Abstract: Formaldehyde is a colorless, easily soluble gas. This gas has significant irritating characteristics and is easily soluble in water and alcohol ethers. It is in gaseous form at room temperature and generally takes the form of aqueous solution. Due to its high toxicity, formaldehyde has become the second most toxic chemical in my country. It can cause cancer and deformities, seriously endangering human health. During people’s renovation, the commonly used materials are coatings, boards and adhesives. It is crucial to control the formaldehyde content of the above materials well. This article analyzes the errors in formaldehyde test results in coatings, adhesives and boards.
Keywords: formaldehyde test results; adhesive; coating; panel; error analysis
The chemical formula of formaldehyde is (HCHO), and its 40% aqueous solution is called formalin. Formaldehyde is a socially recognized source of allergies and a potential strong mutagen. Formaldehyde has very strong cancer-promoting and carcinogenic effects. Formaldehyde poisoning is mainly manifested through olfactory poisoning, allergies and irritation, abnormal liver function, and abnormal immune function. As early as 2001, my country introduced regulations on the limited amount of formaldehyde released, that is, there are clear regulations on the amount of formaldehyde released in adhesives, coatings and boards. However, in actual results, very large errors usually occur. Therefore, it is particularly critical to strengthen analysis and research on the situations that lead to errors in test results.
1.Preparation of formaldehyde standard solution and drawing of standard working curve
The standard curve is a curve made from a standard solution. It describes the quantitative relationship between the content and concentration of the substance to be measured and the response signal value of the analytical instrument. During the spectrophotometric analysis, the concentration response signal value of the substance to be measured has a linear relationship within the corresponding range. The result of measuring the water sample can be observed on the standard curve. Therefore, the quality of the standard curve is good for the final determination. The accuracy of the results has a certain impact.
(1) Calibration of formaldehyde solution
The principle of formaldehyde solution calibration is that a large amount of iodine reacts with formaldehyde, and at the same time, sodium thiosulfate solution is used to titrate excess iodine to finally obtain the formaldehyde concentration. Put a formaldehyde solution (2.5g) with a concentration between 35% and 45% into a volumetric flask (1000mL) and dilute it with distilled water. The formula for calculating the concentration of formaldehyde solution is: c1 (HCHO) = (V0-V) × 15 × c2 × 1000/20. In this formula, c1 represents the concentration of formaldehyde; V0 represents the volume of the sodium thiosulfate standard solution used to titrate the blank solution; V represents the volume of the sodium thiosulfate standard solution used to titrate the formaldehyde solution; c2 represents is the concentration of sodium thiosulfate solution; 15 represents the molar mass of formaldehyde (1/2HCHO); 1000 represents the conversion of mL into L; 20 represents 20mL of formaldehyde solution.
(2) Draw a standard curve
Take the dropped formaldehyde standard solution and prepare formaldehyde standard solution C with different concentrations. At the same time, measure the absorbance A of each tube. The abscissa and ordinate are respectively selecting the formaldehyde mass concentration C and absorbance A to draw the standard curve. During the test, measurement errors are usually prone to occur, that is, one or two points deviate from the straight line. The “b-multiplication” method can be implemented to carry out regression analysis, and then the curve can be drawn, which is the regression straight line. The slope of the regression line is obtained through the regression equation, and its reciprocal is the sample measurement calculation factor.
There are many factors that can affect the slope of the formaldehyde standard curve. During the preparation of the standard solution, the lower the dilution factor, the greater the slope; environmental conditions, that is, there is a positive correlation between the slope and temperature, humidity and air pressure; during the operation of the pipette, automatic pipetting should be adopted. Accurately add the amount from top to bottom, or use the method of accurately measuring and then putting it down; when preparing the solution, you must first use a volumetric flask to set the volume, and then mix thoroughly; in the case of system errors, if the same measurement is performed multiple times In the case of quantitative expansion measurement, there will be a certain error between the final average value and the accurate value of the measured value.
2.Processing samples and collecting formaldehyde
(1) Coatings and adhesives
In terms of sampling time, the GB18582-2008 and GB18583-2008 proposed by our country do not specify the specific storage conditions and time to be followed during the measurement of formaldehyde content inside coatings and adhesives. Although formaldehyde can be dissolved in water, factors that cause errors in detection results include storage conditions and sampling time; heating temperature control during distillation can also have a certain impact on the results of detecting free formaldehyde. The distillation method is a common method for collecting paint. It is simple and convenient, and can produce good temperature control. However, controlling temperature is a difficulty in distillation, especially in the distillation of adhesives. Factors that affect the formaldehyde measurement results include heating temperature and heating method. At the same time, different heating methods and distillation devices, different compositions of coatings and adhesives will also produce different heating temperatures; distillation time can profoundly affect Test results for free formaldehyde. Choosing the appropriate temperature and optimal distillation time can maximize the collection of all formaldehyde, and at the same time find the optimal distillation time according to the actual conditions of the laboratory; the storage time of the distillate can also affect to the results of free formaldehyde detection. Because formaldehyde is very volatile, it should be tested immediately after collection, or it can be refrigerated for a week.
(2) Board
The amount of formaldehyde released in artificial panels can be affected by many factors. The main aspects involve the type of wood, the type and thickness of the board, the adhesive grade, the surface treatment, the speed and temperature of the ambient air flow, etc. In the same section, different environmental conditions in real time will also produce different formaldehyde release results, which are significantly different from the conventional measurement of material composition. Therefore, what must be paid attention to is that when selecting a measurement method, the measurement data should be typical and have good reproducibility and comparison characteristics, so this is also a difficult problem. The dryer method proposed by the United States and Japan places a test specimen rack in a water-filled dryer. The formaldehyde released by the test specimen is absorbed by the water, and the final release amount is obtained. At the same time, this method can simulate a closed indoor environment, that is, the amount of formaldehyde released by artificial panels to the surroundings. In addition, the principle of the perforation method is to extract formaldehyde from toluene through liquid and solid, and then extract toluene and aqueous solution through the perforator. These methods are all simulation or approximate methods and have good application value under certain conditions.
As for the sampling time, there is currently no clear determination. However, no matter what method is used to measure free formaldehyde in wooden materials, the amount of formaldehyde released is a function of time and is closely related to time. In addition, storage conditions can also affect the amount of formaldehyde released.
3.Determination of formaldehyde content
First, acetylacetone develops color. In acetic acid-ammonium acetate buffer with a pH value of 6, formaldehyde and acetylacetone will form a yellow complex when heated. After cooling, the absorbance test is carried out at the wavelength of 412nm, and the free formaldehyde content is measured according to the standard working curve. In this kind of measure, the advantage is that the operation is relatively convenient, and at the same time, good stability can be obtained and errors can be reduced. However, it also has limitations, that is, it is only used in the determination of high-concentration formaldehyde, but it is widely used.
Secondly, the impact of blank on the formation of measurement results. The obtained fractions were collected in acetylacetone and ammonium acetate solutions, and the actual absorbance was measured using a spectrophotometer. Expand a blank test in the same state. The absorbance needs to be controlled below 0.01. The reagent blank method is: first, directly use distilled water as a blank; second, add the color developer to the distilled water to form a blank; third, collect the same amount of distilled water in the desiccator, and under the same conditions, for formaldehyde After adding color developer to absorb the color, it is used as a blank. The reference is distilled water, and the absorbance is measured separately. Finally, the measured absorbance values were 0, 0.0770, and 0.0846 respectively. Therefore, there is a continuous increasing trend in the three blank absorbance values. Therefore, during sampling, the related influencing factors of air and distilled water in the laboratory should be carefully considered, and the third measure should be used as a blank.
Conclusion
During laboratory testing, there are many factors that contribute to the error in formaldehyde test results. It is necessary to accumulate a lot of testing experience while paying attention to analytical experience, master the relevant production processes and formulas, strengthen good communication with enterprises, and then understand the testing methods. Make improvements and provide more valuable detection data.
