Two-stage Temperature Change Chrome Tanning: A More Sustainable Tanning Process
by Hui Zeng, Weixing Xu, Jianfei Zhou and Bi Shi

Under the guidance of molecular simulation of Cr(III) species in water solution, a novel chrome tanning process, the two-stage temperature change chrome tanning, was developed. In stage I, the pickled cattle hide was first tanned by a small amount of chrome tanning agent under room temperature to obtain basic hydrothermal stability. Then, in stage II, the pre-tanned wet-blue was tanned again under a high temperature (more than 60°C) to enhance the reactivity of Cr(III) with collagen fibres. The shrinkage temperature of crusts, the absorptivity of chrome tanning agent and fatliquoring agent, the mechanical property and surface morphology of crusts were characterized to evaluate the tanning effect. The results showed that when the dosage of chrome tanning agent in two stages was 2 wt% (tanned under room temperature) and 1 wt% (tanned under 60°C), respectively, the best performances of crust were achieved. In these conditions, the shrinkage temperature of crust was 104.6°C. The comprehensive absorptivity of chrome tanning agent reached up to 96.3%. The absorptivity of fatliquoring agent in wet-blue was 90.2%. The mechanical property and grain fineness of the crust were comparable to those of conventional chrome tanned crust with 6 wt% chrome tanning agent. As a result, an efficient and more sustainable chrome tanning process with less offer of chrome tanning agent was achieved.  JALCA May 2019

Preparation of Oxidized Poly (2-hydroxyethyl acrylate) with Multiple Aldehyde Groups by TEMPO-mediated Oxidation for Gelatin Crosslinking
by Baohua Liu, Zhuo Wei, Ya-nan Wang and Bi Shi

Oxidized poly (2-hydroxyethyl acrylate) (OPHEA) with multiple aldehyde groups was prepared as a gelatin crosslinker by polymerization of 2-hydroxyethyl acrylate and then 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) -mediated oxidation of poly (2-hydroxyethyl acrylate) (PHEA). The oxidation conditions were optimized so as to form aldehyde groups in OPHEA as many as possible. The maximum aldehyde content reached 3.66 mmol/g (accounts for 42.5% of the total hydroxyl groups in PHEA) when the oxidation was conducted at 5°C and pH 9.4 for 90 min, by using 30% NaClO as oxidant and 0.1% TEMPO as catalyst. FT-IR and 13C-NMR analyses demonstrated the formation of aldehyde and carboxyl groups in OPHEA. The crosslinking reactivity of OPHEA was confirmed by the enhancement of thermal stability of modified gelatin by DSC and TG analyses. Furthermore, the viscosity of the modified gelatin was significantly increased when the crosslinking reaction was performed at 40°C and pH 8.0. These results could provide support for developing novel aldehyde tanning agents without free formaldehyde. JALCA May 2019

Preparation of Antibacterial Fatliquoring Agents Containing Zinc Oxide Nanoparticles for Leather Industry
by Ali Yorgancioglu, Eser Eke Bayramoglu and Manfred Renner

In this study, zinc oxide nano-particles known to have antibacterial properties were emulsified with different chain length paraffins to be used as fatliquoring agents. The research was carried out on chrome tanned upholstery leathers. Different proportions of nano zinc oxide were studied in the paraffin emulsions. The prepared emulsions were investigated underneath a Keyence VHX-1000 digital microscope. The average particle size of the emulsions was measured. After the emulsification process, the leathers were finished in accordance with the industrial upholstery recipe. The emulsions were applied to leather in the fatliquoring process. Antibacterial activities of the finished leather were evaluated according to ASTM Standard E 2149-01, and the results showed significant bacterial reduction on the treated leathers. The impacts of the fatliquoring agents utilized in the research on light fastness were also inspected by using an ATLAS-XENOTEST ALPHA+ test instrument. Light fastness values of treated leathers indicated that nano zinc oxide particles provided the UV absorbing property on the collagen fibres. JALCA May 2019

Exploration of the Diffusion, Binding and Crosslinking of Chromium Complex within Hides During Chrome Tanning
by Chunxiao Zhang, Jieming Hu, Desheng Yu, Cong Xia, Sadaqat Ali Chayyha and Biyu Peng

Understanding the persuasive mechanisms of the accessibility and interactions of chromium complex with collagen is an important fundamental issue for maximizing the utilization of chromium during the transformation of collagen to leather by chrome tanning technology. This study details these mechanisms through process monitoring of the effects of technical conditions of chromium diffusion and its binding with the collagen matrix. The results indicated that there was no discernible impact of carboxylic masking agents on both diffusion and binding behavior of chromium complexes at low pH before basification, but it portentously declined the total chromium absorption at the end of chrome tanning. The results made known that in the course of chrome tanning, the higher pH conditions encouraged the diffusion and binding behavior of chromium complexes with collagen matrix not only before but after the basification as well. Chrome tanning at high pH did not cause excessive surface tanning effects of the leather, but the WAXD study indicated that there was much more crosslinking (both intra and inter triple helix) of collagen fibres in the inner layers of leather matrix, which had a robust impact on the fullness, tightness and stiffness of the finished leather. These findings could provide more theoretical foundations for the development of high exhaustion chrome tanning technology as a method for reduced chromium emission and improved the quality of leather during leather manufacture. JALCA May 2019