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
2003-06-20
2004-11-30
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S450000, C528S354000, C528S361000
Reexamination Certificate
active
06825285
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to biodegradable semicrystalline polyhydroxyalkanoate copolymers and blends containing such copolymers having improved crystallization properties, to methods for improving the crystallization rates and physical properties of such semicrystalline copolymers, to methods of forming shaped articles from such copolymers, and to shaped articles formed by such methods.
Shaped articles formed with such copolymers include, but are not limited to, films, fibers, nonwovens, sheets, membranes, coatings, binders, foams and molded products for packaging. The products exhibit a desirable combination of high crystallization rate, ductility and flexibility, and importantly biodegradability. Additional benefits of such blends are described in the invention. The products are useful for a variety of biodegradable articles, such as diaper topsheets, diaper backsheets, disposable wipes, shopping and lawn/leaf bags, agricultural films, yard waste nets, fishing nets, seeding templates, flower pots, disposable garments, medical disposables, paper coatings, biodegradable packaging, binders for cellulose fibers or synthetics, and the like.
BACKGROUND OF THE INVENTION
This invention relates to the need for alleviating the growing environmental problem of excessive plastic waste that makes up an ever more important volume fraction of what get thrown out in landfills every year. Biodegradable polymers and products formed from biodegradable polymers are becoming increasingly important in view of the desire to reduce the volume of solid waste materials generated by consumers each year. The invention further relates to the need for developing new plastic materials that can be used in applications where biodegradability, compostability or biocompatibility, are among primary desirable features of such applications. Such examples include for instance agricultural films, and the convenience that such films offer to farmers when they do not have to be collected after they have served their purpose. Flower pots or seeding templates are other examples where the temporary nature of the substrate translates into convenience for the user. Similarly, means of disposal of sanitary garments, such as facial wipes, sanitary napkins, pantiliners, or even diapers, may also be advantageously broadened with the use of materials that degrade in the sewage. Such items could be easily disposed directly in the sewage, after use, without disrupting current infrastructure (septic tanks or public sewage), and giving the consumer more disposal options. Current plastics typically used in making such sanitary garments can not be disposed without undesirable material accumulation. New materials to be used in the examples above would ideally need to exhibit many of the physical characteristics of conventional polyolefins; they must be water impermeable, tough, strong, yet soft, flexible, rattle-free, possibly low-cost and must be capable of being produced on standard polymer processing equipment in order to be affordable.
Another application which illustrates the direct benefit of compostable thermoplastic materials are leaf/lawn bags. Today's sole compostable bag which does not require the composter the additional burden of bag removal and the risk of compost contamination is the paper bag. Yet, it fails to provide the flexibility, the toughness and moisture-resistance of plastic films, and is more voluminous to store. Compostable plastic films used to make leaf/lawn bags would provide bags that could be disposed much like paper bags, yet provide the convenience of plastic bags.
It becomes clear in view of these examples that a combination of biodegradability, melt-processability and end-use performance is of particular interest to the development of a new class of polymers. Melt processability is key in allowing the material to be converted in films, coatings, nonwovens or molded objects by conventional processing methods. These methods include cast film and blown film extrusion of single layer structures, cast or blown film co-extrusion of multi-layer-structures. Other suitable film processing methods include extrusion coating of one material on one or both sides of a compostable substrate such as another film, a non-woven fabric or a paper web. Other processing methods include traditional means of making fibers or nonwovens (melt blown, spun bounded, flash spinning), and injection or blow molding of bottles or pots. Polymer properties are essential not only in ensuring optimal product performance (flexibility, strength, ductility, toughness, thermal softening point and moisture resistance) during end-use, but also in the actual product-making stages to ensure continuous operations. Rapid crystallization of the processed polymer melt upon cooling is clearly an essential feature necessary for the success of many converting operations, not only for economical reasons but also for the purpose of building in adequate structural integrity in the processed web (fiber, film) during converting, where for example crystallization times are typically less than about 3 seconds on commercial film and fiber lines.
In the past, the biodegradable and physical properties of a variety of PHA's have been studied, and reported. Polyhydroxyalkanoates are generally semicrystalline, thermoplastic polyester compounds that can either be produced by synthetic methods or by a variety of microorganisms, such as bacteria and algae. The latter typically produce optically pure materials. Traditionally known bacterial PHA's include isotactic Poly(3-hydroxybutyrate), or i-PHB, the high-melting, highly crystalline, very fragile/brittle, homopolymer of hydroxybutyric acid, and Poly(3-hydroxybutyrate-co-valerate), or i-PHBV, the somewhat lower crystallinity and lower melting copolymer that nonetheless suffers the same drawbacks of high crystallinity and fragility/brittleness. PHBV copolymers are described in the Holmes et al U.S. Pat. Nos. 4,393,167 and 4,880,59, and until recently were commercially available from Imperial Chemical Industries under the trade name BIOPOL. Their ability to biodegrade readily in the presence of microorganisms has been demonstrated in numerous instances. These two types of PHA's however are known to be fragile polymers which tend to exhibit brittle fracture and/or tear easily under mechanical constraint. Their processability is also quite problematic, since their high melting point requires processing temperatures that contribute to their extensive thermal degradation while in the melt. Finally, their rate of crystallization is noticeably slower than traditional commercial polymers, making their processing either impossible or cost-prohibitive on existing converting equipment.
Other known PHA's are the so-called long side-chain PHA's, or isotactic PHO's (poly(hydroxyoctanoates)). These, unlike i-PHB or PHBV, are virtually amorphous owing to the recurring pentyl and higher alkyl side-chains that are regularly spaced along the backbone. When present, their crystalline fraction however has a very low melting point as well as an extremely slow crystallization rate, two major drawbacks that seriously limit their potential as useful thermoplastics for the type of applications mentioned in the field of the invention.
Recently, new poly(3-hydroxyalkanoate) copolymer compositions have been disclosed by Kaneka (U.S. Pat. No. 5,292,860), Showa Denko (EP 440165A2, EP 466050A1), Mitsubishi (U.S. Pat. No. 4,876,331) and Procter & Gamble (U.S. Pat. Nos. 5,498,692; 5,536,564; 5,602,227; 5,685,756). All describe various approaches of tailoring the crystallinity and melting point of PHA's to any desirable lower value than in the high-crystallinity i-PHB or PHBV by randomly incorporating controlled amounts of “defects” along the backbone that partially impede the crystallization process. Such “defects” are either, or a combination of, branches of different types (3-hydroxyhexanoate and higher) and shorter (3HP, 3-hydroxypropionate) or longer (4HB, 4-hydroxybutyrate
Autran Jean-Philippe Marie
Melik David Harry
Satkowski Michael Matthew
Matthews Armina E.
Miller Steven W.
Moore Margaret G.
The Procter & Gamble & Company
Zarby Kim William
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