Study On Formaldehyde-free Straw Board Bonding With Soy Protein Adhesive

The demand for Medium Density Fiberboard (MDF) continues to increase because of its outstanding properties, however, wood raw material shortage seriously impact on the production of the MDF. The more commonly used resins in MDF industry are UF (urea formaldehyde), PF (Phenol-formaldehyde) and MUF (Melamine-Urea-Formaldehyde). These resins are derived from non-renewable fossil resources, and will release toxic formaldehyde during its production and use.This research uses straw and soybean byproduct as the raw material to develop the environmentally friendly and safe straw beaverboard. The soybean meals were pretreated and modified to make environmentally adhesive, and straw fibers instead of wood fibers were used to ease wood raw material shortage. The formaldehyde-free straw beaverboard was created through hot press. The factors affecting the fiberboard properties were analyzed and optimized to help provide theoretical basis and quality product for the transformation of the traditional fiberboard industry. This research should help adding value to the straw and soybean meals and improving the environmental friendliness of the fiberboard. The main research components and results are as follows:1. The preparation of soy protein based adhesive through enzymatic treatment of the coarse fiber in the soybean mealsThere has a lot of research on soy protein based adhesive development. The key process used in this study was the pretreatment of the coarse fiber in the soybean using enzymes. According to the research, compared with the traditional two-stepped approach, the soybean protein gum extracted with enzyme pretreatment was less energy intensive since it reduced the need of fine-grinding and homogenizing.2. The development of straw fiberboardThe straw fiber was pretreated using Bordeaux mixture, the silicon content in the straw fiber decreased significantly according to the electron microscopic scanning imaging and colorimetric analysis results. The contents of silicon dioxide were 0.926% and 6.613%, respectively for the treated and untreated straw fibers based on the colorimetric analysis by calculating the absorbance of the straw. Based on the analysis on the main physical and mechanical performance, there were significance in static bend intensity and bonding strength for Bordeaux mixture treated and untreated straws. The maximal value of the static bend intensity appeared at 12% protein addition, and the maximal value of the internal bonding strength of the particleboard appeared at 18% protein addition, both approach the indexes listed in GB/T 21723-2008. The modulus of rupture and internal bonding of particleboard increased significantly as the density of particleboard increased, but did not changed much as the straw particle size changed.3. Optimization of the processing parameters for the straw fiberboard productionEffect of moisture content, press temperature and press time on the functional properties of the soy protein adhesive was investigated using the response surface methodology with a central composite design by means of the statistical software program Design Expert 7.1. Quadratic regression equations of physical and mechanical properties of modulus of rupture and internal bonding were established. According to the significance examination and simulating loses analyses, the model is significant and of good stability, little simulating loses. The functional properties of the straw fiberboard could be analyzed and predicted using the models.According to the response surface and contour map, within the study parameter ranges, it is found that the modulus of rupture and internal bonding of the fiberboard increased as the water content and press temperature increased. But when the moisture content reached over 30%, they both started to decrease. The modulus of rupture and internal bonding of the fiberboard increased as the press time increased. However, when the press time was over 10 minutes, the increases were no longer obvious.Based on the optimization function of the software and taking the production cost into consideration, the best process conditions reached were:the moisture content of 25%, press temperature of 175℃, and press time of 10minitutes.Under these conditions, the modulus of rupture of the fiberboard was 14.3MPa, the internal bonding strength was 0.42MPa, both of which met the requirement of GB/T 21723-2008 (behavior modulus of rupture> 14 MPa, internal bond> 0.4 MPa)4. Preliminary research of the mock hip-board with straw board as core boardsTo improve the usage of straw fiberboard, the use of straw fiberboard as core boards in the mock hip-boards were evaluated preliminary. The modulus of rupture of the hip-board produced with straw board as the core boards met the requirement of GB/T 5849-1999, but the bonding strength is much lower than the requirement of GB/T 5849-1999.