Properties And Mechanisms Of Wood Modified By Paraffin-based Pickering Emulsions

The hydrophobicity and dimensional stability as well as the photostability and decay resistance of wood can be improved by paraffin impregnation.Also,wood can be endowed with good mechanical properties,improved surface hardness and decay resistance by penetrating inorganic solid particles(silica and MMT).Combined with these two effective methods for wood modification,based on the mechanism of solid particles stabilized emulsions(Pickering emulsion),different inorganic nano-particles were used to prepare paraffin-based Pickering emulsions which can be used for the potential application in wood treatment.The properties and modification mechanism of the wood treated by three types Pickering systems and one type silica sol system were investigated by diverse analysis methods,such as FTIR,SEM-EDX,TEM,TG,and LSCM.The aim of this study was to investigate the effect of different emulsion systems(with different concentrations of solid particles)on the properties of emulsion and treated wood.Moreover,the modified mechanism for paraffin-based Pickering emulsion treated wood was clarified,that is,the synergetic effect of paraffin and solid particles was determined to enhance the overall properties of treated wood.Furthermore,DVS and N2 adsorption methods were applied to study the sorption hysteresis behavior and porous characterization of MPTS modified SiO2.The main conclusions are summarized as follows(1)Pickering emulsion,with the droplet size below 200nm,synergistically stabilized by hydrophilic SiO2 and surfactant could be used for wood treatment.The droplet size decreased with the increasing concentration of silica and showed more stability when lwt%was added.Paraffin showed the negative effect on thermal stability of treated wood,but it could be compensated by the positive effect of silica at lwt%and 2wt%loading.The reaction between silica and wood matrix was found by showing the lowing y peak for the emulsion treated wood from the DMA analysis(2)Pickering emulsion synergistically stabilized by surfactant and SiO2/MMT(SMC)particles which were prepared by sol-gel method,was used to treat wood.The higher ratio of TEOS to MMT caused increasing content of Si-OH,resulting in intense self-condensation of Si-OH and influencing the penetration of sol to MMT layer.The droplet size of the emulsion increased with the increasing loading of SMC,which resulted in lower WPG for treated wood compared to the one treated by the emulsion stabilized by silica.The convex structure was observed in the cell lumen that treated by the emulsion with lwt%SMC.This is benefit to the improvement on hydrophobicity.Wood treated by the emulsion with SMC showed better thermal stability than the one treated by silica stabilized Pickering emulsions,but showed inferior properties on WPG and compression strength.(3)Different Si-OH contents on silica surface were obtained by modifying SiO2 with different concentrations of MPTS.The porous structure and moisture sorption behaviors were investigated.Excessive MPTS(>4wt%)did not replace-OH on silica surface but took self-condensation.The porous characterization of silica was influenced by MPTS concentrations,that is,the specific surface area decreased from 271.8 m2·g-1(control)to 90.8 m2·g-1 when 8wt%MPTS was added.This indicated that the pore structure counld be filled by MPTS.Different hysteresis behaviors of modified silica were observed and moisture adsorption behaviors(monolayer moisture adsorption and multilayer moisture adsorption)could be analysised by H-H model.(4)Pickering emulsion synergistically stabilized by surfactant and MPTS modified SiO2/MMT was applied to treat wood.The hydrophobicity of SMC could be improved by MPTS modification and 4wt%was the optimal loading level.The droplet size increased with the increasing concentration of solid particles and tended to be stability when more solid particles were added.Solid particles could be adsorbed on the oil/water interface effectively and penetrated to the wood matrix,resulting in increasing WPG.The convex structure was found at 0.1 wt%loading of solid particles.All the samples treated with Pickering emulsion showed better thermal stability and hydrophobicity(120°)than control.Moreover,the surface hardness and compression strength of treated wood were better than the one treated by silica or SMC stabilized emulsions.(5)Compared with aqueous dispersions of silica powder with different pH values,the silica sols with different pH values could be used as wood modifiers.Based on the DLVO theory,Zeta potential of silica sol was significantly influenced by the pH,resulting in the de-aggregation behavior of sol particles.The wood treated by sols at pH=5 and pH=11 showed better impregnability and overall properties,while the sol with pH=13 resulted in inferior properties(80.4%weight lose and 51.4%water uptake).Moreover,the future study were proposed based on these observations.