Introduction

Wallpaper, also known as wallpaper, is a kind of interior decoration materials used for pasting walls, widely used in residential, office interior decoration and so on. Wallpaper products may produce harmful substances such as vinyl chloride, formaldehyde and heavy metals in the process of processing and production due to raw materials, process formula and other reasons. With the rise of wallpaper industry, the number of enterprises is increasing rapidly, and the problems such as brand confusion, unclear product identification, and irritating smell of products are gradually exposed. In the decoration, the wallpaper pavement area is usually 2.5~4 times the floor area, is one of the largest indoor air contact area of decorative materials, quality problems can not be ignored.

Current research shows that the harm of formaldehyde to the human body is mainly reflected in the stimulating effect of formaldehyde on the skin and mucous membranes of the human body, which causes damage to the central nervous system and retina after entering the human body; High concentration of formaldehyde is a genotoxic substance, when it is inhaled by the human body, it will lead to chromosomal abnormalities, and even cause cancer in the nasal cavity, mouth, nasopharynx, skin and digestive tract. In order to control indoor formaldehyde pollution, the state issued GB50325-2020 "Civil construction engineering indoor environmental pollution control standard", the determination of formaldehyde emission in wallpaper made strict provisions, the standard determination method quoted GB18585-2001 "Limits of harmful substances in interior decoration materials wallpaper". The repeated determination, the removal of the solution in the experiment, the preparation of the standard working solution, the fitting of the standard curve and the measuring instrument will all have an impact on the results of the detection of formaldehyde content in the wallpaper. At present, the measurement uncertainty is mainly used in the world to assess the reliability of the results, and the measurement uncertainty of the product is also a basic requirement of CNAS (China National Accreditation Committee for Conformity Assessment). Therefore, this paper evaluates the uncertainty of the detection result of formaldehyde content in wallpaper by UV-visible spectrophotometry, in order to provide reference for improving the reliability and consistency of formaldehyde content detection data in wallpaper.

1. Experimental part

1.1 Experimental Principles

Dissolve formaldehyde (HCHO) in water, adjust the temperature of the solution to 40~50℃, adjust the pH value of formaldehyde aqueous solution with acetic acid-ammonium acetate to 5.5~7.0, and finally add acetyl acetone. Acetoacetone reacts with formaldehyde to produce light yellow compound C11H15NO2, which has maximum absorption at 412nm. The absorption value of solution at 412nm is measured by UV-visible spectrophotometer, and the formaldehyde content is calculated according to external standard method.

Uncertainty refers to the measurement errors that may occur during the course of the experiment, resulting in incomplete accuracy of the measured value. To some extent, it also shows how trustworthy the measurement results can be. The smaller the uncertainty value, the closer the result is to the true value. Conversely, the larger the value, the lower the utilizable value of the experimental data.

1.2 Instruments and reagents

Instruments: UV-1800PC ultraviolet spectrophotometer (Shanghai Meisei Instrument Co., LTD.), DHG-9050A electric constant temperature blast drying oven (Shanghai Yiheng Technology Co., LTD.), constant temperature water bath (Jingke Huarui Instrument), BSA224S electronic balance (Sedolis, Germany).

Reagent: Ammonium acetate (AR, 98%, Folshanlong Chemical Co., LTD.); Acetyl acetone (AR, 99%, Guangzhou Chemical Reagent Factory). Acetyl acetone solution (0.4% by volume) : Remove 4mL acetyl acetone into a volumetric bottle and dilute it to 1000mL with tertiary water. Store in a sealed container in a dark place for stable storage for 4 weeks. Ammonium acetate solution (200g/L) : Dissolve 200g ammonium acetate into a volumetric bottle with tertiary water and dilute it to 1000mL with tertiary water. Formaldehyde standard solution: 1000μg/mL (Shanghai Anpu Scientific Instrument Co., LTD., uncertainty 2%). The reagents used in this experiment should be analytical pure reagents and tertiary water in line with national standards or professional standards unless otherwise stated.

1.3 Preparation of standard curves

Remove 1.5mL formaldehyde standard solution to 100mL volumetric bottle, shake well at a constant volume, and the mass concentration of this solution is 15μg/mL. Use 10mL pipettes to remove 0, 2, 4, 6, 8, 10mL to 50mL volumetric bottles, and then add 10, 8, 6, 4, 2, 0mL of third grade water successively to obtain a series of standard working solutions, and the mass concentration of formaldehyde is 0, 3, 6, 9, 12, 15μg/mL, respectively.

1.4 Determination of formaldehyde content in wallpaper

Evenly cut 50 samples of width (30±1) mm and length (50±1) mm on the wallpaper. Weigh these 50 rectangular samples and hang them on the hook of the 1000mL wide-mouth bottle cap, so that the decorative coating surface of the samples is opposite, and the samples are not in contact with the wall and liquid level of the wide-mouth bottle. Use the measuring cylinder to remove 50mL tertiary water into 1000mL wide-mouth bottle, tighten the bottle cap to seal, and move the wide-mouth bottle into the oven at (40±2) ℃ for 24h. After 24h, remove the sample from the wide-mouth bottle, and use the pipette to remove 10mL of the absorption liquid from the wide-mouth bottle to the 50mL volumetric bottle. Add 10mL acetyl acetone solution and 10mL ammonium acetate solution to the standard working solution of formaldehyde and the sample absorption solution, heat them in a water bath at (40±2) ℃ for 15min, then remove them from the bath and cool them at room temperature for 1h. At the same time, a blank test was performed, and the absorbance of the standard solution and the absorbance of the absorber at 412nm was measured by UV-spectrophotometer. A standard curve was drawn, and the concentration of formaldehyde released by the sample was read from the curve according to the absorbance of the absorber. Parallel blank test was done at the same time.