Novel Approaches of the use of Polyacrylate Ester-based Polycarboxylates (PCEs) as Leather Retanning Agents

Retanning is one of the main stages for leather manufacturing. Linear anionic polyacrylates are widely used as retanning agents to minimize the use of phenolic and sulfone syntans which are less environmentally friendly polymers. Nevertheless, their use as anionic retanning agents reduce the cationic charge of chrome tanned leathers, fact that influences the following stages: dyeing and fatliquoring. As a result, leathers with low dye uniformity, low colour intensity and rough grain are obtained. Polyacrylate ester-based polycarboxylates can be an alternative retanning agents that do not cause these deficiencies in the dyeing and fatliquoring stages. However, the effects of their chemical structure on the final leather properties are not well understood yet. In this study, an attempt has been made to analyze the influence of the molecular weight of the PCEs polyalcohol side chains in the final properties of the retanned leathers. PCEs with polyalcohol side chains of different molecular weight were synthesized, characterised and subjected to a biodegradability test. Retanning tests with PCEs were carried out in comparison to a commercial linear anionic polyacrylate. Different physical properties of the retanned leathers were analyzed. The internal collagen structure of the retanned leather was evaluated by scanning electron microscopy (SEM). The results revealed that PCEs with low molecular weight polyalcohol side chains were shown to solve the problems of linear polyacrylates in dyeing and fatliquoring stages and improve the final leather softness, colour intensity and physical properties. This study proves that PCEs with low molecular weight polyalcohol side chains can act as a good biodegradable alternative to linear anionic polyacrylates as retanning agents.