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Effective protection against X-ray is the premise of utilizing the X-ray, thus it is critical to develop novel X-ray shielding materials with both low density and high X-ray attenuation efficiency. As the even distribution of high-Z element components is of great significance for increasing the attenuation efficiency of X-ray shielding materials, in this study, the microfiber membrane (MFM), a type of synthetic leather featuring hierarchical structure was chosen to provide large surface area for the dispersion of rare earth (RE) element. Meanwhile, plant polyphenol was utilized to achieve the stable loading and uniform dispersion of the Ce or Er into MFM. Benefiting from the assistance of polyphenol and hierarchical structure of MFM, the even dispersion of RE element was successfully realized. The resultant shielding materials displayed approximately 10% superior X-ray attenuation efficiency compared to that without polyphenol, and an averagely 9% increment in X-ray attenuation efficiency than that without hierarchical structure. Moreover, the obtained composite with a thickness of 2.8 mm displayed superior X-ray shielding performance compared to 0.25 mm lead sheet in 16–83 keV and retained an ultralow density of 1.4 g cm–3. Our research results would shed new light on the manufacture of high-performance X-ray shielding materials with excellent X-ray shielding performance. [ABSTRACT FROM AUTHOR]

The effect of hydrophobic modification on the performances of collagen fibers (CFs) was investigated by using silane coupling agents with different alkyl chains as hydrophobic modifiers. It was found silane could be easily grafted onto CF surface through covalent bonds under 5% water content. This modification led to the transformation of surface wettability of CF from hydrophilic to hydrophobic. Interestingly, the change of surface wettability resulted in substantial improvement of the modified CF properties, presenting well dispersity of collagen fibers, higher thermal stability and enhanced mechanical properties in comparison with natural CF. The degree of improvement mainly depended on the length of alkyl chain in silane. Longer alkyl chain produced strong hydrophobicity and subsequently more superior performances of the modified CF. When the length of alkyl chain increased to 18 carbon atoms, the modified CF possessed durable superhydrophobicity even exposed to aqueous solutions of different pH, UV, and organic solvents, and had excellent thermal and mechanical properties like leather fibers. In general, this work clearly revealed that the properties of CF are closely and positively related to the hydrophobicity, which is suggestive in developing new leather making technology. [ABSTRACT FROM AUTHOR]

Effect of retanning on the thermal stability of leather is eliciting increasing attention. However, the relationship between the hydrophilicity of retanning agents and the heat resistance of leather and the corresponding mechanism remain unclear. Herein, phenolic formaldehyde syntans (PFSs) were selected as models to explore the effect of the hydrophilicity of retanning agents on the thermal stability of retanned leather. The thermal stability of leather was closely correlated to the hydrophilic group content (sulfonation degree) of PFSs. As the sulfonation degree increased, the water absorption rate of PFSs and their retanned leathers decreased, whereas the thermal stability of leather increased. Molecular dynamics simulation results proved that the introduction of PFSs could reduce the binding ability of collagen molecules with water and thus decreased the water molecules around the PFS-treated collagen. These results may provide guidance for the tanners to select retanning agents reasonably to improve the thermal stability of leather. [ABSTRACT FROM AUTHOR]

Gamma rays is widely used in modern science and technology, but it may cause health damage to practitioners. In the present study, natural composites based on leather and high-Z elements (atomic number ≥ 56) were fabricated and used as gamma rays shielding materials. These shielding materials were prepared by coating rare earth nanoparticles (Er2O3 or La2O3) onto the surface of natural leather, which was first impregnated with Bi3+ and Ba2+. Results show that the attenuation efficiency of the prepared Er1.31Bi5.46-NL (1.31 and 5.46 mmol cm−3 loaded elements) with thickness of 3.2 mm was 61.57% for incident rays at 121.78 keV (152Eu) and reached 96.4% in the incident of 59.5 keV (241Am), which is comparable to that of 0.25-mm lead plate (54.54 mmol cm−3). In addition, these natural-leather-based shielding materials exhibited low density (approximately 1/10 of Pb), high strength and wearable behaviors. [ABSTRACT FROM AUTHOR]

Manufacture of eco-friendly chrome-free leather is of great significance for realizing sustainable development of leather industry. Conventional tanning theory believes that it is impossible to convert raw hide to leather without the utilization of cross-linking agent (e.g., chrome salts) among collagen fibers in raw hide. Here, we developed a brand-new leather manufacture strategy that relied on the composite dehydration media enabled self-driven directional dehydration mechanism to accomplish chrome-free leather manufacture for the first time, rather than followed the classic cross-linking mechanism that has been obeyed for more than one century in leather industry. We demonstrated that the essence of leather making is to regulate the water content in raw hide rather than to form cross-linkage among collagen fibers. The composite dehydration media comprised of anhydrous ethanol and molecular sieves (3A activated zeolite powder) successfully guaranteed continuous self-driven directional dehydration of raw hide by establishing stable water concentration gradient between raw hide and ethanol, which significantly increased the dispersity of collagen fibers in raw hide (with the water content reduced from 56.07% to 5.20%), thus obtaining chrome-free leather that is more ecological than chrome-tanned leather due to the elimination of any tanning agent. The as-prepared chrome-free leather exhibited outstanding tear force (174.86 N), tensile strength (24.56 N mm−2), elongation at break (53.28%) and dry-thermal stability, superior to chrome-tanned leather. Notably, the used composite dehydration media was recyclable for chrome-free leather manufacture, therefore facilitating an environmentally benign leather manufacture process. Our investigations are expected to open up a new conceptual leather making strategy that is applicable for realizing substantial manufacture of eco-friendly leather. [ABSTRACT FROM AUTHOR]

An oligosaccharide-based masking agent suitable for chrome-free metal tanning was produced from cellulose via a stepwise degradation and oxidation process. Firstly, an AlCl3-NaCl-H2O/γ-valerolactone (GVL) biphasic solvent system was established for cellulose conversion (87.6%), which allowed in situ separation of the oligosaccharides and valuable small molecules into the two phases. Then, a H2O2 oxidation process enabled further degradation of the oligosaccharides and introduced –CHO/–COOH groups. This process strengthened the surface charge of the oligosaccharides, enhancing their coordination ability with metal ions. The post-oxidized fraction, together with added Zr species, exhibited satisfactory tanning performance, with a shrinkage temperature of 85.2 °C for the tanned leather. Al/Zr species could spontaneously coordinate with O atoms of O＝C(2) in the carboxylic group of post-oxidized oligosaccharides, which promoted the penetration of Al/Zr species into the leather matrix for efficient crosslinking reactions. [ABSTRACT FROM AUTHOR]

Conventionally, the manufacture of leather relies on the utilization of tanning agents that are capable of forming cross-linkages among collagen fibers, thus realizing the transformation of rawhide into leather. This theory has been followed for more than a hundred years. Herein, we realized tanning agent free leather making, which was achieved by controlled dehydration of pelt with ethanol, followed by a superhydrophobic coating. The controlled dehydration of the pelt guaranteed high dispersity of collagen fibers with substantially enhanced porosity, and the dehydrated pelt with the water content of ≤8.90% exhibited leather-like properties. The superhydrophobic coating improved the water repellency of dehydrated pelt significantly, which prevented the re-absorption of water by dehydrated pelt, thus allowing for the as-prepared leather to stably present leather-like properties. Notably, tanning agent free leather exhibited comparable physical properties to those of conventional chrome tanned leather, including the tensile strength (19.24 N mm−2), tear force (94.27 N), elongation at break (49.57%) and fullness. The tanning agent free leather making strategy developed by us might open up a new way for realizing environmentally benign leather manufacture. [ABSTRACT FROM AUTHOR]

Superhydrophobicity is vital to natural rubber‐based materials and can endow materials with intriguing features, such as self‐cleaning. Normally, low surface energy and surfacial micro/nanostructure are the two premises of superhydrophobicity. However, the fragility of micro/nanostructures in natural rubber (NR) composite surfaces makes the maintenance of durable superhydrophobicity under external forces difficult. Thus, the application of NR composite elastomers is limited in industrial fields. In this work, a novel NR‐based elastomer is prepared by uniquely dispersing perfluorooctytriethoxysilane‐modified leather collagen fibers (M‐LCF) with multiscale structures into rubber matrix. The as‐prepared NR composite with 40% M‐LCF content displays excellent superhydrophobicity with a water contact angle of 156°, and the endowed superhydrophobicity is ultradurable and can be retained after 2000 cycles of mechanical abrasion under a pressure of 100 kPa. Moreover, the prepared material features superior self‐cleaning performance and mechanical properties. The reported work may serve as a basic for fabricating materials with durable superhydrophobicity. [ABSTRACT FROM AUTHOR]

A promising and practical chrome-free tanning system has been developed based on a novel Al–Zr bimetal complex tanning agent. However, to achieve satisfactory resultant leather, the retanning process that is compatible with this emerging tannage needs to be investigated systematically. This paper aims to explore the interaction between the bimetal complex tanned wet white and retanning agents. The isoelectric point (pI) of wet white was 7.2, which was nearly the same as wet blue. The electropositivity of wet white was even higher than that of wet blue during post-tanning processes, resulting in higher uptake rate of retanning agents. The distribution of various retanning agents in wet white was analyzed by pI measurement of layered leather and fluorescent tracing technique. The retanning agents were unevenly distributed throughout the cross-section, which might be an important restriction factor in obtaining satisfactory organoleptic properties of the crust leather. This fact is mainly due to the strong electrostatic interaction between anionic retanning agents and wet white. Applying a high dosage of multiple retanning agents in a proper sequence of addition benefited the full penetration of retanning agents in leather matrix and thus improved the organoleptic properties of crust leather. This work provides guidance for optimizing retanning process of the wet white leather. [ABSTRACT FROM AUTHOR]

The development of renewable and non-toxic tanning agents substantially contributes toward the sustainable expansion of the leather industry. Herein, we report a green methodology to synthesize a novel tanning agent consisting of Al-oligosaccharides complexes produced via an efficient AlCl3-catalyzed cellulose depolymerization. Our experimental procedure allowed the production of a high purity tanning agent by the effective removal of the cellulose-decomposed small oxygenates and macromolecular oligosaccharides, via a liquid–liquid extraction using THF as the solvent. This also promoted the decolorization of the leather and enabled the efficient penetration of Al into the collagen matrix of skin. On this matter, experimental work combined with theoretical modeling were used to elucidate the tanning mechanism. In a first step, [Al(OH)1(H2O)4]2+ and [Al(OH)2(H2O)2]+ species weakly interacted or coordinated with the O-1 bond of the oligosaccharides produced. This interaction efficiently prevented the overload of Al species onto the leather surface, thus enhancing their penetration into leather matrix. Then, the active Al species were released from the Al-oligosaccharides complex and strongly coordinated with the –NH2 groups of the collagen fibers present in the leather, which helped to stabilize the fiber bundles, and therefore, contributed to achieve a satisfactory tanning performance. [ABSTRACT FROM AUTHOR]

A green and sustainable approach for leather-making was explored by imparting dehydrated hide (DL) with durable hydrophobicity through reacting with silane coupling agent (TMS). The rational control of hydrolysis and condensation rates of TMS was the key point for achieving efficient penetration and full reaction of TMS in DL, so as to obtain hydrophobic leather (HL-TMS). It was found that the leather-like HL-TMS could be fabricated when the DL with 5% water content reacted with TMS for 12 h under 30 °C at pH 6.0. In these conditions, TMS was evenly distributed in HL-TMS and provided HL-TMS with excellent water resistance, owning a dynamic waterproof time up to 163 h. Moreover, HL-TMS displayed exceptional hydrophobic durability against pH, UV, friction and organic solvents. Compared with DL, the collagen fibers of HL-TMS were well dispersed, and the porosity of which was 59.6% higher than chrome-tanned leather. In addition, the shrinkage area of HL-TMS in heating was 5.03%, remarkably less than chrome-tanned leather (12.11%), while its physical strengths and softness (9.6 mm) were higher than those of chrome-tanned leather. The results suggested that hydrophobic modification could substitute conventional tanning for manufacturing leather, and this hydrophobic modification-based strategy might push leather-making into a cleaner process. [Display omitted] • A tanning-free leather-making approach based on hydrophobic modification of DL by TMS was explored. • HL-TMS was successfully fabricated when DL with 5% water content reacted with TMS for 12 h at pH 6.0. • HL-TMS behaved excellent water resistance with dynamic waterproof time up to 163 h. • The area shrinkage rate of HL-TMS was 5.03% in heating, which was remarkably less than chrome-tanned leather (12.11%). • HL-TMS displayed higher physical strengths and softness than chrome-tanned leather. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ultrasound on titanium tanning of leather were investigated. Either 20 or 40kHz ultrasound was applied to the titanium tanning of pigskins. Five different treatment conditions were carried out and the effects were examined, such as leather shrinkage temperature (T s), titanium content and titanium distribution in the leather. Overall heat loading was carefully controlled. Results showed that 20kHz ultrasound effectively improves titanium agent penetration into the hide and increases the leather’s shrinkage temperature. Doubling the frequency to 40kHz produced negligible enhancements. An impressive 105.6°C T s was achieved using 20kHz ultrasound pretreatment of the tanning liquor followed by 20kHz ultrasound in the tanning mixture (liquor plus pigskins) in a special salt-free medium. Finally, using a unique ultrasonic tanning drum with 26.5kHz ultrasound, the T s reached a record level of 106.5°C, a value not achieved in conventional (no ultrasound) titanium tanning. The ultrasonic effects on titanium tanning of leather are judged to make a superior mineral tanned leather. [Copyright &y& Elsevier]

• The VOC emissions of leather with different grades and the health risk were studied. • The hexanal is the main cause of the unpleasant taste in low grade leathers. • The relationship between VOCs and health risk in sofa leathers were determined. • The leather materials barely pose health effects to residents. Furniture is identified as a vital volatile organic compound (VOC) emission source in the indoor environment. Leather has become the most common raw and auxiliary fabric material for upholstered furniture, particularly with extensive consumption in sofas, due to its abundant resources and efficient functions. Despite being widely traded across the world, little research has been conducted on the VOCs released by leather materials and their health risk assessment in the indoor environment. Accordingly, this study investigated the VOC emissions of leather with different grades and the health risk of the inhalation exposure. Based on the ultra-fast gas phase electronic nose (EN) and GC-FID/Qtof, the substantial emissions of aliphatic aldehyde ketones (Aks), particularly hexanal, appear to be the cause of off-flavor in medium and low grade (MG and LG) sofa leathers. The health risk assessment indicated that leather materials barely pose non-carcinogenic and carcinogenic effects to residents. Given the abundance of VOC sources and the accumulation of health risks in the indoor environment, more stringent specifications concerning qualitative and quantitative content should be extended to provide VOC treatment basic for the manufacturing industry and obtain better indoor air quality. [Display omitted] [ABSTRACT FROM AUTHOR]

Green and efficient acid protease has received increasing attention in bating wet blue (chrome tanned leather). However, acid proteases penetrate slowly in the wet blue, which reduces the dispersion efficiency and uniformity of hide collagen fibers. We explored the factors that affect the penetration of acid proteases in wet blue and the bating performance, including surface charge, molecular weight, particle size, and proteolytic activity of protease. The results show that the most important factor is the surface charge of the acid protease. The acid protease AP-2 derived from Trichoderma reesei had isoelectric point (pI) of 3.6 and penetrated the wet blue more deeply, thereby dispersing collagen fibers and softening the wet blue better than the pepsin (pI 1.9) and the acid protease AP-1 derived from Aspergillus usamii (pI 2.4). This finding is because the negatively charged pepsin and AP-1 are combined easily with the positively charged wet blue at the bating pH of 3.5 and stay on the surface layer rather than transfer into the inner layer of the wet blue. Therefore, choosing acid protease with the pI higher than the bating pH is important for deep penetration and good bating performance. [Display omitted] • Acid proteases had different isoelectric points (pIs) from 1 to 4. • Acid proteases had thermal stability and Cr3+ adaptability for bating environment. • Protease with pI higher than bating pH 3.5 penetrated rapidly in chrome tanned leather. • Positively charged protease penetrated rapidly and dispersed collagen fibers well. • Electrostatic interaction greatly affects protease penetration and bating performance. [ABSTRACT FROM AUTHOR]

Leather shavings are generated as solid waste in the leather industry and may cause environmental pollution if not disposed judiciously. These solid wastes, primarily composed of collagen fibers (CFs), can be recycled as biomass composites. However, CFs are incompatible with natural rubber (NR) due to its hydrophilicity. Conventionally, the compatibility has been improved by utilizing silane coupling agents (SCAs) along with a large number of organic solvents, which further contribute to environmental pollution. In this study, we developed a novel complex coupling agent (CCA) to enhance the compatibility between CF and NR. The CCA was synthesized through a coordination reaction between Cr(III) and α-methacrylic acid (MAA). Cr(III) in the coupling agent coordinates with the active groups in CFs, while the unsaturated double bonds in MAA facilitate covalent crosslinking between the CCA and NR, improving compatibility. The coordination bonding between CF and NR exhibits strong interfacial interaction, endowing the composites with desirable mechanical properties. Moreover, the proposed method is an economical and green approach that can be used to synthesize CF-based composites without requiring organic solvents. Herein, a strategy promoted sustainable development in the leather industry has been established. [Display omitted] • Collagen fiber and natural rubber were blended to prepare the biomass composite. • A complex coupling agent named CCA was synthesized and added into the composite. • The compatibility between collagen fiber and natural rubber was improved by CCA. • The reinforcing mechanism of CCA in the biomass composite was determined. • A promising strategy for solid waste recycling in leather industry was established. [ABSTRACT FROM AUTHOR]

The manufacture of metal-free leather is considered to be favorable for environment compared to conventional technology of chrome tanning. However, metal-free leather crust presents some disadvantages for further processing, like low isoelectric point (pI) and high hydrophilicity. Applying cationic amphiphilic polymer retanning agent is expected to overcome the disadvantages. The aggregation behavior of this polymer, which is influenced by its charged nature, will greatly affect the leather properties. However, the structure-function relationship has not been clarified yet. Here we synthesized a series of cationic amphiphilic acrylic polymers, Poly(SMA- co -DMA)s (PSDs), with increasing protonation degrees (PSD-40 %, PSD-60 %, PSD-80 %, PSD-100 %) and applied them to metal-free leather retanning. Experiments and molecular dynamics simulations show that PSD with higher protonation degree exhibits smaller aggregate size and better dispersion in water. PSD retanning significantly promotes the uptake of anionic fatliquors by leather (>90 %) because PSD enhances the pI of leather. PSD-40 % cannot be uniformly dispersed in water. PSD-60 %, PSD-80 % and PSD-100 % possess suitable particle size (45–90 nm) to penetrate into leather fibrils and form hydrophobic films, thereby greatly improving the hydrophobicity of leather. The hydrophobicity of leather increases with decreased protonation degree of PSD. Moreover, the fiber dispersion and organoleptic properties of leather are positively correlated with leather hydrophobicity because of the separating and lubricating effects of the amphiphilic PSD. [Display omitted] • Cationic amphiphilic polymer poly(SMA- co -DMA) (PSD) was prepared for metal-free leather retanning. • PSD with higher protonation degree exhibits smaller aggregate size and more dispersed state in water. • PSD lifts the pI of leather, thus promoting the uptake of anionic fatliquors by leather. • PSDs with protonation degree not less than 60 % penetrate into fibril hierarchy to form hydrophobic coatings. • Comprehensive performance of leather is enhanced as PSD protonation degree decreases from 100 % to 60 %. [ABSTRACT FROM AUTHOR]

Chrome-free eco-leather manufacture is inevitable in sustainable development of the leather industry. Herein, oxidized sodium lignosulfonate (OSL) was prepared using H 2 O 2 and CuSO 4 catalyst as a biomass-derived tanning agent. H 2 O 2 oxidation of OSL breaks the aliphatic side-chain β -O-4′, β -5′, and β - β ' linkages, transforms the adjacent phenolic hydroxyl group and methoxy group on the benzene ring into carboxyl groups and reduces the colority. OSL120 (120% H 2 O 2 , M w 1498) containing moderate carboxyl (6.27 mmol/g) and phenolic hydroxyl (0.18 mmo/g) appropriately coordinates with aluminum–zirconium salts (AZ), thereby promoting the uniform penetration of OSL–AZ complexes into the leather matrix. Moreover, OSL120 provides essential hydrophobic and hydrogen bonds interactions with collagen to form a rigid multi-point crosslinking network among collagen fibers. Thus, chrome-free tanned leather shows natural flesh color and shrinkage temperature up to 89.5 ℃, and crust leather with satisfactory physical properties are achieved. This work gives new insights into the low-carbon leather manufacture with lignin-based tanning system and provides a novel approach for the resource utilization of sodium lignosulfonate. [Display omitted] • OSLwas prepared using H 2 O 2 and CuSO 4 catalyst as a biomass-derived tanning agent. • H 2 O 2 oxidation introduces abundant carboxyl groups and reduces the colority of OSL. • The carboxyl and phenolic hydroxyl in OSL coordinate with AZ to form complexes. • OSL provides essential hydrogen and hydrophobic bonding for OSL–AZ tanning system. • OSL strongly supports the formation of robust multi-point crosslinking network. [ABSTRACT FROM AUTHOR]

In various sectors, including medical radiotherapy, aerospace exploration, and nuclear energy, the necessity for advanced neutron-shielding materials has escalated. However, these materials often exhibit poor mechanical performance and limited adaptability. To address these shortcomings, this study introduces a novel approach inspired by ferroconcrete construction to develop wearable neutron-shielding materials. This method utilizes the collagen fiber-supported framework present in natural leather, serving as a flexible skeleton, and employs functionalized B 4 C nanoparticles and paraffin as fillers. The interconnected voids and the unique hierarchical structure of the collagen fibers work synergistically to enable uniform dispersion of B 4 C nanoparticles, thus enriching the resultant composites with superior neutron-shielding performance. The composite material prepared through this method exhibits a remarkable neutron-shielding effectiveness of 96.93 % and a high linear attenuation coefficient of 17.46 cm−1, outperforming other shielding materials. Additionally, the three-dimensional (3D) woven network of the collagen fiber-supported framework offers impressive mechanical properties, including a tensile strength of 28.59 MPa. This innovative design strategy for creating new wearable neutron-shielding materials paves the way for manufacturing advanced neutron-protective clothing and propels a new structural design with elevated shielding and mechanical performance. [Display omitted] • B 4 C nanoparticles were uniformly dispersed in natural leather. • The interfacial compatibility between different materials were improved. • The resultant materials feature excellent shielding and mechanical performances. • Monte Carlo simulations unveil the effect of the dispersion of B 4 C nanoparticles. [ABSTRACT FROM AUTHOR]

An extracellular keratinase gene from Bacillus sp. LCB12, isolated from saline-alkali soil, was cloned and high-effectively expressed in Bacillus subtilis SCK6. The enzyme was purified by ammonium sulphate precipitation and cation-exchange chromatography. Its molecular mass was estimated to be 30.95 kDa by SDS-PAGE. The optimum conditions for catalytic activity of the enzyme were pH 10.0 and 60 °C. The enzyme activity was completely inhibited by PMSF, while it was slightly inhibited by EDTA. Moreover, the surfactants Tween 20, Tween 80 and Triton X-100, showed little effect on enzyme activity respectively. The crude enzyme was used as an alternative to sodium sulfide for dehairing of goat skins. The goatskin was dehaired by the enzyme at 33–35 °C in 6 h. The enzymatic dehaired pelt showed better general appearance and better whiteness by visual tests, and the grain surface of enzymatic dehaired pelt revealed absence of hair shaft with empty follicles by stereoscopic observation. Meanwhile, the epidermis was completely removed and the collagen fiber structure of enzymatic dehaired pelt was more opened, regular and even in dermis comparing with conventional dehaired pelt by histological analysis. • A keratinase gene was cloned and highly expressed by Bacillus subtilis SCK6. • The goatskin was completely dehaired by keratinase without use of sodium sulfide at 33–35 °C. • The enzymatic dehaired belt showed better overall appearance and better whiteness. • The keratinase showed great potential application in leather industry. [ABSTRACT FROM AUTHOR]

Graphical abstract Leather, the evolved version of thermal insulation materials from animal hides, is one of the oldest but still popular natural clothing materials. Herein, we develop a multifunctional thermal camouflage armor by direct editing the natural insulation structure of leather. The armor simultaneously exhibits exceptional thermal and non-thermal functionalities, including persistent camouflage performance, hydrophobicity, flame-resistance and arbitrary tailorability. Highlights • Leather enables the synthesis of multifunctional thermal camouflage armor. • Thermal convection, conduction and radiation are suppressed simultaneously. • The armor exhibits persistent camouflage performances. • Non-thermal functionalities are also provided. Abstract Realizing persistent thermal camouflage of heat objects remains challenging. A variety of biological species have evolved extraordinary thermal insulation strategies that represent an exciting source of inspiration for developing high-performance thermal camouflage materials. However, we are still far from being able to faithfully mimic these natural insulation materials not only because of the difficulty to imitate the intricate structural hierarchy but also due to the challenge to simulate the way used by nature, that is, each level of structural hierarchy collaborates together to achieve efficient insulation. Instead of biomimicing the biological structures, we here make a direct structure editing on the natural insulation structure of cowhide for obtaining multifunctional thermal camouflage armor. SiO 2 nanoparticles (SiO 2 NPs) were in situ grown on the 3D hierarchically fibrous scaffold of leather, which played multiple roles in trapping stagnant air as thermal insulator, blocking infrared absorptive groups and reflecting infrared radiation from heat objects. The thermal camouflage armor exhibited a high porosity to 61.4%, as well as low thermal diffusivity (1.24 × 10−7 m2 s−1) and thermal conductivity (0.04 W m−1 K−1). The thermal camouflage armor exhibited persistent camouflage performance (1.0 h) and exceptional non-thermal functionalities, including hydrophobicity, flame-resistance, flexibility and arbitrary tailorability. [ABSTRACT FROM AUTHOR]

Abstract In this study, an extracellular metalloprotease (EMPr) from Bacillus sp. LCB14 was cloned, successfully expressed in Bacillus subtilis SCK6, and utilized to dehair goat skins in leather-making processes. Through optimization of fermentation conditions, the expression level of EMPr reached 6973 U/mL after 72 h of incubation. Then the crude enzyme was purified 6.30 fold through a three-step purification process of centrifugation, dialysis and SP Sepharose Fast Flow. The purified protease EMPr was established by 12.5% SDS-PAGE and showed 40.08 kDa. It exhibited highest activity 77,302 U/mg at pH 6.5 and 50 °C respectively. Protease activity was slightly enhanced by Li+ and K+. Interestingly, the protease activity was enhanced by the surfactants, such as, Tween 20, Tween 80, SDS, and Triton X-100 respectively. The dehairing experiments showed that the crude EMPr completely dehaired goatskins during 6 h at 33–35 °C without use of sodium sulfide. The enzymatic dehaired belt showed well opening up of fiber structure and the collagen was not damaged. Therefore the protease EMPr displayed great potential application in dehairing process without using sodium sulfide. Highlights • A metalloprotease gene was cloned and highly expressed by Bacillus subtilis SCK6. • The goatskin was completely dehaired by EMPr without use of sodium sulfide at 33–35 °C. • The enzymatic dehaired belt showed better overall appearance and better whiteness. [ABSTRACT FROM AUTHOR]

Feather waste is produced in millions of tons globally every year, resulting in a waste of biomass resources and even environmental pollution. A sustainable strategy for utilizing feather waste was proposed by preparing a clean deliming agent for ammonia-nitrogen (NH 3 –N) reduction in leather manufacture and biological treatment efficiency improvement of tannery wastewater. Briefly, chicken feather wastes were deeply hydrolyzed with sulfuric acid, and the optimized keratin hydrolysate (KH opt) that contained 53.6% crude protein and 41.2% amino acids, such as glutamic acid, serine, proline, leucine, phenylalanine, glycine, valine, and arginine, was obtained and used to delime limed cattle hides. The appropriate ratio of amino acids in KH opt gave KH opt a great pH-buffering capacity and maintained a stable float pH of approximately 9 throughout the deliming process. The isoelectric points of KH opt (3.8) and the limed hide (6.3) were both lower than the float pH, thereby bringing about an electrostatic repulsion between the KH opt and the hide surface, which is helpful for KH opt to penetrate and deswell the limed hide rapidly. Moreover, the KH opt deliming effectively removed calcium from the limed hide and achieved leather comparable to conventional leather for commercial applications. KH opt reduced the NH 3 –N concentrations of deliming effluent and tannery wastewater by 91.1% and 80.6%, respectively, compared with the conventional deliming agent (ammonium sulfate), and dramatically increased the biological treatment efficiency of tannery wastewater. The results showed that efficient and high-value use of feather waste was made by preparing KH opt for sustainable leather manufacturing. [Display omitted] • A novel resource utilization of feather waste was developed. • Keratin hydrolysate (KH) was obtained by deeply hydrolyzing feather waste. • KH had efficient and environment-friendly leather deliming performance. • KH deliming greatly reduced ammonia-nitrogen pollution in tannery wastewater. • KH deliming improved the biological treatment efficiency of tannery wastewater. [ABSTRACT FROM AUTHOR]

A series of highly-oxidized starch (HOS) were prepared using H 2 O 2 and a copper-iron catalyst as a desired ligand for zirconium tanning of leather. The effects of catalyst and H 2 O 2 dosages, and reaction temperature on the oxidation degree (OD, represented as the amount of carbonyl and carboxyl groups derived) of starch were investigated. The OD reached 76.2% when oxidation was conducted using 60% H 2 O 2 and 0.015% catalyst at 98 °C for 2 h. 13 C NMR and FT-IR illustrated carbonyl and carboxyl groups were formed in HOS after oxidation. GPC and laser particle size analyses indicated the decrease of HOS molecular size with increasing H 2 O 2 dosage and OD. HOS with moderate OD and molecular weight was able to coordinate with zirconium and remarkably improve tanning process. Leather tanned by Zr complexes using HOS-60 (60% H 2 O 2 , Mn 3516 g/mol) as ligand presented considerably better physical and organoleptic properties than those of traditional Zr-tanned leather. [ABSTRACT FROM AUTHOR]

Reducing or eliminating chrome pollution from leather processing is an essential task for the sustainable development of leather industry. Herein, we established a chrome-free tanning system based on biomass-derived hydroxycarboxylic acid (BHCA)–zirconium complexes. The synergistic tanning mechanism of BHCA and zirconium salt was investigated by exploring the interaction among BHCA, zirconium salt, and collagen fiber (CF). Results show that the hydroxyl and carboxyl groups in BHCA coordinated with zirconium ion to form Zr complexes, while BHCA caused changes in the morphology and conformation of collagen through ionic and hydrogen bonding. The order of the contribution of active groups in CF involved in the coordination reaction in BHCA–Zr tanning presented as amino group > carboxyl group > hydroxyl group. Moreover, BHCA with multiple functional groups and large molecular size provided indispensable non-covalent binding sites for BHCA–Zr tanning system, resulting in the formation of multi-point crosslinking network structure among CFs. Thus, BHCA–Zr exhibited an obvious synergistic effect, and its tanning performance was remarkably better than that of conventional lactic acid–zirconium complexes. This work provides new insights into the development of novel chrome-free eco-tanning system. [Display omitted] • A chrome-free synergistic tanning system was established to eliminate Cr pollution. • The hydroxyl and carboxyl groups in BHCA coordinated with Zr ion to form complexes. • BHCA–Zr mainly coordinated with amino groups in CF. • BHCA provided indispensable non-covalent bonding for BHCA–Zr tanning system. • A robust multi-point crosslinking network was formed to show synergistic effect. [ABSTRACT FROM AUTHOR]

Highly-oxidized starch (HOS) is an excellent ligand for zirconium tanning in leather making. However, oxidation reaction can only be undertaken in diluted solution due to the high viscosity of starch, which leads to high oxidant consumption and low solid content of HOS, and therefore greatly limits its industrial application. Starch was predegraded by using HCl followed by H 2 O 2 oxidation for preparing a practical oxidized starch (OST) ligand with high solid content. HCl (5%) remarkably reduced the viscosity of starch and simplified the subsequent oxidation, resulting in a decrease in H 2 O 2 dosage from 60% to 40% and an increase in solid content from 10% to 38%. HCl broke the α-(1–4) glycosidic bond between glucose units, and H 2 O 2 oxidation led to the generation of abundant carboxyl groups in OST. The OST with moderate molecular weight (Mw 5609 g/mol) and carboxyl content (6.48 mmol/g) made the tanning performance of OST–Zr comparable to those of HOS–Zr and chrome tanning agents. Therefore, this work gives new insights into the crop-polysaccharides based ligands application and exhibits huge potential for promoting industrial applications of zirconium tanning. [Display omitted] • Starch was predegraded by using HCl to reduce its viscosity and simplify oxidation. • Predegraded starch was oxidized by using H 2 O 2 to introduce carboxyl group. • H 2 O 2 dosage reduced from 60% to 40%, and solid content increased from 10% to 38%. • Oxidized starch promoted the penetration and fixation of zirconium salt in leather. • Starch-based ligand with high solid content greatly improved its practicability. [ABSTRACT FROM AUTHOR]

Chrome-free metal tanning agent has been considered as eco-friendly in the leather industry. However, extensive crosslinking reactions of metal species on the leather surface restrain their uniform penetration into the hierarchical nanoscale leather matrix. Thus, masking agents with appropriate coordination ability are needed. Herein, the selective degradation of hemicellulose in corncob was achieved with 92.5% of conversion in an AlCl 3 –H 2 O system, obtaining oligosaccharides masking agent with high purity and leaving cellulose and lignin in the solid residue for other valuable use. Subsequently, H 2 O 2 oxidation was performed to introduce –CHO/–COOH into oligosaccharides and reduce their molecular weights, thereby enhancing coordination ability and reducing ligand dimension. The post-oxidized reaction fluids together with additional Zr species were subjected to leather tanning, in which the oligosaccharides could coordinate with Al/Zr species and promote the penetration of metal species into the leather matrix. By controlling the hemicellulose degradation and oligosaccharide oxidation, an appropriate concentration of oligosaccharides with proper –CHO/–COOH contents allowed the efficient masking effect of the oligosaccharides. As a result, a uniform distribution of Al/Zr species was observed on the cross section, and 83.5 °C of shrinkage temperature was obtained for the chrome-free tanned leather. [Display omitted] • Hemicellulose in corncob was selectively degraded into oligosaccharides. • Bi-functional AlCl 3 acted as catalyst for biomass conversion and tanning agent. • H 2 O 2 oxidation brought –CHO/–COOH to oligosaccharides to improve masking ability. • 83.5 ℃ Ts of the tanned leather was obtained with even penetration of metal ions. [ABSTRACT FROM AUTHOR]

• A novel hide bating technology was developed by using soybean flour (SF). • Trypsin activity was effectively inhibited with SF in the initial stage of bating. • Hide surface damage caused by trypsin was reduced by SF's reversible inhibition. • Trypsin activity completely returned after trypsin penetrated through hide. • Enzymatic hydrolysis on the collagen fiber network of hide became more uniform. Trypsin is used to remove non-collagenous proteins from cattle hide in leather processing but prone to damage hide surface and reduce leather quality due to its rapid protein hydrolysis action on the hide surface and slow penetration through the whole hide. A novel trypsin bating method was developed using a reversible inhibition of trypsin with high-yield, low-cost and environment-friendly soybean flour (SF). When the mass ratio of trypsin to SF was 1:20, the trypsin activity was decreased by 77 % at a reaction time of 5 min and completely returned in 100 min because of the competitive Kunitz trypsin inhibitor in SF. Bating with trypsin-SF mixture avoided the damage to hide surface caused by trypsin, improved the dispersion uniformity of hide collagen fibers and increased the softness and the mechanical strength of leather. This work exhibits huge potential for improving the leather quality and provides new insights into the soybean application. [ABSTRACT FROM AUTHOR]

• Wearable co-doped Bi/Ce-natural leather X-ray radiation protection materials are fabricated. • Favorable X-ray shielding ability is obtained and superior than that of commercial lead plate. • Low bulk density and excellent mechanical properties of natural leather is well maintained. • This novel advanced protection material with features of light-weight, high flexibility and high X-ray shielding. Natural leather (NL) based composite protection materials with lightweight, flexibility, wearability and high shielding efficiency will remarkably innovate the current research on X-ray protection materials. A co-doped Bi/Ce-NL composite with outstanding X-ray attenuation in the energy range of 20−120 keV is successfully fabricated. The uniform distribution of Bi 2 O 3 and CeO 2 nanoparticles in the hierarchical structure of natural leather significantly promotes the X-ray attenuation by improving the weak absorption region of Bi with Ce via synergistic effects of the two elements. The fabricated Bi/Ce-NL loading with 0.755 mmol cm−3 Bi 2 O 3 and 1.51 mmol cm−3 CeO 2 achieves approximately 100% X-ray shielding when the energy below 40 keV. Thus, the fabricated Bi/Ce-NL with superb X-ray attenuation can safely and comfortably protect human from the risk of X-ray exposure with low bulk density, high water vapor permeability, exceptional mechanical properties and excellent bending resistance, presenting significant advantages in wearability and flexibility compared to both traditional lead-based and polymer-based protection materials. [ABSTRACT FROM AUTHOR]

• Low-molecular chitosan (LMC) could be prepared by H2O2 depolymerization. • H2O2 had dual functions to depolymerize and modify the structure of chitosan. • LMC had lower positive charge that was favorable for the fatliquoring of leather. • LMC favored improving crosslinking intensity and lubricating degree of leather. • LMC contributed to strengthening biomass-derived polyaldehyde tanned leather. Tanning leather using green biomass-derived polyaldehyde (BPA) is a promising approach to eliminate the widespread Cr pollution in leather industry, but unsatisfactory thermal stability and mechanical strength of the correlated resultant leather limited its industrial application. Herein, we report a green methodology to strengthen BPA tanned leather via introducing chitosan derivatives to crosslink with free aldehyde groups on dialdehyde carboxymethylcellulose (DCMC) tanned leather. H 2 O 2 was employed for purposely modifying chitosan to prepare low-molecular chitosan (LMC) with lower positive charge. The interactions between chitosan/LMC and DCMC were investigated to elucidate the strengthening mechanism. Owing to the weakened hydrogen bonding network and higher accessibility of amino groups on LMC, LMC could react much easier with aldehyde groups on DCMC. Moreover, LMC could efficiently penetrate into the internal fiber networks of leather for further interlocking, which enhanced the thermal stability and the lubricating degree of crust leather and, as a result, the tensile and tear strengths were significantly improved by 79.3% and 25.3%, respectively. Therefore, the use of LMC can promote the widespread application of BPA tanned leather, benefiting to the complete elimination of hazardous Cr pollution. [ABSTRACT FROM AUTHOR]

Ammonium-free deliming technology is becoming popular in the leather industry because conventional deliming with ammonium salts results in high ammonia-nitrogen (NH 3 –N) concentration of tannery wastewater. However, existing ammonium-free deliming agents have inadequate buffering capacity and slow penetration rate in limed pelt. In this study, glycine with p K a of –NH 3 + = 9.6 was used to delime limed cattle hides. Glycine penetrated the entire limed pelt in only 10 min because a buffer of pH 8.0–9.5 was rapidly formed by the reaction between glycine and the alkali in pelt, thereby leading to a negatively charged pelt surface (isoelectric point 6.3). The appearance and physical properties of the crust leather produced by glycine deliming process were very similar to that produced by ammonium sulfate deliming procedure. The concentration of NH 3 –N in glycine deliming effluent was dramatically reduced by 99%. Moreover, glycine deliming benefitted the biological treatment of mixed tannery wastewater because of the introduction of additional carbon source to the tannery wastewater. This addition brought the ratio of total organic carbon (TOC) to total nitrogen (TN) in the wastewater much closer to the proper ratio of 10:1 for aerobic biological treatment. After aerobic biological treatment for 24 h, the concentrations of NH 3 –N, TOC, and TN in the treated tannery wastewater using glycine deliming were reduced by 99%, 20%, and 53%, respectively, compared with those using ammonium sulfate deliming. Image 1 • A clean deliming technology was developed by using glycine. • Glycine penetrated limed pelt as quickly as ammonium sulfate. • Glycine and alkali in limed pelt formed a buffer, maintaining the float pH around 9. • Glycine eliminated ammonia-nitrogen pollution in the deliming effluent. • Deliming with glycine benefitted the biological treatment of tannery wastewater. [ABSTRACT FROM AUTHOR]

• Na-CMC was pre-degraded by peroxide to prepare solution with high solid content. • DCMC was further prepared by periodate oxidation for practical leather tanning. • DCMC could endow leather with favorable tanning effect and physical properties. • DCMC with high solid content has potential to be used as a tanning agent product. Dialdehyde carboxymethylcellulose (DCMC) solution generally has quite low solid content, which inevitably limits its industrial application. In this work, carboxymethylcellulose sodium (Na-CMC) was pre-degraded using H 2 O 2 followed by periodate oxidation for preparing DCMC with high solid content as practical tanning agent. Pre-degradation conditions optimization showed that H 2 O 2 dosage most impacted the tanning effect of DCMC, and the M w and viscosity of Na-CMC underwent remarkable reduction. FT-IR and 1H NMR illustrated that aldehyde group was successfully introduced into DCMC after periodate oxidation. Under the optimized conditions, the solid content of DCMC could be improved to around 30%. This DCMC could endow tanned leather with high shrinkage temperature and satisfactory fiber dispersion. Besides, DCMC tanned leather had comparable physical and organoleptic properties to those of leathers tanned by chrome tanning agent and commercial polyaldehyde tanning agent TWT. This suggests the prospect of DCMC with high solid content as useful tanning agent. [ABSTRACT FROM AUTHOR]