WO2022224150A1

WO2022224150A1 - Method for the functionalizing treatment of hides for the improvement of the elastic properties

Info

Publication number: WO2022224150A1
Application number: PCT/IB2022/053672
Authority: WO
Inventors: Maria IANNONE; Paolo Antonio Netti
Original assignee: Leather Plus S.R.L.
Priority date: 2021-04-20
Filing date: 2022-04-20
Publication date: 2022-10-27
Also published as: EP4341446A1; IT202100009920A1

Abstract

A method (1, 10) for the functionalizing treatment of hides of the type comprising a dermis of animal origin comprising fibers and/or fibrils of collagen and an aqueous component, in order to improve the elastic properties of the hides, comprising the steps of: a1) removing selectively the aqueous component of the dermis of the hides, by using one or more organic solvents; a2) performing a dehydrothermal treatment for the activation of reactive groups present in the collagen, provided by arranging the hides in an environment in which the pressure is equal to or lower than 100 mTorr and the temperature is equal to or higher than 90°C.

Description

METHOD FOR THE FUNCTIONALIZING TREATMENT OF HIDES TO IMPROVE ELASTIC PROPERTIES

The present invention relates to a method for the functionalizing treatment of hides in order to improve their properties. More particularly, the invention relates to a method for improving the elastic properties of hides of animal origin.

The term "hides" refers the known material of animal origin constituted at least partly by dermis of animal origin and commonly also called "leather". Therefore, the method can be applied, in a fully general way, to any leather or hides of animal origin.

The method according to the present invention mainly finds application in the tanning industry, in the hide processing steps upstream of known tanning processes.

As is known, animal leather, to which the present invention relates, is formed by the epidermis (also called grain side) and the dermis (also called flesh side), the structure of which consists of fibers and fibrils of collagen spatially ordered and organized to form a highly interconnected structure.

The method according to the present invention consists therefore of a functionalizing treatment for hides, i.e., a treatment that gives the hides additional functions and/or properties.

In greater detail, the functionalizing treatment according to the present invention is aimed at improving the elastic properties of hides, i.e., at controlling, modulating and improving the properties of elastic extension and recovery of the animal dermis, therefore giving leather articles greater elasticity without compromising native organoleptic characteristics such as softness to the touch and breathability.

Currently, various methods for making hides elastic are used.

In a first known type of methods for giving elasticity to hides, one proceeds to create a hybrid of hides/Lycra or other synthetic materials that have elasticity. The coupling of a very thin layer of leather with Lycra makes said leather acquire elastic characteristics.

In a second known type of methods for giving elasticity to hides, during the steps of the known tanning and retanning process, mixes of polyurethanes, elastomers or other exogenous molecules that can give elasticity and softness to the hides are added.

For both types of methods listed above, some considerable limitations and drawbacks are known.

In particular, in the first case the provided fabrics are not made of natural leather, since a layer of synthetic material is added to a very thin layer of natural leather, in many cases one even starts polyurethane or PVC materials similar to leather. Therefore, what is obtained downstream of these processes is actually a synthetic, leather-like fabric with elastic characteristics.

Instead, as regards the second known type of methods for giving elasticity to hides, the degree of elasticity that can be given is related to the quantity/percentage of polymer or elastomer or polyurethane that is used during the tanning and retanning steps: the greater the quantity/percentage, the greater the degree of elasticity; however, increasing excessively the quantities of these molecules reduces some of the main characteristics of natural hides, such as softness to the touch, fullness and breathability.

The aim of the present invention is to provide a method for functionalizing treatment of hides capable of solving the problems and overcoming the limitations of the background art mentioned above, improving the elastic properties of the hides without adding exogenous and/or synthetic molecules or in any case without altering the main characteristics of natural hides such as softness to the touch, fullness and breathability.

Within this aim, an object of the present invention is to provide a method for functionalizing treatment of hides that is capable of improving the extensional characteristics of animal dermis, giving high elasticity to leather articles, modulating and increasing the stretching and elastic recovery properties, without adding exogenous and/or synthetic molecules.

Another object of the present invention is to provide a method for functionalizing treatment of hides which allows to give elasticity to the hides by keeping unchanged the natural breathability and softness and also making the hides adaptable to different shapes, with improved performance and characteristics with respect to the background art.

Another object of the present invention is to provide a method for functionalizing treatment of hides that can be inserted within the processes of the supply chain and the standard processes used currently in the tanning field.

Another object of the present invention is to conceive a functionalizing treatment method that is highly reliable, relatively simple to provide and at competitive costs if compared with the background art. This aim and these and other objects that will become better apparent hereinafter are achieved by a method according to claim 1.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of a method for functionalizing treatment of hides to improve the elastic properties of said hides, illustrated by way of non-limiting example with the aid of the accompanying drawings, wherein:

Figure 1 is a flowchart showing the essential steps of the method according to the invention;

Figure 2 is a flowchart showing the steps of a preferred embodiment of the method according to the invention.

With reference to the figures, the method is generally designated by the reference numerals 1 and 10 depending on the embodiment.

The method 1, 10 as already mentioned, is a method for functionalizing treatment of hides of the type comprising a dermis of animal origin which in turn comprises fibers and/or fibrils of collagen and an aqueous component. The method is aimed at improving the elastic properties of the hides.

In its essential traits, with reference to Figure 1, the method comprises the following two main steps (performed in this order): al) selective removal of the aqueous component of the animal dermis (i.e., of the interstitial water), which is advantageously performed so as to not alter the micro structure of the collagen lattice that constitutes said dermis; a2) performing a dehydrothermal treatment for the activation of reactive groups present in the collagen and more precisely of the reactive groups of chemical terminals on the macromolecular chain of the protein and promotion of transesterification reactions in an anhydrous environment.

The first step of selective removal of the aqueous component of the animal dermis, more specifically, provides for the complete removal of the aqueous component of the animal dermis without significant alteration of the macromolecular structure of the dermis, i.e., with a total volumetric change of the tissue of less than 5% with respect to the hydrated product, i.e., this step is performed so as to cause a total volumetric reduction of the dermis of less than 5%.

The 5% limit in total volumetric contraction of the dermal tissue ensures that the correct structure i.e., the native structure (therefore, the mean space between collagen fibrils), is preserved, and therefore ensures that any reduction of the molecular mobility of collagen as a consequence of the step of removing the interstitial water is limited.

According to the invention, the practical execution of this step of selective removal of the aqueous component entails the use of one or more organic solvents with which the hides are treated and conveniently includes the simultaneous and concurrent use of organic solvents characterized by: suitable properties, which give them the capacity to replace the aqueous phase, and at the same time suitable surface tensions, which allow their subsequent removal from the organic matrix without entailing a variation of the macromolecular structure of the dermis, i.e., of the collagen network that constitutes the hides.

Preferably, one or more mixtures of organic solvents are used.

The solvents, or the mixtures of solvents, that have proven themselves effective in performing the step of selective removal of the aqueous phase comprise preferably but not exclusively:

- acetone,

- ethanol,

- propanol,

- isopropyl alcohol.

The controlled removal of the aqueous phase can occur also by means of the use of solvents “in critical conditions”.

The methods by which the controlled removal of the interstitial water can occur provide for the execution of one or more treatment cycles with solvents and preferably 1 to 10 different solvent treatment cycles.

The different cycles can provide for alternating the use of different solvents; for example, it is possible to alternate acetone, isopropyl alcohol, ethanol.

The duration of the solvent treatment cycles can vary from 10 minutes to 10 hours.

The temperature of the water extraction process can vary from 2-4 °C up to 37-40 °C.

The quantity of solvent used can vary from 1 to 500% with respect to the weight of the hides to be treated.

With reference now to the subsequent step of execution of a dehydrothermal treatment for the activation of the reactive groups present on the collagen macromolecule, more specifically, this step is performed in order to promote intramolecular reactions. This can be obtained by means of a specific control and modulation of the environmental conditions, by performing a process for the stabilization of the collagen network known as dehydrothermal treatment or by its acronym DHT.

DHT is a physical cross-linking process commonly used to stabilize collagen networks or collagen-based materials by forming zero-length chemical bridges; more specifically, the dehydrothermal treatment step leads to the formation of intermolecular cross-link bonds by virtue of reactions of condensation by esterification or formation of amides.

Furthermore, DHT is mainly used to induce the forming of chemical condensation reaction between reactive groups present on the protein chain, such as for example the forming of amide bonds between carboxyl and amine groups, as well as ester bonds between carboxyl and hydroxyl groups.

The forming of zero-length chemical bridges is obtained when the cross-link reactions are formed directly between the collagen chains without any exogenous/bridge molecule being incorporated in the network of collagen fibers.

In order to allow the above reactions to take place, it is necessary to have fine control over the environmental conditions that are established; more specifically, it is appropriate to establish both a temperature that is high enough to ensure the necessary molecular mobility and a completely anhydrous reaction environment. The above conditions are obtained in environments with a high degree of vacuum (<100 mTorr) and at a temperature above 90 °C. In this respect, it is important to emphasize that the use of vacuum is essential to promote cross-link reactions, zero-length chemical bridges, as well as to reduce the risks of denaturation and proteolysis facilitated by the increase in the levels of residual moisture.

Basically, therefore, the activation of reactive groups present in collagen is achieved by means of a dehydrothermal treatment that is provided in practice by placing the hides in an environment in which the pressure is equal to or lower than 100 mTorr (i.e., lower than 13.33 Pa) and the temperature is equal to or greater than 90 °C.

The dehydrothermal treatment (DHT) can occur at temperatures varying from 90 to 150°C.

The duration of the treatment can vary from 2 to 48 hours. Optionally, the dehydrothermal treatment (DHT) is preceded by a hide drying step which can occur for a time that varies from 2 to 10 hours at a temperature that varies from 25 to 55 °C.

By increasing the temperature and duration of the dehydrothermal treatment (DHT) it is possible to stabilize the collagen network and also to increase the mechanical properties of the collagen fibers. The high temperatures used during said process entails a denaturation of the collagen, i.e., the rearrangement of the collagen triple helix in a random configuration of said chain. This phenomenon leads to the destruction of the native conformation of the collagen and thus to the collapse of the macromolecular structure and the loss of the characteristic properties of the collagen network.

The method according to the invention allows to overcome this limitation, since said dehydrothermal treatment step is preceded by the step of selective removal of the aqueous component from the animal dermis. This water removal step which precedes DHT allows to preserve the micro- and macroscopic components of the collagen fibers, their spatial organization and their intrinsic mobility.

It is well-known that the micro- and macroscopic components of collagen fibers, their spatial organization and their intrinsic mobility, determine the final physical-mechanical properties of the leather item as well as its organoleptic properties and performance.

Performing the dehydrothermal treatment (DHT) on a native animal hide subjected to a dehydration process, with the step described above (i.e., by selective removal of the interstitial water), avoiding to cause significant changes in the interfibrillar space, allows to increase the interfibrillar movement constraints and avoids altering the intrinsic mobility of the fibrils. All this results in a significant increase in the elastic recovery of the collagen network consequent to any deformation imposed.

The increase in elastic recovery is due to the presence of nodal points generated by virtue of the dehydrothermal treatment, which does not entail an appreciable variation of the elastic modulus of the manufactured article.

Therefore, the combination of the two main steps al) and a2) just described allows to modulate the extensional properties of the dermis but above all given a significant increase in elastic recovery to the collagen network, following an imposed deformation, since nodal points are generated between the fibers; there is therefore an increase in the interfibrillar movement constraints while leaving unchanged the intrinsic mobility of said fibers.

Preferably, prior to the step of removing the aqueous component there is a step bl) of neutralization and bating, i.e., the execution in sequence of a neutralization process followed by a bating process.

The neutralization process is used to reduce the acidity of the semi finished (pickled) hides from a pH of about 3 to a pH of about 6.5. This pH value is operative for better enzymatic activity and to be able to modify with an easier manipulation the pH of the dermis in order to be able to perform successfully some chemical and physical treatments. Neutralization can be performed with a two-step treatment, treating the hides (more precisely the dermis) initially with sodium formate and subsequently with sodium bicarbonate.

The bating process follows the neutralization process and provides an enzymatic degradation that consists in treating the hides (and more precisely the dermis) with synthetic/industrial enzymes adapted to modify the protein composition of the animal dermis.

It is possible to use lipogenic enzymes to eliminate any lipidic component or enzymes with elastinolytic activity to remove any elastin fraction (or both types). The final goal is to obtain looser/more open meshes of the collagen network so that the fibers are better exposed and to facilitate the subsequent steps of the treatment according to the invention.

The enzymes used for bating are chosen preferably, but not exclusively, from:

- Novocor AX, this denomination referring to an enzymatic mix of subtilisin and a-amylase that both in the case of wet blue and in the case of pickled leather preferentially degrade elastin, showing a very low degrading action with respect to the collagen; this enzyme performs its action at a pH comprised between 5.5 and 9.5;

- Basozym CIO, which consists of a bating mixture of pancreatic extracts for all types of leather with different tanning state, performs its action at a pH comprised between 5.5 and 9.5;

- Prozyme OR-R, which consists of a mixture comprising a combination of enzymes based on active ingredients of trypsin, amylase and lipase, performs its action at an acid pH comprised between 3 and 5.5;

- Prozyme PK, which consists of an enzyme mix, bating in an acid environment (optimum pH for its action comprised between 3 and 5.5);

- Prozyme WB (optimum pH for its action comprised between 3 and

5.5);

- Prozyme VE (optimum pH for its action comprised between 3 and

5.5);

- Globalbatin WB, which is an agent indicated for acid bating (optimum pH for its action comprised between 3 and 5.5);

- Globalbatin VP, which consists of a microbiologically based bating agent that performs its action in a weakly acidic range (optimum pH comprised between 6 and 6.5);

- NS45 for bating for 6 and 18 hours, performs its action at a pH comprised between 10 and 11.

Preferably, after step al) of selective removal of the aqueous component and before step a2) of dehydrothermal treatment, a step b2) of mechanical traction is performed on the hides.

This step of mechanical traction entails that the hides (and more precisely the animal dermis) is subjected to mechanical stress by traction performed in the direction of the vertebral axis (which corresponds to the head-tail axis of the animal from which the hides originate) so as to transfer the elasticity only in one direction (side-to-side).

In the preferred embodiment, with reference to Figure 2, the method is composed of all the previously described steps, performed in the following order: bl) neutralization and bating; al) selective removal of the aqueous component; b2) mechanical traction; a2) dehydrothermal treatment (DHT).

At the end of said steps, the organoleptic properties of the hides, such as silky feel, round handfeel and breathability, remain unaltered but, in addition, enhanced characteristics of stretching and elastic recovery of deformations are obtained.

At the end of the different steps of which the method according to the invention is composed, the hides can be tanned by following the standard supply chain processes and treatments currently used in the tanning industry.

In practice it has been found that the method for functionalizing treatment according to the present invention achieves the intended aim and objects, since it allows to improve the elastic properties of the hides without adding exogenous and/or synthetic molecules.

Another advantage of the method according to the invention is that it improves the extensional characteristics of the animal dermis by giving high elasticity to the leather articles, modulating and improving the properties of stretching and elastic recovery, without adding exogenous and/or synthetic molecules.

Another advantage of the method according to the invention resides in that it gives elasticity to the hides while maintaining furthermore unchanged the natural breathability and softness and also making the hides adaptable to different shapes, with improved performance and characteristics with respect to the background art.

Yet another advantage of the method according to the invention resides in that it can be inserted within the standard supply chain processes and treatments used currently in the tanning field. Not last advantage of the method according to the invention resides in that it is highly reliable, relatively easy to provide and at competitive costs if compared with the background art.

The method for functionalizing treatment of hides thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the accompanying claims.

All the details may furthermore be replaced with other technically equivalent elements.

In practice the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and the state of the art.

The disclosures in Italian Patent Application No. 102021000009920 from which this application claims priority, are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A method (1, 10) for the functionalizing treatment of hides of the type comprising a dermis of animal origin comprising fibers and/or fibrils of collagen and an aqueous component, in order to improve the elastic properties of said hides, characterized in that it comprises the steps of: al) removing selectively the aqueous component of the dermis of said hides, by using one or more organic solvents; a2) performing a dehydrothermal treatment for the activation of reactive groups present in the collagen, provided by arranging the hides in an environment in which the pressure is equal to or lower than 100 mTorr and the temperature is equal to or higher than 90°C.

2. The method (1, 10) according to claim 1, wherein said step al) of removing the aqueous component of the dermis is provided so as to cause a total volumetric reduction of the dermis of less than 5%.

3. The method according to claim 1 or 2, wherein said organic solvents are chosen from:

- acetone,

- ethanol,

- propanol, - isopropyl alcohol.

4. The method according to one or more of the preceding claims, wherein in said step al), which consists in selectively removing the aqueous component, one or more cycles of treatment of the hides in said one or more solvents are performed, each cycle having a duration comprised between 10 minutes and 10 hours and being performed at a temperature comprised between 2°C and 40°C; the quantity of solvent used in each cycle being comprised between 1% and 500% of the weight of the hides to be treated.

5. The method according to one or more of the preceding claims, wherein said dehydrothermal treatment is performed at a temperature comprised between 90°C and 150°C for a duration comprised between 2 and 48 hours.

6. The method according to one or more of the preceding claims, wherein prior to step al), which consists in removing the aqueous component, a step is provided of: bl) neutralizing and bating, in which the following are performed in sequence:

- a neutralization process, adapted to reduce the acidity of the hides, followed by

- a bating process, which consists in treating the hides with one or more enzymes adapted to modify the protein composition of the dermis.

7. The method according to claim 6, wherein said neutralization process is performed by treating the hides first with sodium formate and then with sodium bicarbonate.

8. The method according to claim 6 or 7, wherein in the bating process one or more lipogenic enzymes are used to eliminate any lipidic component and/or one or more enzymes with elastinolytic activity are used in order to remove any elastin fraction.

9. The method according to one or more of claims 6 to 8, wherein said one or more enzymes are chosen from:

- Novocor AX;

- Basozym CIO;

- Prozyme;

- Prozyme PK;

- Prozyme WB;

- Prozyme VE;

- Globalbatin WB;

- Globalbatin VP;

- NS45.

10. The method according to one or more of the preceding claims, characterized in that after step al), which consists in removing selectively the aqueous component, and prior to step a2) of dehydrothermal treatment, a step is performed which consists of: b2) mechanical traction, in which the hides are subjected to a mechanical traction performed in the direction of a vertebral axis that corresponds to the head-tail axis of the animal from which the hides originate.

11. The method according to one or more of the preceding claims, wherein said step a2) of execution of a dehydrothermal treatment is preceded by a step of drying the hides for a time comprised between 2 and 10 hours and at a temperature comprised between 25 and 55°C.