PLLA/CA composites porous ultrafine fibers with diameters of 0.89 ～ 1.21 μm and mesopores of 61 ～ 123 nm were prepared by electrospinning using DMF/DCM or acetone/DCM as solvent.The effects of composition of solvent,ratio of solvent,concentration and environment humidity on the diameter and porosity of PLLA/CA composites porous ultrafine fibers were investigated.The fiber diameter and surface morphology were studied using scanning electron microscopy (SEM),and specific surface area was calculated by N2 adsorption/ desorption isotherms.The PLLA/CA composites porous ultrafine fibers electrospun from acetone/DCM showed smaller pore diameter and larger specific surface area compared with those from DMF/DCM solvent.This was attributed to the boiling point of acetone/DCM was lower than that of DMF/DCM,the more decrease of polymer temperature when solvent was volatized,the sharper thermal induced phase separation,so the density of pore was increased.Moreover,with increasing of DCM content,the density of pore and specific surface area of PLLA/CA composites porous ultrafine fibers were increased.With increasing of polymer concentration from 3 ％ to 15％,the morphology was transformed from "porous particle" to "bead on the string",and finally forming uniform porous fibers.The characteristic PLLA/CA porous fibers was formed by thermal induced phase separation (TIPS) mechanisms,because of the sharp temperature drop caused by the quick solvent evaporation in the electrospinning process.Moreover,because the interconnected porous structure was formed,the phase separation took place in a spinodal decomposition mechanism in this system.
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