon atoms and two alkyl groups of 1 to 4 carbon atoms. Then, if primary alcohol sulphate is the anionic surfactant the weight ratio of amine oxide:alcohol sulphate is preferably in the range from 82:18 to 65:35, better 80:20 to 65:35, even better 80:20 to 70:30.

The weight ratio of amine oxide to alkane sulphonate (when this is used) is preferably in the range from 80:20 to 50:50 or better 65:35, and preferably in the narrower range from 70:30 to 65:35.

If the surfactant is not being relied upon for a contribution to thickening, other surfactants may be used.

Possibilities are primary alcohol sulphate or alkane sulphonate used without a nonionic surfactant present.

Further possibilities are alkyl ether sulphate, betaine, sulphosuccinate, and ethoxylated fatty alcohol. Each of these when used as the sole surfactant, and with not more than 0.5% of non-surfactant electrolyte present, has little effect on the viscosity of the composition. Of course the invention is not limited to these: other surfactant may be used.

The total concentration of surfactant may lie in a range from zero to 6% by weight based on the whole composition. More likely the amount will not exceed 3% by weight. If present, a suitable amount is likely to range from 0.1 to 3%, possibly 0.75 to 3%. Concentrations above 6% by weight might be used but are less preferred.

The electrolyte concentration in a composition of this invention may be such that the total amount of salts other than surfactant is not more than 2% by weight, better not more than 0.75%. The electrolyte level may be such as to give a concentration of electrolyte not exceeding 0.2 molar, preferably not exceeding 0.1 molar.

Higher concentrations may be used but are less preferred.

As already mentioned, stabiliser for the hydrogen peroxide may be a phosphonate sequestrant in accordance with EP-B-9839, which defines the phosphonate compounds as of the general formula:

wherein n = 1-4; and X is H or a water-soluble cation selected from the group consisting of alkali metals, ammonium, substituted ammonium and alkaline earth metals.

Such a sequestering agent may be used in an amount of 0.01 to 1% by weight. This is approximately 1.5 x 10 4 to 2 x 10-2 molar.

Colloidal hydrous stannic oxide as described in our European application 89313625.9 may be included in compositions of this invention. We have found it to be effective in alkaline solution against decomposition caused by transition metals including both iron and manganese.

An appropriate viscosity for a pourable composition having the appearance of a thick liquid is a dynamic viscosity in the range from 40 to 250 centipoise (0.05 to 0.25 Pa.sec), preferably about 100 centipoise (0.1 Pa.sec). More viscous liquids for example with viscosity in the range from 250 to 1000 centipoise or more are also within the scope of the invention.

Since the compositions of this invention are generally aqueous, they will usually have specific gravity close to unity. Consequently values of kinematic viscosities (in stokes) will be numerically approximately the same as values of dynamic viscosity (in poise).

Dynamic viscosities expressed in Pascal. sec will be approximately 1000 times kinetic viscosities expressed in m.sec-1.

The pH of the solution is preferably in the range from 8.0 to 10.5, better 8.5 to 9.8 or 10.0. With a phosphonate stabiliser it is further preferred that the pH is in the narrower range from 9.2 to 9.8, while with colloidal stannic oxide as stabiliser it is preferable to use a slightly lower pH in the range from 8.7 to 9.3.

The concentration of hydrogen peroxide in compositions of this invention, reckoned as pure H202, desirably lies in the range from 1 to 15% by weight preferably 2 to 10% by weight.

EXAMPLES A number of formulations were prepared. All percentages are by weight unless otherwise stated. Some materials, conveniently referred to by short names, were as follows: Secondary alkane sulphonate (SAS): derived from an n-alkane mixture which is princi pally C13 to C18 AES: sodium C12-C13 alkyl ether sulphate with average 2 ethoxy groups Amine oxide (AO): tallow dimethylamine oxide Pyrophosphate: anyhydrous tetrasodium pyrophosphate Dequest 2060: phosphate stabiliser as disclosed in EP-B-9839 Water was deionised in all instances.

A standard preparative procedure commenced by adding laponite clay to most of the water used and stirring for 30 minutes to disperse the clay. The remaining ingredients were then added to the composition and finally a small quantity of water was added to make up the composition to the intended volume. If surfactant is included it may be added before or after the clay.

In the following Examples percentages are by weight, although percentages expressed as weight per volume would be almost identical.

Viscosities were measured using a Ubbelohde capillary viscometer at 25"C.

Evolution of gas (oxygen liberated from hydrogen peroxide) was measured by collecting the gas liberated over 20 hours from a 250g sample of the test composition stored at 37"C. Such measurement was used in some examples. It provides a check on stability.

Example 1 A composition was prepared as set out in the table below. A control composition omitted laponite but contained pyrophosphate, secondary alkane sulphonate and amine oxide. This control composition therefore followed the teaching of our European application 89313623.4 (Case C3290) mentioned above which states that pyrophosphate can provide stabilisation against manganese and that the surfactants in the presence of electrolyte give thickening.

Control (%) Example 1 (t) Laponite XLS - 1.0 Pyrophosphate 1.79 AO 0.98 SAS 0.48 Dequest 2060S 0.30 0.30 Hydrogen peroxide 5.00 5.00 Sodium hydroxide 0.30 0.28 Perfume and dye 0.101 0.101 Water Balance to 100% pH 9.6 9.6 Stabilisation against manganese was tested by deliberately adding manganese sulphate to samples of the compositions, storing the samples at room temperature (approximately 200C) and periodically removed aliquots and analysing for hydrogen peroxide. The amounts of manganese sulphate were such as to provide either lppm or 3ppm of manganese in the composition.

Percentages of hydrogen peroxide remaining, in the presence of 3ppm manganese, were: Storage time (days) Control Example 1 0 (initial) 4.8 5.0 1 4.8 4.9 2 4.6 4.8 5 4.2 4.4 8 3.6 4.0 12 3.1 3.4 15 2.8 3.0 21 2.3 2.3 Percentages of hydrogen peroxide remaining, in the presence of lppm manganese, were: Storage time (days) Control Example 1 0 (initial) 4.8 5.0 1 4.8 5.0 2 4.8 4.9 5 4.7 4.8 8 4.4 4.7 12 4.1 4.4 15 3.9 4.3 21 3.5 3.9 The quantity of laponite used was less than that required to give adequate thickening, but it was nevertheless providing preservation in the presence of manganese contamination.

Example 2 Four compositions were prepared with the following formulations: Composition number 2.1 2.2 2.3 2.4 % Laponite XLS 1.00 1.00 2.00 3.00 % SAS - 1.50 1.50 1.50 % Dequest 20605 0.30 0.30 0.30 0.30 % hydrogen peroxide 5.00 5.00 5.00 5.00 % sodium hydroxide 0.28 0.29 0.30 0.31 % perfume and dye 0.101 0.101 0.101 0.101 Water B a 1 a n c e to 1 0 0 % pH 9. 6 9. 6 9. 6 9. 6 Viscosity (cS) 2 5 69 Over 300 It is apparent that the secondary alkane sulphonate contributed only a very small thickening action, whereas 2% of laponite gave effective thickening.

Addition of 1% sodium tallow soap to a composition which was otherwise the same as 2.1 led to a viscosity in excess of 300. This demonstrates that thickening can be provided by soap and laponite used in conjunction.

Example 3 A series of compositions was prepared as set out in the following table. A control composition, as for Example 1, was included.

Example No. 3.1 3.2 3.3 3.4 3.5 Control % Laponite XLS 0.30 0.60 1.00 0.60 - % Laponite XLG - - - - 0.60 % SAS 0.48 0.48 0.48 0.48 0.48 0.48 % Amine oxide 0.98 0.98 0.98 0.98 0.98 0.98 % pyrophosphate - - - - - 1.80 % hydrogen peroxide 5.00 5.00 5.00 5.00 5.00 5.00 % Dequest 2060S 0.30 0.30 0.30 0.60 0.30 0.30 % sodium hydroxide 0.33 0.34 0.33 0.47 0.34 0.33 % Perfume and dye 0.08 0.08 0.08 0.08 0.08 0.08 pH 9. 6 9. 6 9. 6 9. 6 9. 6 9. 6 Over Over Over Viscosity (cS) 21 257 300 300 300 93 Gassing rate 8.6 11.0 10.3 9.6 10.2 (ml/250g/20hr/37 0C) Comparison of composition 3.1 with the control confirms that the surfactant mixture gave more thickening in the presence of pyrophosphate than in its absence.

However, by comparison with the previous Example it is evident that the surfactant gives some thickening.

Incorporation of laponite in quantities greater than 0.3% gives greatly increased thickening.

ExamPle 4 A series of compositions was prepared as set out in the following table.

Composition No. 4.1 4.2 4.3 4.4 % Laponite XLS 0.50 0.50 0.50 0.50 % SAS 0.10 0.20 0.30 0.40 % Amine oxide 0.20 0.40 0.60 0.80 % Dequest 2060S 0.30 0.30 0.30 0.30 % hydrogen peroxide 5.00 5.00 5.00 5.00 % sodium hydroxide 0.35 0.34 0.34 0.39 Perfume 0.08 0.08 0.08 0.08 pH 9.6 9.6 9.6 9.6 Viscosity (cS) 3 6 17 50 Gassing rate 15.5 12.0 13.8 15.8 (ml/250g/20hr/37 0C) For these compositions a constant level of laponite was used but the level of surfactants was varied, further demonstrating that the surfactant gives some thickening, additional to the effect of the laponite. Comparison 6f composition 4.4 with composition 3.1 of the previous example confirms that the laponite is also contributing to the thickening action.

Example 5 A series of compositions thickened with AES and laponite was prepared, as set out in the following table.

Composition no: 5.1 5.2 5.3 % Laponite XLG 0.5 1.0 1.5 % AES 0.2 0.2 0.2 2 O2 5.0 5.0 5.0 % Dequest 2060S 0.15 0.15 0.15 % NaOH 0.38 0.40 0.39 % Perfume 0.08 0.08 0.08 Water --------to 100-------- Viscosity cS 3 13 72 Gassing rate 10.5 16.0 17.2 (mlt250g/37 C/20h) Comparisons with Example 2 shows that the AES gave some thickening.

Example 6 Compositions were prepared at two different pH values, and with varying concentrations of laponite, as set out in the following two tables: Composition No.: 6.1 6.2 6.3 6.4 6.5 % Laponite XLG 0.20 0.40 0.60 0.80 1.00 % H2O2 -----------all 5.00-------------- % NaOH 0.04 0.04 0.04 0.04 0.04 % Water ---------- to 100 --------------- pH 9.0 9.0 9.0 9.0 9.0 Gassing rate 0.3 0.2 0.2 2.6 2.0 (m1/250g/23 0C/20h) Appearance thin slightly thixo- thixo- thick thixo- tropic tropic thixo tropic tropic Composition No.: 7.1 7.2 7.3 7.4 7.5 % Laponite XLG 0.20 0.40 0.60 0.80 1.00 % H2O2 -----------all 5.00-------------- % NaOH 0.009 0.007 0.004 0.006 0.005 % Water ------------to 100--------------pH 8. 4 8. 4 8. 4 8. 4 8. 4 Gassing rate 1.5 1.0 1.1 < 0.1 < 0.1 (ml/250g/23 0C/20h) Appearance thin thin thin very very thixo- thixo tropic tropic

Claims

CLAIMS 1. A pourable liquid bleaching composition comprising an aqueous alkaline solution containing hydrogen peroxide and a synthetic hectorite clay.
2. A composition according to claim 1 wherein said clay is present in an amount from 0.01 to 5.0% by weight of the composition.
3. A composition according to any preceding claim wherein said clay is present in an amount from 0.1 to 3.0% by weight of the composition.
4. A composition according to any preceding claim wherein said clay is present in an amount from 0.3 to 2.5t by weight of the composition.
5. A composition according to any preceding claim further comprising a surfactant in an amount not exceeding 6% by weight of the composition.
6. A composition according to any preceding claim wherein the pH of the solution lies in the range from 8.0 to 10.5
7. A composition according to any preceding claim wherein the concentration of hydrogen peroxide lies in the range from 1 to 15% by weight of the composition.
8. A pourable liquid bleaching composition substantially as hereinbefore described with reference to the Examples.