July 2018 Abstracts

Ammonia – Reduced Deliming using Glycolic Acid and EDTA and its Effect on Tannery Effluent and Quality of Leather

by Murshid Jaman Chowdhury, Md. Tushar Uddin, Md. Abdur Razzaq, Al-Mizan, and Ariful Hai Quadery

In leather processing, deliming is traditionally carried out using ammonium salt which generates a large amount of ammonia in tannery waste water. This may result in water pollution as well as toxic effect on aquatic organisms. This research work is an attempt to develop an alternative deliming agent to minimize the pollution load of tannery waste water. The current research was performed using mixture of 90 wt. % of glycolic acid and 10 wt. % of ethylenediaminetetraaceticacid (EDTA), which evolves no ammonia and relatively inexpensive. Deliming value, buffer capacity, calcium solubility and penetration in limed pelts of the developed deliming agent were determined to assess its effectiveness. Sulphide content, Ammonia Nitrogen (NH3-N) Content, Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) values of the resulting discharge water were analyzed and examined in contrast with traditionally delimed discharge water. The developed deliming agent was applied on leather and its properties, such as tensile strength, elongation at break, tear strength, softness, chromium uptake, and morphological characteristics were compared to conventionally delimed leather as well as the standards.

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Enzymatic Bating Technology for Wet Blue: I. Characterization of Protease Activities Towards Chrome-tanned Elastin and Collagen Fibers

by Xu Zhang, Xiaozhen Wan, Jiao Xian and Biyu Peng

To characterize the reacting performances of proteases against chrome-tanned leather, the methods to quantitatively measure protease activities against chrome-tanned elastin and collagen fibers were established through detecting the produced amount of Desmosine (DES) or Hydroxyproline (Hypro) in unit time. Chrome-tanned elastin and collagen fiber substrates with different Cr content were prepared, and the influence of the Cr content on the enzymatic hydrolysis resistance of tanned substrates was investigated. The activities of several typical proteases against chrome-tanned elastin and collagen fibers were tested based on the methods, and the relationship between the activities and bating effectiveness on wet blue was also preliminarily investigated. The results showed that the two kinds of activities of proteases decreased with the increase of Cr content in the substrates. When the Cr contents in elastin or collagen fiber reached 0.5% or 2.0%, the corresponding activity approached to the lowest level, respectively. Different protease showed different activity decrease extend towards tanned protein fibers. Meanwhile, the bating effectiveness of proteases on wet blue was positively related to their activities towards the chrome-tanned protein fibers measured by the established methods, i.e. proteases with highly chrome-tanned elastin and collagen fiber activities could significantly improve the softness of leather. The new methods can be used as an available tool to correctly select proteases and optimize process parameters for wet blue bating.

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Application of Carboxyl-functionalized Epoxy Resin in the Leather Tanning Process

by Bin Lyu, Yajuan Li, Dangge Gao, Jianzhong Ma and Leihong Lv

Chrome tanning is widely used in the tanning process; however, it can cause environmental pollution. Leather tanned with epoxy resin was considered as a more environmentally friendly process, but it takes as long as five days for reaction, and results in poor performance of leather. The aim of the present study was to tan leather collagen with a carboxyl-functionalized epoxy resin, which was thought to be an eco-friendly tanning process and the reaction time was shortened to 12h. The reaction between carboxyl-functionalized epoxy resin and leather collagen can be divided into two stages, the reaction of epoxy group with leather collagen and the reaction of carboxyl group with leather collagen. The influences of tanning conditions (medium pH, epoxy resin amount and reaction time) on the properties of tanned leather were also discussed. In the first stage, the epoxy group was reacted with leather collagen in basic conditions. The results showed that the carboxyl-functionalized epoxy resin could better penetrate into the leather fibers when the pH value was 8.5, and the best effect of tanned leather collagen was found using reaction condition of pH 7.0. In the second stage, it was the reaction of carboxyl group to leather collagen in acid conditions, and the best effect was found under the condition of pH was 3.5. Meanwhile, it provided a better tanning effect when the carboxyl-functionalized epoxy resin amount was 6% and the reaction time was 12h. The chrome-less tanning process that carboxyl-functionalized epoxy resin combination with 3% chrome was studied. The results showed that the hydrothermal stability and strength properties of leather tanned by carboxyl-functionalized epoxy resin with 3% chrome were close, even superior, to those of the leather produced by conventional chrome tanning with 8% chrome.

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Quantitative Determinations of Isoelectric Point of Retanned Leather and Distribution of Retanning Agent

by Ying Song, Ya-nan Wang, Yunhang Zeng, Haopeng Wu and Bi Shi

Neutralized chrome leathers (pH 6.3) were retanned with typical anionic retanning agents acrylic resin (AC), amino resin (AR) and mimosa extract (ME) alone or together. The isoelectric points (pIs) of the retanned leathers were determined using a zeta potential analyzer for solid-state materials, and the penetration as well as the uptake of the retanning agents in the leathers was analyzed using a fluorescent tracing technique. It was found that the pIs of the surface layers of the leathers retanned with 3% of AC, AR or ME alone became below 5.4, while the pIs of their middle layers were still around 7.4. The pIs of the upper, the middle and the lower layers of the leather retanned with 3% AC, 3% AR and 3% ME together were very close and below 3.6. Additionally, greater penetrations and uptakes of the retanning agents were obtained after retanning with AC, AR and ME together compared to alone. These results indicate that retanning with more and various anionic retanning agents is very useful for a more thorough decrease in the pI of the chrome-tanned leather and favors the penetration and the uptake of the retanning agents in the leather.

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