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    Home > Coatings News > Paints and Coatings Market > Advances in the detection and detection of toxic and harmful elements in coatings

    Advances in the detection and detection of toxic and harmful elements in coatings

    • Last Update: 2020-11-28
    • Source: Internet
    • Author: User
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    Paint, as a functional material for anti-corrosion protection, is widely used in ships, automobiles, machinery manufacturing, construction and other fields of the national economy, almost every corner of people's daily life. In 2009, China's paint production has leapt to the top of the world, becoming a veritable paint production and consumption of large countries. With the expansion of coating applications and people's awareness of health and environmental protection, the safety of coatings has been more and more attention, laws and regulations and standards have been issued at home and abroad to control the use of various harmful substances in coatings, including toxic and harmful elements on human health and environmental impact has been widely concerned and studied
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    harmful elements in the coating through direct contact with the human body during the use of the paint, as well as biological accumulation through the food chain into the human body, and accumulated in the human body, resulting in varying degrees of poisoning. Such as lead will cause damage to the human blood system and nervous system, children's health and intellectual growth and development of more serious harm, hexavalent chromium can destroy the normal function of enzyme systems and cells, arsenic and so on in the human body has a clear accumulation effect, resulting in organ damage.
    1 The source of harmful elements in coatings and the current control type
    infecting elements in coatings are mainly from a variety of raw materials used in the production of coatings, such as various pigments, additives, etc. will bring a variety of elements. Because the toxicity of the element is related to its form, concentration and price state, the soluble element and the total amount of element are generally required in the relevant regulations and standards of the coating. At present, many regulations and standards at home and abroad have clear requirements for the limits of harmful elements in coating products, such as the European Union WEEE and ROHS Directive on lead, cadmium, mercury, hexavalent chromium 4 substances to limit requirements, the latest revision of the U.S. toy safety standards consumer safety regulations (ASTM F 963-2008) Not only limits the soluble lead, cadmium, chromium, mercury, vanadium, arsenic, vanadium and selenium in toy coatings, but also further limits the total lead content in toy coatings.
    China began to implement the solvent-based wood coating and interior wall coating in 2001 harmful substances limit standards, soluble lead, cadmium, chromium, mercury 4 substances to control, in order to deal with ROHS directive requirements and international trade barriers, the introduction of electronic information products pollution control management measures and corresponding support standards, the harmful heavy metal content control put forward clear requirements. In recent years, we have formulated and implemented the limit of certain harmful elements in the paint of consumer products in contact with human body (GB/T 23994-2009), the limit of harmful substances in automotive coatings (GB 24409-2009), the limit of harmful substances in toy coatings (GB 24613-2009) and other series of standards to further strengthen the control of harmful elements in paint products to protect the environment and human health.
    2 Overview of harmful element determination methods in coatings
    Due to the generally low content of harmful elements in coatings, coupled with the presence of a large number of organic substances in the coating, proper pre-treatment must be carried out before analysis, common pre-treatment methods are acid solution, high temperature graying method, wet acid dissolution method, high-pressure dissolving method, alkaline dissolving method, microwave desmodation method and alkali melting method. At present, the detection methods of harmful element content in coatings are spectrophotography, atomic absorption spectroscopy (AAS), inductively coupled plasma emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometrography (ICP-MS), atomic fluorescence spectroscopy (AFS) and X-ray fluorescence spectroscopy (XRF). Harmful element detection can be divided into soluble element detection and element total detection, the purpose of testing also determines different pre-processing methods and analysis methods.
    2. 1 Sample pre-treatment
    coating sample pre-treatment is one of the most labor-consuming and time-consuming parts of the testing work, and has a direct impact on the accuracy of the test results, to a considerable extent, is the key to control the accuracy of the test. In the analysis of harmful elements in coatings, it is necessary to select the appropriate pre-treatment method according to the physical and chemical properties of the samples and target elements to be tested, and with the development of instrument analysis technology, the pre-treatment technology of samples is also moving towards simplicity, speed, efficiency and automation. The pre-treatment of soluble element analysis in coatings is to simulate the conditions of human stomach acid to dissolve the corresponding elements in the coating, usually the paint sample crushed and milled fine, at a constant temperature of 37 degrees C with 0. 07 mol /L hydrochloric acid solution is soaked for a certain period of time, so that soluble elements are transferred to the solution, and then analyzed with instruments such as AAS, ICP-OES, or ICP-MS.
    many standards at home and abroad are required for soluble heavy metals, can be referred to as: EN71 - 1, GB 18582 -2008, GB 24613 - 2009 and so on. There are many pre-test processing methods for the total amount of elements in the coating, unlike soluble element extraction, the total amount of elements test to extract all the target elements, the commonly used methods as described earlier. High temperature graying method as a classic sample pre-treatment method, widely used in the coating industry, many domestic and foreign standards are using this method, the paint sample evaporated to dry at a temperature of about 500 degrees C graying, so that the sample contains organic matter decomposition volatilization, the method has the advantages of unlimited sample size, but volatile metals easy to lose, recovery rate is relatively low. Wetting acid is also one of the commonly used methods of pre-treatment, using different acids and hydrogen peroxide and other reagents to work together to dissolve the destruction of organic matter in the paint sample, compared with dry graying, wet method of dissolving is not easy to lose metal elements, equipment is relatively simple, the deficiency is the amount of acid, perchloric acid and other polyic acid mixed with organisms coexist with the risk of explosion. Alkaline dissolving method is suitable for quantitative determination of hexavalent chromium in coatings, alkaline extract is beneficial to reduce the mutual redox reaction between hexavalent chromium and trivalent chromium, the extraction effect is better than acid solution. High-pressure antidote method is widely used in the extraction of hazardous substances in electrical and electronic equipment samples, but also for the extraction of heavy metals in coatings, sample processing is relatively thorough, suitable for simultaneous processing of large quantities of samples, but the processing cycle is slightly longer. Alkaline melting method is mainly used for decomposition of inorance samples, is one of the most commonly used methods for the dissolving of geological mineral samples, can be used in coating pigments, fillers and other mineral varieties of the solution. Microwave excretation method is an effective method of dissolution which has been developed and applied in recent years, which makes the dissolution and chemical reaction of samples easier, reacts more quickly, and can effectively avoid the loss of volatile trace elements in samples.
    2. 2 Instrument analysis and detection techniques for harmful elements Overview
    hydrolight method as one of the classic analytical methods, is to paint samples after processing to add different color agents and elements to be tested, form complexes or other colored substances and determine their absorbance, according to the absorption and concentration of elements to be measured linear relationship. This method is used in many standards for heavy metal analysis, such as soluble lead in varnishes and paints, hexavalent chromium, etc. Because many metal elements are close in nature and some color agents have poor selectivity, the application of spectroscopic photometelectricity method is limited, and with the maturity of new instrument analysis technology, other traditional element analysis is more inclined to choose atomic absorption spectroscopy or emission spectroscopy.
    atomic absorption spectroscopy (AAS) has been developed to date, the instrument is relatively simple, with high sensitivity, low detection limit, fast analysis speed and wide range of applications and other advantages. The detection limit of the flame atomic absorption method can be up to × 10 - 9 levels, and the detection limit of the graphite furnace atomic absorption method can reach 10 - 10 to 10 - 14 g. The relative standard deviation of the flame atom absorption method for determining medium and high content elements can be less than 1%, and the analytical accuracy of the graphite furnace atomic absorption method is generally about 3% to 5%. At present, AAS has become a conventional technique for elemental content analysis, with more than 70 measurable elements, adopted by many domestic and foreign standards, and has become almost one of the necessary analytical methods in modern laboratories. WANG Z H and others studied cadmium in spectroscopic paint with temperature-controlled graphite furnace atom absorption, and its detection limit reached 9. 6 ng /L.
    Xiao Leqin and others discussed the dry ash method digestive coating samples, graphite furnace atomic absorption spectroscopy to determine lead in the paint, the results of the paint sample RSD of 1.3%, the mark-up recovery rate of 99.2% to 102.1%, obtained good accuracy and precision. Xia Zhengbin et al. used mobile injection hydrogenation to measure As, Sb, Se and Hg in the coating by atomic absorption spectroscopy, and the sample mark-up recovery rate was 98. 9% to 101. 6%, 99. 0% to 102. 6%,99. 2% to 101. 4% and 99. 1% to 101. 3%。 AllabashiR(7) compares the differences in element selenium in the FI-HG-AAS, ET-AAS, HG-ET-AAS 3 methods. The determination of copper, nickel, cobalt and lead ions was studied using pre-concentration-flame luminosity. Fabrinar SBentlin and others have studied the direct analysis of trace elements in high-viscosity liquid paints using graphite furnace atomic absorption spectroscopy. The deficiency of atomic absorption spectroscopy is that it is difficult to measure multiple elements at the same time, the sensitivity of some elements is not satisfactory, the interference with complex sample analysis is also serious, and the reproducible is relatively poor.
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