A new system to measure leather shrinkage temperature

Content: A characteristic of leather is that if it is gradually heated in aqueous solution it reaches a temperature where sudden and irreversible shrinkage occurs. This phenomenon is related to the denaturalization of the collagen protein that conforms the hide and is known as leather shrinkage. Specifically, the internal bonds break thus causing a shortening of the skin that can be up to a 35% from its original length. Accordingly, one of the most used methods to check the quality of the leather tanning process is the determination of the contraction temperature according to the ISO 3380:2015 standard. This method measures the leather shrinkage when constantly increasing the sample temperature. The shrinkage temperature corresponds to the temperature when the sample suddenly contracts. The value of this temperature indicates the degree of collagen stability and therefore, when higher, the leather will have better quality and resistance. The process of leather shrinkage can be divided in different stages. Several authors discriminate temperature A1 (when the first fibre starts to shrinkage), temperature C (when there is a massive shrinkage) and finally temperature A2 (when the last fibres are contracted individually). The method that describes the ISO 3380:2015 standard uses a device where the determination of the shrinkage temperature is performed visually by the laboratory technician. Consequently, the method tends to be imprecise and subjective. It should also be noticed that the device proposed by the standard does not allow differentiation between the different stages of the contraction process. There are other methods to determine leather shrinkage temperature including differential scanning calorimetry, microscopic hot table, thermogravimetric analysis, differential thermal analysis and thermomechanical analysis. All these methods involve complex devices and are only suitable for specialized personnel. In this work, a new device is developed to precisely measure the leather shrinkage temperature and to distinguish the different contraction stages. In addition, the proposed device is simple, easy to use and inexpensive, which facilitates its use in any industry. The developed system consists basically of a load cell to measure the strength produced by the shrinkage of the leather. With the logged data during the test a strength versus temperature graph is built. By means of its interpretation, the different stages of shrinkage can be determined. Different mathematical analysis of the logged data is proposed to determine the shrinkage stages temperatures, thus achieving a high degree of certainty and repeatability. Take-Away: A new device, simple and inexpensive, is developed to precisely measure the leather shrinkage temperature and to distinguish the different contraction stages

En torno a un hallazgo del Neolítico Antiguo en la Valldany (Oliana, comarca del Urgellet, Lérida)

Hablar con unos esquemas rígidos de una unidad cultural neolítica en Cataluña es menospreciar el papel que representa el marco geográfico de este país, desconocer los tres grandes conjuntos geológicos regionales: la costa, el llano y la montaña; cada uno de ellos aporta su nota de originalidad; sin embargo, tampoco cada uno de éstos va a representar una uniformidad monótona, sin~o que se escinden formando un rompecabezas complicado, donde sus piezas, con características propias, son las comarcas

Hide unhairing: achieving lower pollution loads, decreased wastewater toxicity and solid waste reduction

This study aims to diminish the pollution being discharged into wastewaters through changes in the unhairing process. To this aim, we are replacing a reductive hair degrading process with a process which combines a reductive hair degrading process with an oxidative hair degrading process. Hydrogen peroxide is used to decrease the supply of sulfide as unhairing chemical. As a result, commercially acceptable leather regarding both costs and quality is obtained and significant reductions in the contaminant load of the wastewater being discharged are observed. Results indicate that wastewater conductivity is cut by 26%, suspended solids decrease by 75%, observable sulfide disappears, while the amount of chromium being absorbed by the hides is increased. This leads to considerable savings in the chromium salt offer in hide tanning and, consequently, a decrease in the amount chromium in the wastewater.Postprint (published version

Study of several variables in the penetration stage of a vegetable tannage using ultrasound

This study concerns the implementation and improvement of a 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 investigated the influence of several variables on the tannins absorption by the hides. The results show significant differences in the tanning degree of the leathers tested in relation to the work system tested, the ultrasonic power used and the resting time of the leather after tanning. The leathers we obtained showed no scratches, which is 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 kind of tannages.Peer ReviewedPostprint (published version

La competencia documental en la enseñanza universitaria

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