| Recycling is an effective way to reduce environmental pollution and prevent resource depletion.Wood plastic composite is mainly made of recycled wood and thermoplastics,which is an environmentally friendly material.Wood plastic composite has a good processing performance,moisture resistance,corrosion resistance,non-flammable,non-toxic,recyclable and other advantages.Wood plastic composite with veneer has the advantages of excellent processability,exquisite appearance,highly cost effective,and outstanding physical and chemical properties.This paper focuses on the problem of low polarity,smooth and non-porous surface of wood-plastic composites that are difficult to glue,developing easy-to-operate and environmentally friendly process for the preparation of wood veneer decorating wood plastic composites,and conducting an in-depth analysis of the bonding mechanism.The research results are important for promoting the application of green composite materials in furniture and interior decoration industries,and for alleviating the contradiction between wood supply and demand in China and implementing sustainable development strategies.The main research contents and results of this paper are as follows.(1)Effect of surface morphology of WF/HDPE composites on surface bonding propertiesThe surfaces of wood-plastic composites were treated with four mechanical sanding materials:sandpaper,nylon,steel needle and steel wire wheel,and veneerdecorating wood fiber/high density polyethylene(WF/HDPE)composites with high interfacial bondingstrength were prepared using isocyanate cross-linked polyvinyl acetate as adhesive.The surface bonding strength and impregnation peel properties of the veneered WF/HDPE composites were tested,and the morphological and chemical properties of the sanded surfaces were analyzed by Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and surface contact angle and roughness tests.The results showed that all four mechanical sanding materials removed the plastic matrix from the surface layer of WF/HDPE composites and exposed the wood fibers,but the surface of WF/HDPE composites showed different morphological states and affected the wettability of the surface.Proper surface roughness and sufficient fiber exposure are necessary for WF/HDPE composites to form a tight bond.Surface sanding treatment is a simple and effective method,in which nylon wheel(nylon substrate wound with silicon carbide)treated wood-plastic composite veneer was the best,and the surface bonding strength could reach 1.74 MPa with good water resistance.(2)Mechanism of the effect of surface implantation of natural fibers on improving the surface bonding strength of WF/HDPE compositeTo improve the bonding strength between veneer and WF/HDPE composite,jute fabrics or fibers were first implanted on the surface of WF/HDPE composite,and then laminated with veneer.The test results of surface bonding strength and impregnation peel performance showed that when the least density of the three jute fabrics was used as the interlayer,the surface bonding strength was improved most advantagesously;when part of the jute fibers was retained as the interlayer,the bonding strength between the substrate and veneer was improved more substantially to 1.27 MPa and had better water resistance.The presence of the interlayer caused the gluing area of WF/HDPE composite and veneer to be separated into two parts.One part was the bonding between jute and veneer,and the other part was the bonding between jute and WF/HDPE composite.During the gluing process,the veneer and jute fibers were firmly bonded together with the help of the chemical reaction of the isocyanate cross-linked polyvinyl acetate adhesive;the other end of the jute fiber was embedded in the HDPE matrix on the surface of the substrate,and the mechanical interlocking force played an important role.(3)Surface decoration of WF/HDPE composite by one-time hot-pressing methodThe WF/HDPE substrate,glued jute fabric and veneer were laminated by hot-pressing,using the HDPE matrix on the surface of the substrate to bond the fabrics to the substrate,while the fabrics and veneer were bonded to each other by adhesive.The process was simpler and the adhesive strength between the substrate and veneer could reach 1.28 MPa by one-time hot pressing.The surface bonding strength of 1.65 MPa could be achieved by directly hot pressing two types of veneers,black walnut and sapele with a non-woven backing to the WF/HDPE composite,using the hot-melt properties of the non-woven backing and the HDPE matrix on the surface of the substrate,and the water resistance could be greatly improved compared with the bonding method using traditional adhesives,and could reach the level of Class Ⅰ,Level 0.(4)Analysis of the strain distribution of veneered WF/HDPE composite using the DSCM methodThe WF/HDPE composite and the veneered WF/HDPE composites were analyzed by DSCM test to study the strain distribution under different stresses.The results showed that the strain patterns of various composites were basically the same during the continuous increase of stress until the bending fracture of the composites.The maximum strain values on the upper surface were mainly concentrated at the center line of the loading roll,and the maximum strain values on the lower surface were also located near the center line,but the distribution range was larger.The strain spread along the length of the specimen to both ends with the increase of load,which was due to the fact that the wood fibers inside the WF/HDPE composite had certain orientation during extrusion,and the stress spreaded along the fiber direction when the specimen was under pressure.The strain value also changed along the thickness direction,the middle layer of the specimen had the smallest strain value,increasing from the middle layer to the upper and lower surfaces respectively.The maximum load of the WF/HDPE composite itself was 11.25 kN,and the maximum load of the veneered WF/HDPE composite treated by nylon wheel reached 13.32 kN.The maximum load of veneered WF/HDPE composites with jute fabric and jute fiber as the intermediate medium layer were 12 kN and 8 kN repectively.The maximum load of the veneered WF/HDPE composites with black walnut and sapele were 11.61 kN and 13.12 kN.Except for jute fibers as the intermediate layer,all other veneer methods increased the maximum bearing capacity of the composites. |
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