Randal L. Shogren

Water vapor permeability of biodegradable polymers

The water vapor transmission rates (WVTR) of several biodegradable polymers were evaluated to determine their suitability as water-resistant coatings and to understand WVTR better in terms of polymer structure. Values of WVTR at 25‡C ranged from 13 to 2900 g/m2 /day and increased in the order PHBV PLA (cryst.) PLA (amorph.) PCL Bionolle BAK 1095 CAP CA. Values of WVTR were positively correlated with higher polymer solubility parameters, lower crystallinities, and higher free volumes. Although the WVTR of biodegradable polymers are much higher than those of good barrier materials such as low-density polyethylene, they are sufficient for short-term (hours to days) protection of polysaccharide-based materials against water.

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)

Starch-plastic materials—Preparation, physical properties, and biodegradability (a review of recent USDA research)

Recent starch-plastic research at the National Center for Agricultural Utilization Research is reviewed and related worldwide efforts are noted. Properties of starch that influence its formulation and performance in plastics are discussed. Methods are given for preparation of starch-poly(methyl acrylate) graft copolymer, starch-poly(ethylene-co-acrylic acid), and starch-poly(ethylene-co-acrylic acid)-polyethylene plastics. Their physical properties are discussed, as is degradability by enzymes or amylolytic organisms from soil, ponds, and streams.

Distribution of Octenyl Succinate Groups in Octenyl Succinic Anhydride Modified Waxy Maize Starch

The location of octenyl succinate groups within octenyl succinic anhydride (OSA)-modified waxy maize (WM) starch granules was studied in order to better understand the relationship between the structure and physical properties of OSA starches. OSA starches of D.S. 0.03—0.11 were prepared by reaction between starch, OSA and NaOH in aqueous suspension; the native granular structure of starch was retained after reaction. Backscattered electron imaging of osmium-stained, sectioned OSA starch granules showed a uniform distribution of OSA groups over the cross-section of the granules. Anion-exchange chromatography of OSA starches solubilized in water showed that most of the amylopectin molecules contain some negative charge, suggesting that most of the starch granule is accessible to and reacts with OSA. However, after partial debranching with pullulanase, more of the resulting chains were neutral than would be expected on statistical grounds, suggesting heterogeneity in OSA substitution at the branch level. X-ray photoelectron spectroscopy suggested that the concentration of OSAgroups on the immediate surface of the OSA starch granules was about 3—4 times that of the bulk.

Starch–poly(vinyl alcohol) foamed articles prepared by a baking process

Composite foam plates were prepared by baking a mixture of granular starch and aqueous poly(vinyl alcohol) (PVOH) solution inside a hot mold. Foam strength, flexibility, and water resistance were markedly improved by addition of 10–30% PVOH to starch batters. The improvement in strength at low humidity was greater for partially (88%) hydrolyzed PVOH while strength at higher humidities improved most with fully (98%) hydrolyzed PVOH. Foam flexibility increased with higher PVOH molecular weight. Scanning electron micrographs of the surface of the foams revealed a phase-separated morphology in which swollen starch granules were embedded in a matrix of PVOH. The starch component was gelatinized (melted) during baking while the PVOH component crystallized to a high degree during baking. Crosslinking agents such as Ca and Zr salts were added to starch batters to give further increases in water resistance. Respirometry studies in soil showed that the starch component of starch–PVOH foams biodegraded relatively rapidly (weeks) while the PVOH component degraded more slowly (months). Baked foams prepared from starch and PVOH have mechanical properties that are adequate for use as packaging containers over a wide range of humidity.

Baked starch foams: starch modifications and additives improve process parameters, structure and properties

Abstract Single-use packaging articles made of expanded polystyrene (EPS) are currently used to serve and pack a variety of food and non-food products. Recently, there have been efforts to develop and commercialize materials from renewable resources such as starch to replace EPS. Starch based foams are, however, brittle and sensitive to water, and thus require expensive coating steps when exposure to cold or hot liquids is required. In this report, various modified starches and additives were tested in baked foam plate formulations to improve strength and water resistance properties in lieu of coating. Foam plates made from chemically modified starches had shorter baking times, lighter weights and higher elongations at break than unmodified starch. Plates made from genetically modified (waxy) starches and polyvinyl alcohol (PVOH) had elongations to break at low humidities, which were much higher than those made from normal starches and PVOH. Addition of softwood fibers increased starch foam plate strengths at low and high humidities. Addition of monostearyl citrate to starch batter formulations gave the best improvement in water resistance among the compounds tested. Baked foams made from potato amylopectin, PVOH, aspen fiber and monostearyl citrate appeared to have adequate flexibility and water resistance to function as clamshell-type hot sandwich containers.

Steam jet cooking of high-amylose starch-fatty acid mixtures. An investigation of complex formation

We have investigated the formation of helical inclusion complexes when aqueous mixtures of high-amylose starch and lauric, myristic, palmitic and stearic acids are processed by steam jet cooking at 140°C. The amount of free fatty acid that complexes with amylose was compared with the amount complexed when the fatty acid was present in its water-dispersible, sodium salt form. Air-dried and finely-ground products prepared from lauric and myristic acids and their sodium salts were extracted to remove uncomplexed fatty acid. A quantitative Fourier transfrom infrared spectroscopic (FTIR) method, based upon absorption of the carboxylic acid carbonyl, was then developed to determine the amount of complexed fatty acid remaining in the product. For both of these fatty acid systems, only small differences in complex formation were observed between the free acid and the sodium salt. Although water solubility of these fatty acids is negligible at room temperature, solubility is apparently sufficient for complex formation under the high-temperature, high-shear conditions of the steam jet cooking process. Products prepared from lauric, myristic, palmitic and stearic acids and their respective sodium salts were also examined by X-ray diffraction. This technique confirmed the results obtained by FTIR and also showed that differences between free acid and sodium salt become more pronounced as the fatty acid increases in molecular weight, and water solubility is reduced. For the stearic acid system, complexation of free acid was roughly half that observed with the sodium salt.

Complexes of starch with telechelic poly(ε-caprolactone) phosphate

Abstract The interaction of starch with poly(e-caprolactone) having end-linked phosphate groups (PCL phosphate) was studied in order to determine if aliphatic polyesters could form inclusion complexes with starch similar to those formed from amylose and fatty acids. Normal cornstarch co-jet cooked with aqueous PCL phosphate solutions formed highly viscous gels on cooling, whereas jet-cooked starch solutions had low viscosities. Solutions of waxy maize starch had low viscosities after jet cooking either with or without PCL phosphate, while high amylose starch formed gels with or without PCL phosphate. Essentially all amylose precipitated from a dilute solution upon addition of PCL phosphate solution. After extraction with a solvent for the PCL phosphate, about 0·1 g PCL phosphate remained bound per g of amylose. X-ray diffraction and CP/MAS C-13 NMR studies showed that the PCL phosphate/amylose complexes adopt a semi-crystalline, V-type helical inclusion structure.

Aging properties of extruded high-amylose starch

The structural and mechanical properties of extruded high-amylose and normal cornstarch were studied as a function of time and humidity to determine the suitability of high-amylose cornstarch for use in biodegradable plastic materials. After extrusion at 170°C and 20–30% moisture, high-amylose starch was mostly amorphous, with small amounts of V- and A-type crystal structures. Tensile strengths for the extruded high-amylose starch ribbons were rather stable with time (65, 50, and 35 MPa at 20, 50, and 80% RH) and were higher than those for normal cornstarch (25, 40, and 15 MPa after 84 days at 20, 50, and 80% RH). Elongations at break declined gradually with time for high-amylose starch (6, 11, and 11% after 84 days at 20, 50, and 80% RH), while rapid declines were seen for normal cornstarch at higher humidities (3, 9, and 3% after 84 days at 20, 50, and 80% RH). Differential scanning calorimetry revealed that normal cornstarch aged at a high humidity had much larger sub-T g endotherms than high-amylose cornstarch. These endotherms reflect decreases in enthalpy and free volume which occur in amorphous polymers due to structural relaxation. It appears, therefore, that plastic materials prepared from gelatinized or melted high-amylose cornstarch should have greater strength and flexibility and slower physical aging than those prepared from gelatinized normal cornstarch.

Formation of crystalline aggregates in slowly-cooled starch solutions prepared by steam jet cooking

Abstract Spherocrystalline particles were formed in dilute, jet cooked solutions of normal cornstarch, high amylose cornstarch, rice starch and wheat starch, when hot solutions were allowed to slowly cool in insulated Dewar flasks. Yields ranged from approximately 7 to 12%, and particles were composed largely of amylose. Spherocrystals were not obtained from waxy cornstarch, defatted cornstarch or potato starch. Normal cornstarch, high amylose cornstarch and rice starch yielded mixtures of two different particulate species, each having its own unique size and morphology. Both species were strongly birefringent, and no significant loss of birefringence was observed when particles produced from normal cornstarch were heated in water to 97–99°C. Scanning electron microscopy (SEM) showed that smaller-sized particles were disc or torus-shaped and often exhibited spiral surface striations. The larger particles were approximately spherical in shape, and had rough surface textures. Wheat starch yielded only a single spherical small-particle species. X-ray powder diffraction patterns of small particle material matched patterns previously reported for the 61 amylose V-helical complex in the hydrated form. In contrast, diffraction patterns for large particle material suggested the 71 V-helical conformation for amylose. These results are consistent with the theory that spherocrystalline particles result from crystallization of helical inclusion complexes formed from amylose and the native lipid material present in cereal starch granules.