Evaluation of plectranthus barbatus as a potential vegetable tanning agent in Nyamira county, Kenya

Abstract

Chrome tanning is popular in industrial production of leather but the residual chrome in tannery waste pollutes the environment with concerns of oxidation of chrome(iii) to carcinogenic chrome (vi) in leather articles. Eco-friendly vegetable tanning is an alternative to chrome tanning but the technology is not widely used in Kenya due to lack of cheap sources of these tannins in the market. This study was designed to evaluate Plectranthus barbatus for its potential use as a vegetable tanning agent. The tannin content in Plectranthus barbatus was determined using the hide powder method while the tanning potential was assessed by tanning wet salted goat skins using Plectranthus barbatus leaves and stem extracts and thereafter determining the quality of the leather produced. Anova statistical test was used to compare the mean tannin content in leaves, stems and a combined leaves and stems extracts and also the physical properties of tanned leather. Plectranthus barbatus crude extracts were found to contain hydrolysable tannins ranging between 8-20 % depending on the part of the plant. The tannin contents in leaves and stems were significantly different (p<0.05) with values of 20% and 8% and respectively. The physical properties of Plectranthus barbatus extracts tanned leathers significantly improved after retanning to attain the following mean values: Shrinkage temperature: 67.5°C ; Grain crack range: 8.7 mm; Grain burst range: 9.1 mm; Tear strength: 78.2 N with % elongation: 75.9; Tensile strength: 40.8N/mm2 with % elongation of 42.2 and thickness of 1.2 mm. They also endured 100,000 dry flexes without damage and all these figures were above the recommended values.