Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-03-24
2002-10-08
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S425000, C524S434000
Reexamination Certificate
active
06462120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to biodegradable films. Particularly, this invention relates to biodegradable films having agricultural applications and more particularly, agricultural biodegradable films that are subject to degradation after contacting a triggering composition. The present invention also concerns dimensionally stable shaped articles that are subject to degradation after contacting a triggering agent.
2. Background of Invention
Agricultural mulch films have been used in the production of fruit and vegetable crops for many years. The benefits of using these films include weed control, plant growth enhancement via solarization (warming) of the soil, extension of the growing season allowing for double and triple crops, reduction of pest infestation, efficient fumigation, moisture retention, improved irrigation efficiency, reduction in labor needed for crop production, increased crop output, enhanced crop quality, prevention of soil erosion, prevention of nutrient leaching and reduction in fruit rot by minimizing contact with soil.
In using an agricultural film, the farmer initially prepares the field by tilling the soil. A raised portion of the field, termed the field bed, is prepared and the agricultural mulch film is applied over the field bed and the edges of the film are sealed. The crop is planted by cutting holes in the film and planting the crop through these holes. Agricultural mulch film is often used in conjunction with irrigation systems either between the rows or under the film and often the soil is fumigated during the application of the film to reduce the infestation of pests. Growers will often plant a second or a third crop without removing the film to more efficiently utilize the film.
After harvesting the crop, the mulch film is removed in a very labor-intensive process. Typically, the plant mass is removed from the field either manually or by burning. The plastic is split and irrigation piping (if present) is removed. The mulch film is pulled from the ground, either by hand or mechanically, and collected for disposal.
This process has several disadvantages. Firstly, it is very labor intensive. Secondly, the disposal of the film can be problematic. Frequently, the film is contaminated with plant mass, dirt and possibly chemicals, such as, pesticides, herbicides and fertilizers. The weight of film removed from the field is often 25-200% of the initial weight of the film applied, and the volume of film removed is often 3-4 times the original volume of the film.
Other problems with the removed film are that it is often poor quality due to the film tearing during planting, harvesting and removal. Polyethylene film may also lack integrity due to photodegradation. These problems make reusing the film almost impossible.
There are few outlets for recovered material and little recycling of the material is carried out due to its contamination. In some areas, the removed material is legally prohibited from recycling streams due to the perception of contamination. In areas where recycling has been attempted the rejection rate for film is very high. For example, a Vermont study indicated that the rejection rate for recovered agricultural films is 70-90% after the users had cleaned the films and delivered them to the recycler.
Disposal of the film varies by region. Typically, the film is landfilled, either on site or in a commercial landfill, or burned. Landfill tipping fees can be high at commercial landfills, and there is a reluctance for landfills to accept used agricultural film due to the large bulk of the film after it is removed from the soil.
Numerous attempts have been made to develop degradable or biodegradable films suitable for agricultural applications. For example, U.S. Pat. Nos. 5,559,171 and 5,580,911 disclose a binary blend of cellulose esters and articles made therefrom. The blend includes (a) about 5% to about 98% of a C1-C10 ester of cellulose having a number of substituents per anhydroglucose unit of about 1.7 to 3.0 and an inherent viscosity of about 0.2 to about 3.0 deciliters/gram as measured at a temperature of 25° C. for a 0.5 g sample in 100 ml of a 60/40 parts by weight solution of phenol/tetrachloroethane, and (b) about 2% to about 95% of an aliphatic-aromatic copolyester having an inherent viscosity of about 0.2 to about 2.0 deciliters/gram as measured at a temperature of 25° C. for a 0.5 g sample in 100 ml of a 60/40 parts by weight solution of phenol/tetrachloroethane wherein the percentages are based on the sum of the weights of components (a) and (b).
As reported in Buchanan, (
J. Appl. Poly Science
, vol. 52, pp 1477-1488 (1994)), cellulose or cellulose derivatives with a low degree of substitution, i.e., less than one, are biodegradable at a relatively rapid rate. Cellulose is degraded in the environment by both anaerobic or aerobic microorganisms. Typical end products of this microbial degradation include cell biomass, methane (anaerobic only), carbon dioxide, water, and other fermentation products. The ultimate end products will depend upon the type of environment as well as the type of microbial population that is present. U.S. Pat. No. 5,580,911 discloses that the biodegradability of cellulose esters varies substantially with a degree of substitution. For example, cellulose esters having a degree of substitution of about 1.5 will exhibit a relatively fast rate of biodegradation while cellulose acetate having a degree of substitution as high as 2.5 can be degraded by certain microorganisms but the rate is slow. As used herein the term “degree of substitution” or “DS” refers to the number of substituents per anhydroglucose unit where the maximum degree of substitution is 3. As used herein, the term “biodegradable” refers to that type of degradability which is brought about by microorganisms and/or their enzymes when a substrate is exposed to the microorganisms under conditions which promote assimilation of the substrate by the microorganismns.
U.S. Pat. No. 5,594,068 discloses a biodegradable blend of cellulose esters. The blend includes from about 4 weight % to about 97 weight % of a C1-C10 cellulose ester having a DS of about 2.3 to about 3.0; from about 2 weight % to about 95 weight % of a second C1-C10 cellulose ester having a DS of about 1.5 to about 2.2; and from about 1 weight % to about 94 weight % of an aliphatic polyester or an aliphatic-aromatic polyester.
Presently, all degradable materials suffer from the same basic problem; weather has a substantial influence on the degradation rate. Since weather conditions are highly variable over time and locality this is a major problem in developing a material that will work consistently and particularly in agricultural applications. The weather may cause a material to decompose either too quickly or too slowly. For example, a hydrolytically degradable material may degrade too quickly if the crop season is wet but slowly or not at all if the crop season is dry and there is insufficient moisture to cause degradation. Similarly, a photodegradable material may decompose too quickly if the crop season is unusually sunny while a cloudy crop season may result in the material not decomposing. These complications have caused degradable mulch films to gain only small acceptance by the agricultural community.
Accordingly, there is a need for a biodegradable agricultural film that will retain its structural integrity independent of the weather conditions for a specified period of time with minimal or no degradation. There is also a need for a biodegradable agricultural film that can, at the desired time, be triggered to degrade.
SUMMARY OF THE INVENTION
Broadly, the present invention provides a process for enhancing biodegradability of a shaped article and more particularly a film. The process includes contacting a dimensionally stable shaped article with a biodegradability triggering agent. The biodegradability triggering agent is selected from chemical agents, enzymes, biological microbes and/or fungi, or combinations thereof.
It is an o
Boshears Betty J.
Eastman Chemical Company
Graves, Jr. Bernard J.
Rajguru U. K.
Seidleck James J.
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