Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2003-03-12
2004-06-29
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C521S050000, C521S142000, C523S100000, C523S122000, C523S128000, C424S404000, C424S408000, C424S413000
Reexamination Certificate
active
06756428
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to biodegradable polymers and articles manufactured therefrom, which polymers include a microbe-inhibiting agent.
2. Description of the Related Art
Degradable polymers have found applications in diverse areas such as garbage bags, golf tees, food containers, foamed packing materials, chewing articles for pets, and even writing pens. Degradable polymers can be chosen for an application for many different reasons, including their tendency to break down under appropriate biological or disposal conditions, their ability to serve as a digestible or otherwise harmless mastication material for people or animals, or for public relations purposes.
A common class of biodegradable polymers is starch-based. Pure starch polymers do not possess the desired properties for most applications, as they are brittle and are unduly affected by moisture. They are therefore commonly blended and/or reacted with other polymers. U.S. Pat. No. 5,321,064 discloses a class of biodegradable polymers in which starch is reacted with synthetic polymeric material such as polyethylene, polystyrene, polypropylene and polyvinyl chloride. U.S. Pat. No. 5,409,973 discloses a class of materials based on starch and an ethylene copolymer. U.S. Pat. No. 5,360,830 discloses a similar material produced in expanded form. U.S. Pat. No. 5,459,258 discloses a class of biodegradable materials based on the combination of hydrophobic polysaccharides, one thermoplastic and the other non-thermoplastic.
Biodegradable starch-based resins are available commercially from a number of manufacturers, such as Starchtech™ and Novamont™. Starchtech™ sells a series of such polymers under the “Re-NEW™” trade name. Novamont™ offers several classes of such polymers under the trade name, “Mater-Bi™.”
Biodegradable poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) resins, as well as PLA-PGA copolymers have numerous desirable properties. (See: Ratner, B D et al., Eds.,
Biomaterials Science
, Academic Press, New York, 1996, p. 64; Naitove, M.,
Plastics Technology
, March 1995, p. 15.) A variety of commercial grades are available from Cargill, under the name “EcoPLA™,” and also from various biomedical suppliers. Adjustment of the PGA:PLA ratio in a material can be used to fine-tune the texture, degree of hydrophilicity and rate of biodegradation. For example, PGA is more hydrophilic than PLA, so that increasing the PGA content will increase the hygroscopic property (uptake of water, saliva, or any other fluid). In addition, although PGA is highly crystalline, which generally slows its degradation, it becomes markedly less crystalline, and more degradable, when blended with PLA.
Materials based on polyhydroxybutyrate (PHB) are also attractive. One example, available commercially under the name Biopol™ comprises a blend with 3-hydroxyvaleric acid (PHV). PHB is generally highly crystalline, inflexible, and difficult to process. Blending with PHV diminishes the crystallinity, resulting in more flexible, more easily processed materials.
Polycaprolactone, either pure or blended with other materials, is a generally attractive degradable material that has found uses in medical applications such as sealing materials for wounds.
Other attractive degradable materials include, the poly(amino acids), the polyanhydrides, poly (ortho esters), and polyphosphazenes.
The mechanism by which the materials of interest are degraded typically involves the metabolic or digestive action of microbes or enzymes generally derived from those microbes breaking down the molecular structure or catalyzing the hydrolysis of the materials. In many cases, however, significant hydrolysis occurs in the absence of direct microbial or enzymatic action.
The deliberate exposure of degradable materials to microbial or digestive conditions, such as in composting or mastication, is expected to bring about their relatively rapid degradation. Unfortunately, however, such materials are naturally susceptible to microbial action over their entire lifetime. Articles constructed from biodegradable materials therefore may support microbial growth long before they are degraded or otherwise consumed. Biodegradable materials often readily absorb water which generally promotes microbial growth. This property may be a serious problem for materials requiring prolonged storage, especially if the storage environment is humid or otherwise encourages growth of fungi or bacteria (e.g., dark, poor ventilation, dirt, etc. ). This is an especially serious problem for materials that are particularly intolerant of microbial proliferation, such as materials designed to contact food. Examples of the latter include plastic cutlery and tableware, plastic or paper/plastic composite cups, plastic or paper/plastic composite food containers, etc. Items the use of which involves contact with warm, dirty, and/or humid conditions are also particularly at risk, such as chewing articles for pets.
U.S. Pat. No. 5,744,516 discloses biodegradable resin molded articles made from biodegradable resin raw material, a biodegradable additive and an additive made of a substance existing in the nature. Also disclosed are (a) injection molded articles made of a biodegradable resin and an anti-biotic substance, and (b) resin molded articles having a layer of a biodegradable resin, and a layer of a photolytic resin covering the resin layer and also containing an antibiotic. This document states that prolonged use of a biodegradable resin requires first that degradation by bacteria be restricted, as by adding an antibiotic to the resin (citing Japanese Unexamined Patent Publication (Kokai) No. 5-51073).
It is often desirable to fine-tune (or even to reduce markedly) the degree of biodegradability of a polymer. For blended or reacted biodegradable polymers, this can be accomplished by altering the proportion of, and/or degree of, reaction with the degree of branching, cross-linking, etc.) can be varied or a protective coating added. These techniques for adjusting the degree of biodegradability, however, suffer from the fact that they often require complex engineering and can have unwanted side effects on useful properties (e.g., strength, impact resistance, processability, UV- or heat-resistance, etc.). There is thus a need for a simple way to alter the degree of biodegradability of a polymer without affecting other desirable properties.
SUMMARY OF INVENTION
The present invention provides a simple approach to altering the biodegradability of a polymer without affecting other properties and thereby overcomes the shortcoming of the prior art.
The invention provides compositions and methods that incorporate an effective amount of a microbe-inhibiting (MI) compound or cocktail of compounds (all of which are referred to herein interchangeably as “compound” or “agent”) into a biodegradable polymer, most preferably, starch-based polymers. The starch can be complexed with synthetic organic polymeric materials such as polyethylene, polypropylene and copolymers of ethylene and propylene. The synthetic polymers are preferably linked to the starch by organic linkers such as maleic anhydride. Such polymers linkers are described in U.S. Pat. 5,321,064, which is incorporated herein by reference. This patent discloses a class of biodegradable polymers in which starch is reacted with synthetic polymeric material such as polyethylene. Although post-incorporation of the agent can be effective (e.g., via soaking or high-pressure impregnation), it is preferred to incorporate the agent into the structure of the polymer at the time of compounding or at the time of formation (e.g., molding) of the final polymer article.
According to one embodiment of the invention, a formed body in the shape of a useful article comprises a biodegradable polymer composition including a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles. The microbe-inhibiting compound or compounds are s
McGarry Bair PC
Sanders Kriellion A.
Seefar Technologies, Incorporated
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