August 2019 Abstracts

Particle Size Evolution of Chrome Tanning Agent on Tanning Effect

by Yahui Wang, Haojun Fan, Yi Chen and Jun Yan

In a traditional method of chrome tanning, the particle size (PS) of tanning agent is critical for its penetration and the performance of resultant leather. The temperature, pH value and concentration of chrome solution are the important parameters to influence the size scale of the chromium complex. In present study, the PS evolution of chrome tanning agent (CTA) with pH value and temperature changes was investigated firstly, then the influence of the evolution of PS on the tanning process and hydrothermal stability of crust leather was also investigated. The results indicated that with the temperature varied from 25°C to 30°C and 35°C, the pH of the chrome solution increased from 2.5 to 3.8, the PS of CTA increased from 982 nm to 2899 nm, 1265 nm to 3384 nm and 1289 nm to 3630 nm, respectively, showing a rapid increasing tendency. Correspondingly, due to the PS of CTA increased, the chromium absorption rate increased from 31.0% to 53.6% at 25°C, 33.8% to 55.9% at 30°C and 34.5% to 56.4% at 35°C, whilst the uniformity of the chromium distribution in crust leather was gradually reduced. At the same initial tanning temperature, the shrinkage temperature (Ts) of wet blue tend to increase first and then decrease with the increase of the CTA’s PS, and reached above 100°C when the PS was in a range from 2000 nm-2700 nm. As the PS continues to increase, the inner layer was insufficient tanned due to excessive tanning of surface, leading to a decrease in hydrothermal stability of crust leather.

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Microwave Irradiation: An Innovative Routine to Promote Goat Skin Chrome Tanning Process

by JinweiI Zhang, Wuyomg Chenand and Carmen Gaidau

The chemical reaction with microwave assistant has faster rate, higher yield and milder condition. In order to study the influence of microwave on chrome tanning process, the chrome tanning with microwave heating (MW) was carried out at different initial pH and terminal pH regraded as experimental samples and with water bath heating (WB) at corresponding condition was control in the study. The shrinkage temperature, chrome content and chrome distribution of wet blue were determined to obtain the influence of microwave on tanning effect. In addition, the pickled skins were modified by esterification and deamination and then the modified skins were tanned under microwave to know whether microwave would affect the combination sites between collagen and chromium complex or not. The results showed that microwave had positive effect on chrome tanning process, representing as higher shrinkage temperature and chrome content as well as more uniform chrome distribution for leather. Especially, the shrinkage temperature of MW leather exceeded 100°C when tanning terminal ending pH was only 3.3, indicating the tanning with microwave assistance could complete under a lower pH than the usual. Moreover, the combination sites between collagen and chromium of MW leather were the same as WB, indicating the effect of microwave could not change the combination sites. In sum, microwave could promote chrome tanning and make it finish at a milder condition, which might innovate the tanning technology and provide a new chrome tanning method in the future.

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Organic-inorganic Hybrid Coatings via Sol-gel Route for Leather Finishing

by L. de Ferri, A. Lorenzi, F. Tassi and L. Draghi

Despite its popularity in other industries, including textiles, for the preparation of inorganic and hybrid coatings, the use of sol-gel for leather finishing is a barely explored field. To exploit its unique and versatile chemistry, we have here evaluated the potential of sol-gel route for preparing protective coatings and achieve, at the same time, water- repellency on treated leather. To this aim, tetra-ethyl-ortho-silicate (TEOS) and functionalized Si-alkoxides, containing either alkyl or fluorinated groups were selected and compared.

The results of characterization indicate that, for the chosen formulations, alcohol-based sols were patently more effective than their water-based counterparts. Very high contact-angles were obtained for both alkyl- and fluorinated alkoxides, but, not surprisingly, fluorinated coatings provided a longer-lasting hydro-repellency. Sols well preserved leather grain, with no patent accumulation on pores or ridges, while only minor changes in color was observed in most formulations.

Overall, our results suggest that a careful optimization of sol-gel formulation can offer unexplored, versatile and very effective solutions in leather finishing.

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Insight into Understanding Incorporation of Glycidoxypropyltrimethoxysilane for Improving Hydrothermal Stability and Porous Structure of Silicic Acid Tanned Leather

by Zetian Zhang, Jun Liu, Junchao Wang and Zhengjun Li

Tanning with silicic acid, a kind of silicon-containing materials, is considered as a more environmentally benign process; however, the obtained leather would become stiff and brittle during storage in spite of possessing acceptable shrinkage temperature (Ts). Herein, we incorporated organosilicon material attaching silicon atoms with T linkage structure (e.g. glycidoxypropyltrimethoxysilane, GPTMS) in the leather-making process to investigate hydrothermal stability and porous structure, in particular their variation along with different storage time, through Ts determination, DSC analysis, SEM observation and SEM-EDS test. The results confirmed that the introduction of GPTMS stabilized properties of the resultant leather during accelerated ageing process, which may be ascribed to that GPTMS could prevent silicon hydroxyl groups existing in collagen fiber matrix from further condensation. Besides, the tanning mechanism of chrome-free tanning agent based on silicon materials such as silicic acid and GPTMS was investigated preliminarily by means of FT-IR and XPS analysis, indicating hydrogen bonds between silicon hydroxyl groups and amino groups in collagen molecules, and the covalent bonding formed by epoxy group of GPTMS and carboxyl groups of collagen fibers are beneficial to improvement of the properties of silicon-based materials tanned leather. These findings provide an effective and promising strategy to control condensation of silicon hydroxyl groups, and are of great significance to the development of a chrome-free tanning technology based on silicon materials.

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