Microstuctural And Micromechanical Properties Of Pinus Massoniana Wood Cell Wall With Phenolic Resin

In this paper,Pinus massoniana lumber was impregnated with low molecular weight phenolic resin?PF?to study the resin impregnation of Pinus massoniana wood with different solid content?15%,20%,25%and 30%?.Macroscopic physical and mechanical properties.Characterization of the distribution and filling of resin in wood by confocal fluorescence microscopy.Using Raman spectroscopy,nanoindentation and dynamic modulus imaging techniques,the changes of resin composition and impregnation amount on the chemical composition,structure and micro-dynamic and static mechanical properties of modified wood cell wall were investigated.The mechanism of wood impregnation modification is studied at the cell wall level,which provides a theoretical basis for the effective utilization of wood materials.The results show:?1?After the impregnation of Pinus massoniana wood with different solid content PF resin,the wet weight gain rate is basically stable at about 80%.The absolute dry weight gain rate and basic density increase with the increase of resin solid content,and the maximum absolute dry weight gain rate is 39.5%.The basic density is 0.68g/cm³;The hardness and the compressive strength of the impregnated modified wood gradually increase with the increase of the solid content of the resin,and increase by 39.24%and 21.66%respectively under the 30%solid content impregnation;Impregnation treatment has a significant impact on the shrinkage rate of wood shrinkage.With the increase of the solid content of the resin,the radial shrinkage shrinkage rate of the wood string shows a downward trend,and the radial shrinkage and wetness increase is about1/2 of the chord direction.The dry shrinkage rate of wood is reduced by up to 67.73%,and the saturated volume of wetness is reduced by up to 58.91%.?2?It can be seen from the scanning electron microscope that the PF resin is first immersed in the wood micron scale by the large pore structure in the wood,filled in the axial tracheid,wood ray and cell gap of the wood,and combined with the inner wall of the wood cell.It is relatively tight and has no obvious gap.It can be seen by confocal fluorescence microscopy that with the increase of solid content of PF resin,the surface resin permeation area and the number of permeation cells increase gradually,and the permeability area and number of core layer increase first and then decrease.The surface penetration area and the number of permeations are 2 to 8 times and 1.5 to 6 times,respectively,of the core layer.The penetration uniformity of the 20%solid content resin in the wood core layer is better.?3?Raman spectroscopy analysis found that low molecular weight PF resin can not only be distributed on the micrometer scale of wood cell cavity and pit,but also enter the cell wall through the microfibril gap in the cell wall,and penetrate at the nanometer scale;In the Raman spectrum,not only the characteristic peak of PF resin appeared,but also a new characteristic peak was formed in the range of 1000⁸50cm^-1.It is speculated that the PF resin chemically crosslinks with the cell wall component of wood.Infrared spectroscopy analysis showed that the wavenumber position of the absorption peak of the modified material was basically the same as that of the original wood,but the intensity of the peak was greatly different,and a weak absorption peak appeared at 1110cm^-1.X-ray diffraction technique showed that the crystallization peak position of wood cell wall was not shifted after impregnation with resin,indicating that the immersion treatment did not destroy the crystal structure of wood;the relative crystallinity of cell wall decreased with the increase of solid content of resin,suggesting that PF resin molecule It penetrates into the amorphous region of the cell wall by osmotic diffusion,causing a decrease in crystallinity.?4?The static nanoindentation test further indicates that the low molecular weight PF resin can be immersed and filled with the cell wall layer of Pinus massoniana wood,and can significantly affect the mechanical properties of the wood cell wall.After being impregnated with different solid content resins,the cell wall hardness and elastic modulus of the surface layer of the modified material were improved to different extents,and the surface cell wall growth was significantly larger than that of the core layer;with the increase of resin solid content,the cell wall hardness and elastic modulus of the wood The amount increased first and then decreased,and the maximum increase was at 58%solid content,which increased by 58.8%and 27.1%respectively.Whether the PF resin filled the cell cavity had no significant effect on the increase of cell wall hardness and elastic modulus of the modified wood.?5?Dynamic modulus mapping technology can acquire complete dynamic mechanical parameters such as interfacial storage modulus and loss modulus,so different parts of impregnated wood with different mechanical information?such as resin filling area,cell wall area,intercellular layer area,etc.?can be distinguished by scanning graph.PF resin has lower storage modulus and loss modulus,showing brittleness;wood cell wall has higher storage modulus and loss modulus,showing viscoelasticity;the modulus of composite intercellular layer is slightly lower than that of cell wall,approximately showing a"w"shape modulus distribution.After impregnated with different solid content resin,the energy storage modulus of the cell wall in the surface core layer of the modified material increased to varying degrees,and the increase of the cell wall in the surface layer was slightly larger than that in the core layer.With the increase of resin solid content,the storage modulus of wood cell wall first increases and then decreases,but the change of loss modulus is not obvious,and there is a downward trend.The change trend of elastic modulus and storage modulus of wood cell wall after resin impregnation is similar,but storage modulus is about1.08-1.13 times of elastic modulus.