Preparation And Properties Of Polyurethane Modified Decomposed Wood

Removing hemicellulose and lignin from the wood fraction and modifying it with environmentally friendly polyurethane can improve the dimensional stability,elasticity and other properties of wood and produce functional wood.In this study,the wood was treated with polyurethane by removing the hemicellulose from poplar(Populus tomentosa Carr.)wood and part of the lignin from paulownia(Paulownia tomentosa(Thunb.)wood,and then impregnated with polyurethane to analyse the effect of the removal of different components and the modification of polyurethane on the properties of the wood.Analysis of changes in fractional content of hemicellulose removed poplar and lignin removed paulownia wood using UV spectrophotometry and high performance liquid chromatography;Observation of the changes in the cellular structure of the wood and the distribution pattern of the resin impregnation after the removal of the component wood and the polyurethane modification in combination with scanning electron microscopy;Analysis of chemical changes in decomposed wood as well as in wood modified with polyurethane,using Fourier infrared spectroscopy and X-ray polycrystalline diffraction;Analysis of the effect of polyurethane on the dimensional stability of hemicellulose stripped burl wood by means of moisture absorption and swelling resistance tests;Analysis of the elastic properties of polyurethane-modified delignified paulownia wood by mechanical properties testing.The main findings of the study are as follows:(1)The hemicellulose content of woolly poplar wood decreases with increasing removal time.The polyurethane-modified de-hemicellulose wood has a lower rate of volume change and a higher rate of weight gain as the dehemicellulose treatment time increases.The partial removal of wood half-fibres increases the porosity of the wood and the removal of half-fibres results in a thinner wood cell wall.The increased pore space in the wood provides more space for the impregnation of the polyurethane resin,resulting in an increase in the thickness of the radial cell wall.(2)Removal of the wood hemicellulose and impregnation with polyurethane improves the dimensional stability of the wood.The hygroscopic properties and hygroscopic swelling resistance of modified wood are related to the hemicellulose removal rate: the higher the degree of hemicellulose removal,the lower the hygroscopic rate of wood and the increased ASE value of hygroscopic swelling resistance.The longer the hemicellulose removal time at the same relative humidity,the lower the moisture absorption of the polyurethane-modified wood,the greater the ASE value of the polyurethane-modified wood and the increased dimensional stability of the modified wood.The dimensional stability of the wood is presented as follows: polyurethane impregnated desiccated hemicellulose poplar wood >desiccated hemicellulose poplar wood > polyurethane impregnated poplar control.(3)Removal of wood lignin,thinning of the wood cell wall and entry of polyurethane into the modified wood cell wall.The production of more microporous structures in the cell walls of delignified paulownia wood as observed by scanning electron microscopy and the formation of closed films on the surface of the cell walls of delignified wood after polyurethane impregnation;Further analysis by energy spectroscopy showed that nitrogen was present throughout the cell wall,indicating that the polyurethane penetrated into the interior of the cell wall.Using FTIR spectroscopy,the hemicellulose and lignin characteristic peaks of the decomposed wood diminished,indicating the removal of hemicellulose and lignin from the wood,while the presence of polyurethane related characteristic peaks indicated the successful impregnation of the resin into the cell walls of the wood.(4)Polyurethane modified delignified wood with good elastic properties and energy absorption.The modified wood requires 30% less stress than natural wood to reach 70% of the maximum strain.At strains of up to 60%,the modified wood can be fully restored to its original shape after releasing the stress;At a maximum strain of 30%,after 15 minutes of unloading and 100 compression recovery cycles,the modified wood achieves a recovery rate of 80%.In the small ball impact test,the energy absorption of modified wood and corrugated paper,plastic film,foam and other cushioning materials were investigated.The results show that the minimum height of the small ball bouncing after impacting the modified wood is 24 mm,and the energy absorbed by the modified wood is 0.29 J,which is twice as much as that of foam,and the modified wood has better energy absorption performance.In summary,this study was conducted to improve the dimensional stability of poplar wood and the elastic properties of paulownia wood by removing the hemicellulose and lignin from the wood and impregnating the wood with polyurethane modified decomposites.To investigate the mechanism of the effect of wood component removal on wood properties,to provide a theoretical basis for the functional modification of wood with resin to improve the performance of fast-growing wood,and to further broaden the application prospects of functional improved wood in planted fast-growing forests.