CA2057668A1

CA2057668A1 - Degradable foam

Info

Publication number: CA2057668A1
Application number: CA002057668A
Authority: CA
Inventors: Speros P. Nemphos; James T. Mcqueen
Original assignee: Novacor Chemicals International SA
Current assignee: Camelot Technologies Ltd
Priority date: 1991-12-13
Filing date: 1991-12-13
Publication date: 1993-06-14

Abstract

Degradable Foam ABSTRACT OF THE DISCLOSURE
Compounds of polymers of lactic acid may be foamed to provide a degradable polymeric foam.

Description

~lELD OF I~VENTION -The present invention relates to degradable foams of polymers or polymer alloys. More particularly the present invention relates to foams of polymers or polymer alloys which will begin to degrade or will totally degrade when left in the natural environment.
BACKGROU~QF 1~: IN~NTION
There are a number of polymers which are referred to as biodegradable polymers. Until quite recently these polymers have been used in high value add applications such as the medical and/or pharmaceutical field. Polymers such as polylactic acid or p~lylactides, polyhydroxybutyrate (PHB) and copolymers of hydroxy bu~rate and valerate ~PHBV) have been used to make articles such as ., .
' 20 absorbable sutures, osteo pins and screws, and in the field of controlled release ; drugs.
` These types of polymers will "biodegrade" within a relatively sho~t -period of time, iFor example from about 6 to 12 weeks depending on the molecular weight and the polymer stereo chemistry.
There are some patents which disclose the use of such polymers in ~:
~; 30 applications which are typically met by commodity polymers. These applications include for example films such as disclosed in Chemical Abstracts 95:63389r of Japanese Kokai JP 56/22324 which discloses a biodegradable mulch film; Chemical Abstracts 84:135650d and 84:18707e of United States patent 3,932,319 and 3,867,324 both assigned to Union Carbide which disclose -2- :

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2 0 ~ 7 ~ ~ 8 films and molded plant holders of biodegradable polymers. Additionally, there is some art relating to films u3ed in food packaging such as disclosed in Chemical Abstracts 110:153035e of European Patent Application 273 069 which discloses films of glacomannan as a food paclcaging and Chemical Abstracts 93:225641e of WO 80/659 which disclose latices of ethyl cellulose as a food coating. None of this art suggests a foamed degradable polymer.
The above art does not disclose that such polymers could be foamed.
However, there is a need for degradable foamed polymeric products. Such products could be formed into trays for packaging cold products such as meat trays, or insulators for cold drinlcs, or for higher temperature applications such as containers for hot foods such as hot drinks or "fast food" such as hamburgers and the like (e.g. ~oamed trays and/or "clam shells").
Unfortwnately tbe above type of packaging may be discarded by insensiti~e individuals causing unsightly was~e. If such contain~rs could be made from a polymer or polymer alloy which was degradable ~e problem of litter would be lessened.
Accordingly, there is a need for a degradable foamed polyme~ic composition. The present invention seeks to provide such a composition.

The present invention provides a degradable polymeric foam having a density of not more than 16 lb/cubic foot comprising a polymer alloy comprising:

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. . . .. : . ..
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(i) from 50 to 100% of one or more co or homopolymers having a molecular weight of greater than 41),000 comp~ising the residues of one or more monomers of the Formula:
-OCRIR2(CR3R4)"CO-and -OC:~I(CH[3~CO- II
wherein in Formula I, R~ R3, and R4 are independently selected firom the group consisting of a hydrogen atom and a Cl4 allyl radical, and n is O or an inte~er from 1 to S, provided that when a monomer residue of Formula II is present, and in Formula I n is 1 and R2, R3, and R4 are hydrogen, Rl can not be a methyl radical; and 20 (ii) from 0 to 50 weight % of one or more polymers selected firom the group consisting of polymers having a Hildebrand parameter (~r) of not more than 3 MPAln different from that of said one or more co or homopolymers.
The present invention also provides a process for preparing a polymeric ~' ~oam having a den3ity of not more than 16 lb/cubic foot comprising a polymer ' 30 alloy compr~sing: :
(i) from Sû to 100% of one or more co or homopolymers having a molecular weight of greater than 40,000 comprising the residues ~ one or more monomers of the Formula:
-OClRIR2(CR3R~)nCO- I

2~7~8 and Q(: H(CH3)CO- II
whereirl in Pormula I3 Rl, R2, R3, and R4 are independell~y selected ~rom the group consisting of a hydrogen atom and a Cl, allyl radical, and n is O or an integer from 1 to 5, provided that when a monomer residue of Formula II is present and in Fo~rnula I n is 1 and R2, R3, and R4 are hydrogen, Rl can not be a methyl radical; and (ii) from O to 50 weight % of one or more polymers selected from the group consisting of polymers having a Hildebrasd parameter (~) of not more than 3 MPA~'2 different firom that of the above co or homopolymer which comprises passing a melt of said polymer alloy through a heated shear 2o zone and concurrently injecting into said melt at pressures up 6,000 psi a gaseous or liquid blowing agen~ which will not significantly decompose the polymer alloy; extruding the melt; and letting the melt expand.
DET~ED DESC~
~e foams of the present invention should have a density of less than 16, more pre~erably less than 12, most preferably less than 8 lb/cubic foot.
~he foamed compositions of the present invention may co:mprise a biode~radable polymer per se or an alloy of a biodegradable polymer. In the polymers noted above if the polymer is a homopolymer containirlg only the residues of ~ormu1a II the polymer is a polymer of lactic acid or lactide. I~e monomer~ of 1: ormula II may be in either a D or L configuration. If the ..

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2 ~ 6 8 polymer is prepared ~rom lactide, the lactide may be in either the D, L, or meso configuration.
The degree of crystallinity in the polymer may have some impact on the formation of the foam and ~he foam structure. ~or example, it may be desirable to orient the polymer to ~y to increase its heat distor~on temperature.
For lactide polymer3 (e.g. homopolymers of Formula I~ e de~ee of crysta11inity falls off rapidly with increasing amounts of the D or meso configuration. That is polymers having at least 80, preferably 90, most preferably 95 weight ~ of the monomer in the L configuration tend to have increasing crystallinity. Conversely if the polymer contains less than about 8û
weight % of monomer in the L configuration then the polymer tends to be 2 o amolphous.
If the polymer is a p~lymer containing monomer residues of Formula I it may be a number of polymers. If in ~ormula I R3, R4, and one of either R2, or Rl, are hydrogen atoms and the other of R2, and R~ is a methyl radical and n is 1 then the polymer would lbe a homop~lymer of ~$-hydroxy butyrate, sometimes referred to as PHB. If in Formula I R3 or R4 o~ hydrogen and one of Rl and R2 30 iS hydrogen and the other is an ethyl radical and n is 1 then the polymer would be a homopolymer of ~B-hydroxy valerate, sometimes re~erred to as PHV. Of course it is possible to have copolymers of such monomers as in the case oif poly hydroxy butyrate-valerate copolymers, sometimes refe~red to as PHBV.
Genera11y these polymers are obtained from the biofermentation of a suitable , ', ', : ' `" 2~7~

substrate using a m;croorganism which produces the polymer.
If the polymer contains residues of 3;~rmula I and n is 0 and Rl9 and R2 are hydrogen atoms then the monomer i9 glycolic acid. Similar to the case wi~h lactic acid the polymer may be pr~pared from the monomers or from glycolide.
Preferably the polymers containing monomer residues of ~ormula I
0 and/or II above will have a molecular weight of not less than 40,000 preferably not less than 80,000. Preferablly the polymers should ha~e an in~rinsic viscosity of not less than about 1.5 more preferably 2.0 or greater (as determined by ASTM method D2857, pre~erred solvent chloro~orm).
The present invention may be practised using degradable polymers of monomers residues of Formula I or II ab~ve or blends of such polymers or 2 o blends of such polymers with other polymers ha~ing a Hildebrand parameter (a) of not more then 3, preferably less than 2 MPA~2 different from that of the polymers of monomer residues of Formula I and II abo~e.
However, when blending the polymers not only is polymer compatibility a eoncern but the viscosity of the melt is also a concern. The melt of dle polymer alloy should not separate under shear and the viscosity of the polymer 3 o melt should be such at to permit the blowing agent to be un~formly dispers~
throughout the melt and to permit the melt to ~orm and retain a ~oam st~ucture on leaving the reactor. Additionally, the physical properties such as the heat distoilion temperature and/or melting temperature of the al10y are also of concern.

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2~ 8 Preferably the less degrad~le polymers are selected from the group consisting of:
(i) polymers comprisillg:
(a) ~om 80 to 20, preferably from 40 to ~) weight % of one or more C8 12 vinyl aromatic monomers which are unsubstituted or substituted by 0 a Cl~ allyl radical; and (b) from 20 to 80, preferably from 60 to 40 weight % of one or more monomers selected from the group consisting of C~ 6 alkyl esters of C3-6 ethylenically unsaturated carboxylic esters, anhydrides of C46 ethylenically unsaturated dicarboxylic acids and C3 6 aL~enyl nitriles which polymers may optionally contain up to 15 % of an impact modifier which is a rubbes~ polymer of one or more C~6 conjugated diolefins;
(ii) polymers comprising:
(a) homopolymers of C2 6 alkenyl halides;
(iii) polymers comprising co and homopolymers of C2~ olefin~;
(iv) polycarbonates;

30 (v) polymers complising:
firom 100 to 50 weight ~b oi one or more Cl 6 alkyl or hydroxy alkyl acrylates or methacrylates; from 0 to 50 weight % oiF one or more C8 12 vinyl aromatic monomers which are unsubstituted or substituted by a Cl~ allyl radical which polymers have been imidized to at least 10%;

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(vi) polymers of amides of C3 6 ethylenically unsaturated carboxylic acids;
(vii~ poly phenylene ethers (also called polyphenylene oxides);
(viii) polysulphones;
(ix) polysiloxaines;
(x) polyimines;
o (xi) polyesters of C~10 aromatic dicarboxylic acids and C2 4 alkylene glycols;
(xii) polyacetals;
(xiii~ cellulose esters; and (xiv) ionomers.
Suitable polymers of alkenyl halides include polyvinyl chloride.
Sui~able co and homopolymers of C2~ olefins include polyethylene, polypropylene and ethylene-propylene copolymers.
Suitable C~}12 vinyl aromatic monomers include styrene, ~-methyl styrene, ~methyl styrene and t-butyl s~rene.
Suitable Cl.6 alkyl esters of C3 6 ethylenically unsaturated carboxylic acids include me~hyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate.
Suitable anhydrides of C~4.6 ethylenically unsaturated carboxylic acids include ma1eic anhydride.
Suitable C3-6 all~enyl nitriles include acrylonitrile and methacrylonitrile.
Accordingly, the non- or less degradable polymers may com~ise homopolymers of polystyrene wllich may or may not have a specific steric g .. .. , . .. ~.. ,. ... .,., . " .. .. .... .. -,.. ........ . . ..... .

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configuration such as syndiotactic polystyrene and possibly isotactic polystyrene. The polymer could ~ a copolymer of various s~renic monomers such as a copolymer of styrene and ~-me~yl styrene.
The non- or less degradable polymer could be a copolymer compris;ng one or more of styrene, a-metllyl s~rrene, ~methyl styrene and t-butyl styrene 0 and up to 50 weight % of one or m~re monomers selected from the above noted monomers. Accordingly, the polymer could be a copolymer of: styrene and methyl methacrylate; s~yrene and ethyl methacrylate; styrene and butyl acrylate;styrene and methyl acrylate; styrene and ethyl acrylate; styrene and bu~l ac~ylate; s~yrene and maleic anhydride; styrene and acrylonitrile; and styrene - and methacrylonitrile. However, it should be noted that the polymer does not have to be a copolymer. It could contain a third or fourth monomer. 3~or exampleg all of the above polymers could be carboxylated. That is they could contain a copolymerizable carboxylic acid which is a C3 6 ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid. Further polymers within the scope of the present disclosure are iknown to tho~e skilled in the art.
The biodegradaUe polymer may be blended with a polycarbonate. The polycarbonate may be based on one or more polyphenols selected from the :

- 2~7~8 group cons;sting of hydroquinone1 resorcinol and polyphenols of the Pormula Rl R3 HO ~ x ~r ~ OH III

R2 \ R~

wherein Rl, R2, R3 and R4 are independently selected from the group consis~ing of a hydrogen atom, a chlo~ine atom, a bromine atom and a Cl 4 alkyl radical;
and X is a bond or divalent radical selected ~om the group consistillg of Cl ~O
allylene radicals, C2-8 alkenylene radicals and C6-8 cycloallylene radicals.
Preferably, the polycarbonate is based on a diphen~l selected from the group consisting of 4,4'd;11ydroxydiphenyl; 2,2-bis-(4-hydroxyphenyl) propane;

2,4-bis-(4-hydroxyphenyl)-2-methylbutane; 1,1-bis(4-hydroxyphenyl)-cyclohexane, ,~"~-bis-(4-hydroxyphenyl)-p-diisopropylbenzene; 2,2-bis-(3-chlor~hydroxyphenyl)propane; 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane.
The biodegradable polymer may be blended with a polymer comprising:
firom 40 to 95 weight % of one or more C8-l2 vinyl aromatic monomers which a~e unsubstltuted or substituted by a Cl~ alkyl radical; Cl 6 alkyl or hydroxy allyl acrylates or methacrylates; from 5 to 40 weight ~ of an anhydride of a C~6 ethylencially unsaturated dicarboxylic acid; from 0 to 50 weight % of one or more Cl 6 allyl or hydroxy alkyl acrylates or methacrylates. : --1~- ' , . , . , ".................. . . .
. . . . ..... . . ........ . . . . .

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Pre~erably, the vinyl aromatic monorner may be present in the polymer in an amount from 40 to 80 weight %. ~e anhydride may be present in the polymer in an amount from S to 35 weight % and the ac~ylate or methacrylate may be present in the polymer in an amount from 2 to 30 weight %.
In the above non-biodegradable polymer ~e aromatic monomer may selected from the group consisting of styrene, a-methyl styrene and t-bu~yl styrene; the anhydride may maleic anhydride; and the Cl~ a11yl or hydro~cy allyl acrylate or methacrylate may be selected from the group consis~ing of methyl acrylate, e~yl acrylate, methyl methacrylate and ethyl methacrylate.
The biodegradable polymer may be blended with an imide. The imide may comprise: from 100 to 50 weight % of one or more C~ 6 allcyl or hydroxy allyl acrylates or methacrylates; fiom 0 to 50 weight % of one or more C~12 vinyl aromatic monomers which are unsubstitu~d or substituted by a C,4 allyl radical which polymers have been irnidized to at least 10%.
Preferably, the polym~r will ha~e been imidized to from 10 to 95%, most preferably from about 50 to 95 %, most preferably ~rom 65 to 95 % . A
process ~or preparing such polymers i5 disclosed in Un~ted States Patent :

4,246,374 issued January 20, 1981, assigned to Rohm and Hass (:ompany.
Preferably, the polymer may comprise from 100 to 70 weight % of (meth)ac~ylate monomers and from 0 to 30 weight % of vinyl aromatic monomers.

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2 ~ 8 In the above non-biodegradable polymers the Cl 4 alkyl or hydroxy allyl acrylate or methacrylate may be selected from the group consis~ing of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate and ~e vinyl aromatic monomer may be selected from the group consisting of styrene, a-methyl styrene and t-butyl s~rene.
The biodegradable polymer m~y Ibe blended with polymers of amides C3 6 ethylenically unsaturated carboxylic acids. Acrylamide and methacrylamide and co and homopolymers thereof are suitable for use in accordance with the present invention.
The biodegradable polymer may be blended with a polyphenylene ether (also called oxides). Generally, polyphenylene ether are polymers having a 2o backbone containing recurring monomer units of the Formula ~ ~

_ _ n ~:
wherein Rl, R2, 1~37 and R4 are independently selected from the group consisting of a hydrogen atom, a halogen atom, preferable chlorine or bromine, an allyl radical, preferably containing less than 10, most preferably containing firom 1 to 4 carbon atoms, and a C~O aromatic radical which is unsubstituted or .. . , ~ , , , , ~ , ~

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substituted by an alkyl radical, preferably containing less than 10, most preferably containing from 1 to 4 carbon atoms; and n is an integer from 300 to 700. The polymer may contain other monomeric units; that is, it need not be a homopolymer of only one 1,4 phenylene oxide monomer. For example, the polymer could be poly [oxy-2-acetoxytrinethyleneoxy -1,4-pherlylenemethyl 0 (phenyl) methylene -1,4-phenylene], haYing Tg of llO~C.
The biodegradable polymer may be blended with a polysulphone.
Generally, polysulphones comprise a backbone of one or more r~curring units selected ~om the group consisting of:
R3 R, >_ ~
~ O ~ SO2--''' >--< '' R4 R2 ~:
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R7 Rs R3 R
3 o ~ CH3 )~
CH3 ~ S02-, ~ ~ . . - , , .

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~R7 R5 R.3 Rl ---~ O ~_ O ~ SO2~and R~ R5 R3 1 ~ ' .

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;~ ' wherein Rl, R2, R3, ~, Rs~ R6, R77 and R8 are independently selected ~rom ~e group consistlng of a hydrogen atom, a halogen atom, preferably chlo~ine or bromine, or an alkyl radical, preferably containing less than 10, most preferably containing from 1 to 4 carbon atoms and a C~10 aromatic radical which is 30 unsubstituted or substituted by an allyl radicai preferably containing less than 10, most preferably containing from 1 to 4 carbon atoms.

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The biodegradable polymer may be Uended with a polysiloxane.
Typically, polysiloxones contain a baskbone of recurring units of the ~ormula:

-- 3; -- O -- Sj A suitable siloxane is poly loxy (methyl) phenysilyleneo~y -1,4 -phenylene] (Tg 95C3.
The biodegradable polymer may be blended with an imine. Typically, imines contail the ~nctional group--NH--. The imines are cyclic compounds and may be onsidered nitrogen homologues of epoxides. A
suitable imine is poly (benzoyliminoethylene3 ~g 1~).
2 o The Siodegradable polymer may be blended with polyeste~s of C8 10 aromatic dicarboxylic acids and C24 allylene glycols. Such este~s amy optionally ffirther comprise up to about 15, prefierably less than 10 weight % of one ~r more saturated aliphatic dicarbo~ylic acids such as adipic acid. These saturated aliphatic dicarboxylic acids may make the polyester more susceptiUe to degradation. Industrially, the most common aromatic dicarboxylic acids are the terephthalic acids. Industrially, the most common diols are ethylene and butylene glycols. The polyesters may be selected from the group consisting of polyethylene terephthalate (P~l~ and polybutylene terephthalate.

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The non-degradable resin may be a polyacetyl. Ihese thermoplastic resins have repeating formaldehyde units in their backbone. The polymerization is initiated using an ionic ini~ator such as a tertiary amine or an ammomum salt. The polymer is then end capped to yield a polyoxymethylene polymer.
The polymer other than one of l~ormula I or II may be a lower, Cl 6 alkyl 0 ester of a polyssacharide such as cellulose. An indus~rially avaLlable ester is cellulose acetate.
- The non-degradable polymer may be an ionomer. Typically ~e ionomer is a partially neutralized polymer of methacrylic acid and ethylene. Typically these types of polymers are neutralized with sodium and/or zinc cations al~ough other cations may also be suitable. Commercially ionomers are 2 o availaUe under the tratemark SURLYN~.
Typically t~e polymers alloyed or Uended with the polymer containing monomer residues of Formula I and/or II will have a molecular weight of not less than 100,000, preferably from 100,000 to about 300,000.
I~e polymers or alloys of the present inven¢ion may be filled. Ihat is they may contain up to about 50 preferably less than 45, more preferably from 3~) about 5 to 45, most preferably firom 10 to 35 weight % of one or more fillers.
While conventionial inorganic fillers such as talc9 calcium carbonate, clay, mica and the like may be used it is also possible to use organic fillers. A particularly useful class of organic fillers include polysaccharides. Particu~arly useful polysaccharides include starch, functionalized starch, ~unctionalized c~llulose, , ~ ~ - , ; ~ . . . .
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wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof. Particularly useful orgaDic fillers include cellulose, a-cellulose, wood flour, alld nut ~hell flour. While either the organic or inorganic fillers may be used the organic fillers are al~o degrada~le and are particularly useful iFrom the pvint of view of prep~ring a foam based on a degradable 0 polymer and degradable filler.
If there are problems with ~oaming the polymer or alloy it may be due to poor polymer rheology. In such a case the rheology may be improved by incorporating a plastici7,er into the polymer or alloy. Many plasticiærs are known to ~hose skilled in the art. Generally one would seek to use an innocuous plasticizer. E;or some biodegradable polymers such as the polylactic 2 o acids the monomer may also serve as a plasticiær. The plasticiser could be used in amounts up to about 10 weight %, preferably from about 3 to 7 weigl~t %. Of course if the polymer is not too "stiff" in the form of a melt the plasticizer could be dispensed wi~h.
In the process of the present invention a melt of ~he polymers containing monomer residues of Formula I and/o~^ ~I and alloys thereof optionally 30 containing filler are pas~ed through a shear zone. Typically the shear zone will constitute the barrel of an extruder. The extruder may be twin or single screw extruder. In many ~oaming operations baclc to back ~xtruders are used. In the first extru~er the polymer mixture forms a melt. C;as is injected into Ihe first extruder, and the gas and melt are passed through a series of mixers and into .. .. . . .
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the second extruder. The second extruder brings the temperature of the melt to that most desirable to create foam.
The extruders may be operated at balTel zone temperatur~s up to 180C, pre~erably from 120 to 170C and the die temperatures may be up to about 1~0C preferably from 100 to 130C. Due to ~e relatively low temperature 0 dliff~rential between the extrusion temperature and the ambient temperature it may, particularly in cases where the polymer or alloy has a low melt viseosity desirable either to ext~ude the foam into a cooling environment such as a chiller or to extrude the foam onto a moving support until the fo~m stabilizes.
The shear within the extruder is provided by the screw which may be operated at speeds from about 50 to 150, most preferably from about 80 to 120 RPM's.

20 Typically the screw for the ex~uder will have a D/L ratio firom about 20/1 to 40/1 preferably ~om about 24/1:36/1. In some embodiments of the pr~sent invention it is possible to use an extruder in series with a static mixer.
Typically in the extruder one or more sections of flights of the serews downstream ~om the injection of the blowing agent may be fitted wi~h mixing pins. These are short generally cylindrical pins extending from the screw to 3 0 pro~ide a close tolerance with the internal wall ~ the exttuder barrel. These pins serve to mix the molten polymer and blowing gas to provide a uniform dispersion of the blowing gas or agent through out the polymer melt prior to extrusion.

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Preferably, in accordance w;th the present invention a gaseous or liquid blowing agent is injected into the polymer melt in the extruder. Typically the blowing agent or gas may be injected at pr~ssures up to 6,00Q, most pre~erably up to about 4,0~, preferably less than 3,000 psi. I~e injection pressure ~equired is a function of a number of variables includirlg ~he final densi~y of the foam, the s~lubility of ~e blowing a,~ent in the polymer melt a~d the ~e of blowing agent. In the past the blowing agents were lower (C46) aLtcanes such butane pentane and even hexane. l~ese blowing agents would vapori~e at the temperatures in the melt. The biggest drawback of such agents was their flammability. These types of Uowing agents were replaced by the CFC's (chlorofluorocarbons) such as FREON (tradename~ and the like. Typically, these blowing agents may be characterized as Cl4 alkanes which are substituted by not less than two halogen atoms selected from the group consisting of chlorine and fluorine atoms. l~cently, these blowing agents have come under scrutiny due to concerns ~egarding ozone depletion in ~e upper atmosphere.
Cu~ently there is a move towards usin~g gases taken from the atmosphere such as carbon dioxide and nitrogen which are well known and industrially used in '. 30 some foaming operation. -Care should be exercised in selecting ~e blowing agent. The solubility of the blowing agent in the polymer or polymer blend will affect the quality of foam. If the blowing agent is very soluble in the polymer or alloy itmay act as a plasticizer reducing the viscosity of the polymer or alloy melt - . . ... . . . .
.. . .. . .. ..

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making it difflcult to maintain a good cell structure in the foam. If the blowing agent is not sufficiently soluble in the polymer or alloy it i3 not dispersed e~enly through out the melt of polymer or alloy and tends to "pop" out of ~e melt of polymer when it exits the e~truder.
In accordance with good marw~acturing practice ~e compositions in the extruder may contain a nucleating agent ~or t}le blowing agent. The nucleating agent or system may comprise a system which forms voids or bubbles or places for voids or bubbles to form. Some nucleating agents are inorganic particulates such as talc. Some nucleation systems comprise a carbonate or bicarbollate salt such as sodium bicarbonate and an organic acid such as citric acid. ll~e acid and bicarbonate are mixed in about equal weight ratios typically from 40:60 to 60:40, most preferably about 50:50. The nucleation system may be used in amounts from 0.5 to 5, preferably from 1 to 3 weight % based on the weight of the components in the polyrner or polymer alloy.
The melt of polymer or polymer alloy will be extruded in m~lten fo~n from ~e extruder. When it is subjected to the reduced atmospheric pressure outside the extruder the Uowing agent or gas expands or ~urther expands. The foamed polymer may be extruded as a sheet or as a ~ube or some such other fo~m. The foamed product may be subsequently hea~d and thermoformed into final products.
The present invention will now be illustrated by the following non-limiting examples in which unless other wise specified parts are parts by weight - ., , . " ~ . .

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and ~ is weight %.
~xample 1 An amorphous poly lactic acid polymer was prepared from lactide which contained a total of 86 weight ~i of both the D and L configura~ion of monomer and 14 weight % of monomer in the meso configuration (e.g. the polymer 0 contained less than 80 w~ight ~ of either ~e D or L configuration of monomer). The polymer was pr~pared by polymerizing the lactide in the presence of stannous octoate. The polymer had an int~insic viscosity of about - 1.0 and a molecular weight of about 80,000. The polymer had a residual monomer content of about 4 weight % which acted as a plasticizer reducing the melt viscosity and strength.
The polymer was fed to a brabender extruder which fed into a heated static mixer. The brabender/static mixer tandem wns operated under the following temperature conditions:
Melting Zone 140 - 160C
Foaming Agent Mixing Zone 150 - 170C
StaticMixers/Cooling Zone 120 - 150C
3 0 Die 100 -130C
The RPM's of the brabsnder was 40.
The screw on the brabender was modified by having a zone which had mixing pins in the flights of the screw. The blowing agent was injected into thebrabender shor~y above the zone of the modification to the screw as describ¢d.

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The blowing agent was halocarbon 22 (CHCLF2) and it was injected at a - pressure of 15000 psi.
Ihe foam was extruded ~rough a 1/16 inch capillary die and expanded to yield foams rods having a diameter from 1/4 to 3/4 inches. The foam densi~ was in the order of about 10 - 20 lb/cubic ~oot. The 3tarting polymer had a densi~ on the order of 70 lb/cubic foot. The ~oam was a clo3ed cell foam.

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Claims

1. A degradable polymeric foam having a density of not more than 16 lb.cu ft. comprising a polymer alloy comprising:
(i) from 50 to 100% of one or more co or homopolymers having a molecular weight of greater than 40,000 comprising the residues of one or more monomers of the Formula:
-OCR1R2(CR3R4)nCO- I
and -OCH(CH3)CO- II
wherein in Formula I, R1, R2, R3, and R4 are independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical, and n is O or an integer from 1 to 5, provided that when a monomer residue of Formula II is present and in Formula I n is 1 and R2, R3, and R4 are hydrogen, R1 can not be a methyl radical; and (ii) from 0 to 50 weight % of one or more polymers selected from the group consisting of polymers having a Hildebrand parameter (.sigma.) of not more than 3 MPA1/2 different from that of said one or more co or homopolymers.

2. The degradable polymeric foam according to claim 1, having a density of less than 12 lb/cubic foot.

3. The degradable polymeric foam according to claim 2, wherein said polymer having a Hildebrand parameter of not more than 3 MPA1/2 is selected from the group consisting of:
(i) polymers comprising:
(a) from 100 to 50 weight % of one or more C8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C1-4 alkyl radical; and (b) from 0 to 50 weight % of one or more monomers selected from the group consisting of C1-6 alkyl esters of C3-6 ethylenically unsaturated carboxylic esters, anhydrides of C4-6 ethylenically unsaturated dicarboxylic acids and C3-6 alkenyl nitriles which polymers may optionally contain up to 15% of an impact modifier which is a rubbery polymer of one or more C4-6 conjugated diolefins;
(ii) polymers comprising:
(a) homopolymers of C2-6 alkenyl halides;
(iii) polymers comprising co and homopolymers of C2-4 olefins;
(iv) polycarbonates;
(v) polymers comprising:
from 100 to 50 weight % of one or more C1-6 alkyl or hydroxy allyl acrylates or methacrylates; from 0 to 50 weight % of one or more C8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C1-4 allyl radical which polymers have been imidized to at least 10%;
(vi) polymers of amides of C3-6 ethylenically unsaturated carboxylic acids;
(vii) poly phenylene ethers (also called polyphenylene oxides);
(viii) polysulphones;
(ix) polysiloxaines;
(x) polyimines;
(xi) polyesters of C8-10 aromatic dicarboxylic acids and C2-4 alkylene glycols;
(xii) polyacetals;
(xiii) cellulose esters; and (xiv) ionomers.

4. The foam according to claim 3, wherein having a density of not greater than 8 lb/cubic foot.

5. The foam according to claim 4, wherein said polymer having monomer residues of Formula I and/or II has an intrinsic viscosity of not less than 1.5.

6. The foam according to claim 5, wherein said polymer comprises a homopolymer of monomer residues of formula II.

7. The foam according to claim 5, wherein said polymer is a co or homopolymer of Formula I and is selected from the group consisting of homopolymers of glycolic acid, homopolymers of .beta.-hydroxy butyrate, homopolymers of hydroxy valeric acid and copolymers of B-hydroxy butyric acid and hydroxy valeric acid.

8. The foam according to claim 5, comprising a blend of polymers of comprising monomer residues of formula II and polymers comprising monomer residues of Formula I.

9. The foam according to claim 8, where in said polymer comprising monomer residues of Formula II is a homopolymer of lactic acid and the polymer comprising monomer residues of Formula I is a co or homopolymer of one or more monomers selected from the group consisting of .beta.-hydroxy butyrate and hydroxy valeric acid.

10. The foam according to claim 5, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

11. The foam according to claim 10, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

12. The foam according to claim 6, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

13. The foam according to claim 12, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

14. The foam according to Claim 7, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

15. The foam according to claim 14, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

16. The foam according to claim 8, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

17. The foam according to claim 16, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

18. The foam according to claim 9, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

19. The foam according to claim 18, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

20. A process for preparing a polymeric foam having a density of not more than 16 lb/cubic foot comprising a polymer alloy comprising:
(i) from 50 to 100% of one or more co or homopolymers having a molecular weight of greater than 40,000 comprising the residues of one or more monomers of the Formula:
-OCR1R2(CR3R4)nCO- I
and -OCH(CH3)CO- II
wherein in Formula I, R1, R2, R3, and R4 are independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical, and n is O or an integer from 1 to 5, provided that when a monomer residue of Formula II is present and in Formula I n is 1 and R2, R3, and R4 are hydrogen, R1 can not be a methyl radical; and (ii) from 0 to 50 weight % of one or more polymers selected from the group consisting of polymers having a Hildebrand parameter (.sigma.) of not more than 3 MPA1/2 different from that of said one or more co or homopolymers which comprises passing a melt of said polymer alloy through a heated shear zone and concurrently injecting into said melt at pressures up 5,000 psi a gaseous or liquid blowing agent which will not significantly decompose the polymer alloy; extruding the melt; and letting the melt expand.

21. The process according to claim 20, wherein said heated shear zone comprises the barrel of an extruder.

22. The process according to claim 21, where in said heated shear zone is heated to temperatures up to 180°C.

23. The process according to claim 22, wherein said heated shear zone is operated at pressures up to 5,000 psi.

24 The process according to claim 23, wherein said extruder is a single screw extruder.

25. The process according to claim 24, wherein the screw in said single screw extruder comprises one or more zones with or without flights and which contain mixing pins.

26. The process according to claim 25, wherein said blowing agent is selected from the group consisting of C3-6 alkanes, C2-4 alkanes which are substituted by not less than three halogen atoms selected from the group consisting of chlorine and fluorine atoms; and carbon dioxide.

27. The foam according to claim 26, wherein said polymer having monomer residues of Formula I and/or II has an intrinsic viscosity of not less than 1.5.

28. The process according to claim 27, wherein said polymer alloy comprises a homopolymer of monomer residues of Formula II.

29. The foam according to claim 28, wherein said polymer is a co or homopolymer of Formula I and is selected from the group consisting of homopolymers of glycolic acid, homopolymers of .beta.-hydroxy butyrate, homopolymers of hydroxy valeric acid and copolymers of .beta.-hydroxy butyric acid and hydroxy valeric acid.

30. The foam according to claim 27, comprising a blend of polymers of comprising monomer residues of Formula II and polymers comprising monomer residues of Formula I.

31. The foam according to claim 30, where in said polymer comprising monomer residues of Formula II is a homopolymer of lactic acid and the polymer comprising monomer residues of Formula I is a co or homopolymer of one or more monomers selected from the group consisting of .beta.-hydroxy butyrate and hydroxy valeric acid.

32. The foam according to claim 27, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

33. The foam according to claim 32, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

34. The foam according to claim 28, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

35. The foam according to claim 34, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

36. The foam according to claim 29, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

37. The foam according to claim 36, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

38. The foam according to claim 30, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

39. The foam according to claim 38, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.

40. The foam according to claim 31, wherein said polymer has been filled with from 5 - 45 weight % of a filler.

41. The foam according to claim 40, wherein said filler is selected from the group consisting of starch, functionalized starch, functionalized cellulose, wood flour, flour of nut shells, cotton and linen fiber, flock or flour, or a mixture thereof.