Iris Publishers_Journal of Textile Science & Fashion Technology (JTSFT)

Ecology of Matter and the Surface Design in the Leather Fashion Industry

Abstract

Leather is a natural and durable material, unmatched by any synthetic product in terms of hygienic and protective properties. The processing of the oldest fiber-based material used for man’s clothing combines the highest knowledge in chemistry with traditional craftsmanship. Nowadays leather industry is directly related to meat consumption and declares that it is by definition a sustainable activity through reclaiming a valuable byproduct. The challenge regarding the leather processing sustainability involves important steps from raw material preservation through wet-white tanning and more ecological surface finishing by using nanomaterials.

Our contributions regarding the innovative processes for chromium salts reduction and elimination from hide and skin tanning will be presented. Ecological tanning of hides and skins will be approached with new ecological mineral tanning, vegetable and organic materials in view of cleaner wastewater releasing and more biodegradable leather design. The leather surface finishing will take into consideration the use of multifunctional nanoparticles for smart leathers or handmade painting on vegetable tanned leathers for creative industries.

Surface Design is an interface between material, technology and consumer, being both a scientific and technical interface and a socio-cultural one. In the fashion industry the added value is only reflected by an efficient surface design, but the Surface Design is not just a type of finish, it is an art-science act that, if well-known and coordinated, can be spectacular and sustainable at the same time.

Laboratory experiments conducted by interdisciplinary teams will highlight the structure of cultural sustainability in fashion products, associated with the scientific sustainability of leather chemistry oriented towards the ecology of materials. The whole approach is the result of research projects carried out in the institute together with the industry.

Keywords: Leather; Ecology; Surface design; Collaborative research

Introduction

Any production of objects, images, culture, energy, etc. uses matter existing in nature and generates useful and useless energy, loading the toxicity of the planet together with unused material residues, it can be said that sustainability of human concepts, products, processes and actions is not only necessary, but becomes mandatory. In future years there will be no production without sustainable technologies and products that, after consumption, will not be recycled or biodegradable. In the field of eco-design, ethical-fashion, green product, etc., the theme of sustainability is not just a trend but a constant research topic under all aspects of the human-product-technology-consumption-environment relationship, developing the circular economy, based on four pillars: environment, economy, social and culture [1].

The context of the pressure of environmental problems on the industries, the practice of calculating the carbon footprint of the product, as an indicator of LCA, the management of waste and orientation towards the development of circular economy, legitimize bringing into question consumption and its relation with the industry, the relation between the quantity of consumer goods and their value and quality. At the socio-cultural level, it is observed, at the consumer level, that the more ecological culture and awareness of the responsibility towards the environment, towards society and its own carbon footprint, the greater the attention paid to purchased products, green economy, eco-design, biotechnologies, etc. For consumer goods with personal impact and status, such as those in the fashion industry, life-style industry, interior design industry, multimedia, home appliances, furniture industry, creative industries etc., production sizing becomes more and more difficult without suitable tools for measuring the typology of consumption given that customization, of the demand for consumption culture and green knowledge are becoming permanent indicators of the market quality.

Developing research in product design and industrial design in the last years has enabled a more concrete assessment of relationships between science and design or technology and design, the innovative values and cultural meanings expressed by the product, as well as the result of the collaborative actions of the research teams. These collaborative actions are specific to interdisciplinary research, although, in general, people are more accustomed to cooperating than collaborating. The difference between the two types of actions is like the one between a puzzle and a Rubik’s cube or, as the artists say, it is the difference between juxtaposition and mixture. While there is a lot of talk about creativity in the field of fashion, whether it is clothing, accessories, furniture or interior design, there are few collaborative teams working together to create a product, from research to design, technology or marketing. For environmentally friendly leather products, technological standards impose exclusive limitations on linear technological activities, which are absolutely necessary. The cooperation between design and marketing demonstrates that the durability of a leather product for fashion is built from the parameters of leather manufacture, functionality, social status and aesthetic parameters [2]. This is why written labels, explanations and demonstrations are required to attest to the authenticity of the product. If all these indications are set aside, the leather product, through its appearance, texture, touch, smell, should suggest the comfort indicated in all written specifications. Since a garment, a bag, shoe or coat cannot be destroyed, the entire expression of durability is given by the surface of the material. That is why leather surface design research is necessary and requires collaborative research, being an interdisciplinary field by definition.

Surface design is an interdisciplinary working environment, for the section of 0.6-1.5mm in the structure of materials. This environment called finishing, texture, touch, in which materials science is combined with the technologies of hide processing and finishing, the theory and practice of product design, in which the cultural sustainability component clearly expresses the aesthetic and socio-human value of the product, represents, basically, the motivation of a purchase decision. Thus, Surface Design is an interface between material, technology and consumer, being both a scientific and technical interface, as well as a socio-cultural one. Leather is a natural and durable material, unmatched by any synthetic product in terms of hygienic and protective properties. On the substrate of a raw, ecological material, by its nature, processing technologies work by bringing a high-quality material structure to the semi-processed stage for creative industries where the fashion industry is an important cultural peak. Processing of the oldest fiber-based material used for human clothing combines the highest knowledge in chemistry with the traditional craft or artistic performance. The challenge regarding the sustainability of leather processing involves important steps from the conservation of the raw materials to wet finishing and the more ecological finishing of the surface through the use of nanomaterials. The document presents the research in the surface design technology, chemical nanotechnology structure of the leather and particular aspects related to the cultural and technical sustainability of leather products in the fashion.

Surface Design as a Process and Leather Texture as Product, from a Technical Perspective

Leather processing is one of man’s oldest tasks. Yesterday, just as today, the raw material was the hides and skins of domestic and wild animals from which various types of footwear, clothing, belts and other household items were made. The processing operations involve the transformation of rough, easily degradable hide into finished leather – a stable product, used to produce a wide range of items with various uses. Leather tanning can be carried out with very different substances in terms of chemistry – mineral salts, vegetable tannins, syntans, fats, aldehydes – with a complex structure and which behave differently from skin proteins. Chromium tanning is the most widespread process in the world (90% of processed leather). The vegetable tanning process is not considered as an alternative to the chrome salt tanning process, because they are completely different processes that yield different products, which are highly appreciated by artists and environmentalists for their natural qualities, both in structure as well as in texture, and which can outline better directives in slow fashion.

The current ecological standards impose strict regulations in technological processes with hexavalent Cr, so that the carbon footprint of all processes, both technological and social, is as small as possible. In this context, the wet finishing of natural leathers is achieved using auxiliary retaining materials based on acrylic polymers, tannin resins, synthetic and vegetable tannins, fat liquoring oils, and dyes for dyeing, giving natural leathers the following characteristics: softness, dimensional stability, dyes in uniform colors.

Finishing by coating

This is the last operation in leather processing, on which the appearance and value of the finished product depends to a large extent. It aims to beautify, give a glossy and pleasant touch, cover defects and form a surface layer that protects the leather during wear. The coating finish also improves the resistance to external factors (light, rubbing, scratches, water). Current directions in the field of leather processing are aimed at improving the technological processes, processing machines and auxiliary materials used in order to obtain finished leather that corresponds to the quality, ecological and fashion requirements. Leather finishes stand out by the novelty of their effects. Thus, leather with contrasting, antique, cracked, wrinkled, pleated, polished, printed, glossy, matte, pearly effects, with a silky or waxy touch, aniline, semi aniline, hydrophobicized, in a very varied color range, or imitations of other animals’ skins, which can be made from pressed bovine leather imitating reptile (crocodile, python, iguana), ostrich or kangaroo skin, if finished properly, with materials that convey the desired aesthetic characteristics, is very fashionable. The main characteristics imposed on finished leather are color, gloss, matting, touch, resistance to repeated bending, aesthetic appearance, printing, water resistance, water vapor permeability, light fastness (white leather). Almost all types of hides (bovine) and skins (sheep, goats, reptiles, fish, etc.) can be finished in various assortments for footwear, clothing, leather goods, furniture upholstery, cars, book binding, etc. [3].

Leather is finished using dispersed systems in which the following auxiliary materials are used: pigments, binders, natural and synthetic waxes, preservatives, plasticizers, thickening agents, fillers, odorizing substances, penetrators, solvents, ant fungicides or anti bactericides. Natural leather is finished by applying the dispersed finishing systems on the dermal substrate by spraying or using ecological finishing machines with rollers (Roll-Coating and Reverse-Coating). The types of finishes differ depending on the work procedures or the desired effects.

A large number of technologies are used in leather finishing, yielding different characteristics of the finished product. Varying the components or working methods, even the same finishing process can lead to different gloss, matting or coating effects, as well as different characteristics of the film’s texture and softness [4].

Auxiliaries used in disperse finishing systems

The elaboration of the formulations of dispersed filmforming systems to finish leather must take into account the final characteristics of the layer in the whole dermal surface coating film (appearance, thickness, physical-mechanical resistance, fashion) [6,7].

Pigments:Issues currently affecting the leather finishing industry include bans on the use of heavy metal salts (chromium, cadmium, lead, cobalt, mercury, nickel) in pigment pastes, ethoxylated alkylphenols as dispersing agents for waxes, formaldehyde and other toxic crosslinkers. Environmental and toxicity concerns have led to new alternatives for the finishing auxiliary’s industry. Pigments are inorganic or organic chemical compounds that constitute the dye base of coating paints. In order to be used for leather finishing, the pigments must have certain characteristics, of which the most important are: light resistance, the action of atmospheric agents and high temperatures, bright and vivid color, without tanning, high coverage power, high dispersion degree, compatibility with other coatings. Organic pigments give brighter, livelier and more intense colors than inorganic ones, but the disadvantage is that they have low coverage power and produce a tanning effect. To increase the coating power, organic pigments are most often used in combination with inorganic ones [8,9].

Binders:Binders are film-forming macromolecular compounds used in all stages of finishing to give leather flexibility, adhesion and resistance to wear and to external factors. The composition of leather surface finishing systems includes acrylic, polyurethane, butadiene and nitrocellulose binders. Depending on molar masses and hardness, binders are used in various finishing coats (basecoat or dressing) to obtain the desired finish.

Polymers of acrylic acid esters are solid, transparent, colorless, resistant to water, alcohol, light and acids, are elastic and have a high degree of adhesion. They are used in all stages of finishing, from impregnation to the final layer, and generally provide a film with good flexibility, adhesion, and resistance to light. The films obtained from polyesters of acrylic acid are very elastic, thermoplastic, resistant to light, repeated bending and ageing.

Polyurethane binders are poly addition compounds, obtained by the reaction of isocyanates and polyols. The aliphatic ones are most commonly used, giving leather the best physical and mechanical properties. The aromatic ones are less used, as the resistance to light of films is poor. An important step that stimulated the development of new technologies to obtain polyurethanes was perfecting aqueous polyurethane dispersions. These yield soft and elastic leather, such as Napa for furniture upholstery and footwear uppers.

Butadiene binders have high coverage power, but reduced light fastness, and are particularly used in finishing polished and split leather.

Protein binders may be based on casein, albumin and synthetic polyamides. They are used on a large scale to obtain glossy finishes that imitate patent leather [10,11].

In the composition of coating dyes are used binders and lustre agents based on natural products enhanced by chemical treatment (Ethoxylated casein) [12].

Aqueous nitrocellulose emulsions are oil-in-water emulsions in which the dispersed phase contains cellulose nitrate solution, optionally in a mixture of solvents, and the dispersed phase is water. They are used in the final finishing coat. Because of their low resistance to light, they are not used in finishing white leather or leather for upholstery.

Waxes:Both natural and synthetic wax is used in natural leather finishing in order to reduce the stickiness of thermoplastic binders and give a nice touch and color darkening effects (in waxed leather assortments, which are fashionable).

Waxes are esters of the higher monocarboxylic acids with higher primary monohydroxyl alcohols. Natural waxes, such as beeswax, are mixtures of several esters, with varying amounts of acids, free alcohols and alkanes. Synthetic waxes are mixtures of esters of higher fatty acids (normal chain monocarboxylic acids and even carbon atoms) with normal monohydroxyl (C22) higher alcohols, which are emulsified with nonionic emulsifiers (ethoxylated fatty alcohols).

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