WO2023131273A1

WO2023131273A1 - Preparing leather composite and product thereof

Info

Publication number: WO2023131273A1
Application number: PCT/CN2023/070908
Authority: WO
Inventors: Gloria YAO; John Leung; Tom SIU; Tsz Kin IP
Original assignee: The Hong Kong Research Institute Of Textiles And Apparel Limited
Priority date: 2022-01-07
Filing date: 2023-01-06
Publication date: 2023-07-13
Also published as: CN118525117A

Abstract

Provided herein is a method of preparing a leather composite using leather fiber, leather composites formed therefrom, and multilayer leather composites comprising the same. Leather fibers derived from, e.g., virgin leather sheet waste, leather sheet of post-industrial or post-consumer leather products can be used in the method.

Description

PREPARING LEATHER COMPOSITE AND PRODUCT THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from United States Provisional Patent Application No. 63/297,271, filed on January 7, 2022, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a leather composite material and methods of preparation thereof.

BACKGROUND

Turning a piece of cow skin into a pair of cowboy boots or a fancy handbag is a very time and labor intensive process requiring highly skilled work. During the manufacturing process of any leather product, a large amount of solid waste is generated. Typically, the total yield of common leather products is much less than 50%; this is very true, especially when talking about high-end fine leather products, such as luxury car upholstery of, high-end sofa and the leather coverings for large furniture and appliances. Usually, the original design for these expensive applications calls for a whole piece of near perfect leather. In other words, more than 50%of the raw hide will be dumped as leather shaving, cutting scrap or even down-graded for other applications.

In the European Union, about 1,200,000 tons of tannery solid waste is generated annually. Common tannery leather waste has high chromium content, which is harmful to human health and potentially toxic to the environment. Tannery byproducts typically include high amounts of fats and protein, which can be recycled using suitable technologies. Leather manufacturers must sustain high costs for waste disposal and must adhere to local and national environmental regulation standards due to the production of large quantities of waste. Moreover, leather manufacturing waste treatment can be very expensive, owing to the transport, handling, physical treatment and disposal of toxic compounds and the high energy consumption involved.

There thus exists a need for improved methods to recycle leather waste materials in an eco-friendly fashion.

SUMMARY

The present disclosure relates to methods for preparing a leather composite involving reaction of a carbohydrate or a carbohydrate derivative and optionally arginine through the Maillard reaction with the amino groups in leather fiber to form bonding sites for a binding material. The leather fiber used to form the leather composite can be extracted from virgin leather sheet waste or post-industrial or post-consumer leather sheet products. It gains advantages by forming bonding sites ready for effective reaction with other protein groups and binding materials to interconnect the leather fibers. Foldability, tensile strength, and water resistance properties can be adjusted by appropriate selection of binding material. The methods described herein are particularly suitable for chromium-tanned leather waste since the stable chromium content linking the collagen inside leather fiber has already served as an antiseptic to protect the leather and retard microbe growth.

In a first aspect, provided herein is a method comprising: contacting a leather fiber with a carbohydrate or a carbohydrate derivative and optionally arginine thereby forming a treated leather fiber.

In certain embodiments, the method further comprises contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and optionally molding the leather composite.

In certain embodiments, the leather fiber is or is derived from a leather waste product, a post-industrial leather product, a post-consumer leather product, or an animal hide selected from the group consisting of cattle hide, deer hide, goat hide, lamb hide, sheep hide, pig hide, wolf hide, rabbit hide, kangaroo hide, crocodile hide, fish hide, snake hide, alligator hide, mule hide, horse hide, mouse hide, donkey hide, and camel hide, or a mixture thereof.

In certain embodiments, the leather fiber is chromium-tanned leather fiber.

In certain embodiments, the method further comprises the step of extracting a portion of the chromium in the chromium-tanned leather fiber prior to the step of reacting the leather fiber with the carbohydrate or the carbohydrate derivative and optionally arginine.

In certain embodiments, the step of extracting a portion of the chromium in the chromium-tanned leather fiber comprises contacting the chromium-tanned leather fiber with water, ethylenediaminetetraacetic acid (EDTA) , diethylenetriaminepentaacetic acid (DTPA) , NH ₄OH, NH ₄NO ₃, a phosphate buffer, or a mixture thereof.

In certain embodiments, the carbohydrate is selected from the group consisting of glucose, fructose, galactose, lactose, maltose, glyceraldehyde, arabinose, maltodextrin, corn syrup solid, starch, cellulose, and mixtures thereof; and the carbohydrate derivative is starch oxide or oxidized cellulose.

In certain embodiments, the step of contacting the leather fiber with the carbohydrate or the carbohydrate derivative is conducted at pH between 6-8.

In certain embodiments, the step of contacting the leather fiber with the carbohydrate or the carbohydrate derivative is conducted at a pH between 6.8-7.2.

In certain embodiments, the drying oil is selected from the group consisting of linseed oil, tung oil, poppy seed oil, perilla oil, walnut oil, sunflower oil, linoleic acid, poppy oil, soyabean oil, safflower oil, stand oil, blown oil, and mixtures thereof.

In certain embodiments, the step of molding the leather composite forms a leather composite sheet.

In certain embodiments, the leather fiber and the carbohydrate or the carbohydrate derivative are contacted in a mass ratio between 1: 0.1 to 1: 10.

In certain embodiments, the leather fiber and the arginine are contacted in a mass ratio between 1: 0.01 to 1: 0.1.

In certain embodiments, the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.05 to 1: 0.5.

In certain embodiments, the method comprises: contacting leather fiber with glucose thereby forming a treated leather fiber; contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and molding the leather composite, wherein the leather fiber and the glucose are contacted in a mass ratio between 1: 5 to 5: 1 and the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.1 to 1: 1.

In a second aspect, provided herein is a leather composite sheet prepared in accordance with the method described herein.

In a third aspect, provided herein is a multilayer leather composite comprising a first leather composite sheet, a second leather composite sheet, and a skeleton layer, wherein the skeleton layer is disposed between the first leather composite sheet and the second leather composite sheet and wherein each of the first leather composite sheet and the second leather composite sheet are independently prepared in accordance with the method described herein.

In certain embodiments, the skeleton layer comprises a woven, non-woven, or knit material select from the group consisting of silk, wool, leather, cellulose, cotton, and combinations thereof.

In certain embodiments, the each of the first leather composite sheet and the second leather composite sheet are independently prepared by a method comprising: contacting leather fiber with glucose thereby forming a treated leather fiber; contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and molding the leather composite, wherein the leather fiber and the glucose are contacted in a mass ratio between 5: 1 to 1: 5 and the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.1 to 1: 1.

In certain embodiments, a surface of at least one of the first leather composite sheet and the second leather composite sheet is embossed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present disclosure will become apparent from the following description of the disclosure, when taken in conjunction with the accompanying drawings.

Figure 1 depicts a flow chart show the steps of an exemplary method of preparing a leather composite comprising Part 1 and Part 2 in accordance with certain embodiments described herein.

Figure 2 depicts a multilayer leather composite in accordance with certain embodiments described herein.

Figure 3 depicts an exemplary reaction sequence showing reaction products and intermediates of the Maillard reaction of an aldose and an amino compound.

Figure 4 depicts exemplary heterocyclic products of the Maillard reaction.

Figure 5 depicts an exemplary flowchart for processes for preparing bio-based PU.

DETAILED DESCRIPTION

Definitions

Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, or comprising specific process steps, it is contemplated that compositions of the present teachings can also consist essentially of, or consist of, the recited components, and that the processes of the present teachings can also consist essentially of, or consist of, the recited process steps.

In the application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that the element or component can be any one of the recited elements or components, or the element or component can be selected from a group consisting of two or more of the recited elements or components. Further, it should be understood that elements and/or features of a composition, an apparatus, or a method described herein can be combined in a variety of ways without departing from the spirit and scope of the present teachings, whether explicit or implicit herein

The use of the terms "include, " "includes" , "including, " "have, " "has, " or "having" should be generally understood as open-ended and non-limiting unless specifically stated otherwise.

The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term "about" is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term "about" refers to a ±10%, ±7%, ±5%, ±3%, ±1%, or ±0% variation from the nominal value unless otherwise indicated or inferred.

It should be understood that the order of steps or order for performing certain actions is immaterial so long as the present teachings remain operable. Moreover, two or more steps or actions may be conducted simultaneously.

When trade names are used herein, applicants intend to independently include the trade name product formulation, the generic drug, and the active pharmaceutical ingredient (s) of the trade name product.

The method for preparing the leather composite described herein can be divided into three steps. The first step is an optional pre-treatment step in which any contaminants can be washed away from the recycled leather waste, then its shape must be reduced to proper size to allow easy handle, and its pH has to bring back to near neutral. The second step is carrying out the modified Maillard reaction, where the pre-treated leather fiber will be converted to leather composite material namely pretreated leather fiber will react with a carbohydrate or a carbohydrate derivative optionally in the presence of arginine. The third step is the fabrication methods of sheet of leather composite material, such as by drying oil approach, a natural latex solution comprising graphene oxide approach, casein approach, bio-based PU approach, and amino silicone approach. Below examples are the application methods.

Provided herein is a method of preparing a leather composite, the method comprising: first, the optional pre-treatment of the recycled leather waste, which includes washing away contaminants, chopping to proper size, and adjusting pH to near neutral (e.g., about pH 7) ; second, reacting leather fiber with a carbohydrate or carbohydrate derivative and optionally arginine thereby forming treated leather fiber; third, reacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming the leather composite; and fourth, optionally molding and embossing the leather composite.

The leather fiber can be derived from many sources, such as virgin leather, leather waste product, a post-industrial leather product, a post-consumer leather product, or a mixture thereof; or the leather fiber can be derived from a leather waste product, a post-industrial leather product, a post-consumer leather product, or a mixture thereof.

Examples of post-consumer and post-industrial products include, but are not limited to, shoes, garments, luggage, handbags, gloves, fabrics, textiles, furniture, clothing, sporting goods, and the like.

Leather waste products can also include wet blue shavings, tanning shavings, split hide waste, reject/off specification hides, buffing powder, pattern trim, binder waste, die cut waste, and sewing waste.

The leather fiber can be derived from any type of animal hide. In certain embodiments, the leather fiber is an animal hide leather fiber selected from the group consisting of cattle hide leather fiber, deer hide leather fiber, goat hide leather fiber, lamb hide leather fiber, sheep hide leather fiber, pig hide leather fiber, wolf hide leather fiber, rabbit hide leather fiber, kangaroo hide leather fiber, crocodile hide leather fiber, fish hide leather fiber, snake hide leather fiber, alligator hide leather fiber, mule hide leather fiber, horse hide leather fiber, mouse hide leather fiber, donkey hide leather fiber, and camel hide leather fiber, or a mixture thereof. In certain embodiments, the leather fiber is cattle hide leather fiber.

The length of the leather fibers can range between 0.1 to 50 mm, 0.1 to 40 mm, 0.1 to 30 mm, 0.1 to 20 mm, 0.1 to 10 mm, 0.1 to 9 mm, 0.1 to 8 mm, 0.1 to 7 mm, 1 to 7 mm, 1 to 6 mm, 1 to 5 mm, 1 to 4 mm, 1 to 3 mm, or 1 to 2 mm.

In certain embodiments, the average diameter of the leather fiber can range between 0.1 to 0.001 mm.

Collagen is the major structural protein found in leather. The most common peptide motif in collagen protein is Gly-X-Y, wherein X and Y can be any amino acid residue other than glycine. Nucleophilic functionality in collagen, such as amines, mercaptans, alcohols, and the like that is capable of reacting with the carbonyl groups in carbohydrates.

Carbohydrates suitable in the methods described herein can include monosaccharides, disaccharides, oligosaccharides and polysaccharides comprising at least one moiety selected from the group consisting of a hemiacetal, acetal, hemiketal, ketal, aldehyde, and ketone, which is capable of undergoing reaction with nucleophiles (such as side chain amines and N-terminal amines) present in leather. Carbohydrates or carbohydrate derivatives comprising ketal, hemiketal, and ketone moieties may undergo isomerization under acidic or basic Maillard reaction conditions to yield acetal, hemiacetal, and/or aldehyde moieties in situ, which are can undergo reaction with nucleophiles present in the leather fibers. In certain embodiments, the carbohydrate or carbohydrate derivative is a reducing sugar.

Exemplary carbohydrates include C ₃-C ₈ aldoses, such as, trisoses, such as glyceraldehyde, glucic acid, tetroses, such as erythrose and threose, pentoses, such as arabinose, lyxose, ribose, and xylose, hexoses, such as allose, altrose, glucose, mannose, gulose, idose, galactose, and talose; C ₃-C ₈ ketoses, such as trioses, such as dihydroxyacetone, tetroses, such as erythrulose, pentoses, such as ribulose and xylulose, and hexoses, such as fructose, psicose, sorbose, and tagatose; and disaccharide reducing sugars include, such as lactose, sucrose, fructose, maltose, trehalose, and cellobiose. In certain embodiments, the carbohydrate is glucose. In certain embodiments, carbohydrate derivative is selected from the group consisting of starch oxide and oxidized cellulose.

As illustrated in Figure 3, depending on the pH that the step of contacting the leather fiber with the carbohydrate is conducted, treated leather fiber comprising different chemical products can result. In certain embodiments, the pH of the step of contacting the leather fiber with the carbohydrate is 4-7, 4-6.5, 4-6, 4-5.5, 4-5, 4.5-6.5, 5-6.5, 5.5-6.5, 6-7, 7-10, 7-9.5, 7-9, 7-8.5, 7-8, 7.5-10, 8-10, 8.5-10, or 9-10.

The step of contacting the leather fiber with the carbohydrate or the carbohydrate derivative and optionally arginine can be conducted in any solvent in which the carbohydrate or carbohydrate derivative and optionally arginine are at least partially soluble. In certain embodiments, the solvent comprises water.

In certain embodiments, the method further comprises the step of adjusting the pH of the leather fiber prior to the Maillard reaction between leather fiber and carbohydrate or carbohydrate derivative. Since the leather fiber may be subjected to lye soaking and acid washing steps; the pH of raw material collected may vary. On the other hand, the Maillard reaction is typically conducted at high temperature with slightly acidic pH (e.g., between 5-7, 5.5-7, 6-7, or 6.5-7) . Under high temperature, either strongly acidic or basic conditions may lead to carbohydrate degradation. Therefore, it may be necessary to neutralize the pH of the leather fiber prior to the Maillard reaction.

In this aspect, the acid is not limited to any particular type of acid. Suitable acids can be an organic or an inorganic

acid or Lewis acid comprising relatively non-reactive anion (s) (e.g., anions that are not a strong oxidants and/or nucleophiles) . Exemplary acids include, but are not limited to, HCl, H ₂SO ₄, HSO ₄ ^-, H ₃PO ₄, H ₂PO ₄ ^-, methanesulfonic acid (MsOH) , trifluoromethanesulfonic acid (Triflic acid or TfOH) , benzenesulfonic acid, p-toluenesulfonic acid (pTsOH, or tosylic acid TsOH) , trifluoroacetic acid (TFA) , fumaric acid, maleic acid, succinic acid, benzoic acid, acetic acid, citric acid, tartaric acid, and combinations thereof.

The base can be an organic or inorganic

base. In certain embodiments, the base is an organic amine, metal hydroxide, metal carbonate, metal alkoxide, and mixtures thereof. Exemplary bases include, but are not limited to, ammonia, Hünig's base (N,N-diisopropylethylamine, DIPEA, DIEA, or i-Pr ₂NEt) , ethanolamine, di-ethanolamine, tri-ethanolamine, dimethylethanolamine (DMEA) , pyridine, pyrazine, trimethylamine (TMA) , triethylamine (TEA) , morpholine, N-methyl morpholine, piperdine, piperazine, pyrrolidine, 1, 4-diazabicyclo [2.2.2] octane (DABCO) , imidazole, N-methylmorpholine, NaOH, CsOH, LiOH, NaOH, KOH, Na ₂CO ₃, K ₂CO ₃, Cs ₂CO ₃, LiOtBu, NaOtBu, KOtBu, and the like.

The leather fiber and the carbohydrate or carbohydrate derivative can be combined in any ratio. In certain embodiments, the leather fiber and the carbohydrate or carbohydrate derivative are contacted in a mass ratio between 1: 0.1 to 1: 4, respetively.

The reaction of the leather fiber and the carbohydrate or carbohydrate derivative can be conducted at 20-100 ℃. In certain embodiments, the leather fiber and the carbohydrate or carbohydrate derivative are contacted at 25-100 ℃, 25-95 ℃, 30-90 ℃, 30-80 ℃, 30-70 ℃, 30-60 ℃, 30-50 ℃, 30-40 ℃, 40-90 ℃, 50-80 ℃, 60-80 ℃, 70-80 ℃, 40-80 ℃, 50-70 ℃, or 60-70 ℃.

The leather fiber and arginine can be combined in any mass ratio. In certain embodiments, the leather fiber and arginine are contacted in a mass ratio between 1: 0.01-1:0.1.

The reaction of the leather fiber and arginine can be conducted at 20-100 ℃. In certain embodiments, the leather fiber and the arginine are reacted under 25-100 ℃, 25-95 ℃, 30-90 ℃, 30-80 ℃, 30-70 ℃, 30-60 ℃, 30-50 ℃, 30-40 ℃, 40-90 ℃, 50-80 ℃, 60-80 ℃, 70-80 ℃, 40-80 ℃, 50-70 ℃, or 60-70 ℃.

The treated leather fiber is contacted with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby binding the leather fibers together and forming the leather composite, which can optionally be molded.

In certain embodiments, the protein isolates includes, but is not limited to, the isolate of gelatin, whey protein, casein, egg protein, milk protein, silk gel protein (e.g., sericin) and combinations thereof.

The natural latex solution can comprise graphene oxide at a concentration of 0.01-5%m/m. In certain embodiments, the natural latex solution comprises graphene oxide at a concentration of 0.01-5%m/m, 0.01-4.5%m/m, 0.01-4%m/m, 0.01-3.5%m/m, 0.01-3%m/m, 0.01-2.5%m/m, 0.05-2.5%m/m, 0.01-2%m/m, 0.01-1.75%m/m, or 0.033-1.63%m/m. In certain embodiments, the natural latex solution comprises graphene oxide at a concentration of 0.05-2.0%m/m, 0.05-1.5%m/m, 0.05-1.0%m/m, 0.5-2.5%m/m, 1.0-2.5%m/m, 1.5-2.5%m/m, or 2.0-2.5%m/m.

Drying oils are triglycerides composed from polyunsaturated fatty acid (PUFA) , which contains lots of highly active, double allylic position (e.g. RCH=CH-CH ₂-CH=CHR) hydrogen atoms, which are activated twice (c. f. by double bond from both sides) . This chemical structure character, makes the molecule easily initiated by atmospheric oxygen or other radical initiators under room to elevated temperature. In order to start the polymerization easily, the polyunsaturated fatty acid part of the triglyceride must have at least two double bonds located in one fatty acid. These double bonds may or may not be conjugated. However, triglycerides composed from monounsaturated fatty acid (MUFA) such as the triglyceride of oleic acid (e.g. olive oil) does not count as drying oil.

When exposed to air, oxygen will trigger free radical polymerization reactions and solidify the liquid drying oil into a rubbery mass. Any drying oil known to those skilled in the art can be used in the methods described herein. Drying oil can include semidrying oils (e.g., drying oils with iodine values between 100-130) as well as drying oils (e.g., drying oils with iodine values between 130-190) . The drying oil can be naturally occurring or synthetic. Exemplary drying oils include, but are not limited to linseed oil, tung oil, poppy seed oil, perilla oil, walnut oil, sunflower oil, linoleic acid, poppy oil, soybean oil, safflower oil, and mixtures thereof.

In certain embodiments, the amino silicone oil is a diamino capped polydimethylsiloxane, such as an diaminoalkyl-dialkylsiloxane block polymer. In certain embodiments, the amino silicone oil is represented as: -R’ (CH ₂) _mNH- [Si (Me) ₂O] _n- [SiR” MeO] _p -or a conjugate sale thereof, wherein each of m, n and p is independently a whole number selected from 1-1,000; R’ for each instance is independently OH, NH ₂, alkyl, or alkoxy; and R” is - (CH ₂) _q-NR- (CH ₂) _r-NR ₂, wherein each of q and r is independently a whole number selected from 0-6; and R for each instance is independently alkyl or H; or R” is - (CH ₂) _q-NR ₂, wherein q is a whole number selected from 0-6; and R for each instance is independently alkyl or H. In the interest of simplicity the chemical structure: -R’ (CH ₂) _mNH [Si (Me) ₂O] _n [SiR” MeO] _p is depicted as a block copolymer. However, random copolymers, regiorandom copolymers, regioregular copolymers alternating copolymers are also contemplated.

Crosslinkers, such as genipin, can also be used to bind the treated leather fibers. Genipin is a non-toxic naturally occurring crosslinker capable of crosslinking nucleophilic moieties present in the leather fiber. Other crosslinkers useful in the methods described herein include, but are not limited to these di-or multiple-electrophiles such as carbonyl, azidirine (ethylene imine, N) , epoxide (ethylene oxide, O) , thiirane (ethylene sulfide, S) isocyanates, vinyl ketones and vinyl sulfones and their derivatives. For example, the di-carbonyl compounds include but not limited to adipaldehyde (C6) , glutaraldehyde (C5) , succinaldehyde (C4) , malondialdehyde (C3) and glyoxal (C2) .

The treated leather fiber and the binding material can be contacted in any mass ratio. The addition ratio and the intrinsic nature of the binding material (e.g. carbohydrate, protein isolate, drying oil, reactive amino silicone oil, and crosslinkers) will determine the final outcomes -the physical properties of leather composite –such as its foldability, tensile strength, water resistance will be dramatically changed by the binding material. In certain embodiments, the treated leather fiber, carbohydrate or carbohydrate derivative and the protein isolate is mixed in a mass ratio between 1: 0.4 to 1: 4.

The steps of conducting the Maillard reaction between the leather fiber and the carbohydrate or the carbohydrate derivative; optionally, it is possible to enhance the Maillard reaction by adding arginine to the reaction mixture. Since the tensile strength of the composite leather sheet (e.g., the Maillard product) is not as strong as the original leather; therefore, it is better to further stabilize its structure with a binding material. Optionally, the binder stabilization process can be repeated one or several times, thereby forming a complex multiple layer structure, which has several thin layers of composite leather and the binder layers deposited over each other. Additionally, this thin-film combination can also include the arginine enhanced Maillard product.

The formed leather composite can optionally be molded under pressure thereby forming a molded leather composite. The molded leather composite can take any shape, for example, the molded leather composite can be formed as a flat sheet, belt, boot, glove or hat. The leather composite can be molded using any method known to those of ordinary skill in the art. Exemplary methods include, but are not limited to, manual molding by hand, 2-piece molding, autoclave compression, hydraulic molding or diaphragm molding, and the like.

The present disclosure provides leather composites prepared in accordance with the methods described herein. In certain embodiments, the leather composite is molded into a flat composite leather sheet; however, the leather composites can optionally be shaped in any mold, which included but not limited to embossed and/or perfumed (spraying deodorant) . In other words, the leather composite sheet can be forced to form (2D) two-dimensional sheet or three-dimensional (3D) hollow ball shape.

Also provided herein is a multilayer leather composite comprising a first leather composite sheet, a second leather composite sheet, and a skeleton layer, wherein the skeleton layer is disposed between the first and the second leather composite sheet.

The skeleton layer can comprise a woven, non-woven, or knit material select from the group consisting of silk, wool, leather, cellulose, cotton, and combinations thereof.

Finally, these three layers are sandwiched together by two binder films (e.g. double sided adhesive film) and wherein the first and the second leather composite sheet are independently prepared in accordance with the method described herein. The binder film can be prepared from any adhesives such as gelatin or other protein isolate, natural latex, drying oil, bio-based PU, amino silicone, and genipin. Alternatively, the skeleton layer can be soaked in the binder solution, or spray the thick binder solution evenly over both sides to form a double-side adhesive film.

A binding material can disposed between the first leather composite sheet and the skeleton layer and between the second leather composite sheet and the skeleton. The binding material can be any adhesive typically used to adhere leather and/or textiles; or the binding material is selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based-polyurethane, an amino silicone, and genipin.

Leather Fiber Pretreatment : the leather fiber is extracted from waste leather by first chopping to proper size by cut mill. The small pieces of waster leather is then soaking in sufficient amount of detergent solution under raised temperature (e.g. 40～55 C, warm to touch) for several days with sufficient stirring to remove both hydrophilic and hydrophobic contaminations such as dust, dirt, grease, oil, salt, base and acid. The excess amount of water in the cleaned wet leather is removed by centrifugal or vacuum filtration. The pH of this wet leather is adjusted to near neutral by adding proper amount of acid or base solution. The neutral wet leather is dried for the second time by centrifugal or vacuum filtration.

The extracted leather fiber can undergo below process for pre-treatment before they are applied on fabrication of sheet of leather composite material.

i. Chromium stabilizing

ii. Maillard reaction or arginine enhanced Maillard reaction

In step i, the application of Na ₂EDTA helps to stabilize the free dangling chromium in the leather waste. It removes the loosely connected chromium from the first step. For chromium tanned leather waste, this step would be appreciated, if the buyer minds the “leaking chromium” issue. Since the waste leather are collected from different sources, in different stages of the leather preparation process. Therefore, adding a pre-wash step will guarantee all dangling (e.g. free) chromium to be removed from the very beginning of the recycling. Hence, the residue chromium content from the different batches of the recycling waste leather would be reduced dramatically.

After chrome tanning process, the chromium is in the form of Cr (III) , which bonds to the collagen fibers to form a thermally-stable structure. After pulverizing leather sheet into leather fibers, some Cr (III) may be loosened from leather fiber and exposed to air. This transformation largely increases its chance of oxidation to toxic Cr (VI) by air. It is not preferred to remove all Cr (III) , since this will make leather more vulnerable to microbial decomposition. Therefore, only small amount of Na ₂EDTA is applied to stabilize the loosely connected chromium from the beginning of waste leather recycling process. For examples, 25ml -100ml room temperature saturated Na ₂EDTA at pH 10 was used to soak 4 grams of leather fibers. The wet fibers was first washed by water then filtered over mild vacuum; the wet filter cake was further followed by soaking in 20 ml of 95%ethanol then filtered over mild vacuum to dryness. This removes dangling chromium and water.

The remaining Cr (III) linking the collagen inside the leather fiber has also served as an antimicrobial to protect the leather composite material from microbes. Thus, only a small amount of Na ₂EDTA is used to avoid over-extraction of chromium thereby ensuring at least some stable Cr (III) remains in the leather fibers.

During the Maillard reaction, when carbohydrates is incubated with collagen fibers, the remaining Cr (III) also helps to ensure the growth of microbe under control.

In step ii, Maillard reaction happens between the amino side chains (e.g. Lys, Arg) of collagen with carbohydrates and carbohydrates derivatives, to form stable heterocyclic compounds, as shown in Figure 3. Without the carbohydrates or carbohydrates derivatives, the leather fiber may not be able to form stable bonding with other protein or chemicals easily.

For example of application of Maillard reaction, 100 ml of 4～25%w/w carbohydrate (includes but no limited to glyceraldehyde, glucose, starch, cellulose) or carbohydrate derivatives (includes but not limited to glucic acid, gluconic acid, starch oxide, oxidized cellulose) is mixing thoroughly with 5-20 g of pre-treated leather fiber to form a homogeneous suspension. This suspension is then poured into a stainless-steel baking pan, then put in a baking oven for 1-4 hours at 30-95℃ to allow most of water to evaporate smoothly to form a film, and then other proteins or binding material, for example, casein, drying oil, a natural latex solution comprising graphene oxide, bio-based PU and amino silicone, can be added over the film to bond with the middle product, also for 1-4 hours at 30-95℃. The semi-dried film after this process can be directly punched by a cutting mold and formed. The molded leather can then go through the processes of skeleton adding, perfumed (spraying deodorant) , compression, surface finishing and embossing to form a sheet of leather composite material.

Arginine can also be added though similar way to enhance Maillard reaction. For example, 0.3-1.2M arginine aqueous solution can be mixed with 1-10 g of treated leather to incubate under 30-95℃ for 1-4 hours, and then adding the other proteins or binding material, for examples, casein, drying oil, natural latex solution comprising graphene oxide, bio-based PU and amino silicone, can be added into the solutions to bond with the arginine, also for 1-4 hours at 30-95℃ in a shallow dish to form a film. After this incubation period, the semi-dried film can be directly punched by a cutting mold to form a sheet in specific shape. This shaped, sticky film can either wait for dry up, or directly go through the following processes such as skeleton adding, perfuming (spraying deodorant) , compression, surface finishing and embossing to form the designated leather composite material.

Two or multiple pieces of the semi-dried tacky films can be directly compress-binding together to build a thicker but yet flexible sheet of composite leather. Alternatively, it is also possible to repeat the addition steps over the already formed thin film. For example, the addition of arginine and other binder can be applied, to form a long molecule chain to make the leather composite material more flexible. In one example, 0.3-1.2M arginine solution can be mixed with 1-10 g of leather to incubate under 30-95℃ for 1-4 hours in a shallow pan to form a film. Then, the other proteins or binding material, for examples, casein, drying oil, natural latex solution comprising graphene oxide, bio-based PU and amino silicone, can be added over the formed tacky film to bond with arginine, also for 1-4 hours at 30-95℃.

The arginine enhanced Maillard reaction –it happens between arginine, chromium stabilized collagen, carbohydrate or carbohydrate derivatives. It already mentioned above, which can be optionally applied depend on the chemical content and desired physical properties needed. No matter leather fibers has first gone through these pre-treatment processes or not, leather fibers can still go through this arginine enhanced Maillard reaction to form a sheet of composite material. Except the arginine enhanced Maillard reaction, there are also the other approaches available. Examples are as shown below.

Example 1 Drying Oil Approach

This fabrication method of leather composite material by applying drying oil on leather fiber involve below steps:

i. The spray on leather-drying oil suspension is prepared as the ration stated here: 10.0 g of dry collagen fiber (as fine powder) , 3.0～5.0 g of drying oil (e.g. 3.0 for viscous stand oil, 5.0 for thinner oil) , diluted with at least 50～100 ml of organic solvent to form a stable homogeneous suspension.

ii. Spray this leather fiber suspension to the mold till a continuous film is form. This film is allowed to stand until semidried.

iii. Spreading the solution of protein isolate to the semidried surface

iv. Adding sheet of silk/wool/cellulose as skeleton material over the layer of casein

v. Repeating step ii and iii to allow the leather composite sheet to reach the desired thickness

vi. Apply sufficient amount of heat and pressure to assist the solidification process

vii. Perfuming (e.g. spraying deodorant) the finished leather composite

viii. Applying bio-based PU or another coat of drying oil as top coating for the sheet of composite leather

ix. Passing the sheet of leather composite through an embossing roller to apply leather texture, then followed by cutting die to form the designated pattern

In step i, leather fiber with a length of 1 mm –5 mm is mixed with proper amount of drying oil to form a homogeneously suspension; this suspension is sprayed by an air gun into a mold to deposit a continuous film with even thickness.

In step i, the preparation of spray-on leather fiber suspension, the drying oil including but not limited to, linseed oil, tung oil, poppy seed oil, perilla oil, and walnut oil -either used in the form of stand oil or blown oil. This suspension is spread over the surface of the forming table to form a continuous sheet and let the sheet of leather fiber to semidried. The drying oil is diluted with common organic solvent such includes but not limited to methylene chloride, acetone, butanone or ethyl acetate or any combination.

The spray-on method as mentioned in step ii, can be replaced by dry-lay method, which means to cover the forming table surface with sufficient thickness of dry leather fiber to form a mesh first, then spray the drying oil solution homogenously all over the leather fiber mesh. After the leather fiber mesh has soaked enough drying oil solution, and allowed the leather fiber sheet sufficiently dry to form an intact piece, then it is allowed to taken out for step iii.

In step iii, since drying oil mainly bond with leather fiber, other binder must be applied to stick firmly between the skeleton and the leather fiber sheet. A thin layer of casein solution (chloroform/methanol, triethylamine) is spread homogenously over the semi-dried surface of leather fiber composite sheet after step ii.

In step iv, skeleton is added over the layer of casein to stick the skeleton to the sheet of leather fiber composite.

In step v, the step ii is repeated to fabricate another side of sheet of leather fiber to cover the skeleton.

If the leather fiber before step i was already treated with Maillard reaction and bonded with drying oil to form a sheet of leather composite already, step i, ii can be skipped, only carry out step iii. The skeleton can be directly put on this sheet of leather composite material which covered by binder protein. Then another one of same kind of sheet of leather composite material can be put on the skeleton to form a sandwich structure. The process then can go to step vi.

In step vi, the assembled sheet of leather composite (e.g. plyleather) is dried under proper heat-press process; usually the temperature is below 95℃, the pressure is ranging from 5 kPa (0.05 ATM, forms very soft and flexible sheet) to 10 kPa (0.1 ATM, form rigid sheet) depending on the specific requirement.

In step vii, the sheet of leather composite material is perfumed by soaking into deodorant solution, allow the sheet to dry, then washed thoroughly with methanol or ethanol.

In step viii, the sheet of leather composite can be further pressed by hydraulic press to the desired thickness and shape such as 1mm -3mm, hemisphere shape. Residual liquid may be optionally pressed out at this stage.

In step ix, diluted bio-based PU or another coat of drying oil solution is spread on the surface of the sheet of leather composite as a clear finish coating.

In step x, pressing the sheet of leather composite material on the surface with finishing under hydraulic press to form leather texture with mold of leather pattern.

Example 2 Natural Latex + Graphene Oxide Approach

This fabrication method of leather composite material by applying natural latex with graphene oxide as binder on leather fiber involve below steps:

i. Laying treated leather fiber into a mold to form the shape of a sheet

ii. Adding solution of a natural latex solution comprising graphene oxide over the sheet of leather fiber in the mold and wait till the solution are fully absorbed.

iii. Adding skeleton of silk/wool/cellulose skeleton material, over the layer a natural latex solution comprising graphene oxide

iv. Repeating step ii and iii

v. Solidifying

vi. Pressing the sheet of leather composite material under hydraulic press to a desired thickness

vii. Application of bio-based PU binder or drying oil as finishing composite material

viii. Pressing the sheet of leather composite material under hydraulic press with a mold of leather pattern to apply leather texture

In step i, leather fiber with a length of 1 mm –5 mm is laid homogeneously into a mold, at density of, e.g., 0.01 g/cm ² -2 g/cm ², to form a sheet.

In step ii, binder solution of natural latex comprising graphene oxide is spread homogenously over the surface of the sheet and allowed to penetrate into the sheet of leather fiber. The binder solution is diluted by ethanol with proportion at least 20ml for 5ml natural latex solution comprising graphene oxide with 4 grams leather fibers. For 3g of latex, 0.001 -0.05 gram of graphene oxide can be applied.

The dry-lay method as mentioned in step i and ii, can be replaced by wet-lay method, which means the leather fiber is mixing with proper concentration of latex to form a suspension, this leather suspension is sprayed by an air gun into a mold first, then the dry leather fiber powder can be air sprayed over the wet film homogenously. After the leather fiber has soaked enough solution, then sheet of leather fiber is taken out to be ready for step iii.

In step iii, skeleton is added over the sheet of leather composite material with binder to stick the skeleton to the sheet of leather fiber.

In step iv, the step i and ii is repeated to fabricate another side of sheet of leather fiber to cover the skeleton.

If the leather fibers before step i were already subjected to the Maillard reaction and bonded with natural latex solution comprising graphene oxide to form the shape of a sheet of leather composite material already, step i, ii can be replaced. The skeleton can be directly put on this sheet of leather composite material. The same or different type of sheet of leather composite material can be put on the skeleton to form a sandwich structure. The process then can go to step v.

In step v, the binder in the sheet of leather composite material is dried and solidified in air or oven below 95℃.

In step vi, pressing the sheet of leather composite material under hydraulic press to desired thickness, including but not limited to, 1mm –3mm. Residue water may be pressed out in this stage.

In step vii, diluted bio-based PU or drying oil solution is spread on the surface of the sheet of leather composite material as finishing.

In step viii, pressing the sheet of leather composite material on the surface with finishing under hydraulic press to form leather texture with mold of leather pattern.

Example 3 Casein Approach

This fabrication method of leather composite material by applying casein on leather fiber involve below steps:

i. Laying treated leather fibers into mold to form the shape of a sheet

ii. Adding solution of casein over the sheet of leather fiber in the mold and wait until the casein is absorbed.

iii. Adding skeleton of silk/wool/cellulose skeleton material, over the layer of casein

iv. Repeating step i and ii

v. Solidifying

vi. Perfuming the sheet of leather composite material

vii. Pressing the sheet of leather composite material under hydraulic press to desired thickness

viii. Application of bio-based PU binder or drying oil as finishing composite material

ix. Pressing the sheet of leather composite material under hydraulic press with a mold of leather pattern to apply leather texture

In step i, leather fibers of length, including but not limited to, 1mm –5mm, would be laid homogeneously into a mold at density of e.g., 0.1 g/cm ² -2 g/cm ², to form a mesh.

In step ii, solution of casein is spread homogenously over the surface of the sheet and allow it to penetrate the mesh of leather fiber. The casein, for example of 20 g, is dissolved in least 20～30 ml of 30-70%methylene chloride /methanol and triethylamine mixture.

The dry-lay method as mentioned in step i and ii, can be replaced by wet-lay method, which means to prepare a pool of solution of binder of suitable concentration in a mold first, then distribute the leather fiber inside homogenously. After the leather fiber has soaked enough casein solution, the sheet of leather fiber is taken out to be ready for step iv.

In step iii, skeleton is added over the layer of casein to stick the skeleton to the sheet of leather fiber.

If the leather fiber before step i was already treated with Maillard reaction and bonded with casein to form the shape of a sheet of leather composite material already, step i, ii can be replaced. The skeleton can be directly put on this sheet of leather composite material. Then another one of same kind of sheet of leather composite material can be put on the skeleton to form a sandwich structure. The process then can go to step v.

In step vi, the sheet of leather composite material is perfumed by putting into solution of baking powder and/or tea leave, and then wash by ethanol.

In step vii, pressing the sheet of leather composite material under hydraulic press to desired thickness, including but not limited to, 1mm –3mm. Residue water may be pressed out in this stage.

In step viii, diluted bio-based PU or drying oil solution is spread on the surface of the sheet of leather composite material as finishing.

In step ix, pressing the sheet of leather composite material on the surface with finishing under hydraulic press to form leather texture with mold of leather pattern.

Example 4 Bio-Based PU Approach

This fabrication method of leather composite material by applying bio-based PU as binder on leather fibers involve below steps:

i. Laying treated leather fibers into mold to form the shape of a sheet

ii. Adding the solution of bio-based PU over the sheet of leather fiber in the mold and wait till the solution are fully absorbed.

iii. Adding skeleton of silk/wool/cellulose skeleton material, over the layer of bio- based PU

iv. Repeating step i and ii

v. Solidifying

vi. Pressing the sheet of leather composite material under hydraulic press to desired thickness

In step i, leather fibers of length, including but not limited to, 1mm –5mm, would be laid homogeneously into a mold, at density, including but not limited to, 0.01 g/cm ²–2 g/cm ², to form a shape of a sheet.

In step ii, binder solution of bio-based PU is spread homogenously over the surface of the sheet and let it infiltrate into the sheet of leather fiber. The binder solution is diluted by ethanol with proportion at least 20ml to 5ml bio-based PU.

The dry-lay method as mentioned in step i and ii, can be replaced by wet-lay method, which means to prepare a pool of solution of binder of suitable concentration in a mold first, then distribute the leather fiber inside homogenously. After the leather fiber has soaked enough solution, the sheet of leather fiber is taken out to be ready for step iii.

If the leather fibers before step i was already treated with Maillard reaction and bonded with bio-based PU to form the shape of a sheet of leather composite material already, step i, ii can be replaced. The skeleton can be directly put on this sheet of leather composite material. Then another one of same kind of sheet of leather composite material can be put on the skeleton to form a sandwich structure. The process then can go to step v.

Example 5 Amino Silicone Approach

This fabrication method of leather composite material by applying amino silicone binder on leather fibers involve below steps:

i. Laying treated leather fibers into mold to form the shape of a sheet

ii. Adding solution of amino silicone (e.g., amino silicone sold by Sigma-Aldrich ^TM 480304) over the sheet of leather fiber in the mold and wait till the solution are fully absorbed.

iii. Adding skeleton of silk/wool/cellulose skeleton material, over the layer of amino silicone

iv. Repeating step i and ii

v. Solidifying

In step ii, binder solution of amino silicone is spread homogenously over the surface of the sheet and let it infiltrate into the sheet of leather fiber. The binder solution is diluted by ethanol with proportion at least 20ml to 5ml amino silicone.

If the leather fibers before step i was already treated with Maillard reaction and bonded with amino silicone to form the shape of a sheet of leather composite material already, step i, ii can be replaced. The skeleton can be directly put on this sheet of leather composite material. Then another one of same kind of sheet of leather composite material can be put on the skeleton to form a sandwich structure. The process then can go to step v.

Claims

A method comprising: contacting a leather fiber with a carbohydrate or a carbohydrate derivative and optionally arginine thereby forming a treated leather fiber.
The method of claim 1 further comprising contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and optionally molding the leather composite.
The method of claims 1 or 2, wherein the leather fiber is or is derived from a leather waste product, a post-industrial leather product, a post-consumer leather product, or an animal hide selected from the group consisting of cattle hide, deer hide, goat hide, lamb hide, sheep hide, pig hide, wolf hide, rabbit hide, kangaroo hide, crocodile hide, fish hide, snake hide, alligator hide, mule hide, horse hide, mouse hide, donkey hide, and camel hide, or a mixture thereof.
The method of any one of claims 1-3, wherein the leather fiber is chromium-tanned leather fiber.
The method of claim 4 further comprising the step of extracting a portion of the chromium in the chromium-tanned leather fiber prior to the step of reacting the leather fiber with the carbohydrate or the carbohydrate derivative and optionally arginine.
The method of claim 5, wherein the step of extracting a portion of the chromium in the chromium-tanned leather fiber comprises contacting the chromium-tanned leather fiber with water, ethylenediaminetetraacetic acid (EDTA) , diethylenetriaminepentaacetic acid (DTPA) , NH ₄OH, NH ₄NO ₃, a phosphate buffer, or a mixture thereof.
The method of claim 1, wherein the carbohydrate is selected from the group consisting of glucose, fructose, galactose, lactose, maltose, glyceraldehyde, arabinose, maltodextrin, corn syrup solid, starch, cellulose, and mixtures thereof; and the carbohydrate derivative is starch oxide or oxidized cellulose.
The method of claim 1, wherein the step of contacting the leather fiber with the carbohydrate or the carbohydrate derivative is conducted at pH between 6-8.
The method of claim 1, wherein the step of contacting the leather fiber with the carbohydrate or the carbohydrate derivative is conducted at a pH between 6.8-7.2.
The method of claim 3, wherein the drying oil is selected from the group consisting of linseed oil, tung oil, poppy seed oil, perilla oil, walnut oil, sunflower oil, linoleic acid, poppy oil, soyabean oil, safflower oil, stand oil, blown oil, and mixtures thereof.
The method of any one of claims 3-11, wherein the step of molding the leather composite forms a leather composite sheet.
The method of any one of claims 1-11, wherein the leather fiber and the carbohydrate or the carbohydrate derivative are contacted in a mass ratio between 1: 0.1 to 1: 10.
The method of any one of claims 1-12, wherein the leather fiber and the arginine are contacted in a mass ratio between 1: 0.01 to 1: 0.1.
The method of any one of claims 2-13, wherein the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.05 to 1: 0.5.
The method of claim 1, wherein the method comprises: contacting leather fiber with glucose thereby forming a treated leather fiber; contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and molding the leather composite, wherein the leather fiber and the glucose are contacted in a mass ratio between 1: 5 to 5: 1 and the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.1 to 1: 1.
A leather composite sheet prepared in accordance with the method of any one of claims 2-15.
A multilayer leather composite comprising a first leather composite sheet, a second leather composite sheet, and a skeleton layer, wherein the skeleton layer is disposed between the first leather composite sheet and the second leather composite sheet and wherein each of the first leather composite sheet and the second leather composite sheet are independently prepared in accordance with the method of any one of claims 2-15.
The multilayer leather composite of claim 17, wherein the skeleton layer comprises a woven, non-woven, or knit material select from the group consisting of silk, wool, leather, cellulose, cotton, and combinations thereof.
The multilayer leather composite of claim 17, wherein the each of the first leather composite sheet and the second leather composite sheet are independently prepared by a method comprising: contacting leather fiber with glucose thereby forming a treated leather fiber; contacting the treated leather fiber with a binding material selected from the group consisting of a protein isolate, a natural latex solution comprising graphene oxide, a drying oil, a bio-based polyurethane, an amino silicone, and genipin thereby forming a leather composite; and molding the leather composite, wherein the leather fiber and the glucose are contacted in a mass ratio between 5: 1 to 1: 5 and the treated leather fiber and the binding material are contacted in a mass ratio between 1: 0.1 to 1: 1.
The multilayer leather composite of claim 19, wherein a surface of at least one of the first leather composite sheet and the second leather composite sheet is embossed.