Electrospinning of Poly(vinyl alcohol) Nanofibers Loaded with Hexadecane Nanodroplets

Abstract

The feasibility of producing poly(vinyl alcohol) (PVA) nanofibers containing fine-disperse hexadecane droplets by electrospinning a blend of hexadecane-in-water emulsions and PVA was investigated. Hexadecane oil-in-water nanoemulsions (d(10)= 181.2 +/- 0.1 nm) were mixed with PVA at pH 4.5 to yield polymer-emulsion blends containing 0.5 to 1.5 wt% oil droplets and 8-wt% PVA. The solution properties of emulsions and emulsion-PVA blends (viscosity, conductivity, surface tension) were determined. Solutions were electrospun and the morphology and thermal properties of deposited fiber mats characterized by scanning electron microscopy and differential scanning calorimetry. Fiber mats were dissolved in buffer to liberate incorporated hexadecane droplets and the buffer solutions analyzed by optical microscopy, UV-spectroscopy, and light scattering. Analysis of dry fiber mats and their solutions showed that emulsion droplets were indeed part of the electrospun fiber structures. Depending on the concentration of hexadecane in the initial emulsion-polymer blends, droplets were dispersed in the fibers as individual droplets or in form of aggregated flocs of hexadecane droplets. Nanofibers with spindle-like perturbations or nanofibers containing bead-like structures with approximately 5 times larger than the size of droplets in the original nanoemulsion were obtained. Remarkably, incorporation of hexadecane droplets in fibers did not alter size of individual droplets, that is, no coalescence occurred. The manufacture of solid matrix containing nanodroplets could be of substantial interest for manufacturers wishing to develop encapsulation system for lipophilic functional compounds such as lipid-soluble flavors, antimicrobials, antioxidants, and bioactives with tailored release kinetics. Practical Applications: The paper describes the formation of electrospun nanofibers from hydrophilic polymers that contain fine-disperse emulsion droplets. By incorporating emulsion droplets, a large variety of lipophilic ingredients can be easily loaded into the fibers' hydrophilic polymer matrix. This is of practical importance as to date the only way to include a lipophilic ingredient in a nanofibers is by dissolving the lipophilic ingredient and polymer in an organic solvent followed by electrospinning. However, use of an organic solvent is (a) not feasible if one wants to electrospin hydrophilic polymers, and (b) use of organic solvents is generally highly undesirable in the food industry. Our results should be of interest to a number of industries such as the food, pharmaceutical, chemical, and personal care industries that are generally in need of novel matrices that can serve as carrier vehicles and release functional components such as flavors, antimicrobials, antioxidants, drugs, and bioactives.