Thermal stability of shoe upper leather: Comparison of chestnut and quebracho as vegetable tanning agent

Abstract

Thermal stability is one of the most important factors in the leather tanning process and mainly affected by the tannin type used to tan the hides. Vegetable-tanned leather for shoe upper is a material that could be used and preserved for a long time. However, it makes leather easily degraded because of temperature and time. Additionally, one of the stages in shoe making process is the heating process to stick the upper leather into midsole material. Therefore, this study aims to compare the effect of different tanning agents, chestnut and quebracho, on the thermal stability of shoe upper leather. Measured were degree of tannage and thermal stability, using shrinkage temperature, thermogravimetric analysis and differential scanning microscopy. The morphology of leathers tanned with chestnut and quebracho in different concentration were also observed. The shrinkage temperature of leather tanned with chestnut was lower than that of quebracho-tanned leathers. Leathers tanned with 20 and 25% of chestnut showed higher degree of tannage than the ones tanned with quebracho. Thermogravimetric analysis (heating rate of 10 °C min-1; gas flow of 60 ml min-1) showed that the maximum weight loss rate decreased with the increase in the concentration of chestnut or quebracho. The differential scanning calorimetry results showed that quebracho-tanned leather had a higher heat resistance than chestnut-tanned one. The presence of vegetable tanning agent improved the thermal stability of leather. Furthermore, it was shown that leather tanned with 20% and 25% of chestnut resulted in almost equal thermal stability. Quebracho calf leather was more resistant against heat than chestnut calf leather.