LEATHER-LIKE MATERIALS AND METHODS OF MAKING THE SAME

BACKGROUND

The fashion industry is the second largest polluter of the environment after the oil industry. Animal and faux leathers like those made from vinyl can negatively impact the environment and human health for hundreds of years since there is no natural process to break them down. Perfluorinated or “forever chemicals” used in leather production and in functional and performance clothing damage the environment and harm human health for hundreds or possibly thousands of years since there is also no natural process to break them down. While some vegan synthetic leathers offer an alternative to animal leather, many are often made from petroleum-based plastics, contain hazardous chemicals, are not biodegradable, produce enormous amounts of waste, and release microplastics and toxic fumes into the environment. Currently, many clothing items are also made with materials that are not biodegradable and will remain on the planet for ages.

With a carbon cost of 17 kg per square meter, greenhouse gas emissions from the cleaning process, and deforestation from raising livestock, animal leather production greatly contributes to climate change. Deforestation in the Amazon rainforest has a direct impact on the atmosphere of the globe. According to the Higg Materials Sustainability Index, leather made from cow's skin contributes more to global warming, water pollution, water depletion, and greenhouse gas emissions than synthetic or plant-based vegan leather. In addition, the tanning of animal leather uses toxic chemicals like chrome, acids, and ammonium salts and exposes workers to arsenic, which can increase their risk of developing cancer by as much as 50%. Synthetic petroleum-based leather (polyurethane or PU and polyvinyl chloride or PVC) may generate fewer emissions than animal leather production but still retains a significant carbon footprint. The production of current synthetic leather has a carbon cost of 15.8 kg per square meter. Synthetic petroleum-based leather materials do not biodegrade, contribute to microplastic production, and release toxic chemicals during manufacturing. While these synthetic leathers do not use animals and are cheap and durable, they are not an answer to the environmental concerns of leather production.

Despite advances in the synthesis of synthetic leather materials, there is still a scarcity of production processes and raw materials that are both safe and sustainable, as well as imparting desired properties. What is needed is a synthetic leather product made using a clean manufacturing process and without the use of toxic chemicals, thus ensuring worker safety and minimizing environmental impact. Ideally, the synthetic leather product would also be biodegradable and would have value-added properties, including antimicrobial properties, flame-retardant properties, and the like. Raw materials could include agricultural waste by-products, thus making the production of synthetic leather products sustainable. In one aspect, the disclosed artificial leather can support farmers by optimizing the output of their yield by providing another end-use for their waste and added value to the textile industry as well. These needs and other needs are satisfied by the present disclosure.

SUMMARY

In accordance with the purpose(s) of the present disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to synthetic leathers comprising an organic layer comprising agricultural waste such as, for example, ground nutshells and/or hulls, wherein the organic layer further comprises embedded natural fibers. In another aspect, the synthetic leathers further include a resin topcoat and a natural fabric backing. In yet another aspect, the synthetic leathers contain no animal products and are antimicrobial, biocompatible, and compostable. The synthetic leathers have excellent mechanical properties and can be produced without the use of environmentally harmful chemicals. Also disclosed are methods of making the synthetic leathers and articles comprising the synthetic leathers.

Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments, are combinable and interchangeable with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIGS. 1A-1C show structures of different natural and synthetic leathers. The structures of animal leather (FIG. 1A), and traditional synthetic leather (FIG. 1B) are shown compared to the biodegradable bio-based synthetic leather (FIG. 1C). Animal leather (FIG. 1A) has four dermal layers, the grain membrane 100, grain 102, corium 104, and flesh 106. Synthetic leather (FIG. 1B) mimics these layers with petroleum-based materials, with a topcoat 108, a compact plastic layer 110, a foamed plastic layer 112, and a synthetic fabric backing 114. The biodegradable bio-based synthetic leather (FIG. 1C) cross section shows the similar pattern, including a resin topcoat 116, an organic layer 118 with fibers 120 embedded in the layer. It is also strengthened with a natural fabric backing 122.

FIGS. 2A-2C show the physical appearance of bio-based synthetic leathers with different colors before applying the resin and natural fabric backing. FIG. 2A shows a bio-based synthetic leather with rich, medium brown coloration and realistic texture similar to animal leather. FIG. 2B shows a black-colored bio-based synthetic leather dyed with the addition of black pigment, which produced bio-based synthetic leather with a deep black color and muted shine. The bio-based synthetic leather in FIG. 2C was made with a lighter yellow/brown color with a unique texture.

FIG. 3 shows a flow chart illustrating one embodiment of the disclosed process.

FIG. 4 shows a light micrograph (40× magnification) of the bio-based synthetic leather according to one embodiment of the present disclosure. The scale bar represents 200 μm.

FIGS. 5-20 show exemplary bio-based synthetic leathers made using different nutshell and/or nut hull powders according to embodiments of the present disclosure. Sections shown are approximately 30 cm×45 cm.

Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION

As the fashion and textile industries are continuously producing more pieces of clothing and products, there comes the point where it is necessary to account for the effects this has on the environment. Plastics, including nylon, polyester, and acrylic, are all synthetically made and cannot be degraded in the environment by microorganisms or physicochemical impact. These materials now make up 60% of clothing made worldwide. Synthetic textile materials also contribute to as much as 35% of all microplastics and produce even more emissions than natural fibers like cotton. In recent decades, the “fast fashion” industry, whose goal is to reduce costs while maximizing profit, has been a dominant contributor to the deterioration of the environment with the growth in the magnitude of both production and waste. Synthetic fibers used in textiles can take anywhere between 20-200 years to fully decompose. These materials will remain on the earth for generations past their use.

Animal leather production also uses an exorbitant number of natural resources while producing more waste than product and emitting large percentages of methane and ammonia from raising livestock. Concerns over price and production have driven the growth in the market for leather alternatives. In a side-by-side comparison of compound annual growth rates from the year 2020 to 2028, it is evidenced that the market for leather alternatives is growing at a much faster rate than that of animal leather. The compound annual growth rate for the global synthetic leather market within this time frame is 7.8 percent, compared to only 3 percent for genuine animal leather.

Today, the most universally used alternatives to leather are polyurethane (PU) and polyvinyl chloride (PVC) synthetic leathers, which are both plastics. Alternatives to animal leather are designed to be functionally equivalent to animal leather and also combat the high costs and animal cruelty that are consequences of producing authentic animal leather. However, these are not biodegradable. While PU and PVC synthetic leathers are low-cost and can be produced very quickly; their production requires chemicals that pose both human and environmental risks. PVC releases dioxins, and plasticizers such as phthalates are often used to make these leathers flexible.

It is thus important to find a more suitable alternative to animal leather using biodegradable materials. Despite their negative attributes, plastic-based synthetic leathers have dominated the synthetic leather market in recent years, but many companies and consumers are seeking out more ethical and environmentally friendly solutions. Herein is disclosed a biodegradable alternative to animal and synthetic leathers, with a cradle-to-cradle design system, a circular economy that would produce little to no waste, with all potential waste being biodegraded or reused in the production of new bio-based leather-like products.

Authentic leather shows numerous highly valued properties, such as unmatched strength and elasticity, water vapor permeability, abrasion resistance, durability, and longevity. The goal of synthetic leather is to mimic these properties to the highest degree possible. Genuine leather is mostly made of collagen (FIG. 1A), which is not found in plant-based materials. However, the right combinations of cellulose and lignin found in nutshells and nut hulls, such as pecan, peanut, cashew, walnut, and almond shells, can replicate genuine leather closely, and they have different shades of brown color similar to genuine leather.

In one aspect, disclosed herein is a bio-based leather-like material made of nutshells and/or nut hulls from lignocellulosic materials from agri-waste, including but not limited to pecans, peanuts, cashews, walnuts, and almond shells and/or hulls. In a further aspect, this large-yield crop residue, also described as biomass nutshell and/or hull, has typically previously been discarded or incinerated, polluting the environment and wasting many natural resources.

In an aspect, agri-waste from nutshells and/or nut hulls makes up a large percentage of the overall fruit weight and could be used instead of being dumped or burned. In a further aspect, some of the agri-waste sources such as walnut, pecan, and peanut shells and/or hulls inherently contain bioactive compounds that offer excellent antioxidant and antimicrobial properties.

Bio-Based Synthetic Leathers

In one aspect, disclosed herein is a bio-based synthetic leather including at least the following components:

- (a) an organic layer including ground nutshells and/or nut hulls, at least one fatty acid, at least one texture-modifying additive, at least one natural fiber, and a nanocellulose hydrogel;
- (b) a resin topcoat; and
- (c) an optional natural fabric backing,
- wherein the natural fabric backing is chosen based on the mechanical properties needed for final textile application and end use.

In a further aspect, the ground nutshells and/or nut hulls can be sourced from a variety of nutshell and/or nut hull materials, including but not limited to pecan, peanut, cashew, walnut, almond, or any combination thereof. In any of these aspects, the ground nutshells and/or nut hulls can be agricultural waste (“agri-waste”).

In another aspect, the at least one fatty acid can be lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof. In still another aspect, the at least one texture-modifying additive can be sodium alginate, pectin, or any combination thereof. In an aspect, the texture-modifying additive can be a thickener, a gelling agent, a stabilizer, or any combination thereof. In some aspects, the organic layer includes embedded natural fibers. In some aspects, the embedded natural fibers can be cellulosic fibers from cotton, linen (flax), hemp, eucalyptus, other cellulosic fibers, and combinations thereof.

In one aspect, the nanocellulose hydrogel can be or include a homogenized cellulosic pulp. In some aspects, the homogenized cellulosic pulp includes at least one material sourced from a low-value waste stream such as, for example, cotton noil, woody pulp from paper production, or a combination thereof. In another aspect, the homogenized nanocellulosic pulp is or includes nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC), or any combination thereof. In some aspects, the nanocellulose hydrogel further includes carboxymethylcellulose.

In one aspect, the disclosed bio-based synthetic leathers include nanocellulose hydrogels. In a further aspect, nanocellulose hydrogels are well-suited for being a carrier of functional properties as well as increasing the mechanical properties because they 1) contain amorphous regions that make the coatings malleable for processing and textile application, 2) contain a high specific surface area, 3) and are rich in surface hydroxyls that can readily form hydrogen bonds with other materials, allowing for robust adhesion with many points of contact.

In a further aspect, the nanocellulose hydrogels used to make the disclosed bio-based synthetic leather are generated through a high-pressure homogenization process using cellulosic pulps as the input material. In a still further aspect, this means the process can be carried out using many different source materials as available, including those otherwise considered low-value waste streams (e.g., cotton noil from cotton plants and woody pulp from paper production). In a further aspect, the use of low-value waste streams contributes to the overall sustainability of the disclosed approach.

In a still further aspect, nanocellulose is readily tailorable to create various porosities, thicknesses, and microstructures. In the disclosed synthetic leathers, the focus has primarily been on the use of nanofibrillated cellulose (NFC) and nanocrystalline cellulose (NCC) particles, which present with nanofiber and whisker structures, respectively, wherein the different microarchitectures can be used to optimize the functionality of the bio-based synthetic leather. In an aspect, NFC is a random material composed of cellulosic fibers typically 10-50 nm in diameter and several micrometers long with a broad size distribution. This results in about a 1:50 average aspect ratio of the microfibrils, apt for entanglement with the nutshells and nut hull powders. In a further aspect, NFC pulp can be mixed with carboxymethlycellulose (CMC) to form an NFC-hydrogel that can be used as a carrier for functional properties as well as strengthen the structure of the disclosed bio-based synthetic leather. Further in this aspect, the NFC network is strengthened by hydrogen bonds, mechanical interlocking, electrostatic interactions, interdiffusion of cellulose molecules, and van der Waals forces. In one aspect, and without wishing to be bound by theory, the self-adhesive nature of cellulosic materials makes NFC and NCC hydrogels particularly suited for efficient adhesion.

In another aspect, nanocellulose is amenable for functionalization using physical and chemical cross-linking agents, which can be added to the NFC/NCC components useful herein to enhance the properties of the bio-based synthetic leather. In yet another aspect, functional molecules or particles can be borne by the nanocellulose hydrogels, either through chemical bonding or physical entrapment in the hydrogel structure, which then attaches to bio-based synthetic leather surfaces via hydrogen/covalent bonds and physical interlocking mechanisms. In one aspect, the compatibility of NFC hydrogels for functionalization opens the door to a wealth of opportunities for bio-based synthetic leather processing methods.

In one aspect, the natural fabric backing can be a nonwoven, woven, or knitted fabric. In another aspect, the natural fabric backing can be cellulosic fabric from cotton, linen (flax), hemp, eucalyptus, other cellulosic fibers, or any combination thereof. In another aspect, the resin topcoat includes a plasticized fatty acid such as, for example, lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof.

In any of these aspects, the bio-based synthetic leather further includes at least one natural pigment. Further in this aspect, the pigment can be a pigment from a plant source, a lake pigment, an earth pigment, or any combination thereof. In an aspect, the bio-based synthetic leather can be antimicrobial, biocompatible, compostable, or any combination thereof.

In one aspect, the bio-based synthetic leather can have a weight of from about 1.1 to about 1.2 kg/m², or from about 1.125 to about 1.175 kg/m², or from about 1.14 to about 1.16 kg/m². In another aspect, the bio-based synthetic leather can have a thickness of from about 0.5 mm to about 6 mm, or from about 1 mm to about 5 mm, or from about 2 mm to about 4 mm. In still another aspect, the bio-based synthetic leather can have a tensile strength of from about 8 to about 12 N/mm², or from about 9 to about 11 N/mm², or from about 9 to about 10 N/mm². In some aspects, the bio-based synthetic leather can have a tear strength of from about 7 to about 12 N/mm, or from about 8 to about 11 N/mm, or from about 10 to about 11 N/mm. In one aspect, the bio-based synthetic leather has a water vapor permeability of from about 1.5 to about 2.5 mg/(cm²·h), of from about 1.75 to about 2.25 mg/(cm²·h), or from about 1.9 to about 2.1 mg/(cm²·h).

In another aspect, the bio-based synthetic leather is thermostable to at least 200° C. and can have a melting temperature of from about 200 to about 300° C., about 225 to about 275° C., or about 240 to about 260° C. In a further aspect, the bio-based synthetic leather decomposes at around 800° C.

Method for Making a Bio-Based Synthetic Leather

In one aspect, disclosed herein is a method for making a bio-based synthetic leather, the method including at least the following steps:

- (a) grinding nutshells and/or nut hulls to a fine powder;
- (b) mixing the ground nutshells and/or nut hulls with at least one fatty acid, at least one texture-modifying additive, a nanocellulose hydrogel, and a cross-linking agent to form a precursor mixture;
- (c) transferring the precursor mixture to a mold;
- (d) distributing natural fibers in the precursor mixture; and
- (e) drying the precursor mixture and natural fibers in an oven to produce the bio-based synthetic leather.

In a further aspect, the ground nutshells and/or nut hulls can be from pecan, peanut, cashew, walnut, almond, or any combination thereof, and can be agricultural waste.

In another aspect, the at least one fatty acid can be lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof, and the at least one texture-modifying additive can be sodium alginate, pectin, or any combination thereof. In a further aspect, the cross-linking agent can be citric acid, diglycidyl ether of bisphenol A (DGEBA), or any combination thereof.

In another aspect, the method further includes removing the bio-based synthetic leather from the mold, drying it in a vacuum oven, and flattening the synthetic leather in a heat press operating at from about 100 to about 150° C. In some aspects, the method includes an optional admixing of a natural pigment with the precursor mixture.

In a further aspect, the method further includes applying a resin topcoat to the bio-based synthetic leather by a method such as, for example, pouring. In some aspects, the resin topcoat includes a fatty acid such as, for example, lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof. In a further aspect, the method further includes the step of plasticizing the fatty acid. In one aspect, plasticizing the fatty acid includes applying epoxied oil such as, for example, epozidized soybean oil, heat, a chemical initiator such as, for example, benzoyl peroxide, or any combination thereof to the fatty acid.

In one aspect, the method further includes applying a natural fabric backing to the bio-based synthetic leather, such as a nonwoven, woven, or knitted fabric. In some aspects, the natural fabric backing is adhered to the bio-based synthetic leather using a biodegradable hot melt adhesive. In a further aspect, the adhesion of the biodegradable hot melt adhesive is activated using a heat transfer sublimation process.

Articles Including the Bio-Based Synthetic Leathers

In another aspect, disclosed herein is an article including the bio-based synthetic leathers disclosed herein. In a further aspect, the article can be selected from an article of clothing, luggage, a handbag, furniture, automotive upholstery, marine upholstery, an article of footwear, athletic equipment, a watch band, or any combination thereof.

Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain, having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.

Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to the arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only, and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.

It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.

Definitions

As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.

As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a nutshell,” “a fabric,” or “an epoxidized plant oil,” include, but are not limited to, mixtures or combinations of two or more such nutshells, fabrics, or epoxidized plant oils, and the like.

It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

When a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g., the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g., ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y′, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y′, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.

It is to be understood that such a range format is used for convenience and brevity and, thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.

As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter, or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs, and instances where it does not.

“Leather” or “natural leather” as used herein, refers to a flexible and durable material made from animal skins or hides. The skins or hides are tanned or otherwise chemically treated to prevent decay. Leather is typically sourced from common livestock animals (cattle, swine, sheep, goats) or reptiles (e.g., alligators).

“Synthetic leather” or “artificial leather” as used herein, refers to a material intended to be a substitute for natural leather. Synthetic leather may be natural or can contain natural materials (“bio-based”) or can be made from synthetic polymers such as polyurethane or polyvinyl chloride. Synthetic leathers retain the flexibility and durability of natural leather without using animal products either for ethical or cost concerns.

As used herein, “antimicrobial” refers to a material that destroys or inhibits the growth of microorganisms, including bacteria and fungi. Antimicrobial materials may be especially useful in destroying or inhibiting the growth of pathogenic microorganisms and/or microorganisms that would otherwise cause a material (such as natural leather) to decay. In one aspect, the synthetic leathers disclosed herein are antimicrobial.

“Biocompatible” refers to a material that is not harmful to living tissue. In one aspect, the bio-based synthetic leathers disclosed herein are biocompatible. Further in this aspect, the bio-based synthetic leathers can be used to make articles of clothing, footwear, and the like that can be worn next to the skin without causing irritation.

“Compostable” as used herein, refers to a material that can disintegrate into non-toxic components. A compostable material may require microorganisms, humidity, and heat to yield a finished product, which can then be used to fertilize plants such as food crops, ornamental crops, or the like. In one aspect, the bio-based synthetic leathers disclosed herein are compostable.

“Agri-waste” or “agricultural waste” as used herein refers to a plant residue from agriculture that is not used for human food, animal food, or another value-added process (e.g., ethanol fermentation). In one aspect, the bio-based synthetic leathers disclosed herein make use of agri-waste such as nutshells and/or nut hulls, thereby decreasing the amount of material dumped, sent to landfills, or burned.

Unless otherwise specified, temperatures are ambient, and pressures referred to herein are based on atmospheric pressure (i.e., one atmosphere).

Now, having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.

ASPECTS

The present disclosure can be described in accordance with the following numbered Aspects, which should not be confused with the claims.

Aspect 1. A bio-based synthetic leather comprising:

- (a) an organic layer comprising ground nutshells and/or nut hulls, at least one fatty acid, at least one texture-modifying additive, and a nanocellulose hydrogel;
- (b) a resin topcoat; and
- (c) an optional natural fabric backing.

Aspect 2. The bio-based synthetic leather of aspect 1, wherein the ground nutshells and/or nut hulls comprise pecan, peanut, cashew, walnut, or almond shells or hulls, or any combination thereof.

Aspect 3. The bio-based synthetic leather of aspect 1 or 2, wherein the ground nutshells and/or nut hulls comprise agricultural waste.

Aspect 4. The bio-based synthetic leather of any one of aspects 1-3, wherein the at least one fatty acid comprises lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof.

Aspect 5. The bio-based synthetic leather of any one of aspects 1-4, wherein the at least one texture-modifying additive comprises sodium alginate, pectin, or any combination thereof.

Aspect 6. The bio-based synthetic leather of any one of aspects 1-5, wherein the nanocellulose hydrogel comprises a homogenized cellulosic pulp.

Aspect 7. The bio-based synthetic leather of aspect 6, wherein the homogenized nanocellulosic pulp comprises at least one material sourced from a low-value waste stream.

Aspect 8. The bio-based synthetic leather of aspect 7, wherein the low-value waste stream comprises cotton noil, woody pulp from paper production, or any combination thereof.

Aspect 9. The bio-based synthetic leather of any one of aspects 6-8, wherein the homogenized nanocellulosic pulp comprises nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC), or any combination thereof.

Aspect 10. The bio-based synthetic leather of any one of aspects 1-9, wherein the nanocellulose hydrogel further comprises carboxymethylcellulose.

Aspect 11. The bio-based synthetic leather of any one of aspects 1-10, wherein the organic layer comprises embedded natural fibers.

Aspect 12. The bio-based synthetic leather of aspect 11, wherein the embedded natural fibers comprise cellulosic fibers from cotton, linen (flax), hemp, eucalyptus, other cellulosic fibers, and combinations thereof.

Aspect 13. The bio-based synthetic leather of any one of aspects 1-12, wherein the natural fabric backing comprises a nonwoven, woven, or knitted fabric.

Aspect 14. The bio-based synthetic leather of aspect 13, wherein the natural fabric backing comprises cellulosic fabric from cotton, linen (flax), hemp, eucalyptus, other cellulosic fibers, or any combination thereof.

Aspect 15. The bio-based synthetic leather of any one of aspects 1-14, wherein the resin topcoat comprises a plasticized fatty acid.

Aspect 16. The bio-based synthetic leather of aspect 15, wherein the plasticized fatty acid comprises lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof.

Aspect 17. The bio-based synthetic leather of any one of aspects 1-16, further comprising at least one natural pigment.

Aspect 18. The bio-based synthetic leather of aspect 17, wherein the at least one natural pigment comprises a pigment from a plant source, a lake pigment, an earth pigment, or any combination thereof.

Aspect 19. The bio-based synthetic leather of any one of aspects 1-18, wherein the bio-based synthetic leather is antimicrobial, biocompatible, compostable, or any combination thereof.

Aspect 20. The bio-based synthetic leather of any one of aspects 1-19, wherein the bio-based synthetic leather has a weight of from about 1.1 to about 1.2 kg/m².

Aspect 21. The bio-based synthetic leather of any one of aspects 1-20, wherein the bio-based synthetic leather has a thickness of from about 0.5 mm to about 6 mm.

Aspect 22. The bio-based synthetic leather of any one of aspects 1-21, wherein the bio-based synthetic leather has a tensile strength of from about 8 to about 12 N/mm².

Aspect 23. The bio-based synthetic leather of any one of aspects 1-22, wherein the bio-based synthetic leather has a tear strength of from about 7 to about 12 N/mm.

Aspect 24. The bio-based synthetic leather of any one of aspects 1-23, wherein the bio-based synthetic leather has a water vapor permeability of from about 1.5 to about 2.5 mg/(cm²h).

Aspect 25. The bio-based synthetic leather of any one of aspects 1-24, wherein the bio-based synthetic leather is thermostable to at least 200° C.

Aspect 26. The bio-based synthetic leather of any one of aspects 1-25, wherein the synthetic bio-based leather has a melting temperature of from about 200 to about 300° C.

Aspect 27. The bio-based synthetic leather of any one of aspects 1-26, wherein the bio-based synthetic leather decomposes at around 800° C.

Aspect 28. A method for making a bio-based synthetic leather, the method comprising:

- (a) grinding nutshells, nut hulls, or both to a fine powder;
- (b) mixing the ground nutshells, nut hulls, or both with at least one fatty acid, at least one texture-modifying additive, a nanocellulose hydrogel, and a cross-linking agent to form a precursor mixture;
- (c) transferring the precursor mixture to a mold;
- (d) distributing natural fibers in the precursor mixture; and
- (e) drying the precursor mixture and natural fibers in an oven to produce the synthetic leather.

Aspect 29. The method of aspect 28, wherein the ground nutshells, nut hulls, or both comprise pecan shells, peanut shells, cashew shells, walnut shells, almond shells, or any combination thereof.

Aspect 30. The method of aspect 28 or 29, wherein the ground nutshells, nut hulls, or both comprise agricultural waste.

Aspect 31. The method of any one of aspects 28-30, wherein the at least one fatty acid comprises can be lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof.

Aspect 32. The method of any one of aspects 28-31, wherein the at least one texture-modifying additive comprises sodium alginate, pectin, or any combination thereof.

Aspect 33. The method of any one of aspects 28-32, wherein the nanocellulose hydrogel comprises a homogenized cellulosic pulp.

Aspect 34. The method of aspect 33, wherein the homogenized nanocellulosic pulp comprises at least one material sourced from a low-value waste stream.

Aspect 35. The method of aspect 34, wherein the low-value waste stream comprises cotton noil, woody pulp from paper production, or any combination thereof.

Aspect 36. The method of any one of aspects 33-35, wherein the homogenized nanocellulosic pulp comprises nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC), or any combination thereof.

Aspect 37. The method of any one of aspects 28-36, wherein the nanocellulose hydrogel further comprises carboxymethylcellulose.

Aspect 38. The method of any one of aspects 28-37, wherein the cross-linking agent comprises citric acid, diglycidyl ether of bisphenol A (DGEBA), or any combination thereof.

Aspect 39. The method of any one of aspects 28-38, further comprising removing the bio-based synthetic leather from the mold, drying the bio-based synthetic leather in a vacuum oven, and flattening the bio-based synthetic leather in a heat press.

Aspect 40. The method of aspect 39, wherein the heat press operates at from about 100 to about 150° C.

Aspect 41. The method of any one of aspects 28-40, further comprising admixing at least one natural pigment with the precursor mixture.

Aspect 42. The method of any one of aspects 28-41, further comprising applying a resin topcoat to the bio-based synthetic leather.

Aspect 43. The method of aspect 42, wherein the resin topcoat is poured over the bio-based synthetic leather.

Aspect 44. The method of aspect 42 or 43, wherein the resin topcoat comprises a fatty acid.

Aspect 45. The method of aspect 44, wherein the fatty acid comprises lauric acid, capric acid, palmitic acid, stearic acid, myristic acid, oleic acid, or any combination thereof.

Aspect 46. The method of aspect 44 or 45, further comprising plasticizing the fatty acid.

Aspect 47. The method of aspect 46, wherein plasticizing the fatty acid comprises applying epoxidized soybean oil; heat, a chemical initiator, or any combination thereof to the fatty acid.

Aspect 48. The method of aspect 47, wherein the chemical initiator comprises benzoyl peroxide.

Aspect 49. The method of any one of aspects 28-48, further comprising applying a natural fabric backing to the bio-based synthetic leather.

Aspect 50. The method of aspect 49, wherein the natural fabric backing comprises a nonwoven, woven, or knitted fabric.

Aspect 51. The method of aspect 49 or 50, wherein the natural fabric backing is adhered to the bio-based synthetic leather using a biodegradable hot melt adhesive.

Aspect 52. The method of aspect 51, further comprising activating adhesion of the biodegradable hot melt adhesive using a heat transfer sublimation process.

Aspect 53. A bio-based synthetic leather made by the method of any one of aspects 28-52.

Aspect 54. An article comprising the bio-based synthetic leather of any one of aspects 1-27 or 53.

Aspect 55. The article of aspect 54, wherein the article comprises an article of clothing, luggage, a handbag, furniture, automotive upholstery, marine upholstery, aircraft upholstery, an article of footwear, athletic equipment, a watch band, or any combination thereof.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices, and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.

Example 1: Materials, Methods, and Tests
Materials

The chemical composition and interactions of the bio-based synthetic leather components were investigated to mimic the properties of genuine animal leather and synthetic polyurethane (PU) leathers using non-toxic and biodegradable materials. The basis of the disclosed bio-based synthetic leather is agri-waste derived from nutshells and/or nut hulls, and because of its composition and structure, the disclosed material has a color and structure similar to animal leather. The formulation of the organic bio-based synthetic leather combines biodegradable ingredients to reinforce the material while still preserving its flexibility. The agri-waste is less water-soluble, more resistant to bacterial attack, provides the bio-based synthetic leather with higher mechanical properties, and increases the bond interactions of the bio-based synthetic leather framework. The material is combined with other chemicals to enhance its gel-forming abilities and is cross-linked primarily with calcium ions. The disclosed bio-based leather-like material consists of a resin topcoat and an organic layer with natural fibers embedded in the layer. The organic layer consists of agri-waste, non-toxic chemicals, and nanocellulose hydrogels. Nanocellulose hydrogels, owing to their small dimensions, high mechanical characteristics, high specific surface area, biocompatibility, and compostability, allow for a higher uptake of functional particles such as antimicrobial and flame-retardant and add to the strength of the bio-based synthetic leather. It is also strengthened with a natural fabric backing. The resin functions by starting with a fatty acid component, which increases the water barrier properties of the material due to its hydrophobic nature. Then, a plasticizer was created using epoxidized plant oil. This reaction is initiated by heat and a chemical initiator. The cross-linker was used to introduce amine groups for further stabilization, resulting in flexible yet durable bonds. Natural pigment and functional agents may be added to the organic layer depending on the functionality and color needed. FIGS. 1A-1B show the physical appearance of natural brown and black bio-based synthetic leathers. To evaluate the samples, tests were performed to determine thickness, tensile strength, tear resistance, and water vapor permeability according to ASTM standard methods, as well as morphology and thermal analysis of the samples. The results show comparable mechanical properties and thickness to animal and synthetic leathers and are higher than other bio-based leather alternatives (Table 1). Thermal analysis was conducted using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to determine the thermal stability and decomposition behavior of the bio-based synthetic leather. The results indicate that the material begins significantly degrading between 200° C. to 400° C. and is completely decomposed around 800° C., which shows good thermal stability compared to the alternatives.

The disclosed bio-based leather-like material includes at least resin topcoat 116, organic layer 118 with natural fibers 120 embedded in the layer. It is also strengthened with a natural fabric backing 122 (see FIG. 1C). The resin functions by starting with a fatty acid component, in this case, the lauric acid, and plasticizing it using an epoxied oil. This reaction is initiated by heat and a chemical initiator, benzoyl peroxide. Cross-linking agents were also explored to stabilize the material and increase its strength. The citric acid functions by symmetrically linking the acid and oil. Diglycidyl ether of bisphenol A (DGEBA) was also used as a cross-linker with the goal of introducing amine groups for further stabilization. The result is bonds that are flexible yet durable for a material that can be bent easily but not pulled apart.

The organic layer consists of nutshells and/or nut hulls, lauric acid, sodium alginate, pectin, and nanocellulose hydrogels. Natural pigments and other functional agents can be added to the organic layer depending on the functionality and color needed.

Methods

An industrial grinder was used for crushing the nutshells and/or nut hulls into a fine powder. For different samples, various concentrations of the materials were used and mixed with a homogenizer. Molds were prepared by mixing the cross-linking agent evenly with the materials. Fibers were separated to be evenly distributed in the solution. Then, samples were dried in the oven at varying temperatures. A heat press was used for varying times and temperatures up to 150° C. to flatten the sample.

The resin coating was added by first combining the ingredients at varying concentrations, then pouring the solution over the dried bio-based synthetic leather. The sample was then left in the oven to dry at varying temperatures. To apply the backing, a biodegradable adhesive was used on natural nonwoven, woven, or knitted fabrics, and a heat transfer sublimation machine was used to adhere it to the bio-based synthetic leather (FIG. 3).

Tests

To evaluate the samples, tests were performed to determine the thickness (ASTM D1814-70(2021)), tensile strength (ASTM D2209-00(2021)), tear resistance (ASTM D1424), water vapor absorption (ASTM (D6015), morphology, and thermal analysis of the samples. For comparison, samples were made with a thickness of 1.1±10% (Table 1).

Bio-based synthetic leather morphology. The microstructural analysis of the films was conducted at 40× objective to view the different components of the samples (FIG. 4). At this level, the fibers are seen to be intertwined and enclosed by the bio-based synthetic leather mixture. This overlapping structure provides the strength needed to perform similarly to animal-based leathers.

Mechanical properties. The mechanical properties were evaluated through the standardized testing methods described herein in accordance with their respective ASTM procedures.

Tensile strength. Tensile strength was measured using an Instron Tensile Tester to determine the force in Newtons required to break the specimen. The samples were cut into 171 mm long strips and loaded into the equipment. The crosshead speed and initial grip separation were 254 mm/min and 101 mm, respectively. To calculate the results, the force was divided by the cross-sectional area (in mm²) of the midsection of each specimen (Table 1).

Tear strength. Tear strength was measured using a Digital Elmendorf Tear Tester to determine the torsion force required to tear a specimen. The samples were cut to 100 mm×63 mm rectangles and loaded into the equipment. A 20 mm long slit was cut from the bottom of the sample using a built-in knife, and the pendulum was allowed to complete its forward swing. The tearing strength is calculated by dividing the force (in Newtons) by the thickness of the sample (in mm) (Table 1).

Thickness. Table 1 shows the average thickness of the organic layer to be 1 mm to 5 mm±10% using a digital thickness gauge. Five equally spaced measurements were taken from each sample and then averaged together for uniformity. After the addition of a resin topcoat and fabric backing, the thickness is expected to increase slightly, but the exact measurements of the final product are easy to control.

Water vapor permeability. Water vapor permeability was measured by determining the rate at which water vapor passes through a test specimen after being exposed to moist air on one side and dry air on the other (Table 1).

Thermal analysis: TGA. Thermogravimetric analysis (TGA) was conducted on the specimens to determine their thermal stability and decomposition behavior using TGA 8000 Thermogravimetric analyzer from PerkinElmer. The data shows the material begins significantly degrading between 200° C. to 400° C. and is completely decomposed around 800° C.

Thermal analysis: DSC. After analyzing the TGA data to obtain a temperature range for the decomposition of the samples, differential scanning calorimetry (DSC) analysis was performed to determine how the bio-based synthetic leather heat capacity is changed by temperature using DSC 8000 from PerkinElmer. The samples were hermetically sealed in aluminum pans and heated from 30° C. to 400° C. at a rate of 20° C./min (Table 1).

TABLE 1

Physical and Thermal Properties

Physical and Thermal Properties
Pecan
Peanut
Cashew
Walnut
Almond

Weight (g/m²)**
1,100-
1,100-
1,100-
1,100-
1,100-

1,200
1,200
1,200
1,200
1,200

Thickness (mm)
1 mm to 5
1 mm to 5
1 mm to 5
1 mm to 5
1 mm to 5

mm ± 10%
mm ± 10%
mm ± 10%
mm ± 10%
mm ± 10%

Tensile Strength (N/mm²)**
10.48
9.63
8.44
11.44
11.20

Tear Strength (N/mm)**
8.22
8.20
7.79
11.60
11.20

Water Vapor Permeability
1.65
1.50
2.40
2.30
2.10

(mg/(cm²× h))**

Melting Temperature (° C.)**
250
200
200
290
220

Decomposition Temperature
Around
Around
Around
Around
Around

(° C.)**
800
800
800
800
800

* Values were calculated for the raw bio-based synthetic leather- without any backing or resin coating

**For comparison, samples were made with a thickness of 1.1 mm ± 10%

Example 2: Discussion/Chemical Interactions

Cellulose has a high crystallinity because of hydrogen bonding and Vander Waals interactions between adjacent molecules. Hemicellulose and lignin are amorphous. Lignin's three-dimensional and highly branched structure has a covalent bond between lignin and polysaccharide, which significantly increases the strength between the bonds of the cellulosic fibers and the lignin matrix. Therefore, it plays a role in bonding and strengthening. Lignin also improves thermal properties. It has flame-retardant properties, which are important for leather-like materials. Hemicellulose has a ring and hydroxide structure, which delivers a higher reactive activity than cellulose. Using the nutshell and/or nut hull with appropriate amounts of lignin, cellulose, and hemicellulose is a key factor in successfully making the bio-based leather alternative. Table 2 shows the compositions of nutshells and/or nut hulls used to make the disclosed biodegradable leathers.

The material is combined with pectin to enhance its gel-forming abilities and is cross-linked primarily with calcium ions. Glycerin acts as a plasticizer to soften the material and increase its flexibility. Lauric acid is a medium-chain saturated fatty acid, also acting as a plasticizer due to its mobility from its shorter chain length and increasing the water barrier properties of the material due to its hydrophobic nature.

The bio-based synthetic leather also contains nanocellulose hydrogels from renewable sources and agricultural by-products like wood pulp and cotton noils. Nanocellulose hydrogels, owing to their small dimensions, high mechanical characteristics, high specific surface area, biocompatibility, and composability, allow for a higher uptake of functional particles such as antimicrobial and flame-retardant and add to the strength of the bio-based synthetic leather.

TABLE 2

Chemical Composition (%) of Nutshells (Biomass)

Lignocellulosic

material
Cellulose, %
Hemicellulose, %
Lignin, %

Almond shell
38.47%
28.82%
29.54%

Peanut shell
44.80%
5.60%
36.10%

Walnut shell
23.90%
22.40%
50.30%

Cashew shell
23.05%
28.30%
28.80%

Pecan shell
17.00%
33.00%
34.00%

Conclusion

A cradle-to-cradle system was designed, and sustainable and compostable leather-like materials were developed from nutshells and/or nut hulls with possible functionalities such as antimicrobial and flame-retardant properties. In this process, toxic chemicals that are normally used in the production of natural, synthetic, and vegan leathers were eliminated. The formulation of the organic bio-based synthetic leather combines biodegradable ingredients to reinforce the material while still preserving its flexibility. This method allows the production of various bio-based synthetic leathers by changing the ratio of the ingredients and adding patterns, textures, and colors (FIGS. 5-20).

It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

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