Evaluation of the Tanning Viability of Tannins From Coffee Pulp in Thika Sub-county, Kiambu County, Kenya.

Abstract

The tanning industry utilizes chrome salts for tanning despite them being considered environmental pollutants. Vegetable tanning is considered to be a greener alternative to chrome tanning with mimosa extract being the most commonly used. The presence of inadequate acacia trees in Kenya for mimosa production means that the country majorly relies on imports which results in an increase in their prices leading to an increase in cost of production. This study was formulated to determine the viability of coffee pulp as a source for vegetable tannins. Twelve samples were collected from Yadini coffee factory in four different days. The tannin content was quantitatively determined by the hide powder method. The quality of the leathers was determined by carrying physical tests on tanned goatskins according to IUP methods. A statistical t test was used for comparison of coffea arabica pulp and mimosa tannin content and physical properties of resultant leathers. It was established that C. arabica pulp had a tannin content of 5.04% and a tanning strength of 2.26 compared to mimosa extract with a tanning content of 64% and a tanning strength of 2.82 with the two tannins being of the condensed type. This showed that there was a significant difference (p<0.05) between the tannin content and tanning strength of mimosa and C. arabica tannins. The physical characteristics of C. arabica pulp tanned leather was 14.72±2.22N/mm2 and →19.09±1.60N/mm2 tensile strength, 62oC shrinkage temperature, 48.00±14.15 N/mm, →38.12±3.13N/mm tear strength, grain crack and grain burst of 4.52±0.31mm and 5.93±0.28mm respectively and a change in colour at 100000 flexes for flex endurance. Mimosa tanned leather had 24.19±2.25N/mm2 and →27.20±3.26N/mm2 tensile strength, 83oC shrinkage temperature, 75.97±8.68N/mm, →→72.08±8.19N/mm tear strength, grain crack and grain burst of 7.47±0.09mm and 8.25±0.15mm respectively. There was no damage at 100000 flexes for flex endurance. The t test used for comparison showed that there was a significant difference (p<0.001) for tensile strength, tear strength, shrinkage temperature, ball xiv burst and flex endurance. The study concluded that the tanning strength of coffee pulp was more than the minimum 1.5 recommended for vegetable tanning materials. The physical properties exceeded the minimum recommended limits although they were less comparable to mimosa tanned leather. It was recommended that further research to be conducted on the penetration of C. arabica pulp tannins in the pelt as the coffee tannins in their natural form did not penetrate making their use in tanning in this state difficult.