Leather industry is facing new trends on production and consumption patterns due to society concerns. Circular economy is proposing a transition from the current economic model to a more sustainable one, in which waste is designed out and resources will be reused and recycled as long as possible. In this transition, Life Cycle Assessment (LCA) is an important tool to help decision-making. In the present review, 39 English-written peer-reviewed papers related to LCA and leather have been found, 30 of which were published in the last 6 years, meaning LCA is nowadays an important subject. Papers are presented within 4 types, focused on: 1) the whole leather production process, 2) a single step in the production process (e.g, new technologies for unhairing), 3) waste treatment and recycling, and 4) life cycle thinking with ideas on long-term strategies for leather industries. As discussed in the literature review, leather industry has important challenges to address: increasing sustainability and transparency on the supply chain, and strengthening the beauty of leather. Taking up these challenges from a life cycle perspective will help leather industry flourish in the coming future.Graphical abstract

The production of leather from animal skins and hides through tanning processes began in the pre-historic ages. Despite the origination of new leather making techniques such as chrome tanning which is being employed extensively today, the traditional method of leather production primarily through vegetable tanning is still being practised mostly in artisanal tanneries in developing nations including Ghana. Artisanal leather making, thus, contributes beneficially to rural livelihood. Nevertheless, the growth of this sector has been stifled by the lack of innovative technologies to enhance productivity. This challenge could be partly linked to the knowledge gap on the scientific principles governing artisanal leather production processes. This study, therefore, elaborates on various process steps and materials employed in traditional leather making in Ghana and the scientific principles underlying each of the processes. It also makes a comparison between traditional and modern leather manufacturing processes and identifies knowledge and technological gaps which would inspire in-depth scientific research into artisanal leather making.Graphical abstract

As other causes decline in importance, chromium-tanned leather has become a more important source for chromium allergy, which affects around 1% of the general population. The aim of this review is to give suggestions on how to minimize the risk of leather-related allergic contact dermatitis, which can be elicited in chromium-allergic persons by hexavalent and trivalent chromium released from leather. Hexavalent chromium is the more potent chromium form and requires a lower skin dose to elicit allergic reactions. It is formed on the surface of some, antioxidant-free, leathers at dry conditions (< 35% relative humidity) and is influenced by the tanning process and other conditions, such as UV irradiation, contact with alkaline solutions, and leather age. Trivalent chromium is the dominant form released from chromium-tanned leather and its released amount is sufficient to elicit allergic reactions in some chromium-allergic individuals when they are exposed repetitively and over longer time (days – months). A low initial test result (< 3 mg/kg) for hexavalent chromium with the current standard test (ISO 17075) does not guarantee a low release of chromium from the leather or a low release of hexavalent chromium under typical exposure conditions during the service life of the leather. Information, labels, and certificates regarding leather products are often insufficient to protect chromium-allergic individuals. Correct labelling and information on the possible content of different allergens, as well as different tanning alternatives for certain leather products, are crucial.Graphical abstract

The aim of this research is to develop a novel non-leaching antimicrobial waterborne polyurethane (WPU) leather coating material with covalently attached quaternary phosphonium salt (QPS). The structure of the QPS-bearing WPU has been identified, and their thermal stability, mechanical property, and antimicrobial performance have been investigated. The results reveal that the incorporation of QPS slightly reduces the thermal stability of WPU material but would not affects its usability as leather coating. Despite the presence of hydrophobic benzene in QPS structure, the strong hydration of its cationic groups leads to the increased surface contact angle (SCA) and water absorption rate (WAR) of the films, suggesting that the water resistance of the films needs to be improved for the purpose of leather coatings. Antibacterial tests demonstrate that when the QPS content is 20 wt%, QPS-bearing WPU shows effective antimicrobial activity against bacteria. The WPU containing QPS prepared in this study is a non-leaching antimicrobial material and has great potential application as leather coating.Graphical abstract

The dissolution of collagen in ionic liquids (ILs) was highly dependent on the polarity of ILs, which was influenced by their sorts and concentrations. Herein, the solubility and dispersion degree of collagen in two sorts of ILs, namely 1-ethyl-methylimidazolium tetrafluoroborate ([EMIM][BF4]) with low polarity and 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) with high polarity in a concentration range from 10% to 70% at 10 °C were investigated. When 150 mg of collagen was added to 30 mg of ILs, the minimum soluble collagen concentration was 0.02 mg/mL in 70% [EMIM][BF4] with lowest polarity and the maximum was 3.57 mg/mL in 70% [EMIM][Ac] with highest polarity, which indicates that soluble collagen and insoluble collagen fibers were both present. For insoluble collagens, differential scanning calorimetry showed that the thermal-stability was weakened when increasing the ILs concentration and polarity, and the fiber arrangement was looser with a more uniform lyophilized structure, observed by atomic force microscopy and scanning electron microscopy. For soluble collagens, electrophoresis patterns and Fourier transform infrared spectroscopy showed that no polypeptide chain degradation occurred during dissolution, but the thermal denaturation temperature decreased by 0.26 °C~ 7.63 °C with the increase of ILs concentrations, measured by ultra-sensitive differential scanning calorimetry. Moreover, the aggregation of collagen molecules was reduced when ILs polarity was increased as determined by fluorescence measurements and dynamic light scattering, which resulted in an increased loose fiber arrangement observed by atomic force microscopy. If the structural integrity of collagen needs to be retained, then the ILs sorts and concentrations should be considered.Graphical abstract

Green solvents, such as propylene carbonate (PC), can be used in leather processing to improve the efficiency of chrome tanning and reduce wastewater. Here we report a combined small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) study on PC and its efficacy as a carrier medium during chrome tanning. SAXS analysis on the collagen structure of chrome tanned leather using PC, compared to conventionally tanned leather using water, showed an increase in Cr uptake in addition to the more uniform penetration of Cr through the leather cross-section. The increased binding of Cr to the collagen matrix drives the decreased hydration environment of the collagen triple helix. Furthermore, DSC studies show a uniform hydrothermal stability for the PC samples due to the more even distribution of Cr through the collagen matrix. Understanding the mechanisms by which chrome tanning occurs in non-aqueous solvents can guide us towards a more sustainable future for the leather industry.Graphical abstract

Leather making is the process of converting raw hides into leather. Amounts of solid waste containing hazardous and high value components are generated during this process. Therefore, the elimination of the potential pollution and resource utilization of leather solid waste are the primary research hotspots. Herein, we comprehensively review the recent advances in the resource utilization of leather solid waste generated from chrome tanning including the utilization of tannery hair waste, untanned solid waste, chrome-containing leather solid waste, tannery sludge and finished leather waste, emphasizing on the general and novel utilization approaches. Finally, the remaining challenges and perspectives were summarized, in order to accelerate the development of resource utilization of leather solid waste.Graphical abstract

Processing polyvinyl chloride (PVC) artificial material requires plasticizer that softens the PVC coating. Currently, utilizing unsaturated fatty acid methyl esters to obtain epoxidized fatty acid methyl ester (EFAME) bio-plasticizers constitutes an environmentally responsible solution to substitute conventional ortho-phthalates that are endocrine disruptors or probable carcinogens. However, commercial EFAMEs, even with the highest epoxy value (ca. 5.5–5.8%) so far, still suffer from fast leaching from the PVC matrix, burdening the environment and shortening lifespan of the artificial material. Here, we report a proof-of-principle demonstration of a new strategy to obtain migration-resistant EFAME that harnesses the midchain hydroxyl of methyl ricinoleate and covalently attachment of a pendant acetate ester. Despite a low epoxy value (3.0%), the engineered bio-plasticizer displays significantly suppressed migration in multiple scenarios compared with one conventional EFAME with much higher epoxy value (5.8%). Circumventing the limit confronting previous strategy that highlights the sole contribution of epoxy value to achievable migration resistance, the rationale herein may provide guidance for designing new EFAMEs with comparable performance to ortho-phthalates, thus bringing the old and oft-maligned PVC artificial material industry one step closer to sustainability.Epoxidized methyl ricinoleate bio-plasticizer with a pendant acetate ester for PVC artificial leather: Circumventing existing limit on achievable migration resistance