Changes to the Collagen Structure using Vibrational Spectroscopy and Chemometrics: A Comparison between Chemical and Sulfide-Free Leather Process

Abstract

Chemical and physical changes take place when hides and skins are processed to leather that affect the quality and strength of the material. Understanding the structure at each leather-making stage is the basis of this study but also intend to improve the process through a biochemical approach, employing a proteolytic enzyme for processing leather more cleanly with reduced environmental impact. Raman and ATR-FTIR spectroscopy in conjunction with chemometrics was used to investigate each leather-making stage from fresh green cattle hide to dry crust leather. The changes in proteins, lipids, nucleic acids and other biomolecules with leather processing was measured and reported using three novel Raman ratiometric markers, 920/1476, 1345/1259 and 1605/1476 cm-1, to discriminate the structural changes in collagen of hide using standard chemical and enzymatic method. Amide I band was deconvoluted to investigate thecollagen secondary structures using curve fitting by Gaussians function. The results of Principal Component Analysis are well-corroborated with the ratiometric markers of structural changes.

Leather-like composite materials prepared from natural rubber and two leather wastes: Wet blue leather and finished leather

“…The WBL (Figure 2(a)) and inner side FL (Figure 2(b)–(d)) shows the same characteristic spectra appeared at 3300 cm −1 assigned to O-H stretching of moisture, 32 1633 cm −1 attributed to N-H bending of amide I complex and reflected chromium with carboxylate groups (-Cr-OOC-), 32,33 1550 cm −1 attributed to the combination of the N-H bending or C-N stretching of amide II and including chromium interaction with amino groups (-Cr-NH-), 32,33 1450 cm −1 attributed to the CH 2 bend of phospholipids, 32,33 and 1240 cm −1 attributed to the N-H bending of amide III. 32,33 In addition, the top grain FL in Figure 2(e)–(g) observed spectra at 1729 cm −1 corresponds to C=O of from fat liquoring products that typically used in final step of leather finishing, 34,35 1645 cm −1 associated to N-H bending of amide I, 32,33 sharp spectra at 1278 cm −1 associated to N-H deformation and C-N stretching, 36 broad spectra in the range of 1100-1000 cm −1 corresponding to monomeric chromium stretching (-Cr=O-), 37 and strong spectra at 840 cm −1 also related to Chromium vibration (-Cr-O-Cr-). 37

Figure 2.ATR-FTIR spectra of (a) WBL and (b)–(g) various FL.

Figure 3.ATR-FTIR spectra of the samples (a)–(e) and thermal aged samples (f)–(j) of NR and NR_WBL.

Figure 4.ATR-FTIR spectra of the samples (a)–(e) and thermal aged samples (f)–(j) of NR and NR_FL.

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“…Moreover, the WBL-filled NR composites demonstrated higher hardness than the FL-filled NR composites when compared at the similar loading levels due to softening effect of fatty acid at the final stage of FL manufacturing. 34,35

Figure 5.Shore A hardness of the samples.

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“…Moreover, the WBL-filled NR composites demonstrated higher hardness than the FL-filled NR composites when compared at the similar loading levels due to softening effect of fatty acid at the final stage of FL manufacturing. 34,35 Tensile properties, in terms of the tensile strength, elongation at break, and M200, of the samples evaluated both before and after aging at 70°C for 7 days are illustrated in Figure 6 and the corresponding values are also summarized in Table 3. Before aging, the unfilled NR compound exhibited the tensile strength, elongation at break and M200 at 6.7 MPa, 690%, and 0.6 MPa, respectively.…”

Monitoring the curing efficiency of a plant-based green engineered additive on caprine skin: a spectroscopic and chemometric novel approach

“…By figuring the distance amid samples, the HCA way shows their resemblance and difference [ 31 ]. The application of Chemometrics has been reported in leather-making processes [ 32 , 33 ], distinguishing the origin of skin and leather [ 34 ] and the artificial deterioration of vegetable-tanned leather [ 35 ].…”