Preparation And Characterization Of Crosslinked Polyester-based Electrospun Fibers

Electrospinning is a simple, versatile and efficient fabrication process that can produce submicron- and nano-scale polymer fibers. Applied and potential uses of electrospun fibers include ultrafine filters, porous membranes, protective coatings, nano-catalysts, vascular grafts and tissue engineering scaffolds. However many applications have been limited for the common defects of electrospun fibers and mats such as weak heat-stability, solvent-stability and poor strength.Aiming at these problems, many physical and chemical methods are used to make improvements. Among these methods, chemical crosslinking is an effectual one. Polymer molecules in electrospun fibers can be chemical crosslinked so that the fibers will not dissolve in solvents and also can be applied at a much higher ambient temperature. Polyester macromonomers, which are easy to be crosslinked and common used, were chosen to be the raw material. In this work, a kind of novel unsaturated polyester macromonomer (HIPIH) is synthesized and its crosslinked ultrafine fibers are fabricated by blending electrospinning and subsequent crosslinking. This kind of crosslinked ultrafine fibers has the potential application in ultrafiltration and protective coating. The unsaturated polyester macromonomer (HIPIH) was synthesized by a two-step reaction among poly(2-methyl-l,3-propylene adipate), diol terminated (Mn = 2000) (PMPA), isophorone diisocyanate (IPDI) and 2-hydroxyethyl methacrylate (HEMA) in acetone. Many influencing factors, such as feed proportion, reaction time, reaction temperature and catalyst dosage were studied. FTIR and NMR results indicated that PMPA and HEMA were linked successfully by IPDI and seldom side-reactions were arisen. HIPIH terminated with two reactive double bonds was successfully prepared.HIPIH had poor processability and could not be electrospun directly due to its low solution viscosity which attributed to its low molecular weight. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (Mn = 460,000, HV content = 3%), another aliphatic polyester, was added to the HIPIH dichloromethane solution in order to improve the processability. The HIPIH/PHBV blend solution in dichloromethane could be successfully electrospun by controlling the spinning parameters properly. Influence of the spinning parameters, including the mass ratio of the HIPIH to PHBV, solution properties (concentration, viscosity and conductivity) and ambient conditions (applied voltage, solution feeding rate and work distance) were investigated via observing the morphologies of the HIPIH/PHBV electrospun fibers by SEM.Two ways of chemical crosslinking of the electrospun HIPIH/PHBV fibers were taken. One was thermal-crosslinking and the other was UV-crosslinking. The effect of different crosslinking time and crosslinking temperature on the degree of crosslinking was investigated.Thermal- and solvents-stabilities of the HIPIH/PHBV electrospun fibers were tested. Fibers prepared with the best crosslinking condition had good stabilities. After soaked in acetone for 24h, the morphology of the fibers kept well, no dissolving, breaking and shrinking were observed by SEM. Fibers soaked in dichloromethane had less uniform morphologies than those in acetone, some of them dissolved, but most of the fibers only swelled instead of dissolving. The ultrafine fibers had good thermal-stability. The decomposition temperature of the crosslinked HIPIH component in electrospun fibers was around 340℃.Solution cast membranes were also prepared and characterized for comparison. The swelling behavior and surface property of both electrospun mats and solution cast membranes were studied. Electrospun mats had the same swelling behavior as the cast membranes but had higher swelling rate than the cast membranes. It was affected by the proportion of the HIPIH and PHBV. The cast HIPIH/PHBV membranes were slightly hydrophobic but the electrospun HIPIH/PHBV mats were moderately hydrophobic. It was possible to obtain a superhydrophobic surface by properly controlling the spinning parameters even though the material itself was not hydrophobic.