Abstract:

Objective: In this paper, the Chinese fir (Cunninghamia lanceolata) and radiata pine (Pinus radiata) lumber with 40 mm thickness were subjected as materials. During high temperature kiln drying, formaldehyde concentration was analyzed as effected by temperature and moisture content of lumber, and was compared to that of conventional kiln drying radiata pine lumber. Method: During the lumber drying, according to the temperature in kiln and moisture content distribution of lumber, as for high temperature drying, the discharged gas of Chinese fir and radiata pine lumber were sampled 7 and 9 times, respectively; while for conventional drying, the discharged gas of radiata pine lumber was sampled 10 times. The extraction speed was 1.0 L·min^-1 and the time was 30 min. Referring to EPA method 0011, two 200 mL gas washing bottles with 40 mL distilled water were put in series in ice bath to make aldehydes fully dissolved in the water. Then the formaldehyde concentration was measured by acetyl acetone method. Result: As for Chinese fir and radiata pine lumber in high temperature ranged from 90℃ to 120℃, the minimum and maximum formaldehyde concentrations were 4.21 mg·m^-3 and 11.43 mg·m^-3, 3.66 mg·m^-3 and 12.71 mg·m^-3, respectively, which were all higher than the requirement limit of the non-organized emission standard that formaldehyde concentration didn't beyond 0.20 mg·m^-3. The drying temperature was linear with the released formaldehyde concentration in the temperature range of 90-120℃, and the determination coefficients (R²) were 0.668 and 0.934, respectively. When the drying temperature was 105℃, the concentration of formaldehyde increased gradually with the decrease of moisture content of radiata pine, they were negatively linear relationships, and the determination coefficients (R²) was 0.885. However, the drying temperature was the most important factor affecting the weight of formaldehyde release. During the conventional kiln drying, when the temperature of kiln did not beyond 90℃ and the moisture content of radiata pine lumber decreased gradually, the released formaldehyde concentration was almost constant with (0.19±0.03) mg·m^-3, and was less than the requirement limit of the non-organized emission standard of formaldehyde concentration. Conclusion: When the drying temperature is higher than 90℃, the gas discharged during drying should be recycled to avoid environmental pollution.

Key words: Chinese fir, radiata pine, high temperature drying, moisture content, formaldehyde release