[en] The use of ultrasound in the vegetable tanning processes, show nowadays, some advantages compared with the standard industrial systems like: dynamic vegetable tanning processes where drums are used as a reactor and static vegetable tanning processes where pits are used as a reactor. The dynamic vegetable tanning process is the most common method to produce full vegetable tanned articles. The production time is quite short (between 1 to 4 days), based on the quick diffusion of the vegetable agents due to mechanical effect produced inside the drums. In contrast, the mentioned mechanical effect can produce irreversible damages in the grain side that decreases the quality of the final product. The static vegetable tanning processes are mainly used in those kind of articles (sole Leather and similar) where the amount of tanning agents to make the product is so high that even the right control of the main parameters involved in the process can't avoid heavy damages in the grain side. With this kind of articles, the skins are immersed in pits with different tannin offers. In this case, the mechanical effect is none, which makes the process long in time (between 7 to 90 days). This point reduces the productivity and forces to administrate a bigger leather stock. The main objective of this PhD is to design a vegetable tanning process assisted by ultrasound, which could take advantage from the standard processes used nowadays and could solve the problems related with each one. This could bring us to a final product with a better quality and a possible process optimization that could make it industrially viable. The system uses the ultrasound waves to reduce the molecular size of the tanning agent's micelles, producing a quick diffusion through the skin without the use of any mechanical effect, and speeding up the process compared to the static system. In order to achieve the exposed objectives the thesis has been structured in 3 parts: Initial study: Pilot study to determine the performance of the parameters involved in the ultrasonic tannage and selection of the ideal conditions in order to prepare the next steps of the process. Study in the penetration stage: Based on the results obtained in the pilot study, an assessment in the penetration stage is proposed. In this phase, the parameters that take part in the tanning agent's diffusion all over the fiber structure of the skin will be studied. Study in the fixation stage: Based on the results obtained in the penetration stage the study in the fixation stage will be proposed. In this phase, the parameters performing in the fixation of the tanning agents will be studied once it has penetrated completely, in order to optimize the fixation and complete the tanning process. In order to evaluate the trials done in the experimental stages, the tanning degree will be used as an indicator. This parameter links the percentage of fixed tannin with the percentage of hide substance, enabling to quantify the absorption. Due to the difficulty to obtain this parameter and the amount of trials done to make this thesis, it will be worth to use new methodologies to obtain this value for future studies. After assessing the 3 stages, an ultrasonic working process alternative to the existing systems will be proposed.

[es] La utilización de los ultrasonidos en sistemas de curtición vegetal presenta ventajas frente a los sistemas más consolidados en la industria en la actualidad: curticiones vegetales dinámicas donde se utilizan los bombos como reactor, y curticiones vegetales estáticas donde se utilizan las tinas como reactor. Las curticiones vegetales dinámicas se utilizan en la mayoría de artículos curtidos al vegetal y presentan un tiempo de proceso reducido (1 a 4 días) basado en la rápida difusión del tanino debido al elevado efecto mecánico que se produce en el interior de los bombos. En contrapartida este efecto es el causante de daños irreversibles en la dermis de la piel que pueden reducir la calidad del producto considerablemente. Las curticiones vegetales estáticas se utilizan principalmente en aquellos artículos (suelas y similares) donde la oferta de tanino para curtir la piel es tan elevada que ni el estricto control de los principales parámetros que intervienen en la curtición evitan daños muy graves en la dermis de la piel. En estos casos se opta por sistemas estáticos de curtición donde la piel se sumerge en tinas a diferente concentración de tanino para realizar la curtición. En estos sistemas el efecto mecánico es prácticamente nulo, pero el tiempo de proceso es largo (7 a 90 días) hecho que reduce la productividad y obliga a gestionar un stock más elevado. El objetivo principal de esta tesis es diseñar un sistema de curtición vegetal por ultrasonidos a nivel industrial que aproveche las ventajas de los sistemas que se utilizan actualmente i evites sus problemáticas a fin y efecto de conseguir un producto final con una mayor calidad y un grado de optimización del proceso que le permita ser viable industrialmente. El sistema prevé utilizar la potencia ultrasónica para disminuir el tamaño molecular de las micelas de tanino y de esta manera conseguir una rápida difusión a través de la piel, sin necesidad de aplicar efecto mecánico a bombo, acelerando mucho el proceso respecto a un sistema estático.