Consideration ofthe present market situation that the physical and mechanical properties of the straw particleboard is inferior and formaldehyde content cannot eliminated completely, we have studied the ingredient of adhesive and manufacturing process of straw particleboard. In this paper, MgSO4, MgCO3, active silicon and ALSiO4 etc. were selected as inorganic gelled material, soybean pulp were alkalized and acidified of separation to acquire the bean gum, then, the bean gum and modified MDI(diphenylmethanediisocyanate) were added deionized water according to the mass ratio of 100:1 - 10 as organic gelled materials. Finally, the four types of compounded adhesive were made according to the ratio of the inorganic gelled materials to the organic gelled materials: T1(1:4), T2(1:9), T3(9:1), T4(4:1). The compounded adhesive additive proportion(AAP) were the percent of the total quality of pre-compressive materials, they were 15%, 30%, 45%, 65% respectively for each ratio corresponding with the percent of effective solid composition in the straw particleboard of8.25%, 16.5%, 24.5%, 35% for each ratio, respectively. The experimental levels of the pressure in the hot compression were set to 10, 40, 60, 80MPa, and the experimental levels of the duration of hot compression were set to 1, 3, 6 and 10min. The compressive technological parameters of straw particleboard was optimized through L16 (45) orthogonal experiment. The straw particleboard of 10±2mm thickness was compressed to two pieces with rice straw and corn stalk respectively.The test samples were cut from the compressed particleboard according to the national standard for the test of performance parameters. The optimal technological process was obtained. The ratio of inorganic gelled material to organic gelled material quality was 4:1, the additive proportion of adhesive (AAP) in the pre-compressive straw material was 65%, namely, the solid effective composition in the straw board was 35%. The optimal condition in the hot compression also included the duration of hot compression 5min, hot-pressing temperature 120℃, and hot-pressing pressure 80 MPa. The range analysis to the experimental results showed that the pressure, the proportion of the inorganic gelled material and additive proportion of compounded adhesive were significant influence on the performance indexes of the straw particleboard. The higher proportion of inorganic gelled material in compounded adhesive increased density, internal bonding strength and static bending strength, and decreased thickness swelling rate of water absorption except enhancement of flame resistance. Moreover, thermo-gravimetric analysis of materials and micro-observation of straw particleboard were performed. The results showed that compounded adhesive made thermal weight loss of straw material down to 48% when the straw was heated to 1000℃, straw coated with adhesive carbonized in the heat process and the mass loss rate was the largest at about 340℃. Micro-observation indicated that adhesive biochemical reacted in the surface layers of material, the straw material were connected by white crystal (alkaline magnesium sulfate) together, thus improved the internal binding force and static bending intensity and other performance index. Adhesive had great influence on the thermogravimetric characteristic of straw materials, the microstructure of straw particleboard. The straw particleboard could reach or exceed the national standard of medium density fiberboard (MDF) under the optimum technological condition. This study is significant on the development and utilization of straw resources and the production of man-made board. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
