Performance Study Of European Ash Wood Based On Deep Eutectic Solvents Treatment

Deep Eutectic Solvents(DES)are binary or ternary eutectic mixtures composed of certain molar ratios of hydrogen bond acceptors(such as quaternary ammonium salts)and hydrogen bond donors(such as amides,carboxylic acids,and polyols).Due to their good solubility for cellulose,DESs have shown great potential in selectively changing the chemical composition and structure of wood,providing new ideas for wood modification research.This article mainly focuses on the modification of european ash with DES and aims to observe its physical and chemical properties,as well as to explore its application in molding process.Different DESs were designed and synthesized to react with cellulose of wood through various physical/chemical methods,allowing for the design and improvement of the structure and composition of the wood.This article mainly includes four parts: compression performance,bending performance,molding process research,and microstructure analysis of modified european ash.The microstructure of modified european ash was analyzed using scanning electron microscopy and transmission electron microscopy,and its chemical functional groups and structure were analyzed using infrared spectroscopy and X-ray photoelectron spectroscopy.The cellulose,hemicellulose,and lignin content of modified european ash were analyzed using the NREL method,and its crystal structure was analyzed using X-ray diffraction.The macroscopic properties of modified european ash were analyzed using colorimeters,gloss meters,Shore hardness testers,and universal testing machines.The main conclusions of this article are as follows:(1)The use of a low eutectic solvent system composed of choline chloride and lactate can effectively improve the elasticity and softness of Fraxinus mandshurica wood.After treatment with the low eutectic solvent,some hemicellulose and lignin are removed,and the modified european ash produces looseness between the cell walls,resulting in excellent toughness,good elasticity,and good compressibility.To further improve its elasticity and compressibility,treatment with sodium hydroxide solution can further remove hemicellulose and lignin,thin the wood cell walls,and form a highly porous mesh structure,increasing elasticity and achieving flame retardancy.After 50% repeated compression,the rebound rate is still as high as 95%.(2)Adding anhydrous ferric chloride to the lactic acid/choline chloride deep eutectic solvent system can enhance the processing effect and increase the flexibility and torsional resistance of european ash.Ferric chloride can act as an active site and provide acidic protons,thereby improving the processing efficiency of the deep eutectic solvent.A moderate amount of water can reduce the viscosity of the deep eutectic solvent system.Experimental results show that when the water content is 10%by weight,the most lignin can be removed from the wood,and the modified european ash can obtain the best mechanical properties and tensile rebound rate,which are 97 MPa and 13.6%,respectively.(3)Adding 10 wt% polyvinyl alcohol(degree of polymerization 2000)to the lactic acid/choline chloride deep eutectic solvent system as an active component can make the deep eutectic solvent self-adhesive.Then,the modified european ash is molded by double-layer hot pressing and crushed material hot pressing.The selfadhesive property of the deep eutectic solvent can make the modified european ash not require additional adhesives during the hot pressing process.The deep eutectic solvent can form a protective film on the wood surface,thereby giving it excellent waterproof properties(24 h water absorption rate decreased from 38% to 14%,and water swelling rate decreased from 36% to 12%)and mechanical properties(tensile strength increased from 70 Mpa to 83 MPa,flexural strength increased from 82 Mpa 90 MPa).