June 2018 Abstracts

A Novel Approach for Enhanced Color Intensity and Uniformity in Leather Dyeing

by Sujata Mandal, J. Durga, G. Jothi, Malathy Jawahar and C. Muralidharan

Dyeing is a significant process step in leather making that is carried out to enhance the aesthetics of the tanned hides and skins. Due to the heterogeneous nature of the skin matrix, obtaining leathers with consistent color is challenging. The present study describes application of hydrotalcite-like inorganic synthetic material (HTLM) during leather dyeing to bring color uniformity among leathers by maximizing the color intensity within the skin and among the skins processed in a batch. The HTLM has been used in an interim step between two phases of dyeing that enhanced shade intensity as well as color consistency through modification of the leather surface chemically. The efficacy of the HTLM for enhanced color intensity and uniformity in leather has been investigated. Influence of the HTLM on the physicals characteristics like, perspiration, color fastness to light and dry/wet rub are also studied.

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Potentilla Erecta (L.) Raeusch as an Alternative Source of Environmentally Friendly Polyphenols for Leather Tanning

by Virgilijus Valeika, Birute Sapijanskaite, Justa Sirvaityte, ViktoriiaI Plavan and Rasa Alaburdaite

High content of polyphenols in plant extracts explains their biological activitity. These extracts also can be used in antimicrobial therapy as an alternative to chemical drugs. A large number of hydroxyl and other functional groups in the polyphenols preconditions formation of strong cross-links with proteins and other macromolecules. The leather tanning technology, known as vegetable tanning, was the prevailing process for leather manufacturers over centuries until it has gradually been displaced by tanning with a use of inorganic chromium compounds by the end of the 19th century. Unfortunately, the vegetable sources with importance for leather tanning are limited in number of plant materials. Potentilla is considered as a tannin-rich plant. It is estimated that tannin content in Potentilla Erecta (L.) Raeusch is approx. 15-22%. The results of the present study have shown that Potentilla Erecta (L.) Raeusch can be characterized as a potential tannin rich plant source for leather tanning industry. The extracts of Potentilla mainly contain condensed tannins, but also some amounts of hydrolysable tannins are present. The yield of the extractives from Potentilla rootstocks was found to be 21.3%: 11.5% tannins and 9.8% non-tannins. The tannin content in Potentilla is comparable to the ones extracted from Ouebracho and Chestnut wood, tannins that are used widely in leather industry.

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A Novel Approach for Lightfast Wet-white Leather Manufacture Based on Sulfone Syntan-aluminum Tanning Agent Combination Tannage

by Long Zhang, Xinyu Zhao, Chunhua Wang and Wei Lin

Wet-white tanning as an eco-friendly leather-making process has been attracting considerable attention. Herein, we have investigated a novel combination tannage for lightfast wet-white leather based on sulfone syntan and aluminium tanning agent. By optimizing the technology, 10% sulfone syntan and 3% aluminum tanning agent at final pH 4.0 - 4.5 can raise the shrinkage temperature (Ts) of the wet-white leather to ~81°C. The synergistic tanning mechanism of the two has been illustrated. As verified by Zeta potential measurements, the introduction of Al3+ into the sulfone syntan system led to the increase in the isoelectric point (IEP) of wet-white leather, which is favorable for the subsequent post-tanning process. Scanning electron microscope-Energy dispersive X-ray spectroscopy (SEM-EDX) results reveal that sulfone syntan and aluminum tanning agent can be evenly bound within the leather matrix and promote the formation of tightly woven networks of collagen fibers. The novel combination tanning approach not only improves light fastness and lighter shade, but also confers high physical and mechanical properties to the wet-white leather.

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Preparation of Formaldehyde-free Melamine Resin using Furfural as Condensation Agent and its Retanning Performances Investigation

by Zhou Ji-bo, Li Pei-lin, Zhou Jian-fei, Liao Xue-pina, and Shi Bi

Amino resins are one of the most important retanning agents used in the leather industry. However, the generally presence of formaldehyde greatly restricts the widespread application of amino resins. In this study, furfural, an organic compound derived from biomass material, was used to substitute for formaldehyde in the synthesis of melamine resin based on an alkaline-acid procedure. The as-synthesized formaldehyde-free melamine resin (MRf) showed excellent performances in leather processing. FTIR and 13C-NMR were used to characterize the chemical structure of MRf. The particle size as well as zeta potential were also determined. The retanning performances of MRf indicated that the overall performances of MRf are comparable to conventional formaldehyde contained melamine resin (MR) and commercial melamine resin (CMR). In particular, the thickness of the leather retanned by MRf was enhanced around 10.33%, which is significantly higher than that of controls MR (6.16%) and CMR (5.94%). Color measurements showed that MRf imparted leather with higher dark intensity. This present work demonstrated that furfural could be a potential candidate to replace formaldehyde in the production of formaldehyde-free melamine resin.

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