John W. Lawton

Effect of starch type on the properties of starch containing films

Ultimate tensile strength (UTS), percent elongations at break (%E), tear resistance, and impact strength were investigated for starch-poly(vinyl alcohol) (PVA) cast films. Films contained 41% starch, 41% PVA, 15% glycerol and 3% poly(ethylene-co-acrylic acid) (EAA). Films were made with each of the following starch types: normal cornstarch, waxy cornstarch, high amylose cornstarch (50% amylose and 70% amylose), wheat starch, potato starch, and tapioca starch. Films were aged before testing from 7 to 168 days, or stored at 15 to 93% relative humidity (RH) for 7 days prior to testing. All films showed an increase in %E and a decrease in UTS as RH increased. The high amylose films showed the greatest stability over the RH range for %E. The largest decrease in UTS of the films occurred between 15 and 33% RH, followed by a linear decrease in UTS as RH increased. The large decrease in UTS was thought to be due to the Tg of the films. Tear resistance of the films was effected by RH. Films stored at high RH (93%) absorbed so much water that they became weak and had very little tear resistance. Film stored at low RHs (15 and 33%) also had low tear resistance. Films stored at intermediate RHs had high tear resistance. The difference in tear resistance is thought to be due to chain mobility. At low RH the polymer chains in the films have less mobility to absorb the stress associated with tearing. Impact strengths of the films were about the same, except films made with waxy cornstarch, which were significantly lower. Aging the films for 28 days did not significantly effect the impact strength of the films. All films, except films containing high amylose cornstarch, showed a large decrease in %E after aging for 168 days. Films made with waxy cornstarch showed the greatest loss in %E after aging, going from 144% after 7days to 34% after 168days. UTS of the films increased with aging, except films made with waxy cornstarch. Films other than those containing waxy cornstarch showed no %E less than 100% or an UTS of greater than 35MPa, even after aging for 168 days. Films containing high amylose cornstarch had the most consistent properties over the entire range of test conditions.

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–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.

Glycerol-plasticized films prepared from starch—poly(vinyl alcohol) mixtures: effect of poly(ethylene-co-acrylic acid)☆

Abstract Equations were obtained from response surface models to show how the ultimate tensile strength (UTS) and percent elongation at break (%E) of solution-cast films vary with relative amounts of starch, poly(vinyl alcohol) (PVA), poly(ethylene-co-acrylic acid) (EAA) and glycerol in the formulation. Equations found from the response surface methodology were used to optimize the relative amounts of the four components with respect to the physical properties of cast films. The model showed that only glycerol content was important to predict the UTS of the films. The model for %E was more complicated, since there was a three-way interaction between EAA, PVA and glycerol. This model also contained two other terms: a two-way interaction evolving glycerol and EAA. and a (PVA)3 term. In general, %E increased as EAA, PVA and glycerol were increased together. However, increased amounts of EAA could decrease %E if EAA was the only component increased. It is believed that EAA forms complexes with both starch and PVA, thereby increasing compatibility of the two polyhydroxy polymers. As %E increases, UTS of the films decreases. All the films produced in this paper were made with starch contents above 50% to insure an optimum film formulation with at least 50% starch. A mixture of 55·6% starch, 2·8% EAA, 28·3% PVA and 13·3% glycerol is believed to be close to the optimum formulation to obtain films having at least 100%E and UTS of 25 MPA, while still maintaining starch concentrations above 50%.

Effect of moisture level on the morphology and melt flow behavior of thermoplastic starch/poly(hydroxy ester ether) blends☆

Abstract The effect of moisture content and temperature on the melt flow behavior and the resulting morphology of thermoplastic starch (TPS)/poly(hydroxy ester ether) blends is studied. The viscosity ratio (λ) was found to vary over two orders of magnitude (0.1–10) with changes in the TPS moisture content (15–30%) and temperature (120–160°C). This had a substantial effect on the level of mixing, nature of dispersion and the onset and nature of co-continuity. Deformation (in the flow direction) of the dispersed starch phase was possible under high moisture conditions (higher λ), leading to fibrillar and laminar types of morphologies at 50–80% starch level, whereas processing at a low moisture level (lower λ) produced a more dispersed morphology. When the viscosities of the two phases were significantly different, the low-viscosity polymer migrated to the surface. Surprisingly λ increased with temperature at 20% moisture TPS but decreased with temperature at 30% moisture TPS. Hence, moisture content and temperature greatly affected the surface enrichment of the lower viscosity polymer. Water partitioning took place between TPS and PHEE during extrusion, dependent on the pre-extrusion moisture content of TPS but independent of the relative concentrations of the two polymers.

Effect of Specific Mechanical Energy on Protein Bodies and α-Zeins in Corn Flour Extrudates

ABSTRACT Zeins, the storage proteins of corn, are located in spherical entities called protein bodies. The disruption of protein bodies and zein release during extrusion may influence the texture of corn-based extruded foods. In this work, chemical and microscopic studies were conducted on corn flour that had been extruded under mild to extreme conditions to determine the specific mechanical energy (SME) required to break apart protein bodies and release α-zein, and to assess changes in protein-protein interactions. Transmission electron microscopy with immunolocalization of α-zein revealed that starch granules and protein bodies remained intact under mild processing conditions (SME 35–40 kJ/kg), but under harsher conditions, protein bodies were disrupted and α-zein was released. At SME ≈100 kJ/kg, protein bodies appeared highly deformed and fused together with the α-zein released, whereas at higher SME, protein bodies were completely disrupted and α-zein was dispersed and may have formed protein fibrils....

Microwave-Assisted Rapid Modification of Zein by Octenyl Succinic Anhydride

ABSTRACT Corn is one of the most important food and industrial crops in the United States. Zein constitutes about half of the endosperm proteins in corn. Potential applications of zein include use in fibers, adhesives, inks, cosmetics, textiles, and chewing gum. Recently, attempts have been made to utilize zein for food coatings and biodegradable materials. The new applications of zein require it to be resistant to water. Thus, we are interested in new routes for chemical modification of zein (Biswas et al, unpublished). 2-Octenyl succinic anhydride (OSA) is extensively used in modifying food starches. Our objective was to take advantage of OSA hydophobicity, flexibility, and compatibility with nonpolar groups and incorporate OSA onto zein. This OSA-modified zein would possess the best of both OSA and zein. A zein solution in dimethyl formamide (DMF) was reacted with various levels of OSA to give modified zein. In a microwave reactor, the reactions proceeded tremendously fast and they were over in 5 min. ...

Isolation of zein using 100% ethanol.

ABSTRACT Traditionally, zein is isolated and recovered from corn gluten meal (GCM) using aqueous alcohol as the solvent. Recovery of zein from this solvent is inconvenient and costly. Zein is insoluble in 100% ethanol at room temperature, but it is soluble at 120°C in ethanol. Absolute ethanol effectively extracted zein from CGM, distillers dried grains (DDG), and ground corn. Zein was extracted from CGM with absolute ethanol in a high-pressure reactor at 130°C. After extracting at 130°C for 45 min, the solution was pumped out of the extractor and allowed to cool. Upon cooling, the zein precipitated from solution. The precipitate was removed from the solution and air-dried, resulting in 14% recovery of the starting material. The recovered precipitate had an average protein content of >90% on a dry basis, accounting for ≈20% of the CGM protein and recovered ≈35% of its zein. No differences were seen in the amount of zein extracted from CGM samples that were hand-collected off the dewatering screen and gent...