Study On Preparation And Performance Of EVA Film-Poplar Plywood

The rapid development of China’s furniture industry and the implementation of multiple environmental policies have greatly stimulated the demand for green and environmentally friendly panels.The use of thermoplastic film as an adhesive for bonding wooden materials has the advantages of no formaldehyde release,simple production process,and high production efficiency,which meets the needs of green and high-quality development in the furniture industry.This paper uses ethylene vinyl acetate copolymer(EVA)film with low melting temperature to bond poplar veneer and prepare EVA film poplar plywood.The influence of preparation process and interface compatibilization modification on the performance of plywood is explored,in order to provide a theoretical basis for the application of thermoplastic resin plywood in the field of furniture.The main conclusions of this study are as follows:(1)Using EVA film and poplar veneer as raw materials,EVA film poplar plywood was prepared using the flat pressing process.The significant effects of hot-pressing temperature,hot-pressing time,EVA film dosage,secondary setting temperature,and secondary setting pressure on the performance of the plywood were analyzed.The result showed that the hot-pressing temperature,hot-pressing time,and EVA film dosage have a significant impact on the bonding performance.When the hot-pressing temperature was 120℃,the hot-pressing time was 1 min/mm,and EVA film dosage was 163 g/m~2,the tensile shear strength of the plywood after secondary setting(secondary setting pressure was 0.5 MPa,secondary setting temperature was 25℃)was1.06 MPa after soaking in cold water at(20±3)℃for 24 hours,which was 45%higher than the tensile shear strength of the plywood without secondary setting,and can meet the requirements for Class III plywood use in GB/T 9846—2015 standard.However,due to the poor interface compatibility between EVA film and poplar veneer,there was a large gap at the bonding interface,and the tensile shear strength of EVA film poplar plywood cannot meet the performance requirements of Class II indoor plywood.(2)In order to improve the interfacial compatibility between EVA film and poplar veneer,a silane coupling agent(KH-171)solution was used to pre spray the poplar veneer.The surface properties of the poplar veneer were measured using Fourier transform infrared absorption spectroscopy(FTIR),scanning electron microscopy(EDS-SEM),and X-ray photoelectron spectroscopy(XPS),The results showed that a new chemical structure(Si-O-C Covalent bond)was formed on the surface of poplar veneer modified by silane coupling agent.Through water contact angle testing,it was found that silane coupling agent effectively deposited on the surface of the veneer,forming a hydrophobic coating.After 20 s of water droplets falling,the contact angle on the surface of the poplar veneer increased from 22°to 121°.By using EVA film and modified veneer for composite,the performance of plywood is significantly improved.Research has shown that the modification treatment conditions(hydrolysis time,amount of silane coupling agent,curing temperature)and hot-pressing temperature have an impact on the performance of EVA film poplar plywood,with the most significant impact of the amount of silane coupling agent.When the hydrolysis time of silane coupling agent was 2 hours,the dosage was 2%of the mass of the veneer,the curing temperature was 120℃,and the hot pressing temperature was 130℃,the bonding gap between poplar veneer and EVA film is significantly reduced,forming a tight adhesive layer structure.The bonding strength of the plywood reaches 1.04 MPa,meeting the performance requirements of Class II indoor plywood.(3)Micron oligomeric semisiloxane(MS)was prepared using silane coupling agent(KH-171)and neutral silicon as raw materials.Poplar veneer was sprayed with MS solution and composite with EVA film to prepare MS modified plywood.Due to the addition of neutral silicon,a significant amount of silicon element was deposited on the surface of the MS modified veneer,resulting in a decrease in surface polarity.The contact angle reached 113°after 20 s of water droplets falling.The results of FTIR,XPS and EDS-SEM showed that the surface of poplar veneer modified by MS formed a rough structure and generated Si-O-C Covalent bond,which was conducive to improving the interfacial adhesion.The MS modification treatment conditions(reaction time,KH-171 dosage,neutral silicon dosage)and hot-pressing temperature have a significant impact on the performance of plywood.When the reaction time was 3 hours,the KH-171 dosage was 5%,the neutral silicon dosage was 15%,and the hot-pressing temperature was 130℃,the wet tensile shear strength of the plywood reached 1.16 MPa,and the modification effect is the best,which is better than the modification of a single silane coupling agent.The DMA results showed that the storage modulus(E’)of plywood significantly decreases near the melting temperature of EVA.Both silane coupling agent and MS modification can improve the retention rate of the energy storage modulus of EVA film poplar plywood.(4)Using red beech wood veneer as the decorative material and EVA film as the adhesive,the decorative EVA film poplar plywood was prepared using both integrated and secondary molding processes.The effect of hot-pressing temperature on the performance of different decorative plywood was analyzed.The results showed that when the hot-pressing temperature is between 100～110℃,the surface bonding strength of the veneer plywood prepared under both molding conditions reaches above 0.75 MPa,and the impregnation peeling performance was good,both of which meet the requirements of national standards.The integrated molding process was simple,but the hot pressing time was long,which may cause discoloration on the surface of decorative veneer;For the secondary molding method,EVA film poplar plywood requires secondary hot pressing,and the re melting of EVA film would affect its own tensile shear strength.The appropriate hot-pressing temperature has a positive effect on the bonding performance of plywood,while it can cause a decrease in bonding ability.