Preparation And Performance Of High-strength Multifunctional Wood-based Composite Materials

Poplar,as one of main tree species of fast-growing forest,has the disadvantages of low strength and poor quality,which severely limits its application.Therefore,the modification of fast-growing poplar has important academic and practical significance to render the high added value of poplar,which is also important for alleviating the contradiction between wood supply and demand,reducing energy consumption,and promoting the sustainable development of our society.In this thesis,fast-growing poplar wood was used as raw material,and multi-step modification processes were adopted to develop high-strength,multi-functional wood-based composite materials.The modification mechanisms of poplar wood were revealed through structural characterization and performance analysis.In addition,laminated veneer lumber was prepared by the integration of modified wood,which provides a new strategy for high value-added utilization of wood.The main results and conclusions of this thesis are as follows:（1）High strength wood was prepared by delignification and densification of fast-growing poplar.Its flexural strength and tensile strength are 402.9 MPa and 313.6MPa,respectively,showing excellent mechanical properties.The LOI value is 27.9%,indicating an excellent fire-resistance behavior.After being immersed in water for 120h,the final spring-back rate is 88.8%.The wear rate along the fiber direction and the perpendicular fiber direction are 37.8 and 45.2 10^-6mm³/Nm,respectively.（2）Silica/poplar composite material was prepared through a three-step modification process,including delignification,in-situ growth of nano-silica and densification.The flexural strength and tensile strength of silica/poplar composite are395.6 MPa and 253.4 MPa,respectively.The LOI value is 36.7%,which outperforms the densified poplar without silica.After being immersed in water for 120 h,the spring-back rate is 66.7%.the wear rate along the fiber direction and perpendicular to the fiber direction are 18.0 and 20.7 10^-6mm³/Nm,respectively.（3）Poplar/epoxy veneer was firstly prepared by a three-step modification process of delignification,soaking epoxy resin,and densification.Then,the laminated veneer lumber was prepared by the integration of three layers of poplar/epoxy veneer with parallel lay-up.The flexural strength and flexural modulus of veneer are 358.7 MPa and 27 GPa,respectively.The static flexural strength and elastic modulus of laminated veneer lumber are 170.7 MPa and 12.5 GPa,respectively.When immersed in water for120 h,the thickness expansion rate is 28.0%.The results reveal that the high strength wood prepared in this work has a dense intertwined laminate structure,which not only results in its excellent mechanical properties,but also offers enhanced flame retardant,water resistance and wear resistance.In addition,the delignified poplar wood was further compounded with silica and subjected to a densification treatment,which can further improve its flame retardancy,waterproofing,and wear resistance.Moreover,laminated lumber with excellent mechanical properties and good dimensional stability was prepared by the integration of delignified poplar wood/epoxy veneer,which is meaningful to obtain large-size wood.Compared with fast-growing poplar,the densified poplar and its composite materials developed offer extraordinary mechanical properties and functionalities,which would have wide application in construction,transportation,home furnishing and other industries.