Title:  Highly flexible starch-based films

United States Patent:  6,528,088

Issued:  March 4, 2003

Inventors:  Gilleland; G. M. (Madison, GA); Turner; J. L. (Decatur, IL); Patton; P. A. (Decatur, IL); Harrison; M. D. (Decatur, IL)

Assignee:  A. E. Staley Manufacturing Co. (Decatur, IL)

Appl. No.:  585846

Filed:  June 1, 2000

Film-forming compositions are disclosed that can comprise, on a dry solids basis, 25 to 75 percent by weight of certain starch derivatives and 25 to 75% primary external plasticizer. The starch derivatives can be chemically modified starches that range in molecular weight from 100,000 to 2,000,000. The high levels of plasticizer in the films give excellent film flexibility and integrity.

SUMMARY OF THE INVENTION

One aspect of the present invention is a gelatin-free film-forming composition that comprises starch material and a primary external plasticizer. The starch material is selected from the group consisting of modified starch and waxy starch, and has a dextrose equivalent (DE) of less than about 1, and preferably has no measurable DE (using the Lane-Eynon method). The weight ratio of plasticizer to starch material in the composition preferably is at least 0.5:1, more preferably is from about 0.5:1 to about 3:1, and most preferably is from about 1:1 to about 3:1. This composition optionally may include, in addition to starch and plasticizer, gums, hydrocolloids, synthetic polymers, and/or other additives, but is preferably free of protein. "Gelatin-free" and "protein-free" are used herein to mean that no more than trace amounts (e.g., no more than about 0.1 weight percent) of the listed material is present in the composition.

The composition can be prepared with water, and preferably has a solids concentration of about 30-70%. (All composition percentages given herein are by weight unless otherwise stated.) In one preferred embodiment of the invention, the solids in the composition comprise 25-50% starch material and 50-75% plasticizer.

The starch material preferably comprises starch that has been chemically modified with a monoreactive moiety to a degree of substitution of at least about 0.015. In a particularly preferred embodiment, the starch material is selected from the group consisting of ether and ester derivatives of starch, such as hydroxypropyl, hydroxyethyl, succinate, and octenyl succinate starch. One specific embodiment of the invention comprises hydroxypropylated potato starch having a degree of substitution of about 0.015-0.30 and a molecular weight of about 200,000-2,000,000. Another specific embodiment of the invention comprises hydroxyethylated corn starch having a degree of substitution of about 0.015-0.3 and a molecular weight of about 200,000-2,000,000. Another specific embodiment of the invention comprises hydroxypropylated high-amylose corn starch with a degree of substitution of 0.015-0.3 and a molecular weight of about 200,000-2,000,000.

In some embodiments of the invention, one or more water soluble gums are added to the mixture of starch and plasticizer. The gum is preferably 0-15% of the total solids in the mixture. The gum preferably is selected from the group consisting of carrageenan, locust bean, xanthan, gellan, agar, alginates, guar, gum arabic, and pectin. A combination of kappa carrageenan and iota carrageenan, most preferably in a weight ratio of about 1:1, is especially preferred.

In another embodiment of the invention, water soluble synthetic polymers may be added to the starch and plasticizer mixture. The synthetic polymer is preferably 0-50% of the total solids in the mixture. The preferred synthetic polymer is polyvinyl alcohol.

In another embodiment of the invention, organic or inorganic filler or pigment particles can be added. The pigments may be chosen from a list including clays, calcium carbonate, titanium dioxide, and synthetic organic pigments.

Industrial plasticizers are discussed in the Encyclopedia of Chemical Technology, 4^th ed., Vol 19, pp 258-280, 1997. A plasticizer is a substance which, when added to another material, increases the softness and flexibility of that material. Without being bound by theory, it is believed that plasticizers increase flexibility of polymeric materials by increasing the free volume within the material. Randomly distributed within the material and interspersed among the polymer chains, the plasticizer molecules interfere with the polymer's ability to align its chains and pack into ordered structures. Molecular ordering increases the density of the material (decreases free volume) and impedes mobility of the polymer chains within the material. The increase in free volume imparted by the plasticizer allows room for chain segments to move. The material can then more readily accommodate an applied force by deforming.

Polymers can be plasticized in two general ways: "internally" and "externally." Internal plasticization can occur, for example, through the incorporation of a variety of chemical moieties along the starch molecular chains through ether or ester linkages. These moieties include hydroxypropyl, hydroxyethyl, carboxymethyl, succinyl and octenylsuccinyl, to name a few. An irregular array of substituents along the polymer backbone prevents close and regular chain packing, and increases free volume in the material.

External plasticizers are relatively small molecules that are miscible with the polymer, and impede chain alignment. External plasticizers are of two distinct classes: primary and secondary. Primary plasticizers are effective in modifying the mechanical properties of the material on their own. Secondary plasticizers may be incompatible, or ineffective, at plasticizing the material on their own, but when added in combination with the primary plasticizer, can be very effective. They are sometimes called "extenders."

The plasticizers required in this invention are primary, external plasticizers, such as sugars and low molecular weight polyols. The properties of the composition optionally can be further enhanced by using internal and/or secondary external plasticizers. A suitable secondary external plasticizer is water. The polyhydric alcohols are hygroscopic; their presence in the starch compositions increases the water content relative to an un-plasticized starch.

Preferred plasticizers for use in the present invention have the general formula C_n O_n H_x, wherein n has a value between 3 and 6, and x has a value between 2n and (2n+2), where at least 80% of the oxygen is in the form of hydroxyl groups, and the remaining are in the form of ether groups. This group of preferred plasticizers also includes dimers, disaccharides and low molecular weight (e.g., 300-1800 MW) oligosaccarides of these compounds, and may also include ether or ester derivatives of these compounds. Particular examples of suitable plasticizers include glycerol, diethylene glycol, sorbitol, sorbitol esters, maltitol, sucrose, fructose, invert sugars, corn syrup, and mixtures of one or more of these.

In preparing the films described in this invention, the mixture of starch and water is heated with stirring to hydrate fully all components in the mixture. The hydration of starch by heating is termed "cooking." The preferred conditions for cooking the starch mixture are 80-200^oC. for 5-60 minutes. Those versed in the art of starch cooking will recognize that a variety of cooking techniques may be employed, including but not limited to, open kettles or high-pressure jet cookers. In another embodiment of the invention, instant, pre-gelled or cold-water swelling starches may be used. For these starches, it is not required that the mixture be heated to hydrate fully the starch.

The plasticizer, may be, but is not required to be, mixed with the starch and water prior to cooking. The gum, synthetic polymer, or other components of the film-forming mix, may be, but are not required to be, mixed with the starch and water prior to cooking. Whether or not the non-starch components are mixed with the starch and water prior to cooking will depend on a number of considerations, including the hydration requirements of the other components, their thermal stability, viscosity constraints, and convenience.

Another aspect of the invention is a flexible adhesive for paper tape and other paper-based articles comprised of the above-described starch-based composition, usually with much of the water removed. Yet another aspect of the invention is a flexible paper coating comprised of the above-described composition. Yet another aspect of the invention is a flexible coating in which the starch-based composition is a film-forming component, but which may also include fillers or pigments, latex emulsions or other additives.

Another aspect of the invention is an edible film that comprises the above-described starch-based composition, usually with much of the water removed. Yet another aspect of the invention is a soft gel capsule that comprises a sealed capsule wall and a first substance that is encapsulated by the sealed capsule wall. The capsule wall comprises the above-described starch-based composition. In one embodiment of the invention, the film or the capsule wall consists essentially of the combination of starch material and plasticizer.

The first substance encapsulated by the capsule wall can be any of a variety of materials that have been encapsulated by gelatin in the past. Many such substances are edible, including drugs, vitamins, nutritional supplements, and pre-measured food ingredients such as flavorings. It can also comprise, for example, photographic or dye solutions.

Another aspect of the invention is a method of encapsulating a first substance. This method comprises the steps of providing a first substance and an edible film as described above, and encapsulating the first substance in the film. Preferably, the film used in this method has been formed on a surface having a temperature of at least about 100.degree. F.

In one preferred embodiment of the invention, the film or capsule wall consists essentially of the combination of starch material, plasticizer, and optionally gum.

The present invention provides an economical alternative to the synthetic polymers currently used to impart dimensional stability and binding strength in adhesives and industrial coatings. It also provides an economical means for replacing gelatin in compositions utilized in the production of soft gel for food, pharmaceutical, and industrial applications. Further, the starch-based materials of this invention are compatible with existing application equipment used for manufacture of tapes, coated papers, and various products that in the past have been primarily comprised of gelatin.

In compositions of the present invention, the starch, plasticizer, and any other solid ingredients preferably make up from about 30 to 70% by weight of an aqueous slurry. Flexible films are prepared by blending together the starch, plasticizer, and water, and heating the mixture to a temperature and for a time sufficient to gelatinize the starch fully, (e.g., 80-200^oC. for 5-60 min). Additional materials may be added to the mixture of starch and plasticizer in order to impart improved functionality. These materials may be added before or after heat treatment. The mixture is then sheeted, while warm or hot, to form a thin film. The mixture may be sheeted directly onto paper, board or other surface when used as a coating or adhesive, or onto a casting surface from which the cooled film can be lifted and transfer to rolls, or to fabrication equipment.

The present invention has a number of benefits. Starch is a low cost and readily available material. The starch may be modified using a number of chemical and physical means to enhance its properties while maintaining its status as a material approved as a food additive by the FDA. It may be subjected to a number of additional modifications while maintaining its FDA acceptability for use in contact with foods. It is biodegradable. It is water soluble and therefore does not require expensive, hazardous and/or volatile solvents that many other polymers require for processing. A range of materials are available for plasticizing starch which are both inexpensive and FDA approved for food use. In addition, the compositions of the present invention can be cooked more easily than the high amylose compositions that have been used in the past.

A film comprising the above-described composition can function as a pressure sensitive adhesive. The combination of a high plasticizer content and a highly substituted starch plasticizes the film to the point of providing tack through a broad humidity range.

Claim 1 of 21 Claims

What is claimed is:

1. A gelatin-free film-forming composition, comprising:

starch material having an average molecular weight of about 100,000-2,000,000 and a dextrose equivalent less than about 1 and selected from the group consisting of (a) starch which has been chemically modified with a monoreactive moiety to a degree of substitution of at least about 0.015 and is selected from the group consisting of ether and ester derivatives of starch and (b) waxy starch; and

a primary external plasticizer;

wherein the weight ratio of plasticizer to starch material is at least about 0.5:1.
 

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