PROCESS FOR SCOURING AND BLEACHING OF TEXTILE FIBERS USING NATURAL POLYGLYCEROL ESTERS

Abstract

 The use of biodegradable surfactants based on natural polyglycerol esters for scouring and bleaching textile fibers is described. In addition, a method is provided for scouring and bleaching textile fibers, based on the use of said surfactants.

Description

FIELD OF THE ART

[0001] The present invention refers to the treatment of scouring and bleaching textile fibers. In particular, the present invention refers to the use of biodegradable surfactants, based on natural polyglycerol esters, for scouring and bleaching textile fibers.

BACKGROUND ART

[0002] As known to those skilled in the art, scouring and bleaching are fundamental preliminary operations in the textile fiber ennoblement cycle, allowing the removal of substances extraneous to the fiber which can interfere in the subsequent dyeing and finishing steps, compromising the quality of the final product. Surfactants play an essential role among the products involved in the scouring and bleaching steps. However, the presence of surfactants in the effluents of dyeing waste poses environmental problems, given the well-documented toxicity of these molecules, e.g. to aquatic organisms.

[0003] The ecological aspect of the industrial production processes is today a major socio-environmental issue. In addition to the ethical aspects, the interest in environmental protection also has economic implications: the most advanced sectors of consumers are increasingly orienting their choices towards products that are more environmentally friendly. In particular, biodegradability, especially short term biodegradability, is a very desired property.

[0004] An important and widely used parameter as an indicator for assessing the biodegradability of a substance or mixture of substances is the "chemical oxygen demand", generally indicated in the sector by the acronym COD. In short, this parameter indicates the milligrams of oxygen per litre (mgO₂/L) required for the complete chemical oxidation of the organic and inorganic compounds present in a water sample. In Italy, the method for determining COD is codified in the publication "METHOD 5135 - CHEMICAL OXYGEN DEMAND (COD) IN A WATER MATRIX BY MEANS OF CUVETTE TEST", Manuals and Guidelines 117/2014 by ISPRA - Higher Institute for Protection and Environmental Research.

[0005] The problem of the presence of surfactants in dyeing waste has caused attention to be focused in recent years on problems related to the environmental impact of such wastewater. Under the pressure of increasingly environmentally conscious product demands - aimed at the development of more rapidly biodegradable formulations - the major textile auxiliary industries have increased their research and development efforts in this direction, in order to improve the quality of their effluents, which are mainly penalised by high COD values.

[0006] Chinese patent CN 103911864 B describes a solution for scouring cotton comprising, by weight, between 100 and 200 parts of water, between 1 and 3 parts of sodium hexametaphosphate, between 2 and 4 parts of sodium dodecylbenzenesulfonate, between and 3 parts of sodium sulphite, between 3 and 8 parts of polypropylene alcohol, between 3 and 6 parts of sodium lauryl ether sulfate, between 10 and 20 parts of a polysorbate, between 10 and 20 parts of ricinoleate polyglycerol, between 6 and 8 parts of a fatty acid ester of polyethylene glycol and between 3 and 5 parts of a polyoxyethylene ether of a fatty alcohol. Some of the components of this mixture, such as alkali or alkaline/earth metal polyphosphates (sodium hexametaphosphate), alkylbenzenesulfonates (sodium dodecylbenzenesulfonate), ethoxylated sulfates (sodium lauryl ether sulfate) and polyoxyethylene alcohols have a low biodegradability in the resulting aqueous effluents, and therefore the system in this document is not optimal from an environmental point of view.

[0007] Patent application US 2012/0207858 A1 describes a biocidal composition in which the main component is an acyl polyoxychloride having the following general formula:

wherein X is a chlorate or perchlorate group. This document discloses the possible use of a wide range of organic compounds, including polyglycerol esters, as compatibilisers useful for maintaining the active biocidal product in solution. However, acyl polyoxychloride is itself a compound with poor biodegradability.

[0008] At the moment, research into new formulations is mainly oriented towards products containing non-ionic surfactants (known in the industry as "BiAS", from "Bismuth Active Substance"), which are currently used in a prevalent manner with respect to the previously used anionic surfactants (MBAS, from "Methylene Blue Active Substances") such as for example alkylarylsulfonates (LAS, from "Linear-Alkyl Sulfonates"), alkylsulfates (AS), which are generally biodegradable in relatively long times and are derived from non-renewable sources, due to their excellent performance.

[0009] Currently, linear ethoxylated alkanols (AE), such as for example those disclosed in patent application US 2020/0139323 A1 and in the documents cited therein, are widely used as BiAS for scouring and bleaching treatments. In order to ensure good performance, these products are used in large quantities, between 1% and 10% by weight of the fiber to be treated, and may not be completely degraded within the 24-48 time period spent in the consortium or company sewage treatment plant, thus constituting a criminal offence towards to the receiving water body according to the regulations in force. In addition, the presence of ethylene oxide derivatives, also derived from non-renewable sources, may adversely affect the toxicological characteristics of the formulation itself. Finally, AE-based formulations may not be effective in the complete removal of spinning oils and other substances extraneous to the fiber, interfering in the subsequent processing steps.

[0010] Because of these drawbacks, the known processes do not allow the optimisation of the scouring and bleaching steps with a view to the realisation of an environmentally-friendly and sustainable textile economy.

[0011] There is therefore still a need for the provision of a method for scouring and bleaching textile fibers which, in addition to overcoming the disadvantages mentioned above, is able to guarantee the same or higher performance than traditional methods.

[0012] The main object of the present invention is to overcome the technical disadvantages outlined above by using a mixture of components used in the scouring process that does not contain compounds which cause a high COD value or which require long biodegradation times.

SUMMARY OF THE INVENTION

[0013] This object is achieved by the present invention, which relates to a process of scouring and bleaching of textile fibers, comprising the following stages:

a) loading, in which a defined quantity by weight of fiber to be treated is transferred to the treatment equipment;

b) closure, in which the equipment is closed, once the loading is completed;

c) introduction into the equipment of an aqueous solution in a weight ratio between 5:1 and 15:1 with respect to the mass of fiber to be treated, wherein said aqueous solution contains between 0.5% and 5% by weight with respect to said fiber of a biodegradable surfactant consisting of one or more natural polyglycerol esters, between 0.1 and 0.5% by weight with respect to said fiber of at least one alkaline agent and optionally between 0.1 and 0.3% by weight with respect to said fiber of at least one oxidizing agent;

d) heat treatment, in which the mass, depending on the nature of the fiber, is treated at a temperature between 50 °C and 110 °C for a period between 15 minutes and 2 hours;

e) cooling, in which the temperature is lowered to a value that allows the subsequent safe opening of the treatment equipment;

f) opening, in which the treatment equipment is opened;

g) discharge of the treated mass and of the treatment effluent.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The term "biodegradable surfactant" indicates a surfactant that is decomposable into at least two smaller fragments by bacteria, fungi, enzymes or other biological agents naturally occurring in a biological environment. A biodegradable surfactant may be derived from a biological source or synthesised by chemical synthesis or semi-synthesis. A semi-synthesis is a type of chemical synthesis using at least partly compounds isolated from biological sources (such as for example plant material or bacterial or cell cultures) other than fossil sources. In particular, the biodegradable surfactants used in the present invention can be produced from plant and renewable sources.

[0015] The term "natural esters" in the present description refers to compounds obtained by esterification of polyglycerols with carboxylic acids (or derivatives thereof) obtained from natural sources.

[0016] All other terms used in the description of the present invention, unless otherwise specified, are to be interpreted according to their ordinary meaning known to the person skilled in the art.

[0017] In a first aspect, the present invention refers to the use of biodegradable surfactants based on natural polyglycerol esters for the preparation of a bath for scouring and bleaching textile fibers.

[0018] The scouring and bleaching treatment preferably takes place through the stages a) to g) indicated above.

[0019] After completion of the discharge stage g), the cycle starts again from stage a).

[0020] In a second aspect of the present invention, biodegradable surfactants used in the present invention comprise natural polyglycerol esters, such as for example for example those disclosed in US 8,227,399 B2 and US 2020/0129397 A1 and in the documents cited therein, prepared starting from raw materials of plant origin and from renewable sources.

[0021] The polyglycerols-X to be used in the invention are commercially available products; they may be prepared by means of methods established in the art comprising, for example, homopolymerization of pure glycerol, the latter being obtained from natural sources such as for example vegetable oils.

[0022] Natural polyglycerol esters may be prepared by mixing in an inert environment (for example, under nitrogen atmosphere) and under stirring pure polyglycerol-X (PG-X), wherein X, the average degree of polymerization of the glycerol units, is any integer in the range 3-12, alone or in combination of at least two (e.g. a pure polyglycerol-4 or a mixture of pure polyglycerol-4 and pure polyglycerol-6) with monocarboxylic fatty acids, consisting of chains in the range C8-C30, to produce an esterification. When used in combination of two, the polyglycerols-X are found in a ratio preferably between 1:1 mol/mol and 1:3 mol/mol, more preferably 1:1 mol/mol.

[0023] In another aspect, natural polyglycerol esters may be prepared by mixing in an inert environment (for example, under nitrogen atmosphere) and under stirring pure polyglycerol-X (PG-X), wherein X, the average degree of polymerization of the glycerol units, is any integer in the range 3-12, alone or in combination of at least two (e.g. a pure polyglycerol-4 or a mixture of pure polyglycerol-4 and pure polyglycerol-6) with dicarboxylic acids derived from natural sources, consisting of chains in the range C4-C10, to produce an esterification. Examples of said dicarboxylic acids comprise succinic acid, adipic acid, sebacic acid. When used in combination of two, the polyglycerols-X are found in a ratio preferably between 1:1 mol/mol and 1:3 mol/mol, more preferably 1:1 mol/mol.

[0024] In another aspect, natural polyglycerol esters may be prepared by mixing in an inert environment (e.g., under nitrogen atmosphere) and under stirring of pure polyglycerol-X (PG-X), wherein X, the average degree of polymerization of the glycerol units, is any integer in the range 3-12, alone or in combination of at least two (e.g., a pure polyglycerol-4 or a mixture of pure polyglycerol-4 and pure polyglycerol-6) with fatty hydroxy acids derived from natural sources, such as for example 12-hydroxy stearic acid and ricinoleic acid, to produce an esterification. When used in combination of two, the polyglycerols-X are found in a ratio preferably between 1:1 mol/mol and 1:3 mol/mol, more preferably 1:1 mol/mol.

[0025] Carboxylic acids can also be added as a second step of the synthesis after the polyglycerols-X have been mixed. Carboxylic acids may be of a single type or be a mixture of, for example, two types of fatty acids, such as for example caprylic and capric acid, but they are preferably of a single type (such as for example lauric) to optimise the reproducibility of the performance of the surfactant. The fatty acids are added at a concentration such as to obtain a substitution between 0.9 and 1.5 hydroxyl groups per polyglycerol-X molecule, preferably a substitution of one hydroxyl group per polyglycerol-X molecule, i.e. a 1:1 molar equivalent of polyglycerols-X with respect to the fatty acid chain. The ratio of fatty acid:polyglycerol can vary between 1:1 and 2.5:1.

[0026] The polyglycerols-X and the fatty acids are mixed at a temperature between 70 °C and 110 °C, preferably between 75 °C and 90 °C, and more preferably at 90 °C.

[0027] Optionally, the reaction is carried out in the presence of catalysts suitable for the esterification process. Suitable catalysts comprise any catalyst that can be used in the preparation of esters including, but not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methylate, sulfuric acid, methanesulfonic acid (MSA), paratoluenesulfonic acid (PTSA), and other acid catalysts supported on a solid base.

[0028] The esterification reaction is carried out at a temperature between 140 °C and 180 °C, depending on the starting raw materials. The reaction is carried out under conditions that prevent oxidation of the ingredients (e.g. under a nitrogen atmosphere). The duration of the reaction is between 30 minutes and two hours, preferably one hour. Any secondary reactions, such as for example for example the cyclization of polyglycerols-X to give sorbitan derivatives, can progressively increase their entity with reaction times exceeding one hour.

[0029] In a further aspect, natural polyglycerol esters may be prepared by mixing in an inert environment (e.g., under nitrogen atmosphere) and under stirring of pure polyglycerol-X (PG-X), wherein X, the average degree of polymerization of the glycerol units, is any integer in the range 3-12, alone or in combination of at least two (e.g., a pure polyglycerol-4 or a mixture of pure polyglycerol-4 and pure polyglycerol-6) with oils derived from plant sources, such as for example olive oil, rapeseed oil, sunflower oil, soyabean oil, linseed oil, to produce a transesterification under the same conditions as the esterification reactions described above. When used in combination of two, the polyglycerols-X are found in a ratio between 1:1 mol/mol and 1:3 mol/mol, more preferably 1:1 mol/mol.

[0030] In all of the above cases, the esterification reaction can be pushed to completion using methods known in the art, such as for example by continuous distillation of water formed as a by-product of esterification, at atmospheric pressure or at reduced pressure.

[0031] Yields are higher than 98% and the natural polyglycerol esters obtained can be purified by means of techniques known in the art, such as for example extraction in aqueous or aqueous-alkaline environment to remove traces of unreacted raw materials and catalysts.

[0032] In step c) of the process, an aqueous solution containing a biodegradable surfactant as defined above, at least one alkaline agent and optionally an oxidizing agent is used as the composition for the scouring and bleaching of the textile fibers.

[0033] The aqueous solution is used in a weight ratio between 5:1 and 15:1, preferably between 8:1 and 12:1, and more preferably about 10:1 with respect to the mass of fiber to be treated.

[0034] The amount of biodegradable surfactant (single or surfactant mixture) used is between 0.5 and 5% by weight, preferably between 1% and 3% by weight, and more preferably about 2% by weight, with respect to the mass of fiber to be treated.

[0035] Examples of alkaline agents for use in stage c) of the process of the present invention comprise alkali or alkaline earth metal hydroxides, such as for example sodium, potassium, magnesium, calcium, barium hydroxide, alkali carbonates, such as for example sodium, potassium carbonate, used as such or in an aqueous dispersion. A preferred alkaline agent is a solution of sodium hydroxide in water 50% by weight, used at a ratio with respect to the scouring and bleaching bath between 1 mL/L to 5 mL/L, preferably 3 mL/L. Another preferred alkaline agent is sodium carbonate, used as such at a concentration in the scouring and bleaching bath between 1 g/L to 3 g/L, preferably 2 g/L.

[0036] The alkaline agent is used in step c) in an amount between 0.1 and 0.5% by weight with respect to the fiber to be treated.

[0037] Examples of oxidizing agents for use in stage c) of the process of the present invention comprise hydrogen peroxide, sodium perborate, peracetic acid, or chlorinated products, such as for example sodium hypochlorite, calcium hypochlorite, sodium chlorite, sodium dichloroisocyanurate (DCIC), chloramine-T, used as such or in an aqueous dispersion. The preferred oxidizing agent of the present invention is a solution of hydrogen peroxide in water 35% by weight, used at a ratio with respect to the scouring and bleaching bath between 3 mL/L and 7 mL/L, preferably 5 mL/L.

[0038] The oxidizing agent, when present, is used in step c) in an amount between 0.1 and 0.3% by weight with respect to the fiber to be treated.

[0039] Step d) of the process of the invention is carried out at a temperature between 50°C and 110 ° C, preferably between 80 and 100°C, for a period between 15 minutes and 2 hours, preferably between 30 and 60 minutes.

[0040] The person skilled in the art will agree that, depending on the nature and problems of the fiber to be treated, other additives such as reducing agents (e.g. sodium hydrosulphite), sequestering agents and stabilising agents may be used.

[0041] The method of the present invention may be advantageously employed for scouring and bleaching prior to dyeing and subsequent processings of articles based on textile fibers of plant origin (comprising cellulose derivatives, such as for example cotton, linen, hemp, jute), of animal origin (e.g. wool, silk, alpaca, cashmere), of artificial origin (e.g. rayon, rayon acetate, viscose), of synthetic origin (e.g. polyamides, polyesters, polyacrylates, polyvinyls, polypropylenes, polyurethanes, elastomers), and combinations thereof. The person skilled in the art will appreciate that, given the wide range of natural and renewable sources available for the synthesis of biodegradable surfactants such as those used in the present invention, the chemical and physical properties of the latter, especially the hydrophilic-lipophilic balance (HLB), can be tuned in accordance with the required performance.

[0042] In addition, the discharged effluent has the advantage of being readily biodegradable and complying with discharge regulations in view of environmentally friendly and sustainable processes.

[0043] Finally, the person skilled in the art will appreciate that the method described in the present invention is applicable to industrial processes and continuous and discontinuous plants for scouring and bleaching textile fibers.

[0044] The present invention is illustrated in more detail by the following examples.

[0045] In the examples, the measurement of the COD values after the different scouring and bleaching treatments according to the invention and according to the prior art was carried out following the IRSA-CNR 5135 method.

EXAMPLE 1

[0046] This example refers to the preparation of esters obtained from PG-4 and a mixture of caprylic and caprinic acids (i.e. n-octanoic and n-decanoic acids, respectively).

[0047] In an inert environment due to nitrogen atmosphere and under mechanical stirring, 69 g of PG-4 and 35 g of a commercially available mixture of caprylic acid and caprinic acid (approximately 1:1 weight/weight) were heated at a temperature of 140-160 °C. The system was kept under these conditions until residual acidity < 10 mg KOH/g by continuously distilling the water formed by the esterification reaction. The final mixture was then cooled and discharged.

EXAMPLE 2

[0048] This example refers to the preparation of the ester of PG-6 and lauric acid.

[0049] In an inert environment due to nitrogen atmosphere and under mechanical stirring, 65 g of PG-6 and 38 g of lauric acid were heated at a temperature of 160-180 °C. The system was kept under these conditions until residual acidity < 10 mg KOH/g by continuously distilling the water formed by the esterification reaction. The final mixture was then cooled and discharged.

EXAMPLE 3

[0050] This example refers to the preparation of the ester of PG-6 and olive oil.

[0051] In an inert environment due to nitrogen atmosphere and under mechanical stirring, 54 g of PG-6 and 45 g of olive oil were heated at a temperature of 180-210 °C. The system was kept under these conditions for one hour until complete clarity. The final mixture was then cooled and discharged. Number of acidity: < 10 mg KOH/g.

EXAMPLE 4

[0052] This example refers to the preparation of a mixture of esters of PG-4, PG6, succinic acid and stearin.

[0053] In an inert environment due to nitrogen atmosphere and under mechanical stirring, 35 g of PG-4, 25 g of PG-6 and 8 g of succinic acid were heated at a temperature of 160-180 °C. The system was kept under these conditions until residual acidity < 10 mg KOH/g by continuously distilling the water formed by the esterification reaction. Then 25 of commercial stearin was added and the mixture was kept at a temperature of 160-180 °C until residual acidity < 10 mg KOH/g, by continuously distilling the water formed by the esterification reaction. The final mixture was then cooled and discharged.

EXAMPLE 5

[0054] This example refers to a scouring and bleaching process with a surfactant of the present invention consisting of the natural polyglycerol esters of Example 1.

[0055] The treated fabric consisted of 92% cotton and 8% elastomer.

[0056] Recipe of the bath made with laboratory equipment:

Polyglycerol esters: 2% on the weight of the fiber to be treated.

NaOH at 50%: 3 mL/L of bath

H₂O₂ at 35%: 5 mL/L of bath

Bath ratio: 10:1

Treatment conditions: 98 °C for one hour.

Bath COD after treatment: 284 mg/Kg.

EXAMPLE 6 (COMPARATIVE)

[0057] The test of Example 5 is repeated under the same conditions, with the only difference that a C12-C13 ethoxylated surfactant of the prior art is used as the surfactant.

[0058] Bath COD after treatment: 338 mg/Kg.

EXAMPLE 7

[0059] This example refers to a scouring and bleaching process with a surfactant of the present invention consisting of a 1:1 mixture by weight of the natural polyglycerol esters obtained in Examples 1 and 3.

[0060] An 80% viscose and 8% elastomer knitted fabric is treated.

[0061] Recipe of the bath made with laboratory equipment:

Polyglycerol esters: 2% on the weight of the fiber to be treated.

Na₂CO₃: 2 g/L of bath

H₂O₂ at 35%: 5 mL/L of bath

Bath ratio: 10:1

Treatment conditions: 80 °C for one hour.

Bath COD after treatment: 260 mg/Kg.

EXAMPLE 8 (COMPARATIVE)

[0062] The test of Example 7 is repeated under the same conditions, with the only difference that a C12-C13 ethoxylated surfactant of the prior art is used as the surfactant.

[0063] Bath COD after treatment: 350 mg/Kg.

EXAMPLE 9

[0064] This example refers to a scouring and bleaching process with a surfactant of the present invention consisting of a 1:1 mixture by weight of the natural polyglycerol esters obtained in Examples 1 and 3.

[0065] The treated fabric consisted of 80% polyamide and 20% elastomer.

[0066] Recipe of the bath made with laboratory equipment:

Polyglycerol esters: 2% on the weight of the fiber to be treated.

Na₂CO₃: 2 g/L of bath

Bath ratio: 10:1

Treatment conditions: 80°C for 40 minutes.

Bath COD after treatment: 410 mg/Kg.

EXAMPLE 10 (COMPARATIVE)

[0067] The test of Example 9 is repeated under the same conditions, with the only difference that a C12-C13 ethoxylated surfactant of the prior art is used as the surfactant.

[0068] Bath COD after treatment: 450 mg/Kg.

EXAMPLE 11

[0069] A test with activated sludge was carried out in order to further verify the biodegradability of the natural esters of the invention. A test was prepared in a batch activated sludge pilot reactor (ISO 14851 method), comparing the times of reduction of the reference lactulose, of a C12-C13 ethoxylated surfactant of the prior art and of a surfactant based on natural polyglycerol esters (mixture 1:1 weight/weight of the products obtained from Examples 1 and 3).

[0070] After 24 hours, a reduction of 84% of lactulose, 81% of the surfactant based on natural polyglycerol esters and only 32% of the ethoxylated C12-C13 surfactant was recorded. After 48 hours, the reductions of lactulose and surfactant based on natural polyglycerol esters were higher than 95%, while the removal of the C12-C13 ethoxylated surfactant was only 46%.

Claims

1. Process of scouring and bleaching of textile fibers, comprising the following stages:

a) loading, in which a defined quantity by weight of fiber to be treated is transferred to the treatment equipment;

b) closure, in which the equipment is closed, once the loading is completed;

c) introduction into the equipment of an aqueous solution in a weight ratio between 5:1 and 15:1 with respect to the mass of fiber to be treated, wherein said aqueous solution contains between 0.5% and 5% by weight with respect to said fiber of a biodegradable surfactant consisting of one or more natural polyglycerol esters, between 0.1 and 0.5% by weight with respect to said fiber of at least one alkaline agent and optionally between 0.1 and 0.3% by weight with respect to said fiber of at least one oxidizing agent;

d) heat treatment, in which the mass, depending on the nature of the fiber, is treated at a temperature between 50 °C and 110 °C for a period between 15 minutes and 2 hours;

e) cooling, in which the temperature is lowered to a value that allows the subsequent safe opening of the treatment equipment;

f) opening, in which the treatment equipment is opened;

g) discharge of the treated mass and of the treatment effluent.

2. Process according to claim 1, wherein the weight ratio of said aqueous solution to the fiber to be treated is between 8:1 and 12:1.

3. Process according to any one of claims 1 or 2, wherein said aqueous solution contains said biodegradable surfactant in an amount between 1% and 3% by weight with respect to said fiber.

4. Process according to any one of the preceding claims, wherein said natural polyglycerol esters used in stage c) are formed by esterification of pure polyglycerols-X, in which X represents the number of glycerol units and is an integer in the range 3-12, with one or more carboxylic fatty acids.

5. Process according to claim 4, wherein said natural polyglycerol esters contain between 0.9 and 1.5 radicals derived from carboxylic acids per unit of polyglycerol-X.

6. Process according to any one of claims 4 or 5, wherein said one or more polyglycerol-X esters are two of said esters in a ratio between 1:1 mol/mol and 1:3 mol/mol.

7. Process according to any one of claims 4 to 6, wherein said carboxylic fatty acids are C8-C30 monocarboxylic acids derived from natural sources.

8. Process according to any one of claims 4 to 6, wherein said carboxylic fatty acids are C4-C10 dicarboxylic acids derived from natural sources, preferably succinic acid, adipic acid and sebacic acid.

9. Process according to any one of claims 4 to 6, wherein said carboxylic fatty acids are fatty hydroxy acids derived from natural sources, preferably 12-hydroxy stearic acid and ricinoleic acid.

10. Process according to any one of claims 4 to 6, wherein said natural polyglycerol esters are produced by transesterification of said polyglycerols-X with an oil selected from olive oil, rapeseed oil, sunflower oil, soyabean oil and linseed oil.

11. Process according to any one of the preceding claims, wherein the alkaline agent used in stage c) of the process is selected from hydroxides or carbonates of alkali or alkaline earth metals or mixtures thereof.

12. Process according to any one of the preceding claims, in which the oxidizing agent used in stage c) of the process is selected from hydrogen peroxide, sodium perborate, peracetic acid, chlorinated products and mixtures thereof.