Moisture Sorption And Deformation Response Mechanisms Of Furfurylated Poplar Wood To Cyclically Changing Relative Humidity

Fast-growing wood is relatively abundant,but its high-value application is still restricted by its poor quality.Furfuryl alcohol was used as the modifier to improve wood properties for its superiority over environmental friendliness and excellent modification effects,such as prominent improvement of dimensional stability.However,previous researches were almost conducted under the equilibrium condition or static condition where the temperature and relative humidity were constant,which is far from the practical condition for wood processing or serving,where the temperature or relative humidity is changing continuously,that is the dynamic condition.To improve the dimensional stability of fast-growing wood for higher use value,wider application and longer service life.Fast-growing poplar wood(Populus euramericana Cv.)was chosen as the specimen and modified by the furfuryl alcohol in this study.Dynamic moisture sorption and deformation responses of furfurylated wood to cyclically changing relative humidity were studied.On this basis,the physical-chemical environments for wood-water interactions were reconstructed and the effects of chemical components were further investigated by varifying the relative percentage of chemical components in wood cell walls through different-level removal.Some advanced methods,such as scanning electron microscope,confocal laser scanning microscopy,fourier transform infrared spectroscopy,nuclear magnetic resonance,nitrogen adsorption,low field nuclear magnetic resonance and dynamic vapor sorption were used to analyse the relation between wood structures and properties and clarify the modification mechanism.The main results of this study can be summarized below:(1)Poplar wood was charaterized by naturally hierarchical structure,and exhibited rich hydroxyl accessibility,which provided the physical-chemical environment for wood-water interactions.The dynamic moisture sorption and deformation responses were much less than the static value.Partial hemicellulose removal caused decreases of moisture sorption and dimensional changes,while partial delignification brought about reverse effects,indicating that lignin was relatively hydrophobic in wood.(2)Furfurylation changed the physical-chemical environment for wood-water interactions.Hydrophobic furfural resin was in situ polymerized in both cell lumens and cell walls,which reduced the wood porosity,the hydroxyl accessibility,and the attraction to water molecules,at the same time,the cell walls of wood were bulked.As a result,the dynamic moisture sorption and deformation responses decreased suggested by over 30% reduction of average moisture content and dimensional changes,over 20% decrement of moisture and dimensional amplitudes as well moisture sorption coefficient and humidity expansion coefficient.(3)Partial hemicellulose removal contributed to more uniform distribution of furfural resin in wood and higher weight percent gain and bulking rate as well as lower hydroxyl accessibility,which helped reducing the hygroscopicity and improving dimensional stability of furfurylated wood.Due to the synergistic effects of hemicellulose loss and furfurylation,the physical-chemical environment for wood-water interactions was changed.Dynamic moisture content,dimensional changes,their amplitudes,moisture sorption coefficient and humidity expansion coefficient all fell with the most scope above 50%,indicating the prominent performance by combining hemicellulose removal with furfurylation to reduce hygroscopicity and improve dimensional stability of wood.(4)Some degree of delignification could help improving the porosity and hydroxyl accessibility of furfurylated wood generally,so that larger moisture sorption and dimensional changes were generated.On the other hand,more uniform distribution of furfural resin in wood and better cell wall modification benefited a lot from the porosity changes due to partial delignification.As a result,furfurylated wood after partial delignification exhibited lower porosity and hydroxyl accessibility.Moreover,the dynamic moisture content,dimensional changes,their amplitudes,moisture sorption coefficient and humidity expansion coefficient of furfurylated wood after delignification were all maximally lower than those of control wood by over 20%.The results implied the potential application value in terms of improving the properties of wood suffered from natural or artificial lignin degradation.