Preparation And Properties Of Rosin/Boron Nitride Modified Compressed Poplar Wood Thermally Conductive Materials

To expand the application of fast-growing wood in the field of thermal management,wood-based thermally conductive composites have been developed in recent years and are commonly used in geothermal flooring,electronic substrates,and other fields.In this study,fast-growing poplar（CW）was used as the base material,rosin（R）and boron nitride（BN）were used as impregnating fillers,and the wood was treated by vacuum followed by pressure impregnation,and then the wood was hot pressed with compression ratios of 50%and 75%.Compressed wood（W）,impregnated rosin/boron nitride compressed wood（R/BN）,and delignified impregnated rosin/boron nitride compressed wood（D-R/BN）were prepared.The thermal conductivity,heat transfer properties and thermal stability of the wood before and after modification were characterized by transient planar heat source method,infrared thermography and thermogravimetric analyzer;the structural changes were analyzed by infrared spectroscopy and X-ray diffractometer;the changes in microstructure of the samples were analyzed by scanning electron microscopy,laser confocal microscopy and energy spectrum;the changes in weight gain and density of the samples were analyzed to investigate the water contact angle,moisture absorption and water absorption of the wood before and after modification The changes in water contact angle,moisture absorption and water uptake,and mechanical properties of the wood before and after modification were investigated.The main research contents and results of this paper are as follows:（1）After hot pressing,the fibers are more neatly and tightly arranged so the relative crystallinity increases.The thermal conductivity of W-_50%is to 0.21 W·m^-1·K^-1 at 50%compression and to 0.27 W·m^-1·K^-1 at 75%compression,which is 80.0%higher relative to the material CW;the bending properties and cross-grain resistance increase with compression;the water contact angle of the wood surface increases.The moisture absorption resistance and water absorption resistance were improved.（2）After rosin/boron nitride modification and compression,infrared showed C=O and B-N-B stretching vibration peaks at 1690 cm^-1 and 810 cm^-1,respectively.With the increase of compression rate,the impregnated modified wood was more densely and the weight gain rate and density increased;the thermal conductivity of R/BN-_75%increased to 0.37 W·m^-1·K^-1,an increase of 37.0%relative to W-_75%.When subjected to heat,the temperature of R/BN-_75%increased the fastest and the thermal conductivity was the strongest;after modification,the bending strength of R/BN-_75%was 156.4 MPa,which increased with the increase of compression rate,and the compressive strength of R/BN-_75%was 400.2 MPa,which was 15.4and 2.1 times higher than that of R/BN and R/BN-_50%,respectively;the wood surface became hydrophobic;the moisture absorption rate and water absorption rate both decrease are 5.1%and 78.6%,and the dimensional stability of wood is obtained.（3）After delignification impregnated with rosin/boron nitride modified and compressed,FTIR showed weakened absorption peaks at 1730 cm^-1,1590 cm^-1 and 1505 cm^-1,indicating partial removal of lignin.The presence of C=O and B-N-B stretching vibration peaks at 1690cm^-1 and 810 cm^-1,respectively,indicates that rosin and boron nitride are present inside the wood.The weight gain and density increased with increasing compression;the thermal conductivity of D-R/BN-_75%increased to 0.42 W·m^-1·K^-1,which was 13.5%and 55.6%higher relative to R/BN-_75%and W-_75%,respectively.When subjected to heat,the temperature of D-R/BN-_75%increased the fastest and the thermal conductivity was the strongest;after modification,the bending properties were reduced and the cross-grain compression resistance increased;the surface of the wood was hydrophobic and the moisture and water absorption rates were reduced,which improved the dimensional stability of the wood.In summary,the thermal conductivity and dimensional stability of wood can be improved by vacuum-pressure impregnation of rosin/BN followed by hot pressing of modified wood.This study provides theoretical reference for the functionalization of wood for thermal conductivity,which makes the application of wood in the field of heat dissipation materials possible.