Study On Cellulose Nanocrystals Reinforced Polycaprolactone-based Composites By Electrospinning

Cellulose is the most abundant polymer in nature.Large quantities of cellulose can be extracted from wood,cotton,bamboo and even microbes.Cellulose will have many applications in the future due to its excellent properties,such as high strength,biodegradable,non-polluting and reproducible,etc.Among the many preparation methods of nanomaterials,electrospinning technology has attracted a great deal of attention from many researchers for its simplicity,high efficiency and low cost.In particular,the coaxial electrospinning technology developed in recent years provides the technical conditions for the preparing of core-shell composite fiber with multi-level structure.In the study of the preparation of nanocomposites by electrospinning,much attention has been paid to the influence of different polymer matrix and electrospinning parameters on the structure and properties of the composites.However,there are few researches about reinforcing coaxial nanocomposite fibers with CNCs.In this study,polycaprolactone(PCL)was selected as the polymer matrix,and cellulose nanocrystals(CNCs)were implanted into PCL matrix.Electro spinning technology was used to prepare nanocomposite fibers.The effect of CNCs loading on the morphology and properties of PCL/CNCs nanocomposite films were discussed.The influence of CNCs loading on the cytocompatibility of nanocomposite films was also investigated.Furthermore,the effect of different CNCs loading level on the morphology and properties of the coaxial electrospun fibers was also explored,which is of great significance to provide more application possibility for the biomaterial enhanced polymer via electrospinning.The specific research contents are as follows:(1)According to the study of optimizing the preparation process of CNCs,the preparation of CNCs by hydrolyzing microcrystalline cellulose(MCC)with 48%,56wt%,and 64wt%H2SO4 solution was investigated;CNCs were also prepared by hydrolysis MCC with H2SO4 solution at 35?,45? and 55? respectively;Cellulose powder and MCC were hydrolyzed under the same conditions to prepare CNCs;and the factors influencing the morphology and structure of CNCs were discussed.The morphology and structure of the prepared CNCs were analyzed by TEM and XRD.The results indicated that the size of CNCs decreased with the increased acid concentration and hydrolysis temperature.Under the same hydrolysis conditions,the average lengths of CNCs prepared from cellulose powder and microcrystalline cellulose were approximately 180.4±32.7 and 210.5±24.3 nm.,respectively,and the average diameters were approximately 14.3±5.3 nm and 19.3±6.5 nm,respectively.The aspect ratio were approximately 7.5 to 23.3 and 7.4 to 18.1,respectively.(2)The effects of different CNCs loading on the morphology and properties of electrospun PCL nanofiber films were investigated.A systematic analysis including the morphologies,thermal properties,mechanical properties and cell compatibility of the prepared electrospun PCL/CNCs nanofibrous films were conducted.The results indicated that the optimal reinforcement conditions of PCL fibrous films were obtained,the mass ratio of m(CNCs)/m(PCL)was 5.25%.The mechanical strength and elongation at break of the PCL/CNCs films at 5.25%CNCs loading were increased by 291%and 320%respectively compared with the pure PCL fibrous films.Pancreatic ductal cancer cells(Panc-1)and hepatic cells(HL7702)derived from human adult were successfully cultured on the PCL/CNCs nanocomposite fibrous films.Mono factor analysis of variance indicated that CNCs did not increase the cytotoxicity of PCL composite fibrous films.CNCs could be used as a reinforcing material to fabricate nanocomposite fibrous films with good mechanical properties and cytocompatibility through electrospinning,which provides feasible approaches for the application of CNCs in tissue engineering.(3)Through the preparation of coaxial electrospinning PCL/PVP composite film,the suitable concentration of shell solution was explored and the coaxial electrospinning fiber film was successfully prepared.The PCL was dissolved in dimethylformamide(DMF)and dichloromethane(DCM)as sheath electrospun solution,and the concentration of the solution was 5wt%,6wt%and 8wt%,respectively.The polyvinylpyrrolidone(PVP)was dissolved in DMF as the core layer electrospun liquid,the concentration of the solution was 25wt%,and core-shell composite nanofibers were prepared by coaxial electrospinning.The core layer diameter accounted for 50%of the coaxial diameter for coaxial nanofibers which sheath electrospun solution was 6wt%,the core layer diameter accounted for 95%of the coaxial diameter for coaxial nanofibers which sheath electrospun solution was 8wt%.coaxial.The morphology and coaxial structure which shell sheath electrospun solution was 6 wt%are the best..(4)Through the study of the preparation and performance of coaxial electrospinning CNCs-PCL/PVP composite films,the CNCs were composited into the shell of coaxial electrospun fibers.The effects of different contents of CNCs on the morphology,thermal,and surface wettability effects the coaxial electrospun fibers were investigated.Different content of CNCs were complexed with 6wt%PCL solution as sheath electrospun solution,and the content of CNCs was 1%,3%,5%,7%and 9%of the mass of PCL,respectively.The PVP solution was as the core layer electrospun solution.Coaxial electrospinning technology was used to prepare coaxial nanocomposite fibers.The effects of CNCs different loading level on the thermal and mechanical properties of the core-shell composite nanofibers were investigated.It was found that the thermal properties of nanofibers increased slightly with the addition of CNCs.Whereas,the mechanical properties did not improved.In summary,CNCs extracted from wood can significantly improve the thermal and mechanical properties of electrospun PCL fibers,and will not affect the cell compatibility of electrospun fibers.Under the experimental conditions,the thermal and mechanical properties of coaxial electrospun fibers are not significantly improved,which may be related to the destruction of the coaxial structure of fibers by CNCs.This dissertation is of great significance to further expand the application of cellulose.