Potential Application of Used Coffee Grounds in Leather Tanning

Safety of environment and human health is an essential requirement of modern industrial techniques. Therefore, using natural agents in tanning industry may emerge as a trusted method to avoid the chemical contamination caused by using traditional chromium salts in tanning process. This study aimed to evaluate the hot water extract of used coffee grounds (UCGs) as a vegetable tanning agent. The collected UCGs were dried and extracted with hot water at 90 °C for 2h. The phytochemical screening properties of UCGs extract were determined. Sufficient amount of extract was prepared to be used in leather tanning. Three groups were tanned with UCGs extract solely at concentrations of 20, 30 or 40% of pelts’ weight, while another three groups were tanned with the same concentrations and then re-tanned with 10% of a synthetic tanning agent “Phenol sulfonates”. On tanned leathers, organoleptic, physical and chemical properties were determined; scanning electron micrographs were depicted to examine the leather surface and collagen fiber bundles. Analysis of UCGs extract revealed that it has good tanning properties, as it contained tannins (14.92%), tannins/non tannins ratio (2.06), hide powder (39.57) and Stiasny number (21.16). The results of leather properties showed that using UCGs extract alone at concentration of 40% achieved the best results for the vegetable tanning where the tanned leather had higher (P<0.05) tensile strength, tearing strength and shrinking temperature than that treated with the lower level of 20% UCGs extract. However, 40% of UCGs extract is highly recommended to be used to accomplish the required shrinkage temperature that should be ≥ 70 °C. UCGs extract could be successfully used as tanning agent in vegetable tanning to produce durable leathers with good fullness; it may be used for different manufacturing products, such as footwear and bags. Moreover, using a combination of UCGs extract at any of the used concentrations with phenol sulfonates 10% led to significant improvement in all studied traits as compared with using UCGs extract alone.