| Wood is a naturally renewable composite materials and has been ubiquitously used for thousands of years,most commonly for construction,furniture and tools due to its intrinsic mechanical strength,unique sustainability,light weight,and processability.With the rapid development of the country's economy,people have a growing demand for sustainably produced wood.However,China is one of the countries that have poor forest resources and low forest resource utilization,which leads to an imbalance in the supply and demand of forest products.Forest resources can be used high efficiently through bonding and coating technology.There are over 85%wood-based products by formaldehyde-based resin,which lead to the emission of toxic formaldehyde and volatile organic pollutants in the manufacture and use stage and is damage for the health of people.It is very important to develop wood adhesive with low cost,green,and good bonding property for wood-based products.1.In this work,we develop new bionic adhesive(BA)from polyvinyl alcohol and 3,4-dihydroxybenzaldehyde.The BA is successfully used as adhesive for plywood,particleboard,wood-metal composite,and as a coating for wood.BA was synthesized by grating the catechol moieties into polyvinyl alcohol bone based on inspired-mussel protein.BA is a new thermoset resin that can rapidly be cured by the heat process that transforms from the original linear thermoplastic resin into a three-dimensional thermoset resin via SN2 and El reaction.The cured BA has an excellent water-resistant,acid-resistant,and alkaline-resistant,and has 2.34 times increase in tensile strength than the un-cured BA.Moreover,BA as an adhesive for wood,bamboo,and metal,exhibits outstanding bonding strength and water-resistant properties due to the rich hydroxyl groups and the strong adhesion of catechol moieties.Compared with the current mainstream commercial wood adhesives,BA has the advantages of green,excellent bonding performance,and low cost.BA was pilot scale produced successfully via mature adhesive production equipment due to a simple synthesized route,which is a promising application in adhesive and coating.2.Plywood is the largest volume of wood-based panel production in China.In this chapter,BA was used as a wood adhesive to fabricate the plywood.The solid content and viscosity of BA for plywood can be improved by flour filler added.The flour filler can reduce the production cost of BA for plywood and shorten the hot exhaust time,improve production efficiency,and reduce energy consumption.The optimum glue spread,assembly time,hot press temperature,pressure,and time of BA for plywood is 350 g/m2,2h,150?,7 min,and 1 MPa by the design of experiments(single factor experiment and orthogonal experiment),respectively.The prepared poplar,eucalyptus,birch,and radiata pine plywood had a 200%,162%,225%,and 108%increase than GB/T 9846-2015 in dry strength,and 71%,96%,84%,and 43%higher than the standard in wet strength,respectively,which displayed good bond strength,water resistance,and universality for wood species.The large-scale production test for plywood with BA was conducted using the mature plywood production line in Shandong Xingang Enterprise Group Co.,Ltd.Poplar,eucalyptus,birch,and radiata pine plywood were produced,with 1.22m width x 2.44 m length,and the thickness specifications including 3,5,7,and 11 layers.The bonding strength of all produced plywood met the requirements of the latest national standard(GB/T 9846-2015)class II plywood.Free formaldehyde release of the prepared plywood was about 0 mg/L by the 1m3 climate chamber method,which is a formaldehyde-free plywood product.BA is used as adhesive for plywood with the advantages of low cost,good bonding performance,no pollution,easily large-scale manufacture compared with the current commercial wood adhesives,which has a broad prospect for commercial production.3.BA had good bonding performance and water resistance when be used to bond wood and metal according to chapter 2.In this chapter,we successfully fabricated the wood-metal composite by BA.The prepared wood-metal composite had a good bond strength that met the requirements of the latest national standard(GB/T 9846-2015)class II plywood,and with an electromagnetic Interference Shielding of 60 dB that met the requirements of electromagnetic shielding civil standards(30-60 dB)in 9 kHz-1500 MHz.The wood-metal composite combined the mechanical properties of lightweight and high strength of wood and the conductive and electromagnetic shielding functions of metal,which has broad application prospects in the fields of decoration,transportation,and construction as a structural electromagnetic shielding material.4.Particleboard was be widely used in home decoration and construction due to its lightweight,high strength and low price.In this chapter,BA was successfully used to bond wood particle for particleboard.BA could be spread uniformly to the surface of wood particles by spray gun at 60? based on the viscosity of BA decreased with increasing temperature.The water-resistance of particleboard could be improved by adding a paraffin emulsion waterproofing agent.The water-resistance and mechanical properties of the prepared poplar particleboard can meet the P2 national standard at the spread glue content of 6%,the paraffin emulsion content of 1%.BA is a promising candidate wood adhesive for particleboard due to the zero-emission of free-formaldehyde and good mechanical performance.5.Coatings are generally applied to the wood surface for improving the dimensional stability,mechanical strength,and water resistance of wood.In this chapter,BA was used as the coating for wood.The strong peel strength and adhesion,with wood could be obtained by adjusting the curing degree of the BA.BA as a new wood coating has excellent pencil hardness,abrasion resistance,and water resistance when BA was heat treatment for 20 min,which is beneficial for extending the service life of the wood.Moreover,compared to solvent-based coatings,BA coatings,as a new type of water-based wood coatings,has a green environmental impact.BA has advantages of the combination of simplicity(both for synthesis and application),outstanding bonding performance,and green as wood adhesive and coating for wood.It is expected to solve the health problems caused by the release of free formaldehyde and volatile organic pollutants in the production,circulation,and use of bonded wood-based panels,and met people's demand for sustainable and environmentally friendly wood products. |
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