Preparation And Mechanistic Studies Of Functional Wood Materials From The Decoration Of Wood Fiber Cells

Fast-growing deciduous trees have a short cultivation time;however,there are some undesirable inherent properties,such as poor physical and mechanical properties,poor dimensional stability and lack of functions,which limit its potential applications.The aim of this work was to utilize natural hierarchical structure of wood to fabricate functional wood materials by wood cell wall chemical modification,lumen filling enhancement,modular modification and “nacre mimic” techniques.In the process,wood fiber cell functional groups were decorated in molecular level.The physical structure,chemical components,and performance of functional wood material were evaluated and characterized via universal mechanical testing machine,scanning electron microscope?SEM?,X-ray diffractometer?XRD?,X-ray photoelectron spectroscopy?XPS?and Thermogravimetric analyzer?TGA?and the functional mechanism was analyzed.The main results of this work were summarized as follows:?1?The functional organic/inorganic compound modifier was synthesized by Urea-formaldehyde acting as base,dimethyloldihydroxyethyleneurea?DMDHUE?acting as crosslinker,Lewis acid catalyst,and nano-Si O2 acting as inorganic enhancer and this compound modifier has good penetrability and high reactivity.The natural wood was modified using above modifier.Compared to the natural wood,the modified wood has an enhanced physical and mechanical performance and the water uptake has a significant decreasement.The performance improvement of modified wood was ascribed to chemical crosslinking reactions between modifier and hydroxyl groups of wood fiber molecule that can fill micropore structure of wood cell wall,inducing the improvement of physical and mechanical performance and hydrophobicity.?2?The functional composite modifier was prepared by nano TiO₂ as semiconductor material,nano Si O2 as dispersant and linker,GO as conductive material.The wood was modified using above modifier and modified wood can produce negative oxygen ions?NOI?.The ability of producing NOI is 1710 ions?cm-3 after 60 min irradiation,higher than the “fresh air” standard?1000-1500 ions?cm-3?of WHO.The excellent photocatalytic activity of nano TiO₂ was ascribed to GO's good electron transfer capacity.The photoexcited electrons could rapidly transfer from the conductive band of TiO₂ to GO through interfacial interactions.The recombination of electron-hole?e--h+?pairs having redox function could therefore be greatly suppressed in the TiO₂.So,the photocatalytic activity of TiO₂ was strongly enhanced.?3?Itaconic acid?IA?/nano-Si O2 enhance the wood cell wall by modular modification technique.In the first step,the wood fiber was activated by IA,introducing grafting anchor-carboxyl groups?-COOH?;In the second step,hydrophobic nano-Si O2 copolymerized with the activated wood fibers,causing a thicker wood cell wall?increased by 65%?.The subsequent treatment of wood with IA and nano-Si O2 improved the physical mechanical strength and thermal stability.The modified wood has a higher hydrophobicity as shown by the contact angle?CA?greater than 135°.?4?IA/polystyrene?PS?improve the performance of wood by modular modification technique.The wood composite was prepared by the impregnation of the IA solution introducing double bond?-C=C?grafting anchor into wood matrix,follow by in situ polymerization of styrene monomer upon heating to form a hydrophobic polystyrene within the wood lumens and cell walls,which achieved an improvement in the mechanical properties,dimensional stability?ASE = 50.46%?,and thermal stability of wood.The improvement of properties was ascribed to wood cell wall chemical modification and cell lumen filling enhancement.?5?The ultrastrong and tough bulk material was fabricated by a three-step process of delignification,drying-induced assembly,and water molecules-induced hydrogen bonding under compression using top-down method,Typically,strength and toughness are two material properties that mutually exclusive.Surpisingly,our prepared material showed simultaneously enhanced tensile strength?352 MPa vs.56 MPa for natural wood?and toughness?4.1 MJ?m-3 vs.0.42 MJ?m-3?.Delignification increased cellulose nanofiber surface exposure and enhanced hydrogen bonding capacity;and water molecules can assist the assembly of cellulose nanofibers by participating in hydrogen bonding as structural molecules in the mechanical compression for improved mechanical properties.