Research On Formaldehyde Emission During Hot-pressing Of Particleboard

Urea-formaldehyde adhesive (UF) was widely used in the wood-based panel boards produced, which were usually applied in the furniture products and interior decoration. The workplace and indoor air pollution produced when the UF-boards were in the processing, also in the productions using, which is very harmful to the human health. Therefore, the studies on formaldehyde emission rule and the releasing mechanism had great significances on the preventing of indoor air pollution. This dissertation was focused on formaldehyde emission about particleboard which was manufactured by UF resin. The formaldehyde emission would be different when the raw materials and production technology were changed. The effects of technological parameters on the formaldehyde emission during particleboard hot-pressing, the desiccator's value, the main physical and mechanical properties were investigated. The changed rules of the three inner links and the reaction mechanism were also analyzed systemically. The main results were as follows:(1) A set of collecting device for formaldehyde emission during hot-pressing of wood-based panel was designed with good sealing performance and repeatability, which ensured that formaldehyde was fully collected during hot-pressing process. So far, it hadn't been seeing in the reports of china.(2) The value of unit mass of the particleboard formaldehyde emission during hot-pressing was reduced when the particleboard's density increasing, the formaldehyde emission value was reduced by 32.4% when the density increased from 500kg/m3 to 800kg/m3, however, the influence of density by the desiccator method was unobviously.(3) Along with the increasing of particleboard's moisture content, both the value of formaldehyde emission during hot-pressing and the desiccator value had a logarithmic growth. When the moisture content of particles increased from 2% to 8%, the formaldehyde emission value during hot-pressing increased by 175.3%, and the desiccator value increased by 49.8%.(4) Both the formaldehyde emission value during hot-pressing and the desiccator value increased linearly with the content of adhesive increased. The formaldehyde emission value during hot-pressing increased 81.7% and the desiccator value increased by 63.3% when the content of adhesive increased from 6% to 12%.(5) With the hot-pressing temperature increasing, the formaldehyde emission value during hot-pressing presented a curve upward trend, but the desiccator value decreased linearly. The formaldehyde emission value during hot-pressing increased 32.5% and the desiccator value dropped 41.3% when the hot-pressing temperature increased from 160℃to 180℃. (6) With the extension of hot-pressing time, the value of formaldehyde emission during hot-pressing presents an exponential upward trend, but the desiccator value decreased in a power function trend. The formaldehyde emission value during hot-pressing increased by 240.1% and the desiccator value dropped by 48.2%(7) When the hot-pressing time increased from 15 s/mm to 30 s/mm. The formaldehyde pollution was serious during wood-based panel's hot-pressing. In the experiments, all of the particleboard's maximum allowable concentration (MAC) value during hot-pressing was much more than the occupational exposure limits (MAC:0.05mg/m3) except the particleboard without resin. The MAC mean value of all the boards was 2.27mg/m3, which was 4.54 times of the national occupational exposure limits.(8) Along with the changes of technological parameters, the main physical mechanical properties and the formaldehyde emission value during hot-pressing had certain correlations.(9) If the process parameters were optimized, the formaldehyde could be reacted much more in the curing during hot-pressing, so the better-quality boards with good physical mechanical properties and lower formaldehyde emission both during hot-pressing and after the production were probably produced.