A SOAP BAR STRUCTURED USING TRANS FATTY ACIDS

Technical Field

The invention relates to a soap bar and particularly to a soap bar which has high cleaning efficiency and desirable hardness.

Background and Prior art

Soaps predominantly contain salts of fatty acid and have conventionally been used for cleaning purposes. Soaps have been sold in many forms e.g. as liquids, pastes, flakes and bars. Among all the forms, the bar form is preferred by many consumers since soap bars have a predetermined shape which is generally retained till such time that the soap bar is substantially used up by the consumer.

Soap bars are widely used for personal cleaning application and these types of soaps are called toilet soaps. They are also used for cleaning fabrics and these types of soaps are called Laundry soaps. Soaps have been traditionally prepared by saponification of oils of either plant, animal, mineral or synthetic origin or by neutralization of a fatty acid mixture, usually with an alkali.

Traditional soap bars generally contain total fatty matter (TFM) usually in the range of 70-85% by weight of the soap bar, although soap bars with far lower amount of fatty matter are also prepared. A soap bar with such a high amount of total fatty matter provides good cleaning and such bars possess high level of structural integrity during storage and use, but it tends to be expensive due to the high cost of the raw materials viz. fatty acids or the oils. It has been determined in the past that acceptable level of cleaning can also be achieved by soap bars with relatively lower TFM.

Fatty acids used for making soaps having from 8 to 22 carbon atoms. The fatty acids could be saturated or unsaturated. It is well known that soaps made from saturated fatty acids, especially those having carbon chain length greater than 16 do not generally contribute towards cleaning action. As the carbon chain length of the soaps increases to greater then 16, the solubility in water decreases and concomitantly the cleaning efficacy decreases. However these saturated fatty acids having carbon chain length of 16 or 18 e.g. soaps made from palmitic acid or stearic acid, provide very good structuring to the soap bar. Hence soap bars have been made with a judicious mix of salts of saturated and unsaturated fatty acids of varying carbon chain length. However, there has been a compromise between getting cleaning efficacy on the one hand and bar integrity on the other hand. All this has to be attained while ensuring that the cost of the soap bar is kept at a minimum.

Many people have tried to incorporate soaps of lower carbon chain length and higher amounts of unsaturated higher carbon chain length fatty acids to ensure better cleaning while incorporating relatively inexpensive non-fatty matter e.g. materials of mineral origin like clays, talc, aluminium hydroxide etc to achieve structural integrity. IN177828 (Hindustan Lever, 1997), WO2006094586 (Unilever, 2006) are a few publications that describe such soaps and processes to make them.

Another approach has been to prepare certain synthetic structurants insitu during the preparation of the soap bar.

Processes to prepare such synthetic structurants insitu during soap manufacture, like colloidal aluminium hydroxide and

alumino-silicates are described in IN187129 (Hindustan Lever Ltd., 1997) and in US6207636 (Unilever, 2001).

While the soaps described above provide for better cleaning efficacy and improved structuring of soaps while keeping the costs low, consumers always welcome products that provide more cleaning as compared to products available in the past so long as they get products that have the same integrity and hardness and also have similar, if not better properties like low mush, low rate of wear and smoothness and mildness during use. At the same time, manufacturers are always researching to develop how they can provide this to the consumer at lower cost.

The present inventors have worked to solve this problem and tried to incorporate soaps of higher carbon chain length and high levels of unsaturated fatty acid soaps which properties are known to provide good cleaning. The present inventors found that incorporation of high levels of unsaturated fatty acid soaps especially those soaps having an iodine value greater than 70, have relatively poor bar integrity. Incorporating high levels of unsaturated fatty acid soaps also have other problems e.g. instability in colour, poor odour etc. The present inventors have surprisingly found that incorporation of certain selective ranges of a specific isomeric form of unsaturated fatty acids viz. trans fatty acids provides desirable cleaning as well as the desired bar integrity and hardness. Most of the naturally occurring oils having high degree of unsaturation and fatty acids made there from, are predominantly in the cis isomeric form. The trans isomeric form in naturally occurring oils is present in very small quantities. Hence most soaps prepared in the past with unsaturated fatty acids predominantly contain the cis isomer.

However, attempts have been made in the past to make soap bars containing trans fatty acids. JP3244699 (Lion Corp, 1991) describes a soap composition which lathers well and contains elaidic acid salts and oleic acid salts. However, the ratio of elaidate: oleate is in the range of 5:95 to 70:30.

GB1033421 (Unilever, 1966) describes a soap bar which comprises isomerising a fat rich in unsaturated acid radicals to form 7 to 30% trans-acid radicals based on total fat charge therein, followed by saponification to produce the soap.

The above two publications illustrate soaps having high amount of saturated (greater than 50 %) fatty acids like coconut oil, palm oil, palm kernel oil, and soyabean oil and either incorporating therein or forming insitu elaidic acid. Structuring in these soaps comes predominantly from the relatively high levels of saturated fatty acid soaps present therein i.e. the iodine value of the soaps prepared is typically much lower than 70.

Objects of the invention

It is thus an object of the present invention to provide for a soap bar having high level of unsaturated soaps providing relatively superior cleaning efficacy as compared to the soaps available in the past while ensuring the desired hardness of the bar.

It is yet another object of the present invention to provide for a soap bar which has relatively superior cleaning efficacy and acceptable hardness and there is no compromise on the user desired properties like low mush and high lather.

Summary of the invention

The present invention relates to a soap bar having an iodine value higher than 70 grams/100 grams and containing less than 30% saturated fatty matter by weight of total fatty matter in the soap bar, wherein more than 70% by weight of the total unsaturated fatty matter is trans fatty matter.

Detailed description of the invention

The invention relates to a soap bar having high levels of unsaturated fatty matter i.e. soap having an iodine value greater then 70 grams/lOOgrams . The invention works very well even for soaps having iodine value greater than 90 grams/100 grams which otherwise tend to be very soft. The soap bar of the invention could be used for personal washing applications like bathing, face wash, body wash, shaving bar etc, and for washing laundry, upholstery, carpets, and hard surfaces.

The invention provides for a soap bar that gives superior cleaning while retaining the properties desired by the user. The term total fatty matter, usually abbreviated to TFM is used to denote the percentage by weight of fatty acid and triglyceride residue present in soaps without taking into account the accompanying cations, as soaps are salts of fatty acids .

For a soap having 18 carbon atoms, an accompanying sodium cation will generally amount to about 8% by weight. Other cations may be employed as desired for example zinc, potassium, magnesium, alkyl ammonium and aluminium, without departing from the scope of the invention.

The term soap denotes salts of carboxylic fatty acids. The soap may be derived from any of the triglycerides/oils

conventionally used in soap manufacture: consequently the carboxylate anions in the soap may contain from 8 to 22 carbon atoms. It is however preferred that the soap contains 12 to 18 carbon atoms, more preferably ".^ to - carbon atoms.

The soap may be obtained by saponifying a fat/oil or neutralising a fatty acid.

A soap prepared from any of the known and available oil/ fatty acid sources having unsaturated fatty acids may be used, but the invention is specifically targeted to soaps having an iodine value greater than 70, more preferably greater than 90 i.e. the total fatty matter is high in unsaturated fatty acids. Known unsaturated fatty acids which may be used in the present invention include oleic, linoleic, ricinoleic or linolenic acid. Suitable sources of oils which provide the fatty matter in the desired iodine value range are tallow, tallow stearines, soya bean oil, fish oil, castor oil, ground nut oil, rice bran oil, or palm olein and others. Alternately the starting material for making the soap of the invention is distilled fatty acid (DFA) made from saponifying oils from various sources rich in unsaturated fatty acids.

Tallow fatty acids are derived from various animal sources. Fatty acid composition of tallow is about 1-8% myristic acid, about 21-32% palmitic acid, about 14-31% stearic acid, about 0- 4% palmitoleic acid, about 36-50% oleic acid and about 0-5% linoleic acid. A typical distribution is 2.5% myristic acid, 29% palmitic acid, 23% stearic acid, 2% palmitoleic acid, 41.5% oleic acid, and 3% linoleic acid.

Ricebran oil, gives a mixture of fatty acids with IV~90. It comprises of 45% oleic, 35% linoleic and 15% palmitic acids and

yields a soft soap on saponification. Castor oil also has IV-90 having ~90% Ricinoleic acid and gives soft and sticky soap.

Geometrical Isomers have similar chemical formula but differ in spatial arrangement around C=C double bond. This phenomenon of geometrical isomerism is also applicable to unsaturated fatty acids having c-c double bonds. Unsaturated fatty acids exhibit geometrical isomerism and predominantly occur in cis configuration in nature. The main sources of unsaturated fatty acids are vegetable oils and animal fats. There are no abundant natural sources of Trans isomers of unsaturated fatty acids. They are found in small amounts in animal fats (2-6%) , hydrogenated vegetable oils (1-30%), processed food(upto 1%) etc. Trans fatty acids are more resistant to oxidation than the corresponding cis acids and are less prone to rancidification which is responsible for bad odour and colour darkening of the fatty acids.

H H H H H H H

I I I I

C-C -C-C- -c-c C-C

I I I I I

H H H H H cis trans

The soap bar is preferably prepared from fatty matter having 8 to 22, more preferably 12 to 18 carbon atoms in the carbon chain. The soap bars according to the invention preferably have 30 to 60%, more preferably 35 to 50% by weight total fatty matter (TFM) . Of the total fatty matter it is preferred that 70 to 90% of the total fatty matter by weight is unsaturated in order to be in the desired IV range.

In order to have desired iodine value the soap bar has less than 30%, more preferably less than 10% saturated fatty matter by weight of total fatty matter. The soap bar preferably has a density of less than 1.1 g/cm , more preferably less 1.05 g/cm .

Oleic acid (C18 fatty acid) is the most abundantly found unsaturated fatty acid found in nature. Oleic acid has cis sterio isomeric structure. The transisomer of oleic acid is known as elaidic acid. Thus transisomer of oleic acid soap i.e. elaidic acid soap is the most preferred transisomer that is used to make the soap bars according to the invention. Other suitable transisomeric fatty acids are ricinelaidic (C18:l, hydroxyl group at 12 ^th position) and linelaidic (C18:2).

The soap bars of the invention can have high amounts of water, preferably from 20 to 50 weight%, more preferably from 35 to 45 weight % .

Although the soap bars of the invention are preferably prepared by the melat cast process, other known processes like milling and plodding may also be used.

Optional ingredients

The detergent bar of the invention may optionally comprise synthetic surface active agents or surfactants which may be chosen from anionic, cationic, amphoteric, non-ionic or zwitterionic types. When present they are generally in amount not higher than 10 weight percent.

The bar of the invention may include water insoluble inorganic particulates e.g. talc, clays, china clay or calcium carbonate. When present, they are added as fillers and are generally not

required to be present in an amount greater than 1% to achieve structuring benefits.

Other structuring systems: While the primary structurant of the invention i.e. the trans fatty matter at the indicated amounts is sufficient to provide the overall structuring function while also giving good cleaning, other known structuring agents may also be used along with the present invention, for additional benefits. Other suitable structuring compounds are inorganic alumino silicate, preferably generated in situ using a source of monomeric aluminium to condense with silicate anion. Optionally, inorganic particulate structurant calcium silicate may also be used, preferably generated in situ from precursor material selected from a soluble calcium compound e.g. calcium hydroxide reacting with sodium silicate. Such optional structurants can generally be present in an amount in the range of 0.5 to 10%, more preferably 0.5 to 5% by weight of the composition.

Other optional ingredients

Personal washing applications: Benefit agents e.g. moisturisers, emollients, sunscreens, or anti ageing compounds may be incorporated in the composition of the invention when used for personal washing application. Examples of moisturisers and emollients include humectants like polyols, glycerol, cetyl alcohol, carbopol, ethoxylated castor oil, paraffin oils, lanolin and its derivatives. Silicone compounds such as silicone surfactants like DC3225C (Dow Corning) and/or silicone emollients, silicone oil (DC-200 Ex-Dow Corning) may also be included. Sun-screens such as 4-tertiary butyl-4 ' -methoxy dibenzoylmethane (available under the trade name PARSOL 1789 from Givaudan) and/or 2-ethyl hexyl methoxy cinnamate (available under the trade name PARSOL MCX from Givaudan) or

other UV-A and UV-B sun-screens may also be incorporated. Water soluble glycols such as propylene glycol, ethylene glycol, glycerol, may be employed at levels upto 10%.

Other additives such as one or more water insoluble particulate materials e.g. inorganic structurants like talc, polysaccharides such as starch or modified starches and cellulose may be incorporated. However, the water insoluble structurants are generally present in amounts less than 1% by weight of the soap bar. Minor additives include colour, preservatives and perfumes, may optionally be incorporated.

Fabric washing applications: The soap bar may optionally comprise one or more builders. The builders are preferably selected from one or more of sodium carbonate, Zeolite, sodium silicate or sodium tripolyphosphate . Additionally other optional ingredients in the powder form e.g. fillers like sodium chloride or sodium sulphate are incorporated. Other optional ingredients that may be used to provide improved user properties include anti-redeposition agents, fluorescers, whitening agents, or enzymes.

Process :

The process employed for preparing soap bar of the invention preferably comprises the steps of (i) neutralizing a fatty acid mixture having trans acids of desired IV to form soaps, (ii) melting the soap mix in desired amount of water and (iii) casting the resulting mixture into a bar of desired shape.

The trans isomer of the fatty acid is preferably prepared using an isomerisation process comprising the step of reacting unsaturated cis isomer fatty acid mixture with nitrous acid which is generated insitu. The nitrous acid could be generated

in situ by any known method but the preferred method is by reacting a nitrite salt with a strong acid. The nitrite salt is preferably a water soluble alkali metal or alkaline earth metal salt. Of these sodium nitrite is preferred. The strong acid could be hydrochloric acid, sulphuric acid or nitric acid, nitric acid being preferred. The isomerisation reaction is generally carried out by stirring the reaction mixture at temperatures in the range of 45 to 65 ⁰ C. The reaction time is preferably from 1 to 3 hours. The reaction is preferably carried out in an inert atmosphere, preferably in the presence of nitrogen gas.

The invention will now be illustrated with reference to the following non-limiting examples.

Examples

Comparative Examples A, B and Example 1, 2

Soap bars with compositions as listed in Table-1 were prepared by the following method:

Soap Preparation: Fatty acids were melted in a three neck round bottom flask provided with overhead stirrer and kept in a hot water bath. The molten fatty acids were neutralized at 85 ⁰ C using 50% NaOH with continuous stirring. Electrolytes were added along with the desired quantity of water. The end of neutralization was tested with phenolphthalein indicator. The hot melt was then cast into soap bars in molds.

Isomerization reaction: The cis-trans isomerism of unsaturated fatty acids was carried out via insitu generation of nitrous acid. The unsaturated fatty materials were taken in a three neck round bottom flask provided with overhead stirrer a facility to maintain an atmosphere of nitrogen was provided.

Sodium nitrite and nitric acid were added to the flask in a proportion so as to generate 2-4% insitu nitrous acid by weight of fatty material taken. The mixture was stirred for 2hrs at 6O ⁰ C. The crude product was then washed with hot water in a separating funnel three times and once with 1% sodium bicarbonate solution. The trans fatty materials were converted to soap by the method already described above.

Iodine value, or iodine number, is a measure of the total amount of unsaturated fatty acids in an oil and is a measure of the number of grams of iodine which will combine with 100 grams of the oil. This method involves reacting samples of oil or fatty acid with iodine. The iodine value can also be calculated from the fatty acid composition.

Determination of Trans content:

FTIR Quantification: The trans content in the product of isomerization reaction was determined using Perkin Elmer Fourier Transform Infra Red Spectrometer. Different concentrations of the products were prepared in Carbon Tetrachloride and scanned between 900cm ^"1 to 3500cm ^"1 . The characteristic peak of trans double bonds at 970cm ^"1 was detected in product and spectra was found to be matching with standard Elaidic acid (Sigma Aldrich, 99% pure) . The calibration and quantification was done with peak area and peak height at different concentrations.

GC Quantification: Further quantification was done using Gas chromatography. BPX70 100m polar column with 0.22 internal diameter was used. Temperature profile was programmed from

14O ⁰ C to 21O ⁰ C at a rate of increase of 2 ⁰ C per min. Carrier gas was helium at 60psi. FID detector was used to detect the signals .

The bar hardness was measured in terms of penetration value and yield stress and the results are also summarized in Table-1.

Penetration and yield stress measurement: The penetration value in mm was measured using a Penetrometer with total load on sample to be 200gm, half cone angle of 15 degrees and cone tip radius (truncated) of 0.1795 mm. The yield stress (KPa) was calculated using the following formula: Y. S = W*g/ ϋ(d*tanl5 + 0.1795) ²

Where, d= penetration value in mm, w= load on sample in gm, g= gravitational constant

Table-1

% unsaturates is the weight percent of unsaturated fatty matter by weight of total fatty matter.

*% trans soap is the weight percent of trans fatty acid soaps by weight of unsaturated fatty acid soaps

The other user desired properties viz. foam and detergency were measured for all of the above samples and were found to be acceptable .

The data in table-1 indicates that the soap bars of the invention (Examples 1 and 2) are superior to those of the prior art (Comparative Examples A and B) both in terms of penetration value and yield stress.

Comparative Example-C and Examples 3 to 5 Various soap bar formulations within the invention were prepared (Examples 3 to 5) as per the process described for Examples 1 & 2. A commercially available soap prepared by similar process ^λ Sunlight' was taken as control (Comparative Example - C) . The ingredients are summarized in Table - 2.

Table-2

AOS Alpha olefin sulphonate (Carbon chain length of 12)

The soap bars of Example 3 to 5 were evaluated for penetration and yield stress and compared with the values of Comparative Example - C. The hardness was comparable in that the penetration value of all the samples was about 3 mm and the yield stress value was around 570 KPa, which are acceptable to the consumer. The other user properties namely foamability, detergency and rate of wear were also comparable. The

invention thus provides for soap bars (Examples 3 to 5) that are prepared with relatively lower amount of fatty matter but these bars are comparable to a commercially available soap in terms of all user desired properties.