Research On Preparation Process And Performance Of Corn Straw Particleboard

With the development of national economy,people's demand for household products is increasing.Wood and wood-based boards are the main raw materials for household products.Due to the influence of the national policy of forest harvesting and the improvement of ecological environment requirements,the raw materials of wood-based board become more and more tense.Using crop straw instead of wood to make wood-based board is an important way to alleviate the shortage of raw material supply.Corn straw is an important agricultural residue.There are two main difficulties in the preparation of straw particleboard with corn straw.One is that the smooth and dense waxy layer covered on the surface of corn straw epidermis will hinder the penetration of adhesive,making it difficult for straw particleboard to achieve stable adhesion,which has adverse effects on the mechanical properties of straw particleboard;the other is that with the development of mechanization,mechanical harvesting has become the main way of corn harvesting.The straw treated by mechanical harvesting is 3-5 cm long,which can not be directly separated by the separation machine.The pith and leaf group in the straw can significantly reduce the comprehensive performance of straw board.In addition,the coupling of particle size and resin content will directly affect the performance of corn straw board.It is important to study the effects of particle size and resin content on the performance of corn straw board for manufacturing high-performance corn straw board.The main contents and conclusions are as follows:(1)The effects of different treatment methods on the adhesion properties of waxy layer of corn straw epidermis were studied.The corn straw was treated by hydrothermal acid,hydrothermal alkali and sanding treatment,which were compared with the untreated straw.The surface of corn straw was characterized by contact angle tester,infrared spectrometer and scanning electron microscope,and the mechanism of wax layer removal was explored.In order to analyze the effect of different treatment methods on the removal of wax layer,the shear test of adhesive surface was carried out.Based on the experiment results,the effects of different treatment methods on improving the adhesive strength were compared.According to the micro morphology of shear fracture surface,the micro mechanism of the effect of wax layer on the adhesive strength of straw was explored.The results showed that 2%hot alkali treatment could remove the wax layer of straw,2%hot acid treatment could not remove the wax layer,and mechanical grinding treatment could remove the wax layer.The waxy layer of straw peel can be completely removed after 2%thermal alkali treatment for 20 minutes,and the bonding shear strength can reach 5.34 MPa.(2)The separation efficiency of the resin,pith and leaf of five different separation processes for mechanical harvesting corn straw were compared,and the mechanical properties of particle boards made from five raw materials were tested,which verified the importance of optimizing the separation process.It is concluded that grinding technology and grading screening are beneficial to improve the separation efficiency of corn straw rind,pith and leaf.The best separation method is crushing,screening,grinding,air separation and drying.The proportion of skin,leaf and pulp is 93.56%,5.79%and 0.65%respectively.In addition,in order to remove the pith and leaf in the straw rind fully,this paper further explored the influence of screening gradient on the separation effect.The research shows that the multi-step grading and fine screening can effectively improve the separation effect of the pith and leaf from the straw rind,and the purity of the obtained straw rind can be up to more than 95%.(3)Based on the process of multi-step grading and fine screening,the effects of particle size and resin content on the properties of straw particleboard was studied.Urea formaldehyde resin was used to manufacture pure corn straw,and the comprehensive performance of the boards were tested.By dynamic thermal mechanical analysis,the dynamic thermal mechanical properties of different particleboards were explored.In addition,scanning electron microscope was used to observe the fracture surface of the particle board after the inter bonding strength test.The micro morphology of the fracture surface was used to analyze the micro mechanism of the effect of particle size on the internal bond strength.Based on the analysis results of the comprehensive performance of corn straw particleboard with different particle size and resin content,a three-layer straw particleboard with fine surface and coarse core was designed.The comprehensive performance of the board was optimized by changing the particle size distribution.The board was made of 30-40 mesh straw as surface layer and 24-30 mesh straw as core layer.The modulus of rupture of the board was 32.50 MPa,the modulus of elasticity was 3.83 GPa,the internal bonding strength was 0.93 MPa,the 2 h thickness swelling is 7.30%,and the 24 h thickness swelling is 14.21%.It meets the requirements of heavy-duty particleboard(P4 type)used in dry state specified in GB/T 4897-2015.