Lingyan Kong

Role of Molecular Entanglements in Starch Fiber Formation by Electrospinning

We have demonstrated a method of fabricating pure starch fibers with an average diameter in the order of micrometers. In the present study, correlation between the rheological properties of starch dispersions and the electrospinnability was attempted 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 1.2-2.7 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.

Quantitative relationship between electrospinning parameters and starch fiber diameter.

The diameter of the starch fibers produced by electrospinning is a key parameter for most potential applications. In this study, 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 and predict the direction to minimize and maximize the fiber diameters.

Characterization of starch polymorphic structures using vibrational sum frequency generation spectroscopy.

The polymorphic structures of starch were characterized with vibrational sum frequency generation (SFG) spectroscopy. The noncentrosymmetry requirement of SFG spectroscopy allows for the detection of the ordered domains without spectral interferences from the amorphous phase and also the distinction of the symmetric elements among crystalline polymorphs. The V-type amylose was SFG-inactive due to the antiparallel packing of single helices in crystal unit cells, whereas the A- and B-type starches showed strong SFG peaks at 2904 cm(-1) and 2952-2968 cm(-1), which were assigned to CH stretching of the axial methine group in the ring and CH2 stretching of the exocyclic CH2OH side group, respectively. The CH2/CH intensity ratios of the A- and B-type starches are significantly different, indicating that the conformation of hydroxymethyl groups in these two polymorphs may be different. Cyclodextrin inclusion complexes were also analyzed as a comparison to the V-type amylose and showed that the head-to-tail and head-to-head stacking patterns of cyclodextrin molecules govern their SFG signals and peak positions. Although the molecular packing is different between V-type amylose and cyclodextrin inclusion complexes, both crystals show the annihilation of SFG signals when the functional group dipoles are arranged pointing in opposite directions.

Patents on fiber spinning from starches.

Starch is a promising bio-based material to replace synthetics in a number of applications. The production of starch-based fibers has been actively pursued in the patent literature. This article reviews patents on starch fiber technology, including fiber spinning from amylose, thermoplastic starch compositions, and non-thermoplastic starch compositions. Some new fiber spinning techniques, e.g. electrospinning and rotary jet spinning, employed for spinning starch fibers are also presented.

Fabrication of κ-Carrageenan Fibers by Wet Spinning: Spinning Parameters

This study demonstrates the fabrication of κ-carrageenan fibers by a wet-spinning method and discusses three important spinning parameters: coagulation bath composition, spinning rate and post-spinning mechanical drawing. The as-spun fiber diameter decreased with KCl and ethanol concentration in the coagulation bath. In general, the ultimate tensile stress and elongation at break both increased for KCl concentration from 0.1 to 0.5 M with and without ethanol, with no significant change above 0.5 M. Spinning rate affected the dope flow and thus the polymer orientation (apparent viscosity) and fiber morphology. At spinning rates between 0.25 mL/min and 0.33 mL/min, the fiber diameter reached a minimum and the fiber surface was smooth. Both an increase and decrease from this spinning rate range increased the fiber diameter and roughness of the fiber surface. Post-spinning drawing of the fiber resulted in even smaller fiber diameter.

Molecular Entanglement and Electrospinnability of Biopolymers

Electrospinning is a fascinating technique to fabricate micro- to nano-scale fibers from a wide variety of materials. For biopolymers, molecular entanglement of the constituent polymers in the spinning dope was found to be an essential prerequisite for successful electrospinning. Rheology is a powerful tool to probe the molecular conformation and interaction of biopolymers. In this report, we demonstrate the protocol for utilizing rheology to evaluate the electrospinnability of two biopolymers, starch and pullulan, from their dimethyl sulfoxide (DMSO)/water dispersions. Well-formed starch and pullulan fibers with average diameters in the submicron to micron range were obtained. Electrospinnability was evaluated by visual and microscopic observation of the fibers formed. By correlating the rheological properties of the dispersions to their electrospinnability, we demonstrate that molecular conformation, molecular entanglement, and shear viscosity all affect electrospinning. Rheology is not only useful in solvent system selection and process optimization, but also in understanding the mechanism of fiber formation on a molecular level.