Study On The Preparation Of Polymer Composite Microspheres Via Electrospraying

Electrospraying (also known as electrostatic spraying) is a novel way to prepare polymer composite microspheres under high voltage. Compared to the traditional methods, electrospraying features in its simple operation, high purity of the product, wide application range of polymer species. In this paper, the process of the polymer microspheres and composite microspheres (including polymer-inorganic microspheres and polymer-polymer microspheres) preparation was studied, as well as the influence of various parameters and the application of this method.The process of the microspheres formation with coagulation bath was studied with the polymer model of PC (Polycarbonate) and PHBV(Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)). The influence factors were also researched, such as mass concentration (w), potential (V), collecting distance (D), flow rate (φ), conductivity (ε). It was revealed that the microspheres formation via electrospraying-to-bath was divided into two parts:solvent evaporation in air and double diffusion in the bath. The most influential factor is the solution concentration. Specifically, the microsphere size and the distribution were raised with the increasing of w. Beaded fibers were founded when PHBV concentration was raised to 3wt%. With V increased, the size was decreased. Meanwhile, with D increased, the size was reduced first and then increased. Especially While D was small, PHBV microspheres were shaped blood cell or bowl. The particle size was increased as the growing of flow rate. Besides, with the value ofεincreased, size was decreased and beaded fibers trended to be obtained.CDA/ZnS composite microspheres were in situ precipitated in ZnSO4 bath with the electropraying of CDA/(NH4)2S/acetone composite solution. ZnS particles coated in CDA were formed with the diffraction of Zn2+ and S2 along with the diffraction of solvent and nonsolvent. The composite microspheres were characterized by optical microscope, scanning electron microscope(SEM), transmission electron microscope(TEM), X-Ray diffraction(XRD) and fluorescent microscope. Compared with pure ZnS nanoparticles electrosprayed by in-situ precipitation, it was founded that pure ZnS particles were around 20-50nm and fluorescent while particles were aggregated at a certain degree; CDA/ZnS composite size was approximately 1μm with ZnS particles around 5-20nm dispersed better in the composites. It was indicated that the ZnS particles were best dispersed and coated in the 3wt% CDA. The fluorescence intensity would be higher while ZnS particles were dispersed better and particle size was decreased. The overall morphology of CDA/ZnS composite was more decided by the polymer content and composite size was slightly reduced with the addition of inorganic salt solution.The preparation of drug delivery system was imitated through coaxial electrospraying with egg white and PCL (Polycaprolactone) as the templates of protein drugs and drug carrier respectively. FITC (fluorescein isothiocyanate) was used to mark egg white in order to observe the microcapsule structure. The influence of three parameters including solution concentration, applied voltage and feeding ratio was studied. Meanwhile, SEM was used to observe the surface morphology and fluorescence microscope was used to investigate the composite structure of the microcapsules. Additionally, solution properties such as viscosity and electrical conductivity were worked out. The electrospraying parameters of PCL solution were optimized as:w PCL=2～3%, V=8-10 kV,φ=10μL/min, D=15cm. Size was reduced and increased respectively as the raising of conductivity and viscosity. The most important parameter was feeding ratio against the other two conditions such as mass concentration of PCL and egg white. Microcapsules could only be obtained while feeding rate was greater than 10. The coated structures including core-shell, gourd-like and cystic structure were founded. It was shown by SEM that the surface of PCL-egg white microcapsule was wrinkled and porous. The PCL concentration was more influential rather than that of egg white and the surface of microcapsule was more smooth and round with the growing of PCL concentration. Egg white was better coated with 2wt% PCL against 3wt% PCL.In general, polymer microspheres with homogeneous morphology were prepared via electrospraying-to-bath. Inorganic nanoparticles and organic-inorganic composite microspheres were in situ precipitated through electrospraying. Inorganic particles were well dispersed in polymer content. Polymer-polymer microcapsules were fabricated by coaxial electrospraying and could be used as the template of drug release system. It was very important to the application of electrospraying in the preparation of nanomaterals, inorganic/organic hybrid materials and microcapsules.