Leather Collagen Research Articles

A paper sizing agent based on leather collagen hydrolysates modified by glycol diglycidyl ether and its compound performance

In this research, collagen hydrolysates with different average molecular weights (Mn¯) from leather collagen were chosen as raw materials. Five environmental-friendly sizing agents (SA) were prepared by cross-linking collagen hydrolysates with glycol diglycidyl ether (GDE) and further grafting them with butyl acrylate (BA) and styrene (St). Then the compound sizing agents (SGDESA-x, x = 1, 2, 3 and 4) were obtained by simple physical mixing of GDESA and starch. The surface sizing performance of GDESA and compound sizing agents were studied. The research result shows that both physical, mechanical properties and water resistance of the corrugated paper coated by GDESA were significantly improved when Mn¯ of collagen hydrolysate was about 10,000, and its emulsion exhibited robust stability in long standing time. Furthermore, when the SGDESA-2 was used as a sizing agent, the coated corrugated paper exhibited strong water resistance, good physical and mechanical properties even after refolded for 20 times.

An environmental polyurethane retanning agent with the function of reducing free formaldehyde in leather

Chromotropic Acid Grafted Amphoteric Polyurethane (CAGAPU) was synthesized with Chromotropic Acid (CA) as a modifier for Polyurethane (PU). The structure of CAGAPU was confirmed by FT-IR, 1H-NMR. The retanning process and the experiments of CAGAPU with formaldehyde indicate the following: (1) The leather retanned by CAGAPU can be comparable or surpassed to the market PU-based retanning system in terms of shrinkage temperature and sensory performance. (2) The leather collagen fibers are smoother and orderly which provides a potential value for the appearance of the leather and fur industry. (3) The CAGAPU retanned system can bring down the free formaldehyde content in aldehyde tanned leather significantly. (4) The optimum dosage of CAGAPU is 20 g and the best retanning time is 6 h (5) The CAGAPU retanned system can reduce the free formaldehyde, Biochemical Oxygen Demand (BOD), Total Dissolved Solids (TDS) and Total Suspended Solid (TSS) from the source which retard pound on the economy and environment greatly compare to the traditional governance. Therefore, this paper provides the possibility for the sustainable development of leather. The work has changed the traditional way of “terminal treatment” and realized the “initial treatment” and may also offer a new idea of solving the problem of formaldehyde in the newly decorated houses or in the air.

PEGylated chitosan protected silver nanoparticles as water-borne coating for leather with antibacterial property

Development of eco-labeled and effectively antibacterial coatings for final leather products has been desiderated both by industry and by consumers. Herein, PEGylated chitosan modified silver nanoparticles (PEG-g-CS@AgNPs) were prepared and characterized by UV–vis spectroscopy, transmission electron microscopy and dynamic light scattering. The antimicrobial activity of such silver nanoparticles was investigated against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), exhibiting much lower minimum inhibitory concentration (MIC) than chitosan or PEG-g-CS. Water-borne coating was formed by immobilizing the PEG-g-CS@AgNPs onto the leather surface through the electrostatic interaction between amino groups of chitosan and carboxyl groups of leather collagen. Scanning electron microscopy and water contact angle were employed to study the coating’s morphology and hydrophilicity, respectively. After coating, leather samples showed significantly high bactericidal efficiency with reusability after release of dead cells from the coating by simply water washing. The excellent antibacterial property of PEG-g-CS@AgNPs coating was ascribed to the combination of bacteria-resistance and bacteria-release by PEGylation, and dual bacteria-killing based on chitosan and Ag+ release.

Application of thermal analysis methods for damage assessment of leather in an old military coat belonging to the History Museum of Braşov—Romania

The aim of this work has been the assessment of the thermo-oxidative, hydrothermal and crystalline zone stabilities of several leather samples taken by the conservators from a military coat dated sixteenth–seventeenth centuries, belonging to the History Museum of Brasov—Romania. For this purpose, the thermo-gravimetry/derivative thermo-gravimetry (TG/DTG), differential scanning calorimetry (DSC) and micro hot table (MHT) methods have been employed. The thermo-oxidative damage of leather has been characterized by the rate of the first thermo-oxidation process highlighted in TG/DTG curves recorded in static air atmosphere. The hydrothermal denaturation of leather has been characterized by MHT method and DSC analysis in excess water conditions. The damage of crystalline zone of collagen in leather has been determined by DSC analysis in nitrogen flow. The qualitative damage for each leather sample and each kind of deterioration has been evaluated using the criteria resulted by thermal analysis of a large number of collagen-based materials (pure collagens, new and old parchments and leathers). The obtained results could facilitate the choice of the restoration and conservation procedures applicable for the investigated military coat.

Study of the effect of tannins and animal species on the thermal stability of vegetable leather by differential scanning calorimetry

Micro-differential scanning calorimetry was used to reveal the deterioration patterns of collagen in vegetable-tanned leather. The influence of both the tannin type, i.e. hydrolysable or condensed, and collagen animal species, i.e. calf and sheep, was investigated. Comparison with the behaviour of unmodified collagen in parchment was made to explain the thermal destabilisation and denaturation of the chemically modified collagen in leather. Both leather and parchment were subjected to accelerate ageing by heating at 70 °C in controlled atmosphere at 30 % RH. The synergistic effect of the daylight exposure was studied by irradiating the samples in the visible domain with 4000 lx. The destabilisation effect induced by the hydrothermal ageing treatment was evident since the 8th day and reached a critical level after 32-day ageing time. The formation of damaged intermediate states with progressively lower thermal stability was the main feature of the deterioration pattern independent of the tannin type and collagen species. Quebracho-tanned calf leather was the most resistant against ageing, whereas chestnut-tanned sheep leather underwent de-tanning after a 32-day ageing period. Exposure to visible light irradiation induced an evident thermal stabilisation due to cross-link formation. The balance between thermal stabilisation and destabilisation processes in leather during visible light exposure was influenced by the tannin type.

Green chemistry approaches to leather tanning process for making chrome-free leather by unnatural amino acids

In the present study, green and sustainable method or eco-friendly approaches to tanning process based on unnatural d-amino acids (d-AA)-aldehyde (Ald) as a substitute for chrome-free tanning has been attempted. The distribution of optically active d-AA in tanned leather, the hydrothermal stability, the mechanical properties and resistance to collagenolytic activity of tanned leather, the evaluation of eco-friendly characteristics were investigated. Scanning electron microscopic (SEM) and Atomic force microscopic (AFM) analyses indicate the surface morphology and roughness, respectively, of the tanned leather collagen matrix. Shrinkage and Differential scanning calorimetric (DSC) analyses shows that the shrinkage temperature (Ts) and denaturation temperature (Td) of tanned leather are related to the content of d-AA+Ald present in the leather matrix. It has been found that the Ts of d-AA tanned leather is more than that of Ald tanned leather and also more or less equal to chrome tanned leather. Environmental impact assessment (EIA) shows that the developed process results in significant reduction in total solids content (TSC) and improves better biodegradability of organic compound present in the effluent compared to chrome tanning.

Collagen Fibril Orientation in Ovine and Bovine Leather Affects Strength: A Small Angle X-ray Scattering (SAXS) Study

There is a large difference in strength between ovine and bovine leather. The structure and arrangement of fibrous collagen in leather and the relationship between collagen structure and leather strength has until now been poorly understood. Synchrotron based SAXS is used to characterize the fibrous collagen structure in a series of ovine and bovine leathers and to relate it to tear strength. SAXS gives quantitative information on the amount of fibrous collagen, the orientation (direction and spread) of the collagen microfibrils, and the d-spacing of the collagen. The amount of collagen varies through the thickness of the leather from the grain to the corium, with a greater concentration of crystalline collagen measured toward the corium side. The orientation index (OI) is correlated strongly with strength in ovine leather and between ovine and bovine leathers. Stronger leather has the fibrils arranged mostly parallel to the plane of the leather surface (high OI), while weaker leather has more out-of-plane fibrils (low OI). With the measurement taken parallel to the animal's backbone, weak (19.9 N/mm) ovine leather has an OI of 0.422 (0.033), stronger (39.5 N/mm) ovine leather has an OI of 0.452 (0.033), and bovine leather with a strength of (61.5 N/mm) has an OI of 0.493 (0.016). The d-spacing profile through leather thickness also varies according to leather strength, with little variation being detected in weak ovine leather (average=64.3 (0.5) nm), but with strong ovine leather and bovine leather (which is even stronger) exhibiting a dip in d-spacing (from 64.5 nm at the edges dropping to 62 nm in the center). This work provides a clear understanding of a nanostructural characteristic of ovine and bovine leather that leads to differences in strength.

Preparation of Terminal Phenolic Hydroxyl Triazine Dendrimer and its Combination Tanning Properties with the Aluminum Salts

Terminal phenolic hydroxyl triazine dendrimer (HTHP) was prepared by putting cyanuryl chloride and 1,3,5-benzenetriol into acetone and then adding K2CO3 into the mixture as deacid reagent, which is called “One Step Process”. HTHP can be used in the leather tanning process as an additive. The result shows that adding HTHP into leather tanning process can improve the combination tanning property of leather collagen. When we add 10% (based on the mass of pickled skin) of HTHP, the shrinkage temperature of crust is 63.11°C and the mechanism of tanning is same as the vegetable tannin which has abundant of plant polyphenol. When the usage of HTHP is 10% and the aluminum salts is 2.5% (consider the mass of Al2O3), the shrinkage temperature of crust can reach to 82.2°C. It can be concluded that it shows synergism when there are both HTHP and aluminum salts in the process.

Tannin Fingerprinting in Vegetable Tanned Leather by Solid State NMR Spectroscopy and Comparison with Leathers Tanned by Other Processes

Solid state 13C-NMR spectra of pure tannin powders from four different sources – mimosa, quebracho, chestnut and tara – are readily distinguishable from each other, both in pure commercial powder form, and in leather which they have been used to tan. Groups of signals indicative of the source, and type (condensed vs. hydrolyzable) of tannin used in the manufacture are well resolved in the spectra of the finished leathers. These fingerprints are compared with those arising from leathers tanned with other common tanning agents. Paramagnetic chromium (III) tanning causes widespread but selective disappearance of signals from the spectrum of leather collagen, including resonances from acidic aspartyl and glutamyl residues, likely bound to Cr (III) structures. Aluminium (III) and glutaraldehyde tanning both cause considerable leather collagen signal sharpening suggesting some increase in molecular structural ordering. The 27Al-NMR signal from the former material is consistent with an octahedral coordination by oxygen ligands. Solid state NMR thus provides easily recognisable reagent specific spectral fingerprints of the products of vegetable and some other common tanning processes. Because spectra are related to molecular properties, NMR is potentially a powerful tool in leather process enhancement and quality or provenance assurance.

Study of leather and gelatin specimens original, and processed with traditional and new reagents

The change of properties of leather and gelatin after the treatment by poly(hexamethyleneguanidine) derivatives was studied. The study of thermal transformation was performed by means of derivatograph Q-1500-D (MOM, Hungary). The dehydration process, melting of crystal areas of anhydrous collagen, the destruction of poly(peptides) chains proceed one after another in the range from 20 to 250°C. The computer program TA 1B for the non-isothermal kinetics (on the basis of the integer method) was used for data processing. The best kinetic description for the thermal dehydration in all cases was the equations of diffusion processes. We believe that this process can be considered as inner chemical diffusion: the hindrance for water molecules removal from the sample because of alternate breaking and forming of hydrogen bonds with aminoacids chains on the contact surface of pores. Both the difference in water content, and the slight difference in values of kinetic parameters (E and A) are discussed; they are attributed to the structure difference between leather collagen and gelatin and processing effect.

Studies on the microbial degradation of ancient leather bookbindings. Part 2

Studies were carried out on the role of microorganisms in the decomposition of ancient vegetable tanned leather. The samples were neutralized or sterilized to study the changes in chemical composition of extracts after their long-term humidification. The extracted (soluble compoounds and tannins) leather powder inoculated with various microorganisms was analyzed after 8 months of microbial development. It was shown that neutralization of leather causes an abundant development of microorganisms accompanied by chemical changes and that autoclaving does not cause the accelerated chemical hydrolysis of leather. The most active organisms in the decay were Chaetomium globosum, Scopulariopsis brevicaulis and Streptomyces sp. 1. Heavy deterioration of old leather collagen fibres was proved by chemical and SEM analyses.