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Effect of Finishing Auxiliaries on Permeability of Leathers 
by M. Sthish, Z. Azhar, N. Fathima and J. Raghava Rao
Volume: 110      Number: 11     Page: 372-378     Year: 2015
The unique fibrous arrangement and architectural marvel of collagen in skin matrix are the basis for various physical properties of leather. Air permeability is one of the unique features of skin, which makes the leather matrix superior to synthetic materials. In leather manufacturing finishing process determines the air permeability of the final leather. Therefore, knowledge of the impact of different finishing auxiliaries on the permeability of leather may helpful in selecting an appropriate finishing system for a particular type of leather. In this work, an attempt has been made to analyze the effect of various auxiliaries used in protein, acrylic and polyurethane (PU) based finish coatings on the air permeability of leather. Capillary flow porometer was used to monitor the air permeability (Flow rate cc/sec) at different pressures (psi). The results show that the effect of wax/filler/slip and dye solution on air permeability reduction is low when compared to pigment and binder. In protein and PU finishes, the binder alone and season (combination of all finishing auxiliaries like pigment, binder, and other auxiliaries) has a strong influence on permeability reduction whereas in case of an acrylic based finish, the pigment and binder plays an important role in permeability reduction. Leather coated solely with protein binder shows minimal permeability reduction than compared to leather coated with acrylic or polyurethane binders, whereas in season, acrylic based finishing has a lower permeability profile than that of protein and PU. In that case the permeability profile of protein and PU season coated leathers is almost similar.
 
 
Chrome-Reduced Combination Tanning for Cleaner Dyed Sheep Fur Processing 
by Wei Ding, Yihan Cheng, Ya-nan Wang and Bi Shi
Volume: 110      Number: 11     Page: 363-371     Year: 2015
Chrome tanning is essential for conventional processing of dyed sheep fur as it can provide fur with high hydrothermal stability suitable for dyeing of wool at a temperature around 70°C. However, a long float length and a big offer of chrome tanning agent (16 g/L) are required for the tanning process, which lead to poor uptake of chrome and excessive discharge of chrome in wastewater. In this study, reduction of chrome offer in dyed sheep fur production was investigated to develop a cleaner tanning technology. It was found that the even distribution of chrome and satisfactory dispersion of fur collagen matrix were achieved even though chrome tanning agent offer was reduced to 2 g/L and 4 g/L. But the shrinkage temperature of the furs was only 79°C and 85°C, respectively, which resulted in a sharp area shrink of fur in following high temperature dyeing. In the combination tannage using 10 g/L amphoteric organic tanning agent (TWT) and 2 g/L or 4 g/L chrome tanning agent, the shrinkage temperature of fur was higher than 90°C accompanied by a higher utilization of chrome. These combination tanned furs were capable of enduring dyeing process at 68°C for 8 h, and presented a high uptake of post tanning chemicals because they had an isoelectric point close to that of chrome tanned fur. More importantly, the physical properties of the combination tanned dyed furs were comparable to the dyed fur made by conventional chrome tanning using 16 g/L chrome tanning agent.
 
 
Fatliquor Effects on Collagen Fibril Orientation and D-spacing in Leather during Tensile Strain 
by K. Sizeland, G. Holmes, R. Edmonds, N. Kirby, A. Hawley, S. Mudie and R. Haverkamp
Volume: 110      Number: 11     Page: 355-362     Year: 2015
Strength is a very important property of leather and is known to depend on the arrangement of the collagen fibrils within the material. The addition of fatliquor (penetrating oils) is an essential part of the manufacture of leather and enhances the strength and feel of leather. However, the mechanism by which fatliquor leads to increased strength is not understood. Here we use synchrotron based small angle X-ray scattering (SAXS) to monitor the collagen fibril rearrangement and internal strain of leather during tension. Differences in internal structural changes under strain with varying levels of fatliquor are investigated. It is found that when a strain of up to 40-70% was applied to leather, the orientation index (OI) of the collagen fibrils changed up to 21.8% and the d-spacing changed by up to 1.8% with no consistent differences at different levels of fatliquor. The extensibility of leather increases by 11.3% with as little as 2% fatliquor addition and the elastic modulus decreases with fatliquor addition but not in proportion to the amount of fatliquor. This change in extensibility is not reflected in differences in OI or d-spacing changes during strain. As reported previously, the fatliquor modifies the d-spacing of collagen. While fatliquor is traditionally considered to lubricate the fibers in leather, here the evidence suggests that this does not occur at the level of collagen fibrils. This provides an insight in the action of fatliquor in leather manufacture.
 
 
Chemistry of Syntans and Their Influence on Leather Quality 
by J. Ammenn, C. Huebsche, E. Schilling and B. Dannheim
Volume: 110      Number: 11     Page: 349-354     Year: 2015
The first syntan, Neradol D, was a condensate of phenolsulfonic acid and formaldehyde. While this chemistry allowed more efficient use of vegetable tannins, it was not advantageous to be applied on leather alone and has to be considered an auxiliary. Incorporating urea into the phenolsulfonic acid - formaldehyde condensation established a second generation of syntans with significantly improved lightfastness. Replacement syntans were developed to substitute vegetable tannins, giving rise to leathers of good softness and fullness. The formaldehyde condensation of dihydroxy diphenyl sulfone (sulfone) can be considered a further development of the replacement syntans with lower residual monomers. In order to compare these four generations of syntans, poly-condensates of a comparable molecular size had to be synthesized. These tested in hydrothermic denaturation of skin powder and applied in sole tanning and re tanning. The resulting leathers were compared in various aspects of performance including shrinkage temperature, softness, fullness, light fastness, and rest monomers.
 
 
Characteristics of Aldehyde Reactive Dyes for Leather Dyeing and Retanning Process 
by Xiao Chen, Jun Liu, Jie Ding and Keyi Ding
Volume: 110      Number: 10     Page: 338-345     Year: 2015
Dyeing and re-tanning properties of nine aldehyde reactive dyes synthesized in our previous work were studied using aluminum pretanned wet-white sheep leather as a substrate. Their washing fastness and four dyeing property indexes, i.e., substantivity (S), exhaustion (E), reactivity (R) and fixation (F) were measured. The relationship between the colormatching effect and the relative difference values of the four dyeing property indexes of the combined dyes were investigated, and the simultaneous tanning-dyeing property of reactive dyes with a glutaraldehyde backbone were tested. The results were as follows: (1) The synthesized aldehyde reactive dyes could dye wet-white leather under mild conditions (T = 35-45°C, pH =4.0-6.5) within 1.5 h, and the dyed leather possessed a satisfactory washing-fastness. (2) Reactive dyes with a glutaraldehyde backbone had better dyeing performance than mono-aldehyde reactive dyes. (3) The less the relative difference value of the dyeing property indexes of the combined dyes, the better was the color matching effect. (4) The tested reactive dyes with a glutaraldehyde backbone increased the Ts of wet-white leather to 11-17°C in addition to dyeing it to the corresponding color.
 
 
Chrome-melamine Syntan: A Step Towards Developing Fuller Leather 
by P. Balasubramanian, M. Azhar Zakir, R. Aravindhan, K. Sreeram, J. Raghava Rao and B. Unni Nair
Volume: 110      Number: 10     Page: 332-337     Year: 2015
The leather industry operates in stages. Many of the finished leather manufacturers source their wet blue leathers from various regions or tanners. In order to have uniformity of metal oxide content, almost all the leathers are rechromed. For this, the industry employs masked chromium(III) salts provided by the leather auxiliary industry in the form of complexes co-linked to phenol/ naphthalene condensates. Also, tanners who use hides/skins from ill fed animals treat their tanned substrate with melamine condensates, so as to get a preferential filling of the belly region. Metal ion complexes co-linked to melamine condensates are rather scarce. For the first time, this paper reports the application studies using a chromium melamine condensate devoid of formaldehyde as cross linker. The said product has been employed in rechroming and evaluated for multiple properties such as providing an equalization of chrome content and filling of belly region. Our studies clearly indicate a marked advantage of employing such a product in the place of commercial chrome syntans alongside melamine condensates, more so for ill fed cowhides.
 
 
Synthesis of Biological Based Anionic Fatliquor and Its Application on Leather 
by M. Pervez, F. Ahmed, S. Mahboob, R. Dewani, H. Nawaz, M. Zeeshan and T. Ayaz
Volume: 110      Number: 10     Page: 326-331     Year: 2015
In this study, three types of anionic fat liquors are prepared from various vegetable oils by sulfation process. One fatliquor is made from pure canola oil, the second one from castor oil and the third one is made from a mixture of different oils, which is termed here as ‘Blended oil’. Canola oil is used for fat-liquoring purpose and has been compared with other natural oil based fat-liquors and a commercially available sulfated fat-liquor. Different chemical and physical studies were carried out to find out the fat-liquor producing the best results. Chemical studies of fat-liquor such as pH, fat content, solid content, moisture and organically combined sulfuric anhydride were determined before its application on leather. The physical studies such as tear strength, tensile strength, elongation, burst load, softness and distention were carried out on crust leather. The fat content test was carried out to check the uptake of fat-liquors by leather samples. On the basis of chemical and physical analysis the blended oil based fat liquor was found to be better than the castor & canola oil based fatliquors and commercially available sulfated fat-liquor.
 
 
Investigating the Cell Rotary Conditioning Mechanism Using Dynamic Mechanical Thermal Analysis 
by K. Flowers, A. Peruzzi, W. Wise and A. Covington
Volume: 110      Number: 10     Page: 317-325     Year: 2015
Jeyapalina et al. established that dynamic mechanical thermal analysis (DMTA) can be used to gauge the progression of leather drying. This work has now been advanced in order to understand the mechanism surrounding sorption/desorption of moisture during cell conditioning, e.g., cell rotary conditioning (CRC). This paper will demonstrate how the use of DMTA could be used to monitor changes in leather stiffness. A gravimetric moisture analysis was performed on identical leather samples to gauge the progression of desorption. The change in storage modulus (E’) was coupled to the moisture content (leather moisture and atmospheric relative humidity) to obtain a better understanding of the physical properties (specifically stiffness) of leather during a drying process. The research presented illustrates how DMTA can indicate leather fiber response to changes in atmospheric humidity and facilitate real-time adaptation of drying conditions during leather dehydration. The use of a cell conditioning system allows a tanner to control the flexibility of the material through the tension applied and the drying conditions. DMTA shows that the favorable conditions inside a CRC unit result in detectable changes to the leather fiber, similar to findings by Abrahamson and Williams-Wynn. Using this technique a researcher can dry chromium-containing and chromium-free leathers in a manner that is highly customizable to produce desired physical properties. Difficulties experienced in chromium-free leathers can also be investigated in detail using this technique.
 
 
Low Carbon Products to Design Innovative Leather Processes. Part III: Optimization of an Eco-friendly Formulation Using Tara 
by A. Bacardit, J. Diaz, C. Casas and L. Olle
Volume: 110      Number: 9     Page: 302-309     Year: 2015
The aim of this work was to design a new pretanning formulation by using the fruit of the Tara tree (Cæsalpinia Spinosa) as the sole source of vegetable tannin. The innovative aspect of this work embodies a new-tailored tara product which gave its tannin the enhanced ability to readily penetrate the leather cross section, and thus made it unnecessary for the tanner to add aldehydes, syntans, other common vegetable tannins and mineral salts. Specifically, physical modifications had been developed in part II of this broad study to obtain a modified tara with a higher percentage of tannins and with a better ability to penetrate/fix in leather by sieving and milling (see Low carbon products to design innovative leather processes. Part I: determination of the optimal chemical modification of tara1 and Low carbon products to design innovative leather processes. Part II: determination of the optimal physical modification of tara).2 We developed in this work an innovative, eco-friendly and optimal wet white formulation which has a maximum offer to leather of 9% modified tara and a maximum 2% naphthalene sulphonic syntan dispersing agent.
 
 
Value Added Leather Auxiliaries from Paper and Pulp Industry Waste 
by M. Vedhanayagam, T. Teddy, K. Sreeram, J. Raghava Rao and B. Unni Nair
Volume: 110      Number: 9     Page: 295-301     Year: 2015
The present work involves the preparation of a retanning agent from the organics present in the black liquor generated by paper and pulp industry. Black liquor organics was extracted by using solvent extraction method and subsequently separated as acidic, non-acidic and organic compounds that were not degraded. Acidic and non acidic organics were sulfonated and further condensed with formaldehyde to obtain a product ideal for application. Sulfonation – condensation reactions were modulated to achieve particle size on par with that of commercial syntans. Condensed products from both acidic and non-acidic components were used in lieu of synthetic tanning agents in retanning. The final leathers exhibit offwhite color with good mechanical strength as compared to leathers from commercial phenolic syntan. This work reveals that the black liquor, which is a by-product of paper and pulp industry could through an innovative process, be turned into a retanning agent for leather processing. The product has the advantage of being able to replace phenol – a product with high market fluctuation.