Formaldehyde-free aromatic syntan and method for producing

Introduction

[1] Formaldehyde emission is an issue for leather since polymers based on formaldehyde are commonly used in leather manufacturing. These polymers typically comprises unreacted formaldehyde moreover during the lifetime of these polymers additional formaldehyde is formed. Considering formaldehyde is classified as a Carcinogen category 1 B “presumed human carcinogen” and germ cell mutagen category 2 (ECHA, European Chemical Agency). For this reason, the use of formaldehyde is regulated. For example based on the current EU regulations, for leather components for toys, a limit of 30 mg/kg is in place (tested in accordance with EN ISO 17226-1). Consumer leather articles other than baby articles have a limit of 75 mg/kg with the similar methods. There are also limits on formaldehyde for EU eco labels for clothing (< 20 mg/kg for infant and children’s products, < 30 mg/kg and for products in direct contact with the skin and < 75 mg/kg for other than clothing and textile products).

[2] Over the years, commercially an even lower level of formaldehyde emissions after retanning of leather is required. Several leather auxiliary chemicals used in leather manufacturing are a source of formaldehyde.

[3] Aromatic syntans are one of the important group of leather auxiliary chemicals during the retanning or wet-end process of leather process. Aromatic syntans are the retanning agents, which modify the haptic properties of the leather and give the required softness and fullness to the leathers during the retanning. In general aromatic syntans are condensation polymers formed from aromatic compounds with phenolic hydroxy groups with formaldehyde where urea is also optionally used (Ammenn et al., JALCA, Vol. 110, p349, 2015). Formaldehyde is an inevitable starting material in the current manufacturing processes of aromatic syntans. Formaldehyde based aromatic syntans are generally synthesized with an excess of water to keep the viscosity low.

[4] Amino resins are another group of leather auxiliary chemicals that are commonly used during the retanning process. Amino resins help the leathers to fill the loosely parts of the leather and to achieve the required grain tightness to the grain side of the leathers. Common amino resins are synthesized by the condensation polymerization of dicyandiamide and melamine with formaldehyde. In this regard, there are alternatives available based on glyoxal as aldehyde. These glyoxal based amino resins are marketed as formaldehyde-free retanning agents. DD-001 is one such product marketed by Smit&Zoon in the market. These retanning agents are claimed as zero formaldehyde contributors because no formaldehyde is used in the manufacturing process.

[5] There are two important types of aromatic syntans that are sold in the market: (i) Phenolsulfonic acid based syntans and (ii) dihydroxy diphenyl sulfone based syntans (or sulfone syntans). Both types of syntans may further comprise phenol. Best in class aromatic syntans of type (i) have emissions of 5-10 mg/kg on wet blue (WB) leathers (chrome tanned leathers) and 10-20 mg/kg on wet white (WW) leathers when applied at 10 and 20 wt.% in WB and WW respectively. Note that these emissions increase or decrease by varying the amount of syntan on the leather. Best in class aromatic syntans of type (ii) have emissions of 0 to 4 mg/kg on WB and 2 to 4 mg/kg on WW leathers when applied at 10 and 20 wt% in WB and WW respectively. Sulfone syntans are offering very low formaldehyde emission in the both WB and WW leathers. With respect to the formaldehyde emissions, the sulfone syntans are good alternative despite using formaldehyde as starting material.

[6] However sulfone syntans have the drawback of the presence of big amounts of bisphenol S, in the range of 20.000 to 50.000 ppm. Bisphenol S has 90-100% uptake on the leathers. When applying sulfone syntans when manufacturing leather, the resulting leathers have bisphenol S in the range of 2000 to 5000 ppm in WB and 4000 to 10000 ppm in WB leathers when applied at 10 and 20 wt.% respectively. EU is reviewing the bisphenol S as reprotoxic B which means the chemical has potential toxicity for the reproduction health. Proposals are under review of the ECHA to limit the bisphenol S in chemicals and end products well below the levels present in sulfone syntans and leather manufactured with sulfone syntans.

[7] In the class of amino resins there are formaldehyde-free retanning agents are available. However there are no formaldehyde-free alternatives are available in the case of aromatic syntans. Therefore there is a need for aromatic syntans that have low or no formaldehyde content or emission and a low level of bisphenol S. Moreover there is a need for aromatic syntans that are versatile in their use and provide for good leather quality.

Summary of the invention

[8] The inventors surprisingly found that optimal leather (re)-tanning can be obtained by using a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea, wherein the aldehyde compound is selected from the list consisting of glyoxal, glyoxal sodium bisulphite, propanedial, butanedial, pentanedial, glyoxylic acid, 3-oxopropanoic acid, 4-oxobutanoic acid, 5-oxopentanoic acid and any combination thereof, and wherein the sulfonated phenolic compound is selected from the list consisting of sulfonated phenol, cresol, catechol, resorcinol, hydrochinon and any combination thereof. This condensate does not comprise formaldehyde and therefore the leather retanned with this condensate has no emission of formaldehyde. Also considering no dihydroxy diphenyl sulfone is used for the condensate only very low levels of bisphenol S are present in the condensate and in the leather.

[9] The inventors demonstrated excellent leather properties for leather retanned with the inventive condensate. The condensate provided for leather with a high resistance to heat yellowing and high light fastness. With the inventive condensate excellent haptic properties can be obtained. Resistance to heat yellowing, high light fastness and/or haptic properties are improved over formaldehyde based syntans. Moreover haptic properties of the leather can be varied as a function of specific properties of the inventive condensate and as a function of related synthesis conditions. One of these properties is a sufficient high molecular weight which is needed for good retanning. At the same time the solubility in water and related storage stability should not be affected by this higher molecular weight.

[10] The inventive condensate is fully dissolvable in water and no precipitates form upon storage. Such dissolvability is important for retanning considering undissolved condensate does not contribute to the retanning effect and is not accepted in the market. Furthermore the condensate has a low amount of unreacted sulfonated phenolic compound as this unreacted sulfonated phenolic compound has less retanning effect, moreover in general a high amount of unreacted material relates to an undesirable low molecular weight of the condensate. Also the level of unreacted free phenolic compounds is low, which is beneficial as such compounds in general are toxic and undesirable in syntans.

[11] In the art only dihydroxy diphenyl sulfone compounds were developed to lower the formaldehyde emission of aromatic syntans. There was no suggestion to use other aldehydes for the production of aromatic syntans such as the aldehydes of the invention, as it was believed that such aldehyde compounds do not provide for sufficient high molecular weight and for good leather properties. Although the reaction between aldehyde and sulfonated phenolic compound is not an equilibrium reaction and therefore the water formation does not limit the conversion, the complexation of di-aldehydes in aqueous solutions was thought to stand in the way of the formation of condensates that are suitable for retanning.

[12] In remote fields polymers of a di-aldehyde and phenol are suggested. For example US 2011/0184104 A1 claims a process for the preparation of phenolsulfonic acid - aldehyde condensates and their use as drying agents. Although a variety of aldehydes are claimed, these aldehydes are not enabled as only examples with formaldehyde are provided. US 2004/0014824 A1 described a process for the preparation of alkylphenol glyoxal resins and their use as demistifiers. The condensation process uses an aromatic solvent and the method comprises a second alkoxylation step providing for a different polymer. Non-aqueous solvents are not preferred in leather manufacturing. WO 01/94435 A1 is in the field of coatings for electronics and printed circuits and concerns glyoxal-phenolic condensates with enhanced fluorescence. WO 01/94435 A1 is silent on phenolsulfonic acid and the resulting condensate has a molecular weight below 700. The molar ratio glyoxal/phenol is about 0.2 and a considerable amount of phenol is present after the reaction.

[13] For the first time, the current invention describes a condensation polymerization process to manufacture condensates suitable for the retanning process by employing aldehydes other than formaldehyde. Surprisingly, by keep the water level low during the reaction a condensate could be obtained that is suitable for retanning having a sufficient molecular weight. The inventors found that keeping the water level low is essential to obtain a suitable condensate for retanning of leather. It is believed the water removal is necessary to steer the complexation of di-aldehydes in aqueous solutions in such a way that the di-aldehydes are available for the condensate formation. For the current standard being formaldehyde based aromatic syntans the reaction is performed at high water levels to keep the viscosity low and prevent a runaway reaction, Lowering the water content is therefore against common practice. [14] In addition the inventors found that under certain reaction circumstances undesirable precipitate could form, either directly or after storage of the condensate. The inventors discovered that only within a specific molar ratio of aldehyde compound to sulfonated phenolic compound and phenolic compound when present precipitate formation could be prevented. Not bound by theory it is believed that unreacted phenolsulfonic acid and phenol may be the cause of the precipitation. Therefore also a too high water content during the reaction may affect the stability.

[15] Optionally the condensation comprises a second reaction step. In this step the condensate can be further tailored, for example by introducing phenolic compound that are not sulfonated in the condensate. Adding a phenolic compound is known from formaldehyde based aromatic syntans. These phenolic compounds affect the retanning properties and therefore can be used to tailor the retanning properties. Moreover urea may be provided during the first and/or second reaction step. Also adding urea is known from formaldehyde based aromatic syntans. Also urea affect the retanning properties and therefore can be used to tailor the retanning properties.

Detailed description

[16] In this document and in its claims, the verb "to comprise" and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one”.

[17] ppm stands for parts per million and is expressed in weight so concerns weight per weight. 10,000 ppm equals 1 wt.%.

[18] In a first embodiment the invention concerns a method for manufacturing of a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea suitable for retanning of leather wherein in a first reaction step the sulfonated phenolic compound is reacted with the aldehyde compound and optionally with urea to form the condensate wherein during this reaction step:

- the pH is below 1 ,

- the reaction temperature is between 50°C and 120°C,

- the water level is below 25 wt.% based on the weight of the total reaction mass,

- the total amount of sulfonated phenolic compound and aldehyde groups provided is in a molar ratio of sulfonated phenolic compound to aldehyde groups of between 1.0:1.0 and 1 .0:3.0,

- the total amount of urea provided when provided is less than 100 mole% of the total amount of aldehyde compound provided, and the aldehyde compound is provided to the phenolic compound in at least two steps, wherein the aldehyde compound is selected from the list consisting of glyoxal, glyoxal sodium bisulphite, propanedial, butanedial, pentanedial, glyoxylic acid, 3-oxopropanoic acid, 4- oxobutanoic acid, 5-oxopentanoic acid and any combination thereof, and wherein the sulfonated phenolic compound is selected from the list consisting of sulfonated phenol, sulfonated cresol, sulfonated catechol, sulfonated resorcinol, sulfonated hydroquinone and any combination thereof.

[19] In a further embodiment the invention concerns a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea and /or a phenolic compound for retanning of leather having

-a weight average molecular weight of at least 3000 Dalton,

-an amount of unreacted sulfonated phenolic compound of less than 10 wt.% based on total weight of the condensate, and

- an amount of unreacted phenolic compound of less than 1000 ppm based on total weight of the condensate, wherein the aldehyde compound is selected from the list consisting of glyoxal, glyoxal sodium bisulphite, propanedial, butanedial, pentanedial, glyoxylic acid, 3-oxopropanoic acid, 4- oxobutanoic acid, 5-oxopentanoic acid and any combination thereof and wherein the sulfonated phenolic compound is selected from the list consisting of sulfonated phenol, sulfonated cresol, sulfonated catechol, sulfonated resorcinol, sulfonated hydroquinone and any combination thereof, and wherein the phenolic compound when present is selected from the list consisting of phenol, cresol, catechol, resorcinol, hydroquinone and any combination thereof, and wherein the amount of urea when present in the condensate is less than 100 mole% of the amount of aldehyde compound in the condensate, and wherein the amount of phenolic compound when present in the condensate is less than 50 mole% of the amount of sulfonated phenolic compound in the condensate.

[20] In another embodiment the invention concerns an aqueous composition for retanning of leather having a pH from 2.0 to 7.0 comprising

- 2 - 70 wt.% based on total weight of the aqueous composition of the water soluble condensate,

- an amount of bisphenol S lower than 100 ppm based on total weight of the aqueous composition,

- an amount of bisphenol F lower than 100 ppm based on total weight of the aqueous composition,

- an amount of formaldehyde lower than 30 ppm based on total weight of the aqueous composition, and

- optionally, 0.05 - 10.0 wt.% based on total weight of the aqueous composition of a buffering agent, preferably dicarboxylic acid, preferably wherein the dicarboxylic acid is selected from the list consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and any combination therefore, more preferably the dicarboxylic acid is a mixture of adipic acid, glutaric acid and succinic acid (an AGS mixture).

[21] The invention furthermore concerns a water dissolvable powder for retanning of leather comprising

- 70 - 100 wt.% based on total weight of the powder of the water soluble condensate,

- an amount of bisphenol S lower than 200 ppm based on total weight of the powder,

- an amount of bisphenol F lower than 200 ppm based on total weight of the powder,

- an amount of formaldehyde lower than 60 ppm based on total weight of the powder, and

- optionally, 0.10 - 20.0 wt.% based on total weight of the powder of a buffering agent, preferably dicarboxylic acid, preferably wherein the dicarboxylic acid is selected from the list consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and any combination therefore, more preferably the dicarboxylic acid is a mixture of adipic acid, glutaric acid and succinic acid (an AGS mixture).

[22] The invention also concerns the use of the water soluble condensate or the aqueous retanning composition or the water dissolvable powder of the invention for retanning of leather. Moreover the invention concerns a method for retanning of leather wherein leather is contacted in an aqueous solution with the water soluble condensate or the aqueous retanning composition or the water dissolvable powder of the invention. Also the invention concerns leather obtained by the method for retanning of leather or leather comprising the water soluble condensate of the invention.

[23] When ‘the invention’ is mentioned in this document this concerns the method for manufacturing a condensate of the invention, the condensate of the invention, the aqueous composition of the invention, the water dissolvable powder of the invention, the use of the invention, the method for retanning leather of the invention and/or the leather of the invention.

[24] When for this application the amount or molar ratios of phenolic compound, sulfonated phenolic compound, urea and aldehyde compound is mentioned for the condensate this concerns the sum of reacted and unreacted compound. Moreover even though some or all of these compounds change upon reaction, for example the aldehyde group of the aldehyde compound disappear upon reaction, the reacted compound is counted and named as its unreacted counterpart for the amount and/or molar ratio in the condensate.

Method for manufacturing of a condensate suitable for retanning of leather

First reaction step

[25] The condensation reaction is best under acid conditions and therefore in the method for manufacturing of a condensate the pH is below 1 in the first reaction step and second reaction step when present. Preferably the pH is below 0, more preferably below -1. Typically the acid conditions are obtained by providing the sulfonated phenolic compound as the sulfonation is with a molar excess of sulphuric acid and the remnant of the unreacted sulphuric acid provides for a low pH.

[26] The reaction temperature during the first reaction step is between 50°C and 120°C, preferably between 50°C and 100°C, more preferably between 55°C and 90°C, most preferably between 60°C and 80°C. Through reaction temperature the properties of the condensate towards retanning may be steered. At low reaction temperatures the reaction mixture may be too viscous. The reaction time of the first reaction step preferably is between 10 and 1200 minutes, more preferably between 50 and 800 minutes, even more preferably between 100 and 500 minutes. Any water removal step forms part of the reaction time.

[27] The total amount of sulfonated phenolic compound and aldehyde groups provided is in a molar ratio of sulfonated phenolic compound to aldehyde groups of between 1.0:1.0 and 1 .0:3.0. Preferably the molar ratio is between 1.0:1.05 and 1.0:2.5, more preferably between 1.0:1.1 and 1.0:2.0. Within these ratios a condensate with sufficient molecular weight can be obtained that does not precipitate in a watery solution upon storage. The total amount is the total amount provided during the first reaction step.

[28] Urea is used in the condensate suitable for retanning of leather for modifying the properties of the core structure which is the condensate of an aldehyde compound and a sulfonated phenolic compound. Such modifications are known from formaldehyde based systems (Ammenn et al., JALCA, Vol. 110, p349, 2015). Considering urea is used to modify the core structure and does not form the core structure as in amino resins the amount of urea has an upper limit. As urea reacts with the aldehyde compound stoichiometrically the total amount of urea provided in the first reaction step when provided is less than 100 mole% of the total amount of aldehyde compound provided, preferably less than 75 mole%, more preferably less than 50 mole%, most preferably less than 25 mole%.

[29] For the method for manufacturing of a condensate preferably first the sulfonated phenolic compound is provided in the first reaction step, optionally together with urea. Subsequently the aldehyde compound is provided to the phenolic compound in at least two steps, preferably in at least four steps, more preferably in at least six steps. By adding the aldehyde compound in different steps the temperature of the reaction mixture is better controllable. Also rapid viscosity increase and relating to a possible run-away reaction is prevented. Moreover upon water removal the unreacted aldehyde compound tends to be removed as well together with the water which is undesirable as it affects the reaction. This is especially the case when water is removed through distillation. When the aldehyde compound is provided in steps, the aldehyde compound first can react at a relative low water content. Subsequently the water that is formed upon condensation can be removed without removing the aldehyde compound as it already reacted. After that new aldehyde compound can be added.

[30] In a preferred embodiment water is removed during the first reaction step, preferably by distillation. Preferably the water is removed until the water level is below 25 wt.% based on the weight of the total reaction mass, more preferably below 23 wt.%, even more preferably below 20 wt.%. Preferably water removal starts when the water level exceeds 20 wt.% based on the weight of the total reaction mass, more preferably 23 wt.%, even more preferably 25 wt.%, most preferably 30 wt.%. The inventors believe the low water content is necessary to to steer the complexation of di-aldehydes in aqueous solutions in such a way that the di-aldehydes are available for the condensate formation. In one embodiment the amount of aldehyde compound provided in each step is such that the water level stays below 30 wt.% based on the weight of the total reaction mass, more preferably 25 wt.%, most preferably 23 wt.%. In a preferred embodiment the water removal is independent of the moment of aldehyde compound addition. In a preferred embodiment water is removed in two or more steps during the first reaction step, preferably in two or more steps during the first reaction step by distillation.

[31] Preferably the water level during the first reaction step is below 25 wt.% based on the weight of the total reaction mass, more preferably below 23 wt.% even more preferably below 20 wt.% most preferably below 15 wt.%. Preferably the water level during the first reaction step is above 0 wt.% based on the weight of the total reaction mass, more preferably above 10 wt.% even more preferably above 15 wt.%.

[32] Water removal may be batch-wise or continuous, preferably batch-wise. When water is removed, preferably only small amounts of the reaction compounds are removed together with the water, such as less than 10 wt.% of reaction compounds are removed based on the amount of water removed, more preferably less than 5 wt.%, even more preferably no amounts are removed. Preferably water is removed by distillation, membrane separation, falling film evaporation or adsorption, preferably by distillation, more preferably by distillation under reduced pressure. A preferred reduced pressure is below 0.5 bar, more preferably below 0.3 bar, even more preferably below 0.2 bar. Water is preferably removed at the reaction temperature.

[33] Preferably for the method for manufacturing of a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea suitable for retanning of leather the weight average molecular weight of the formed condensate is at least 3000 Dalton, preferably at least 5000 Dalton, most preferably at least 7000 Dalton. Preferably the weight average molecular weight of the formed condensate is at most 50,000 Dalton, more preferably at most 30,000 Dalton, most preferably at most 20,000 Dalton. In a preferred embodiment the weight average molecular weight of the formed condensate is in the range of 3000 - 50,000 Dalton, more preferably in the range of 5000 - 30,000 Dalton, most preferably in the range of 7000 - 20,000 Dalton.

[34] In a preferred embodiment for the method for manufacturing of a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea suitable for retanning of leather no phenolic compound is provided during the first reaction step, more preferably no lignin is provided during the first reaction step. We note that a phenolic compound is not a sulfonated phenolic compound. Preferably the condensate of the invention does not comprise lignin. Optional second reaction step

[35] To further tailor the condensate optionally a second reaction step is performed after the first reaction step. During this second reaction step an aldehyde compound, a phenolic compound and/or urea is provided to the reaction product of the first reaction step and when the second step is present the condensate formed in the method for manufacturing of a condensate is the reaction product of the second step. This condensate concerns a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea and/or a phenolic compound. As for the urea the phenolic compound alter the product properties of the condensate and may be introduced to tailor the retanning properties of the condensate.

[36] The reaction temperature during the second reaction step is between 50°C and 120°C, preferably between 50°C and 100°C, more preferably between 55°C and 90°C, most preferably between 60°C and 80°C. Through reaction temperature the properties of the condensate towards retanning may be steered. The reaction time of the second reaction step preferably is between 10 and 600 minutes, more preferably between 20 and 200 minutes, even more preferably between 40 and 100 minutes. Any water removal step forms part of the reaction time.

[37] Preferably the water level during the second reaction step is below 25 wt.% based on the weight of the total reaction mass, more preferably below 23 wt.% even more preferably below 20 wt.% most preferably below 15 wt.%. Preferably the water level during the second reaction step is above 0 wt.% based on the weight of the total reaction mass, more preferably above 10 wt.% even more preferably above 15 wt.%. In a preferred embodiment water is removed during the second reaction step, preferably by distillation, membrane separation, falling film evaporation or adsorption, preferably by distillation, more preferably by distillation under reduced pressure. A preferred pressure is below 0.5 bar, more preferably below 0.3 bar, even more preferably below 0.2 bar. Water is preferably removed at the reaction temperature.

[38] . In one embodiment water removal starts when the water level exceeds 20 wt.% based on the weight of the total reaction mass, more preferably 23 wt.%, even more preferably 25 wt.%, most preferably 30 wt.%. Preferably the water is removed until the water level is below 25 wt.% based on the weight of the total reaction mass, more preferably below 23 wt.%, even more preferably below 20 wt.%. In a preferred embodiment the water removal is independent of the moment of aldehyde compound addition.

[39] Also for the second reaction step care should be taken that directly after addition of the aldehyde compound and/or phenolic compound the molar ratio of the unreacted phenolic compound to aldehyde groups present on unreacted aldehyde compound is within boundaries as to prevent precipitation of the condensate during storage. Directly after addition of the aldehyde compound and/or phenolic compound the molar ratio of the unreacted phenolic compound to aldehyde groups present on unreacted aldehyde compound is therefore between 1.5:1.0 and 1.0:3.0, preferably between 1.25:1 and 1.0:3.0, more preferably between 1.25:1 and 1.0:1.0. In one preferred embodiment the aldehyde compound, the phenolic compound and/or the urea is provided in at least two steps, preferably at least three steps. For each of these additions directly after addition of the aldehyde compound and/or phenolic compound the molar ratio of the unreacted phenolic compound to aldehyde groups present on unreacted aldehyde compound is therefore between 1.5:1.0 and 1.0:3.0, preferably between 1.25:1 and 1 .0:3.0, more preferably between 1.25:1 and 1.0:1.0.

[40] For this second reaction step the amount of urea in the condensate is less than 100 mole% of the total amount of aldehyde compound in the condensate, preferably less than 75 mole%, more preferably less than 50 mole%, most preferably less than 25 mole%. The condensate concerns the condensate formed during this second reaction step. For this second reaction step the amount of phenolic compound in the condensate is less than 50 mole% of the amount of sulfonated phenolic compound in the condensate, preferably less than 40 mole%, more preferably less than 30 mole%, most preferably less than 20 mole%. Again the condensate concerns the condensate formed during this second reaction step.

Standardisation

[41] In a preferred embodiment after the first reaction step or after the second reaction step when present the condensate is standardized. The standardization is according to industry standards for aromatic syntans. Preferably after the first reaction step or after the second reaction step when present the condensate is brought to a pH range from 2.0 to 7.0, preferably to a pH range from 3.0 to 6.0, most preferably from 3.5 to 5.0. Preferably the condensate is brought to a pH range by providing NaOH. Preferably after the first reaction step or after the second reaction step when present the condensate is brought to a water content of 30 - 98 wt.% based on total weight of the condensate, more preferably to a water content of 40 - 80 wt.% based on total weight of the condensate, even more preferably to a water content of 50 - 70 wt.% based on total weight of the condensate. In a preferred embodiment after the first reaction step or after the second reaction step when present the condensate is brought to a solid content of 20 - 70 wt.% based on total weight of the condensate, more preferably to a solid content of 30 - 60 wt.% based on total weight of the condensate, even more preferably to a water content of 35 - 50 wt.% based on total weight of the condensate.

[42] Typically an aromatic syntan is combined with a buffering agent. In a preferred embodiment after the first reaction step or after the second reaction step when present 0.05 - 10.0 wt.% based on total weight of the condensate of a buffering agent is provided, preferably wherein the buffering agent is a dicarboxylic acid, preferably wherein the dicarboxylic acid is selected from the list consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and any combination therefore, more preferably the dicarboxylic acid is a mixture of adipic acid, glutaric acid and succinic acid (an AGS mixture).

Aldehyde compound

[43] For the invention the aldehyde compound is selected from the list consisting of glyoxal, glyoxal sodium bisulphite, propanedial, butanedial, pentanedial, glyoxylic acid, 3-oxopropanoic acid, 4-oxobutanoic acid, 5-oxopentanoic acid and any combination thereof. Preferably the aldehyde compound is selected from the list consisting of glyoxal, glyoxal sodium bisulphite, glyoxylic acid and any combination thereof, more preferably the aldehyde compound is glyoxal and/or glyoxylic acid, even more preferably glyoxal. An aldehyde compound may comprise more than one aldehyde group. Unreacted aldehyde compound or aldehyde groups has meaning that the aldehyde compound or aldehyde groups did not (yet) react with a phenolic compound.

Phenolic compound

[44] For the invention the phenolic compound is selected from the list consisting of phenol, cresol, catechol, resorcinol, hydroquinone and any combination thereof. Preferably the phenolic compound is phenol and/or cresol, more preferably phenol. The phenolic compound may be present during the reaction steps in unreacted form, which has meaning that the phenolic compound did not react with a aldehyde compound. Phenolic compounds are known in the art and concerns compounds having an aromatic ring provided with a hydroxyl group. As for urea phenolic compounds are sometimes present in aromatic syntans to modify the retanning properties of the condensate. Considering that too much phenolic compound, when compared to the amount of sulfonated phenolic compound, affects the water dissolvability negatively, typically the amount of phenolic compound provided and present in the condensate is lower than that of sulfonated phenolic compound.

Sulfonated phenolic compound

[45] For the invention the sulfonated phenolic compound is selected from the list consisting of sulfonated phenol, sulfonated cresol, sulfonated catechol, sulfonated resorcinol, sulfonated hydroquinone and any combination thereof. Preferably the sulfonated phenolic compound is phenolsulfonic acid and/or sulfonated cresol, more preferably sulfonated phenol. The sulfonated phenolic compound may be present during the reaction steps in unreacted form, which has meaning that the sulfonated phenolic compound did not react with a aldehyde compound.

[46] Sulfonated phenolic compounds are known in the art and point to a HSO3 group that is attached to the aromatic ring of the phenolic compound. Typically sulfonated phenolic compounds are synthesized by reacting the phenolic compound with a small molar excess of sulfuric acid. In a preferred embodiment the sulfonated phenolic compound is obtained by reacting the phenolic compound with a molar excess of sulfuric acid, preferably at a temperature in the range of 80°C - 120°C. Preferably the molar ratio of phenolic compound to sulfuric acid is between 1.0:1.0 and 1.0:1.3, more preferably between 1.0:1.05 and 1.0:1.2, most preferably between 1 .0:1 .05 and 1 .0:1 .1 .

[47] In a preferred embodiment of the invention the sulfonated phenolic compound is sulfonated phenol, the phenolic compound when present is phenol and the aldehyde compound is glyoxal and/or glyoxylic acid. Condensate for retanning of leather

[48] The invention also concerns a condensate of an aldehyde compound and a sulfonated phenolic compound and optionally urea and /or a phenolic compound for retanning of leather. A condensate is the product of a condensation reaction. The condensate for retanning of leather is a liquid or a water-dissolvable solid. Preferably at 25°C the condensate for retanning of leather is a liquid or a water-dissolvable solid. The weight average molecular weight of the condensate is at least 3000 Dalton, preferably at least 5000 Dalton, most preferably at least 7000 Dalton. Preferably the weight average molecular weight of the condensate is at most 50,000 Dalton, more preferably at most 30,000 Dalton, most preferably at most 20,000 Dalton. In a preferred embodiment the weight average molecular weight of the condensate is in the range of 3000 - 50,000 Dalton, more preferably in the range of 5000 - 30,000 Dalton, most preferably in the range of 7000 - 20,000 Dalton. A too high molecular weight affect the dissolutions properties negatively whilst a too low molecular weight affects the retanning properties negatively.

[49] The condensate has a molecular weight distribution. A molecular weight distribution describes the relationship between the number of moles of each polymer species (Ni) and the molar mass (Mi) of that species. The molecular weight distribution can be measured by chromatography as size exclusion chromatography (SEC) also named gel permeation chromatography (GPC). Representative molecular weight values as the weight-average molecular weight (Mw), number average molecular weight (Mn), minimum molecular weight, maximum molecular weight, molecular weight range and/or peak molecular weight can be derived from the molecular weight distribution. The weight average molecular weight Mw = Si Ni • Mi ² / Si Ni • Mi . The representative molecular weight may be expressed in Da (Dalton) or in kg/mol (kilogram I mol). The peak molecular weight is the molecular weight of the highest peak in the molecular weight distribution. The molecular weight range is the range from the minimum molecular weight to the maximum molecular weight. In a preferred embodiment the weight average molecular weight is determined by gel permeation chromatography, preferably wherein the molecular weight distribution is determined by gel permeation chromatography and the weight average molecular weight is calculated based on the measured molecular weight distribution. Suitable GPC columns for the separation of sulfonated polymers in aqueous solutions are known in the art. Also suitable calibration standards are known in the art.

[50] The amount of unreacted sulfonated phenolic compound in the condensate is less than 10 wt.% on total weight of the condensate, preferably less than 8 wt.%, more preferably less than 5 wt.%. Unreacted sulfonated phenolic compound does not contribute to the retanning effect, moreover a large amount of unreacted sulfonated phenolic compound is an indicator that the reaction did not reach completion. Also unreacted sulfonated phenolic compound may be a cause of precipitation. Preferably the amount of unreacted sulfonated phenolic compound is determined by HPLC. Preferably by the method of example 14. [51] The amount of unreacted phenolic compound in the water soluble condensate is below 1000 ppm on total weight of the condensate, preferably below 500 ppm, more preferably below 300 ppm, even more preferably below 150 ppm, even more preferably below 100 ppm, most preferably below 50 ppm. Preferably the amount of unreacted phenolic compound is determined by HPLC. Preferably by the method of example 14. Phenol is toxic and therefore not preferred in the water soluble condensate.

[52] The amount of urea in the condensate when present in the condensate is less than 100 mole% of the amount of aldehyde compound in the condensate, preferably less than 75 mole%, more preferably less than 50 mole%, most preferably less than 25 mole%. The presence of urea is explained in a previous paragraph of this document.

[53] The amount of phenolic compound in the condensate when present in the condensate is less than 50 mole% of the amount of sulfonated phenolic compound in the condensate, preferably less than 40 mole%, more preferably less than 30 mole%, most preferably less than 20 mole%.

[54] In a preferred embodiment the amount of sulfonated phenolic compound and aldehyde groups in the water soluble condensate is in a molar ratio of sulfonated phenolic compound to aldehyde groups of between 1 .0:1 .0 and 1 .0:3.0, preferably the molar ratio is between 1 .0:1 .05 and 1.0:2.5, more preferably between 1.0:1.1 and 1.0:2.0. Preferably the aldehyde compound has 2 aldehyde groups and the amount of sulfonated phenolic compound and aldehyde compound in the water soluble condensate is in a molar ratio of sulfonated phenolic compound to aldehyde compound of between 1.0:0.5 and 1.0:1.5, preferably the molar ratio is between 1.0:0.53 and 1.0:1.25, more preferably between 1.0:0.55 and 1.0:1.0; or the aldehyde compound has 1 aldehyde group and the amount of sulfonated phenolic compound and aldehyde compound in the water soluble condensate is in a molar ratio of sulfonated phenolic compound to aldehyde compound of between 1.0:1.0 and 1.0:3.0, preferably the molar ratio is between 1.0:1.05 and 1.0:2.5, more preferably between 1.0:1.1 and 1.0:2.0.

[55] In case phenol is present in preferably the amount of the sum of sulfonated phenolic compound and phenolic compound and the aldehyde groups in the water soluble condensate is in a molar ratio of sulfonated phenolic compound + phenolic compound to aldehyde groups of between 1.0:1.0 and 1.0:3.0, preferably the molar ratio is between 1.0:1.05 and 1.0:2.5, more preferably between 1.0:1.1 and 1.0:2.0. Preferably the aldehyde compound has 2 aldehyde groups and the amount of sulfonated phenolic compound and aldehyde compound in the water soluble condensate is in a molar ratio of sulfonated phenolic compound + phenolic compound to aldehyde compound of between 1.0:0.5 and 1.0:1.5, preferably the molar ratio is between 1.0:0.53 and 1.0:1.25, more preferably between 1.0:0.55 and 1.0:1.0; or the aldehyde compound has 1 aldehyde group and the amount of sulfonated phenolic compound + phenolic compound and aldehyde compound in the water soluble condensate is in a molar ratio of sulfonated phenolic compound to aldehyde compound of between 1.0:1.0 and 1.0:3.0, preferably the molar ratio is between 1.0:1.05 and 1.0:2.5, more preferably between 1.0:1.1 and 1.0:2.0. [56] In a preferred embodiment the water soluble condensate is obtained or obtainable by the method for manufacturing of a condensate suitable for retanning of leather. In a preferred embodiment the properties of the condensate as described in the above paragraphs also apply for the condensate formed in the method for manufacturing of a condensate suitable for retanning of leather.

[57] In a preferred embodiment the water soluble condensate has a water content below 25 wt.% based on total weight of the condensate, more preferably below 23 wt.%, even more preferably below 20 wt.%. In a preferred embodiment the water soluble condensate has a dry matter content above 70 wt.% based on total weight of the condensate, more preferably above 75 wt.%, even more preferably above 80 wt.%.

Aqueous composition for retanning of leather

[58] The invention furthermore concerns an aqueous composition for retanning of leather. This aqueous composition has a pH in the range from 2.0 to 7.0, preferably a pH in the range from 3.0 to 6.0, most preferably in the range from 3.5 to 5.0. These pH ranges are typical for aromatic syntans used in the leather industry, and provides for good retanning. The aqueous composition comprises the condensate for retanning of leather in an amount of 2 - 70 wt.% based on total weight of the aqueous composition, preferably in an amount of 10 - 60 wt.% based on total weight of the aqueous composition, more preferably in an amount of 20 - 50 wt.% based on total weight of the aqueous composition, even more preferably in an amount of 30 - 50 wt.% based on total weight of the aqueous composition. In a preferred embodiment the water content of the aqueous composition for retanning of leather is between 30 and 90 wt.% based on total weight of the aqueous composition for retanning of leather, preferably between 40 and 80 wt.%, more preferably between 50 and 70 wt.%. In a preferred embodiment the dry matter content of the aqueous composition for retanning of leather is between 10 and 70 wt.% based on total weight of the aqueous composition for retanning of leather, preferably between 20 and 60 wt.%, more preferably between 30 and 50 wt.%.

[59] The aqueous composition preferably comprises no or low amounts of bisphenol S, bisphenol F and formaldehyde. Bisphenol S, bisphenol F and formaldehyde are all considered to affect human health and/or the environment in a negative way and therefore the presence of bisphenol S and bisphenol F in the aqueous composition for retanning of leather and in leather should be prevented. As these compound are not fully contained in leather some of it will be released. Moreover at the end of the leather lifetime these compound provide problems for reuse or processing of the spend leather. In comparison with conventional aromatic syntans the invention provides for very low amounts or even absence of bisphenol S, bisphenol F and formaldehyde.

[60] The aqueous composition for retanning of leather comprises an amount of bisphenol S lower than 100 ppm based on total weight of the aqueous composition, preferably lower than 70 ppm, more preferably lower than 50 ppm, most preferably lower than 30 ppm. The aqueous composition for retanning of leather comprises an amount of bisphenol F lower than 100 ppm based on total weight of the aqueous composition, preferably lower than 70 ppm, more preferably lower than 50 ppm, most preferably lower than 30 ppm. The aqueous composition for retanning of leather comprises an amount of formaldehyde lower than 30 ppm based on total weight of the aqueous composition, preferably lower than 20 ppm, more preferably lower than 10 ppm, most preferably lower than 5 ppm. In one preferred embodiment the preferred ranges for bisphenol S, bisphenol F and formaldehyde listed in this paragraph also apply for the condensate for retanning of leather.

[61] Bisphenol S and F may be determined by HPLC. Preferably for the determination by HPLC a phenyl-based column system is used for isolation and a Mass Spectroscopy (MS) and/or UV detector for detection. The determination of the amount of formaldehyde is common knowledge and the amount of formaldehyde is preferably determined by HPLC.

[62] The amount of unreacted phenolic compound in the aqueous composition for retanning of leather is below 1000 ppm on total weight of the condensate, preferably below 500 ppm, more preferably below 300 ppm, even more preferably below 150 ppm, even more preferably below 100 ppm, most preferably below 50 ppm. Preferably the amount of unreacted phenolic compound is determined by HPLC. Phenol is toxic and therefore not preferred in the water soluble condensate.

[63] An aromatic syntan typically comprises a buffering agent such as a dicarboxylic acid. The buffering agent provides for storage stability of the syntan as they keep the pH stable. Also the buffering agent keeps the pH stable during retanning. A buffering agent is an agent that limits the pH change of an aqueous solution when a small amount of a strong acid or base is added. In a preferred embodiment the aqueous composition for retanning of leather comprises a buffering agent, more preferably a weak organic acid, even more preferably a dicarboxylic acid; preferably wherein the dicarboxylic acid is selected from the list consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and any combination therefore, more preferably the dicarboxylic acid is a mixture of adipic acid, glutaric acid and succinic acid (an AGS mixture). Preferably the aqueous composition for retanning of leather comprises 0.05 - 10.0 wt.% based on total weight of the aqueous composition of a buffering agent, more preferably 0.10 - 8.0 wt.%, even more preferably 0.50 - 7.0 wt.%, most preferably 1.0 - 5 wt.%.

[64] An aromatic syntan typically comprises a chelating agent. A chelating agent is a chemical compound that reacts with metal ions to form stable, water-soluble metal complexes. The chelating agent scavenge small amount of trace metals if any present in the syntan. In a preferred embodiment the aqueous composition for retanning of leather comprises a chelating agent, preferably a chelating agent selected from the list consisting of Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodisuccinic acid (IDS), polyaspartic acid, S,S-ethylenediamine-N,N'-disuccinic acid (EDDS), methylglycinediacetic acid (MGDA), L-Glutamic acid N,N-diacetic acid, tetrasodium salt (GLDA) and any combination thereof, more preferably the chelating agent is EDTA and/or GLDA. Preferably the chelating agent is present in an amount of 0.1 - 1.0 wt.% on total weight of the aqueous composition, more preferably in an amount of 0.3 - 0.7 wt.%.

Water dissolvable powder for retanning of leather

[65] The invention furthermore concerns a water dissolvable powder for retanning of leather. The water dissolvable powder comprises the condensate for retanning of leather in an amount of 70 - 100 wt.% based on total weight of the water dissolvable powder, preferably in an amount of 80 - 98 wt.%, even more preferably in an amount of 85 - 95 wt.%. In a preferred embodiment the water content of the water dissolvable for retanning of leather is between 1 and 20 wt.% based on total weight of the water dissolvable powder for retanning of leather, preferably between 1 and 10 wt.%, more preferably between 2 and 5 wt.%. In a preferred embodiment the dry matter content of the water dissolvable for retanning of leather is above 80 wt.% based on total weight of the water dissolvable powder for retanning of leather, preferably above 90 wt.%, more preferably above 95 wt.%.

[66] The water dissolvable powder for retanning of leather comprises an amount of bisphenol S lower than 200 ppm based on total weight of the water dissolvable powder, preferably lower than 140 ppm, more preferably lower than 100 ppm, most preferably lower than 60 ppm. The water dissolvable powder for retanning of leather comprises an amount of bisphenol F lower than 200 ppm based on total weight of the water dissolvable powder, preferably lower than 140 ppm, more preferably lower than 100 ppm, most preferably lower than 60 ppm. The water dissolvable powder for retanning of leather comprises an amount of formaldehyde lower than 60 ppm based on total weight of the water dissolvable powder, preferably lower than 40 ppm, more preferably lower than 20 ppm, most preferably lower than 10 ppm.

[67] The amount of unreacted phenolic compound in the water dissolvable powder for retanning of leather is below 1000 ppm on total weight of the condensate, preferably below 500 ppm, more preferably below 300 ppm, even more preferably below 150 ppm. Preferably the amount of unreacted phenolic compound is determined by HPLC. Phenol is toxic and therefore not preferred in the water soluble condensate.

[68] In a preferred embodiment the water dissolvable powder for retanning of leather comprises a buffering agent, more preferably a weak organic acid, even more preferably a dicarboxylic acid; preferably wherein the dicarboxylic acid is selected from the list consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and any combination therefore, more preferably the dicarboxylic acid is a mixture of adipic acid, glutaric acid and succinic acid (an AGS mixture). Preferably the water dissolvable powder for retanning of leather comprises 0.10 - 20.0 wt.% based on total weight of the water dissolvable powder of a buffering agent, more preferably 0.20 - 16.0 wt.%, even more preferably 1 .0 - 14.0 wt.%, most preferably 2.0 - 10 wt.%.

[69] In a preferred embodiment the water dissolvable powder for retanning of leather comprises a chelating agent, preferably a chelating agent selected from the list consisting of Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodisuccinic acid (IDS), polyaspartic acid, S,S-ethylenediamine-N,N'-disuccinic acid (EDDS), methylglycinediacetic acid (MGDA), L-Glutamic acid N,N-diacetic acid, tetrasodium salt (GLDA) and any combination thereof, more preferably the chelating agent is EDTA and/or GLDA. Preferably the chelating agent is present in an amount of 0.1 - 1.0 wt.% on total weight of the water dissolvable powder, more preferably in an amount of 0.3 - 0.7 wt.%.

Leather manufacturing

[70] Leather manufacturing starts with raw hides (or furs) and generally has four stages referred to as beamhouse, tanning, post-tanning and finishing. Each stage usually has several steps.

[71] Beamhouse operations prepares raw hides for tanning by removing all non-collagenous materials from the hides through a series of treatments that may include soaking, (green) fleshing, unhairing, liming, lime splitting, deliming, bating, degreasing and pickling. Tanning protects the hides from putrefaction when wet and improves the mechanical properties. Tanning transforms hides into leather. During the tanning process tanning agents penetrate the hides and interact with collagen. Most commonly, hides are tanned with chromium salts, but several alternatives exist. Leather tanned with chromium is often called wet-blue (WB) leather, whilst tanned leather tanned with aldehyde is often called wet-white (WW) leather.

[72] Tanned leather is sorted and mechanically processed (e.g. split, shaved), before posttanning starts. During post-tanning leather’s organoleptic properties are significantly improved and largely defined. The above mentioned post-tanning, like tanning, is a wet process in which leather is submerged in an aqueous phase and specific components penetrate in the leather and alter its properties. In other words, the leather is impregnated with the specific components. Post-tanning comprises several steps that are sequentially or (partially) simultaneously performed. Since post-tanning is specifically aimed to tailor the final leather properties and there is a need of a wide variety of properties, and since there is a large variety in tanned leather and each variant of tanned leather may need a specific post-tanning treatment the leather manufacturer makes a selection of the steps to be carried out, the types of chemicals used during these steps and the specific conditions as well as order of the steps.

[73] Typically during post-tanning, or during post-tanning steps, different (combinations of) chemicals are sequentially added to the aqueous phase at specific time intervals. If needed the aqueous phase is drained and fresh water or a new aqueous phase is added. The following post-tanning steps are commonly applied:

Neutralizing: during neutralizing the pH of the leather is adjusted.

Retanning: During retanning one or more compounds are added that diffuse in the leather and interact with collagen. Retanning among others (further) strengthens the collagen structure; improves the overall organoleptic properties such as softness and fullness; fills the loose and empty parts of the leather thus improve the evenness and general cutting value; improves buffing properties and grain appearance. Mineral retanning such as rechroming is a retanning step.

Dyeing: During dyeing a dye is added which penetrates the leather and gives the leather a uniform shade of color.

Fatliquoring: during fatliquoring an oil or fat emulsion is provided, the oil or fat penetrates the leather and interacts with the collagen fibers. Fatliquoring aims at lubricating collagen fibers, preventing the fiber structure sticking together during drying, and to render specific characteristics (e.g. organoleptic, mechanical and/or waterproof properties).

[74] These steps may also be combined in any combination, for example neutralizing and retanning, neutralizing and dying, neutralizing and fatliquoring, retanning and dyeing, retanning and fatliquoring, dyeing and fatliquoring, retanning and dyeing and fatliquoring or neutralizing and retanning and dyeing and fatliquoring. These steps may also be repeated, for example retanning and/or dyeing may be performed more than one time.

[75] The invention also concerns the use of the water soluble condensate or the aqueous retanning composition or the water dissolvable powder of the invention for retanning of leather. Retanning of leather is contacting leather in an aqueous solution with a retanning agent. For this embodiment the retanning agent is the water soluble condensate or the aqueous retanning composition or the water dissolvable powder.

[76] The invention furthermore concerns a method for retanning of leather wherein leather is contacted in an aqueous solution with the water soluble condensate or the aqueous retanning composition or the water dissolvable powder of the invention.

[77] For the use and/or the method for retanning of leather the aqueous solution preferably comprises 5 - 50 wt.% of the aqueous composition for retanning of leather based on total weight of the leather, preferably 10 - 45 wt.%, more preferably 15 - 45 wt.%; or the aqueous solution preferably comprises 3 - 25 wt.% of the water dissolvable powder for retanning of leather based on total weight of the leather, preferably 5 - 23 wt.%, more preferably 7 - 23 wt.%.

[78] The invention also concerns leather obtained by the method for retanning of leather or leather comprising the water soluble condensate of the invention. Preferably for these embodiments the leather comprises 0.1 - 10 wt.% based on the weight of the leather of the water soluble condensate, more preferably 0.2 - 5.0 wt.%, most preferably 0.5 - 3 wt.%. In one preferred embodiment the leather obtained by the method for retanning of leather comprises the water soluble condensate of the invention. Examples

Example 1

[79] 3.27 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 3.48 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 75 °C. Next an amount of 3.93 moles of glyoxal (40 wt.% in water) was added to the reaction mixture in 13 batch dosings. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 75 °C to lower the water concentration below 18.1 - 20.7 wt.%. Vacuum distillation was started when the water level exceeded 22.4 - 25.9 wt.%. Vacuum pressure of 30 to 150 mbar was applied for this purpose. The reaction mixture was cooled down to 50 °C followed by the addition of 0.41 moles of phenol. This mixture was heated to 70 °C and left to react for 90 minutes. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with sodium hydroxide 50% to a pH of 3.83. The mixture was further diluted to a solid concentration of 41.16 wt.%.

Example 2

[80] 3.23 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 3.43 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 75 °C. Next, an amount of 3.88 moles of glyoxal (40 wt.% in water) was added by batch dosing in 11 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 65 °C to lower the water concentration in the range of 14.6 - 17.1 wt.%. Vacuum distillation was started when the water level exceeded 19.9 - 23.3 wt.%. Vacuum pressure of 30 to 100 mbar was applied for this purpose. The reaction mixture was cooled down to 70 °C followed by the addition of 0.405 moles of phenol. This mixture was heated to 70 °C and left to react for 60 minutes. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with sodium hydroxide 50% to a pH of 3.36. The mixture was further diluted to a solid concentration ~40 wt.%.

Example 3

[81] 3.82 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 4.07 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 75 °C. Next, an amount of 3.85 moles of glyoxal (40 wt.% in water) was added by batch dosing in 12 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 65 °C to lower the water concentration in the range of 18.8 - 20.3 wt.%. Vacuum distillation was started when the water level exceeded 20.9 - 25.5 wt.%. Vacuum pressure of 30 to 100 mbar was applied for this purpose. The reaction mixture was cooled down to 70 °C followed by the addition of 0.24 moles of phenol. This was left to react for 10 minutes before a second addition of 0.24 moles of phenol addition. This mixture was kept at 70 °C and left to react for 60 minutes. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with sodium hydroxide 50% to a pH of 3.9. The mixture was further diluted to a solid concentration 40.9 wt.%.

Example 4

[82] 4.28 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 4.56 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 55 °C. Next, an amount of 3.44 moles of glyoxal (40 wt.% in water) was added by batch dosing in 11 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 65 °C to lower the water concentration in the range of 17.0 - 18.0 wt.%. Vacuum distillation was started when the water level exceeded 19.1 - 22.5 wt.%. Vacuum pressure of 30 to 100 mbar was applied for this purpose. The reaction mixture was heated to 70 °C followed by the addition of 0.54 moles of phenol. This mixture was and left to react for 25 minutes at 70 °C. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with sodium hydroxide 50% to a pH of 3.7. The mixture was further diluted to a solid concentration 40 wt.%.

Example 5

[83] 3.45 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 3.67 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 65 °C. Next, an amount of 3.45 moles of glyoxal (40 wt.% in water) was added by batch dosing in 11 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosing 4 vacuum distillations were carried out at 65 °C to lower the water concentration to 13.5 - 15.0 wt.%. Vacuum distillation was started when the water level exceeded 19.7 - 20.9 wt.%. Vacuum pressure of 30 to 100 mbar was applied for this purpose. The reaction mixture was heated to 70 °C followed by the addition of 0.43 moles of urea in 2 dosages. This mixture was left to react for 30 minutes. The mixture was diluted with water, cooled down to 50 °C and finally the pH was adjusted with Sodium hydroxide 50% to a pH of 4.51 . The mixture was further diluted to a solid concentration ~40 wt.%.

Example 6

2.98 moles of phenol was melted in 2L 4 necked round bottom flask at 50 °C. While stirring 3.18 moles of sulfuric acid was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 65 °C. Next, an amount of 1 .42 moles of glyoxal (40 wt.% in water) was added by batch dosing in 7 portions After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. Temperature during the reaction was varied between 65 to 75 °C. In between the batch dosages, 3 distillations were carried by heating the reaction mixture to 97 - 115 °C for 1 - 2 hours. The reaction mixture was diluted with water and cooled down to 50 °C. The pH was adjusted using sodium hydroxide 50% to pH 3 - 4 and the solids was adjusted to ~40 wt.% using water.

Example 7

[84] 2.98 moles of phenol was melted in 2L 4 necked round bottom flask at 50 °C. While stirring 3.18 moles of sulfuric acid was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 65 °C. Next, an amount of 0.9 moles of glyoxal (40 wt.% in water) was added by batch dosing in 5 portions. Water was not removed from the reaction mixture. After each dosing, 20 minutes reaction time was allowed for the next dose of glyoxal. Temperature during the reaction was varied between 65 to 85 °C. The reaction was cooled down to 60 °C and left to react for 180 minutes. The reaction was cooled down to 50 °C before the mixture was neutralized to pH 4.9 with sodium hydroxide 50%. The solid concentration was brought down to ~40% using water.

Example 8

[85] 3 moles of phenol was melted in 2L 4 necked round bottom flask at 50 °C. While stirring 3.28 moles of sulfuric acid was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 65 °C. Next, 2.5 moles of glyoxalic acid ( 40 wt.% in water) was added by batch dosing in 6 additions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxalic acid. Temperature during the reaction was varied between 65 to 100 °C. After the completion of the addition of glyoxalic acid, the reaction temperature was increased to 100 °C and left to react for another 6 h. No distillation was carried out during the additions of glyoxalic acid. Then reaction mixture was diluted with water and cooled down to 50 °C. The pH was adjusted using sodium hydroxide 50% to pH 3 - 4 and the solids was adjusted to ~40 wt.% using water.

Example 9

[86] 2 moles of phenol was melted in 2L 4 necked round bottom flask at 50 °C. While stirring 2.2 moles of sulfuric acid was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 65 °C. Next, an amount of 1.5 moles of glyoxalic acid ( 40 wt.% in water) was added by batch dosing in 10 additions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxalic acid. In between the additions, distillations were carried out during the additions of glyoxalic acid by heating the reaction to 100°C by purging with nitrogen gas. Condensation reaction was carried out at 90- 100 °C for 6 h. Then reaction mixture was diluted with water and cooled down to 50 °C. The pH was adjusted using sodium hydroxide 50% to pH 3 - 4 and the solids was adjusted to ~40 wt.% using water. Example 10

[87] 2.94 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 3,14 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 55 °C. Next an amount of 2.35 moles of glyoxal (40 wt.% in water) was added by batch dosing in 11 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 55 °C to lower the water concentration in the range of 19.0-21.9 wt.%. Vacuum distillations were started when the water level exceeded 19.1 - 22.5 wt.%. The reaction mixture was heated to 70 °C followed by the addition of 0.37 moles of phenol addition. This mixture was heated to 70 °C and left to react for 25 minutes. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with Sodium hydroxide 50% to a pH of 3.7. The mixture was further diluted to a solid concentration 40 wt.%.

Example 11

[88] 3.33 moles of phenol is melted in a 2L glass reactor at 50 °C. While stirring 3.53 moles of sulfuric acid 96% was added. The mixture was heated to 102 °C to react for 15 minutes. The reaction mixture was cooled down to 75 °C. Next an amount of 2.66 moles of glyoxal (40 wt.% in water) was added by batch dosing in 11 portions. After each dosing, 10 minutes reaction time was allowed for the next dose of glyoxal. In between the batch dosings, 4 vacuum distillations were carried out at 75 °C to lower the water concentration in the range of 19.1-21.8. The vacuum distillation was carried out is dependable on when the water concentration was between 19.1 - 22.5 wt.%. The reaction mixture was cooled down to 70 °C before 0.54 moles of phenol was added. This mixture was heated to 70 °C and left to react for 25 minutes. The mixture was diluted with water, cooled down to 45 °C and finally the pH was adjusted with Sodium hydroxide 50% to a pH of 3.7. The mixture was further diluted to a solid concentration 40 wt.%.

Example 12

[89] COMP-01 is a commercial retanning agent. COMP-01 main component is a condensation polymer of formaldehyde, phenolsulfonic acid (phenol +96 wt% H2SO4), phenol and urea. Preparation is similar to examples 1-11 , however no water was removed during the reaction, instead water was added to a water content of about 50 wt.% on total weight. The reaction with phenol was carried out under less acidic conditions.

Example 13:

[90] COMP-02 is a commercial retanning agent. COMP-02 main component is a condensation polymer of formaldehyde, phenolsulfonic acid ((phenol +96 wt% H2SO4), phenol and urea. Preparation is similar to examples 1-11 , however no water was removed during the reaction, instead water was added to a water content of about 50 wt.% on total weight. The molecular weight of the end product and the ratio formaldehyde, phenol, phenolsulfonic acid and urea is different compared to example 12.

Example 14 - Analytical methods

Stability

[91] The stability of the formed polymer was determined by visual observation of the sample. The end product, so after dilution and pH-stabilization was tested for its stability . Stability was determined at room temperature, 90 days after synthesis. Stability is defined as clear solution without trace of precipitation after long storage.

Molecular weight distribution

[92] Samples were analyzed for molecular weight distribution using a Shimadzu HPLC system equipped with PSS MCX column combination medium. The columns were conditioned at 30 °C. A 0.05M phosphate buffer comprising 20%THF at pH=8 was used as eluent at a flow rate of 1.00 mL/min and the injection volume was 10 pL. A sample concentration of 4 mg/ml of the end product (so after dilution and pH standardization) was analyzed. A dual beam UV detector operating at 280 nm was used together with a refractive index detector (RID-20A Shimadzu). The column was calibrated using polystyrenesulfonate standards in the range of 891-976000 Da. Analysis was performed with Shimadzu Labsolutions software and the weight average molecular weight was calculated.

Phenol & phenolsulfonic acid level

[93] Samples were analysed for phenol and phenolsulfonic acid levels by HPLC. The HPLC settings were as follows:

Detection: Diode array detector 200-350nm (phenol @270nm)

Column: Phenomenex Kinetex C18, TMS endcapped, particle size 5pm, 150x4.6mm

Eluent: A: 0.01 M TBAS

B: Acetonitrile

Gradient (A/B): 90/10 (10.0 min) > ( 1.0 min) > 5/95 (5.0 min) > (1.0 min) >90/10 (6.0 min)

Flow rate: 1 .00 ml/min

Column temp.: 35°C

Inj. volume: 1 and 10pl

Calibration: external, using phenol standard solutions

Sample cone.: 2 - 10%

The weight percentage (wt.%) as listed in the tables is the weight percentage based on total weight of the sample. Glyoxal level

[94] Samples were analysed for phenol and phenolsulfonic acid levels by HPLC. The HPLC settings were as follows:

System: Shimadzu HPLC

Detection: RID

Column: PSS MCX column combination medium

Eluent: 0.05M phosphate buffer

Flow rate: 1 .00 ml/min

Column temp.: 30°C

Injection volume: 10pl

Calibration: External using polystyrenesulfonate standards 891-976000 Da

Sample cone.: 10-100% pH: 8.0

The weight percentage (wt.%) as listed in the tables is the weight percentage based on total weight of the sample.

Haptic properties of retanned leather

[95] Experimental leathers are assessed with a comparative leather as a reference. The haptic property softness, fullness, grain tightness, dye intensity, dye levelness, grain smoothness, size of milling and levelness of milling are assessed on a 1 to 7 scale. A score of 4 indicates the same performance between the experimental leather and reference on a specific property, a score lower of 4 means more of that property for the experimental leather compared to the comparative leather. Leathers assessments are performed according to industry standards by a minimum of 4 technicians and the ratings are averaged to present the final assessment of the leathers for each haptic property separately.

Heat yellowing and light fastness

[96] To determine the leather properties heat yellowing and lightfastness leather is manufactured without dye and fat liquor but with the aromatic syntan. In this way exclusively the effect of the syntan can be determined.

[97] For the determination of the heat yellowing of the leathers leather pieces (6.0 x 7.0 cm) are conditioned in a ventilated oven for various time periods such as 24, 48, 72, 144 hours at 100 or 110 °C. Color determination was performed according to ISO 105-A05:1996 using a Xrite SP60 portable spectrophotometer. Grey scale value and AE are determined. A high grey scale value represents higher heat resistance and high lightfastness. Alternatively a high AE value represents poor heat resistance and poor lightfastness.

Determination of the lightfastness of the leathers: radiation of leather pieces (6,0 x 7,0 cm) using an Atlas Suntest CPS+ at 50°C for 72 hours. Color determination according to ISO 105- A05:1996 was performed using a Xrite SP60 portable spectrophotometer. [98] GS value is grey scale value and which has scale from 1 to 5. The number indicates colour difference to the reference. Higher value indicates good heat resistance and good light fastness of the leather piece. Another indicator AE value is inversible proportional to the GS scale. Higher the AE value indicates poor lightfastness and poor heat resistance.

Formaldehyde emission and content

[99] Formaldehyde emission of the leather was determined with the standard method ISO17226-3 [2011 : IULTCS/IUC 19:3] while the formaldehyde content of the leather was measured by the standard method ISO 17726-3 [2011 :IULTCS/IUC 19:1], For determining formaldehyde emission and content leather is manufactured without dye and fat liquor but with the aromatic syntan. In this way exclusively the effect of the syntan can be determined.

Example 15 - Synthesis results

Phenolsulfonic acid level in the end product

Table 1: Process parameters of different examples (example 8 and 9 with glyoxalic acid instead of glyoxal), nd = not determined, na = not applicable, PSA = phenol sulfonic acid. For the ratio of phenol to glyoxal at the start of the second condensation the amount of glyoxal was measured before proving the phenol and the amount of phenol was as added during the second condensation. In table 2 the concentration of phenolsulfonic acid in the end product (before bringing down the solid concentration) for the different examples is listed. A comparison of examples 1-6 and 9-11 with examples 7 and 8 teaches that conversion of the phenolsulfonic acid is improved by distillation of the reaction mixture during the first step. In examples 1-6 and 9-11 the amount of phenolsulfonic acid in the end mixture is in the range of 5 to 13 wt.%. Alternatively relatively high amount of the phenolsulfonic acid was found in the end reaction mixture in the absence of distillation, as depicted in comparative examples example 7 (36 wt.%) and 8 (>30 wt.%). This relative high amount cannot be explained by the absence of a second condensation step or a high ratio of phenol to glyoxal, as examples 6 (distillation but no second condensation) and 9 (distillation but no second condensation) have low PSA levels. The results surprisingly indicate that relatively high amount of the water in the reaction mixture during the progress of condensation polymerization stops the progress of reaction. For retanning purposes a low conversion is not helpful, as the polymer and not the monomer is responsible for the retanning effect on the leather. It is further believed that polymers with somewhat higher molecular weight are beneficial for tanning.

Precipitate formation / stability of the product upon storage

[100] A stable aromatic syntan is necessary for the use in retanning. Especially the liquid products need to be stable while applying on the leather for the maximum performance. Minimum 1 year stability is common for the products in the leather chemicals. Precipitate formation is undesirable as precipitated material is not effective for retanning. Hence the composition for retanning should be stable during storage. Surprisingly the molar ratios of phenol and phenolsulfonic acid to di-aldehyde compound is found to be crucial for the conversion of phenolsulfonic acid and phenol and the end solubility of the product mixture in the water. In the examples, examples 6 and 7, the molar ratios of PSA: glyoxal are 1 :0.47 and 1 :0.3 respectively and the inventors found that in case of a low amount of glyoxal the resultant product has issue with the generation of soluble product (table 1 and 2).

[101] Also the ratio of phenol to glyoxal at the start of the second condensation when present was found to be of importance. Table 1 and 2 point to that whenever the ratio of phenol to glyoxal ratio is equal or above 3.4 : 1 the product was found to be unstable during the storage as precipitates did form. Examples 10 and 11 with phenoI to glyoxal ratios of 3.4 :1 and 16.1 : 1 led to form products with poor stability and which have solubility issues under storage. Alternatively the examples 2 and 4 with phenol to glyoxal ratios 1 : 1 and 2.5 : 1 respectively are stable and soluble in water during the storage.

[102] Conversion of phenolsulfonic acid is another crucial importance for the stability of the product. Irrespective of the molar ratios of phenolsulfonic acid and phenol to glyoxal, when there is no sufficient conversion of reactants, the resultant mixture is not stable. In the examples, 6,7 and 8 there are no efficient distillations for the removal of water. For this reason, the progress of the reaction is not sufficient and that is reflected in the storage stability of the product. [103] Moreover adding phenol in two different steps during a second condensation when present was found to negatively affect the solubility as example 3 demonstrates (table 1 and 2). Possibly the ratio of phenol to glyoxal for one or both of these steps was not within the required boundaries.

Table 2: Characteristics of phenolic syntans synthesized in different examples. Phenol and phenolsulfonic acid were measured in the undiluted condensate and the weight percentages relate to the total weight of the condensate. Phenolsulfonic acid was measured after the first condensation, phenol after the second condensation. Molecular weight (MW) is that of the end product. Stability tests were performed with solids and pH standardized product. Example 16 - Retanning experiments

Method 1: Retanning of Glutaraldehyde tanned (or Wet White) leather for automotive leather article (WW AML)

[104] Glutaraldehyde tanned leather was washed and raising the pH to pH 4.3-4.4. Then 40 wt.% of phenolic syntan liquid (40 wt.% solids) from the above examples, two different amino resins, DD-001 (Smit&Zoon) and MW005 (Smit&Zoon) at 5 and 3 wt.% respectively, 2 wt.% Black BT dye, two fat liquors Synthol CS 588 (Smit&Zoon) and Sulphirol HF 377 (Smit&Zoon) at 8 and 4 wt.% respectively were added to leather at 100% water dilution. All wt.% are based on the weight of the leather. With another 100% solution (100 wt.% in relation to the weight of the leather), the above chemicals were fixed at pH 3.5-3.6 by the addition of polyacrylic acid polymer, RS540 (Smit&Zoon). Once the fixation was completed the water was drained followed by two more drains at 200% dilutions. Retanning process was carried out for 6 h at 45 to 50 °C. After the fixation, the leathers are dried and milled with standard practises.

Method 2: Retanning of chrome tanned (or Wet Blue) leather for shoe-upper leather article (WB shoe)

[105] Chrome-tanned leather was washed and wet back to the pH 3.2-3.5. Then the chrome- tanned leather was re-chromed by using chrome syntan (syntan CR515 supplied by Smit&Zoon) and neutralizing syntan (NN555 from Smit&Zoon) at pH 5.2 at 150 % water. Neutralized leather was rinsed one more time with 300% water. At this stage, 20 wt.% phenolic syntan liquid (solids 40 wt.%), 2.5 wt.% polyacrylic acid polymer (RS540 from Smit syntan), amino resins, dicyanamide resin (DF585 from Smit&Zoon) and melamine resin (LF187 from Smit&zoon) at 6 wt.% each and dye Brown BBN at 3 wt.% were applied in the retanning at 100% water. With another 100% addition of hot water, fat liquors Synthol PL 565 (from Smit&Zoon) and Synthol LC (from Smit&Zoon) were applied on the leather. Retanning process was carried out for 6 h at 25 to 30 °C. Once the fixation was completed the water was drained followed by one more drain at 300% water. After the leathers are kept overnight on horse and dried in the following days with standard mechanical operations. All wt.% are based on the weight of the leather.

Method 3: Retanning of chrome tanned (or Wet Blue) leather for Automotive leather article (WB AML)

[106] Initially chrome-tanned leather was washed and set to the pH 3.2. Then the chrome- tanned leather was re-chromed by using a basic chromium sulphate, 2 wt.% chrome 26/33 (Vblpker) followed by neutralization syntan, NN555 from Smit&Zoon and 1 ,5 wt.% fat liquor (Synthol PF 991 from Smit&Zoon). The leather was neutralized to pH 5.2 in 200% water. Neutralized leather was rinsed one more time with 200% water.

[107] Then 20 wt.% phenolic syntan liquid (40 wt.% solids) from the above examples, 2.5 wt.% polyacrylic acid polymer (RS 3 from Smit&Zoon), 1 wt.% dispersing syntan (syntan SN from Smit&Zoon), two different amino resins, DD-001 (Smit&Zoon) and MM002 (Smit&Zoon) at 4 wt.% each, 3 wt.% dye stuff were added to leather at 100% water. With another 100% water and the addition of two fat liquors namely Synthol CS 588 (from Smit&Zoon) and Sulphirol HF 377 (from Smit&Zoon) at 8 and 4 wt.% respectively were lubricated. Followed by a fixation of 2h at 40 - 45 °C. The pH was lowered to 3.5-3.6, water was drained followed by a rinse at 200% water. Retanning process was carried out for 6 h at 25 to 30 °C. After the leathers are kept overnight on horse and dried in the following days with standard mechanical operations. All wt.% are based on the weight of the leather.

Example 17 - Results

Formaldehyde emissions

[108] In table 3 the formaldehyde emission and content of leather retanned with a retanning agent according to the invention is compared with a blank piece of leather (so a piece of leather that not has been retanned) and pieces of leather retanned with conventional commercial available retanning agents (COMP-01 , COMP-02, COMP-03). COMP-03 is a powder phenolic syntan which is a two-step condensation product with phenolsulfonic acid and phenol as backbone and formaldehyde as aldehyde during the condensations. The condensations are at water levels exceeding 50 wt.%.

Table 3: Formaldehyde emission and content. For these leathers the retanning agent was applied at 10 wt.% and 20 wt.% for WB and WW respectively. (40 wt.% liquids applied at 20 and 40 wt.% respectively on WB and WW leathers).

[109] The formaldehyde emission and content of the leathers made by example 9 from the current invention is comparable to the blank leather (within the standard deviations of the measurement method). On the other hand, the retanning agents based on formaldehyde demonstrate a much higher formaldehyde content and emission. Table 4: Bisphenols (emission) in the aromatic syntans. All the 3 samples have bisphenol A and Bisphenol B in below detection limits, <20 ppm

[110] Bisphenol levels in the aromatic syntans were determined by HPLC. Example 3 of this invention has displayed very low emission of Bisphenols S and F compared to the COMP-01 and COMP-02. Lightfastness and heat yellowing

[111] Lightfastness and heat yellowing of leather retanned with conventional commercial available retanning agents and retanning agents of the invention was determined. The results are in table 5. Table 5: Heat yellowing (HY) and lightfastness (LF) of different retanned leathers. Blank leathers are without retanning agents. Time-temperature for the different tests is in the header. GS is grey scale. [112] Heat yellowing and lightfastness values of the leathers with the products from the current invention are compared to the references and which are formaldehyde-based commercial products now named COMP-04, COMP-03, and COMP-01. Examples from the current invention have displayed better heat resistance compared to the references, see the GS value and AE value. Performance is almost equal to the blank leather. When comes to the lightfastness, leathers with the examples of the current invention are better than COMP-04 and COMP-03 while they are comparable to COMP-01. COMP-04 is a liquid phenolic syntan which is a two-step condensation product with phenolsulfonic acid and phenol as backbone and formaldehyde as aldehyde during the condensations. The condensations are at water levels exceeding 50 wt.%.

Haptic properties of the leather

[113] In table 6 the haptic properties of the leather is listed. Leathers with the products prepared from the examples 1 , 2, and 9 (current invention) have resulted to produce comparable leathers or better leathers with regards to haptic properties than the references (tanned with commercial syntans TD626, SL868, DM626 and SF156 of Smit&Zoon). Importantly leathers of example 1 are somewhat tighter and somewhat fuller compared to the reference in both WB shoe upper and WW AML articles. Leathers from example 2 are comparable to the reference TD626 in WB shoe upper article recipe. Leathers from the example 9 are somewhat tighter and somewhat fuller and which is better compared to the reference SF156.

[114] During synthesis example 3 demonstrated precipitation which was believed due to inadequate amount of glyoxal in the second condensation. Still, the leathers retanned with the retanning agent of example 3 are somewhat harder and fuller in WB shoe upper article; alternatively displayed somewhat tighter, somewhat emptier, softer leathers and somewhat better levelness in the dyeing in the WW AML leathers. The leathers are good despite the product issues with the stability (precipitation)on storage.

[115] The leathers obtained from retanning with the retanning agent of example 4 are somewhat harder and less full. This may be attributed to a lower amount of polymer, which is shown from the somewhat higher amount of PSA in the polymer. Leathers of example 5 are somewhat harder and emptier. Presence of urea and absence of phenol in the second condensation seems to have a negative effect. Leathers of Example 8 have produced harder and emptier leathers. During the synthesis of the product no distillation was conducted and consequently higher PSA is left unreacted in the reaction mixture. Table 6: Haptic properties of the leathers prepared by the retanning agents prepared from the current invention compared to the references. Type of article refers to example 16 in which the different retanning methods are listed according which the leathers have been produced.