Research On Preparation And Functionalization Of Wood-Based Composites By Vacuum-Assisted Resin Transfer Molding

Wood,as a plentiful natural and renewable resource,exhibits tremendous potential for various applications in many fields.However,untreated natural wood possesses several drawbacks,which often limit its direct utilization as a raw material.Therefore,it is necessary to enhance the mechanical strength of natural wood and imbue it with new properties through physical and chemical treatments to meet diverse application requirements.Vacuum-assisted resin transfer molding（VARTM）is a widely used technique for improving the mechanical performance of composite materials.In this study,focusing on the limitations of natural poplar wood,such as its low mechanical strength,poor water resistance,inadequate thermal conductivity,and limited mechanical properties,we employed VARTM to reinforce the mechanical performance of composite materials,using low-strength poplar veneer as the matrix.Furthermore,we designed and modified the laminate structure of the composite material,introducing carbon fiber fabric as a reinforcing phase to impart new electromagnetic shielding properties and enhance the mechanical performance.Additionally,we explored the multifunctionality of the wood-based composite material by modifying the fiber surface structure at the scale of poplar fibers,thereby controlling the composite material’s structural system to bestow multiple functionalities.We systematically investigated the microstructure and chemical composition of the fabricated wood-based composite materials and studied the influence of these factors on their mechanical properties.Moreover,we examined the formation mechanisms of the material’s mechanical strength,water resistance,thermal conductivity,and electromagnetic shielding properties.The impact of composite material structure on performance and the potential applications of the multifunctional wood-based composites in specific novel fields were also discussed.The main research conclusions of this study are as follows:（1）High-strength multilayer composite materials were successfully prepared using the VARTM technique.The porosity of the multilayer composites was reduced from 59.4%（in the raw wood）to 9.2%.The majority of the internal voids within the wood structure were filled with epoxy resin,resulting in a densified structure.Consequently,the mechanical strength of the samples significantly surpassed that of traditional plywood and raw wood.The newly developed multilayer composite materials exhibited a flexural strength of 261.0 MPa and tensile strength of 120.2 MPa,which were considerably higher compared to traditional plywood（flexural strength of 76.7 MPa and tensile strength of 39.6 MPa）and natural poplar wood（flexural strength of 90.1MPa and tensile strength of 52.0 MPa）.Furthermore,the epoxy resin filling and reduced porosity contributed to excellent water resistance（12.7%-72 h）and superior surface hydrophobicity（contact angle of 102.8°）.（2）high-strength wood-based composite material with electromagnetic interference（EMI）shielding effectiveness was successfully fabricated using the VARTM technique by incorporating a carbon fiber fabric-poplar veneer sandwich structure.The composite material exhibited shielding effectiveness of 40 d B against electromagnetic waves in the frequency range of 8.2-12.4 GHz（X-band）.The flexural and tensile strengths of the composite material were significantly enhanced,measuring 442.3 MPa and 195.5 MPa,respectively,which were approximately six times and three times higher than those of natural poplar wood（flexural strength of 69.8 MPa and tensile strength of 55.6 MPa）.Additionally,compared to poplar,the composite material demonstrated excellent thermal conductivity,good water resistance,and surface hydrophobicity.The incorporation of carbon fiber fabric not only improved the mechanical performance of the samples but also endowed them with the capability to shield electromagnetic waves,thus enabling potential applications of the wood-based composite material in the field of EMI shielding.（3）Using the VARTM process and starting from the fiber scale of poplar wood resources,poplar wood was treated with delignification and mixed with a clay-like Ti₃C₂T_x solution to establish a mixed system.A new type of multifunctional bio-based composite material was successfully prepared,which has high density,high thermal conductivity,water resistance,and excellent flame retardant performance.Due to the technical characteristics of the VARTM process and the stable mechanical properties of MXene,the MXene-poplar fiber composite material exhibits good mechanical properties.As MXene is attached to the surface of the fiber,the thermal conductivity of the composite material(0.92 W·m^-1·K^-1)is significantly improved.Compared with natural wood(0.41 g·cm^-3),the composite material with a densified structure has a higher density(1.43 g·cm^-3).In addition,the composite material also has excellent water resistance and good surface wettability.Due to the TiO₂ nanolayer formed by the decomposition of Ti₃C₂T_x at high temperature,the composite material exhibits excellent flame retardant performance.This high-strength,environmentally friendly,and multifunctional composite material is expected to be used in electronic components and their packaging materials.Building upon the previous research,a new multifunctional bio-based composite material has been successfully developed using wood fibers and MXene,which exhibits high mechanical performance,high density,high thermal conductivity,water resistance,and excellent flame retardancy.Poplar was treated with delignification and then mixed with the clay-like Ti₃C₂T_xsolution to establish a hybrid system.The mixture was then molded using the VARTM process and infused with epoxy resin,followed by hot pressing to produce the new composite material.Due to the technical characteristics of the VARTM process and the stable mechanical performance of MXene,the MXene-wood fiber composite material demonstrated excellent mechanical properties.MXene attachment on the fiber surface also significantly improved the thermal conductivity of the composite material(0.92 W·m^-1·K^-1).The composite material with a densified structure had a higher density(1.43 g·cm^-3)compared to natural wood(0.41 g·cm^-3).Additionally,the composite material exhibited excellent water resistance and good surface wetting.The TiO₂ nano-layer formed by the decomposition of Ti₃C₂T_x at high temperatures had a flame-retardant effect,resulting in excellent flame retardancy of the composite material,which did not show any signs of combustion even under alcohol lamp flames.This high-strength,eco-friendly,and multifunctional composite material is expected to find applications in electronic components and their packaging materials.The preparation process of the novel wood-based composite materials developed in this paper provides ideas for the full utilization of wood resources in different forms,starting from the two scales of veneer and fiber.Compared with natural poplar wood,the multifunctional high-strength wood-based composite material prepared by the VARTM process has significantly improved both in mechanical properties and functional diversity.The idea of molding waste wood after treatment is also significant for protecting the environment and improving resource utilization,providing a new strategy for the multifunctional application of natural wood resources in different fields.