VOC detection of automotive interior materials in China

Abstract: in recent years, automobile has become an indispensable part of people's daily life, but the air pollution in the car seriously threatens human health, and the main factor causing air pollution in the car is the volatilization of harmful gases in the interior materials of the car. This paper analyzes the status quo of VOC testing standards in China, and introduces the existing VOC detection methods of automotive interior materials from the aspects of principle and test process. The advantages and disadvantages of each method and the applicable scope are discussed, which provides theoretical reference for the correct selection of the appropriate testing methods.

With the improvement of living standard in recent years, people's environmental awareness is becoming stronger and stronger, so more and more attention has been paid to the air quality in the car. The main factors affecting the quality of the vehicle are volatile organic substances released by automobile parts and interior materials, namely VOC (volaile organic components), which mainly include benzene, toluene, xylene, ethylbenzene, styrene, formaldehyde, acetaldehyde, etc. [1]. VOC pollution in automobiles mainly comes from automobile parts and interior materials. When the temperature in the vehicle is high, these harmful substances will be released. When VOC reaches a certain concentration, it will cause headache, nausea, physical weakness and other symptoms. When it is serious, it will even damage the human system, cause memory loss, and even cause cancer. Therefore, it is very urgent to comprehensively manage it, More and more countries have also issued corresponding standards.

01 the status of VOC testing standards for automotive interior materials in China

At present, the national standards issued in China for the air quality problems in vehicles are only gb/ t 27630-2011 guide for air quality evaluation in passenger cars [2] and hj/ T400 sampling and testing methods for volatile organic compounds and aldehydes in vehicles [3]. The limit values of eight common VOCs concentrations in the air in the vehicle are clearly specified in gb/t 27630-2011, which is of guiding significance to the detection of air quality in the vehicle to a certain extent, but it is not compulsory compared with other countries. Hj/ t 400-2007 specifies the sampling and testing methods of volatile organic compounds and aldehydes in the vehicle. However, the standard is only applicable to vehicles in static state and under constant temperature, constant humidity, static wind and clean environment conditions. It is not applicable to vehicles in operation, and the standards do not specify the indicators and limits of air pollutants in vehicles.

These two standards play a great role in the control of pollutants in the automobile industry in China, but there are still a series of problems in the control of volatile and harmful substances. And these two standards are for the whole vehicle. There is no relevant requirement for the detection of raw materials and parts of the vehicle, so the release of harmful substances cannot be controlled from the source.

02 research status of VOC detection method for interior materials in China

In order to make the air quality in the vehicle meet the requirements of the above standards, the automobile enterprises need to detect and control the VOC release of the interior materials and parts of the vehicle. There are different detection methods for different organic compounds in different vehicle enterprises. At present, the content detection methods of VOC in China are as follows: sampling bag method, detection cabin method, headspace method, thermal analysis method and formaldehyde volatilization method.

2.1 sampling bag method

The main principle of bag method is to put the interior parts of automobile in sealed sampling bags, simulate the use of samples in the vehicle, put proper amount of nitrogen into the sampling bag, adjust the temperature and time as required, make the volatile organic compounds volatilize into the sampling bag, and then collect certain gas samples by using Tenax pipe and DNPH pipe, Thus, the benzene hydrocarbon and aldehydes are analyzed qualitatively and quantitatively.

This method is widely used in Japanese automobile enterprises and joint ventures, and is also the main method of VOC detection in China. The specific test process is as follows: put the sample to be tested into the sampling bag, wash it with high-purity nitrogen for three times, then fill the sample bag with high-purity nitrogen with volume of 50%. After placing in the high temperature test chamber at 65 ℃ for 2 hours, the benzene hydrocarbon substances and aldehydes are collected by Tenax pipe and DNPH pipe respectively, Then, the two kinds of substances were analyzed by gc-gc-gcms and HPLC respectively.

The sampling bag method is simple and easy to operate, and it is not limited by the size of the sample, and can simultaneously detect benzene and aldehydes, and can detect the whole sample. The data is representative and can directly reflect the pollution of each part to the whole vehicle [8]. But the sampling bag has a certain service life, and needs to consume DNPH adsorption pipe, and the detection cost is relatively high.

Sunchengwu et al. [9] used bag method to detect VOC of automobile interior parts, and feedback the parts that need to be rectified according to the test results of the whole vehicle, and then reduce the content of the exceeding substances by controlling the raw materials and manufacturing process of the parts to meet the standard limit requirements. Wang Li et al. [10] used bag method and gmw15634/15635 method to test VOC of raw materials for automobile. The results showed that there were many indexes not detected by GMW method, only a few indexes of bag method could not be detected, and the result value GMW method was generally lower than bag method, and bag method was closer to the actual vehicle emission state.

2.2 detection cabin method

The detection cabin method is mainly used to determine the VOC concentration of components or components in the cab. The method is to put the parts to be tested into a closed test chamber with a volume of about 1m3, and process the samples under certain temperature, relative humidity and air exchange rate, and then extract the air in the test chamber for qualitative and quantitative analysis. The specific test process is as follows:

(1) Adjust the temperature and humidity of the detection chamber, the temperature is about 70 ± 1 ℃, and the humidity is (5% ± 2%);

(2) 30 minutes before the test, adjust the temperature of the test chamber to (65 ± 0.5) ℃, then put the sample in the test chamber, and then seal the test chamber;

(3) VOC collection of benzene and aldehydes and ketones;

(4) Test the sample after atomization and condensation.

The method can detect the volatile organic compounds of benzene and aldehydes, and it can also be used for atomization detection. The method can simulate the use of samples in the vehicle and study the variation of VOC emission with time. But the cost of testing is high, which is suitable for large-scale automobile enterprises and third-party testing institutions.

In addition, the volume of the test chamber is small. If the large interior trim parts need to be cut, they can be put into the test box. The bag law can select the appropriate sampling bag according to the sample size, and the sample is not required to be cut.

Zhang Xiaoyan et al. [11] compares the sampling bag method with the detection cabin method from three aspects: the test object, the test principle and the test step. The results show that the content of benzene and aldehydes obtained by the same material or assembly of the same parts is generally lower than that of the sampling bag method.

2.3 headspace method

Headspace method is mainly used to detect the volatile organic compounds of benzene and hydrocarbon in automotive interior materials, and is a more common method for European and American automobile enterprises. The main principle is to put the sample to be tested into a closed headspace bottle, release the volatile organic compounds by heating and heating, and then extract the top gas into the GC-MS for analysis. The specific test process is relatively simple.

(1) First, the sample is dried, and then the sample of certain quality is cut into the headspace bottle and sealed;

(2) The temperature parameters such as headspace injector, quantitative tube and transfer tube are set, and the sample is balanced under certain temperature conditions;

(3) A certain amount of gas was extracted from the headspace bottle with syringe, and analyzed by gas chromatography and FID detector.

Headspace method is sensitive to the detection of benzene VOCs, the detection process is simple and easy to operate, and the pretreatment steps are less, and organic solvents will not be introduced, which reduces the secondary pollution caused by the solvent. The headspace sampling bottle can be reused and the detection cost is low. But the sample test quantity of headspace method is small, and the data representation and repeatability are poor, so it is limited in the application process.

Qinjianqiang [12] tested the samples by headspace method and bag method respectively. The results show that the headspace method has good stability and sensitivity. The linear range and stability of VOC data of benzene series detected are better than that of bag method, and bag method is more suitable for the detection of aldehydes and ketones VOC.

Chen Lin et al. [13] put the sample into the headspace bottle after drying and weigh a certain mass, and put it into the headspace injector after sealing. Set the parameters of the headspace sampler. The temperature of the top space furnace is 65 ℃, the temperature of the quantitative pipe is 100 ℃, the temperature of the transfer tube is 110 ℃, and the sample balance time is 30 minutes. Under the test conditions, the content of benzene volatile organic compounds in the samples was determined. Results the linear correlation coefficient of the standard curve of each benzene series can reach above 0.999, the relative standard deviation is 4.2% ~ 6.9%, and the recovery rate of the standard addition is 97.9% to 101.5%. The results are satisfactory, and the VOC content of Benzene Series in automotive interior parts can be determined accurately.

2.4 thermal analysis

Thermal analysis is a method to measure volatile organic compounds of benzene hydrocarbons, and it is widely used in European automobile enterprises. The method is mainly used to analyze the volatile organic compounds released by automobile parts and interior materials by the combination of thermal desorption gas chromatography mass spectrometry. The specific detection process is as follows:

(1) Cut a certain quality sample from the sample to be tested and put it into the heat analysis tube;

(2) Put the heat analysis tube into the thermal analyzer and analyze it for 30 minutes at a given temperature, so that the VOC in the sample can be released fully;

(3) The VOC content and TVOC content of benzene series were obtained by GC-MS.

Compared with other methods, this method is simple and easy to operate and has high automaticity. In addition, the heat analysis tube can be reused, and the test cost is low, which is suitable for the detection of large-scale test samples. But the sample test quantity of this method is small and the data representation is low.

Hongying et al. [14] put the material to be tested directly in the heat analysis tube, and the content of VOCs was detected by thermal analysis method. The time of thermal analysis was 30 min. Results the results showed that the mass concentration of benzene series was linear correlated with the corresponding peak area in the range of 10-500 μ g / ml. the recovery was 80.3% ~ 98.1%, and the relative standard deviation was 3.37% ~ 5.42%. The method is easy to operate, high efficiency and automatic, and it is suitable for the detection of VOCs in automobile parts and interior materials. Wang Jinling et al. [15] firstly collected the samples by micro pool thermal extraction, then determined the volatile organic compounds in the samples by thermal desorption gas chromatography mass spectrometry, and optimized the sampling time and flow rate. Results the recovery rate of the standard addition was 89.1% ~ 94.0%, and the relative standard deviation was 2.13% ~ 5.14%, and the results were satisfactory.

2.5 formaldehyde volatilization

Formaldehyde volatilization is a method to analyze the content of aldehydes and ketones released from automotive interior materials, and is widely used in European automobile enterprises.

The detection process is as follows:

(1) Add 50ml deionized water into 500ml clean wide mouth bottle, cut the specified size sample from the sample, hang it in the wide mouth bottle with wire, and seal the bottle;

(2) Put the bottle in an oven at 60 ℃ for a certain time, and then cool the bottle to room temperature;

(3) A certain amount of solution was taken out from the jar and injected into the volumetric flask, and a certain amount of DNPH solution was added to make the two react chemically;

(4) The solution after reaction was quantitatively or qualitatively analyzed by liquid chromatography. Formaldehyde volatilization is simple and the cost is low. But the test data is single, so it can only measure the content of various aldehydes and ketones. It can not analyze the content of benzene hydrocarbon components, and the accuracy of the results of the determination of formaldehyde by spectrophotometry is not high. Therefore, this method should be used relatively widely in China.

03 conclusion

This paper analyzes the current situation of VOC testing standards in China, and introduces the VOC detection methods of automobile parts and interior materials. Each method has its own characteristics, advantages and disadvantages and applicable scope. Therefore, in the actual test process, a simple and easy test method should be found according to the actual situation of the sample to be tested, Thus, the cost of detection is reduced and the accuracy of the test results is improved.

At the same time, domestic relevant enterprises can learn from the experience of foreign automobile industry on VOC detection of automotive interior materials, and combine with the current situation of air quality in China, standardize the VOC detection methods of automotive interior accessories, avoid the use of harmful and high volatile materials from the source, improve the smell in the vehicle, and provide a safe, environmental protection and comfortable in car environment for the majority of consumers.

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