The Thermal and Non-Thermal Effects of Microwave in the Chrome Tanning Process

摘要

Microwave power is an effective and energy-saving heating resource. When microwave power is used to assist in leather making, the leather always shows better performances. In order to apply microwave in chrome tanning further and explain the detailed effects of microwave in the process, the hide powder chrome tanning process was warmed by water bath heating (WB) and microwave irradiation (MW). After tanning, the pH, conductivity, dielectric constant and chrome content of tanning effluents were tested. Meanwhile, DSC, TG, FTIR and XPS were used to determine the thermal behaviours, collagen conformation and product structure of chrome tanned hide powders.Through comparing the similarities and differences between WB and MW samples, the results showed that the pH and chrome content of WB effluents were larger than those from MW while the conductivity and dielectric constants were smaller. On aspects of chrome-tanned hide powders, MW samples had higher Cr2O3 content, denaturation temperature and enthalpy as well as better thermal resistance. However, the collagen's fundamental structure, conformation and pattern of combination between collagen and chromium for MW samples were almost same as for WB. In sum, both a thermal effect and a non-thermal effect existed when microwave power was used as heating resource in chrome tanning, and both promoted the tanning process and other effects together.The higher chrome exhaustion, better thermal behaviour of products was achieved under microwave irradiation and caused by non-thermal effect without any negative effect on leather structure or changes to the tanning mechanism. The achievements in the work might be an important hint and reference for applying microwave power in chrome tanning to diminish pollution and in improving leather properties.