The inadequate treatment of municipal solid waste that is being put in landfills and the increasing addition of nondegradable materials, including plastics, to municipal solid waste streams are combining to drastically reduce the number of landfills available and to increase the costs of municipal solid waste disposal. While recycling of reusable components of the waste stream is desirable in many instances, the costs of recycling and the infrastructure required to recycle materials is sometimes prohibitive. In addition, there are some products that do not easily fit into the framework of recycling. The composting of non-recyclable solid waste is a recognized and growing method to reduce solid waste volume for landfilling and/or making a useful product from the waste to improve the fertility of fields and gardens. One of the limitations to marketing such compost is the visible contamination by undegraded plastic, such as film or fiber fragments.
It is desired to provide components that are useful in disposable products and are degraded into less contaminating forms under the conditions typically existing in waste composting processes. These conditions can include temperatures up to about 70 degrees C., averaging in the 55–60 degrees C. range, humid conditions as high as 100 percent relative humidity, and exposure times ranging from weeks to months. It is further desirable to provide disposable components that will not only degrade aerobically/anaerobically in composting, but will continue to degrade in the soil or landfill. In the presence of water, it is desirable that the components further break down into low molecular weight fragments, which can be ultimately biodegraded by microorganisms into biogas, biomass, and liquid leachate, as occurs with naturally occurring organic materials such as wood.
Articles for which biodegradable materials are desirable include films and sheets. Biodegradable films are well known and are described, for example, by Wielicki, in U.S. Pat. No. 3,602,225, which discloses the use of barrier films comprising plasticized, regenerated cellulose films. Comerford, et. al., in U.S. Pat. No. 3,952,347, disclose biodegradable films comprising a non-biodegradable matrix, such as poly(vinyl alcohol), and about 40 to 60 weight percent of a biodegradable material, such as starch.
Polyesters are known for use in biodegradable articles. The biodegradable polyesters can be described as belonging to three general classes: aliphatic polyesters, aliphatic-aromatic polyesters and sulfonated aliphatic-aromatic polyesters.
Sulfonated aliphatic-aromatic polyesters are polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids and, in addition, have incorporated therein a sulfonated monomer, such as a salt of 5-sulfoisophthalic acid. Heilberger, in U.S. Pat. No. 3,563,942, discloses aqueous dispersions of solvent soluble linear sulfonated aliphatic-aromatic copolyesters having incorporated therein from 0.1 to 10 mole percent of a sulfonated aromatic monomer. Popp, et. al., in U.S. Pat. No. 3,634,541, disclose fiber-forming sulfonated aliphatic-aromatic copolyesters that include 0.1 to 10 mole percent of xylylene sulfonated salt monomers. Kibler, et. al., in U.S. Pat. No. 3,779,993, disclose linear, water-dissipatable sulfonated aliphatic-aromatic copolyesters that include 2 to 12.5 mole percent of a sulfonated monomer.
Gallagher, et. al., in U.S. Pat. No. 5,171,308, discloses compostable sulfonated aliphatic-aromatic copolyesters and films made therefrom. However, the disclosed compositions have an undesirably low biodegradation rate. Warzelhan, et. al., in U.S. Pat. No. 6,018,004, U.S. Pat. No. 6,114,042, and U.S. Pat. No. 6,201,034, disclose certain sulfonated aliphatic-aromatic copolyester compositions and their use for substrate coatings, films, and foams. The relatively high level of aliphatic dicarboxylic acid incorporated in the exemplified composition results in a crystalline melting point of 92° C. Thus, some known sulfonated aliphatic-aromatic copolyester materials do not have the desired balance of properties, including a relatively high crystalline melting point and a relatively high level of crystallinity and crystallization rate, for some end uses of polyesters, particularly in films. As disclosed in WO 02/16468 A1, blends have been used in order to provide optimized film physical properties. As one skilled in the art would appreciate, the use of polymeric blends necessarily complicates the processes used to produce films, coatings, and laminates.
A higher level of crystallinity and crystallization rate than possessed by known sulfonated aliphatic-aromatic copolyesters would allow simplified production processes, such as a reduction of film sticking during the formation of polymeric films and faster mold cycle times in the production of molded shaped articles. Such compositions that are biodegradable are also desired.
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