Study On Chestnut Bur/poplar Low-formaldehyde Emission Particleboard

China is a country with relatively scarce wood resources but relatively abundant non-wood plant resources.A new way to effectively solve the problem of wood resource shortage has been opened up by the rational use of non-wood plant resources.Chestnut bur is a tannin-rich agro-waste material generated in the chestnut production.In this study,the characteristics of chestnut bur were analyzed to assess its application value for composite panel.Particleboards were manufactured from the mixture of chestnut bur/poplar particles,urea-formaldehyde(UF)resin was used as bonding adhesive.And the formaldehyde reduction mechanism of particleboard was explored.In this study,the possibility of chestnut bur as raw materials for particleboard production was explored by fiber morphology and chemical composition.The surface morphology and thermal properties of chestnut bur were studied by scanning electron microscope-energy dispersive spectrum(SEM-EDS)analysis and thermogravimetric analysis.Chestnut bur is a spherical bur and the fiber morphology is very similar to that of hardwood.Chestnut bur showed low cellulose,hemicelluloses and lignin contents but high extractives and ash contents compared with poplar wood.The content of hot water extract of chestnut bur is 29.30%,the content of alcohol benzene extractive is 10.90%,the content of Klason lignin is 18.30%and the content of holocellulose is 52.87%.The ash content is 3.28%,and the total phenol content is 13.79%.The results of SEM-EDS analysis showed that there were many silicon-rich protuberances on the fiber surface.Thermogravimetric analysis showed that the thermal stability of chestnut burs is not as good as that of poplar,and the residual carbon rate is higher than that of poplar.Therefore,the chestnut bur is a material rich in phenols and similar to some hardwoods,but when the chestnut bur was used as the raw material for particleboard production,it needed to be composited with other woods.Five-type particleboards were manufactured from the mixture of chestnut bur/poplar particles with the weight ratios of 0/100,25/75,50/50,75/25 and 100/0,UF resin was used as bonding adhesive.The results showed that with the increase of chestnut bur content,the IB,MOR and MOE of particleboard showed a downward trend.However,the dimensional stability,flame-retardant and smoke-suppressing properties of the particleboard have been improved,and the release of free formaldehyde has also been significantly reduced.When the chestnut bur content in the composite board was not higher than 75%,the mechanical properties of particleboards could meet the requirement of Chinese national standard GB/T4897-2015 for P2 type particleboard.The free formaldehyde emission is 0.47 mg/L of particleboard could conform to the F***standard of Japanese JIS(0.5 mg/L).By comparing the particleboard prepared with OF resin as the adhesive and the particleboard prepared with isocyanate,it can be seen that the MOR and MOE of the particleboard prepared with isocyanate do not increase significantly.This study disscussed the relationship between the hot-pressing temperature(145?,160?,175?,190?),hot-pressing time(3.5min,5min,6.5min)and the particle size(A,B,C)with the physical and mechanical properties of particleboard and the influence of free formaldehyde emission.The results showed that the best process parameters within the test range are the hot-pressing temperature of 160?,the hot-pressing time of 5min and the crushed material form B.Using pyrolysis gas chromatography-mass spectrometer and Fourier infrared spectrometer,as well as the analysis of the remaining total phenol content of particleboard with different ratios,the mechanism formaldehyde reduction of particleboard was explored.The experimental results show that the chestnut bur contains phenolic substances that can react with formaldehyde.Through the addition of the chestnut bur,the phenolic substances in the chestnut bur react with formaldehyde to generate more characteristic peaks of C-H and C-O in ortho and para positions of the phenolic hydroxyl group of the phenol ring.Through the analysis of the remaining total phenol content of the particleboard with different proportions,it can be known that the phenolic substances in the chestnut bur reacted with free formaldehyde,thereby reducing the free formaldehyde release of the particleboard.