Revealing Molecular Level Indicators of Collagen Stability: Minimizing Chrome Usage in Leather Processing

Abstract

Chromium­(III) sulfate is extensively used in leather processing to stabilize the collagen molecules in hides and skins. Although its excess usage causes severe environmental pollution and health concerns, the role of chromium in stabilizing collagen still remains poorly understood. For the first time, by integrating a number of techniques, including real-time small-angle X-ray scattering, differential scanning calorimetry and natural cross-link analysis, we reveal crucial molecular-level indicators of collagen stability. The results indicate that collagen molecules achieve maximum molecular stability at concentrations as low as 1.8 wt % even if excess chromium (>3.7%) is introduced into the collagen matrix. At low concentrations (1.8% to 3.7%), the active amino acid residues are saturated via covalent bonding with chromium. Any excess chromium interacts purely non-covalently with the collagen molecule and, we propose, can be substituted by environment-friendly alternatives. Further, important natural cross-links, which are crucial in imparting mechanical strength, were observed to decrease with increasing chromium concentration, highlighting the adverse impact of chromium­(III) sulfate on collagen matrix and the importance of identifying alternative cross-linking agents. Our findings provide tools which will enable the evaluation of greener tanning agents to facilitate a more sustainable future for the leather industry.

Quantitative and structural analysis of isotopically labelled natural crosslinks in type I skin collagen using LC-HRMS and SANS

“…When crosslinked, the amino acid residues in telopeptidyl region would be covalently bonded and the axial gaps between molecules were found to expand (Table 1). This is consistent with previous observations [10]. However, the labelled sample exhibited an opposite trend in R 3/1 compared to the reduced sample and the control sample (Fig.…”

“…The stabilised control sample showed a decrease in the amount of HLNL and HHMD from raw to pickled stage as expected, because of the low pH (1.5-2.0) conditions during pickling (acidification). After chrome tanning, the natural crosslinks decreased again, which is in agreement with our previous observation [10].…”

“…Depending on the applications, artificial crosslinkers are used to modify the mechanical properties and denaturation temperature of collagenous materials to meet with different purposes [2,7]. The intermolecular structure of collagen is intrinsically stabilised by the natural crosslinks, however, can also be affected during chemical crosslinking [8][9][10]. One of the largest industrial applications of skins is the manufacturing of leather, which involves both organic and inorganic crosslinking reagents to increase the denaturation temperature and retain its flexibility and organoleptic properties close to the original skins [7].…”

“…One of the largest industrial applications of skins is the manufacturing of leather, which involves both organic and inorganic crosslinking reagents to increase the denaturation temperature and retain its flexibility and organoleptic properties close to the original skins [7]. Chromium sulphate was reported to change the collagen structure significantly while causing a decrease in the overall quantity of natural crosslinks in skin, which would potentially deteriorate the mechanical strength of the final product [10]. The development of insightful analysis of the natural crosslinks in skin collagen and its interaction with artificial crosslinks is therefore, beneficial for the development of greener processing technologies.…”

Influence of UV aging on some rheological properties of footwear leather

“…Moreover, the plasticity property adjusts the leather to the shape of the foot and increases a mechanical comfort [26]. Today in order to determine collagen structures, the wide spectrum of techniques as: small angle X-ray scattering [27][28][29][30], differential scanning calorimetry [31], scanning electron microscopic analysis [32] are used. These abovementioned techniques could give the indicators of leather quality from the molecular level point of view.…”