BIODEGRADATION OF BIODEGRADABLE POLYMERIC

MATERIALS AND OF ARTICLES FABRICATED THEREFROM

BACKGROUND OF THE INVENTION

⁵ 1. Field of the Invention

This invention relates to a method for enhancing the rate of biodegradation of biodegradable polymeric compositions and of articles fabricated therefrom. More par icularly, this invention relates to such a method in ° which biodegradable polymeric compositions exhibit improved biodegradability when exposed to environmental effects such as sunlight, heat, water, oxygen, pollutants, microorganisms, insects, animals and mechanical forces such as wind and rain.

2. Prior Art

Many discardable packaging items such as bags and containers are destined, after a relatively short functional life to arrive as a significant component of urban garbage. Because of the increased use of plastics in the fabrication of these discardable packing materials, it has been proposed to make throwaway materials from biodegradable plastics to ameliorate waste disposal problems. However, the low cost high volume packaging materials such as polyethylene, polypropylene, polystyrene and poly(ethylene terephthalate) are not naturally biodegradable. Several methods have been proposed to enhance the biodegradability of such polymeric materials and/or to develop other useful biodegradable polymeric materials. For example, U.S. Patent No. 4,016,111 discloses that compositions of ethylene acrylic acid copolymer and a starchy material are biodegradable. U.S. Patent No. 4,337,181 describes a biodegradable composition containing up to about 60% gelatinized starch and various levels of ethylene acrylic acid copolymer and optionally

polyethylene. U.S. Patent No. 4,016,117 describes a biodegradable composition which comprises a synthetic resin, a biodegradable granular filler such as natural starch, and a substance which is autooxidizable to yield a peroxide which attacks the carbon to carbon linkages of the resin. PCT Appln. WO 88/09354 describes a degradable polymer composition which is a blend of a normally stable chemically saturated polymer such as polyethylene, a less stable chemically unsaturated polymer or copolymer such as a styrene/butadiene block copolymer, or natural rubber, an anti-oxidant active over a limited period and a latent prooxidant such as an organic salt of a transition metal, e.g. cobalt naphthenate, which may optionally include filler particles of a directly biologically sensitive material such as lignin, a natural starch, a derivative of natural starch, a natural protein, a natural cellulose or a sugar.

The biodegradation of plastics and/or the additives which are incorporated into plastics can be viewed as taking place in two steps or phases. The initial phase results in a deteriorated plastic article by virtue of the removal or degradation of one on the components of the plastic or through the action of other environmental stresses, such as oxidation or ultraviolet light. The resulting material can then be biodegraded only if the deterioration was sufficient to have caused a decrease in molecular weight to the point where microorganisms are capable of transporting the fragments and metabolizing them. The second phase or series of events results in the actual biodegradation, or decomposition of the material. In most of the common attempts to produce biodegradable plastic materials it is the first phase of deteriorization which results in the degradability of the article. For example, in the case of corn starch as an additive to polyethylene the starch is hydrolyzed by extracellular enzymes to produce lower molecular weight oligosacchrides and glucose. Loss of the starch component weakens the article. Likewise, with the addition of prooxidants to

polyethylene the prooxidant reacts with metal salts and oxygen to cause breaks in the polyethylene chain. In either case these primary degradation events cause the deterioration of the material and loss of its desirable physical properties. Whether the products of these deteriora ion events can be metabolized thereby lenging to the complete biodegradation or decomposition of the article is often uncertain.

It is thus the objective of most degradation measurements to determine the rate and extent of the primary degradation. To determine the decomposition of the article is almost inevitably a much slower process and few technologies are available which can reasonably be expected to cause demonstrable decomposition of the polymer chain, in a reasonable period of time. It is the purpose of this study to contribute to the understanding of this initial mechanism of deterioration, specifically the role of microbial enzymes in the hydrolysis of biodegradable additives, and to make possible more efficient and standardized methods for determining "biodegradability" .

SUMMARY OF THE INVENTION

The present invention is directed to a method for enhancing the rate of biodegradation of a biodegradable polymer composition. More par icularly, this invention is directed to a method of enhancing the biodegrada ion of a composition comprising one or more polymeric materials and one or more biodegradable materials, which comprises: contacting said composition with an effective amount of one or more effective surfactants and an effective amount of one or more effective enzymes for a time and at a temperature sufficient to enhance the biodegradation of said composition to any extent.

Yet another aspect of this invention relates to a preferred embodiment of the method of this invention in which the process is used in the assaying of the

biodegradability of a composition comprising one or more biodegradable materials and one or more polymeric materials. This preferred method comprises:

(a) contacting the composition with a solution comprising an effective amount of one or more effective surfactants and an effective amount of one or more effective enzymes for a time and at a temperature sufficient to allow the biodegradation of said composition to any extent; and

(b) measuring the extent of biodegradation of said composition.

Several beneficial effects are provided by the method of this invention. For example, an obvious advantage of the method of this invention is that it allows biodegrada ion of biodegradable materials in shorter periods of time. Other advantages are provided by the preferred assay method of this invention. For example, the assay can be carried out in relatively shorter periods of time as compared to conventional assay systems. Moreover, more complete biodegradation occurs during conduct of the assay which is more representative of actual use conditions of the biodegradable compositions. The assay allows identification of the actual products of biodegradation for evaluation for toxicity, environmental effects and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the invention and the accompanying drawings in which:

Figure 1 is a graph of % starch conversion to glucose as a function of time for various compositions containing starch.

Figure 2, 3, 4 and 5 are graphs indicating the effect of various surfactants on the amount of starch degraded.

Figure 6 is a graph of % cellulosic conversion by weight as a function of time.

Figures 7 and 8 are graphs depicting the effect of surfactants on cellulose degradation.

Figure 9 is a graph depicting the effect of surfactant pretreatment on the degradation of starch/high density polyethylene film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the method of this invention, a biodegradable composition is contacted with an effective amount of an effective surfactant and an effective amount of one or more effective enzymes to enhance the rate of biodegradation of the composition. As used herein" biodegrada ion" means the degradation of a material when exposed to environment effects such as sunlight, heat, water, oxygen, pollutants, microorganisms, insects, fungi, animals and the like. The method and order of contacting the composition, surfactant(s) and enzyme(s) is not critical and may vary widely. For example, the surfactant(s) and enzyme(s) can be sprayed on the composition either individually in any order, or in combination neat or in solution form. The enzyme can be contacted with the composition directly, or can be contacted indirectly by first contacting the composition with microorganism(s) which produce the enzyme(s) in situ. For example, disposed items in a landfill or a compost bed can be treated with a solution of one or more effective surfactants by spraying or the like. Suitable effective enzymes can be conveniently produced iτ\ situ by microorganisms present in the landfill or compost bed.

In the preferred embodiments of the invention where the method is used to assay the biodegradability of a composition, a solution of an effective amount of one or more effective surfactants and an effective amount of one or more effective enzymes is contacted with the composition for a time and at a temperature sufficient to

enhance the rate of biodegradation of the composition to any extent. The solution and composition can be contacted statically or under agitation. In the preferred embodiments of the invention, agitation is used which increases the rate at which biodegradation is enhanced. The solution and composition may be contacted in a system open to the environment or in a closed or sealed system. In the preferred embodiments of the invention, a sealed system is employed which enhances the effectiveness of the assay. For example, in an enclosed system evaporation of the solvent and contamination would be prevented or significantly retarded.

Contact times are not critical and may vary widely and will depend on a number of factors such as the activity of the enzyme(s) and the duration of such activity under use conditions, the activity of the surfactant, contact temperature, and the like. In general, the longer the contact time, the greater the extent to which biodegradation is enhanced and conversely, the shorter the contact time the lesser the extent to which biodegrada ion is enhanced. In those embodiments of the invention where the method is used to enhance the biodegrada ion of the composition in an open environment as for example in a compost bed, landfill or the like, contact times are as long as possible. In these embodiments of the invention, surfactant(s) , enzyme(s) and composition(s) are preferably contacted for as long as the combination of surfactant(s) and enzyme(s) maintains its activity. Such contact times can vary from hours to days to months to years depending on the duration of activity.

In the preferred embodiments of the invention where the method is used as an assay for determining the biodegradability of a composition, contact times are generally shorter. In these embodiments of the invention, the composition, surfactant(s) and enzyme(s) are generally contacted for a time sufficient to at least allow production of a measurable quantity of biodegradation products. In these preferred embodiments of the

invention, contact times are usually at least about 1 minute. Preferred contact times are from about 1 minute to about 60 days, and more preferred contact times are from about 1 hr. to about 800 hrs.

Contact temperatures may vary widely. The requirement is that contact temperatures are in a range such that the activity of the enzyme is not unduly inhibited and are below the boiling point of the solvent. Usually enzymes have optimum activity at certain temperatures and contact temperatures are preferably maintained within this optimum temperature range. This can usually be done in the preferred embodiments of the invention where the method of the invention is used to assay biodegradative activity. However, where the method is used in the open environment constant temperature often can not be maintained. In these instances, the method is practiced such that the contact temperatures are within an operable range as often or as long as possible. Usually contact temperatures are from abut 0 C to about 100°C. Preferred contact temperatures are from about 10 C to about 65°C and most preferred contact times are from about 20°C to about 45°C.

Useful compositions comprise two essential ingredients. One essential ingredient is a polymeric resin. The type of polymeric resin used may vary widely. Illustrative of useful resins are aromatic, aliphatic and cycloaliphatic polya ides such as poly(m-xylylene adipa ide), poly(p-xylylene sebacamide), poly 2,2,2-trimethyl-hexamethylene terephthalamide) , poly (piperazine sebacamide), poly (metaphenylene isophthalamide) (Nomex), poly (p-phenylene terephthalamide) (Kevlar), the copolyamide of 30% hexamethylene diammonium isophthalate and 70% hexamethylene diammonium adipate, the copolyamide of up to 30% bis-(-amidocyclo-hexyl)methylene, terephthalic acid and caprolactam, polyhexamethylene adipamide (nylon 66), poly(butyrolactam) (nylon 4), poly (9-aminonoanoic acid) (nylon 9), poly(enantholactam) (nylon 7),

poly(capryllactam) (nylon 8), polycaprolactam (nylon 6), poly (p-phenylene terephthalamide), polyhexa ethylene sebacamide (nylon 6,10), polyaminoundecanamide (nylon 11), polydodecono-lactam (nylon 12), polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, polycaproa ide, poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(decamethylene sebacamide) (nylon 10,10), poly[bis-(4-aminocyclothexyl) methane 1,10- decanedicarboxamide] (Qiana) (trans), or combination thereof; and aliphatic, cycloaliphatic and aromatic polyesters such as poly(1,4-cyclohexlidene dimethyl eneterephathalate) cis and trans, poly(ethylene-l, 5-naphthalate) , poly(ethylene-2,6-naphthalate) , poly(l, 4-cyclohexane dimethylene terephthalate) (trans), poly(decamethylene terephthalate), poly(ethylene terephthalate), poly(ethylene isophthalate), poly(ethylene oxybenozoate) , poly(para-hydroxy benzoate) , poly(di ethylpropiolactone), poly(decamethylene adipate), poly(ethylene succinate) , poly(ethylene azelate), poly(decamethylene sebacate), poly( 8, β-dimethyl- propiolactone) , and the like.

Also illustrative of useful polymeric resins are polymers copolymers formed by polymerization of α, β -unsaturated monomers of the formula:

R.•» R^—C ⁼ Cri^

wherein:

R. and R_ are the same or different and are hydrogen,hydroxy, halogen, alkylcarbonyl, carboxy, alkoxycarbonyl, heterocycle or alkyl or aryl either unsubstituted or substituted with one or more substituents selected from the group consisting of alkoxy, cyano, hydroxy, alkyl and aryl. Illustrative of such polymers of L,B-unsaturated monomers are polymers including polystyrene, polyethylene, plypropylene, poly(1-octadence) , polyisobutylene, poly(1-pentene) , poly(2-methylstyrene) ,

poly(4-methylstyrene) , poly( 1-hexene) , poly( 1-pentene) , poly(4-methoxys rene) , poly(5-methy1-1-hexene) , poly(4-methylpentene) , poly (1-butene), polyvinyl chloride, polybutylene, polyacrylonitrile, poly(methyl pentene-1), poly(vinyl alcohol), poly(vinylacetate) , poly(vinyl butyral), poly(vinyl chloride), poly(vinylidene chloride), vinyl chloride-vinyl acetate chloride copolymer, poly(vinylidene fluoride), poly(methyl acrylate, poly(methyl methacrylate) , poly(methacrylo-nitrile) , poly(acrylamide) , poly( inyl fluoride), poly(vinyl formal), poly(3-methyl-

1-butene), poly( 1-pentene) , poly(4-methyl-l-butene) , poly( 1-pentene) , poly(4-methyl-l-pentence, poly( 1-hexane) , poly(5-methyl-l-hexene) , poly(1-octadence), poly(vinyl- cyclopentane) , poly(vinylcyclothexane) , poly(a-vinyl- naphthalene) , poly(vinyl methyl ether), poly(vinyl- ethylether), poly(vinyl propylether) , poly(vinyl carbazole), poly(vinyl pyrolidone), poly(2-chlorostyrene) , poly(4-chlorostyrene) , poly(vinyl formate), poly(vinyl butyl ether), poly(vinyl octyl ether), poly(vinyl methyl ketone), poly(methylisopropenyl ketone), poly(4-phenylstyrene) and the like.

Preferred resins for use in the composition of this invention are resins which are commonly used in the fabrication of packaging materials such as polyethylene, polyethylene terephthalate, polystyrene, polyurethane, polyvinyl chloride, polypropylene, polycarbonate and blends of such materials. The above list of preferred is merely intended to be representative of useful and preferred resins, and other resins which are used as packaging materials may also be used. In the most referred embodiments of this invention, the resins of choice are polyethylene (high density, low density and linear low density), polyethylene terephthalate, polyvinyl chloride, polyurethane and blends of such polymers.

The second essential ingredient of the composition is one or more biodegradable materials. Suitable biodegradable materials may vary widely. Any material

which is biodegradable or degradable can be used. As used herein, a material is "degradable" where it degrades as a result of exposure to the environmental effects of sunlight, heat, water, oxygen, pollutants, microorganisms, insects and/or animals. Usually such materials are naturally occurring and are usually "biodegradable". As used herein, "biodegradable" materials are those which are degraded by microorganisms or by enzymes and the like produced by such microorganisms. Illustrative of suitable biodegradable materials are starches and starch derivatives such as rice and maize starch, dextrin, cyclodextrin, amylose, amylopectin, defatted or solvent extracted starch, and the like. Other useful safening materials include sugars and derivatives thereof, such as sucrose, dextrose, maltose, mannose, galactose, lactose, fructose, glucose, glyamic acid, gluconic acid, maltobionic acid, lactobionic acid, lactosazone, glucosazone, and the like. Still other useful safening materials are cellulose and derivatives thereof such as esters of cellulose as for example, triacetate cellulose, acetate cellulose, acetate-butyrate cellulose, nitrate cellulose and sulfate cellulose, ethers of cellulose as for example, ethyl ether cellulose, hydroxymethyl ether cellulose, hydroxypropyl ether cellulose, carboxymethyl ether cellulose, ethylhydroxy ether cellulose, and cyanoethylether ether cellulose, ether-esters of cellulose as for example, acetoxyethyl ether cellulose, propionoxypropyl cellulose, and benzoyloxypropyl cellulose and urethane cellulose as for example, phenyl urethane cellulose. Other useful safening agents include proteins such as zein, soy protein or protein hydrolysates, casein, collagen, elastin, albumins and the like and lignins. Useful biodegradable safening materials also include fats and fatty acids such as mono-, di- and tri-glycerides derived from animal or plant material and the common derivatives of these fats such as fats obtained from peanut oil, corn oil, coconut oil, cottonseed oil, palm oil and tallow, and fatty acids such as oleic acid.

stearic acid, lauric acid, myristic acid and palmitic acid; biodegradable anti-oxidants such as tocophenols, rosemary (rosemari-quinone) and mustard seed extracts, ascorbic acid and compounds closely related to vitamin C such as ascorbic acid-2-phosphates and ascorbic acid-6-fatty acid esters propionic acid; and biodegradable polymers such as poly(glycolide) , poly(tetramethylene carbonate), poly( lactide) , poly(glycolide-co-lactide) , poly(caprolactone) , poly(tartaric acid), poly(ethylene-co-ketone acetal) , poly(hexamethylene azelate), poly(decamethylene succinate), poly(decamethylene azelate), poly(ethylene succinate), poly(hexamethylene sebacate), poly(ethylene azelate), poly(3-methoxy-4-hydroxy styrene), poly(amino triazole), poly(hydroxy butyrate), poly(hydroxyvalerate) , poly(hydroxy butiyrate-co-hydroxy valerate), poly(dihydropyran) , poly(spiro ortho carbonate) and poly(1-phenylalanine/ethylene glycol/1,6-diisocyanato hexane) .

Preferred biodegradable materials are starch and starch derivatives such as cyclodextrins, fats, fatty acids and biodegradable polymers such as poly(carbonates) , and homopolymers and copolymers derived from the polymerization of hydroxy alkanoic acids and their derivatives such as poly( s-hydroxy butyrate), poly(lactide) , polyglycolic acid and copolymers thereof, and particularly preferred biodegradable safening materials are starches and starch derivatives and biodegradable polymers derived from the polymerization of hydroxyalkanoic acids and their derivatives. Most preferred biodegradable safening agents are cyclodextrins, poly(beta-hydroxybutyrate) , poly(lactides) , poly(glycolide) and block copolymers containing β-hydroxybutyrate glycolide and/or lactide recurring monomeric units.

In addition to the above-described essential components, the composition may include various optional components which are additives commonly employed with

polymers. Useful optional components also include fillers, plasticizers, impact modifiers, chain extenders, nucleating agents, colorants, mold release agents, antioxidants, ultra violet light stabilizers, lubricants, pigments, antistatic agents, fire retardants, and the like. These optional components are well known to those of skill in the art, accordingly, only the preferred optional components will be described herein in detail.

The composition is contacted with an effective amount of one or more effective surfactants. As used herein, an "effective surfactant" is a surfactant which is capable of directly or indirectly enhancing the degradation of a polymeric material to any extent.

Useful surfactants include anionic, zwitterionic, cationic and nonionic surfactants.

Useful anionic surfactants include alkali metal, ammonium and a ine soaps and alkali metal salts of alkyl-aryl sulfonic acids, sodium dialkyl sulfosuccinate, sulfated or sulfonated oils such as glycocholic acid sodium salt, glycodeoxycholic acid sodium salt, sodium dioxychalate, cholic acid sodium salt, 1-deconesulfonic acid sodium salt, caprylic acid sodium salt, sodium dodecyl sulfate, taurocholic acid sodium salt, taurodeoxycholic acid sodium salt, sodium decyl sulfate, sodium octyl sulfate, sodium hexyl carboxylate, sodium heptyl carboxylate, sodium octyl carboxylate, sodium nonyl carboxylate, sodium decyl carboxylate and sodium dodecyl carboxylate, disodium dodcyl phosphate, disodium 4-alkyl 3-sulfonatosuccinates and sodium dodecyl benzenesulfonate.

Useful cationic surfactants include salts of long chain primary, secondary and tertiary amines such as oleylamine acetate, cetyla ine acetate, didodecylamine lactate, the acetate of aminoethyl-amino ethyl stearamide, dilauroyl triethylene tetramine diacetate, and l-aminoethyl-2-heptadecenyl imidazoline acetate; quaternary salts such as cetylpyridinium bromide, hexodecyl ethyl morpholinium chloride, didodecyl ammonium chloride, cetylpyridinium chloride, dodecyltri ethyl-

ammonium bromide, hexadecyl trimethylammonium bromide, tetradecyl trimethylammonium bromide, dodecyl ammonium chloride, cetyl trimethyl ammonium bromide, benzalkonium chloride, decomethonium bromide, methylbenzethonium chloride, 4-picoline dodecyl sulfate, sodium perfluorooctanoate, sodium hexyl sulfosuccinate, sodium octyl sulfosuccinate, sodium cyclohexyl acetate, sodium cyclohexyl propionate, sodium cyclohexyl butanoate and sodium cyclohexyl sulfamate.

Useful zwitterionic surfactants include N-alkyl-N,N- dimethyl-3-ammonio-l-propane sulfonates such as N-decyl- N, -dimethyl-3-ammonio-l-propane, N-dodecy1-N,N-dime hy1-3- ammonio-1-propane, N-hexadecy1-N,N-dimethy1-3-ammonio-1- propane, N-octyl-N,N-dimethyl-3-ammonio-l-propane, and

N-dodecy1-N,N-dimethy1-3-ammonio-1-propane, D,L-alρha- phosphatidyl choline and dipalmatioyl.

Useful nonionic surfactants include n-alkyl-D- glucopyranosides and n-alkyl-D-maltosides such as decyl-D-glucopyranoside, dodecyl-D-glucopyranoside, heptyl-D-glucopyranoside, octyl-D-glucopyranoside, nonyl-D-glucopyranoside, decyl-D-maltoside, dodecyl-D- maltoside, heptyl-D-maltoside, octyl-D-maltoside, and nonyl-D-maltoside, condensation products of higher fatty alcohols with alkyiene oxides, such as the reaction product of oleyl alcohol with 10 ethylene oxide units; condensation products of alkylphenols with alkyiene oxides, such as the reaction products of isooctylphenol, octylphenol and nonylphenol with from abut 12 to about 30 ethylene oxide units; condensation products of higher fatty acid amides with 5 or more alkyiene oxide units such as ethylene oxide units; polyethyl glycol esters of long chain fatty acids, such as tetraethylene glycol monopalmitate, hexaethyleneglycol monolaurate, nonaethyleneglycol dioleate, tridecaethyleneglycol monoarachidate, triosaethylene glycol monobehenate, tricosaethyleneglycoldibehanate, polyhydric alcohol partial higher fatty acid esters such as sorbitan trisearate, ethylene oxide condensation products of

polyhydric alcohol partial higher fatty esters, and their inner anhydrides (mannitol-anhydride, called Mannitan, and sorbitol-anhydride, called Sorbitan), such as glycerol monopalmitate reacted with 10 molecules of ethylene oxide, pentaerythritol monooleate reacted with 12 molecules of ethylene oxide, sorbitan monostearate reacted with 10 to

15 molecules of ethylene oxide; long chain polyglycols in which one hydroxyl group is esterified with a higher fatty acid and the other hdroxy group is etherified with a low molecular alcohol, such as methoxypolyethylene glycol 550 monostearate (550 meaning the average molecular weight of the polyglycol ether).

A combination of two or more of these surfactants may be used. For example, a cationic surfactant may be blended with a nonionic surfactant, or an anionic surfactant with a nonionic surfactant.

Preferred surfactants are capable of not only degrading the plastic but also exhibit a beneficial effect by enhancing the biodegradation of any biodegradable component incorporated into the plastic. More preferred for use in the practice of this invention as degradation enhancing materials are nonionic surfactants, or mixtures of nonionic surfactants and other types of surfactants. Particularly preferred for use in the practice of this invention are nonionic surfactants such surfactants are capable of not only degrading the polymers but also exhibit a beneficial effect by enhancing the biodegradation of any biodegradable component in the composition. Preferred nonionic surfactants for use in the practice of this invention are alkylarylpolyethers, such as the condensation products of alkylphenols, such as octylphenol, nonylphenol and isooctyphenol, and alkyiene oxides, such as ethylene oxide; fatty acid alkanol amides; poly-alkoxylated alcohols, such as polyethoxylated tridecanol, idotridecyl alcohol adduct with ethylene oxide; and fatty alcohol polyethers.

The composition is contacted with an effective amount" of one or more effective surfactants. As used

herein, an "effective amount of one or more effective surfactants" is an amount of such surfactants which is capable of enhancing the degradation of the polymeric material to any extent. The amount of surfactants employed may vary widely. In general, the greater the amount of surfactants applied to the composition, the greater the effect; and conversely, the smaller amount of surfactant the smaller the effect. In the preferred embodiments of the invention where the method is used to assay the biodegradability of a composition the surfactant 0 is contacted with the composition in a solution in which the concentration of surfactants in the solution is at least about 0.001 mM. In the preferred embodiments of the invention, the concentration of surfactants in the solution is from about 0.001 mM to about the limit of 5 surfactant solubility in the solvent of choice, and in the particularly preferred embodiments of the invention, the concentration of surfactants in the solution is from about 0.01 to about 10 mM. Amongst these particularly preferred embodiments, most preferred are those embodiments in which 0 the concentration of surfactants is from about 1 mM to about 5 mM.

The composition is directly or indirectly contacted with one or more effective enzymes. As used herein, an "effective enzyme" is an enzyme which is capable ^J catalyzing the biodegradation of the biodegradable material to any extent. Useful enzymes may vary widely. Illustrative of such enzymes are hydrolases such as cellulases, glucoamylases, and α-amylases, carbohydrases, depoly erases, proteases, esterases, lipases, oxygenases 0 and the like.

The composition is contacted with "an effective amount of one or more effective enzymes". As used herein, "an effective amount of one or more enzymes" is an amount which is sufficient to catalyze the biodegradation of the one or more biodegradable materials to any extent. The amount of enzyme employed may vary widely and depends on a number of factors including the activity of the particular

enzy e, the composition and the amount of biodegradable component, the stability of the enzyme and other factors known to those of skill in the art. In general, the greater the amount of enzymes contacted with the composition, the greater the effect, and conversely, the smaller the amount of enzyme the smaller the effect. In the preferred embodiments of the invention where the invention is used as an assay the biodegradability of a composition, the enzyme is contacted with the composition in a solution in which the amount of enzymes employed is at least about 0.01 units where one unit is one nanomole of degradation product formed per minuted. In the preferred embodiments of the invention, the amount of enzymes employed is from about 0.1 to about 100,000 units, and in the particularly preferred embodiments of the invention, the amount of enzyme is from about 0.1 units to about 75,000 units. In the most preferred embodiments of the invention, the amount of enzymes is from about

1,000 units to about 50,000 units.

In those embodiments of the invention where the enzyme(s) and surfactant(s) are contacted with the composition in a solution, useful solvents may vary widely, the only requirement is that the solvent does not interfere or substan ially does not interfere with the activity of enzyme and the surfactant.

Illustrative of useful solvents are water and organic solvents such as long chain aliphatic solvents, such as hexanes, perrtanes, actanes and the like; chlorinated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride and the like; and aromatic hydrocarbons such as benzene, toluene and the like. The preferred solvent is water.

The solution may include various optional ingredients. Illustrative of such ingredients are those which maintain the stability of the enzyme such as buffers, reducing agents, sugars and sugar alcohols, ingredients required for enzymatic activity such as enzyme cofactors and salts, and ingredients for prevention of

microbial growth and contamination such as anti microbial agents such as sodium azide.

The pH of the solution is selected such that the activity of the enzyme and/or the surfactant is not unduly inhibited. The pH is usually maintained in the range of from about 3 to about 9. In the preferred embodiments of the invention, the pH of the solution is from about 4.5 to about 8.5.

In the second step of the preferred embodiments of the invention, the solution is analyzed qualitatively and/or quantatively to determine the extent of biodegradation. Any useful method can be used. For example, solution can be analyzed by direct measurement of the concentration levels of the degradation products. Illustrative of useful direct measurement methods are spectrophotometric, electroanolytical gravimetric, and other biochemical methods known to those of skill in the art. The extent of biodegradation can be determined by indirect measurement. For example, indirect methods include, relating the rate of production of degradation products to the rate of microbial growth and metabolism in a system where microorganisms have been added and their growth has not been inhibited, measuring the increase in cell number, and monitoring metaboHsm by measuring oxygen consumption, carbon dioxide evolution or methane evolution, and observing changes in the physical properties or appearance of the plastic.

The general method of this invention is useful for the enhancement of the rate of biodegradation. For example, such a method can be used to promote biodegradation of disposed items in landfills or compost facilities. There is great value in developing degradable items which can degrade in a reasonable period of time. If the surfactants are sprayed or otherwise added to the items to be degraded or to the general area in which the degradation is taking place, a significant increase in the rate of degradation occurs. This could significantly decrease the land area required for a compost facility or

make such facilities possible in areas which have short periods of warm temperatures. Such additives could also promote the degradation of biodegradable agricultural mulch films when their period of usefulness is over.

Other methods of application and uses are also possible.

It should be noted that many types of surfactants are themselves biodegradable and would therefore not cause a lasting problem after such applications.

The method of this invention may also be used to evaluate the biodgradability of biodegradable polymeric compositions. Through use of this method, it can be determined if a composition is biodegradable, the rate of biodegrada ion and the distribution of biodegradation products can be determined.

The following examples are pres-ented to more particularly illustrate the invention and shall not be construed as limitations therein.

EXAMPLE I

A) Preparation of Enzymes Solutions.

In the standard assay method, the biodegradation of starch alone or in plastic films was based on the measurement of glucose produced by a mixture of amylases in a steril solution containing the test material. The enzyme mixture was prepared as a ten-fold concentrate containing 305 units per ml each of amyloglucosidase (Aspergillus niger), -amylase (A. oryzae), a - amylase (Bacillus) and 0.2 units/ml pullulanase (Enterobacter aerogenes) in 0.1 M acetate buffer, pH 4.8. The enzyme

0 solution was immediately dialyzed at 4 C against the same buffer until the concentration of glucose (present as a contaminant in the commercial enzyme preparations) is below 0.5 - 1 mg/ml. The concentrated enzyme solution was then reconstituted to contain 1 M CaCl and 3 mM sodium azide in 0.01 M acetate buffer, pH 4.8. The final preparation was stored at 4°C after sterilization by filtration through a 0.2 _u filter.

For the enzymatic degradation of cellulose an enzyme solution was prepared containing as a five-fold concentrate with 0.2 g/ml cellulase (Cellulase TV Concentrate, Miles Laboratory, IN) in 0.1 M acetate buffer, pH 4.8. The enzyme solution was dialyzed against the same buffer at 4° C until the glucose concentration was below 2 mg/ml. Due to the rapid degradation of dialysis membranes by the cellulaese solution it was necessary to change the membrane every 30 minutes. In some cases, the glucose was reduced by repeated filtration and dilution of the enzyme solution using a 10,000 molecular weight cutoff Amicon ultrafiltration membrane and filter apparatus (Amicon, Danvers, MA). The solution was reconstituted to contain 0.2 mM sodium azide.and 0.1 M acetate buffer, pH 4.8 and filter sterilized. Unless otherwise indicated, all enzymes were purchased from Sigma Chemical Co., St. Louis, MO.

Degradation Assays. For the determina ion of the rate and extent of starch or cellulose degradation, plastic samples containing either material were immersed in 5 ml of the appropriate enzyme solution in sterile screw capped tubes. The tubes were incubated at 45° C and agitated at

150 rp . At appropriate time intervals, 10 ul samples were removed and glucose concentrations determined using a glucose analyzer (Beckman Instruments, Fullerton, CA) . In all cases, appropriate controls were run simultaneously and included the enzyme only (no plastic), the plastic only (no enzyme), and enzyme with α-cellulose or pearl starch to assure full enzyme activity with a known substrate. In some cases where it was necessary to run the assay for several weeks, fresh enzyme solution was added after removal of the original solution. When this was done, final and new initial glucose readings were recorded and the total degradation based on the commylative glucose production.

Additions to the Standard Degradation Assay. For the determina ion of enzyme degradation in the presence of surfactants or other additives, the addition was made to

the enzyme solution immediately before adding the plastic sample. Appropriate glucose standards were also used as controls to assure no interference of the additive with the measurement of glucose concentration by the glucose analyzer. The surfactants used included Igepal CO-630

(GAF Chemicals Corp., Cincinnati, OH), cetylpyridinium chloride, Triton X100, and sodium dodecyl sulfact (Sigma

Chemical Corp., St. Louis, MO).

Plastic Samples. Plastic films either commercially available materials containing 6% corn starch, or provided by the Northern Regional Research Center, USDA, Peoria, IL

(40% starch, 45% ethylene acrylic acid, 15% urea), or were produced for the purpose of this investigation and consisted of 40% pearl starch or α-cellulose in high density polyethylene.

B) Test

For the determination of the rate and extent of enzymatic hydrolysis, the starch component in starch-containing "biodegradable" plastics, a fairly simple enzyme based testing method was developed. The standard assay procedure was performed using an enzyme mixture containing alpha amylase, glucoamylase, pullulanase, with the addition of sodium azide to prevent microbial growth. The degradation of starch itself can be readily measured in such an assay system by monitoring glucose production as the combined action of the enzymes function to completely hydrolyze starch to glucose. For the purpose of measuring the degradation of plastics, samples were placed in the enzyme solution and incubated at 45 C with moderate agitation. The results are set forth in Figure 1. As shown in Figure 1, the amount of starch which was degraded in these plastics varied significantly with the type of plastic used. However, in all cases, the amount of starch degraded was quite low, less than 20% of the starch present, and with some plastics as little as 5% of the starch was hydrolyzed to glucose.

In an effort to better understand the limiting aspect of the degradation of starch by microbial amylases, a variety of additions were made to the enzyme assay mixture. Figure 2 summarizes the results of these experiments and the significant effect that some of the additions had on the amount of starch which was degraded.

Most notable was the effect of the surfactants Igepal and

Triton X100 and polyethylene glycol on the enzyme degradation. The treatment of the polymer by boiling also resulted in an improvement of the degradation of the starch; however, this physical dissruption of the material was not further examined. The effect of the surfactants on the degradation of the plastic was examined more carefully, using three different starch containing plastics, one of 40% starch in HDPE, one with 40% starch with 45% EAA and one of 6% starch in LDPE. The results are set forth in Figures 3, 4 and 5. In all cases, the surfactants greaty improved the rate of degradation and the extent to which the starch was degraded by the same enzyme assay mix used previously. _.

To determine if this effect was particular to starch, for example due to the surface properties of starch granules or the starch/EAA interaction, we tested the surfactants in an assay mixture designed to measure the degradation of cellulosic materials. Figure 6 shows the degradation of a sample of HDPE containing cellulosics with the addition of surfactants and without and demonstrates the efficacy of the surfactant addition in biodegradation of cellulosic materials as well as starch containing materials.

To determine if this was an effect unrelated to the presence of the starch or cellulose in plastic films, the degradation of starch or cellulose alone (no incorporated into plastic) was measured with the surfactant additives. The results of these experiments are set forth in Figures 7 and 8. As illustrated in Figures 7 and 8, the surfactant had little or no effect on the breakdown of these carbohydrates. The type of surfactant did have an

effect on the degradation enhancement. As shown in the following Table I, the nonionic surfactants Igepal and Triton X100 worked much better than the anionic or cationic surfactants.

TABLE I

Effect of Surfactant Type on Degradation of Starch in Plastic Films

% Degradation of Starch Addition to Pearl 40% Starch 40% Starch Assay Starch + EAA + HDPE

5.7 7.9 8.0 0.8 1.2

7 day assay - no enzyme changes

An effort was made to examine the role of the surfactant by separating the surfactant treatment from the enzyme degradation process. A plastic sample containing 40% starch in HDPE was pretreated with Igepal at 60° C. The sample was then extensively washed in running water for over one hour to remove residual surfactant. After this treatment, the degradation of the sample was measured with an enzyme solution containing no additives and compared to the degradation of a sample washed and treated in the same manner but without the surfactant. Figure 9 shows that the pretreatment did improve the degradation of the starch in the plastic sample.