Leather Surface Research Articles

Detection and localization of defects on natural leather surfaces

Detection and localization of defects on natural leather surfaces

Natural pigment: Preparation of brown pigment from lignin biomass for coloring application

Nanopigment based coatings have attracted considerable interest due to their high surface area, enhanced covering strength, resistance to scratch and abrasion properties. The preparation of nano pigments from industrial waste is challenging and can potentially be used in various industrial applications. As per environmental concerns, utilization of insoluble residues such as black liquor separated from paper and pulp industry waste as value added products is essential for industrial waste management. Tailoring of nanosized pigment colorants with improved surface covering properties from the industrial waste black liquor has been proposed. The acidified and precipitated insoluble organic part of black liquor was used for pigment preparation. Surface modification of pigment with silica coating, through sol-gel method, using synthesized Gemini surfactant, was adopted for size reduction. The prepared nanopigments were characterised through Fourier Transform Infrared Spectroscopy (FT-IR), Reflectance measurement and Transmission Electron Microscope (TEM). The results for optical studies of the prepared pigment confirms the suitability of this surface modified pigment as a brown coloring agent. From the DLS measurements, the dispersion property of prepared pigment was found to be monodispersed with a narrow size distribution of approximately 50–200 nm. The industrial applicability of such nano pigment was analysed by utilizing it as colorant for the leather surface coating as well as in plastics. Commercial viability of nano-pigments as coloring agents, adds value to the paper and pulp industry waste in a sustainable way.

Waterless leather dyeing with dense carbon dioxide as solvent for dyes

Conventional leather dyeing consumes high amounts of dyes and increases pollution of tannery wastewater. We have focused on the reduction of dyestuff and the avoidance of water and additional chemicals for the colorization of leather. Waterless leather dyeing with supercritical CO2 as solvent for the dye 1-(methylamino)anthraquinone was performed in a technical scale autoclave. The intensity and uniformity of the dyed leathers was assessed using spectroscopic color measurements. The rub fastness was assessed according to DIN EN ISO 11640. In the result, waterless dyeing at 100 bar and 40 °C leads to uniform, intensive colorizations of the leather surface at a usage of 0.1 g of dye per square foot of leather. The dyed leathers achieve the highest rub fastness grades. The exhaustion of dyestuff is almost 100%. The waterless dyeing process offers potential to save significant amounts of dyestuff and reduce wastewater emissions by 100%.

Leather‐Based Multi‐Stimuli Responsive Chromisms

AbstractLeather is made from the skin of animals and possesses special micro‐ and nanostructures. Due to the high breathability, durability, strength, elasticity, and softness, leather is widely used in daily life, and is an ideal substrate for future multi‐functional wearable smart devices. Herein, two leather‐based multi‐stimuli responsive chromic devices denoted as UV/thermo/electro chromic device and UV sensor are developed. The UV/thermo/electro chromic device demonstrates instantaneous and reversible chromic responses to applied UV radiation, heat, and electrical voltage with different color changing styles. The pattern design with the assistance of 3D printed molds and the broad selection of dyes/pigments endow the device with high design flexibility and wide applicability. The leather‐based UV sensor exhibits a change in color gradient when exposed to UV radiation with different intensities. For more versatile color options, inactive pigments/dyes can be mixed with stimuli‐responsive ones in this system. Coating the leather surface with a polyacrylic finishing agent is also conducted, which is a practical and effective method to protect the pigments and/or dyes in the leather, and improves the usability/durability of the devices. This study opens a new avenue to design and develop wearable devices and individual customization/anti‐counterfeiting of leather products.

Effect of CO2 laser treatment on the leather surface morphology and wettability

The aim of this research was to determine the influence of pulsed CO2 laser treatment on crust leather surface morphology and wettability. The obtained results revealed that pulsed CO2 laser engraving can be used as an effective tool for crust leather surface treatment. Pulsed CO2 laser treatment only negligible affects the macrostructure of leather, while the morphology and wetting of the leather surface after treatment were changed. It was found that an increase of laser pulses number increases the initial water contact angle value and intensifies the water droplet relaxation process. After laser treatment, the water droplet contact angle relaxation rate increases twofold compare to those for untreated leather. SEM micrographs showed increased defectiveness with rough surface patterns, thermally affected areas, and change of microstructure. The EDX analysis revealed that the engraved leather surface contains a significantly higher amount of carbon but smaller quantities of oxygen compared to those of untreated samples. It was found that only after laser treatment chromium and sulfur in the EDX spectra appear while for untreated samples these elements on the surface were not observed. The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements.

Multifunctional Leather Surface Design by Using Carbon Nanotube-Based Composites.

This paper deals with original research in smart leather surface design for the development of multifunctional properties by using multi-walled carbon nanotube (MWCNT)-based nanocomposites. The conductive properties were demonstrated for both sheepskin and bovine leather surfaces for 0.5% MWCNTs in finishing nanocompositions with prospects for new material design intended for flexible electronics or multifunctional leathers. The photocatalytic properties of bovine leather surface treated with 0.5% MWCNTs were shown against an olive oil stain after visible light exposure and were attributed to reactive oxygen species generation and supported by contact angle measurements in dynamic conditions. The volatile organic compounds’ decomposition and antibacterial tests confirmed the self-cleaning experimental conclusions. Ultraviolet protection factor had excellent values for leather surfaces treated with multi-walled carbon nanotube and the fastness resistance tests showed improved performance compared to control samples. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy analysis confirmed the influence of different leather surfaces on MWCNT dispersion with an effect on nanoparticle reactivity and efficiency in self-cleaning properties. Multifunctional leather surfaces were designed and demonstrated through MWCNT-based nanocomposite use under conventional finishing conditions.

Learning to Recognize Irregular Features on Leather Surfaces

As part of industrial quality control in the leather industry, it is important to identify the abnormal features in wet-blue leather samples. Manual inspection of leather samples is the current norm in industrial settings. To comply with the current industrial standards that advocate large-scale automation, visual inspection based leather processing is imperative. Visual inspection of irregular surfaces is a challenging problem as the characteristics of the abnormalities can take a variety of shape and color variations. The aim of this work is to automatically categorize leather images into normal or abnormal by visual analysis of the surfaces. To achieve this aim, a deep learning based approach is devised that learns to recognize regular and irregular leather surfaces and categorize leather images on its basis. To this end, we propose an ensemble of multiple convolutional neural networks for classifying leather images. The proposed ensemble network exhibited competitive performance obtaining 92.68% test accuracy on our own curated leather images dataset.

PH‐activated polymeric profragrances for dual‐controllable perfume release

AbstractDesign of controllable nanoprofragrances is critically challenging in cosmetic and decoration industries. Given that most profragrances based on physical encapsulation always suffer unreliable controllability, undefined loading efficiency, and poor stability, here we have for the first time constructed dual‐controllable profragrance platform based on pH‐activated polymer to achieve the specific pH‐triggered fragrance release, which consists of hydrophilic PEG unit, hydrophobic pH‐activated unit, and pH‐triggered unit, thereby guaranteeing profragrances with delicate controllability, homogeneous nanoparticles, well‐defined loading efficiency, and high stability. Dynamic laser scattering experiments demonstrate that the activated polymers possess excellent pH‐switchable property with high stability. Particularly, time‐dependent headspace release performance of all three profragrances is fitting to First‐Order kinetic model (R2 > 0.99). Finally, the step‐by‐step controllability of the profragrance platform with pH‐activated behavior and subsequently pH‐triggered release is realized both in aqueous solution and on targeted leather surface, which is highly desirable for the long‐lasting scent.

Bimetallic Copper–Iron Oxide Nanoparticle-Coated Leathers for Lighting Applications

Bimetallic nanoparticles are proven to show superior properties than those for monometallic nanoparticles owing to their additive features. Herein, we synthesized bimetallic copper–iron oxide nanoparticles using a simple chemical precipitation method followed by calcination at 500 °C. The calcined bimetallic nanoparticles are spherical with a size of 54 ± 9 nm and possess both electrical conductivity and ferromagnetic properties. We further coated them on the surface of the leather to form the first-ever reported electrically conductive and magnetically active bifunctional leather. The existence of coated bimetallic nanoparticles with the poly(vinyl alcohol) dispersion noticeably seen on the grain surface of the leather up to 15.7 ± 0.8 μm thickness through the high-resolution scanning electron microscope. The developed bimetallic nanoparticles coated leather surface exhibited an excellent electrical conductivity of 4.7 × 10–4 S/cm and a saturation magnetization of 0.6 emu/g. We further demonstrated the applications of bifunctional leathers for advanced products such as operating the touch screen device and magnetic controlled switch appliances.

Investigation of Flame Retardant Effects of Resins on the Flammability of Leather

Natural leather products, which are by-products of the meat industry, are used because of their high air vapor permeability and elegant appearance compared to synthetic leather. The production of flame retardant leather is important for some leather types such as motorcyclist jackets, flight or automotive upholstery leathers, military boots. It is frequently mentioned in the literature that resinous chemicals create flame retardant effects in textile materials due to their nitrogen content. Urea, melamine and dicyandiamide resins are always used in the traditional retanning process of cattle leathers. It has been investigated which of these resins has the highest flame retardant effect on the leather. In the study, 2%, 3% and 4% ratios were studied for these three resins; flame resistance of the leathers were investigated by LOI and TGA analysis. The study also examined the chemical effects of resins on the leather surface with FTIR and SEM analyses.

Enhancement of multifunctional properties of leather surface decorated with silver nanoparticles (Ag NPs)

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Selective degradation and oxidation of hemicellulose in corncob to oligosaccharides: From biomass into masking agent for sustainable leather tanning

Chrome-free metal tanning agent has been considered as eco-friendly in the leather industry. However, extensive crosslinking reactions of metal species on the leather surface restrain their uniform penetration into the hierarchical nanoscale leather matrix. Thus, masking agents with appropriate coordination ability are needed. Herein, the selective degradation of hemicellulose in corncob was achieved with 92.5% of conversion in an AlCl3–H2O system, obtaining oligosaccharides masking agent with high purity and leaving cellulose and lignin in the solid residue for other valuable use. Subsequently, H2O2 oxidation was performed to introduce –CHO/–COOH into oligosaccharides and reduce their molecular weights, thereby enhancing coordination ability and reducing ligand dimension. The post-oxidized reaction fluids together with additional Zr species were subjected to leather tanning, in which the oligosaccharides could coordinate with Al/Zr species and promote the penetration of metal species into the leather matrix. By controlling the hemicellulose degradation and oligosaccharide oxidation, an appropriate concentration of oligosaccharides with proper –CHO/–COOH contents allowed the efficient masking effect of the oligosaccharides. As a result, a uniform distribution of Al/Zr species was observed on the cross section, and 83.5 °C of shrinkage temperature was obtained for the chrome-free tanned leather.

A waterborne polyurethane–based leather finishing agent with excellent room temperature self-healing properties and wear-resistance

Water-based polymers have been widely used in coating materials, but their durability and service life are often greatly reduced due to macroscopic damage or cracking caused by external forces. In this paper, poly(propylene glycol) terminated with ortho-amiomethylphenyl diboronic acid (AMPBA-PPG) and cross-linked polymer containing boroxine (CLP-boroxine) were synthesized by nucleophilic substitution. Then the CLP-boroxine was introduced into waterborne polyurethane (WPU) to prepare AMPBA-PPG/WPU composite emulsion for leather finishing and CLP-boroxine/WPU composite film. The self-healing characterization results showed that the self-healing efficiency of the 15 wt% CLP-boroxine/WPU film was as high as 93.6% after only 4 h of water stimulation at room temperature. Compared with neat WPU finished leather, the leather samples finished with AMPBA-PPG/WPU exhibited more excellent wear-resistance. More importantly, the leather coating finished with AMPBA-PPG/WPU still showed nice wear-resistance even after wear and self-healing treatment. These results are attributed to that the hydrogen bonds between AMPBA-PPG and WPU, WPU, and WPU, and the dynamic reversible covalent bonds in AMPBA-PPG can improve/increase the self-healing efficiency of the composite coating. In addition, the boron hydroxyl groups in AMPBA-PPG could also react with the hydroxyl groups on the leather surface, thereby further improving the wear-resistance of the leather coating. Dynamic boronate ester bonds can not only endow WPU excellent self-healing properties but also improve wear-resistance of its leather coating.

Modification of Leather Surface Using Low-Pressure Plasma and Antimicrobial Reagent

Investigations, which are related to plasma efficiency on the treated leather surface, are significant in the development of ecologically and economically friendly processes in obtaining material of desired functional properties. Through the pretreatments using plasma different chemical-physical reactions in the surface layer of treated leather are occurred resulting in improved reactivity. In this paper, modification and functionalization of bovine leather using 1,2,3,4-butantetracarboxylic acid and chitosan were explored. Pretreatments of leather samples were realised using argon and oxygen plasma to assess various influence of chemically reactive oxygen and inert argon gas. Two different bovine leathers -chrome tanned leather and leather tanned with synthetic tanning agent (Cr-free) were chosen for treatments. Analyse of the surface morphology was conducted with SEM microscopy, while the chemical changes using ATR-FTIR spectroscopy. Antimicrobial effectiveness of treated leather was tested with qualitative Agar diffusion plate test against two bacterial Staphylococcus aureus and Klebsiella pneumoniae. Obtained results indicated how applied oxygen and argon plasma pretreatments in optimized process conditions contribute to the improvement of tested functional properties. Achieved surface changes positively affected on leather surface reactivity and antimicrobial effectiveness, particularly Cr-free leather.

Perceptron Neural Network Based Machine Learning Approaches for Leather Defect Detection and Classification

Detection of defects in a typical leather surface is a difficult task due to the complex, non-homogenous and random nature of texture pattern. This paper presents a texture analysis based leather defect identification approach using a neural network classification of defective and non-defective leather. In this work, Gray Level Co-occurrence Matrix (GLCM) is used for extracting different statistical texture features of defective and non-defective leather. Based on the labelled data set of texture features, perceptron neural network classifier is trained for defect identification. Five commonly occurring leather defects such as folding marks, grain off, growth marks, loose grain and pin holes were detected and the classification results of perceptron network are presented. Proposed method was tested for the image library of 1232 leather samples and the accuracy of classification for the defect detection using confusion matrix is found to be 94.2%. Proposed method can be implemented in the industrial environment for the automation of leather inspection process.

THE USE OF Cyperus kyllinga EXTRACT IN SYNTHESIS OF SILVER NANOPARTICLE TO ENHANCE QUALITY OF GOAT LEATHER

Improving leather quality with antifungal, antibacterial, and superior mechanical properties is an ongoing effort. The objectives of this research were to synthesize silver nanoparticle using Cyperus kyllinga extract as a bio-agent and to deposit synthesized silver nanoparticle into goat leather by ex situ and in situ, and also to characterize the properties of antibacterial, antifungal, mechanical, and contact angle of goat leather before and after modification. Preparation of silver nanoparticles by reduction method by adding Cyperus kyllinga’s leaf extract. The silver nanoparticle was characterized by using spectrophotometer UltraViolet-Visible and Particle Size Analyzer. The addition of Methyltrimethoxysilane (MTMS) compound on the leather sample to know hydrophobicity properties of the leather. The leather was modified by adding silver nanoparticle and silane compounds. The antibacterial and antifungal test was conducted by the diffusion method and tested the significance by using statistical analysis. The mechanical properties were tested through tensile strength test, elongation, and also modulus Young by using a tensile tester. The modified goat leather surface was tested the contact angle by using the sessile drop method. The characterization results indicated that silver nanoparticles were formed at a wavelength of 406.60 nm, with their particle size were 200.1 nm. The results of the antimicrobial test showed that modified goat leather using two methods of preparation had a different significance to inhibit the S. epidermidis and E. coli, and also fungi of C. albicans. The leather, after modification with nanoparticle via in situ method, had the highest antibacterial activities against S. epidermidis and E. coli. However, leather after modification with adding nanoparticle and MTMS via ex situ method has the highest antifungal activity against C. albicans. The leather after modification nanoparticle and MTMS via in situ method has the highest tensile strength and the largest toughness. All modified leathers had larger antimicrobial activity, contact angle, and also toughness compared to unmodified leather.

Spectrophotometric characterization of plasticizer migration in poly(vinyl chloride)-based artificial leather

Plasticized polyvinyl chloride (PVC) is one of the most commonly used material in the manufacture of artificial leather because of its flexibility, high durability and low cost. While hundreds of plasticizers have been produced to obtain PVC films and artificial leathers, it is important to choose the correct plasticizer to produce the desired products. Therefore, here five non-phthalate type plasticizers with three levels (40 phr, 60 phr and 80 phr); trioctyl trimelliate (TOTM), tributyl trimelliate (TBTM), dioctyl terephthalate (DOTP), dioctyl adipate (DOA) and dioctyl succinate (BIO) were used to prepare plasticized PVC films. They were studied in terms of their compabilities with PVC polymer chains, and their effects on mechanical properties of PVC films. Although, linear plasticizers e.g. BIO and DOA have higher compabilities with PVC, a branched plasticizer e.g. TOTM showed higher mechanical properties. Moreover, a new spectrophotometric method for determination of plasticizer migration from PVC polymer matrix to the surface of artifical leather was developed. According to lightness change on the surface of PVC artifical leather before and after heat treatment at 70 °C, the migration rates of used plasticizers increase in this order: TOTM < TBTM < DOTP < BIO < DOA.

Vision based inspection system for leather surface defect detection using fast convergence particle swarm optimization ensemble classifier approach

Surface defect inspection plays a vital role in leather manufacturing. Current practice involves an expert to inspect each piece of leather individually and detect defects manually. However, such a manual inspection is highly subjective and varies quite considerably from one assorter to another. Computer vision system for natural material like leather is a challenging research problem. This study describes the application of computer vision system to capture leather surface images and use of a novel Fast Convergence Particle Swarm Optimization (FCPSO) algorithm on a set of handcrafted texture features viz., GLCM and classified using supervised classifiers viz., Multi Layer Perceptron (MLP), Decision Tree (DT), SVM, Naive Bayes, K-Nearest Neighbors (KNN) and Random Forest (RF). FCPSO using modified fitness function by selective band Shannon entropy is implemented to segment industrial leather images. Segmentation efficiency of the proposed FCPSO algorithm is evaluated and its performance is compared with other optimization algorithms. Efficiency of the segmentation algorithms is evaluated using performance measures such as average difference (AD), Area Error Rate (AER), Edge-based structural similarity index (ESSIM), F-Score, Normalized correlation coefficient (NK), Overlap Error (OE), structural content (SC), Structural similarity index (SSIM) and Zijdenbos similarity index (ZSI). Correlation of the segmented area using FCPSO with the experts’ ground truth is found to be high with R value of 0.84. Feature extraction is carried out using GLCM texture features and the most prominent features were selected using statistical t-test and correlation coefficient. Experimental results showed encouraging results for random forest classifier confirming the potential of the proposed system for automatic leather defect classification.

Enhancement of antimicrobial properties of shoe lining leather using chitosan in leather finishing

In this study, a chitosan based coating method was developed and applied on the shoe lining leather surface for evaluating its inhibition to bacterial and fungal attacks. At first, chitosan was prepared from raw prawn shells and then the prepared chitosan solution was applied onto the leather surface. Secondly, the characterization of the prepared chitosan and chitosan treated leather was performed by solubility test, ATR-FTIR, XRD pattern, SEM and TGA. Evaluation of antimicrobial efficacy of chitosan was assessed against two gram positive, two gram negative bacteria and a reputed fungi by agar diffusion test. The results of this study demonstrated that chitosan took place in both the surface of collagen fibres and inside the collagen matrix of crust leather. The chitosan showed strong antimicrobial activities against all the tested microorganisms and the inhibition increased with increasing percentage of chitosan. Therefore, the prepared chitosan in this study can be an environment friendly biocide, which functions simultaneously against different spoilage bacteria and fungi on the finished leather surface. Thus by using the prepared chitosan in shoe lining leather, the possibility of microbial attack during shoe wearing can be minimized which is one of the important hygienic requirements of footwear.

Optimized Fuzzy C-means Clustering Methods for Defect Detection on Leather Surface

In this paper, captured images are segmented for the defective part, that is used for the further process of grading the quality of the products using automated inspection systems employed in industries such as leather, fabrics, textiles, tiles... etc.. These industries are the greatest conventional industries that need automatic detection systems as a basic part in diminishing investigation time and expanding production rate. Initially in this work, the input image is wet blue leather fed into a contrast enhancement process that improves the visibility of the image features. This contrast-enhanced image is employed with segmentation process that utilizes Fuzzy C-means algorithm (FCM) technique. This paper proposes two different optimization techniques, Grey Wolf Optimization (GWO) & Monarch Butterfly Optimization (MBO) for executing centroid optimization in FCM and results are compared with Modified Region Growing with GWO of leather segmentation method. The results exemplify that incorporation of optimization technique with FCM has a quite evident impact on segmentation accuracy of 96.90% over context techniques.