Insights into functional polymer-based organic-inorganic nanocomposites as leather finishes

Multifunctional leather finishing vs. applications, through the addition of well-dispersed flower-like nanoparticles

In the present paper, multifunctional flower-like nanoparticles were synthesized to be used in the leather finishing. They are capable of conferring simultaneously and synergistic antimicrobial, self-cleaning, light resistance, hydrophobic, mechanical, thermal, and fluorescent properties due to the presence of Ag, TiO2, and SiO2 NPs. These nanoparticles form a "flower-like" structure in which the "pistil" is made up of TiO2 and the "petals" that surround it of silver nanoparticles and silica nanoparticles, whose dimensions are of the order of ten nanometers. Their surfaces enjoy abundant hydrophilic functionalities to be dispersed within inks commonly used during the leather finishing process. Leathers functionalized with these nanomaterials showed significantly improved self-cleaning properties after 15 h of exposure to UV light, and antibacterial properties 10 times higher than that shown by the untreated samples. Aging tests were performed (ISO 105-B02, ISO 17228, SAEJ 2412). ΔE, color variation decreased by approximately 30%, if compared with samples not refined with flower-like NPs. Furthermore, the results of the mechanical tests (ISO 17076, FCA 50444) evidence amazing properties, e.g. abrasion resistance more than significantly improved, increase in resistance from 1500 cycles for the untreated samples to 3000 cycles for the leathers finished with flower-like NPs. The contact angle analysis, capturing the angle that traces the air-water to water-substrate interface from the origin of the air-water-substrate contact point at the edge, is practically unchanged after 10 s in the case of nanoparticles containing finishing.

Development of a New Collagen Gel Product for Leather Finishing

Leather finishing is a critical process in the leather industry, as it significantly influences the final appearance, durability, and quality of leather products. Traditional leather finishing techniques often involve the use of synthetic chemicals, which may lead to environmental concerns and potential health hazards. In this study, we investigate the feasibility and effectiveness of a new collagen-based product for leather finishing. Collagen, a natural protein found abundantly in animals, has shown promise as an environmentally friendly and sustainable alternative for leather finishing. The new collagen gel product obtained from bovine hide waste by using an alkaline extraction method with lime was functionalized through an enzymatic treatment that allows to achieve a finishing product suitable for coating formulations, and at the same time, a biodegradable finishing. The collagen gel product was optimized by varying parameters, such as temperature, pH, and enzyme quantity. The optimized collagen gel product exhibits a wide particle size range and retains the triple-helical structure of collagen. The leather samples treated with the collagen gel product show enhanced properties compared to those with conventional finishes. The results show that the collagen gel product enhances water vapor permeability, color stability, and touch in the finishes. However, a low resistance to wet rubbing is obtained; therefore, it is necessary to study how to improve this parameter.

Increasing Functionality of Fish Leather by Chemical Surface Modifications

Fish skin is a by-product of the fishing industry, which has become a significant environmental pollutant in recent years. Therefore, there is an emerging interest in developing novel technologies to utilize fish skin as a versatile raw material for the clothing and biomedical industries. Most research on finishing procedures is conducted on cattle leather, and practically very limited information on fish leather finishing is found in the literature. We have developed three functional surface finishing treatments on chromium (CL)- and vegetable (VL)- tanned salmon leather. These treatments include hydrophobic, oil repellent, and electro-conductive ones. The hydroxyl functional groups present on the surface of the leather were covalently grafted with bi-functional aliphatic small molecule, 10-undecenoylchloride (UC), by esterification reaction forming hydrophobic coating. The surface hydrophobicity was further increased via covalent binding of perfluorodecanethiol (PFDT) to the double bond end-groups of the UC-modified leather via thiol-ene click chemistry conditions. The oleophobic coating was successfully developed using synthesized fluorinated silica nanoparticles (FSN) and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), showing oil repellency with a contact angle of about 100° for soybean oil and n-hexadecane. The electrically conductive coating was realized by the incorporation of conjugated polymer, polyaniline (PANI), via in situ polymerization method. The treated leather exhibited surface resistivity of about 5.2 (Log (Ω/square)), much lower than untreated leather with a resistivity of 11.4 (Log (Ω/square)).

Antibacterial and Antifungal Fabrication of Natural Lining Leather Using Bio-Synthesized Silver Nanoparticles from Piper Betle L. Leaf Extract

Leather is often used to make comfortable shoes due to its soft and breathable nature. However, its innate ability to retain moisture, oxygen and nutrients renders it a suitable medium for the adsorption, growth, and survival of potentially pathogenic microorganisms. Consequently, the intimate contact between the foot skin and the leather lining surface in shoes, which are subject to prolonged periods of sweating, may result in the transmission of pathogenic microorganisms and cause discomfort for the wearer. To address such issues, we modified pig leather with silver nanoparticles (AgPBL) that were bio-synthesized from Piper betle L. leaf extract as an antimicrobial agent via the padding method. The evidence of AgPBL embedded into the leather matrix, leather surface morphology and element profile of AgPBL-modified leather samples (pLeAg) was investigated using colorimetry, SEM, EDX, AAS and FTIR analyses. The colorimetric data confirmed that the pLeAg samples changed to a more brown color with higher wet pickup and AgPBL concentration, owing to the higher quantity of AgPBL uptake onto the leather surfaces. The antibacterial and antifungal activities of the pLeAg samples were both qualitatively and quantitatively evaluated using AATCC TM90, AATCC TM30 and ISO 16187:2013 test methods, approving a good synergistic antimicrobial efficiency of the modified leather against Escherichia coli and Staphylococcus aureus bacteria, a yeast Candida albicans and a mold Aspergillus niger. Additionally, the antimicrobial treatments of pig leather did not negatively impact its physico-mechanical properties, including tear strength, abrasion resistance, flex resistance, water vapour permeability and absorption, water absorption and desorption. These findings affirmed that the AgPBL-modified leather met all the requirements of upper lining according to the standard ISO 20882:2007 for making hygienic shoes.

Leather for flexible multifunctional bio-based materials: a review

Nowadays, diverse leather usage conditions and increasing demands from consumers challenge the leather industry. Traditional leather manufacturing is facing long-term challenges, including low-value threshold, confined application fields, and environmental issues. Leather inherits all the biomimetic properties of natural skin such as flexibility, sanitation, cold resistance, biocompatibility, biodegradability, and other cross-domain functions, achieving unremitting attention in multi-functional bio-based materials. Series of researches have been devoted to creating and developing leather-based flexible multi-functional bio-materials, including antibacterial leather, conductive leather, flame-retardant leather, self-cleaning leather, aromatic leather, and electromagnetic shielding leather. In this review, we provide a comprehensive overview of the commonly used leather-based functional materials. Furthermore, the possible challenges for the development of functional leathers are proposed, and expected development directions of leather-based functional materials are discussed. This review may promote and inspire the emerging preparation and applications of leather for flexible functional bio-based materials.

Graphical Abstract

Lightweight and Flexible Bi@Bi-La Natural Leather Composites with Superb X-ray Radiation Shielding Performance and Low Secondary Radiation

A high-shielding, low secondary radiation, lightweight, flexible, and wearable X-ray protection material was prepared by coimpregnating La₂O₃ and Bi₂O₃ nanoparticles in natural leather (NL) with an additional Bi₂O₃ coating at the bottom surface of the leather. The prepared Bi_28.2@Bi_3.48La_3.48-NL (28.2 and 3.48 mmol·cm^-3 are the loading contents of elements) showed excellent X-ray shielding ability (65-100%) in a wide energy range of 20-120 keV with reduced scattered secondary radiation (30%). The bottom surface coating played a critical role in enhancing the X-ray attenuation and reducing the scattered secondary radiation by reflecting and deflecting incident X-ray photons. Excellent mechanical property with superb bending resistance of the NL matrix was properly maintained, and its tensile strength and tearing load were 15.39 MPa and 25.81 N·mm^-1, respectively. This lightweight and wearable high-performance protection material can facilitate safety and comfortability during intensive activities of practitioners in the health care industry.