Properties And Bonding Mechanism Of Steam Explosion Eucalyptus Fiberboard Reinforced With Soluble Adhesive

With the improvement of environmental awareness, plant-based materials attracted the attention of human gradually, and the comprehensive utilization of plant resources has become a hot research topic. Among the plant-based materials, the wood plastic composite(WPC) and wood-based panels are the main large-scale industrial applications. However, there are poor compatibility problems existing between polar plant fibers and nonpolar plastic substrate in the WPC. Meanwhile, fiberboard that using urea formaldehyde resin may contain free formaldehyde and will be threat to human health, and the binderless fiberboard generally possess some low mechanical properties and poor stability. Therefore, it shows the theoretical significance and practical value to prepare environmental-friendly high strength plant-based material and to study its bonding mechanism.In this work, in order to increase the thermal deformation abilities and improve the physical and chemical bonding properties of the fiber, steam exploded eucalyptus fibers were obtained after the eucalyptus chips were subjected to steam explosion. Subsequently, an environmental-friendly high performance eucalyptus steam exploded fiberboard was prepared by employing the eucalyptus explosion fiber as the main substrate, and the polyvinyl alcohol(PVA) and gelatin were used as adhesive to improve the bonding properties of the fiber. The single factor experiment and orthogonal experiment were carried out to study the effect of formulations and processing conditions on the mechanical property, water absorption, morphology and thermal property of the fiberboard. In addition, the mechanisms of PVA and gelatin on steam exploded fiberboard were also studied in depth.The steam explosion had an important effect on the properties of eucalyptus fiberboard. Under the experimental conditions, flexural strength of 60-100 mesh eucalyptus fiberboard without steam explosion was only 8.2 MPa, and the eucalyptus fiberboard with steam explosion reached to 22.0 MPa under the same condition of molding. The mechanical property of eucalyptus fiberboard was further improved and water absorption was decreased after the addition of PVA. The flexural strength and flexural modulus of elasticity(MOE) of fiberboard reached to 50.6 and 6041 MPa, respectively, as the PVA content was 10%(wt/wt). Thus, it was feasible to improve the thermal forming property of fiber through steam explosion treatment and reinforced fiber by PVA.The mechanical property of PVA reinforced fiberboard increases as the moisture content, molding temperature and content of PVA increase, and the water absorption of fiberboard also decreases gradually. The mechanical property of some PVA reinforced fiberboard has reached the national standard. The flexural strength close to the equilibrium value of 60 MPa when the moisture content increases to 8%(wt/wt), while the flexural modulus shows an increase before the moisture content increases to 8%(wt/wt) and decreases after moisture content more than 8%(wt/wt). Therefore, a preferable moisture content is 8-11%(wt/wt). Meanwhile, the high moisture content can promote the bonding properties between PVA and fibers, and the fiber combined together tightly and show the morphology of some pieces of fiber connected together. As the temperature increases, the mechanical property of the fiberboard almost linearly increases. The flexural strength and modulus at 150 oC were 39.0 and 3762 MPa, respectively, while the flexural strength and modulus at 230 oC reach 75.7, 9268 MPa, respectively. Therefore, the preferable temperature range was 170-220 oC. Meanwhile, there is a tight bonding phenomena between fibers, and the thermal deformation properties of the fiber is improved during the higher temperature, and the crushing phenomenon in fiber joint increases and the structure of fibers are destroyed. In addition, the thermal decomposition of fiberboard also reduced at higher temperatures, and the amount of residual carbon increases, indicating that the content of cross-linking and cured reaction products increases as the temperature rises. After the addition of PVA, the pores between the fibers decrease, and the fragments of fiber increase. The PVA play as an adhesive and reinforced agent, not only attached to the fibers through the self-adhesive, but also improved the bonding properties of the fibers. Therefore, the mechanical properties of the fiberboard increases gradually and the water absorption decreases as the content of PVA increased, and the preferable content of PVA was 4-10%(wt/wt).The increase of molding temperature, moisture and the content of gelatin can improve the mechanical properties and reduce the water absorption of gelatin reinforced fiberboard within a certain range. The optimized molding temperature for fiberboard is around 210 oC, and compared to 170 oC, the flexural strength and modulus increases 35.9%, 29.1%, respectively. Meanwhile, there is a slight increase of the mechanical property of the fiberboard, and the preferable moisture content is 9-14%(wt/wt). The preferable content of gelatin for fiberboard was 4-10%(wt/wt), and the flexural strength and modulus increase to 53.9 and 6308 MPa, respectively, as the content of gelatin reaches 7%(wt/wt). In addition, the internal bonding property of fiberboard is improved at higher temperatures, moisture content and the content of gelatin. The boundaries between the fibers becomes blurred and the fiber combines with each other tightly. The maximum degradation peak(DTGmax) of fiberboard reduces and the cured products increase. Moreover, the mechanical property of part of the gelatin reinforced fiberboard has reached the national standard.