| With the comprehensive development and utilization of non-wood plant resources, thecontradiction between supply and demand of China's wood has been alleviated to a certainextent for recent years. Meanwhile with the enhancement of health consciousness in mind,people have put forward higher requests to environmental protection performance ofwood-based panel. Because materials like tea polyphenols can absorbed formaldehyde, whichcan effectively reduce the formaldehyde release of wood-based panel. By usingpolyphenols-rich tea stalk wastes as the raw material of wood-based panel and pressing the teastalk particleboard, will solve the health and environment problems caused by the freeformaldehyde from wood-based panel, at the same time, make efficient use of tea stalk waste,which bear substantial realistic significance to wood-based panel industry and tea industry, andbring up the enormous economical benefits, social benefits and ecological environmentbenefits.This paper took tea stalk crushed aggregates and urea-formaldehyde resin adhesive(UF) asthe main study objects, and researched chemical components, microstructure and fibermorphology applying Fourier Transformation Infrared Ray(FTIR) and Scanning ElectronMicrograph(SEM), and then the tea stalk were screening, after the orthogonal test to press teastalk board, the optimum technological factors were obtained. Application of differentialscanning calorimeter for curing mechanism of UF and gas analysis method for the detection offormaldehyde release from tea stalk particleboard were put in research to analyze formaldehydeemission effects of tea stalk raw materials, moisture content of tea stalk, glue consumption andhot pressing technology, and the control mechanism of formaldehyde emission from tea stalkparticleboard was discussed. The main conclusions of this paper are as follows:(1) The tea stalk cellulose content is10.22%, lignin content of9.81%, lower than thesoftwood and hardwood timber, while the tea stalk hemicelloses, ash, hot water extractive,1%NaOH extractive, alcohol benzene extractive are31.28%,5.62%,31.99%,66.06%,29.39%,respectively, which are much higher than softwood and hardwood timber. According to theanalysis of FTIR, when wave number between1649cm-1and1630cm-1, the absorption band arehydroxyl stretching vibration of tea polyphenols, tea flavins and other structures, whichexplains that there are tea polyphenols and other components in tea stalk raw materials. (2) The cross section of tea stalk material is mainly composed of epidermal tissue, fibroustissue, vascular bundle tissue and pith. The average length of tea stalk crushing fiber cell is855.91μm, the width is13.77μm, the thickness is1.75μm and lumen diameter is10.28μm. Theaverage ratio value of length and width is62.15, and ratio of thickness and lumen is0.170. Thesieve composition of tea stalk crushing below40mesh makes up85%and above60meshmakes up15%. Therefore, the tea stalk crushing materials are suitable for the tea stalkparticleboard.(3) Various technical factors have different effects on physical and mechanical propertiesof tea stalk particleboard. In the test range, with the increasing of hot-pressing pressure,hot-pressing time and glue consumption, the modulus of rupture (MOR), modulus of elasticity(MOE), internal bond strength(IB) and nail-holding power of the board increased while thethickness swelling rate of water absorption decreased. Hot-pressing temperature has asignificant effect on IB. When hot-pressing temperature is too high, the IB of tea stalkparticleboard decreased obviously. The range analysis and variance analysis show the besttechnological parameters of tea stalk particleboard are3.3MPa hot-pressing pressure,55s/mmhot-pressing time,125℃hot-pressing temperature and14%glue consumption.(4) According to the gas analysis method for the tea stalk particleboard formaldehydeemission, the average value is0.376mg/(m2h). But based on a dynamic analysis in differentstages, the formaldehyde emission is in the range of0.476～0.273mg/(m2h). Theformaldehyde emission reduces while the sampling detection time extends. The tea stalk rawmaterial is the important factor of the low formaldehyde emission. In the interaction of tea stalkand formaldehyde, there are chemical absorption and physical absorption at the same time. Thechemical action mainly lied in the interaction of formaldehyde with tea polyphenols, tea flavins,theanine and other active substances. Physical absorption exists because the tea stalk itself is aporous material, the formaldehyde can effectively be released, or bring the occurrence ofchemical action of tube absorbing formaldehyde and tea polyphenols during the process of hotpressing.(5) Technological factors also have an important influence on formaldehyde emission.While the moisture content of board decreased, the formaldehyde emission reduced. The reasonlies in the fact that during hot pressing process, the more outdiffusion of water, the more formaldehyde releases, the less remained formaldehyde, which brings down the boardformaldehyde emission. The increasing glue consumption can increase the formaldehydeemission of tea stalk particleboard. As the hot-pressing pressure increases, the formaldehydeemission shows a tendency of decrease, while the prolonged hot-pressing time or higherhot-pressing temperature can also effectively reduce the formaldehyde emission. |
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