Plywood Wooden Panels Formaldehyde Testing Methods
Oringal source https://www.hindawi.com/journals/ijps/2018/9349721/
Formaldehyde content and formaldehyde emission are two different concepts. Formaldehyde content refers to the number of milligrams of formaldehyde per 100 grams of panel, which is tested by using the perforation method. Formaldehyde emission is the amount of formaldehyde released from wood-based panels to a certain volume of air or a certain amount of water within a specified period of time, which is always tested by using chamber or desiccator method.
Zhu et al. divided the testing methods of formaldehyde as three categories: total amount testing method such as perforation; static emission testing method such as desiccator; and dynamic emission testing method such as chamber. The chamber method is widely used in the United States and Germany. In the EU standards, chamber, gas analysis, and perforation methods are used. In Japanese standards, the desiccator method is used. According to Chinese mandatory national standard GB 18580-2001, MDF and PB are tested by perforation method, and plywood and block board are tested using the (9–11) L desiccator method. For the desiccator method, a 40 L desiccator is usually used to test the laminate flooring and parquet. If there is a controversy for the result, an arbitration method is used using a 1 m3 chamber.
Each testing method has its own advantages and disadvantages. The chamber method is more close to the practical application in terms of temperature, relative humidity, loading rate, air exchange rate, and air velocity on the sample surface. The chamber body is large, and the testing time is long.
The unit and value of formaldehyde limit indicators of all levels (E0, E1, E2, and F★★★★) are different due to different testing methods. The units of formaldehyde content and emission are mg/100 g, mg/L, mg/m3, and mg/m2.h, corresponding to different test methods. mg/100 g is the unit of formaldehyde content in wood-based panel that refers to the formaldehyde content per 100 g wood-based panels, using the perforation test method. Three units mg/L, mg/m3, and mg/m2·h are used for the formaldehyde emission. The unit mg/L corresponds to the desiccator method, which is related to temperature, specimen area, dryer volume, water volume, and collection time. The unit mg/m3 corresponds to the chamber method related to the temperature and humidity, loading rate, ventilation, sampling port, sample size, sampling time, and analysis methods. The unit mg/m2·h corresponds to the gas analysis method using the measured concentration of formaldehyde, extraction time, and exposed area of the specimen to calculate the amount of formaldehyde emission and currently less used.
In the existing formaldehyde emission limited standards of wood-based panels, different types of wood-based panels are usually tested by different methods. Different countries have their own limits, coupled with the testing conditions, the difference between the pretreatment methods, and the type of panel. The test results of formaldehyde content in wood-based panel vary greatly, which is difficult to determine whether it is suitable for other national standards by using proprietary testing methods. Some scholars have analyzed and compared different testing methods, fitting a general formula by using data induction to convert the data of different testing methods. Li and Wang calculated the slope of formaldehyde emission curve by using the one-way regression and analyzed the relationship of testing results between the perforation and the desiccator. Yu et al. concluded that there was a certain linear correlation between the formaldehyde emission from MDF of perforation and gas analysis. Gu et al. analyzed the correlation of different testing methods of formaldehyde emission from wood-based panels and converted the limited value corresponding to different methods of US ASTMD6007-2002, European EN717-2: 1994, Japanese JISA1460-2001, and Chinese GB18580-2001 by using the regression equation, which provide a reference for the enterprises to control formaldehyde emission of the products exporting to different countries. Research on the correlation of the different testing methods of formaldehyde emission from wood-based panels can use one method to predict the results of other testing methods, which provide a reference for the wood-based panel enterprise to control quality.