Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-05-30
2003-10-07
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S054240, C524S051000, C521S109100, C521S182000, C528S354000
Reexamination Certificate
active
06630543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods of making compositions and, more particularly, to a method of making a biodegradable polymer composition.
2. Description of the Related Art
Starches and modified starches have been the focus of considerable research interest in attempts to use these as fillers in order to decrease polymer costs and to use polymers that are biodegradable. Several recent examples, U.S. Pat. No. 5,384,187, issued Jan. 24, 1995, inventors Uemura et al., U.S. Pat. No. 5,391,423, issued Feb. 21, 1995, inventors Wnuk et al., and U.S. Pat. No. 5,412,005, issued May 2, 1995, inventors Bastioli et al., all represent domestic and foreign based attempts to achieve biodegradable polymer compositions in which natural polymers such as starches have been added to synthetic polymers.
One disadvantage associated with the above compositions is in the mixing of the synthetic polymer and the natural polymer. Typically, the natural polymer is in a dry form and is therefore, messy to mix with the synthetic polymer. Also, special handling equipment is needed for the natural polymer. Therefore, there is a need in the art to provide a method of making polymer compositions that are biodegradable reasonably competitive in price with commodity plastics such as polyethylene or polystyrene but which are cleaner to mix and eliminate the need for special handling equipment.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a method of making a biodegradable polymer composition. The method includes the steps of providing a first component being either one of a thermoplastic poly(hydroxy ester ether) or a synthetic, hydroxy-functional polymer and providing a second component being a natural polymer. The method includes the steps of mixing the first component and second component together to form a mixture, compounding the mixture, and pelletizing the compounded mixture to form pellets of a biodegradable polymer composition.
The compositions are useful in various processes such as molding, extruding and casting to form expanded articles, films and laminates. The synthetic, hydroxy-functional polymer may be as described by U.S. Pat. No. 5,171,820, inventors Mang and White, issued Dec. 15, 1992, U.S. Pat. No. 5,496,910, inventors Mang, White and Swanson, issued Mar. 5, 1996 and PCT application published as International Publication No. WO 97/23564, on Jul. 3, 1997, inventors Mang and White. Natural polymers for mixture with the synthetic, hydroxy-functional polymers include polysaccharides, modified polysaccharides, naturally-occurring fibers, and particulate fillers. Particularly preferred as the natural polymer are starches.
One advantage of the present invention is that a method is provided of making a biodegradable polymer composition. Another advantage of the present invention is that the method produces an extrudable composition by melt processing a thermoplastic poly(hydroxy ester ether) or a hydroxy-functional polymer with a natural polymer. Yet another advantage of the present invention is that the method compounds the mixture in at least one compounding step and pelletizes the compounded mixture. Still yet another advantage of the present invention is that the compounded composition is pelletized for further processing in various processes such as extruding. A further advantage of the present invention is that the method is cleaner to mix the natural polymer and eliminates the need for special handling equipment for the natural polymer.
Other features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description examples and the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Broadly, the present invention is a method of making a biodegradable polymer composition comprising two main components: the first component is either a thermoplastic poly (hydroxy ester ether) or a synthetic hydroxy-functional polymer more particularly, an hydroxy-functional polyester having a repeating structure as will hereinafter be described and the second component is a natural polymer. The natural polymer may be, for example, a polysaccharide, a modified polysaccharide, or a naturally occurring fiber or particulate filler, but preferably is starch or a modified starch.
While the amount of hydroxy-functional polymer selected for use depends on a variety of factors including the specific polymer employed and the desired end uses of the composition, in general hydroxy-functional synthetic polymers can be present in an amount of from 1 to 99 wt. %, preferably from 1 to 95 wt. %, and most preferably from 10 to 90 wt. %, based on the total weight of the hydroxy-functional polymer and the natural polymer. Particularly preferred compositions for forming films have natural polymer present as less than about 50 wt. % of the total composition; and hydroxy-functional, synthetic polymer present in amounts from at least about 10 wt. % to about 70 wt. %.
Natural polymers contemplated for use include biodegradable organic fillers, such as cellulose and other fibers and the like, which are well known. Naturally occurring fibers or particulate fillers which can be employed in the practice of the present invention for preparing the composition are, for example, wood flour, wood pulp, wood fibers, cotton, flax, hemp, or ramie fibers, rice or wheat straw, chitin, chitosan, cellulose materials derived from agricultural products, nut shell flour, corn cob flour, and mixtures thereof. Polysaccharides which can be employed in the practice of the present invention for preparing the composition are the different starches, celluloses, hemicelluloses, gums, pectins, and pullulans. Polysaccharides are known and are described, for example, in
Encyclopedia of polymer Science and Technology
, 2nd edition, 1987.
Modified polysaccharides which can be employed in the practice of the present invention for preparing the composition are the esters and ethers of polysaccharides, such as, for example, cellulose ethers and cellulose esters, or starch esters and starch ethers. Modified polysaccharides are known and are described, for example, in
Encyclopedia of Polymer Science and Technology
, 2nd edition, 1987.
The natural polymer is in granular or fiber form (sometimes hereinafter referred to as the “granular embodiment”) or in a gelatinized or thermoplastic form.
When practicing the granule embodiment of the present invention, the granules of natural polymer preferably will have a particle size of less than about 100 &mgr;m, and more preferably have a particle size of up to about 50 &mgr;m and a water content of less than about 15 wt. %, more preferably less than about 10 or 11 wt. %. In the granule embodiment, the two main components may be admixed in varying amounts. The natural polymer may be present in a trace amount or in greater amounts up to a weight ratio with respect to the hydroxy-functional polymer of about 8:1, more preferably up to about 6:1.
When practicing the present invention so as to obtain the gelatinized or thermoplastic form, the preferred starch component is derived from a gelatinized starch or a gelatinized modified starch. “Modified” is meant that the starch can be derivatized or modified by typical processes known in the art (e.g. esterification, etherification, oxidation acid hydrolysis, cross-linking and enzyme conversion). Thus, for example, a modified starch may be a starch ester, a starch ether, or a cross-linked starch. Conventional modifications of starch are described in publications such as
Starch: Chemistry and Technology
, 2nd edition, editor Whistler et al., and
Starch Derivatives: Production and Uses
, Rutenberg et al., Academic Press, Inc., 1984.
When starch is said to be “gelatinized” it has melted and lost its crystalline state. The starch molecules have taken on a random, disordered configuration and the starch chains have become entangled. Thus, the starch is thermoplastic and is sometimes referred to as “destructured.” Whe
Doane William M.
Mang Michael N.
White Jerry E.
Willett Julious L.
Xu Wayne
Biotechnology Research and Development Corporation
Hu Henry S.
McGlynn, P.C. Bliss
Wu David W.
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