Preparation And Performances Of Electrospun Cellulose-enhanced Nanocomposites

Wood-based cellulose,as one of the most abundant polymer in nature,has been widely used as a filler in various polymer matrix due to its excellent properties,such as high crystallinity,high Young's modulus,super-hydrophilicity,etc.Therefore,cellulose is applied to the preparation of nanocomposites with high-performances and special structure.Among various preparation methods for nanocomposites,electrospinning is an advanced technique which is both simple and reproducible to prepare one-dimensional composite nanofibers.The non-woven nanofibrous structure obtained by electrospinning has many application prospects can be used in many fields.However,the super-hydrophilicity of cellulose is an important factor that affects the incompatibility of cellulose with polymer interface,and therefore directly influence the structure and properties of electrospun nanofibers.Furthermore,only organic or aqueous phases were used mostly in traditional electrospinning.The limited in as-spun solutions can also limit the application of many polymer matrix or fillers.In order to solve the addressed issues above,we used two different polymers that one is hydrophilic and the other is hydrophobic as the matrix.Nanocellulose were incorporated into the different polymer matrix to make electrospun cellulose-enhanced polymer namocomposites.The interaction between cellulose and plymers as well as the effect of this interaction on fiber morphology and performances were investigated.Moreover,the electrospinability of cellulose-stabilized emulsions was also explored to provide more application possibility for the biomaterial-strengthed polymer via electrospinning.The specific contents were as below:(1)Polystyrene(PS)dissolved in the mixture of N,N-dimethylformamide(DMF)and/or tetrahydrofuran(THF)was electrospun to prepare fibers with sub-micron diameter.The effects of electrospinning parameters,including solvent combinations,polymer concentrations,and applied voltage,on fiber morphology,tensile and hydrophobic properties of the fiber mats were investigated.Scanning electron microscope(SEM)images of electrospun fibers(23%w/v PS solution with applied voltage of 15 kV)showed that a new type of fibers with double-strand morphology was formed when the mass ratio of DMF and THF was 50/50 and 25/75.The tensile strength of the PS fiber film was 1.5 MPa,indicating the strong reinforcement from double-strand fibers.Bead-free fibers were obtained by electrospinning 40%(w/v)PS/DMF solution at an applied voltage of 15 kV.When the ratio of DMF and THF was 100/0,the maximum contact angle(CA)value of electrospun PS films produced at 15 kV was 148°.(2)Cellulose nanoparticles with different sizes were successfully prepared by applying 64,56,and 48 wt%sulfuric acid hydrolysis process.The rodlike cellulose nanocrystals were obtained with length of 420±38,322±21,?141±28 nm and width of 32±8,21±5,9±3nm.The corresponding aspect ratio were 11.5?13.1?13.2?15.3,and 14.1?15.7.The wide X-ray diffraction(WAXD)results showed that the crystallinity of the obtained cellulose was significantly increased with increasing the concentration of sulfuric acid.CNCs hydrolysised by 64 wt%had the largest crystallinity of 85.6%.An electrospinning process was successfully utilized to manufacture polystyrene/cellulose nanocrystal(PS/CNC)nanofibrous mats,and the morphology,crystallinity,thermal behavior,and mechanical properties as well as hydrophobic properties of electrospun PS/CNC nanofibrous mats were investigated.Morphological analysis of the obtained nanofibrous mats demonstrated that fine nanofibers with smooth and smaller diameter could be obtained with increased CNC contents.Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results showed that PS and CNCs were physically mixed and CNCs were probably distributed on the surface of the electrospun nanofibers.The structural property e.g.crystallinity of the electrospun nanofibers was examined using WAXD.It was indicated that crystallinity could be increased as a result of the increased addition of CNCs and aligned nanofiber orientation.Thermal properties of electrospun PS/CNC nanocomposites were enhanced by increasing CNC loading levels.The tensile strength of electrospun PS/CNC nanofibrous mats was elevated 170%by incorporating 7 wt%CNCs in PS matrix,while the ductility was decreased from 60 to 25%.The hydrophobic property could be increased to 138° when 1 wt%CNCs were incorporated.(3)Uniform fibers composed of two concentrations of poly(vinyl alcohol)(PVA)separately reinforced with cellulose nanocrystals(CNCs)derived from microcellulose crystals(MCCs)had been successfully produced by electrospinning.The morphological,thermal,thermomechanical and mechanical properties of fabricated nanofibrous mats were investigated.The CNCs by sulfuric acid were well dispersed in both 5 wt%PVA(5PVA)and 7 wt%(7PVA)aqueous prior to fiber formation.Bead-free fibers with controllable ultra-thin diameters which were around 200 nm were generated reproducibly at all CNC contents investigated and fiber diameter turned out to be much smaller by increasing the CNC addition.Compared with the nanofibers obtained from lower PVA concentration,the nanofibers electrospun from higher concentration of PVA aqueous could stack more orderly.Shifts in thermal and thermomechanical transitions of PVA with increasing CNC content suggest that the intermolecular hydrogen bonding interactions can be obtained to strengthen properties of PVA/CNC nanofibrous mats.Interestingly,in the case of same CNC addition,nanofibrous mats produced from 7PVA reinforced with CNC nanoparticles have higher degree of crystallinity than nanocomposite with 5PVA as matrix due to the more orderly stack of 7PVA nanofibers as well as the stronger interactions between 7PVA molecular chains and CNC nanoparticles.For the mechanical analysis,composite nanofibrous mats with 7PVA as continuous phase and CNCs as reinforcement showed a modest increase of 1.4 fold in the maximum tensile stress,while those of 5PVA counterparts showed almost the same.(4)In this study,when cellulose nanofibrils(CNF)existed,an ionic surfactant(SDS)-assisted CNF-stabilized emulsion system was successfully fabricated by simply mechanically blending oil and aqueous phases.The interfacial properties of SDS molecules in both CNF solution and emulsion were investigated.The influence of CNF and SDS concentration on the formulation of emulsions,phase behavior,and emulsion stability was studied.The ionic strength of aqueous phase adjusted by sodium chloride was also explored to investigate the electrolyte responsive behavior.It has been found the phase transition behavior of SDS-assisted CNF-stabilized emulsion systems can be controlled to transfer oil-in-water at low salinity,through oil-in-water with irregular droplet morphology at medium salinity,to bi-continuous-like at high salinity.Hydrophilic cellulose nanofibrils(CNFs)were incorporated via emulsification in a hydrophobic polymer for the synthesis of composite nanofibers.Non-ionic surfactants were used to emulsify aqueous dispersions of CNF with an organic phase containing dissolved PS.Varying surfactant-oganic-CNF compositions were tested yielding multiple emulsions of a water-in-oil-in-water type.CNFs allowed formation of stable emulsions,which otherwise phase separated,and made the emulsions can be used as a electrospinning material.The morphology of the nanofiber electrospun from these CNF-stabilized emulsions was studied.The result showed that the electrospun nanofibers were also bead-on-string structure,but not with homogeneous distribution and smooth surface.