Structure-property And Applications Of Electrospun Polylactide Nanofibers

Polylactide(PLA), produced from renewable biomass, is one kind of the most important biodegradable and compatible polymer materials. Moreover, PLA exhibits a series of excellent characters compared to some of petroleum based polymers. These outstanding properties make PLA be widely used in various fields. Nanofibers fabricated from PLA are widely concerned due to their peculiar structure and properties. However, it is the drawback of PLA itself and diameter of nanofibers that restrict further applications. In order to widen the applications, we focused on sterocomplex crystallization of PLA electrospun fibers,preparation and characterizing of PLA fine fibers,as well as modifying PLA fibers via blending with poly(hydroxybutyrate-co-4-hydroxybutyrate)(P34HB). The results are list as follow:(1) Cold crystallization of electrospun fibers from poly(L-lactide)/poly(D-lactide) =5/5 blends results in profuse stereocomplex crystals with little trace of homocrystals. In contrast, homocrystals prevail in the solution cast and melt-quenched films with same composition upon cold crystallization. With aid of FTIR technique it is confirmed that intermolecular ordering between poly(L-lactide) and poly(D-lactide) chains is induced in the electrospun blend fibers because of the interactions from the methyl and carbonyl groups. The intermolecular ordering acts as the precursor to trigger profuse stereocomplex formation in the electrospun blend fibers above glass transition temperature. Moreover, stereocomplex formation in the electrospun blend fibers follows one dimensional growth, as a result of confinement effects in an individual fiber.(2) Electrospinning of polylactide(PLA) solutions produces coarse nanofibers mixed with numerous beads at the adopted conditions. Incorporation of ionic liquids with high conductivity in the solutions, however, promotes formation of fine PLA nanofibers with diameters of about 70 nm. It corresponds to significant stretching of the solutions as well as remarkable molecular alignment under the electrical field. As a result, high amount of mesophase besides a few crystals is induced in the fine PLA nanofibers. It is responsible for the accelerated cold crystallization above glass transition temperature. Notably, an enhancement in the melting point of about 10 ℃ is exhibited by the crystals transformed from the mesophase with remarkable molecular alignment in the fine PLA nanofibers.(3) Polymer membranes produced by electrospinning have great potentials in the separation of oil/water emulsion under gravity. Removal of oils from the emulsion has been realized by superhydrophobic membranes due to selective penetration of oils. We demonstrate that blend electrospinning of polylactide(PLA) with a biodegradable and biocompatible polyester(P34HB) produces membranes with complete water permeability. In contrast, PLA membranes are highly hydrophobic and can not be penetrated by water. The water permeability is correlated with more hydrophilicity of P34 HB than PLA and especially with structural porosity of the membranes. The water-permeable membranes exhibit superior removal of water from the emulsion under gravity, exactly opposite to the situation encountered by superhydrophobic membranes.