Study On Manufacturing Process Of Binderless Medium Density Fiberboard By Fiber Pretreated With NaOH/Urea And Grinding

While the man-made board industry has developed rapidly, the contradictions of the shortage of raw materials and the release of free formaldehyde also have been increasingly emerging. The research is carried wood fiber as a raw material, using sodium hydroxide (NaOH)/Urea as the reagent, combining with grinding method to pretreat wood fiber. Without any adhesive and other additives, using the wet fiberboard production process, to compress the pre-processed wood fiber into medium density fiberboard and explore the feasibility of binderless fiberboard forming. The pretreatment process conditions of the wood fiber and the hot-pressing process conditions of bindeless fiberboard are optimized by through the response surface analysis, also it can analyze the interaction of different influence factors. Besides, by using X-ray diffraction analysis (XRD), scanning electron microscope(SEM) and Fourier transform infrared spectrometer (FTIR), the forming mechanism of binderless fiberboard is investigated preliminarily. The results are as follows:(1) Without any adhesive and other additives, it is ok to obtain a better performance binderless fiberboard whose various physical and chemical properties meet the national standard GB/T 11718-200<<medium density fiberboard>> in dry and humid conditions using medium density fiberboard performance requirements by controlling the related parameters of the pretreatment and the hot-pressing process.(2) The single factor experiments show that within the scope of this test, the grinding clearance has apparent effect on the plank 24 h absorbing water thickness expansion rate (TS), static bending intensity(MOR) and modulus of elasticity (MOE); the various proportions of NaOH/Urea has significant influence on 24 h TS, MOR, MOE, and internal bond strength (IB) of binderless fiberboard; the pretreatment immersion time has obvious impact on MOR; the hot-pressing temperature influence 24 h TS and IB to a certain extent; with the extension of hot-pressing time, IB increases largely, while MOR and MOE increase firstly, and then go down, it is obvious to reduce 24 h TS by extending the hot-pressing time.(3) Basing on response surface experiment analysis: the additive amount of NaOH/Urea, the pretreatment immersion time, the grinding clearance and hot-pressing time influence MOR very significantly, also the interaction of the grinding clearance and hot-pressing temperature affect MOR remarkably. These five factors influence on IB is very prominent, but the interaction of the factors are not significant. Hot-pressing temperature and hot-pressing time of the five factors have the most significant influence on the 24 h TS. The MOE is affected by NaOH/Urea, grinding clearance,hot-pressing temperature and hot-pressing time remarkably, while the influence of the interaction of various factors is not significant.(4) On the basis of the response surface 3D figure contour analysis and model equation optimization, under the premise of meeting the People's Republic of China national standard GB/T 11718-2009-in the dry and wet state using the ordinary type with boards requirements, and combining with actual production cost factor, namely the lowest amount of NaOH/Urea added, the grinding clearance is moderate, the shortest of the pretreatment immersion time, the lowest of hot-pressing temperature, the shortest of hot-pressing time. Finally, get an optimal process parameters of binderless fiberboard: NaOH/Urea content ratio is 1.92%:3.84%, the pretreatment immersion time is 2.5 h, the grinding clearance is 0.34 mm, hot-pressing temperature is 204.19?, hot-pressing time is 5.75 min.Considering the actual operation, the pretreatment and hot-pressing process is set to: NaOH/Urea content ratio is 2%:4%, the pretreatment immersion time is 2.5 h, the grinding clearance is 0.4 mm,hot-pressing temperature is 205?, hot-pressing time is 6 min.(5) According to the XRD and FTIR analysis, within the scope of this test, the crystallinity of fiberboard is lower than the crystallinity of fiber after preprocessing, but both are higher than the original wood fiber, it can be known that the pretreatment conditions make a part of hemicellulose and lignin degradation, and after hot-pressing, the condition of high temperature and high pressure makes cellulose degradation occurred to a certain extent, and its inherent crystalline region is damaged. In the forming process of the binderless fiberboard, a series of changes in fiber itself and the combination of molecular force are both helpful for the self-bonding forming.