Raman and ATR-FTIR spectroscopy towards classification of wet blue bovine leather using ratiometric and chemometric analysis
Mehta, Megha; Naffa, Rafea; Maidment, Catherine; Holmes, Geoff; 2 Waterland, Mark LASRA®NZ Leather and Shoe Research Association; 2 School of Fundamental Sciences, Massey University, Palmerston North, New Zealand
There is a substantial loss of value in bovine leather every year due to a leather quality defect known as “looseness”. Data show that 7% of domestic hide production is affected to some degree, with a loss of $35 m in export returns. This investigation is devoted to gaining a better understanding of tight and loose wet blue leather based on vibrational spectroscopy observations of its structural variations caused by physical and chemical changes that also affect the tensile and tear strength. Several regions from the wet blue leather were selected for analysis. Samples of wet blue bovine leather were collected and studied in the sliced form using Raman spectroscopy (using 532 nm excitation laser) and Attenuated Total Reflectance – Fourier Transform InfraRed (ATR-FTIR) spectroscopy. The purpose of this study was to use ATR-FTIR and Raman spectra to classify distal axilla (DA) and official sampling position (OSP) leather samples and then employ univariate or multivariate analysis or both. For univariate analysis, the 1448 cm – 1 (CH2 deformation) band and the 1669 cm – 1(Amide I) band were used for evaluating the lipid-to-protein ratio from OSP and DA Raman and IR spectra as indicators of leather quality. Curve-fitting by the sums-of-Gaussians method was used to calculate the peak area ratios of 1448 and 1669 cm – 1 band. The ratio values obtained for DA and OSP are 0.57 ± 0.099, 0.73 ± 0.063 for Raman and 0.40 ± 0.06 and 0.50 ± 0.09 for ATR-FTIR. The results provide significant insight into how these regions can be classified. Further, to identify the spectral changes in the secondary structures of collagen, the Amide I region (1600–1700 cm – 1) was investigated and curve-fitted-area ratios were calculated. The 1648:1681 cm – 1(non-reducing: reducing collagen types) band area ratios were used for Raman and 1632:1650 cm – 1 (triple helix: – a-like helix collagen) for IR. The ratios show a significant difference between the two classes. To support this qualitative analysis, logistic regression was performed on the univariate data to classify the samples quantitatively into one of the two groups. Accuracy for Raman data was 90% and for ATR-FTIR data 100%. Both Raman and ATR-FTIR complemented each other very well in differentiating the two groups. As a comparison, and to reconfirm the classification, multivariate analysis was performed using Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). The results obtained indicate good classification between the two leather groups based on protein and lipid content. Principal component score 2 (PC2) distinguishes OSP and DA by symmetrically grouping samples at positive and negative extremes. The study demonstrates an excellent model for wider research on vibrational spectroscopy for early and rapid diagnosis of leather quality.Journal of Leather Science and Engineering February 2020
Identification and characterization of potential biocide-resistant fungal strains from infested leathers – A systematic study
Sundar, Kavitha; Khambhaty, Yasmin; Kannan, CBN
This study is aimed at identification of biocide tolerant/resistant fungal strains afflicting the leather industry. Fungal infestation occurs sometimes despite biocide treatment during leather processing. This persistent growth can be due to the development of biocide resistance which can lead to health hazards and economic loss. As no study has so far been reported to either confirm this or to identify such fungal strains, a systematic approach has been made in this study to address these aspects. Fungal strains were collected from infested leathers from tanneries to identify biocide resistant fungal strains afflicting leather industry. Phenotypic characterization revealed Aspergillus as the most dominant with 58% occurrence. Ten isolates were subjected to 18s rRNA sequencing and four strains were identified as Aspergillus niger . An in-vitro susceptibility to four leather fungicides was assessed to identify the biocide tolerant strains. S-6 A. niger strain was found to be the most tolerant as evidenced by high MIC (7.81μg ml -1 ) against the most effective biocide, 2-(thiocyanomethylthio) benzothiazole. I n-vivo studies on chrome-tanned leathers also confirmed this finding. SEM studies revealed considerable morphological changes in S-6 compared to wild strain providing further evidence that it may have developed biocide resistance.
JALCA February 2020
Influence of benzenecarboperoxoic acid on chamois leather process
Sahu, Bindia; Alla, Jaya Prakash; Jayakumar, Gladstone Christopher; Raj, Ashok
Stabilization of collagen against heat and enzyme is a key objective in the tanning process. In oil tanning, fatty acid present in the oil is oxidised mainly into aldehydes which interects with Ԑ amino groups of collagen to form stable covalent cross links. Conventionally, oil tanning consumes time from two to three weeks which primarily depends on the type of oil and oxidation method for completion of tanning. In the present research, the duration of oil oxidation is reduced using benzenecarboperoxoic acid (PBA). It has been observed that PBA significantly reduces oil tanning duration from two weeks to 4 days. Moreover, the water absorption capacity of experimental leather has also increased by approximately 48% (1% PBA) compared to control leather. Physical strength properties such as tensile and percentage elongation values have also found to meet the standard norms. In addition to this organoleptic properties are also on par with control leather. The present study focus on the accelaration of chamois process for making leather, using PBA as an oxidising agent.
JALCA February 2020
Limiting microbial activity as an alternative approach of bovine hide preservation. Part II
Arker, Majher I.; Yosief, Hailemichael O.; Liu, Cheng-Kung; Latona. Nicholas P.
Wet salting of bovine hide commonly utilizes 95% saturated salt solution or 40-50% salt (w/w) on raw hide weight for preservation. The salt used for the hide preservation ends up being in wastewater and generates enormous environmental pollution. To minimize the environmental pollution problem associated with the traditional method of hide preservation, alternative formulations containing antimicrobial agents and less amount of common salt (35% saturated brine) have been developed. The alternative formulations were found to be more effective in deterring microbial growth than the traditional formulation as demonstrated by the total aerobic bacterial count of the preserved hide soaking liquor. The effect of the newly developed formulations on leather quality was assessed by analyzing the mechanical properties, scanning electron microscopic images, grain pattern and organoleptic properties of the finished leather. The quality analysis of the crust leather revealed that, the leather panels produced from the traditionally and alternatively preserved hides were comparable. The environmental impact of the newly developed formulations was also evaluated by monitoring the leather processing effluents for the pollution indicators such as total solids (TS), total dissolved solids (TDS), chloride content, Chemical oxygen demand (COD) and Bio-Chemical oxygen demand (BOD). Overall, the environmental impact of the newly developed hide preserving formulation was less severe than the traditionally used formulation. Since the newly developed formulations did not affect the quality of the leather produced and their impact on the environments is minimum, they could be considered as viable options for combatting pollution problems associated with the traditional salt curing method.
JALCA February 2020
The quality of leather estimated from airborne ultrasonic testing of hides
Liu, Cheng-Kung; Chen, Nusheng; Latona, Nicholas P.
High-quality hides are paramount for competitiveness in both domestic and export markets. Currently, hides are visually inspected and ranked for quality and sale price, which is not always reliable when hair is present on the hides. Advanced technologies are needed to nondestructively and accurately characterize the quality of hides and enable one to estimate the qualitative and mechanical properties of leather. We were the first to carry out research for airborne ultrasonic (AU) methods to nondestructively characterize the quality of hides. The developed nondestructive method is based on measuring the AU waves transmitted through the hide samples. Research results demonstrated that the average amplitude distribution received from the ultrasonic wave transmitted through the hide samples yielded the best correlation with the AU test variables: gain, speed, and frequency. Observations showed AU parameters derived from the average distribution values for amplitude (AMPa) and time of flight (TOFa) have a correlation with the quality of leather. This study demonstrated that the fullness, overall characteristic, tensile strength, stiffness, elongation, and toughness of leather could be nondestructively estimated by the ultrasonic quantities obtained from AU testing of hides.
JALCA February 2020
Ecological evaluation of leather industry by neural network
Cheng Shuqiang; Luo Juan
At present, the production process of the leather industry is gradually developing towards being green and pollution-free. Therefore, an ecological evaluation of the leather industry is particularly important. In this paper, an ecological model of leather industry was established by using a BP (Back Propagation) neural network, and the appropriate indicators such as wastewater, COD, BOD, SS, Cr, S2- were selected for evaluation. The evaluation method improves the quality of evaluation of the ecological leather industry, and provides a reference for the evaluation of the ecological chemistry industry, which is conductive to the better realisation of the green development of the leather industry.
JSLTC Jan/Feb 2020
Clove essential oil – free and encapsulated for antimicrobial leather
Kopp, V.V.; Dos Santos, C.; Dos Santos, J.H.Z.; Gutterres, M.
Essential oils have antimicrobial properties, with good potential to be used as natural biocides. Microencapsulation is a technological possibility to protect functional natural microbicides and to prevent chemical changes. The performance of the clove essential oil (CEO), free and encapsulated, against bacteria was evaluated. The emulsion extrusion technique was used for CEO encapsulation with alginate and the sol-gel technique was used for the encapsulation with silica. Samples were characterised for antimicrobial activity, size and functional groups present. Strong antimicrobial activity against Staphylococcus aureus and Escherichia coli was observed. FTIR showed the main peaks of the CEO and confirmed its incorporation into the alginate microcapsules obtained and of the silica nanocapsules. The chemical stability of the clove oil after encapsulation gives rise for its bactericidal use in leather manufacturing with advantages of maintaining its properties for more durability and controlled release in leather.
JSLTC Jan/Feb 2020
Study of the chrome hexavalent content in commercial chromium salts
Bacardit, Anna; González. Maria; Mir, Teresa; March, Ricard; Corbera, Jordi
Three forms of chromium are used in industry: Cr(0), Cr(III) and Cr(VI). While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium is both toxic and carcinogenic.
In the leather sector, chromium (III) is used as a tanning agent; however, under specific conditions, chromium (VI) can be formed in the leather post-production. Due to this reason, the objective of this work is to determine the possible hexavalent chromium content in four commercial basic chromium salts and the tendency of these salts to originate hexavalent chromium when applied to leather. The chromium salts studied do not originate Cr(VI) when applied to hide under optimum working conditions. However, it is demonstrated that the appearance of chromium (VI) may be due to bad practices during the tanning and/or post-tanning processes.
JSLTC Jan/Feb 2020
Thermophysical and functional-consumer qualities of shoe upper leather
Pervaia, Nataliia; Andreyeva, Olga; Maisternko, Lesia; Ocheretna, Larysa
Nowadays, the production of shoes having certain functional-consumer qualities requires materials, which meet all final product requirements, are environmentally safe and do not overcomplicate the production cycle. In this paper the influence of conditions of using a polymeric material based on maleic acid prior to dyeing the bovine shoe upper leather was studied. According to the results of electron microscopic examination, as well as evaluation of the physico-mechanical and thermophysical properties of the leather it was revealed that the use of polymeric material contributes to the formation of structure and such important indices of the derma as tensile strength, grain strength, extension, water vapour permeability, apparent density, porosity, heat resistance and thermal absorptivity. On the basis of a generalised objective function, optimal processing variants were defined. Recommendations of leather production parameters taking into account the season of shoe exploitation (autumn/winter, spring/summer) have been made.
JSLTC Jan/Feb 2020
Structure and properties of a novel collagen-soy protein isolate film via self-assembly: a comparative study
Ruirui Wang; Hongru Wang; Liu Pengjie; Yijun Yao; Wanli Ji
A novel collagen-soy protein isolate (SPI) film formed via self-assembly was developed. This research investigated the structure and application properties of the collagen-SPIself-assembled film and the blend film. FTIR and XRD evaluation of structural properties indicated that the self-assembly method could effectively enhance the compatibility between collagen and SPI. The collagen-SPI selfassembled film presented a compact, smooth and continuous microstructure. The tensile strength (Ts) and elongation at break (EAB) values of the collagen-SPIself-assembled films (Ts: 13.991 ± 0.53 MPa, EAB: 84.57 ± 6.21%) were nearly twice those of the blend films. The water vapour permeability (WVP) values of the collagen-SPIself-assembled film were more than 2000 g•m-2•24h. The maximum decomposition peak of collagen-SPIself-assembled films was located at 313.2°C. The collagen-SPI self-assembled films could achieve swelling equilibrium quickly within 2 hours, and the structural integrity of the film was maintained for 24 hours. The collagen-SPIself-assembled film had excellent ultraviolet shielding and visible light transmission qualities. The collagen-SPIself-assembled film had better mechanical properties, optical properties, thermal stability and water resistance properties as opposed to blend film. As a clean and feasible method, the self-assembly method could improve the functional properties of the collagen-SPIfilm. The collagen-SPIself-assembled films could be used as novel wound dressings in the future.
JSLTC Jan/Feb 2020
Factors influencing the wet properties of leather board
Yinghua Ma; Dongsheng Xin; Runting Xia; Shaolan Ding; Fei Ma
The bonded leather board was prepared by hot pressing. Waste chromed cow leather was used as raw materials and bonded with chloroprene rubber adhesive (CR adhesive). The effect of process factors on the surface wettability and the water absorption under complete immersion conditions of the finished product were studied in this article. The study found: When the amount of the CR adhesive was enhanced, the effect was to reduce the surface wettability and the 15 minutes and 24 hours water absorption of the bonded leather; when the temperature increased, the effect was to increase the surface wettability and reduce the 15 minutes and 24 hours water absorption of the bonded leather;the time has no effect on the wet characteristics of the bonded leather; when the pressure was increased, the effect was to reduce the surface wettability of the bonded leather, and the time has no effect on the water absorption. In general, the CR adhesive-prepared bonded leather is an hydrophobic material.
JSLTC Jan/Feb 2020
Re-utilization of biomass resources: preparation and application of a bio-polymer retanning agent based on cattle hair hydrolysate*
Luo Jianxun; Ma Hewei; Feng Yanjuan
In order to promote the development of clean production of leather-making and to re-cycle the cattle hair from a hair-saving process, the hair is hydrolysed and may in some circumstances find an application. But, because the cattle hair hydrolysate has a small molecular weight and poor properties in retanning of leather, it was modified with vinyl monomers by radical co-polymerisation using ammonium persulfate at 80°C for 3 hours to obtain a bio-polymer retanning agent. Comparing the viscosity and retanning properties of the bio-polymer retanning agent, the mol ratio of acrylic acid, acrylamide used was confirmed to be 4.0:1.0 and the consumption of acrylic acid, acrylamide is 80% based on the content of the hydrolysate. The structure of the bio-polymer retanning agent was characterised by FTIR. Application results of the bio-polymer retanning agent on the retanning of the shaved sheepskin wet-blue show that it has good retanning and filling properties. When the optimal consumption of the bio-polymer retanning agent is in the range of 6% and 8%, the retanned leather is full, more uniform than before and lacks any plastic feeling.
Influences of drying methods on the thermal stability of leather
Ren Bianli; Fang Qi; Chai Yuye; Xu Xiaohong; Shen Xiaojun; Zou Xianglong
The bonded leather board was prepared by hot pressing. Waste chromed cow leather was used as raw materials and bonded with chloroprene rubber adhesive (CR adhesive). The effect of process factors on the surface wettability and the water absorption under complete immersion conditions of the finished product were studied in this article. The study found: When the amount of the CR adhesive was enhanced, the effect was to reduce the surface wettability and the 15 minutes and 24 hours water absorption of the bonded leather; when the temperature increased, the effect was to increase the surface wettability and reduce the 15 minutes and 24 hours water absorption of the bonded leather; the time has no effect on the wet characteristics of the bonded leather; when the pressure was increased, the effect was to reduce the surface wettability of the bonded leather, and the time has no effect on the water absorption. In general, the CR adhesive-prepared bonded leather is an hydrophobic material.
JSLTC Jan/Feb 2020