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Towards Sustainable Leather Production: Vegetable Tanning in Non-aqueous Medium 
by N. Bhargavi, G. Jayakumar, K. Sreeram, J. Raghava Rao and B. Unni Nair
Volume: 110      Number: 4     Page: 97-102     Year: 2015
The process of stabilizing the skin collagen against denaturation under heat, enzymes, stress etc. – popularly described as tanning is carried out either using metal ions (predominantly Cr(III)) or vegetable tannins derived from plant sources rich in polyphenols. Conventional leather processing is carried out in aqueous medium and hence the tannins have been extracted into water, sulfited to increase water solubility and then sold as spray dried extracts. Classical drawbacks include the low resistance of the extracts to bacteria and fungi, copious quantities of water required for extraction and tanning etc. In an attempt to make the leather processing sustainable, taking cue from other economically viable methods for tannin extraction, this paper looks at paradigm shift from water extraction of tannins to solvent based extraction, followed by leather processing in solvent. The results presented with ethanol as the green solvent highlights the significance of the developed method, in not only enhancing tannin to non-tannin ratio (T/NT), but also improving thermal stability of the tanned collagen at microscopic rat tail tendon (RTT) and macroscopic leather level.
Inverse Chrome Tanning Technology Based on Wet White Tanned by Al-Zr Complex Tanning Agent 
by Siwei Cai, Yunhang Zeng, Wenhua Zhang, Ya-nan Wang and Bi Shi
Volume: 110      Number: 4     Page: 114-120     Year: 2015
In conventional leather production, the chrome in wet blue will be inevitably released into all the floats in post-tanning processes, which brings about a big amount of chromecontaining wastewaters, which can be difficult to treat. As a solution to this problem, an inverse chrome tanning technology based on wet white tanned by Al-Zr tanning agent (AZ) was investigated in present work. The AZ was the co-complexes of Al3+ and Zr4+ (9:1, mole ratio) with polycarboxylic acids synthesized in our laboratory. The wet white tanned by AZ had a shrinkage temperature (Ts) of 95oC under optimal tanning conditions, and therefore, it met the needs of splitting and shaving operations without generation of chrome wastes. More importantly, the wet white was suitable to be followed by retanning, dyeing and fatliquoring processes because of its satisfactory thermal stability and analogous electric charge characteristic to chrome leather. After fatliquoring and fixing by acid, chrome tanning was undertaken as final step. The leather with Ts around 110oC and comparable physical and aesthetic properties to conventional chrome tanned leather was obtained when 0.5-1% Cr2O3 was used in this inverse chrome tanning technology. The evident advantage of this technology is that no chrome was discharged in whole leather making processes except final chrome tanning and washing processes, and as a result, the volume of chrome-containing wastewater was largely reduced and easier to collect for recovery.
Development of an Alternative Low Salt Bovine Hide Preservation using PEG and Crude Glycerol, Part I: Evaluaation of PEG Molecular Weight Fractions 
by M. Aldema-Ramos, Z. Muir, J. Trusello, N. Truong and J. Uknalis
Volume: 110      Number: 4     Page: 109-113     Year: 2015
Brine curing using sodium chloride is widely used for the short-term preservation of cattle hides. Due to economics and efficiency, it has become the traditional method of hide preservation used by meat packers, hide processors and tanners worldwide. But brine curing is known to cause serious effluent pollution problems in the environment. The main objective of the current study was to develop an alternative brining process that requires less salt to effectively preserve bovine hides by incorporating dehydrating agents. In low salt preservation, the anticipated hardening effect due to over dehydration caused by polyethylene glycol (PEG) polymers was compensated by adding crude glycerol and sodium carbonate. Low molecular weight PEGs were more effective than high molecular weight polymers. Preservation was found to be effective because no sign of putrefaction was observed in alternatively cured hides, and the properties of these hides were comparable to those of traditionally preserved hides. When PEG was incorporated, the salt concentration required for hide preservation could be reduced.
Microbial Transglutaminases as Pre-tanning Agents in the Leather Industry 
by Baozhen Cheng and Jing Chen
Volume: 110      Number: 4     Page: 103-108     Year: 2015
Microbial transglutaminases(MTG) was used to pre-tan hide to investigate its effect on the hydrothermal stability of hide and the improvement for exhaustion of chrome tanning agent. This study tested the shrinkage temperatures of samples treated with MTG only and tanned MTG followed by the chrome tanning agent separately. The Cr2O3 content in effluents was surveyed after chrome tanning. It was shown that the shrinkage temperature of hide sample treated with 0.6% MTG at pH 6.0 for 2h was above 80oC, much higher than 54.8oC, which is the Ts of control. While the Ts of leather sample, which was pre-treated with 0.6% of MTG first, tanned with only 4% chrome tanning agent were higher than 100oC, but initial pH is 2.0. Moreover, the exhaustion of chrome tanning agent in leather was improved significantly when the dosage of chrome salt was less than 4%.
Characterization of Mechanical Properties of Leather with Airborne Ultrasonics 
by C.-K. Liu, N. Latona, M. Taylor, C. Eble and M. Aldema-Ramos
Volume: 110      Number: 3     Page: 88-93     Year: 2015
A nondestructive method to accurately evaluate the quality of hides and leather is urgently needed by leather and hide industries. Effects have been made to develop airborne ultrasonic (AU) testing method using non-contact transducers to evaluate the quality of hides and leather. We previously reported the research results demonstrating the AU technology for revealing defects in hides and leather that were difficult to be found during visual inspection. Recently new research was carried out to develop AU methods to nondestructively characterize the mechanical properties of leather. Observations showed a strong correlation between the mechanical properties of leather and the corresponding AU parameters based on the distribution of the transmission time (time of flight) through leather. We also used this nondestructive method to characterize the grain break of leather. Results showed the difference in grain break could be determined from the AU parameters collected from moving the AU sensors over a leather sample. Observations showed the poorer the grain break, the higher the time of flight distribution. In short, this study demonstrated that the tensile strength, stiffness, toughness and grain break could be nondestructively determined by AU.
Studies on Tara-phosphonium Combination Tannage: Approach Towards a Metal Free Eco-benign Tanning System 
by R. Aravindhan, B. Madhan and J. Raghava Rao
Volume: 110      Number: 3     Page: 80-87     Year: 2015
One of the important criteria determining the sustainability of an industrial activity is the ecological acceptability of the processing methods. Tanners throughout the world are looking for alternative eco friendly tanning systems. In the present work, metal free tanning system using a combination of Tetrakis Hydroxymethyl Phosphonium Sulphate (THPS) and Tara has been developed. This combination tanning is expected to be an effective eco-friendly mineral free tanning. The shrinkage temperature of the leathers obtained is 88oC. The tanning system is versatile in terms of processing both upper and garment leathers. The physical strength characteristics and organoleptic properties of the leathers obtained are comparable to that of chrome tanned leather. Environmental impact assessment shows that there is reduction in total solids when compared to control chrome tanning. Tara as a combination tanning agent not only improves the leather properties but also can act as a scavenger of free formaldehyde present in THPS tanned leather.
Kinetics of Inhibition of Type I Collagenase by Dialdehyde Cellulose in Stabilization of Type I Collagen 
by G. Jayakumar, N. Usharani, A. Yasothai, S. Kanth and J. Raghava Rao
Volume: 110      Number: 3     Page: 72-79     Year: 2015
Collagen is one of the widely studied biomaterial for various industrial applications. However, search of eco-friendly and biocompatible stabilizing agent is a thrust research domain. In this research work, application of dialdehyde cellulose (DAC) was studied to understand the effect on the enzymatic and conformational stability in collagen. The secondary structure of collagen is not significantly altered on interaction with DAC. But, it was found that DAC lead to changes in the amplitude of the circular dichroic (CD) spectrum but did not alter the triple helical conformation of collagen. DAC treated collagen exhibited 93% resistance to collagenolytic hydrolysis. Conversely, DAC treated collagenase exhibited 89% inhibition against collagen degradation and the inhibition was found to be concentration dependent. The kinetics of inhibition of collagenase by DAC was derived from the extent of hydrolysis of (2-furanacryloyl-L-leucyl-glycyl-L-prolyl-L alanine), FALGPA. DAC exhibited non-competitive mode of inhibition against collagenase. CD data on DAC-modified collagenase substantiate the hypothesis that the inhibition of collagenase by DAC arises from secondary and quaternary structural changes in the enzyme. Gaining new insights in understanding the mechanism of stabilization of collagen by DAC through kinetics of inhibition of collagenase was presented.
Collagen D-spacing and the Effect of Fat Liquor Addition 
by K, Sizeland, H. Wells, G. Norris, R. Edmonds, N. Kirby, A. Hawley, S. Mudie and R. Haverkamp
Volume: 110      Number: 3     Page: 66-71     Year: 2015
The physical properties of leather are partly a result of the structure of the leather’s network of type I collagen fibrils. To achieve high strength and a soft, supple feel, penetrating oils(usually polyols) are added to leather during manufacture, and this process is known as fat liquoring. The modification of the collagen structure by fat liquoring (with a lanolin-based fat liquor) is investigated using synchrotron-based small angle X-ray scattering. The axial periodicity, or D-spacing, of the collagen changes as a result of fat liquoring. With no fat liquor, the D-spacing is 60.2 nm; spacing increases by 6% to 63.6 nm at 10% fat liquor. Pure lanolin results in a similar increase in D-spacing. We discuss mechanisms for fibril elongation brought about by fat liquoring. The observations of structural changes taking place within collagen fibrils as a result of fat liquoring provides new insight into the nature of fat liquoring and informs future processing developments.
Histological Analysis of the Skin Dermal Components in Bovine Hides Stored under Different Conditions 
by S. Montelli, L. Corain, B. Cozzi and A. Peruffo
Volume: 110      Number: 2     Page: 54-61     Year: 2015
The leather industries are interested in avoiding post-mortem alterations of the skin components, since degeneration of the dermal structures composing raw hides decreases the quality of leather. The goal of the present study is to realize a histological study of skin samples to assess the tissue alterations at different periods and under methods of conservation (salting and refrigeration) after the skinning of the animals at the slaughterhouse. The papillary region and the reticular dermis were both analyzed. The dermal components considered were the number of cell nuclei, the structure of the collagen and elastic fibers, and finally the presence of acidic polysaccharides. Results showed a progressive reduction of cellular nuclei and acid polysaccharides of the dermal layer during the passage of time in all the conditions considered. A moderate decay of collagen bundles was noted in salted hides whereas the elastic fiber networks maintained their organization over the time. No sign of accumulation of non-functional elements or other morphological alterations were observed in the dermis. These findings can be useful for the leather industry for choosing the desired curing and timing conditions to employ during refrigeration or salt-based treatment of the skins.
Waterborne Dimethylolpropionic Acid-diisocyanate Adducts with Alkali-deblockable Isocyanate Groups as Pretanning Agent for Chrome Tanning 
by Jie Liu, Zhou Xu, Yi Chen and Haojun Fan
Volume: 110      Number: 2     Page: 43-53     Year: 2015
Diisocyanates qualify as tanning agent by virtue of their strong tendency to crosslink collagen molecules by reacting with amino groups. However, due to their sensitivity to water, these compounds cannot be used directly in aqueous environment, which is the basis for leather processing. To address this problem, waterborne dimethylolpropionic acid-diisocyanate adducts (WDDAs) with temporarily-blocked isocyanate terminals were prepared in the present paper by using NaHSO3 as blocking agent, and further evaluated as a pretanning agent for chrome tanning. Fourier transform infrared (FTIR) spectra revealed that the isocyanate terminals in WDDAs were successfully blocked by NaHSO3. The blocked isocyanates were stable under ambient temperature, but prone to deblocking under alkaline condition. The regenerated isocyanates were found still capable of crosslinking collagen molecules to impart hydrothermal stability. In leather tanning, a high shrinkage temperature (Ts>110 oC) was achieved by successively treating goat skin with 5 wt% WDDAs and 4 wt% chrome powder. Stereomicroscope and SEM observation further indicated that the WDDA-chrome tanned leather exhibited tight grain surface and well opened up fiber structure in comparison with semi-chrome tanned leather. Due to the presence of carboxyl group in dimethylolpropionic acid, it was also found that WDDAs enhanced the absorption of chromium in the resultant leathers (% chrome uptake> 90%), resulting in significantly less Cr residual in the tanning wastewater. In addition, it is important to note that the usage of salt in pickling process was avoided owing to previous crosslinking of amino groups, which is very helpful for overcoming the problem of total dissolved solid (TDS) related to neutral salts. The tanning effect of WDDAs and their auxiliary function for chrome tanning allow them to be applicable as a pretanning agent, which efficiently alleviates the environmental impact of traditional chrome tanning for sustainability.