Electrospinning of starch fibers

Author:

Kong, Lingyan

Graduate Program:

Food Science

Degree:

Doctor of Philosophy

Document Type:

Dissertation

Date of Defense:

May 11, 2012

Committee Members:

Gregory Ray Ziegler, Dissertation Advisor/Co-Advisor
Donald B Thompson, Committee Member
John Neil Coupland, Committee Member
Seong Han Kim, Committee Member

Keywords:

electrospinning
starch
fiber
rheology
empirical modeling
encapsulation

Abstract:

Many efforts to spin starch fibers have been reported in the patent and research literature. All reported spinning methods are dependent upon addition of non-starch components, e.g. other polymers, plasticizers or cross-linkers. In the present study, a method of producing pure starch fibers by an electrospinning technique was demonstrated. This method involves choosing an appropriate solvent for native high amylose starch and spinning on a modified electrospinning setup. Resulting starch fibers have diameters in the order of microns. Post-spinning treatments were employed to increase the crystallinity and cross-link the starch fibers. Electrospinning of starch/clay and starch/ microcrystalline cellulose composite fibers was also demonstrated. Correlation between the rheological properties of starch dispersions and the electrospinnability was established via the extrapolation of the critical entanglement concentration, which is the boundary between the semidilute unentangled regime and the semidilute entangled regime. Dispersions of high amylose starch containing nominally 80% amylose (Gelose 80) required 1.2 to 2.7 times the entanglement concentration for effective electrospinning. Besides starch concentration, molecular conformation and shear viscosity were also of importance in determining the electrospinnability. The rheological properties and electrospinnability of different starches were studied. Hylon VII and Hylon V starches, containing nominally 70 and 50 % amylose, respectively, required concentrations of 1.9 and 3.7 times their entanglement concentrations for electrospinning. Only poor fibers were obtained from mung bean starch, which contains about 35 % amylose, while starches with even lower amylose contents could not be electrospun. The diameter of the starch fibers produced by electrospinning is a key parameter for most potential applications. Hence, a quantitative relationship between fiber diameter and certain electrospinning parameters, i.e. starch concentration, applied voltage, spinning distance and feed rate, was established by empirical modeling using a fractional factorial experimental design in a constrained region. Response surface methodology was employed to analyze the interactions of the electrospinning parameters. The starch fiber diameter was found to be more responsive to starch concentration than to voltage and distance in the experiment range. Contour plots were used to predict the direction to minimize and maximize the fiber diameters. The smallest fiber diameter (3.98 µm) can be obtained within the experiment range, whereas the largest fiber diameter is outside of the experimental design region. The starch fibers have potential in various applications, e.g., in the food, textile, and biomedical industries. The formation of starch-guest inclusion complexes is a particular interest for encapsulation of certain molecules. Two methods were used to electrospin starch fibers with starch-guest inclusion complexes: a dope mixing method, where guest material was mixed into the starch dispersion prior to electrospinning, and a bath mixing method, where guest material was mixed into the coagulation bath into which starch dispersions were electrospun. Selected guest compounds, i.e. palmitic acid, ascorbyl palmitate, and cetyl-trimethylammonium bromide, formed inclusion complexes with starch in the electrospun starch fibers. Due to fast precipitation of starch, the coagulation bath containing 100% ethanol was not as efficient as 75% ethanol aqueous solution to induce starch-guest inclusion complex formation. Starch-ascorbyl palmitate inclusion complexes were also formed in electrosprayed powders by a dope mixing method, but this method was less efficient than their formation in electrospun fibers. Encapsulation of these molecules in electrospun starch fibers and electrosprayed starch powders may increase their stability during processing, storage, and in the gastrointestinal tract, while providing controlled release properties. However, further research is necessary to gain a better understanding of the encapsulation and release of the molecules that can be entrapped in starch fibers through intra-helical inclusion complex formation, inter-helical encapsulation, and physical macroscopic entrapment.