Preparation And Performance Of CNCs Reinforced Core-shell Composite Nanofibers By Coaxial Electrospinning

Cellulose is one of the most important raw materials in the field of material and chemical industry in recent years,and it can be extracted in a large number from wood,cotton bamboo and other higher plants,even bacterial microorganisms.Especially,for the rapid development of coaxial electrospinning technology,the technical condition has been provided for the preparation of core-shell composite fibers with multilevel structure.However,the study on the application of cellulose as a reinforcing material to coaxial composite fiber is very little.Because in the traditional electrospinning,the spinning solution is a single component solution,and the cellulose is insoluble in the traditional organic solvent,which limits its popularization and application to a certain extent.On the other hand,the preparation of core-shell nanofibers by coaxial electrospinning technology is affected by many factors,which remains a huge challenge in the preparation of fibers with uniform size and structure to maintain the electrospinning concentration without the reduction of the properties.Therefore,it is of great significance to develop a new method for the preparation of coaxial electrospun fibers with controllable conditions,good morphology and high performance.In order to solve the issue mentioned above,the cellulose nanocrystal(CNCs)was prepared by acid hydrolyzing the cellulose extrated from wood,and the condition of acid hydrolysis was studied.On the basic of this,the prepared CNCs was composited with polymer of polyacrylonitrile(PAN)to research the interactions between CNCs and PAN during the electrostatic spinning process and the effect on the properties and nanofiber morphology in the later process.The morphology and properties of coaxial electrospinning nanofibers were studied by selecting appropriate electrospinning parameters and adding the CNCs.Analysed the metal ions absorption performance of coaxial electrospinning nanofibers which was increased by adding CNCs to expand the application of coaxial electrospinning fibers.The specific research contents and results are as follows.(1)CNCs with different sizes and high crystallinity were successfully prepared by hydrolyzing cellulose with 58、64wt%concentrated sulfuric acid.The wide X-ray diffraction results showed the crystallinity of CNCs was 62.78%hydrolyzed by 64 wt%concentrated sulfuric acid which was higher than obtained by 58 wt%concentrated sulfuric acid.The CNCs was obtained with length of 100±31nm and width of 13.4±5.2nm hydrolyzed with 64 wt%sulfuric acid.The corresponding aspect ratio was 7.7.The CNCs with good size and good crystallinity were successfully prepared by controlling the condition of acid hydrolysis.The main purpose is broading the application of biomaterials and providing raw materials for the electrospinning nanocomposites below.(2)The properties of PAN-based CNCs electrospun nanocomposites were studied in this paper.The electrospinning solution of 12,14,16,18 wt%of PAN/DMF(w/w)were placed.The morphology of the composite fiber was observed by SEM and the best recipe was 16 wt%PAN/DMF solution.As the increase in CNCs content from 3 to 12%,the microstructure and metal ion adsorption properties of PAN/CNCs composite nanofibers was not ideal due to the poor bonding performance between CNCs and PAN without active agent such as surfactant,which greatly affected the properties of the PAN-based composite.(3)A modified coaxial electrospinning process including poly(methyl methacrylate)(PMMA)solution with different CNCs addition as sheath fluid and PAN solution as core fluid was used for preparing excellent composite nanofibrous mats.The effect of physical properties(conductivity,viscosity and surface tension)of the as-spun solutions were investigated.Conductivity of the as-spin solutions increased significantly with increasing CNCs addition which is favor forming uniform fibers.Effect of different CNCs addition on the morphology,thermal behavior as well as multilevel structure of the coaxial electrospun PMMA+CNCs/PAN composite nanofibers were also reported.Morphology analysis of the obtained nanofibrous mats clearly demonstrated that the composite nanofibers with core-shell structure were successfully produced with CNCs presence.The core layer was shown to be well coated by the shell layer by TEM images.Furthermore,diameter of the composite nanofibers was getting smaller and more uniform with increasing CNCs concentrations in the shell fluid.For the thermal performance of the core-shell nanocomposite mats with CNCs reinforced,the maximum thermal decomposition temperature was quite higher than electrospun pure PMMA,PAN as well as core-shell PMMA/PAN nanocomposites.The improved thermal stability of PMMA+CNCs/PAN coaxial nanofibrous mats was ascribed that CNCs could interconnect with each other during coaxial electrospinning to form rigid interconnected network,and also the CNCs could form electrostatic attraction effect with PMMA.The BET results showed that the specific surface area of the CNCs reinforced core-shell composites was larger with increasing CNCs addition,starting from 3.76 m~2/g to 9.62 m~2/g.Dense porous structure formed on the surface of the electrospun core-shell fibers.The addition of CNCs in coaxial electrospinning exhibited a stronger reinforcement compared with the electrospun pure core-shell PMMA/PAN nanocomposites.(4)A modified coaxial electrospinning process including PAN/DMF solution with different CNCs addition as sheath fluid and CA/DMA solution as core fluid was used for preparing excellent nanofibers composite with core-shell structure.To promote the interfacial compatibility of CNCs and PAN,the surfactant was added into the sheath fluid.The morphology,thermal and Cu(Ⅱ)metal ions adsorption performance of nanofibers composite were investigated.Morphological analysis of the nanofibers showed that the nanofibers with uniform morphology could be obtained in the low CNCs concentration.The morphology of nanofibers became more and more anomalous with the increased of CNCs concentration.As for the thermal properties of nanofibers,the maximum thermal decomposition temperature of nanofibers composites with core-shell structure can be obviously improved with the adding of CNCs.As for Cu(Ⅱ)metal ions adsorption,the maximum adsorption capacity of nanofibers composites was up to 68 mg/g,when the concentration of CNCs was 12%.To summarise,the CNCs extracted from wood with good physicochemical properties could obviously improve the morphology structure,thermal stability of the nanofibers composite with core-shell structure.It also can improve the application performance of nanofibers composite with core-shell structure.This studies have great significance to expand the application of CNCs and improve the properties of nanofibers composite with core-shell structure.