Vegetation Composite Mdf Biodegradation Mechanism Of Aldehyde Law And Applied Research

Through analyzing the influences on free formaldehyde releasing from the medium density straw/wood fiber composites (MDSFC) by different ratios of straw fibers to wood fibers, the mechanism of biological means of reducing formaldehyde emission in MDSFC will be discussed in this thesis. Also, how straw fibers absorb free formaldehyde from the urea formaldehyde resin (UF) physically and chemically in order to get the result of reducing free formaldehyde emission from the composites will be investigated in this paper.As a kind of MDSFC with UF resin as its adhesive, the straw fiberboard's free formaldehyde amount is lower than the wood fiberboard's. The effect of reducing free formaldehyde releasing from the panels is the most obvious when the ratio of straw fibers to wood fibers arrives at 25: 75. Composites at this ratio contain almost 66.6 percent lower free formaldehyde emission than wood fiberboards. The free formaldehyde emissions of MDSFC go up to some extent, but they are still lower than the wood fiberboard when the ratios reach 50: 50 and 75: 25. MDSFC's physical and mechanical properties with different ratios of straw fibers to wood fibers are between straw fiberboards and wood fiberboards. Properties of composites will drop dramatically when the ratio of straw fibers to wood fibers is increased.The silicon cells in straw surface layer are the protuberances which arrange regularly. These cells in the straw-particle surface will be pulled away partially or totally in the course of getting the straw particles to straw fibers by braising under the certain pressure and milling process followed. The taken-off tiny silicon cells are absorbed to the surface of straw fibers again in the same process which make the superficial area of the straw fibers increased effectively. It makes effort to explain why straw fibers are available to reduce formaldehyde releasing from the composites in the view of microstructure.The results of Infrared spectrum (IR) show that hydroxyl density on the straw fibers' surface rises sharply after braising under the pressure. High hydroxyl density will do benefits to agglutination, form the favorable interfaces and improve the physical and mechanical properties of the composites. Hydroxyl density of the fiber composites reduces after hot pressing process with other groups increase. IR also shows that near the SiO₂ absorb peak appears a small shoulder harness absorb peak.The results of X-ray photoelectron spectroscopy reveal that there are three kinds of chemical combination modes of oxygen element in the straw/wood fiber composites: C-O-Si, Si-O-H or C=O and C-O-H. Among them, C-O-Si is the new emerging chemical combination...