Study On The Influence Mechanism Of Eucalyptus Prehydrolysis On The Structure And Properties Of Nanocellulose For Bioscaffold

In tissue engineering,biological scaffolds are the core influencing factors.Its purpose is to imitate extracellular matrix,create and maintain spatial structure for cell growth,provide a suitable microenvironment,and promote tissue repair and regeneration.Scaffolds generally require properties such as high porosity,wide pore size distribution,high mechanical strength,large specific surface area,and good biocompatibility.As a member of nanomaterials,nanocellulose has the characteristics of good biocompatibility,non-toxic and degradable,large specific surface area,and excellent mechanical properties.Therefore,in recent years,research on nanocellulose-based bioscaffold has gradually become a hot spot.The microstructure（diameter,length,and surface micropores）of nanocellulose directly affects the structure and performance of its scaffold,and there are few reports on this aspect of research.In this paper,the effect of Eucalyptus pre hydrolysis stage on the microstructure of dissolving pulp based Cellulose Nanofibril（CNF）was studied.The results showed that pre hydrolysis did not change the crystal structure of CNF,but destroyed the intermolecular and intramolecular hydrogen bonds of CNF;When the pre-hydrolysis temperature increases from 145°C to 175°C,the CNF crystallinity index increases from 59.56%to 78.26%;When the pre-hydrolysis time was extended from 30 min to120 min,the CNF crystallinity index increased from 65.89%to 75.37%,and then slightly decreased to 73.71%;This is because the change of the pre-hydrolysis temperature focuses on the degradation of the CNF amorphous region,while the change of the pre-hydrolysis time has an important impact on the intermolecular and intramolecular hydrogen bonds in the amorphous and crystalline regions.SEM and gas adsorption show that there is a nano-scale pore structure on the surface of CNF.As the strength of the pre-hydrolysis increases,the hydrogen bonds in CNF gradually break.Some nanopores on the surface of CNF become larger and larger,and new small nanopores are also produced,which can increase the specific surface area of CNF aerogels.In order to further reveal the effect of prehydrolysis on the hydrogen bond structure of nanocellulose,nanocellulose was directly prepared by prehydrolyzed eucalyptus.The CNF structure was characterized and analyzed by Fourier Transform Infrared Spectroscopy（FTIR）,two-dimensional correlation infrared spectroscopy,X-ray diffraction,transmission electron microscopy（TEM）and thermogravimetric analysis（TGA）.The results show that the crystal structure of CNF is cellulose I_βtype,and pre hydrolysis has little effect on the crystal plane spacing of CNF,but it can increase the crystal size of CNF on the 110 and 200 crystal planes by 24.5%and 22.6%,respectively.The order of effect of prehydrolysis on hydrogen bond of CNF is v（weak hydrogen bond）>v（free hydroxyl）>v（O（3）H…O（5））>v（O（2）H…O（6））>v（O（6）H…O（3′））。To explore the effect of changes in the microstructure of nanocellulose on the structural properties of the scaffold,two sets of samples,CNF without pre-hydrolysis（CNF-0h）and CNF pre-hydrolyzed for 4 h（CNF-4h）,were cross-linked with sodium alginate through Ca²⁺to Prepare aerogel bio-scaffolds（Gel-0h and Gel-4h）.The results showed that the CNF prepared by pre hydrolysis was more favorable for the stability and formation of porous structure of aerogel scaffolds,and the ordered spatial structure also gave the scaffolds more mechanical properties.At the same time,the high crystallinity and larger crystallite size of CNF and chemical bond between CNF and alginate significantly improved the thermal stability of aerogel scaffolds.The maximum decomposition temperatures of Gel-0h and Gel-4h were 315.76°C and 323.51°C,respectively.Compared with Gel-0h,Gel-4h aerogel scaffold has a micron porous structure（20-80μm）,a more concentrated nanopore size（3-10 nm）,a higher porosity（88.3%）,larger specific surface area（40.73 m²/g）and strong mechanical properties,which can provide enough space and mechanical strength for cell growth,and can be used as a biological scaffold.This indicates that the changes in the microstructure of nanocellulose by pre-hydrolysis will have a significant impact on the performance of the bioscaffold.