Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With liberating or forming of particles
Reexamination Certificate
2000-05-03
2003-10-21
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With liberating or forming of particles
C264S118000, C264S119000, C264S176100, C264S280000, C264S291000, C264S340000, C264S141000
Reexamination Certificate
active
06635206
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing articles from a resin comprising corn zein and a fatty acid. More particularly, the present invention relates to a method of manufacturing articles, such as sheets, films, and formed products, from a biodegradable corn zein resin. The zein resin-based articles exhibit improved physical and esthetic properties, and can be used as articles of manufacture for use in commercial applications, like agricultural and food packaging applications.
BACKGROUND OF THE INVENTION
Environmental concerns related to the nondegradable, petroleum-based plastics used in the production of packaging and disposable consumer goods has fostered research in the area of biodegradable materials for packaging and other articles of manufacture. Several biodegradable, biological polymers have been investigated because of their film-forming capabilities. Three major types of biodegradable products are derived from starch, from fermentation of sugars to polyesters, i.e., poly-(3-hydroxybutyrate)-co-(3-hydroxyvalerate), and from synthetic lactic acid polymers.
For example, starch-based resins have been converted into compost bags, disposable food-service items (e.g., cutlery, plates, and cups), packaging materials (e.g., loosefill and films), coatings, and other speciality items. However, a major disadvantage of the starch-based materials is moisture sensitivity due to the hygroscopic nature of starch.
Inexpensive, renewable, and abundant plant proteins constitute a viable source of biodegradable polymers. Accordingly, plant protein-based biodegradable polymers have been studied as potential biodegradable materials for packaging and other disposable consumer goods. For example, a transparent sheet having acceptable strength and biodegradability has been prepared from wheat gluten. Starch mixed with zein has been used in molding applications, in part because the biodegradability of zein is about equal to that of starch.
Corn zein, therefore, has been investigated for use as a structural material in packaging applications to take advantage of the unique properties of zein. For example, corn zein has been used as a base material to produce biodegradable sheets.
Zein is the prolamine in corn, and is an abundant protein in corn gluten meal, which is a coproduct of corn wet milling. Corn gluten meal contains about 70% protein (dry base) with zein amounting to 60% of that protein.
Zein is located in small round particles, 1-2 &mgr;m in diameter, called protein bodies in maize endosperm. Three distinct fractions, &agr;, &bgr;, and &ggr; zein, have been identified by differential solubility in aqueous alcohol solutions. Native zein is a mixture of proteins that differ in molecular size, solubility, and charge.
Zein is separated from the corn gluten meal by solvent extraction, usually with isopropanol. The extract is clarified centrifugally, then chilled to precipitate the zein. Additional extractions and precipitations increase zein purity. The zein then is dried to a powder.
Approximately 80% of native zein is soluble in 95% ethanol, with the remainder soluble in 60% ethanol. These two fractions are designated &agr;-zein and &bgr;-zein, respectively. &bgr;-Zein consists of disulfide-crosslinked &agr;-zein. The reducing environment of the steeping process in corn wet milling cleaves disulfide bonds, leaving-essentially only &agr;-zein in commercial corn gluten and zein. &agr;-Zein is a polypeptide having a molecular weight about 21,000 to about 25,000.
Zein is a unique material in terms of thermoplasticity and hydrophobicity. When zein is heated with starch above 60° C., the mixture becomes a dough and exhibits viscoelastic behavior. The moldable properties of zein classify zein as a plastic, i.e., a polymeric material capable of flowing under applied pressure or heat. The hydrophobic nature of zein is related to its high content of nonpolar amino acids. Because of this hydrophobic property, zein has been used in the food and pharmaceutical industries as coating material for candies, rice, dried fruits, and nuts. Zein also has been used in the pharmaceutical industry to coat capsules for protection, controlled release, and masking of flavors and aromas. Zein possesses the additional benefits of being renewable and biodegradable.
Zein also has been investigated for use as a structural material in packaging applications because of its film-forming properties. In particular, zein forms tough, glossy, scuff-proof, grease-proof films or coatings that are resistant to microbial attack. Zein also has an ability to cure with formaldehyde to provide an essentially inert product. A zein coating, therefore, can function as an oxygen, lipid, and moisture barrier.
Zein-based coatings have been used in numerous applications, for example, to extend the shelf life of almonds, peanuts, pecans, and walnuts. Similarly, zein-based coatings have protected confectioneries, dried fruits, and dried vegetables from moisture absorption, oxidation, and/or lipid migration. Zein coatings also have been used to coat vitamin-enriched rice, thereby reducing or eliminating vitamin loss. A zein-based coating also was used to maintain a high concentration of sorbic acid at the surface of an intermediate-moisture food, and to reduce moisture and firmness loss and delay a color change (i.e., reduce oxygen and carbon dioxide transmission) in fresh tomatoes.
A typical method of producing a zein-based film or coating involves solubilizing the zein in an aqueous alcohol solution, then casting the zein-containing alcohol solution on an inert, flat surface. After the water and alcohol evaporate, a tasteless and glossy film remains. The film then is peeled from the flat surface and used for its intended purpose. Typical disadvantages of zein films formed by casting are the control of film thickness and homogeneity in properties.
Cast films thus formed are very tough and resistant to grease. However, the cast films also are brittle and require the addition of plasticizers to impart flexibility and reduce the possibility of film chipping, cracking, and shattering. Commonly used plasticizers present in zein films include, for example, glycerin, triethylene glycol, fatty acids (like oleic, stearic, and palmitic acid), glycol monoesters, acetylated monoglycerides, dibutyl tartrate, lactic acid, and tricresyl phosphate.
An alternative method of preparing zein films involves plasticization of zein by forming an emulsion with oleic acid, followed by precipitation of the zein-oleic acid mixture to form a soft moldable resin. The dough-like resin then is stretched over rigid frames to obtain thin membranes that set into flexible films, that are ductile and tough. Microstructure images of the films showed a high degree of structural development consisting of fibers and ribbon-like protein structures that are theorized as responsible for the flexibility and toughness of the films.
Another method of preparing zein-based films utilizes corn zein plasticized with palmitic or stearic acid. Using these ingredients, a moldable zein resin was prepared, then cold-rolled into sheets about 0.5 mm thick. Such cold-rolled sheets are too thick for use in many practical applications. Typically, zein films are preferred for practical applications. As used herein, a “film” is defined as having a thickness of about 250 &mgr;m (microns) or less. A “sheet” is defined as having a thickness greater than about 250 &mgr;m.
Zein films exhibit relatively good water vapor barrier properties compared to other biodegradable, edible films, but are inferior compared to low density polyethylene (i.e., LDPE) and hydrolyzed ethylene-vinyl acetate (i.e., EVOH). Zein films also have a water vapor permeability (WVP) about equal to or lower than films made from cellophane, methylcellulose, ethylcellulose, ethylcellulose-polyvinylpyrrolidone, hydroxypropylmethylcellulose, and hydroxypropylcellulose, under similar test conditions. The WVP of zein films increases with increasing plasticizer level and relative humidity surrounding th
Ha Toan Thanh
Padua Graciela Wild
Rakotonirainy Andrianaivo Maherisoa
Greer Burns & Crain Ltd.
Lechert Jr. Stephen J.
The Board of Trustees of the University of Illinois
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