The current international leather identification method is the microscope method, and the standard adopted is ISO 17131:2012. However, this method only provides a mirror image of the cut surface of the specimen including cow, sheep, pig, goat and other leather. my country's national standard is compiling a leather identification method based on the microscope inspection method on the basis of ISO17131. In addition to the microscope method, sensory identification methods are currently used in the industry. This method mainly relies on the knowledge and experience of the appraisers on animal fur. The test
results are subjective and no specific reference standards have been issued. In addition, infrared spectroscopy and DNA identification methods are also being developed in the industry. This article briefly introduces the above identification methods. Infrared spectroscopy Infrared spectroscopy utilizes the difference in the types and composition ratios of amino acids in the leather, and irradiates the surface of the leather sample with continuous wavelength infrared light to cause the transition between molecular vibration and energy level, and obtain different patterns in the infrared absorption spectrum. . However, the actual test results show that for common pig, cow, sheep, horse and other leathers, the content of carbon, hydrogen, nitrogen, oxygen, sulfur and other elements in collagen and the composition of amino acids are relatively close, and the infrared spectrum shows similar laws. , It is difficult to distinguish. In addition, more chemical reagents will be added during leather processing, and the coating of the leather surface will cause greater interference with the infrared spectrum, so this method is still in the exploratory stage in the identification of finished leather. Sensory Appraisal Method Sensory Appraisal Method is a traditional method, simple and fast, but it requires rich experience. Generally, the color, characteristic pattern, arrangement characteristics and thickness of pores, texture shape, thickness of leather fiber and leather quality are observed by human eyes. Texture, including smell when burning. However, sensory detection is easily affected by the environment and season where the animal grows, and even the gender and age of the animal itself. The thickness of the skin, the thickness of the skin fiber, the hair density, the hair length, and the lubricity of the same species are often different, and this Will affect the final appraisal result. On the other hand, with the development of modern animal husbandry, the requirements for the appraisal personnel are getting higher and higher for the selection of many furs through hybridization technology. The sensory identification method is suitable for the identification of whole leather or fur products, and the producer can distinguish leather species through this method at the stage of purchasing the leather. For small-area finished leather products, because of the different skin locations of the same species of leather, the appearance of the leather varies greatly, so it is relatively difficult to detect. At present, two new landmarks under review in Guangzhou-DB 44/T 1358-2014 'Method for Identification of Natural Leather Material' and DB 44/T 1359-2014 'Method for Identification of Transfer Film LeatherTo identify natural leather materials. This method provides a variety of leather sensory characteristics and micro-morphological characteristics of grain and cross-sectional maps. The inspectors identify the morphological features and mirror images between the standard physical samples and the samples. DNA identification method DNA identification method mainly develops a qualitative PCR detection method, which is suitable for qualitative PCR detection of animal-derived ingredients in natural leather products. This method extracts animal-derived DNA in leather products, designs primers for the specific gene sequence of the species, and obtains the gene sequence of the target species by PCR amplification of the mitochondrial endogenous gene. According to the amplified product, fluorescence quantitative PCR method or sequencing comparison is used And other molecular biotechnology to determine leather animal-derived ingredients. DNA identification method is not suitable for regenerated leather, artificial leather, synthetic leather, and has certain requirements for the extracted leather DNA. However, leather products undergo acid hydrolysis, alkali treatment, tanning, and dyeing during processing. Cells in skin tissues are destroyed, DNA degradation is serious, and genetic material content is low. At the same time, tanning agents form covalent cross-links between DNA, DNA and protein, making the separation and extraction of DNA more difficult to achieve. However, some leathers use metal salt tanning agents, which have a strong inhibitory effect on enzymes, and make subsequent Molecular amplification is difficult to perform. Therefore, optimizing the extraction method to increase DNA concentration and purity is the key to identification. Leather microscope identification method (ISO 17131:2012) leather microscope identification method compares the cross-section of the material under a microscope or electron microscope image, and the cross-sectional mirror image of a known type of leather specimen, and observes leather board fibers, man-made materials and textile materials The morphological characteristics of the test sample to identify the material of the test sample. This method is mainly used to identify leather, reclaimed leather, artificial leather, and imitation leather microfiber cloth. The equipment used is an optical microscope and a scanning electron microscope, which need to be magnified at least 20 times, and some materials must be magnified at least 500 times. You can spray a suitable coating of electrons or metal particles to obtain a clearer SEM image. However, the standard only provides cowhide (picture 1), sheepskin (picture 2), goat skin (picture 3), pigskin (picture 4), cow suede leather, microfiber cloth, PVC synthetic material, PU synthetic material, leather Fiberboard, as well as some textile materials laminated leather fibers, synthetic materials laminated leather fibers. The mirror image of leather types is relatively limited, so this method is mainly used to distinguish leather from other materials, and is not suitable for biological species identification of leather materials.
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