May 2018 Abstracts

Study of Several Variables in the Fixation Stage of a Vegetable Tannage after Penetration under Ultrasound

by Felip Combalia, Josep M. Morera and Esther Bartolí

This study concerns the implementation and improvement of a new system that applies ultrasound technology in vegetable tanning, which is an eco-friendly tanning process. The system is versatile and requires no major modifications or expenses for tanneries. In particular, the study investigates the influence of several variables in the fixation stage of a vegetable tannage after penetration under ultrasound. The results show significant differences in the tanning degree of the leathers tested in relation to the pH of the fixation float and the amount of time that the hides remain in it. It has been demonstrated that this tanning system allows to obtain leathers with a high degree of tannin fixation. The leathers we obtained showed no scratches, which are the main cause for their devaluation when applying the traditional tanning system and were suitable for commercialization as high-end leather goods. Ultrasound technology can increase the use of vegetable tannage versus other less eco-friendly types of tannage.

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Phosphorus-nitrogen Flame Retardant Waterborne Polyurethane/Graphene Nanocomposite for Leather Retanning

by Peikun Zhang, Pingfan Xu, Haojun Fan, Zhenyu Zhang and Yi Chen

We demonstrate a facile and green approach to prepare phosphorus-nitrogen containing waterborne polyurethane/graphene nanocomposite (PN/G-WPU) as flame-retardant retanning agent for leather. The PN/G-WPU was synthesized by covalently embedding phosphoramidate-based diol into polyurethane chain, followed by emulsification with graphene oxide (GO) aqueous solution and in-situ reduced with hydrazine hydrate. The structure and emulsion stability of prepared PN/G-WPU were characterized, and the physical mechanical properties as well as the flammability of resulting leathers were investigated. The results indicate the good dispersion and strong interfacial interaction of graphene with polyurethane matrix, which facilitates the PN/G-WPU penetrating into leather fibers. The PN/G-WPU retanning agent can effectively improve the comprehensive performance of resultant leather such as hydrothermal stability, physical-mechanical properties, flame retardancy and smoke suppression performance. Accordingly, our method might provide an alternative strategy for manufacturing high-performance leather.

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Particle Size Evolution of Melamain-formaldehyde Tanning Agent on Tanning Effect

by Mengmeng Chen, Yahui Wang, Haojun Fan, Yi Chen, Jun Yan and Yu Liu

Melamine-formaldehyde [MF] resin is a tanning agent. Its average particle size [PS] is important for penetrating the skin and thus endowing performance of its resultant leather. The synthesis parameters for MF resin such as pH, molar ratio of formaldehyde to melamine, temperature and reaction time affect its PS. We investigated in detail the growth of MF’s PS and its consequent effects on hydrothermal stability, mechanical properties and the apparent properties of leather. The data showed that a broad range of average PS was formed at the different synthesis stages of MF resin. For example, the first reaction stage of methylolation gave an average particle diameter of 250 nm with a narrow size distribution under the conditions of 45°C, 3:1 molar ratio, a pH of 8.5, and a reaction time of 3 hrs. In this case the resultant leather was poor as it had a low shrinkage temperature, lacked fullness and showed a low-valued elongation at break. During the second polycondensation stage, the PS of MF resin increased with increasing reaction temperature and the molar ratio of formaldehyde to melamine. Furthermore, PS increased more rapidly by lowering the pH of the polycondensation and extending its reaction time. Thus, the new average diameter of MF resin particles reached above 3000 nm when the polycondensation reaction was done inside the skin for 2 hours at a pH of 4.5. Consequently, the resultant leather was white and full. It had a high hydrothermal stability and mechanical strength as evidenced by its fully satisfactory elongation at break. Clearly, the cross-links were formed by multiple site interactions between MF resin with large PS and collagen fibers, which enhanced the tanning effect.

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Do Leather Anisotropic Properties Have an Effect on Shrinkage Temperature?

by Ewa Marcinkowska and Gabriela Zielinska

Herein are the results of studies of mechanical properties and shrinkage temperature of cowhide leather tanned with modified glutaraldehyde and chrome. The tests were carried out on samples cut from both kinds of leather parallel and perpendicular to the backbone. The aim of these studies was determining whether the sample orientation to the backbone, thus leather anisotropic properties defined by its tensile strength and ultimate extension, has an effect on shrinkage temperature and kinetics of this process.

Mechanical properties were tested according to PN-EN ISO 3376:2012 Leather – Physical and mechanical tests – Determination of tensile strength and percentage extension. The conditions for shrinkage temperature measurements were set according to guidelines specified in PN-EN ISO 3380:2015-11 Leather – Physical and mechanical tests – Determination of shrinkage temperature up to 100°C. The experiment was carried out by using an instrument of our own design enabling automatic recording of leather specimen length changes during measurement.

The results of mechanical tests allowed the determination of the degree of differentiation of obtained tensile strength and ultimate extension values depending on test sample orientation to the backbone. For leather tanned with modified glutaraldehyde the coefficient of variation with respect to tensile strength in both directions was 0.31, while for chrome tanned leather was 0.44. The coefficient of variation for ultimate extension calculated for both directions was 0.55 and 0.42 for glutaraldehyde and chrome tanned leathers, respectively.

The slope of obtained regression lines was compared to find any statistically significant differences in leather shrinkage rate depending on orientation to the backbone. The results of analyses performed for two differently tanned leathers show no statistically significant differences in shrinkage rate depending on cut orientation. Thus, anisotropy of mechanical properties of leather samples under investigation does not affect both shrinkage temperature and the rate of this process.

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