Control Of Formaldehyde Emission From Medium Density Fiberboard Based On Transport Characteristics

People usually spend80-90%of their time in building environment; hence, indoor air quality significantly influences efficiency of production and comfort of life. However, medium density fiberboard (MDF) is widely used for refurbishment in China, the formaldehyde pollution from which has been hindering industrial development and social harmony. Therefore, it has been a hot issue in the field of material science to control formaldehyde emission based on understanding its transport characteristics.This dissertation focuses on pollution of MDF and explores effect of emission control with the help of technologically simple and economically cheap approaches in the light of transport features. Here, emission process and diffusion mechanism were investigated to analyze key parameters characterizing MDF emission; then, the relationships between several modified methods and formaldehyde emission were studied. According to above researches, a new kind of low formaldehyde emission MDF was designed and applied in production. The main academic contributions are the following six areas:(1) Environmental chamber was applied to simulate actual situation for investigating macroscopic transport characteristics. It is revealed that edge of MDF is the primary channel for formaldehyde emission and a52%reduction in peak chamber concentration was observed after edge sealing. In addition, emission can be promoted by higher environmental temperature and relative humidity but constrained by larger panel thickness and air exchange rate. It is important to guide the effective control of the formaldehyde emission from MDF.(2) Scanning electron microscopy was applied to observe surface and edge of MDF for investigating microscopic transport characteristics. It is illustrated that critical diameter between macroscopic and microscopic pores in MDF is450nm, i.e.,10times of mean free path for formaldehyde molecule; in the two pores, Fick and transition/Knudsen diffusion respectively occur. In terms of characteristic element for MDF, series connection between macroscopic and microscopic pores is considered as the significant transport channel and a macroscopic-microscopic structure model was established for providing a theoretical basis on control of formaldehyde emission.(3) Investigating material in different production stages (including urea formaldehyde adhesive, wood chip, fiber mixed with adhesive and MDF) for initial emittable concentration C0, it is indicated that adhesive is the major source of formaldehyde release from MDF while a liner correlation for formaldehyde emission was fitted. Besides, drying and hot pressing process can respectively reduce emission for47%and66%. It provides guidance to control and predict the formaldehyde emission in MDF production.(4) Investigating effect of adsorbent (including activated carbon fiber, silanated Al2O3, SiO2and zeolite) for partition coefficient Ks, it is demonstrated that2%silanated Al2O3mixed with adhesive for manufacturing MDF is better, leading to63%reduction of formaldehyde emission. Meanwhile, physical and mechanical properties after this treatment can also be acceptable. It is a better method to reducing the formaldehyde emission from MDF.(5) Investigating effect of finishing (with abrasion resistant paper, balance paper and decorative paper) and edge sealing (with paraffin wax, PVC and aluminum foil) for effective diffusion coefficient De, it is shown that finishing with100g balance paper+70g decorative paper+42g abrasion resistant paper and edge sealing with paraffin wax are better, respectively attaining45%and60%reduction of formaldehyde emission and also provide a preferred solution fro the low emission products with optimized barrier material.(6) Linking theory with practice, a new environmentally friendly design of MDF was proposed combined with doping adsorbent, obtaining47%reduction of formaldehyde emission and even95%after further finishing and edge sealing and meeting the need of Japanese Fstandard. On the other hand, this method causes0.04MPa decrease in internal bond strength and1.5-2.5%increase in cost with strong market competitiveness.