Julious L. Willett

Biodegradation of starch/polylactic acid/poly(hydroxyester-ether) composite bars in soil

Abstract Injection molded tensile bars composed of native corn starch (0–70%), poly( d , l -lactic acid) (95% L) (PLA, 13–100%) and poly(hydroxyester-ether) (PHEE, 0–27%) were buried in soil for 1 year in order to study the effects of starch and PHEE on rates of biodegradation. Rates of weight loss increased in the order pure PLA (∼0%/year)

Computational Studies on Carbohydrates: I. Density Functional Ab Initio Geometry Optimization on Maltose Conformations

Ab initio geometry optimization was carried out on 10 selected conformations of maltose and two 2‐methoxytetrahydropyran conformations using the density functional denoted B3LYP combined with two basis sets. The 6‐31G* and 6‐311++G** basis sets make up the B3LYP/6‐31G* and B3LYP/6‐311++G** procedures. Internal coordinates were fully relaxed, and structures were gradient optimized at both levels of theory. Ten conformations were studied at the B3LYP/6‐31G* level, and five of these were continued with full gradient optimization at the B3LYP/6‐311++G** level of theory. The details of the ab initio optimized geometries are presented here, with particular attention given to the positions of the atoms around the anomeric center and the effect of the particular anomer and hydrogen bonding pattern on the maltose ring structures and relative conformational energies. The size and complexity of the hydrogen‐bonding network prevented a rigorous search of conformational space by ab initio calculations. However, using empirical force fields, low‐energy conformers of maltose were found that were subsequently gradient optimized at the two ab initio levels of theory. Three classes of conformations were studied, as defined by the clockwise or counterclockwise direction of the hydroxyl groups, or a flipped conformer in which the ψ‐dihedral is rotated by ∼180°. Different combinations of ω side‐chain rotations gave energy differences of more than 6 kcal/mol above the lowest energy structure found. The lowest energy structures bear remarkably close resemblance to the neutron and X‐ray diffraction crystal structures.

Properties of starch‐graft‐poly(glycidyl methacrylate)–PHBV composites

The use of graft copolymers of starch and glycidyl methacrylate (starch-g- PGMA) to improve the mechanical properties of composites with poly(hydroxy butyrate- co-valerate) (PHBV) has been investigated. In general, the tensile and flexural strengths of the composites were greater with starch-g-PGMA compared to untreated starch and increased with increasing graft content. The modulus and elongation were not significantly changed by grafting. All samples gained weight after immersion in water for 28 days. Tensile strength and modulus decreased with water sorption, while the fracture toughness significantly increased with grafted starch. No differences were observed between properties of grafts prepared with ceric ammonium nitrate or ferrous sulfate-peroxide graft initiators. Scanning electron micrographs of cryogenic fracture surfaces showed improved adhesion between the starch-g-PGMA and the PHBV ma- trix. Although no spectroscopic evidence of reaction between PHBV and the starch-g- PGMA was found, the improvement in mechanical properties is consistent with en- hanced interactions between the starch-g-PGMA and the PHBV matrix compared to ungrafted starch. 0 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1121-1127, 1998

Electroactive Materials Composed of Starch

Extruded films of plasticized starch were doped with metal halides to produce solid ion-conducting materials. The electrical conductance of the material increased from 10−11 to 10−6 Siemens/cm. The type and amount of dopant affects the conductance of the material. Although the materials are moisture sensitive, water content does not have a significant effect on the conductance of doped films. Mechanical properties of doped films indicate that the starch is plasticized and that the ion-conducting material is strong and tractable. Unlike intrinsically conductive polymers, electroactive starch materials can be extruded in thin films or molded into any shape.

Shear-thickening and shear-induced pattern formation in starch solutions☆

Since Dintzis et al. reported shear-thickening behavior and shear-induced pattern formation in semidilute starch solutions for the first time in 1995, considerable efforts have been made to understand the science behind these observations. Despite these efforts, however, many questions regarding this behavior of starch solutions remain. Using a Brookfield programmable rheometer and a custom-built shear microscope, starch solutions in alkaline solution medium were investigated. In this report, we present data leading to the following conclusions: (1) gently prepared starch solutions are macroscopically heterogeneous with regions of highly concentrated gel-like structures dispersed in dilute starch solution; (2) shear breaks up these heterogeneous regions, increasing in viscosity (shear-thickening) which is thus seen to be a result of an increase in the concentration of dissolved starch; (3) pattern formation, observed when the solution is exposed to higher shear rate, is the result of a separate shear-induced aggregation process; and (4) aggregations are not induced below a certain critical threshold shear rate and time is also a factor in the behavior of the aggregate.

Synthesis of an Amine−Oleate Derivative Using an Ionic Liquid Catalyst

A facile (and environmentally friendly) reaction between epoxidized methyl oleate and aniline to produce an oleate-aniline adduct, without the formation of fatty amide, was discovered. This reaction was carried out neat, with a catalytic amount of an ionic liquid. No solvent was used, no byproducts were produced, and the ionic liquid could be recovered and recycled. The reaction products were fully characterized by NMR and GC-MS.

DFT conformational studies of α‐maltotriose

Recent DFT optimization studies on α‐maltose improved our understanding of the preferred conformations of α‐maltose. The present study extends these studies to α‐maltotriose with three α‐D‐glucopyranose residues linked by two α‐[1→4] bridges, denoted herein as DP‐3s. Combinations of gg, gt, and tg hydroxymethyl groups are included for both “c” and “r” hydroxyl rotamers. When the hydroxymethyl groups are for example, gg‐gg‐gg, and the hydroxyl groups are rotated from all clockwise, “c”, to all counterclockwise, “r”, the minimum energy positions of the bridging dihedral angles (ϕH and ψH) move from the region of conformational space of (−, −), relative to (0°, 0°), to a new position defined by (+, +). Further, it was found previously that the relative energies of α‐maltose gg‐gg‐c and “r” conformations were very close to one another; however, the DP‐3s relative energies between hydroxyl “c” or “r” rotamers differ by more than one kcal/mol, in favor of the “c” form, even though the lowest energy DP‐3 conformations have glycosidic dihedral angles similar to those found in the α‐maltose study. Preliminary solvation studies using COSMO, a dielectric solvation method, point to important solvent contributions that reverse the energy profiles, showing an energy preference for the “r” forms. Only structures in which the rings are in the chair conformation are presented here.

Effect of Starch Granule Size on Viscosity of Starch-filled Poly(hydroxy ester ether) Composites

The effect of starch granule size on the viscosity of starch-filled poly(hydroxy ester ether) (PHEE) composites was characterized using size-fractionated potato starch, as well as unfractionated starches (rice, corn, wheat, and potato). Potato starch was separated using an air classifier into four particle size fractions: <18 μm, 18-24 μm, 24-30 μm, and >30 μm. The starch was dried to a moisture content of 0.5% to minimize moisture effects on composite rheology. PHEE and potato starch were extruded with starch volume fractions of 0.46 and 0.66. Stress relaxation, frequency and strain sweep, and temperature-dependence measurements were carried out. Although small variations in viscosity were seen with the different potato starch fractions, differences were not significant at a volume fraction of 0.46. Viscosity differences between the different particle size fractions were more pronounced at a volume fraction of 0.66. The temperature dependence could be described by an Arrhenius relation, with an apparent activation energy of 84 kJ/mole. At a volume fraction of 0.46, the starch/PHEE viscosities increased in the order potato starch < wheat starch ≃ corn starch < rice starch.

27 ps DFT molecular dynamics simulation of α‐maltose: A reduced basis set study

DFT molecular dynamics simulations are time intensive when carried out on carbohydrates such as α‐maltose. In a recent publication (Momany et al., J. Mol. Struct. THEOCHEM, submitted) forces for dynamics were generated from B3LYP/6‐31+G* electronic structure calculations. The implicit solvent method COSMO was applied to simulate the solution environment. Here we present a modification of the DFT method that keeps the critical aspects of the larger basis set (B3LYP/6‐31+G*) while allowing the less‐essential atom interactions to be calculated using a smaller basis set, thus allowing for faster completion without sacrificing the interactions dictating the hydrogen bonding networks in α‐maltose. In previous studies, the gg′‐gg‐c solvated form quickly converged to the “r” form during a 5 ps dynamics run. This important conformational transition is tested by carrying out a long 27 ps simulation. The trend for the “r” conformer to be most stable during dynamics when fully solvated, is confirmed, resulting in ∼20/80% c/r population. Further, the study shows that considerable molecular end effects are important, the reducing end being fairly stable, the O6H pointing at the O5, while the nonreducing end moves freely to take on different conformations. Some “kink” and transition state forms are populated during the simulation. The average H1′···H4 distance of 2.28 Å confirms that the syn form is the primary glycosidic conformation, while the average C1′O1′C4 bond angle was 118.8°, in excellent agreement with experimental values. The length of this simulation allowed the evaluation of vibrational frequencies by Fourier transform of the velocity correlation function, taken from different time segments along the simulation path.

An optical microscope for the study of biopolymer solutions under shear field

Recently, it has been found that some biopolymer solutions show aggregate formation or shear-induced mixing when they are exposed to shear field. An optical microscope was constructed for the study of these behaviors. A phase-contrast microscope is installed to obtain clear images from sample solutions where the refractive index difference of the domains is too small to be observed with common bright field microscopes. A modular type is adopted for the design of microscope for easy adjustment of optical components, alignment, and positioning it to the sample compartment. As a light source, a strobe type flash lamp is employed and its ignition is synchronized with a charge coupled device camera to avoid yielding smeared images. Shear fields are generated by a cone and plate geometry that is directly attached to a microstepper motor with a controllable simple shear rate range of 0.025–2500 s−1. In the case of oscillatory shear, accessible range is 0–120 rad/s. A dual temperature controller allows temperatur...