EP0586575A1

EP0586575A1 - Degradable cellulose polymers

Info

Publication number: EP0586575A1
Application number: EP19920913240
Authority: EP
Inventors: Edward S. Lipinsky; Richard G. Sinclair
Original assignee: Battelle Memorial Institute Inc
Current assignee: Battelle Memorial Institute Inc
Priority date: 1991-05-21
Filing date: 1992-05-20
Publication date: 1994-03-16
Also published as: CA2109618A1; WO1992020738A1; AU2144492A; JPH06507929A

Abstract

L'invention concerne une composition de polymères d'esters cellulosiques thermoplastiques ayant des propriétés de dégradation lorsqu'elle est exposée à l'humidité. La composition comprend un ester de cellulose et un promoteur de dégradation. Le promoteur de dégradation, après transformation de la composition polymère en un produit final et en présence d'humidité, est soluble dans l'eau et peut être extrait par lixivation du produit final polymère ou en présence d'humidité, s'hydrolyse pour former des sous-produits solubles dans l'eau qui sont lixiviables du produit final polymère. Le promoteur de dégradation joue également le rôle d'un catalyseur pour améliorer l'hydrolyse de l'acétate de cellulose, ce qui donne comme résultat un mélange de cellulose et d'acide acétique. La cellulose peut ensuite se dépolymériser en saccharides qui sont davantage biodégradables. Le promoteur de dégradation peut également agir comme agent plastifiant pour le polymère d'ester de cellulose ou peut être utilisé en combinaison avec d'autres agents plastifiants connus.The invention relates to a composition of thermoplastic cellulose ester polymers having degrading properties when exposed to moisture. The composition includes a cellulose ester and a degradation promoter. The degradation promoter, after transformation of the polymer composition into a final product and in the presence of moisture, is soluble in water and can be extracted by leaching the polymer final product or in the presence of moisture, hydrolyzes to form water-soluble by-products which are leachable from the final polymer product. The degradation promoter also acts as a catalyst to improve the hydrolysis of cellulose acetate, which results in a mixture of cellulose and acetic acid. The cellulose can then depolymerize into saccharides which are more biodegradable. The degradation promoter can also act as a plasticizer for the cellulose ester polymer or can be used in combination with other known plasticizers.

Description

DEGRADAB E CELLULOSE POLYMERS

Field of the Invention

The present invention is directed to a cellulose ester composition which may be used to form thermoplastic polymeric materials having improved degradation properties upon exposure to moisture. The compositions include at least one degradation promoter that will leach from the polymeric materials in the presence of moisture after disposal of the polymeric composition in the environment. In one embodiment, the present invention is directed to a thermoplastic cellulose acetate polymer composition having improved degradation properties upon exposure to moisture which includes cellulose acetate, a plasticizer for the cellulose acetate and a hydrophilic degradation promoter.

Background of the Invention

The disposal of modem packaging resins, such as polyethylene, polypropylene, polyvinyl chloride and polystyrene is becoming an increasingly serious problem. Accordingly, significant technical effort has been expended to produce polymeric compositions which are biodegradable. Representative patents directed to producing biodegradable polymers are U.S. Patent No. 3,950,282 to Gilbert, et al., U.S. Patent No. 4,048,410 to Taylor, et al., U.S. Patent No. 4,038,228 to Taylor, U.S. Patent No. 4,051,306 to Tobias, et al., U.S. Patent No. 4,056,499 to Taylor and U.S. Patent No. 3,907,726 to Tomiyana, all of which are related to methods or compositions for producing degradable polymeric materials.

Some of the first polymers developed for commercial use were based on cellulose. These included regenerated cellulose (rayon) and various cellulose esters, such as cellulose acetate, cellulose butyrate, cellulose propionate and mixed esters of cellulose (acetate, acetate butyrate and acetate propionate).

Regenerated cellulose materials, such as cellophane and rayon, are environmentally degradable at a very slow rate. However, to provide cellulose esters in the form of a melt extruded film, a high level of plasticizer is required. Such plasticizer is used to provide cellulose ester compositions which can be formed into a thermoplastic film by melt-fabrication methods. Cellulose acetate in its pure form is not a thermoplastic when melt-fabricated by methods such as extrusion. The use of such high levels of plasticizer produced plastic materials which are highly stable and which do not degrade when exposed to the environment, even in highly moist conditions. The wide variety of soil and microorganisms which are known to have the ability to enzymatically hydrolyze cellulose and pure cellulose esters to soluble intermediates do not react with cellulose esters which are highly plasticized. Nevertheless, films and flexible sheet plastic packaging materials produced from cellulose esters, such as cellulose acetate, are highly desirable in that cellulose acetate is potentially one of the least expensive plastic films to produce. It would be highly desirable to provide a cellulose ester packaging material which can be degraded by exposure to normal ambient environmental conditions. As used herein, the term "normal ambient environmental condition" is meant to include those conditions which prevail during the disposal of most waste materials, such as in a landfill or waste dump.

Accordingly, it is the principal object of the present invention to provide cellulose ester compositions which are degradable by exposure to moisture in a normal ambient environment.

Summary of the Invention The present invention is directed to a thermoplastic cellulose ester polymer composition having improved degradation properties upon exposure to moisture. The composition includes a cellulose ester and a degradation promoter. The degradation promoter, after formation of the polymer composition into an end- product and in the presence of moisture, is water soluble and leachable from the polymer end-product or in the presence of moisture, hydrolyzes to form water soluble by-products which are leachable from the polymer end-product. The degradation promoter also acts as a catalyst to enhance the hydrolysis of the cellulose acetate, resulting in a mixture of cellulose and acetic acid. The cellulose can then depolymerize into saccharides that are more biodegradable. The degradation promoter can act as a plasticizer for the cellulose ester polymer or can be used in combination with other known plasticizers.

Detailed Description of the Invention

Cellulose is a polysaccharide formed from anhydroglucose units. Each of the anhydroglucose units contains three free hydroxyl groups which can be reacted to form esters. The extent to which substitution of an acid takes place is known as the degree of substitution and is expressed as the average number of hydroxyl groups, of the three available in the anhydroglucose unit, that have been replaced. Cellulose esters useful in the present invention have a degree of substitution of from about 2.0 to about 2.6. Expressed in other terms, the cellulose acetates useful in the present invention have an ester content of from about 39% to about 42.5% on an acetyl equivalent basis. In the preparation of cellulose esters having substitutions appreciably below 3, i.e., in the range of 2.0 to 2.6, it has not been possible to make products of good uniformity by esterifying directly to the desired substitution. This is because of the topochemical character of the reaction. Esterification proceeds inwardly from the outer surface of the cellulose fiber and uniformity is poor until the product has completely dissolved in the esterification mixture. Such complete dissolution occurs close to the triester stage. In order to prepare uniform products of substitution 2.0- 2.6, it is necessary to make the triester and hydrolyze the triester in solution to the desired degree of substitution.

Accordingly, early use of cellulose esters utilized the triester formulation. Cellulose triesters, however, are difficult to mold and many early efforts were directed at methods and compositions for improving the molding capability of cellulose triesters. U.S. Patent 2,067,310 to Auden, for example, discloses a process of making molded articles that can use molding temperatures as low as 120° C. to 180° C. and molding pressures of 2,000 to 3,000 psi, which are lower than the usual molding temperatures and pressures for cellulose triacetate. The process of the Auden patent consists in mixing cellulose triacetate and a material taken from group consisting of lactides, and the anhydrides of maleic, succinic and phthalic acids. The addition of the lactides and the anhydrides in combination with the use of plasticizers produced a moldable cellulose triacetate composition.

U.S. Patent No. 2,805,171 to Williams, also discloses a method for providing a moldable composition of cellulose triacetate. As discussed in the Williams patent, cellulose triacetate having an acetyl content of 52.5% to 53.5% (figured as percent acetic acid) are acetone insoluble cellulose esters. The cellulose esters useful in the present invention, having an acetyl content of from between about 39% and about 42.5%, are characterized in the Williams patent as being acetone soluble.

The degradable thermoplastic cellulose ester compositions of the present invention are mixtures of a cellulose ester having an ester content, on an acetyl basis, of from between about 39% and about 42.5% and a degree of substitution of from about 2.0 to about 2.6, a plasticizer and a degradation promoter. While not wishing to be bound by any theory, it is believed that the degradable functionality of the compositions of the invention are at least partially attributable to access by water to the polymer and hydrolysis of the polymer at the pendant acetyl groups and at the acetal linkages.

The degradation promoters of the present invention are hydrophilic materials. The degradation promoters are cyclic internal monoesters, cyclic internal double esters and oligomers of such acids having from 2 to 50 acid moieties. The monoesters have a single oxygen molecule in the ring and can be prepared from any of the hydroxy acids except the α-hydroxy acids. Monoester lactones useful as degradation promoters in the present invention are usually prepared from hydroxy acids. The cyclic double esters can be prepared from α-hydroxy acids. Cyclic internal esters are generally referred to as lactones. The cyclic double 6-membered esters are sometimes referred to as dioxanediones.

While the cyclic internal esters of the invention can be prepared from suitable hydroxy acids, other chemical pathways for their preparation are available. The 7- and δ-lactones are commonly prepared by either hydrolysis or distillation of 7- or δ-halo acids, by treatment of unsaturated acids with aqueous hydrobromic or sulfliric acids, or by partial reduction of cyclic acid anhydrides. β-Lactones result from the reaction of a ketene with aldehydes or ketones. The reaction of ketene with formaldehyde is shown below.

H₂C=C=0 + C=0 ^{" H}2^C — c=o

H₂C 0

Large-ring lactones can be made by oxidation of cyclic ketones with Caro's acid; thus, cyclohexanone yields e-caprolactone. Some lactones are prepared from the reaction of a dicarboxylic acid with a polyhydric alcohol, such as the reaction of malonic acid with ethylene glycol.

Suitable hydroxy acids and dicarboxylic acids for preparation of the lactones useful as degradation promoters of the present invention include 3- hydroxypropionic acid, 2-hydroxy, 1,2,3 propanetricarboxylic acid (citric acid), 3- hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxy-valeric acid, 5-hydroxyvaleric acid, 6-hydroxycaproicacid, 2-hydroxyaceticacid (glycolicacid), 2-hydroxy-propionic acid (lactic acid), 2 hydroxybutyric acid, 2-hydroxyvaleric acid, 2-hydroxycaproic acid, 2-hydroxy-heptanoic acid, 2-hydroxyoctanoic acid, 2-hydroxy-pelargonic acid, 2-hydroxyphenylaceticacid, 1-hydroxy-cyclohexane 1-carboxylicacid, oxalic acid plus ethylene glycol, oxalic acid plus propylene glycol, malonic acid plus ethylene glycol, and malonic acid plus propylene glycol.

In general, the lactones useful in the present invention have from 3 to 6 carbon atoms and 1 or 2 oxygen atoms in the ring. The lactones produced from the hydroxy acids will have structures corresponding to the following formulae:

(4) (5) (6)

(7)

wherein any R can be hydrogen, C^C^ alkyl, or an aryl group selected from benzene, napthalene, benzene substituted with C_t-C₄ alkyl and napthalene substituted with C_rC₄ alkyl. For formulation 1, R_t and R₂ are H when 3-hydroxypropionic acid is used to produce propiolactone; R_t is H and R₂ is methyl when 3-hydroxybutyric acid is used to produce butyrolactone; R_j is methyl and R₂ is methyl when 3- hydroxyisobutyric acid is used to produce 2,3-dimethyl propiolactone; R_j is phenyl and R₂ is H when 3-hydroxy 3-phenyl is used to produce 3-phenyl propio-lactone and R_j is H and R₂ is phenyl when 3-hydroxy, 2-phenyl is used to produce 2-phenyl propiolactone.

For formulation 2, R_t, R₂ and R₃ are H when 4-hydroxybutyric acid is used to produce valerolactone and R_! is methyl, R₂ is H and R₃ is H when 4- hydroxyvaleric acid is used to produce 4-methyl valerolactone.

For formulation 3, R_j through R₅ are H when 6-hydroxycaproic acid is used to produce e-caprolactone and R_x is methyl, R₂-R₅ are H, when 6- hydroxyheptylic acid is used to produce 6-methyl-caprolactone.

For formulation 4, are H when glycolic acid is used to produce glycolide; R_} and R₃ are methyl, R₂ and R₄ are H when lactic acid is used to produce lactide; Rj and R₃ are phenyl, R₂ and R₄ are H when phenyl-2 hydroacetic acid is used to produce 2,5-diphenyl-dioxane-3,6-dione and R_j and R₃ are hexyl, R₂ and R₄ are H, when 2-hydroxyoctanoic acid is used to produce 2,5-dihexyldioxane-3,6-dione.

For formulation 5, R_j and R₂ are H, when oxalic acid and ethylene glycol are used to produce l,4-dioxane-2,3-dione and R_} is methyl, R₂ is H, when oxalic acid and propylene glycol are used to produce 5-methyl-l,4-dioxane-2,3-dione.

For formulation 6, RrR are H when malonic ester and ethylene glycol are used to produce l,4-dioxepine-5-7,dione; R is methyl, R_-R₄ are H when malonic ester and propylene glycol are used to produce 2-methyl-l,4-dioxepineand R R₃ are H, R₄ is methyl when methyl malonic ester and ethylene glycol are used to produce

6-methyl- 1 ,4-dioxepine.

For formulation 7, R_!-R₄ are H when 5-hydroxyvaleric acid is used to produce delta-valerolactone and Rj is methyl, R₂-R are H, when 5-hydroxycaproic acid is used to produce 5-methyl-valerolactone. Oligomers of certain of the hydroxy acids that can be used to make the lactones can also be used as a degradation promoter, either by itself or in combination with a lactone. Oligomers of lactic acid having from 2 to 50 lactic acid moieties are particularly suitable. A preferred degradation promoter is a mixture of lactone from lactic acid or hydroxycaproic acid and oligomers of lactic acid or hydroxycaproic acid having from about 10% to about 95% of the lactone. Plasticizers useful in the polymer compositions of the present invention are conventional plasticizers used in the preparation of thermoplastic cellulose ester compositions. Suitable plasticizers include diethyl phthalate, dimethyl phthalate, ethoxyethylphthalate, methoxyethyl phthalate, dibutyl tartrate, diethylene glycol-butyl ether, diethylene glycol mono-ethyl ether, tripropionin, benzoyl benzoate, triphenyl phosphate, triacetin, diamyl phthalate and ortho-cresyl para-toluene sulfonate.

Many of the plasticizers commonly known for use in the formation of thermoplastic cellulose ester compositions are highly hydrophobic and provide extreme resistance to moisture in the finished polymer product. Some of the plasticizers, however, are relatively hydrophilic. The degradation promoters of the present invention are hydrophilic. Consequently, in one embodiment of the invention, it is desirable to provide a hydrophilic lipophilic balance (HLB) of hydrophobic plasticizers and degradation promoters of the present invention which is within the range of from about 10 to about 40.

In general, the cellulose ester is present in the compositions of the present invention at a level of from about 20 to about 80% by weight. All percentages used herein are by weight unless otherwise indicated. The cellulose esters useful in the present invention may be selected from cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-butyrate and cellulose acetate-propionate. The cellulose esters have a molecular weight of at least about 5,000 and preferably have a molecular weight of from between about 5,000 and about 500,000. The cellulose acetate-butyrate preferably has from about 90 to about 99% acetate and from about 10 to about 1 % of butyrate. The cellulose acetate-propionate preferably has an acetate level of from about 80 to about 99% and a propionate level of from about 20 to about 1%. The plasticizer is present in the polymeric compositions of the invention at a level of from 0% to about 50% by weight of the composition. The hydrophilic degradation promoter is preferably present in the polymeric compositions at a level of from about 1 to about 60% by weight of the composition. The sum of the total level of use of the plasticizer and the hydrophilic degradation promoter is from about 20% to about 80% by weight of the composition. Some of the degradation promoters useful in the present invention also act as plasticizers and can be used without the addition of other conventional hydrophobic plasticizers. Degradation promoters which can be used without a plasticizer include oligomers of lactic acid and lactones made from lactic acid and citric acid. While not wishing to be bound by any theory, it is believed that degradation of the degradable cellulose ester formulations of the inventions result from leaching of the relatively hydrophilic degradation promoter from the composition by water leaving behind a somewhat more open or porous molecular lattice exposed to the water. The cellulose ester is present in an amorphous state when extensively plasticized during melt-fabrication.

Once the porous cellulose ester is in intimate contact with water after leaching of the degradation promoter, there is a higher concentration of water present than with conventional hydrophobic plasticized cellulose esters and the mass action of the water promotes hydrolysis. An acidic degradation promoter provides a source of acid that catalyzes the hydrolysis. Enzymatic degradation is also possible as a result of the exposed, moistened cellulose ester lattice structure. The hydrolysis is accelerated by the formation of an acidic medium arising from certain of the degradation promoters and their hydrolysis and from hydrolysis of the cellulose ester to form an organic acid. The use of plasticized, degradable cellulose esters can expand the market for cellulose esters by significant quantities. The degradable cellulose esters of the present invention provides a plasticized system that is low cost and provides the biodegradability to serve a growing market, particularly in sheet materials, which are used for common products, such as garbage bags. The following examples further illustrate various features of the invention but are intended to in no way limit the scope of the invention which is defined in the appended claims.

EXAMPLES Example 1

In Table 1 are shown prior art cellulose acetate-plasticizer mixtures containing conventional plasticizers and examples of the present invention containing a leachable plasticizer. Sample Nos. 2-2, 2-3, 2-4, 3-3 and -8 can be considered state of the art thermoplastic cellulose acetate controls, with nonleachable hydrophobic plasticizers. By nonleachable it is meant that the compositions prohibits easy access to moisture and is, therefore, essentially nondegradable. Each of the degradation promoters used in the compositions of the invention has a significant solubility in water and/or they hydrolyze readily to water soluble acid components. After hydrolysis, the acid promotes degradation. The addition of an inorganic acid or organic acid to conventional cellulose compositions does not provide similar results. Sample 2-5, containing 1% fumaric acid, and sample 2-6, containing 24% lactic acid, did not show any appreciable degree of weathering after 6 months exposure to seawater. Sample 2-7, containing 1% phosphoric acid, produced a composition that was too brittle to test. When the inorganic acids are buried in a conventional hydrophobic plasticizer matrix, they are effectively shut off from moisture and serving their purpose of promoting hydrolysis. Organic acids combined with the leachable degradation promoters of the invention can accelerate hydrolysis.

The leachable degradation promoters work well in promoting hydrolysis, particularly if they form acids, in situ. Compare the results of -8 and -9 of Table 1, for example. The -8 sample with the conventional plasticizer, diethyl phthalate, displayed no degradation for more than one year. Weathering and degradation tests were performed in Florida seawater, Florida beach air and outdoor panels in Ohio. The -9 sample containing cellulose acetate with diethyl phthalate as the plasticizer, and lactide as the leachable component, weathered promptly. In 21 days it changed from a very flexible, colorless, transparent film into a very brittle, white, opaque material.

The other examples of the invention, -32, -36-3, -37, -42-2, -42-5, and

43-1 were similarly leachable and weatherable. All of these compositions are intimate mixtures, that is, the degradation promoters are efficient, since they produced transparent films that were easily melt processed without degradation into smooth, glossy, thin films.

Tensile strength testing was performed according to ASTM D638. The moduli, or measures of stiffness, varied with the amount of plasticizer and/or degradation promoter. In general, the total amount of plasticizer needs to be greater than 40 weight percent to obtain films that mimic the foldability and extensibility of polyolefins. Samples -37 and -42-5 were thermoformed into a stiff, transparent, colorless salad cover shape. Sample -42-2 was formed into a trash bag shape.

Oligomeric lactic acid and polyethyl lactate are commercially attractive degradation promoters which also function as plasticizers. They are easily prepared by the condensation of lactic acid and ethyl lactate, a simple process that uses economical precursors. Both of these materials intimately melt-disperse with cellulose acetate and provide well behaved thermoplastics.

The cellulose acetate used was a commercial grade that had a weight- average molecular weight of 85,000, as judged by GPC. Higher molecular weights would have provided better strength and higher percent elongations under stress.

TABLE 1 - SUMMARY OF DEGRADABLE PROPERTIES OF CELLULOSE CETATE

a CA-398-3, Eastman Kodak cellulose diacetate b Commercially formulated, Eastman Kodak 036A, molded grade with DEP c C-3782, no DEP d Beach air, Daytona, FL, summer e Seawater, Daytona, FL, summer, pH 7.2 to 7.4, 27 to 29° C, 3.6% salimty f Seawater, Daytona, FL, winter, pH 7.3 to 8.1, 15 to 21° C, 3.5% salinity g Test began Outside, OH, winter -9 to 7° C. h Test began Outside, OH, summer, 21 to 35° C. i Shelf-life, 70 C/50% r.h. is one year j Estimated

KEY: DEP=diethyl phthalate; FA=fumaric acid; LA= lactic acid; PA=phosphoric acid; LD=lactide; OLA=oligomeric polylactic acid having 5 lactic acid moieties; PC=propylene carbonate; EtI_-,A=ethyl lactoyllactate

Example 2

The following example illustrates the use of a 7-membered ring lactone as a plasticizer. The cellulose acetate chosen was a polymer (Eastman Chemicals

Company, "SAMS-E") with an average degree of substitution of 2.5, a weight-average GPC molecular weight of 149,000, and a number-average, GPC molecular weight of

47,000. It contained no plasticizer as supplied and would char before melting.

The cellulose acetate, 55 parts by weight, was mixed with 45 parts of e- caprolactone, a pure liquid, which was immediately soaked up by the polymer with simple hand stirring. The mixture was placed on an open, two-roll mill preheated to 350° F. The counter-rotating mill was set at a tight nip at approximately 10 rpm. Within 5 minutes the mixture clears as evidence of complete mixing. The mix was sheeted out off the mill. The mix fused very easily with no dripping, but some fuming of the caprolactone.

The above melt-blend formulation was compression molded at 300° F to provide approximately 8 to 10 mil, thick films. These were completely colorless and transparent, thus providing evidence of plasticization. The films were pliable, tear- resistant, and easily elongateable at about 37° C with heat supplied by holding in the hand.

The films were evaluated on an Instron tester for tensile properties by ASTM 882, and the results are shown in Table 2. The caprolactone content was estimated as 22.7 percent by isothermal weight loss at 200° C by TGA. The tensile strength, modulus, and elongation-to-break values which are reported in Table 2 resemble those found to be useful for packaging applications, similar to some grades of high-density polyethylene and polypropylene.

Example 3

This example illustrates the use of a 5-membered ring lactone. The procedure of Example 2 was repeated using 4-valerolactone in place of the caprolactone and using the same cellulose acetate. Thus, for example, 55 parts of cellulose acetate was mixed by hand with 45 parts of 4-valeroIactone, mill-rolled 5 minutes at 350° F, and compression molded into 8 to 10 mil films, which were completely transparent and devoid of color. The film was tough, strong, elongateable, and tear resistant. The percent lactone content was 17.0 percent by TGA. Tensile data are shown in Table 2. The properties are approximately those found for crystalline polypropylene used in molding and packaging applications.

Example 4

The same cellulose acetate (powder) as used in Example 2, 55 parts by weight, was intimately stirred with 45 parts of granular, pure, glycolide, a 6- membered ring, cyclic dilactone. The mixture easily fused on the mill roll at 350° F and compression molded to clear, colorless films. The films turned hazy at the surface upon handling, which indicated a trace amount of the glycolide had bloomed to the surface. The percent glycolide by TGA was 22.3 percent. Tensile properties are shown in Table 2 and are approximately similar to those encountered with low- density polyethylene.

TABLE 2. TENSILEPROPERTIES*"* OF LACTONE-PLASTICIZED CELLULOSE ACETATE

Elastic Example Modulus, Tensile Strength, psi Elongation, percent

Plasticizer Number psi Yield Break Yield Break

e-Caprolactone 19

4-Valerolactone 29

Glycolide 45

(a) Average of 5 duplicates of 8 to 10 mil, compression molded film, ASTM 882, using strain rate of 1 inch/inch/minute. Standard deviations shown in parentheses.

Claims

CLAIMSWe claim:

1. A degradable thermoplastic cellulose ester composition comprising a cellulose ester polymer and a hydrophilic degradation promoter, said degradation promoter, after formation of said composition into a thermoplastic material with acceptable product use life in relatively low moisture indoor environmental conditions, will slowly dissolve from said thermoplastic material under relatively high moisture outdoor environmental conditions to provide a cellulose ester substrate that is degradable.

2. A composition in accordance with Claim 1 which further includes a plasticizer.

3. A composition in accordance with Claim 1 wherein said cellulose ester has a degree of ester substitution from about 2.0 to 2.6.

4. A composition in accordance with Claim 1 wherein said cellulose ester is selected from cellulose acetate, cellulose butyrate, cellulose propionate, cellulose acetate-butyrate and cellulose acetate-propionate.

5. A composition in accordance with Claim 1 wherein said degradation promoter is selected from the group consisting of lactones prepared from hydroxy acids, lactones prepared from dicarboxylic acids and polyhydric alcohols and oligomers of said hydroxy acids.

6. A composition in accordance with Claim 5 wherein said lactone has from 3 to 6 carbon atoms and 1 or 2 oxygen atoms in the ring.

7. A composition in accordance with Claim 5 wherein said lactone is prepared from hydroxy acids selected from the group consisting of 3- hydroxypropionic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4- hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, 2-hydroxyacetic acid (glycolic acid), 2-hydroxy-propionic acid (lactic acid), 2 hydroxybutyric acid, 2- hydroxyvaleric acid, 2-hydroxycaproic acid, 2-hydroxy-heptanoic acid, 2- hydroxyoctanoic acid, 2-hydroxy-pelargonic acid, 2-hydroxyphenylacetic acid, 1- hydroxy-cyclohexane 1-carboxylic acid, oxalic acid plus ethylene glycol, oxalic acid plus propylene glycol, malonic acid plus ethylene glycol, and malonic acid plus propylene glycol.

8. A composition in accordance with Claim 5 wherein said oligomer has from 2 to 50 acid moieties.

9. A composition in accordance with Claim 5 wherein said degradation promoter is a lactone prepared from lactic acid.

10. A composition in accordance with Claim 5 wherein said degradation promoter is a mixture of a lactone from lactic acid and oligomers of lactic acid, said mixture having from about 10% to about 95% of said lactone.

11. A composition in accordance with Claim 5 wherein said degradation promoter is caprolactone.

12. A composition in accordance with Claim 5 wherein said degradation promoter is a mixture of a lactone made from hydroxycaproic acid and an oligomer of hydroxycaproic acid, said mixture having from about 10% to about 95% of said lactone.

13. A composition in accordance with Claim 5 wherein said degradation promoter is a mixture having from about 10% to about 95% of a lactone prepared from lactic acid and from about 5% to about 95% of an oligomer of lactic acid having from 2 to 50 lactic acid moieties.

14. A composition in accordance with Claim 1 wherein said degradation promoter is a cyclic ester having a structure corresponding to any of the following formulae:

0) (2) (3)

(7)

wherein any R can be hydrogen, C C^ alkyl, or an aryl group selected from benzene, napthalene, benzene substituted with C_rC₄ alkyl and napthalene substituted with C,-C₄ alkyl.

15. A composition in accordance with Claim 2 wherein said plasticizer is selected from the group consisting of diethyl phthalate, dimethyl phthalate, ethoxyethyl phthalate, methoxyethyl phthalate, dibutyl tartrate, diethylene glycol-butyl ether, diethylene glycol mono-ethyl ether, tripropionin, benzoyl benzoate, triphenyl phosphate, triacetin, diamyl phthalate and ortho-cresyl para-toluene sulfonate.

16. A composition in accordance with Claim 2 having an HLB of from about 10 to about 50.

17. A composition in accordance with Claim 1 wherein said cellulose ester is present at a level of from about 20% to about 80%.

18. A composition in accordance with Claim 2 wherein said plasticizer is present at a level of from about 1 % to about 50% , and said degradation promoter is present at a level of from about 1% to about 60%.

19. A composition in accordance with Claim.15 wherein the total level of the sum of the plasticizer level and the degradation promoter level is from about 20% to about 80%.

20. A composition in accordance with Claim 1 wherein said cellulose ester has a molecular weight of from about 5,000 to about 500,000.

21. A composition in accordance with Claim 1 wherein said cellulose ester is cellulose acetate.

22. A composition in accordance with Claim 1 wherein said cellulose ester is cellulose butyrate.

23. A method for improving the degradation rate of cellulose ester polymers upon exposure to moisture comprising providing a cellulose ester polymer and dispersing in said polymer an effective amount of a degradation promoter that permits the mixture to be a well behaved melt-formable thermoplastic material, permitting the degradation promoter to be slowly leachable or hydrolyzable under relatively high moisture outdoor environmental conditions to effect a slow hydrolysis and degradation of the cellulose ester polymer.

24. A method in accordance with Claim 23 wherein a plasticizer is also dispersed in said cellulose ester polymer.

25. A method in accordance with Claim 23 wherein said cellulose ester has a degree of ester substitution from about 2.0 to 2.6.

26. A method in accordance with Claim 23 wherein said cellulose ester is selected from cellulose acetate, cellulose butyrate, cellulose propionate, cellulose acetate-butyrate and cellulose acetate-propionate.

27. A method in accordance with Claim 23 wherein said degradation promoter is selected from the group consisting of lactones prepared from hydroxy acids, lactones prepared from dicarboxylic acids and polyhydric alcohols and oligomers of said hydroxy acids.

28. A method in accordance with Claim 27 wherein said lactone has from 3 to 6 carbon atoms and 1 or 2 oxygen atoms in the ring.

29. A method in accordance with Claim 27 wherein said lactone is prepared from hydroxy acids selected from the group consisting of 3-hydroxypropionic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5- hydroxyvaleric acid, 6-hydroxycaproic acid, 2-hydroxyacetic acid (glycolic acid), 2- hydroxy-propionic acid (lactic acid), 2 hydroxybutyric acid, 2-hydroxyvaleric acid, 2- hydroxycaproic acid, 2-hydroxy-heptanoic acid, 2-hydroxyoctanoic acid, 2-hydroxy- pelargonic acid, 2-hydroxyphenylaceticacid, 1 -hydroxy-cyclohexane 1-carboxylic acid, oxalic acid plus ethylene glycol, oxalic acid plus propylene glycol, malonic acid plus ethylene glycol, and malonic acid plus propylene glycol.

30. A method in accordance with Claim 27 wherein said oligomer has from 2 to 50 acid moieties.

31. A method in accordance with Claim 27 wherein said degradation promoter is a lactone prepared from lactic acid.

32. A method in accordance with Claim 27 wherein said degradation promoter is a mixture of a lactone from lactic acid and oligomers of lactic acid, said mixture having from about 10% to about 95% of said lactone.

33. A method in accordance with Claim 27 wherein said degradation promoter is caprolactone.

34. A method in accordance with Claim 27 wherein said degradation promoter is a mixture of a lactone made from hydroxycaproic acid and an oligomer of hydroxycaproic acid, said mixture having from about 10% to about 95% of said lactone.

35. A method in accordance with Claim 27 wherein said degradation promoter is a mixture having from about 10% to about 95% of a lactone prepared from lactic acid and from about 5 % to about 95 % of an oligomer of lactic acid having from 2 to 50 lactic acid moieties.

36. A method in accordance with Claim 27 wherein said degradation promoter is a cyclic ester having a structure corresponding to any of the following formulae:

(i ) (2) (3)

(4) (5) (6)

(7)

wherein any R can be hydrogen, Cι~C₁₀ alkyl, or an aryl group selected from benzene, napthalene, benzene substituted with C_t-C₄ alkyl and napthalene substituted with C_rC₄ alkyl.

37. A method in accordance with Claim 24 wherein said plasticizer is selected from the group consisting of diethyl phthalate, dimethyl phthalate, ethoxyethyl phthalate, methoxyethyl phthalate, dibutyl tartrate, diethylene glycol-butyl ether, diethylene glycol mono-ethyl ether, tripropionin, benzoyl benzoate, triphenyl phosphate, triacetin, diamyl phthalate and ortho-cresyl para-toluene sulfonate.

38. A method in accordance with Claim 24 having an HLB of from about 10 to about 40.

39. A method in accordance with Claim 23 wherein said cellulose ester is present at a level of from about 20% to about 80%.

40. A method in accordance with Claim 24 wherein said plasticizer is present at a level of from about 1% to about 50%, and said degradation promoter is present at a level of from about 1 % to about 60%.

41. A method in accordance with Claim 24 wherein the total level of the sum of the plasticizer level and the degradation promoter level is from about 20% to about 80%.

42. A method in accordance with Claim 23 wherein said cellulose ester has a molecular weight of from about 5,000 to about 500,000.

43. A method in accordance with Claim 23 wherein said cellulose ester is cellulose acetate.

44. A method in accordance with Claim 23 wherein said cellulose ester is cellulose butyrate.