Preparation And Performance Investigation Of Steam Exploded Straw-fiber/PVA Molded Product

Straw is a rich renewable resource.The fiber morphology of straw is poor and its epidermis contains a high content of wax and silica,which limits the application of straw.Therefore,it is of great significance to improve the structure and properties of straw.In this paper,the rice straw as the research object,the use of screw-extrusion steam explosion technology to destroy epidermal structure of rice straw and improve its fiber morphology.At the same time,this paper presents a dry sizing method of polyvinyl alcohol(PVA)without adding water,the plasticization of PVA was promoted by the moisture of fiber,and the molding of PVA and pretreated rice straw was realized.The structure and properties of screw-extrusion steam explosion pretreated rice straw were investigated by scanning electron microscopy,ultraviolet-visible absorption spectrum,fourier transform infrared spectroscopy,X-ray diffraction,thermogravimetric analysis,components testing and moisture absorption testing.The results showed that the size of rice straw after pretreatment was obviously decreased,the wax and silica of the epidermis fall off,the lignin of the intercellular layer is stripped and the fiber bundles were separated,the lignin and hemicelluloses were degraded partly,which was beneficial to the improvement of the performance of binderless board.Binderless board were prepared from rice straw pretreated by screw-extrusion steam explosion and mechanical pulverization,and the effects of two pretreatment methods on the properties of board were studied.The results showed that the smaller the size of the rice straw particle,the better the performance of binderless board was obtained.When the particle size of the straw was more than 100 meshes,the modulus of rupture of the board was 15.53 MPa;the modulus of rupture of the board prepared by screw-extrusion steam explosion was 23.04 MPa.In order to further improve the performance of the board,the composite board was prepared by directly mixing PVA dry powder and pretreated rice straw with certain moisture.The effects of PVA polymerization degree,PVA alcoholysis degree,raw material moisture content and temperature on the properties of the composite board were studied.Under the conditions of the hot pressing temperature of 200?,the moisture content of fiber is 10%,the hot pressing time is 7 min and the molding pressure is 10 MPa.The results showed that the plasticizing ability of PVA with 88% alcoholysis degree was better than that PVA with 99% alcoholysis degree,low degree of polymerization of PVA plasticization ability is better than high polymerization PVA plasticization ability.Among them,when the PVA with a degree of alcoholysis of 99% is added,the bending properties of the boards are poor.When adding PVA with a degree of alcoholysis of 88%,the flexural properties of the boards all meet the national standards.In addition,the moisture content of the raw material and the hot pressing temperature will also affect the properties of board.Appropriately increasing the moisture content of the raw material and the hot pressing temperature can enhance the performance of the board,but the raw material moisture content and the temperature are too high will cause the delamination of fibreboard and the degradation of fiber respectively.When the moisture content of the raw material is 10% and temperature is 210?,the modulus of rupture and modulus of elasticity the composite board are as high as 57.92 MPa and 6780 MPa,respectively.The pretreated rice straw was used to prepare molded containers,the effects of mold taper and PVA on the forming properties of the containers were studied.The results showed that increasing the mold taper angle was beneficial to the molding of the molded container.Without the addition of PVA,a complete product can not be obtained.Addition of PVA can effectively improve the flowability of rice straw,molded products can meet the design requirements,and it also has a high compressive strength.When the mold taper angle of 13 o,the ultimate load of molded containers can reach 2.1 KN,it makes the molded container has a higher value.