A brief description of the VOC test method in the coating

0 Introduction
VOC is an abbreviation for Volatile Organic Compound (Volatile Organic Compound), and the current internationally common definition of VOC in coating products refers to any organic liquid or solid that evaporates itself at normal temperature and pressure in the atmosphere in contact with the coating product. VOC is a class of organic pollutants that are common in indoor and outdoor air and have complex parts.
Its outdoor sources are mainly automobile exhaust and exhaust gases released by industrial enterprises, and indoor sources include: building materials, interior decoration materials, organic coatings, cleaning products, as well as spices, deodorants, etc., the emergence of these items caused indoor air pollution, and they are in trace and trace
China
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VOC mostly contains odorous groups, such as carboxyl, carbide, hydroxyl, etc., both to the air odor pollution, but also harmful gases, can directly endanger human health. VOC is mostly fat-soluble solvents and thinners, it is easy to breathe through the lungs, blood and into the nerve center, and then the central nervous system has a strong anaesthetic effect, at this time the human body will show trance, drowsiness, if inhaled VOC too much, there will be dizziness tinnitus, pale, nausea and even muscle spasms and other systemic symptoms. Studies have shown that headache, drowsiness, fatigue, and mental disorders can occur when exposed to a VOC mixture at a concentration of 25 μg/m3, and coma, convulsions, or even death when the concentration reaches 35,000 μg/m3.
long-term exposure to VOC, easy to lead to a variety of chronic diseases and malignant tumors, such as memory loss, neurological weakness, asthma, and so on, serious and even cause fetal malformation, leukemia, cancer. Because volatile organic compounds cause harm to people's health, it is the key to current scientific research. Therefore, in-depth study of VOC pollution is of far-reaching significance to improve indoor air quality and improve people's health.
in order to reduce the harm and pollution caused by VOC, some developed countries abroad are committed to low VOC products research, promote zero VOC has a history of more than ten years, and products have come out. In 2001, China set mandatory limit standards (GB18582-2001) for VOC content of interior wall coatings, and in 2005 introduced a new environmental protection industry standard (HJ/T201-20) 05) In 2008, a newly revised mandatory limit standard GB18582-2008 was promulgated, which put forward higher requirements for VOC content in water-based coatings, and the implementation of these standards has promoted the development of china's domestic wall coatings in the direction of harmless.
At present, there are some domestic scientific research institutions, production enterprises are also developing low VOC and zero VOC latex paint, some have made a breakthrough, the market appears more and more low VOC content latex paint, for these low VOC or even zero VOC latex paint, according to the original standard detection VOC results error is very large, and when the paint products VOC content is low measurement error is large.
So choose a suitable method to accurately represent the VOC content in coating products is currently to solve the problem, research out the simple operation, high sensitivity, high accuracy of indoor air volatile organic compounds detection technology, the system to carry out indoor volatile organic compounds pollution factors, distribution laws and pollution control work, and constantly improve pollution monitoring and control levels, thereby improving the air quality of the human living environment.
of the 1 VOC testing method
different ranges of VOC content of coating products can be used to determine their VOC content. With the progress of science and technology, more and more low VOC content of coatings and resin emulsions appear on the market, which requires the detection of low VOC content, small measurement error methods.
, there are four commonly used international standards for determining VOC content:
ISO11890-1, color and varnish - determination of volatile organic compound (VOC) content - Part 1: Difference method. When the VOC content in the expected coating products is greater than 15% (mass fraction), the method of ISO11890-1 can be used.
method is mainly used for the voC content of conventional solvent-based coating products inspection, the following ASTMD3960-02 method is basically consistent in principle. The principle is that the various parts of the coating product are mixed according to the correct mass ratio or volume ratio, and if dilution is required, diluted with a suitable thinner, as a backup sample for determination. The non-volatile content, water content and exempt compound content in the spare sample were determined separately, and the VOC content was calculated using a suitable formula.
ISO11890-2, color paint and varnish - determination of volatile organic compound (VOC) content - Part 2: gas chromatography. When the expected VOC content in coating products is between 0.1% and 15% (mass fraction), is expected to be determined by ISO11890-2. This method is mainly used for the testing of coating products with low VOC content, such as high solid sub-coating products.
the principle is that the various parts of the coating product are mixed according to the correct mass ratio or volume ratio, and the organic volatiles and exempt compounds in the spare sample are isolated by gas chromatography technology. The volatiles in the spare sample (including organic volatiles and exempt compounds) are qualitatively analyzed, and then the amount of each organic volatile and exempt compound in the spare sample is quantified using the internal standard method at the peak area value. The water content in the sample is determined by an appropriate method and the VOC content in the coating product is calculated using a suitable formula.
ISODIS17895, color paint and varnish - water-based latex paint in the determination of the content of volatile organic compounds, that is, the top air sample method to determine VOC. When the expected VOC content in coating products is between 0.01% and 0.1% (mass fraction), it can be determined by this method, the boiling point of volatile organic compounds determined by this method can be as high as 250 degrees C, mainly used to determine the VOC content in water-based latex paint samples with very low VOC content. The principle is: with the diaphragm closed vial of the top empty sampler sample, and the best with automatic sample converter gas chromatography to analyze.
when the sample is heated to 150 degrees C, the volatile organic compounds are fully vaporized and transferred to the non-polar capillary separation column, with the retention time of the octane (boiling point 252.6 degrees C) as the integral end point, and the peak area integral of all the parts before the integral end point. By measuring the diluted sample without the reserve mixture and the 4 diluted samples containing different mass fractional reserve mixtures, the peak area of the sample was calibrated to 1 mg, and the amount of the added reserve mixture was calculated linearly by the average, and the VOC content in the sample was calculated by the slope of the regression line and the distance of the straight line in ordinates.
assTMD3960.02 to determine the content of volatile organic compounds (VOCs) in color paints and related coatings.
At present, the methods of more accurate analysis of VOC are: gas chromatography (GC), gas chromatography-mass spectrometrometrometrometration (GC-MS), fluorescent spectrophotography and membrane import mass spectrometrometromety, and so on, in addition to reflection interference spectroscopy, offline supercritical fluid extraction-GC-MS method, and pulse discharge detector method, the most used are GC and MS.
E.g. Zhang Lin, using adsorption-pyration/GC-MS method to determine the office, school classrooms and residential 3 kinds of typical indoor environment closely related to people VOC, found that indoor smoking and decoration of higher degree of places than non-smoking and The aromatic hydrocarbon pollution in the simple decoration site is serious, Chen Yudong and so on, through the experiment found that the room decoration materials (especially the plate containing acetaldehyde resin adhesive, coatings and polyurethane paint, etc.) a large number of use of a variety of
VOC, resulting in the bedroom air formaldehyde, benzene, xylene and other serious excess standards.
and analysis of complex unknown samples of VOC
by 2 gas chromatography is one of the hot spots and difficulties in analytical chemistry. Gas chromatography is the most commonly used tool for the analysis of volatile substances and is a basic separation method used in association with mass spectrometrometromety, infrared, etc. Volatile organic matter analysis occupies an important position in environmental research and evaluation, and many toxic organic matter is volatile.
45, or 40 percent, of the 114 organic priority detections specified by the EPA in the United States. Gas chromatography is almost the only method of separating and analyzing this type of group of parts.
gas chromatography is mainly the use of the material boiling point, polarity and adsorption properties of differences to achieve the separation of mixtures. Gas chromatography can measure the low mass fraction VOC according to the reserved value for qualitative analysis, or through peak area for quantitative analysis. Qualitative analysis of gas chromatography can be qualitative by using known pure substance control, or by using literature such as relative retention values and retention indices, and by means of methods used in association with other instruments.
gas chromatography separates the mixture into a single pure component, while infrared, mron magnetic resonance, mass spectrometrometromety, etc. can identify the structure of unknowns, but requires the identified unknowns to be pure components. Therefore, the use of these two methods, to play their respective strengths, is the most effective means to solve the problem of the characteristics of the unknown.
analysis of gas chromatography, the peak area ratio is usually used. Common quantitative methods are:
(1) external labeling method (standard curve method), its advantages are simple to operate, easy to calculate, the stability requirements of the sample technology and chromatography conditions are higher
; The advantages of the internal standard method is quantitative accuracy, operating conditions do not have to be strictly controlled, the amount of sample does not have to be very accurate, the disadvantage is that each analysis, the specimen and the internal subject matter should be accurately weighed
; The normalization method requires all the parts in the sample to peak, and the correction factor of each part is known or measured, and the sample in the coating analysis is more complex, there may be unrecognized impurity peaks in the solvent, so it is not suitable for coating analysis
; The content of the sample to be measured in the original sample can be calculated by adding to the sample the increase in the peak area of the sample caused by the substance to be tested.
need to be noted that the addition of substances to be tested can not make the substation change, otherwise it will affect the activity coefficient of the parts to be tested, destroy its quantitative relationship, and obtain incorrect quantitative results. The sample preparation process of standard addition method is similar to that of internal standard method, but the calculation principle comes entirely from the outer standard method, and the quantitative precision of standard addition method should be between the internal standard method and the outer standard method. For the complex multi-component VOC system in latex paint, the VOC in latex paint is divided into two parts: low boiling point VOC component and high boiling point VOC component. The qualitative and quantitative analysis methods used by the two are different.
the use of gas chromatography to determine VOC, the choice of detector, the choice of column, the choice of sample method, the choice of chromatography conditions, the determination of initial operating conditions and other factors will affect the results of detection and the selection of detection methods. The core of gas chromatography is the column, and the color column temperature directly affects the distribution coefficient K between fixed phase and flow phase, so the choice of column temperature is one of the most important issues in gas chromatography analysis. The selection principle of column temperature is: under the premise that the hard-to-separate parts are well separated, the retention time is suitable, and the chromatography peak is not tailed, the low column temperature is used as far as possible.
, the choice of column temperature must also take into account the boiling point of the test. The mixture with a high boiling point uses a higher column temperature and, conversely, a lower column temperature. Gas chromatography conditions depend on the product being analyzed, and different samples should be conditioned with a known mixture. The sample volume and se through ratio should be adjusted to a sample volume not exceeding the column capacity, and the response signal is within the linear range of the detector.
, the standardized demand for the quality and testing methods of coating products at home and abroad has greatly promoted the application of gas chromatography technology in coatings.
3 Conclusions
VOC test methods in several coatings described in this paper are the basis and international standards of VOC testing. The gas chromatography method plays an important role in VOC determination because of its high detection sensitivity and wide application range. Reducing VOC is the direction of the development of coatings, for which China has invested a lot of manpower and material resources, especially in terms of standards has been to the international standard ISO14020 march. To this end, researchers should carry out in-depth research work in line with national initiatives.