Influence of microwave on chromium complex composition in tanning liquor

Abstract

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. 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. 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. FT-IR was used to characterize the structure of chromium complexes in each composition separated by IEC. Moreover, the chromium tanning liquor after warming was used in hide powder tanning trials to illustrate whether microwave would affect its tanning ability. 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. In addition, microwave has more powerful effect on 33% basicity chromium tanning liquor hydrolysis and olation to generate larger molecular size complexes. In FT-IR results, the combination pattern between chromium and ligands are changed after warming but there is no difference between WB and MW. The chromium exhaustion and thermal stability of hide powder tanned with chromium tanning liquor after microwave irradiation are both higher. It could conclude that both thermal and non-thermal effects of microwave promote the process together, and the nonthermal effect leads to more high positive charge and large molecular size complexes and has stronger influence on high polarity system. In short, this work would provide theoretical basis for applying microwave in tanning agent modification and chrome tanning process further.

A faster and more effective chrome tanning process assisted by microwave

“…The cross-linking effect was strengthened under microwave because there would be more chromium complexes with highpositive charge and molecular-size, which had better affinity to collagen and mainly contributed to the cross-linking generated under microwave heating, and the exhaustion of these kinds of chromium complexes were higher. 29 On the other hand, just as microwave could clearly promote chemical reactions, it could also make cross-linking reaction easier to occur Fig. 1 The influence of different heating methods on leather thermal stability.…”

“…19,20 Furthermore, the T s of leather tanned with the assistance of microwave could exceed 100 C when terminal pH of the tanning liquor was only 3.3; on the contrary, the pH should be above 3.8 to reach the same T s level in the conventional tanning system. 21 With ultrasound and microwave assistance, chrome tanning could be nished within 11 min without basication. 22 These evidences suggest that microwave could accelerate the tanning process and also make tanning more effective.…”

“…Previous studies have demonstrated that stronger tanning effect was obtained during hide powder chrome tanning process. 24,25 However, chrome tanning agent easily reacts with collagen during the tanning process because the powdered tanning material is uniform and without any interwoven structure such as pelt. So far, it is unknown how the microwave affects the pelt chrome tanning process and the properties of the leather.…”

Potential Applicability of Mg/Al-Layered Double Hydroxide (LDH) for Environmentally Friendly Chromium-based Leather Tanning

“…25 Under chromium tanning conditions, the FTIR spectrum of Mg 1 Al 1 -LDH-4h-2%Cr showed the same absorption peaks of single Mg 1 Al 1 -LDH-4h, the sulfateresolved S−O at 1153 cm −1 and the Cr−O band at 996 cm −1 . 28,29 From the XRD patterns in Figure 8b, the characteristic diffraction peaks of the typical Mg 1 Al 1 -LDH-4h hydrotalcite phase were observed at 11.48°(003), 22.97°( 006), 29.48°(009), 60.49°(110), and 61.78°(113). After chromium tanning adsorption, additional diffraction peaks appeared at 10°, 30°, and 40°, corresponding to the existence of chrome tanning complexes in the structure.…”

A new type of multistage structure hydrotalcite material: To promote the absorption of chemicals in wet leather processing

“…[4,5] Therefore, it is necessary to enhance the absorption of leather fibers to these leather chemicals. [6][7][8] Search for high absorption chrome tanning auxiliary materials with and adsorption properties has attracted extensive attention of researchers. [3,9,10] A kind of adsorption material that can improve the absorptivity of chrome tanning agent, dye, and fatliquoring agent in the tanning process has broad application prospect.…”