Preparation Technology And Mechanism Of Laminating Wood Veneer With Wood Plastic Composites

Wood plastic composite has the advantages of high mechanical properties,moisture resistance and recycling.However,its surface lacks wood texture and monotonous color cannot meet people's psychological requirements for touch and vision.This defect restricts its application in architectural decoration and furniture production.Of course,its ecological and environmental advantages cannot be fully developed.Both wood fiber/high density polyethylene(WF/HDPE)and WF/polypropylene(PP)composite have a large amount of application.However,due to the processing technology and material characteristics,there is a layer of low polarity plastic assembled on the surface of WPC composite,forming a smooth and dense layer with high crystallinity,extremely low surface energy and poor wettability.This makes it difficult to bond by traditional adhesives.The purpose of this thesis is to develop methods for bonding wood veneer with WPC and mainly studying their bonding mechanism.Thermoplastic film,such as WAPE/HDPE composite film and two kinds of chlorinated polypropylene(CPP)was used as an adhesive to bond wood veneer no the surface of WPC base board(cross section size of 250×12mm2).In addition,textile fabric was bonding to WPC base board as a decorate material,and textile fabric covered WF/HDPE board was also laminated with wood veneer by adhesives.All these methods are easy to operate without volatile organic compounds and the bonding strength is enough to use as indoor products.The mechanical properties,scanning electron microscope(SEM),infrared spectroscopic analysis(FTIR),water resistant,surface toughness,x-ray photo-electric spectrometry,surface chromatic aberration,contact angle and surface energy were tested to evaluate surface bonding performance and analyze bonding mechanism.The principle of high adhesive strength and good water resistance was revealed.It provides a theoretical foundation for decorating large size wood-plastic plate.The main research contents and results are as follows:(1)MAPE/HDPE compound films were used as intermediate layer to bond WF/HDPE base board and poplar veneer by hot pressing-cool pressing process.The results show that the ratio of MAPE/HDPE did not create significant difference in surface bonding strength of decorated board and all of them can reach 1.9MPa.MAPE/HDPE has a great water resistant as a adhesive layer.MAPE/HDPE composite film has a very tight interface with both wood veneer and WF/HDPE substrate.It was found that MAPE could react with the hydroxyl group of the wood veneer and form a covalent bond.The interface compatibility between MAPE/HDPE film and WF/HDPE base board is good.Comparing to uncovered WF/HDPE panels,the mechanical properties of the veneer covered WF/DHPE board reduced.At high hot-pressing temperature(180?).surface color of poplar veneer changes significantly,surface wettability decreased.(2)Two kind of chlorinated polypropylene(CPP)films with different chlorine content were used as an adhesive layer to bond WF/HDPE board and poplar veneer.The results show that both two kinds of CPP layers provide bond line good water resistance.CPP layers with higher chlorine content provided higher adhesion strength(larger than 0.7MPa).The CPP film mainly relies on the anchor structure to bond wood veneer,which was formed when CPP molt and permeated into the pipe of wood.The bonding between CPP film and WF/HDPE substrate mainly depends on the intermolecular force and diffusion of molecular chains.Comparing to unfaced WF/HDPE panels,the mechanical properties of the decorated WF/HDPE board were not significant difference.When hot pressed at 140?,the surface color of poplar veneer changed little,surface wettability and contact angle almost did not change.(3)As an intermediate layer,CPP film was also used to bond wood veneer onto WF/PP board by hot-cold pressing process.The results show that the surface bonding strength of the veneered WF/PP board was higher than 1.2MPa,and the bond line had good water resistance.WF/PP base board with higher wood fiber content exposed more wood fibers on the surface and presented more severe surface roughness,which benefited to form higher bonding strength.There is no remarkable bonding diffusion and winding between CPP and PP molecular chains,the similar molecular chain structure provide a tightly mutual adsorption force between molecules.CPP film mainly relies on the anchor structure to bond wood veneer.Comparing to uncovered WF/PP based board,veneer covered WF/PP board at 110? shows enhanced bending strength,tensile strength and impact toughness.(4)Three kinds of fabric(canvas,nylon,polyester)were used as decoration materials and the HDPE film accumulated on the surface of WF/HDPE based board was used as adhesive.The fibric covered WF/HDPE board was prepared by hot pressing at different temperature and then cold pressed.The higher press temperature,the higher bonding strength and water resistant of decorated composite board.However,the higher temperature would result to the greater change of the fabric color.At the same temperature,the color change of canvas fabric and nylon fabric were greatest,and the change of polyester fabric was unremarkable.The surface elements and chemical groups of nylon fabric and polyester fabric did not change after hot pressing.Pectin on canvas fabrics partially decomposed when hot temperature was high.There was little change in the morphology of polyester fiber,however,fibers of canvas and nylon were pressed flat.The flexural and tensile properties of WF/HDPE composite declined after decorated with fabrics.However,the impact toughness greatly improved.(5)The polyvinyl acetate(PVAc)emulsion and PVAc-isocyanate compound adhesives were tired to bond wood veneer onto fabric decorating WF/HDPE base board.The results show that the surface bonding strength and water resistance of PVAc were lower than that of PVAc-isocyanate adhesive.PVAc emulsion depends on penetration and solidification to bond the base board and wood veneer.Isocyanates can form covalent bonds with both fabrics and wood to form tighter bonds.Comparing to uncovered WF/HDPE board,wood veneered WF/HDPE improved in mechanical properties.