Structural Control And Properties Of Polymer Electrospun Fibers

Nanofiber technology possesses advantages of easy operation,high productivity and accesss to most polymers,which is widely applied to making polymer nanofiber.The electrospunning is characterized by great surface area,high void content,minimun fiber diameter and small pore size,thus attracting great attention.The thesis focused on forming of polymer nanofiber,formation of polymer nanofiber structure,modification and application of polymer nanofiber.The results are listed as the followings:(1)Via previous research,factors such as concentration of solution,electic field strength,condition of electrospinning will influence the produce of uniform nanofibers by electrospinning.The concentration of the solution is the main factor.Only when the solution reaches above entanglement concentration,it will get uniform nanofibers.On the contrary,electrospinning will get beaded in the nanofiber.In this experiment,polylactic acid with different molecular weight was selected as the experimental materials,based on which it gets nanofiber membrane.Electrospinning from low-molecular-weight PLA solutions yields unbeaded fibers only above the entanglement concentration of about 3.8 %(w/v).In contrast,uniform nanofibers can be electrospun from high-molecular-weight PLA solutions even with a concentration of 0.5 %(w/v).This concentration is below the corresponding entanglement concentration of about 1.1 %(w/v).However,electrospinning from a solution below its entanglement concentration produces uniform nanofibers while high-molecular-weight PLA is adopted.Slow relaxation of high-molecular-weight PLA is expected to preserve chain interconnectivity in the highly stretched liquid jets during electrospinning.Correspondingly,rapid cold crystallization and high modulus are exhibited by the resultant PLA nanofibers because of remarkable molecular alignment.(2)Previous research indicates that temperature,different proportions of PLLA and PDLA affect the formation of polylactic acid stereocomplex crystals,but theory about whether or not the electrospinning can form stereocomplex as well has not yet been confirmed.And research about whether or not the molecular weight will affect the formation of stereocomplexes has not been investigated.Therefore,from three groups of different molecular weight(L-lactide)/poly(D-lactide)=1/1 blends by electrospinning,the error range of fiber diameter is less than 10%.From experiment,low molecule weight PLLA/PDLA can form little stereocomplex by electrosipinning,but high molecule cannot form stereocomplex.Cold crystallization of electrospun fibers results in profuse stereocomplex crystals.(3)The polymer nanofibers are characterized by a large specific surface area and easy modification,which are widely used in the making of sensor,thus greatly improving the sensitivity.In this experiment,the sensors are assembled with hybrid core-shell nanofibers where electrospun poly(acrylonitrile)nanofibers act as mechanical cores and thin polyaniline shells as moister sensing materials,respectively.The polyaniline shells are coated on the electrospun nanofiber via in situ polymerization.The sensors are sensitive to moister breathed out from both mouth and nose,and their sensitivity is determined by the loading and morphology of polyaniline as well as the amount of moister.By controlling the reaction periods 10 min,15min,20 min can get the most sensitive.Experiments have shown that the hybrid nanofibers with a reaction period of 15 min are the most sensitive to monitor breath from both mouth and nose In combination with high porosity and mechanical flexibility,the sensors can be readily integrated with textiles to fabricate wearable electronic devices.