Research On Medium Density Fiberboard From Chinese Pennisetum

This study was conducted to examine the technical feasibility of making Medium Density Fiberboard (MDF) from Chinese pennisetum. The origin and distribution of Chinese pennisetum were investigated, and the material characteristics including macrostructure, microstructure and fiber morphology were explored. The wettability of pennisetum and bonding mechanism of urea-formaldehyde (UF) resin were assessed, UF bonded pennisetum MDF panels were manufactured and the proper processing parameters for manufacturing pennisetum MDF were educed. The study also investigated the feasibility, practicability and economical efficiency of making pennisetum MDF on a commercial basis according to the study of cost analysis and end-application of the final product. The results are summarized as follows:(1) Chinese pennisetum is a genus of grasses in the family of Poaceae. They are large annual or perennial grasses growing 2-3m tall. The cultivated areas of them are on the rise in the Lower-Middle Reaches of the Yangtze River, while in Nanjing they have been planted for many years. Though many reports have shown the comprehensive utilizations of the pennisetum have been achieved, they are now mainly used as fodders. Making composite panels from pennisetum provides3 substitute for wood resource, increases economic value of pennisetum, and helps to protect the environment as well.(2) Pennisetums consists of epidermal tissue, fibrous tissue, basic parenchyma and vascular bundles, and contains many cells like fibrocyte, parenchyma cell, vessel, epidermis cell and so forth. The measurements of fiber morphology revealed that the defibrated fibers averaged about 1.30 mm in length and 3.5μm in wall thickness. The fiber had a mean aspect ratio of 108 and a ratio of wall thickness to cell diameter of 0.32. Those results indicated that the fiber quality of pennisetum was good. Of the thermal-mechanical refined pennisetum fibers,70.8 % was the qualified long fibers and fiber bundles,12.5% was coarse fibers and 11.8% was fine fibers, which proved that the distribution of refined pennisetum fiber was ideal, and pennisetum was a potential feasible raw material for making medium density fiberboard in terms of fiber morphology.(3) The chemical composition analysis indicated that pennisetum composes of 71.83% holocellulose,19.65% pentose,23.84% lignin,2.84% benzene alcohol extraction content and 4.84% ash content as well. It's chemical composition was similar to those of Chinese white poplar, and good for making MDF. Among leaf, stalk, node, branch and central core pith, the highest ash content was found to be 11.21% in the leaf and the lowest was 8.77% in the central core pith, and the stalk had the highest cellulose content while the leaf had lowest cellulose content. The degree of crystallization varies from part to part, and the stalk had the highest degree of crystallization whereas the pith had the lowest value. The degree of crystallization of refined fiber was different from any part of pennisetum and ranked the second highest. Pennisetum presents weak acidity, with a pH value ranging from 4.5 and 6. Among the different parts, leaf was determined to have the highest pH value and buffering capacity. The thermal-mechanically refined fibers presented lower pH value and buffering capacity compared with the raw material, which was helpful to reduce the curing time of UF resin. Since the leaf part has highest.ash content, pH value and buffering capacity, and it is easily damaged and becomes dust during the refining, it may be removed from the stalk before fiber preparation.(4) The results from infrared spectroscopy illustrated that the characteristic absorption peaks of O-H stretching vibration, C-H flexible and curve vibration,C=C stretching vibration and C-O stretching vibration were identified from the samples of pennisetum outer surface, pith and refined fiber. This demonstrated that these three parts all included cellulose, hemicelluloses and lignin. Moreover, Si-O stretching vibration peak was only found from the sample of straw outside surface, which confirmed that SiO2 only existed there, and the4 Si-O bridge broken down after refining. It was also found that the type and number of functional groups increased dramatically after refining, as in the infrared spectrogram the number of characteristic absorption peaks of refined fiber sample was much higher than those of straw and the central core pith. Thermal analysis with differential scanning calorimeter (DSC) showed that exothermic and endothermic peaks were observed from the temperature of 60 to 150℃, which demonstrated that some inner functional groups of raw material were exposed and thus in turn helped to increase the bondability of pennisetum. These results proved that thermal-mechanically refining helped to improve the bonding strength.(5) The inner surface presented a much lower contact angle than that of outer surface, and the wettability of refined fiber was improved compared with the raw material. Again, results from electron spin resonance (ESR) explored that the number of surface free radical of refined fiber was largely increased compared with the raw material while that of resultant MDF decreased. The intensity of associated O-H vibration peak decreased obviously and the location of corresponding peak changed as well. DSC analysis revealed that adding adequate amount of hardener helped to bring forward the react time and enhanced the reactivity between the refined fibre and UF resin under heating. These results demonstrated that theoretically a good bonding could be formed between pennisetums refined fiber and UF.(6) Following the conventional hot pressing technology of wood MDF, preliminary experiment of making pennisetums MDF was conducted with orthogonal experiment design method. The results demonstrated that pennisetums MDF panels which came up to the national MDF standard were able to be made under the proper processing conditions. The optimum manufacturing conditions of making pennisetums MDF were educed based on orthogonal design-direct analysis and analysis of variance.(7) Based on the optimum manufacturing conditions of making pennisetums MDF from the preliminary experiment, verification experiments were conducted, and hot pressing temperature and the resin content were adequately modified with the addition of water repellency. The proper amount of water repellency was found to have efficiently improved the water resistance of MDF panels, whereas no enhancement in panel properties was found by increasing the hot pressing temperature and resin content. The vertical density profile of experimental pennisetums MDF panels were also determined. The ideal manufacture conditions for making MDF from pennisetums were summarized as the following:density5 0.8g/cm3, hot pressing time 20 s/mm, hot pressing pressure 3.5 MPa, temperature 160℃, resin content 12%, hardener 1%(NH4C1), water repellency 1.2%(paraffins emulsion).(8)The implementation of exploitation strategy of coastal area provides opportunity for commercializing the technology of making pennisetums MDF. Growing pennisetum on the seabeach of Jiangsu province not only provides the raw material for making MDF and thus remit the raw material shortage for the mills, but also promotes the development of coastal areas and expands the develop scope of Jiangsu Province. The production cost of making pennisetums MDF was slightly lower than that of wood MDF based on the cost analysis, thus economic benefit can be achieved by producing this product. In addition, study on application of pennisetums MDF showed that the product is suitable to be used as raw materials for furniture manufacturing, indoor decoration and building due to its smooth surface, highly dimensional stability and excellent machining property.