A Review of Natural Plants as Sources of Substances for Cleaner Leather Tanning Technologies

Abstract

The stringent environmental regulations and compliance regarding leather tanning has compelled leather industry to seek alternative cleaner ingredients that have the capacity to minimize or prevent pollution caused by hazardous chemicals. Practical measures have so far involved replacing the current use of synthetic chemicals such as chromium salts, dyes, fatliquors and surfactants or minimizing their usage by incorporating agro-based organic components. Numerous papers have documented the use of different plant extracts at different stages of leather processing such as tanning, retanning, dyeing and fatliquoring. This present article details the specific plants and the leather processing stage at which they are applied and eventually the quality of the resulting leather. This article attempts to compile a considerable number of investigations published on physical properties of leather that is processed using natural plants. It has been shown that there are striking similarities in leather properties of leather processed using natural plants and using synthetic chemicals. This could help in compiling a database that details works on natural plants, stages of application and the corresponding physical properties which could provide a crucial assistance to research focusing on environmental protection and physical properties of leather which would in turn improve the quality of the resulting leather.

Reduction of Water Consumption in Leather Processing and an Investigation of the Leather Quality

“…Schematic diagram of different steps to process raw leather into finished leather Water is used in most of the steps involved in raw leather processing as well as during spraying a coat on the surface of leather. However, tanning is the most significant and required step in the leather preparation system [6]. Tanning processes can alter the molecular structures of leather skins [7].…”

Mitigating the Formation of Hexavalent Chromium in Leather by Using Aloe Barbadensis Miller Mixed with Carrageenan

“…This observation highlights a considerable effect of retanning process using chromium compounds on levels of Cr (VI) due to autoxidation. Although autoxidation occurs in all the samples to form reactive oxygen species (radicals) of hydro peroxides, the complex bonds of Cr (III) with the carboxylic groups of collagen in the leather are too strong to be dismantled by autoxidation [9,30].…”

“…After the retanning process, the levels of Cr (VI) increased to 292.7 mg/kg. The pronounced increase can be attributed to the excess Cr (III), not chemically linked to the carboxylic group of collagen and hence easily oxidizable to Cr (VI) [9]. Furthermore, the use of sodium and ammonium bicarbonates during neutralization and basification or wetting-back processes prior to the retanning process provide mild oxidation agents, especially at high pH, that necessitate the formation of Cr (VI) in retanned wet blue leathers [33].…”

“…The downside of this chromium tanning, however, is that the Kenya https://doi.org/10.31881/TLR.2021. 20 Cr (III) compounds get oxidized to Cr (VI), a carcinogenic and environmentally hazardous compound, which has considerable impact on the environment, public health and general human health [2,[8][9].…”

“…Agents that accelerate the oxidation include atmospheric oxygen, UV rays (photo ageing), extremely high or low pH (such as during neutralization and dyeing), extreme high or low humidity, temperatures higher than 80 °C (thermal ageing), fatliquoring (especially those with double bond, vegetable oils, animal oils) and natural waxes and resins used during dry finishing [8][9][10][11][12][13][14][15][16][17]. Oxidation mechanisms involve radical formation and hydro peroxides necessitated by energy provided by the aforementioned agents.…”