Pullulan-alginate fibers produced using free surface electrospinning

Pullulan-alginate ultrafine fibers, with and without CaCl2, were electrospun from aqueous polymer solutions using a free-surface electrospinning method, without the use of synthetic spinning aid polymer. Aqueous pullulan solution (10%, w/w) could be electrospun into beaded fibers of 110 nm in diameter with a board diameter distribution. By contrast, continuous and smooth fibers were formed when 0.8 to 1.6% (w/w) alginate was added to the 10% (w/w) pullulan solutions, producing smaller fibers ranging from 87 to 57 nm in diameter. The positive effect of alginate can be attributed to the increase in polymer chain entanglement, as well as enhanced hydrogen bonding interaction between pullulan and alginate. The addition of trace amount of CaCl2 (up to 0.045%, w/w) resulted in smooth and ultrafine fibers that were significantly smaller in diameter and greater thermal stability than those prepared without the addition of CaCl2. The production of typical electrospun fibers involves the use of undesirable organic solvents and/or non-food grade synthetic spinning aid polymer. The water-based edible biopolymer systems presented in this study can be useful for the preparation of nano-scale fibers that are more conducive for food, nutraceutical, and pharmaceutical applications.