Microwave‐irradiated tanning reaction of aluminum with collagen

Abstract

Given the toxicity of chrome tanning in leather industry, ecologically compatible alternatives are intensively researched, in particular on the side of aluminum tanning. Herein, the tanning reaction of aluminum with collagen was investigated using microwave irradiation as a new heating method, and the traditional water bath heating (WBH) was used as control. Results from dynamic light scattering and very‐positive differential scanning calorimetry (DSC) analysis reveal that, microwave heating led to larger particle size and increased main denaturing transition temperature of collagen clusters crosslinked by aluminum sulfate. The aluminum‐tanned collagen products obtained under microwave and WBH methods were further compared and characterized using many techniques including circular dichroism, fluorescence spectroscopy, atomic force microscope, and Fourier transform infrared spectroscopy, DSC, and thermogravimetry. Results verified that both heating methods accelerate the crosslinking reaction of aluminum with collagen and increase the crosslinking degrees. The crosslinked products exhibited improved thermal stability, but no change was observed concerning the binding mode of aluminum with collagen. However, compared to WBH microwave heating has a more positive effect on the aluminum‐tanning processes for the improvement of collagen crosslinking processes and product performances, probably due to both thermal and nonthermal effects of microwave irradiation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48682.

A faster and more effective chrome tanning process assisted by microwave

“…17,18 In aluminum and zirconium tanning, leather with excellent thermal behaviors was obtained by microwave-assisted tanning. 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.…”

Aluminum tanning of hide powder and skin pieces under microwave irradiation

“…The residue is composed of the carbonization products of aluminum tanned hide powder. Normally, the MHW samples show higher residue ratios than WBH controls under the same conditions, which is attributed to the firmer combination of aluminum tanning agent with hide fibers due to the thermal and athermal effect of the microwaves [38].…”

“…The former is 7°C higher than the latter, which further proves the promotion of microwaves on aluminum tanning. Namely, microwave irradiation leads to increased cross-linking combination between collagen fibers and aluminum complexes, and the firmness of cross-linking bonds is improved, too [38]. Thus, the higher thermal stability of the tanned product is observed in the microwave heating system.…”

“…At present, the main methods of modification of aluminum tanning are developing new coordination groups [29][30][31][32] and combination with other tanning methods [33][34][35][36]. Notably, microwave irradiation was also investigated for its application in the aluminum tanning process owing to its unique thermal and athermal effects [37,38]. In our previous work, the microwave-heated hydrolysis and olation behavior of aluminum sulfate [37] and their crosslinking reactions with collagen [38] were studied in the homogeneous system.…”

“…Notably, microwave irradiation was also investigated for its application in the aluminum tanning process owing to its unique thermal and athermal effects [37,38]. In our previous work, the microwave-heated hydrolysis and olation behavior of aluminum sulfate [37] and their crosslinking reactions with collagen [38] were studied in the homogeneous system. These investigations confirm the great advantage and potential of microwave heating in aluminum tanning, but the actual aluminum tanning process that is carried out in the heterogeneous system has not yet been covered.…”