Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1997-11-07
2001-05-15
Foelak, Morton (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S317500, C521S063000, C521S064000, C521S150000, C604S358000, C604S369000
Reexamination Certificate
active
06231960
ABSTRACT:
TECHNICAL FIELD
This application relates to biodegradable and/or compostable polymers made from certain conjugated dienes such as isoprene and 2,3-dimethyl-1,3-butadiene, as well as biodegradable articles made from such polymers. This application particularly relates to absorbent foams made from such polymers that are useful in absorbent articles such as diapers.
BACKGROUND OF THE INVENTION
Polymers are used in a wide range of applications due to their stability, elasticity, lightweight, strength, ease of fabrication and formulation, and low cost. These applications include packaging, housewares, buildings, highway construction, insulation (sound, vibration, or heat), ground coverings for agricultural weed and erosion control, adhesives, coatings for controlled release products, absorbents, and the like.
Environmental concerns have suggested a need for materials having polymer-like properties but without the degree of permanence typically associated with synthetic polymers. The decreasing availability of landfill space, as well as the increased costs of municipal solid waste disposal, have put increasing emphasis on minimizing the impact of nondegradable materials, including plastics, on the solid waste stream. Man-made polymers are typically not readily degraded by microorganisms that degrade most other forms of organic matter and return them to the biological life cycle. Although synthetic polymers form a relatively small fraction of the materials in landfills today (about 7% by weight or 15-20% by volume, see Thayer,
Chem. Eng. News.
1989, 67 (4), 7), it would nonetheless be desirable to formulate such materials so they would be sufficiently durable for their intended use but more susceptible to environmental degradation. This would facilitate the development of methods such as industrial composting to convert municipal solid waste materials to useful products. In addition, plastic film products applied to the ground (e.g. to control weeds and/or erosion) would ideally be formulated to degrade after a few months. Improved degradability would also be desirable for “controlled release” of an active from some products, such as encapsulated pesticides, herbicides, and fertilizers.
Several approaches to enhance the environmental degradability of polymers have been suggested and tried. These include: (1) incorporation of a particulate biodegradable materials such as starch; (2) introduction of photodegradation-sensitizing groups into the molecular structure of the polymer; (3) incorporation of small amounts of selective additives that accelerate oxidative and/or photo-oxidative degradation. Each of these methods has certain problems. The inclusion of starch in polymer compositions facilitates mechanical breakdown, but leaves behind residual components of the nonbiodegradable polymer. Photodegradation functions only if the plastic is exposed to light (e.g., in the case of litter), and provides no benefit if the product is disposed of in a dark environment, e.g., in water, soil or a standard landfill. Oxidative accelerators can cause unwanted changes in the mechanical properties of the polymer, such as embrittlement, prior to or during use.
Another approach to environmental degradability of articles made with synthetic polymers is to make the polymer itself biodegradable or compostable. Biodegradation typically refers to the natural process of a material being degraded under anaerobic and/or aerobic conditions in the presence of microbes, fungi and other nutrients to carbon dioxide/methane, water and biomass. Composting typically refers to a human controlled process (e.g., a municipal solid waste composting facility) where the material undergoes physical, chemical, thermal and/or biological degradation to carbon dioxide/methane, water, and biomass Composting is generally conducted under conditions ideal for biodegradation to occur (e.g. disintegration to small pieces, temperature control, inoculation with suitable microorganisms, aeration as needed, and moisture control).
There are a number of polymer-based products for which biodegradability and/or compostability would be desirable. For example, films used in packaging, as backsheets in diapers, and agricultural ground covering are not intended to survive intact for long periods of time. Latex-type polymer products used in binders and adhesives, as well as in paints and coatings, often serve protective roles where stability to the environment is desired. However many products containing latexes are ultimately disposed of in the municipal solid waste stream. These include nonwoven products (e.g., tissue/towel products) where latex binders are used to join discrete fibers into a cohesive web. Although many nonwovens contain degradable cellulosic fibers (e.g. rayon), the latex binder is typically non-degradable, e.g., acrylate latexes. Accordingly, it would be desirable to be able to make polymeric latexes, including those useful as binders for nonwovens, that would be biodegradable or at least compatible with other means of disposal of waste, including standard industrial and municipal solid waste composting operations
Another approach to environmental degradability of articles made with synthetic polymers is to make the polymer itself biodegradable or compostable. See Swift,
Acc. Chem. Res.,
1993, 26, 105-110 for a general overview on biodegradable polymeric compositions. Most of this work has been based on hydrolyzable polyester compositions, chemically modified natural polymers such as cellulose or starch or chitin, and certain polyamides. See, for example, U.S. Pat. No. 5,219,646 (Gallagher et al), issued Jun. 15, 1995 (hydrolyzable polyester). Polyvinyl alcohol is the only synthetic high molecular weight addition polymer with no heteroatom in the main chain generally acknowledged as biodegradable. See also Hocking,
J. Mat. Sci. Rev. Macromol. Chem. Phys.,
1992, C32(1), 35-54, Cassidy et al,
J. Macromol. Sci.—Rev. Macromol. Chem.,
1981, C21(1), 89-133, and “Encyclopedia of Polymer Science and Engineering,” 2nd. ed.; Wiley & Sons: New York, 1989; Vol. 2, p 220. (Limited reports add poly (alkyl 2-cyanoacrylates) to this list of biodegradable synthetic polymers.)
Natural rubber (cis-1,4-polyisoprene) is also readily biodegradable. Natural rubber retains carbon-carbon double bonds in the main polymeric chain that are believed to facilitate attack by either oxygen and/or microbes/fungi, leading subsequently to chain scission, molecular weight reduction, and eventually total degradation of the polymer. See Heap et al,
J. Appl. Chem.,
1968, 18, 189-194. The precise mechanism for the biodegradation of natural rubber is not known. Enzymatic and/or aerobic oxidation of the allylic methyl substituent may be involved. See Tsuchii et al.,
Appl. Env. Micro.
1990, 269-274, Tsuchii et al.,
Agric. Biol. Chem.,
1979, 43(12), 2441-2446, and Heap et al, supra. By contrast, nonbiodegradable polymers such as polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, poly(meth)acrylates and polystyrene have saturated carbon-carbon backbones that do not facilitate attack by either oxygen and/or microbes. This biodegradability has been recognized only for the natural form of rubber. See Tsuchii et al., supra, which reports: “Synthetic polyisoprenes, however, were not degraded completely by the organism.” More recently, it was reported that synthetic “cis-1,4-polyisoprene does not undergo specific biodegradation.” See Kodzhaeva et al.,
Intern. J. Polymeric Mater.,
1994, 25, 107-115.
Unfortunately, natural rubber is biodegradable to the extent that it is too unstable for most uses. Natural rubber also suffers from poor mechanical properties (e.g., strength, creep resistance). Indeed, stabilizers, fillers, and/or crosslinking agents are routinely added to natural rubber to enhance its mechanical properties. Crosslinkers are typically required in order to provide sufficient mechanical integrity for practical use. However, the most common crosslinking process creates a polysulfide linkage, i.e., by vulcanization, that virtually elim
Dyer John C.
Hird Bryn
Wong Pui Kwan
Foelak Morton
Hentz Mary Catherine
Roof Carl J.
The Procter & Gamble & Company
Wei-Berk Caroline
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