![]() ![]() During the process of collagen crosslinked with tannic acid, the Ts, denaturation temperature and enthalpy of product reacted with microwave-assisting increased by 3.5 ☌, 3.9 ☌ and 73.0 J/g. In vegetable tanning, the shrinkage temperature (Ts) of leather tanned under microwave was 1 ☌ higher than conventional moreover, total phenols content and number average molecular weight of tannins in the effluent decreased with microwave inducing. Not surprisingly, microwave also strengthens and enhances the combination between collagen and tanning agent and leads to better tanning effect and efficiency. Raw hides and skin will not convert into leather without tanning, in which chrome tanning is dominant because leather tanned by the method has brilliant hydrothermal stability, excellent mechanical properties and outstanding durability. For example, the leather had better color fastness when microwave was used in dyeing the fat uniformity in leather was better with microwave-assisting fatliquoring enzyme unharing and bating were more effective under microwave leather dried under microwave usually had higher thermal stability. During the processes, it could be found that microwave always has positive effect on promoting the combination between collagen and chemicals. As these advantages, more and more leather technologists and chemists pay attention to applying microwave in leather manufacturing, such as dyeing, drying, tanning and so on. ![]() Microwave has been known to offer faster, simpler, and more cost-effective processes and result in high-yield, high-purity products and mild reaction condition. Microwave lies between radio wave and infrared frequency with wavelengths from 1 mm to 1 m and has been widely used in chemical synthesis for several decades. In short, this work would provide theoretical basis for applying microwave in tanning agent modification and chrome tanning process further. It could conclude that both thermal and non-thermal effects of microwave promote the process together, and the non-thermal effect leads to more high positive charge and large molecular size complexes and has stronger influence on high polarity system. The chromium exhaustion and thermal stability of hide powder tanned with chromium tanning liquor after microwave irradiation are both higher. In FT-IR results, the combination pattern between chromium and ligands are changed after warming but there is no difference between WB and MW. In addition, microwave has more powerful effect on 33% basicity chromium tanning liquor hydrolysis and olation to generate larger molecular size complexes. The results show there are more high positive charge and large molecular size complexes in chromium tanning liquor after warming but the phenomena are more significant in MW samples compared with WB due to non-thermal effect of microwave. Moreover, the chromium tanning liquor after warming was used in hide powder tanning trials to illustrate whether microwave would affect its tanning ability. FT-IR was used to characterize the structure of chromium complexes in each composition separated by IEC. ![]() Ion exchange chromatography (IEC) and gel filtration chromatography (GFC) were used to measure the charge composition and molecular size of chromium complexes in each sample. Chromium sulphate solution (0% basicity) and 33% basicity chromium tanning liquor were subjected microwave (MW) and water bath (WB) heating, and the samples without any warming were regarded as control. Since microwave irradiation could promote hydrolysis and olation of chromium tanning liquor, but the influence of microwave on chromium complex component in the liquor was still unknown. ![]()
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