Process for the manufacture of sulfited polyesters and their use as re-tanning agents

Abstract

The present invention provides a process for the manufacture of sulfited polyesters by esterification of unsaturated carboxylic acids or its anhydrides and optionally saturated carboxylic acids or its anhydrides, and polyols under mild conditions generally below 180°C, preferably below 160°C and subsequent sulfitation under mild conditions, generally below 180°C, preferably below 160°C. The sulfited polyesters can be used as re-tanning agent in the leather process.

Description

[0001] Title: Process for the manufacture of sulfited polyesters and their use as re-tanning agents

[0002] The present invention relates to a novel process for the manufacture of sulfited polyesters, and to the use of the obtained sulfited polyesters as re-tanning agents in the leather manufacturing process.

[0003] Leather is a durable, flexible material created via the tanning of animal rawhide and skin. The leather manufacturing process is divided into three fundamental sub-processes: preparatory stages, tanning and crusting.

[0004] The present invention relates to the sub-process of tanning, especially the re-tanning part thereof.

[0005] In the preparatory stages, hide or skin is prepared for tanning. After trimming, animal skin is soaked to remove salts and other solids, while restoring moisture when the skin was first dried. Then, the flesh side of the wet skin is scraped to remove any remaining traces of flesh or fat, and the skin is optionally dehaired. After an optional bating and pickling step, the skins are subjected to tanning. Other potential steps that may be part of the preparatory stages include preservation, liming, splitting, reliming, deliming, degreasing, frizzing, bleaching and depickling.

[0006] Tanning is the process of preserving the skins by converting the protein, via crosslinking the collagen fibres, of the raw hide or skin into a stable material that does not putrefy and provides tanned leathers with satisfactory properties, such as high shrinkage temperatures Ts, suppleness and suitability for subsequent processing such as neutralization, re-tanning, fatliquoring, dyeing, finishing.

[0007] Tanning is dominantly carried out by treatment of the hides with chromium sulphate (giving so-called wet-blue leather) or by the use of organic reactive tanning agent as aldehydes, especially glutaraldehyde (resulting in wet- white leather). In rare cases the tanning is carried out with vegetable tanning agents — as traditionally done - or by use of synthetic tanning agents (syntans), or other conventional techniques. The product prepared in this subprocess is an intermediate since it is not sufficient to obtain the desired characteristics specified by the customer. The tanned hides are therefore further treated with various products. This process is called re-tanning. Retanning affects the feel of the leather, the dyeability, fullness of the leather, the fineness of the grain and the stability of grain and other factors such as light fastness, to suit characteristics required for the final leather article - whether for automotive or aviation seating, footwear, garments or bags and leather goods. Re-tanning includes dyeing to give colour and fatliquoring to add softness, fullness and touch. Once re-tannage is complete, the leather is known as “crust”.

[0008] Vegetable tanning agents were the first tanning agents. They are now mostly used in the re-tanning, because of the nowadays wide acceptance of chromium sulphate or glutaraldehyde as tanning agents. Common vegetable tanning agents are Mimosa, obtained from the bark of the Acacia tree, and Tara, obtained from the fruit of the Tara bush. They can impose softness and limited filling of the collagen structures to leathers (Hans Herfeld, "Library of Leather; Volume 3: Tanning Agents, Tanning and Retanning", Frankfurt 1985, page 44). Usually, vegetable tanning agents lack fastness properties, such as resistance to light or resistance to heat induced ageing.

[0009] The term syntan refers to the range of synthetic tanning agents. The first syntans were made by condensation of phenol sulfonic acid and formaldehyde (E. Stiasny, 1911, Austrian Patent Nr. 58405). While these syntans were initially used as dispersers and auxiliaries for vegetable tannins, they could be applied to replace some or even all vegetable tannins after further development of their chemistry. US 1841840 describes the incorporation of urea into the polycondensation of phenol sulfonic acid and formaldehyde, as depicted in Scheme 1, by which such a further development was achieved, enabling obtaining leathers with increased technical requirements like fastness properties concerning light or heat induced ageing. Scheme 1: chemistry of synthetic tanning agents

[0010] Because of the wide acceptance of chromium sulphate or glutaraldehyde as tanning agents, syntans are now mainly used in the retanning process, where they help to structure and fill the crosslinked collagen fibres. Unfortunately, syntans can contain a residual amount of free formaldehyde or undesired side products as Bisphenol S or F, which means that they should be handled and used with care due to safety reasons.

[0011] In many applications syntans and vegetable tannins are applied together, since the performance of vegetable tannins alone is considered insufficient. The syntans generally have higher fastness properties and beyond that have dispersing properties. This helps to support the even distribution of vegetable tannins and other leather chemicals like fillers, dyes, and fatliquors (DE 1142173).

[0012] Given the fact that syntans are still made from oil based and toxic phenol and formaldehyde, the search is ongoing for re-tanning agents made from less toxic starting materials, and preferably renewable starting materials, that can substitute syntans. There continues to be a need for chemical products made from bio-based materials instead of petroleum-based materials, and these bio-based materials are thus called renewable materials. There is currently a big driving force for companies, and the chemical industry in particular, for corporate responsibility and the use of sustainable or renewable sources of raw materials. It is of particular interest to use biobased raw materials that do not compete with usage of those biobased raw materials as food source, and hence the usage of biobased waste streams is particularly advantageous.

[0013] EP 3597778B1 describes the condensation products of dicarboxylic acids with 2 to 6 carbon atoms and diethanolamine giving rise to mixed polyesters and polyamides as tanning agents, re-tanning agents or pretanning agents.

[0014] CN 102757552 discloses water-soluble furandicarboxylic acidcontaining aromatic polyesters having a high content of a sulfonate- containing compound of more than 12 mol% in the examples.

[0015] US 4525524 describes polyesters with sulfonate groups, wherein these sulfonate groups are incorporated by the reaction with sulfo phthalates or their alkyl esters, which results in aromatic groups being present in the resulting polyester with sulfonate groups.

[0016] US 3915950 describes sulfurizing an unsaturated polyester product using heating with sulfur in the presence of zinc oxide, resulting in sulfurized products used as additives in lubricating oils.

[0017] GB 1298204 describes the synthesis of flexible unsaturated polyesters from polyether diols and ethenically unsaturated dicarboxylic acids or its anhydrides.

[0018] GB 1214087 describes the synthesis of polyesters with sulfonate groups, wherein the sulfonate group is incorporated by reacting phenolsulphonate salt together with dicarboxylic acids and diols.

[0019] JPS 58122917 describes the synthesis of sulfited polyesters, but the manufacturing process uses harsh conditions, for both the esterification (190°C or higher) and the sulfitation (170-250°C and acidic conditions) step and zinc acetate is used in the esterification step. The obtained polyesters with sulphonate groups are described to be useable as fiber glue, a paper processing agent, a fiber processing agent, an adhesive, a paint, a water- soluble film, a binder or an anionic functional resin. The presence of zinc in a final product is nowadays not desirable anymore.

[0020] US 3018272 discloses using a polyester having the — SO3M group, where M is a metal, as a basic dye sensitizing unit to permit fibers to be readily dyed using basic dyes.

[0021] US 6576717 describes a water-dispersible acrylic-modified polyester resin containing sulfonate groups prepared by addition copolymerization of ethylenically unsaturated vinyl monomers and a polyester. The polyester is prepared from a polycondensation reaction with dicarboxylic acids, glycols, ethylenically unsaturated monomer, and a minor amount of a sulfomonomer.

[0022] A. A. Ibrahim published the use of hyperbranched poly(amidoamine) as pre-tanning agent for leather starting from methyl-acrylate and diamines (International Journal of Polymer Science 2013, 5154). A pretanning agent increases the chromium take up during tanning, which is advantageous.

[0023] The present invention provides a process to obtain sulfited polyesters under mild conditions. The obtained sulfited polyester can be used as re-tanning agent in the leather process that is free of formaldehyde and bisphenols and that provides good re-tanning behaviour.

[0024] It was found that polyesters could be converted under mild conditions into water soluble sulfited compounds suitable for aqueous applications. Surprisingly, it was found that the obtained sulfited polyesters can be used as re-tanning agents and are thus able to replace syntans in retanning of leather. Sulfited polyesters of the prior art obtained via a different process are also suitable to use as re-tanning agents thus enabling them to replace syntans in re-tanning of leather.

[0025] The object of the present invention is to provide a process for the esterification of unsaturated carboxylic acids, optionally saturated carboxylic acids, and polyols and subsequent sulfitation under mild conditions. It is a further object of the present invention to provide sulfited polyesters that can be used as re-tanning agent in the leather process that is free of formaldehyde and bisphenols and that provides good re-tanning behaviour and that is preferably made from partly renewable raw materials.

[0026] In a first aspect, the present invention relates to a process for the manufacture of sulfited polyesters by esterification of unsaturated carboxylic acids or its anhydrides (and optionally saturated carboxylic acids or its anhydrides) and polyols under mild conditions and subsequent sulfitation under mild conditions.

[0027] In a second aspect, the present invention relates to the use of the product obtained by esterification of unsaturated carboxylic acids or its anhydrides (and optionally saturated carboxylic acids or its anhydrides) and polyols under mild conditions and subsequent sulfitation under mild conditions as re-tanning agent in the leather making process.

[0028] In a third aspect, the present invention relates to the use of sulfited polyesters in general as re-tanning agent in the leather making process.

[0029] Water soluble sulfited compounds of the present invention are obtained by condensing polyols with carboxylic acids, wherein some or all carboxylic acids contain one or more multiple double bonds that are subsequently reacted with sulfites to form water soluble sulfited polyesters, which are polyesters with sulfonate groups. The molar ratio of saturated acids to unsaturated acids ranges from 0:1 to 5:1. Saturated acids can be absent, meaning a ratio of 0:1, but their presence is advantageous for their performance as re-tanning agents. Unsaturated acids are required, since they can be sulfited, and the sulfitation leads to water solubility. If the ratio is larger than 5:1, meaning more than 5 times more saturated acids than unsaturated (later sulfited acids), then the water solubility would go down to borderline, which is undesirable.

[0030] The carboxylic acids, both saturated and unsaturated, are preferably dicarboxylic acids, but also a small amount of monocarboxylic acids, tricarboxylic acids or polycarboxylic acids can be present besides the dicarboxylic acids. The amount of monocarboxylic acids should not be too high, because monocarboxylic acids will function as chain stoppers. The amount of tricarboxylic acids or polycarboxylic acids should not be too high, because tricarboxylic acids and polycarboxylic acids will result in branching of the polymeric chain and thus increased viscosity. In the context of the present invention, the molar ratio of monocarboxylic acids to dicarboxylic acids (for the unsaturated as well as the saturated acids) is preferably between 0:100 and 25:75, most preferably between 0:100 and 10:90. In the context of the present invention, the molar ratio of tricarboxylic acids or polycarboxylic acids to dicarboxylic acids is preferably between 0:100 and 10:90, most preferably between 0:100 and 5:95.

[0031] Both the esterification and the sulfitation step were done at mild conditions, meaning at modest temperatures, e.g. temperatures below 180°C, preferably below 160°C for the esterification reaction and temperatures below 100°C, preferably below 90°C for the sulfitation reaction. In addition, the sulfitation reaction is carried out at mild pH values, e.g. at pH values between 6 and 10, preferably between 7 and 9.

[0032] The sulfited polyester can be applied as re-tanning agents on tanned hide. A general reaction sequence is depicted in scheme 2 with itaconic acid as one example of an unsaturated dicarboxylic acid. Scheme 2: General reaction sequence for sulfited polyesters made from unsaturated dicarboxylic acids and polyols, with itaconic acid as example of an unsaturated dicarboxylic acid

[0033] This present invention is not limited to itaconic acid and hence any other unsaturated carboxylic acid, or mixtures thereof, may be used. Examples of unsaturated dicarboxylic acids are maleic acid, fumaric acid, glutaconic acid, traumatic acid, citraconic acid and mesaconic acid. Examples of unsaturated monocarboxylic acids are fatty acids like myristoleic acid, sapienic acid, ct-linolenic acid, stearidonic acid, eicosapentaenoic acid, cervonic acid, linoleic acid, linolelaidic acid, y-linolenic acid, dihomo-y- linolenic acid, arachidonic acid, docosatetraenoic acid, palmitoleic acid, vaccenic acid, paullinic acid, oleic acid, elaidic acid, gondoic acid, erucic acid, nervonic acid and mead acid. An example of an unsaturated tricarboxylic acid is aconitic acid. The present invention is also not limited to carboxylic acids as starting material, because also anhydrides can be used, such as itaconic anhydride or maleic anhydride.

[0034] Unsaturated dicarboxylic acids can be condensed in presence or absence of other dicarboxylic acids, tricarboxylic acids or polycarboxylic acids, as exemplified in scheme 3. Scheme 3: General reaction sequence for sulfited polyesters made from unsaturated dicarboxylic acids, saturated dicarboxylic acids, and polyols

[0035] The polyols used in the present invention can be linear, or branched, can contain other functionalities and can be any component that contains two or more hydroxyl groups, or a combination of such components, such as a monomeric diol, a monomeric triol, or a polymeric diol or a polymeric triol, or a combination thereof. Examples of monomeric polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, bis (hydroxyethyl) terephthalate, neopentylglycol, trimethylol propane, cyclohexane dimethanol, furan dimethanol, glycerol, 1,4-butanediol, 1,3- butane diol, 1,5-pentane diol, 1,6-hexane diol, 1,8-octane diol. Besides monomeric polyols, also polymeric polyols may be used, such as polyester polyols, polyesteramide polyols, polyether polyols, polythioether polyols, polycarbonate polyols, polyacetal polyols, polyolefin polyols or polysiloxane polyols or mixtures thereof.

[0036] Preferably, at least one or more of the unsaturated mono- and polycarboxylic acids, and saturated mono- or polycarboxylic acids, and / or polyols used in the present invention are bio-based. Examples of bio-based saturated dicarboxylic acids include oxalic acid, succinic acid, adipic acid, glutaric acid and azelaic acid. Preferred examples of mono-unsaturated dicarboxylic acids include itaconic acid, which is a biobased product mainly produced by fermentation using certain filamentous fungi, and citraconic acid and mesaconic acid, which can both be prepared from biobased citric acid. Examples of biobased unsaturated monocarboxylic acids are various fatty acids, like palmitoleic acid, vaccenic acid or oleic acid. Examples of biobased saturated monocarboxylic acids are stearic acid, lauric acid, myristic acid and palmitic acids. Examples of bio-based polyols include 1,2-ethanediol, 1,3- propane-diol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, galactitol, fucitol, iditol, inositol, volemitol, isomalt, maltitol, lactitol. The potential combination of bio-based unsaturated mono- and polycarboxyl acids, bio-based saturated mono- and polycarboxylic acids, and bio-based polyols gives plenty of possibilities to obtain polyesters with a high or complete bio-based content and to establish a chance to move away from oil-based products like syntans.

[0037] The obtained sulfited polyesters have preferably more than 50% of their carbon atoms coming from sources that can be biobased.

[0038] The esterification of carboxylic acids and polyols proceeds in the presence of acids, which function as catalysts, while the formed water is removed by distillation. Examples of acids that can be used as catalysts are mineral acids like sulfuric acid or phosphoric acids or organic acids like sulfonic acids. These acids will remain in the products.

[0039] The esterification of anhydrides and polyols can be achieved without solvents or catalyst, by heating the polyols with the anhydrides. In another embodiment, preformed polyesters can be reacted with anhydrides, wherein the preformed polyesters have been previously synthesized from esters and polyols in such a ratio that the preformed esters have hydroxyl end groups.

[0040] The esterification of carboxylic acids or anhydrides with polyols is achieved at relatively mild conditions, at a reaction temperature between 120°C and 180°C, preferably at a reaction temperature between 140°C and 160°C, with a duration of the reaction of between 1 and 3 hours, wherein the reaction time is longest at the lowest reaction temperature and the reaction time is shortest at the highest reaction temperature.

[0041] The esterification of unsaturated carboxylic acids and polyols may be executed in the presence of a small amount of free radical scavenger to ensure that the double bond of unsaturated dicarboxylic acids remains unreacted. Examples of such free radical scavenger include hydroquinone, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ) and 4-methoxy-phenol. The sulfitation reaction of the present invention is reaction of a carbon-carbon double bond, an olefinic bond, into a sulfonate, generally using NaHCOs and sodium bisulfite (NaHSOs), or sodium sulfite (Na2SOs), or sodium meta bisulfite (Na2S20s) under mild conditions, after which effectively a hydrogen and a SChNa group are attached to what was previously the C=C double bond, as depicted in Scheme 2. In the context of the present invention, the degree of sulfitation is 95% or more, preferably 98% or more and most preferable 99% or more, meaning the percentage of conversion from olefinic bond into a sulfonate. The completeness of the sulfitation reaction can be verified by measuring a NMR spectrum of the mixture and in this spectrum the sulfitation can be judged as complete when no longer signals from olefinic bonds, between 5 ppm and 6 ppm, can be detected. This sulfitation reaction is achieved at relatively mild conditions, at a temperature between 50°C and 120°C, preferably between 60°C and 100°C and most preferably between 70°C and 90°C. The reaction is executed for some duration, which is dependent on the reaction temperature and preferably the reaction duration is between 1 and 5 hours, most preferably between 1 and 3 hours, wherein the reaction time is longest at the lowest reaction temperature and the reaction time is shortest at the highest reaction temperature.

[0042] The inventors discovered that sulfited polyesters, such as the sulfited polyesters obtained from the process of the present invention can be applied on leather, such as via an industry standard procedure, for re-tanning. Surprisingly, it was found that leathers treated with sulfited polyesters, preferably made with partially renewable components, gave similar or better properties to the leather than syntans or vegetable tannins, concerning softness, fullness, and lightfastness, while creating no bisphenol or formaldehyde problem. An analysis of toxic formaldehyde or bisphenols is actually not even required for these sulfited polyesters, because none of the ingredients contains or could release formaldehyde or could form bisphenols. These sulfited polyesters represent a novel non-toxic, partially renewable alternative to oil based phenol formaldehyde condensates in the leather industry.

[0043] A retanning agent comprising the sulfited polyesters may also be combined with other components, such as lignin, starch, chitin, caolin, or proteins in a re-tanning composition.

[0044] An industry standard procedure for re-tanning comprises treating a tanned leather, such as wet blue, with water, sodium formiate and sodium bicarbonate for a period of time resulting in a float with a pH of below neutral, after which the re-tanning agent is added followed by further turning of the tanning drum for a certain period of time, followed by discharging the float and washing with water. Afterwards the leather is dried, such as by hang drying at room temperature without vacuum, or in a vacuum chamber. The sulfited polyester is added as a re-tanning agent in an amount of between 2% and 15%, and preferably in an amount of between 4% and 12%, and most preferably in an amount of between 6% and 10%, wherein the percentages refer to the weight percentage of the non-volatile part of the sulfited polyester compared to the weight of the leather.

[0045] The softness of leathers can be quantified according to ISO 17235. In this measurement, a steel cylinder of defined mass is pressed with a defined speed into a framed piece of leather and the resulting area increase of the leather is measured. Larger numbers indicate bigger area increase indicating more softness of the leathers.

[0046] The lightfastness of leather can be determined according to ISO 105-B02, in for example a sun tester. Re-tanned leathers are exposed to light for usually 24 to 72 hours. The resulting yellowing can be quantified in a spectral photometer, or assigned via the blue scale method, assigning numbers from 1 to 8 with increasing lightfastness, wherein a score of 6 or above is considered ‘good’.

[0047] Heat induced ageing of leather can be determined by exposing leathers to heat at 100°C for 48 h and at 130°C for two hours, according to ISO 105-A02. Leather samples can be, after exposure to heat, evaluated according to the grey scale with numbers from 1 to 5. Larger numbers indicate more stability against heat, wherein a score of 3.5 or higher is considered ‘good’.

[0048] Syntans are made from phenol and formaldehyde and as a consequence they can release formaldehyde and can contain phenol, Bisphenol F, or S. A rest monomer analysis for formaldehyde like ISO 27587 is widely applied in the leather industry. Bisphenols and phenol can be analysed with ISO 18218-1 in parallel to alkylphenols. Advantageously, retanning agents comprising sulfited polyesters are free of formaldehyde, phenol, and bisphenols, wherein free of formaldehyde, phenol, and bisphenols is meant to be that the concentration of formaldehyde, phenol, and bisphenols is below 10 ppm, and preferably below 2 ppm.

[0049] Fullness of re-tanned leathers is dominantly determined via haptics. Fullness is an aesthetic quality parameter, organoleptical characteristic, defined by the spacing between the fibres, suggesting (by the tactile sense) a larger or smaller amount of fibres per area. It is the result of a good filling of the interfibrillar spaces and an adequate lubrication of the fibres avoiding their agglomeration.

[0050] The tightness of the grain is an evaluation of the top layer of the leather once it is bended with two hands. The smoother the layer remains the tighter the bended leather is. The more wrinkles observed, the lower the tightness.

[0051] Fullness and tightness of re-tanned leathers are determined via haptics and are generally graded with a number, wherein a lower number is better.

[0052] The sulfited polyesters can be used to prepare leathers for all applications, for example shoe, furniture, car, clothing and bag leathers.

[0053] Any kind of leather which is conventionally treated is suitable to be treated by using sulfited polyestersa, particularly grain leather (e.g. nappa from sheep, goat or cow and box-leather from calf or cow), suede leather (e.g. velours from sheep, goat or calf and hunting leather), split velours (e.g. from cow or calf skin), buckskin and nubuck leather; further also woollen skins and furs (e.g. fur-bearing suede leather).

[0054] The leathers can be of various thicknesses, such as from 0.5 mm to 8 mm, thus, thin leathers, are suitable for garment leather or glove-leather (nappa); leather of medium thickness, is suitable for shoe upper leather, and handbags, or also thick leathers, are for shoe-sole leather, furniture leather, leather for suitcases, for belts and for sport articles; hair-bearing leathers and furs may also be used.

[0055] The leathers obtained by treating with sulfited polyesters can subsequently be further processed, as is customary in the leather industry, by any of the processes of bleaching, colouring, dyeing, fatliquoring, setting to dry, conditioning, staking, milling, tumbling, buffing, pressing, embossing, ironing, finishing with a coating.

[0056] The sulfited polyesters represent a novel non-toxic, partially or entirely renewable alternative to oil-based phenol formaldehyde condensates in the leather industry.

[0057] The sulfited polyesters can be used as re-tanning agents for the treatment of leather outperforming syntans on properties like softness, fullness, and light induced ageing, while resolving the issue of formaldehyde, phenol or bisphenol moieties and in addition enabling for partially or entirely renewable non-toxic starting materials.

[0058] The present invention will be further elaborated by the following non-limiting working examples.

[0059] Examples

[0060] The starting materials used in these examples are commercially available and were used without further purification. A preferred acid catalyst for esterification is sulfuric acid or para-Toluene Sulfonic Acid, abbreviated a pTSA. Nuclear magnetic resonance was measured in a 400 MHz spectrometer. Solid content of aqueous solutions was determined in a Mettler Toledo HG53 Moisture Analyzer. Bis-(3-hydroxy-propyl)-succinate (CAS 1646623-97-3), was synthesized according to: Papageorgiou, G.; Vassiliou, A.; Karavelidis, V.; Koumbis, A.; Bikiaris, D.; Macromolecules 2008, 41(5), 1675-1684.

[0061] Intermediate 1: Ester with Bis-(3-Hvdroxy-PronvD-Succinate and

[0062] Maleic Anhydride

[0063] In a 100 mL 1 neck flask equipped with a water separation device below a reflux condenser 46.8 g bis-(3-hydroxy-propyl)-succinate (M = 234 g / mol; 0.2 mole, 1.00 eq.) were treated with 39.2 g maleic anhydride (M = 98 g / mol, 0.4 mol, 2.00 eq.) at 70°C. The reaction mixture was heated to 120°C - 140°C and stirred for 2 hours.

[0064] 1 g of the viscous reaction mixture was dissolved in 10 mL ethanol and 30 mL water. The pH was measured to be 2.2. Titration with 0.1 N NaOH: 4.65 mL IN NaOH should be needed to neutralize two COOH moieties and 5 mL 0.1 N NaOH were consumed to reach pH = 7. 80 g of a very viscous oil was obtained. M = 430 g / mol.

[0065] 1H-NMR (400 MHz, CDC13): 1.75 - 2.02 (m, 4H, CH2), 2.50 - 2.60 (m, 4H, CH2- C=O), 4,02 - 4.25 (m, 8H, OCH2), 6.25 - 6.28 (m, 2 H, C=C-H), 6.90 - 6.94 (m,

[0066] 2 H, C=C-H), 11.2 (sbr, 2H, COOH). 1,3-Propanediol and succinic acid can be easily sourced biobased, whereas maleic acid has a petrochemical origin. This makes that 10 out of 18 carbons in Intermediate 1 can be biobased. 1: Sulfitation of Intermediate 1 with NaaSaOs

[0067] In a 250 mL 1 neck flask equipped with a reflux condenser, 27.5 g intermediate 1 (M = 430 g / mol; 63.9 mmol) were suspended in 60 mL warm water resulting in two phases. 12.2 g Na2S20s (M = 190 g / mol, 0.035 mol) was added. The two phase suspension was treated with 9.8 g 25% aqueous ammonia solution (144 mmol) raising the pH to 8. The suspension was heated to 80°C for 2 hours: one phase: pH = 7.5. The light yellow solution was acidified with 4 mL of an aqueous solution of 85% formic acid, resulting in a pH of 4.5. An amount of 95 g of a yellow solution was obtained, with a solids content of 38%.

[0068] 1H-NMR (400 MHz, D2O): 1.84 - 1.92 (m, 4H, CH2), 2.36 - 2.94 (m, 10H, CH2- C=O; CH-SCLNa), 4.04 - 4.14 (m, 8H, OCH2).

[0069] During sulfitation, no additional carbons are introduced and therefore the carbon ratio of Example 1 is the same as for Intermediate 1: 10 out of 18 carbons can be biobased. Intermediate 2: Polyester with Propan-1, 3-diol and Succinic Acid In a 250 mL 1 neck flask equipped with a water separation device below a reflux condenser, 76 g propan- 1, 3-diol (M= 76 g / mol; 1 mol = 1.00 eq.) were treated with 88.56 g succinic acid (M = 118 g / mol, 0.75 eq.) and 0.36 g pTSA. The mixture was heated to 140°C — 160°C for 3 hours. An amount of 24 g water (M = 18 g / mol, 1.5 mol) should be distilled off, and 21 g water was obtained. Theoretical yield is 140.9 g, and an amount of 140 g of a yellow oil with low viscosity was obtained; M = 550 g / mol (n = 3).

[0070] 1H-NMR (400 MHz, CDC13): 1.80 - 1.88 (m, 4H, CH2), 1.90 - 1.98 (m, 4H, CH2), 2.56 - 2.64 (m, 12 H, CH2-C=O), 3.00 (sbr, 2H, OH), 3.64 - 3.72 (m, 4H, CH2OH), 4.10 - 4.18 (m, 8H, OCH2), 4.22 - 4.27 (m, 4H, OCH2). 1,3-Propanediol and succinic acid can be easily sourced biobased. This makes that all carbons (24 for n=3) in Intermediate 2 can be biobased.

[0071] with Intermediate 2 (n = 3) and 2 dride

[0072] In a 250 mL 1 neck flask equipped with a reflux condenser, 30 g of intermediate 2 (M= 550 g / mol; 0.054 mol = 1.00 eq.) was treated with 10.7 g maleic anhydride (M = 98 g / mol, 0.108 mol, 2.00 eq.) at 70°C. The reaction mixture was heated to 140°C and stirred for 2 hours.

[0073] 0.31 g of the reaction mass were dissolved in 20 mL of a 1 / 1 mixture of ethanol / water. The pH was 2.5. An amount of 8.3 g of a 0.1 N aqueous sodium hydroxide solution would be required to neutralize two equivalents of COOH groups, and 8.6 g of a 0.1 N aqueous sodium hydroxide solution was required to reach a pH of 7. An amount of 40 g of a viscous oil was obtained. M= 747 g / mol.

[0074] 1H-NMR (400 MHz, CDC13): 1.85 - 1.89 (m, 4H, CH2), 1.90 - 1.98 (m, 4H, CH2), 2.56 - 2.58 (m, 12 H, CH2-C=O), 4.10 - 4.18 (m, 12H, CH2O), 4.10 - 4.18 (m, 4H, OCH2), 6.20 - 6.22 (m, 2 H, C=C-H), 6.28 - 6.30 (m, 2 H, C=C- H), 8.50 (sbr, 2 H, COOH).

[0075] Maleic acid has a petrochemical origin, whereas all carbons in Intermediate 2 can be biobased. This makes that 24 out of 32 (for n=3) carbons in Intermediate 3 can be biobased. Example 2: Sulfitation of Intermediate 3 (n = 3) with NaaSaOs In a 250 mL 1 neck flask equipped with a reflux condenser, 46 g of intermediate 3 (n = 3; M = 747 g / mol; 61.65 mmol) was suspended in 80 mL warm water and treated with 6 mL of an aqueous solution of 25% ammonia to raise the pH to 7. An amount of 11.2 g Na2S20s (M = 190 g / mol, 58.00 mol) was added. The suspension was heated to 80°C for 2 hours, and a one- phase product was obtained with a pH value of 5.0. An amount of 140 g of a yellow solution was obtained, with a solids content of 31%.

[0076] 1H-NMR (400 MHz, D2O): 1.78 - 1.96 (m, 8H, CHa), 2.40 - 2.50 (m, 2H, CHa- C=O), 2.52 - 2.60 (m, 12H, CH2-C=O), 2.80 - 3.15 (m, 2H, CH-SO3Na), 4.00 - 4.16 (m, 16H, OCHa). During sulfitation, no additional carbons are introduced and therefore the carbon ratio of Example 2 is the same as for Intermediate 3: 24 out of 32 (for n=3) carbons can be biobased. Intermediate 4: Polyester with Propan-1, 3-diol and Succinic Acid In a 500 mL 1 neck flask equipped with a water separation device below a reflux condenser, 152.2 g propan- 1, 3-diol (M= 76 g / mol; 2 mol = 1.00 eq.) was treated with 188.9 g of succinic Acid (M = 118 g / mol, 1.6 mol; 0.8eq.) and 0.36 g pTSA. The mixture was heated to 140°C — 160°C for 3 hours. An amount of 57.6 g water (M = 18 g / mol, 3.2 mol) should be distilled off, and an amount of 50 g water was obtained. Theoretical yield is 283.90 g, and 280 g of a yellow oil was obtained. M = 709 g / mol; (C31H48O18).

[0077] 1H-NMR (400 MHz, CDCI3): 1.78 - 1.84 (m, 4H, CH2), 1.92 - 1.98 (m, 6H, CH2), 2.52 - 2.58 (m, 16 H, CH2-C=O), 3.25 (sbr, 2H, OH), 3.62 - 3.66 (m, 4H, CH2OH), 4.10 - 4.14 (m, 12H, OCH2), 4.16 - 4.20 (m, 4H, OCH2). 1,3-Propanediol and succinic acid can be easily sourced biobased. This makes that all carbons (31 for n=4) in Intermediate 2 can be biobased.

[0078] with Intermediate 4 (n = 4) and 2 dride

[0079] In a 250 mL 1 neck flask equipped with a water separation device below a reflux condenser, 140 g of intermediate 4 (M = 709 g / mol, 197.5 mmol = 1 eq.) was treated with 38.7 g maleic anhydride (M = 98 g / mol, 0.395 mol, 2.00 eq.) at 70°C. The reaction mixture was heated to 120°C - 140°C and stirred for 2 hours.

[0080] 1.07 g of the reaction mass was dissolved in 10 mL ethanol and 20 mL water was added, yielding a white suspension with pH = 2.0. In a titration with 0.1 N aqueous sodium hydroxide solution an amount of 30 mL should be needed, and 27.2 mL was consumed. An amount of 164 g of a very viscous oil was obtained (178 g theoretical yield). M = 905 g / mol.

[0081] 1H-NMR (400 MHz, CDC13): 1.86 - 1.92 (m, 6H, CH2), 1.94 - 1.98 (m, 4H, CH2), 2.52 - 2.58 (m, 16 H, CH2-C=O), 4.08 - 4.16 (m, 12H, CH2OH), 4.22 - 4.28 (m, 4H, OCH2), 6.20 (d, J = 2 Hz, 4H, H-C=C-H), 10.42 (sbr, 2H, COOH).

[0082] Maleic acid has a petrochemical origin, whereas all carbons in Intermediate 4 can be biobased. This makes that 31 out of 39 (for n=4) carbons in Intermediate 3 can be biobased. Example 3: Sulfitation of Intermediate 5 (n = 4) with Na2S2Os In a 250 mL 1 neck flask equipped with a reflux condenser, 25 g of intermediate 5 (n = 4; M = 905 g / mol; 27.6 mmol) was suspended in 60 mL warm water. An amount of 5.3 g Na2S20s (M = 190 g / mol, 27.6 mmol) was added. The suspension was treated with 13.8 g of a 25% aqueous ammonia solution (200 mmol) raising the pH to 7, and subsequently the mixture was heated to 90°C for 2 hours, resulting in a one phase product with a pH of 5.6. An amount of 101 g of a yellow solution was obtained, with a solids content of 36.6%.

[0083] 1H NMR in D2O: no olefinic signals identified, new CH and CH2 signals formed, compared to intermediate 5. Complex NMR signals due to regio- isomers.

[0084] During sulfitation, no additional carbons are introduced and therefore the carbon ratio of Example 3 is the same as for Intermediate 5: 31 out of 39 (for n=4) carbons can be biobased. Intermediate 6: Polyester with Bis-(3-Hydroxy-Propyl)-Succinate and 0.5 Equivalents Itaconic Acid

[0085] In a 100 mL 1 neck flask equipped with a water separation device below a reflux condenser, 46.8 g bis-(3-hydroxy-propyl)-succinate (M = 234 g / mol 200 mmol = 1 eq.) was treated with 13 g itaconic acid (M = 130 g / mol, 100 mmol, 0.5 eq.). An amount of 0.3 g pTSA, and 0.6 g 4-methoxyphenol were added. The reaction mixture was heated to 160°C for 1 hour. An amount of 1.8 g water (should be distilled off, and an amount of 1.7 g water was obtained. The theoretical yield is 59.5 g and an amount of 57.9 g of an oil with moderate viscosity was obtained. M = 563 g / mol.

[0086] 1H-NMR (400 MHz, CDC13): 1.74 - 1.85 (m, 4H, CH2), 1.88 - 1.98 (m, 4H, CH2), 2.56 - 2.64 (m, 8H, CH2-C=O), 3.28 - 3.32 (s, 2H CH2-C=O), 3.62 - 3.68 (m,

[0087] 4H, CH2-OH), 4.08 - 4.12 (m, 8H, OCH2), 4.14 - 4.18 (m, 4H, OCH2), 4.40 (sbr, 2H, OH), 5.64 - 5.72 (m, 1H, C=C-H), 6.24 - 6.34 (m, 1H, C=C-H).

[0088] 1,3-Propanediol, succinic acid and itaconic acid can be easily sourced biobased. This makes that all carbons in Intermediate 6 can be biobased. Example 4: Sulfitation of Intermediate 6 with Na2S2Os In a 100 mL 1 neck flask equipped with a reflux condenser, 25 g of intermediate 6 (M = 563 g I mol; 44 mmol) was suspended in 60 mL warm water. An amount of 5.3 g Na2S20s (M = 190 g / mol, 22 mmol) was added. The suspension was treated with 9.8 g a 25% aqueous ammonia solution (144 mmol) raising the pH to 9, and subsequently the mixture was heated to 90°C for 2 hours, resulting in a one phase product with a pH of 8.5. An amount of 91.6 g of a colorless solution was obtained, with a solids content of 33%.

[0089] 1H-NMR (400 MHz, D2O): 1.72 - 1.94 (m, 8H, CH2), 2.60 - 2.66 (m, 8H, CH2-C=O), 2.78 - 3.42 (m, 5H, CH-CH2-C=O, CH2-SO3Na), 3.68 - 3.76 (m, 4H, CH2OH), 4.02 - 4.16 (m, 12H, OCH2).

[0090] During sulfitation, no additional carbons are introduced and therefore the carbon ratio of Example 4 is the same as for Intermediate 6: all carbons can be biobased.

[0091] Intermediate 7: Polyester with Bis-(3-Hydroxy-Propyl)-Succinate and 1.5 Equivalents Itaconic Acid In a 100 mL 1 neck flask equipped with a water separation device below a reflux condenser, 23.4 g bis-(3-hydroxy-propyl)-succinate (M = 234 g / mol, 100 mmol = 1 eq.) was treated with 19.5 g itaconic acid (M = 130 g / mol, 150 mmol, 1,5 eq.). An amount of 0.15 g pTSA, and 0.42 g 4-methoxyphenol were added. The reaction mixture was heated to 160°C for 1 hour. An amount of 3.6 g water (should be distilled off, and an amount of 3.2 g water was obtained. The theoretical yield is 42 g and an amount of 40.1 g of an oil with moderate viscosity was obtained. M = 787 g / mol.

[0092] 1H-NMR (400 MHz, CDC13): 1.75 - 1.98 (m, 8H, CH2), 2.50 - 2.68 (m, 8H, CH2- C=O), 3.20 - 3.28 (m, 6H, CH2-C=O), 4.02 - 4.22 (m, 16H, OCH2), 5.60 - 5.75 (m, 1H, C=C-H), 6.22 - 6.34 (m, 1H, C=C-H), 8.60 (sbr, 2H, COOH).

[0093] 1,3-Propanediol, succinic acid and itaconic acid can be easily sourced biobased. This makes that all carbons in Intermediate 7 can be biobased.

[0094] Example 5: Sulfitation of Intermediate 7 with Na2S2Os

[0095] In a 100 mL 1 neck flask equipped with a reflux condenser, 25 g of intermediate 7 (M = 787 g / mol; 24.8 mmol) was suspended in 60 mL warm water. An amount of 7.1 g Na2S20s (M = 190 g / mol, 37 mmol) was added. The suspension was treated with 6.6 g a 25% aqueous ammonia solution (100 mmol) raising the pH to 8, and subsequently the mixture was heated to 90°C for 2 hours, resulting in a one phase product with a pH of 5.6.

[0096] The solution was acidified with 6 mL of 10% aqueous sulfuric acid solution to reach a pH of 4. An amount of 109 g of a colorless solution was obtained, with a solids content of 29%.

[0097] 1H NMR in D2O: no olefinic signals identified, new CH and CH2 signals formed compared to intermediate 7. Complex NMR signals due to regioisomers.

[0098] During sulfitation, no additional carbons are introduced and therefore the carbon ratio of Example 5 is the same as for Intermediate 7: all carbons can be biobased.

[0099] Example 6: Re-tanning Results

[0100] The novel condensates were tested as re-tanning agents on pelt that had been tanned with chromium sulphate. The re-tanning agents have the role to fill the collagen structures and impose characteristics like softness, grain tightness, and fastness properties. The resulting leathers were analysed and compared with leather re-tanned with syntans.

[0101] Re-tanning was carried out with wet blue, which is an intermediate in leather making derived from the treatment of pickled pelt with 7% chromium sulphate: in a 3.5 L tanning drum 100 g of water and 100 g of bovine wet blue of southern German origin with 1.7 mm strength were treated with 1.2 g sodium formiate and 0.3 g sodium bicarbonate for 90 minutes. The resulting float had a pH of 4.5. 8 g re-tanning agent (referring to the solid content) were added and turning of the tanning drum was continued for 90 minutes. The float was discharged and the leather washed with 200 g water. Afterwards the leather was dried via hang drying over night without vacuum at room temperature.

[0102] The softness of leathers was quantified according to ISO 17235. Here a steel cylinder of a defined size is run into a leather sample with a defined speed and power resulting in an area increase of the leather sample. Larger numbers describe bigger area increase indicating more softness of the leathers.

[0103] Fullness of re-tanned leathers was determined via haptics. Lower numbers indicate better fullness.

[0104] The tightness of the grain is an evaluation of the top layer of the leather once it is bended with two hands. The smoother the layer remains the tighter is the bended leather. The more wrinkles observed, the lower the tightness. Lower numbers indicate better tightness.

[0105] To determine the lightfastness the leathers were exposed to light in a sun tester for 72 h according to ISO 105-B02, also known as the Xenotest. Leather samples were, after exposure to light, evaluated according to blue scale with numbers from 1 to 8. Larger number indicate less colour change and therefore more resistance to light induced ageing.

[0106] To determine the heat induced ageing leathers were exposed to heat at 100°C for 48 h and at 130°C for two hours, according to ISO 105-A02. Leather samples were, after exposure to heat, evaluated according to the grey scale with numbers from 1 to 5. Larger numbers indicate more stability against heat.

[0107] Leathers were re-tanned with examples 1, 2, 3, 4, and 5 and were compared to a leather re-tanned with a commercially available phenolic syntan and a blank, meaning a piece of wet blue, that was just treated with water instead of the poly-condensate. The results are collected in Table 1.

[0108] Table 1: Re-tanning results on wet blue using the sulfited polyesters from Examples 1 to 5, compared to a re-tanning with a phenolic syntan and a blank

[0109] As can be seen in Table 1, all leathers retanned with sulfited polyesters from Examples 1 to 5 showed better softness results in IUP measurement than the leather treated with syntan, as larger numbers describe bigger area increase indicating more softness of the leathers.

[0110] Leathers retanned with sulfited polyesters from Examples 2 and 4 achieved better fullness than the leather treated with syntan. Lower numbers indicate better fullness. The blank leather achieved the lowest performance in fullness.

[0111] Leathers retanned with sulfited polyesters from all examples achieved better results in tightness than the leather treated with syntan, and Example 4 was the best, clearly outperforming the syntan. Lower numbers indicate better tightness. Table 2: Light and heat fastness results of leathers after re-tanning using the sulfited polyesters from Examples 2 and 4, a phenolic syntan, and a blank

[0112] As can be seen in table 2, leathers re-tanned with examples 2 and 4 were significantly better in the light induced ageing test than the leather treated with syntan and also better than the blank, which was made without re-tanning.

[0113] Leathers re-tanned with examples 2 and 4 were significantly better in the heat induced ageing test than the leather treated with syntan and in the same range as the untreated leather piece.

[0114] The free formaldehyde content of the sulfited polyester was measured according to ISO 27587 and was found to be less than 10 ppm. The bisphenols and phenol content of the syntan was measured according to ISO 18218-1 and was found to be 120 ppm for Bisphenol S and below the detection limit for phenol and Bisphenol F.

[0115] The sulfited polyesters of Examples 1 to 5 cannot release formaldehyde and do not contain phenol or bisphenols, because of their different chemical composition. The sulfited polyesters of Examples 4 and 5 contain 4-methoxyphenol as a scavenger, but 4-methoxyphenol is significantly less toxic than phenol.

Claims

CLAIMS1. A process for the manufacture of sulfited polyesters having more than 50% of their carbon atoms coming from sources that are biobased by esterification of unsaturated carboxylic acids or its anhydrides and optionally saturated carboxylic acids or its anhydrides, and polyols at a temperature between 120°C and 180°C and subsequent sulfitation at a pH value between 7 and 9 and at a temperature between 50°C and 120°C and wherein at least one or more of the unsaturated carboxylic acids or its anhydrides and optionally saturated carboxylic acids or its anhydrides are bio-based.

2. A process according to claim 1, wherein the esterification of unsaturated carboxylic acids or its anhydrides and optionally saturated carboxylic acids or its anhydrides, and polyols is done at a temperature between 140°C and 160°C, preferably with a duration of the reaction of between 1 and 3 hours.

3. A process according to claim 1 or 2, wherein the sulfitation reaction is done at a pH value, between 60°C and 100°C and preferably between 70°C and 90°C, preferably with a duration of the reaction of between 1 and 5 hours.

4. A process according to any one of claims 1 to 3, wherein the molar ratio of saturated acids to unsaturated acids ranges from 0:1 to 5:1.

5. A process according to any one of claims 1 to 4, wherein the carboxylic acid, unsaturated and / or saturated are dicarboxylic acids, optionally also monocarboxylic acids in a molar ratio of monocarboxylic acids to dicarboxylic acids of 0:100 to 25:75, optionally also tricarboxylic acids or polycarboxylic acids in a molar ratio of tri- or polycarboxylic acid to dicarboxylic acid of 0:100 to 10:90.

6. A process according any one of claims 1 to 5, wherein the (un)saturated carboxylic acids are selected from the group of bio-based acids.

7. A process according to claim 6 wherein the unsaturated carboxylic acids is selected from the group consisting of glutaconic acid, itaconic acid, citraconic acid and mesaconic acid.

8. A process according to any one of claims 1 to 7, wherein the polyol is selected from the group of biobased polyols comprising 1,2-ethanediol, 1,3- propane-diol, glycerol, eythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, galactitol, fucitol, iditol, inositol, volemitol, isomalt, maltitol, lactitol.

9. Sulfited polyesters obtainable by the process as defined in any one of claims 1 to 8.

10. Sulfited polyesters according to claim 9 wherein the degree of sulfitation is 95% or more.

11. Sulfited polyesters according to claim 9 or 10, wherein the concentration of free formaldehyde, bisphenols and phenol is below 2 ppm.

12. Sulfited polyesters according to any of claims 9 to 11 wherein more than 50% of the carbon atoms come from sources that are biobased.

13. The use of sulfited polyesters preferably as defined in any one of claims 9 to 12 as a re-tanning agent for the treatment of leather, pre-tanned leather, tanned leather, pelts, skins, hides, leather intermediate products or non-finished leather.

14. The use as defined in claim 13 in an amount of between 2% and 15%, and preferably in an amount of between 4% and 12%, and most preferably in an amount of between 6% and 10%, wherein the percentages refer to the weight percentage of the non-volatile part of the sulfited polyesters compared to the weight of the leather.

15. Process for re-tanning of pre-tanned leather, tanned leather, pelts, skins, hides, leather intermediate products or non-finished leather using a sulfited polyester preferably as defined in any one of claims 9 to 12 as retanning agent.

16. Leather, obtainable by the process of claim 15.

17. Leather according to claim 16 having a good fullness, tightness, good softness according to ISO 17235, heat resistance according to ISO 105- A02 and good lightfastness according to IS0105-B02 and / or to IS0105-B02, wherein good softness is meant to be 3.0 and wherein a good heat resistance is meant to be 3.5 or above on grey scale from 1 to 5 and wherein a good lightfastness is meant to be 6 or above on a grey scale from 1 to 8.

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