Polylactide blends

0001The present invention relates to biodegradable polymer alloys. More particularly the present invention relates to polymer alloys comprising a polymer of lactic acid and one or more polymers of the general classes alkylene oxides, vinyl ethers, styrene-butadiene polymers which may be functionalized and which may also be hydrogenated EPDM polymers and polyurethanes.

0002This application is a divisional application of European Patent Application No. 92304651.0 which was published as EP 0 515203A.

0003There are a number of patents relating to co- and homo-polymers of lactic acid or the lactide of lactic acid. Generally these patents relate to the use of such polymers in biodegradable medical applications such as sutures, orthopaedic pins and plates and controlled release delivery systems for drugs. With the current concerns over the problems with land fill and the disposal of waste there has been an increasing awareness that biodegradable polymers might have application in a number of non-medical applications such as packaging.

0004Patent Co-operation Treaty Patent Application WO 90/01521 filed in the name of the Battelle Memorial Institute, published February 22, 1990 discloses that the properties of polylactide polymers may be improved by incorporating into the polymer either residual monomer or lactide oligomers. The patent application also discloses that the plasticized polymers may be further blended with other alloys such as a polymer of ethylene terephthalate or a polymer or copolymer of styrene, ethylene, vinyl chloride, vinyl acetate, alkyl methacrylates, alkyl acrylates and physical mixtures thereof (page 73, line 32 through page 74, line 4). However, the Battelle patent application does not suggest or disclose the polymer alloys of the present invention. Furthermore, none of the rather extensive prior art disclosed in the Battelle Patent Application suggests or discloses the polymer alloys of the present invention.

0005The present invention seeks to provide flexible polylactide polymer alloys. In a preferred embodiment of the present invention the alloys have a high degree of transparency or are translucent.

0006The present invention provides a polymer alloy comprising from 60 to 98 weight % of one or more polymers selected from: co- and homo-polymers of D, L, or DL, lactic acid and from 2 to 40 weight percent of one or more polymers selected from: <ul id="ul0001" list-style="none" compact="compact"><li>(i) co- and homo-polymers of one or more C_2-6 alkylene oxides;</li><li>(ii) co- and homo-polymers of a C_2-6 alkylene ether of a C_2-10 alkanol;</li><li>(iii) polymers comprising at least two C_2-3 alpha olefins;</li><li>(iv) terpolymers comprising from 95 to 99.5 weight % of at least two alpha C_2-3 olefins and from 5 to 0.5 weight % of a non-conjugated diolefin;</li><li>(v) synthetic co- and homo-polymers comprising one or more monomers selected from C_4-6 conjugated diolefins which are unsubstituted or substituted by a halogen atom;</li><li>(vi) copolymers comprising: <ul id="ul0002" list-style="none" compact="compact"><li>(a) from 60 to 99 weight % of one or more monomers selected from C_4-6 conjugated diolefins;</li><li>(b) from 1 to 40 weight % of one or more monomers selected from C_2-4 alkenyl nitriles; and</li><li>(c) from 0 to 5 weight % of one or more monomers selected from: <ul id="ul0003" list-style="none" compact="compact"><li>(1) C_3-6 ethylenically unsaturated carboxylic acids;</li><li>(2) C_4-6 ethylenically unsaturated dicarboxylic acids and anhydrides of such acids;</li><li>(3) amides of C_3-6 ethylenically unsaturated carboxylic acids; and</li><li>(4) C_3-6 ethylenically unsaturated aldehydes;</li></ul></li></ul></li><li>(vii) copolymers of isoprene and isobutylene in a molar ratio from 1:99 to 3:97 which copolymers are unhalogenated or halogenated with up to 3 weight % of chlorine or bomine; and</li><li>(viii) a polyurethane thermoplastic elastomer.</li></ul>

0007The polymers (i) to (viii) listed above may be used alone or in combination with copolymers comprising from 80 to 20 weight % of one or more C_8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C_1-4 alkyl radical, from 20 to 80 weight % of one or more C_4-6 conjugated diolefins and from 0 to 5 weight % of one or more functional monomers selected from: <ul id="ul0004" list-style="none" compact="compact"><li>(a) C_3-6 ethylenically unsaturated carboxylic acids;</li><li>(b) C_4-6 ethylenically dicarboxylic acids and anhydrides of such acids;</li><li>(c) amides of C_3-6 ethylenically unsaturated carboxylic acids; and</li><li>(d) C_3-6 ethylenically unsaturated aldehydes, which polymers are unhydrogenated or hydrogenated to not less than 80%.</li></ul>

0008As used in this specification the phrase homopolymers of D, L, or DL lactic acid is intended to include polymers prepared from lactic acid per se and polymers prepared from the various lactide optical isomers.

0009Lactides are dimers of lactic acid and may have a D, L, or a DL, (or meso) configuration. The polymers of the D or L configuration may have improved thermal and physical properties over the polymers prepared from the DL or a mixture of isomers. The polymers may have a molecular weight greater than about 60,000, preferably greater than 80,000. However, as noted in the Battelle patent application the polymers tend to be stiff and brittle. Therefore, it is desirable to find ways to improve the properties of the polymers.

0010Lactide polymers may be alloyed or blended with the above noted polymers. The ratio of lactide polymer to alloy polymer may range from 60:40 to about 98:2, preferably from 70:30 to 95:5 most preferably from 75:25 to 90:10

0011As used in this specification the term polymer when used in association with polymers other than those of lactic acid means a polymer having a degree of polymerization (DP) of at least 10.

0012The lactide polymer may be alloyed with a polymeric C_2-6, preferably C_2-4 alkylene oxide (also referred to as alkylene glycols) such as polyethylene oxide or polypropylene oxide. The polyalkylene oxide may have a molecular weight from about 8,000 up to about 100,000, preferably from about 8,000 to about 60,000, most preferably from about 10,000 to 40,000.

0013The lactide polymer may be alloyed with a polymeric C_2-6 alkylene ether of C_2-10 alkanol. The ether may have a molecular weight from about 50,000 to about 150,000, preferably from about 80,000 to 120,000. An alkylene ether is vinyl alcohol; although other higher homologues may be used.

0014The lactide polymer may be alloyed with a polymer comprising at least two C_2-3 alpha olefins. Suitable alpha olefins include C_2-3 and alpha olefins. Such polymers may have an ethylene weight ratio from about 75:25 to about 50:50.

0015The lactide polymer may be alloyed with a terpolymer comprising from 95 to 99.5 weight % of at least two alpha C_2-3 olefins and from 5 to 0.5 weight % of one or more C_5-12 non-conjugated diolefin. Preferably the terpolymer may comprise from 97 to 99.5 weight % of at least two alpha C_2-3 olefins and from 3 to 0.5 weight % of a non-conjugated diolefin. Suitable alpha olefins include ethylene and propylene. The weight ratio of ethylene to propylene may be from 75:25 to 50:50. Suitable C_5-12 non-conjugated diene monomers include 5-ethylidene-2-norbornene, 1,4-hexadiene, and dicyclopentadiene.

0016The lactide polymer may be alloyed with a synthetic homo- or co-polymer comprising one or more monomers selected from C_4-6 conjugated diolefins which are unsubstituted or substituted by a halogen atom. Some suitable C_4-6 conjugated diolefins have been listed above. Particularly suitable polymers include polybutadiene and polychloroperne. The polymer of the C_4-6 conjugated diolefin may be stereo specific, that is it may be in a trans- or cis-configuration or have a pendent vinyl group. The polymers may have a medium cis content of at least about 55%. Such polymers are commercially available under the trademrkas TAKTENE 550® available from Polysar Rubber Corporation and DIENE 55® available from the Firestone Company. The polymers may have a high cis content of more than 90, preferably more than about 95%. Such polymers are available from Polysar Rubber Corporation under the trademark TAKTENE®

0017The lactide polymer may be alloyed with one or more copolymers comprising: <ul id="ul0005" list-style="none" compact="compact"><li>(a) from 60 to 99 weight % of one or more monomers selected from C_4-6 conjugated diolefins;</li><li>(b) from 1 to 40 weight % of one or more monomers selected from C_2-4 alkenyl nitriles; and</li><li>(c) from 0 to 5 weight % of one or more monomers selected from : <ul id="ul0006" list-style="none" compact="compact"><li>(1) C_3-6 ethylenically unsaturated carboxylic acids;</li><li>(2) C_4-6 ethylenically unsaturated dicarboxylic acids and anhydrides of such acids;</li><li>(3) amides of C_3-6 ethylenically unsaturated carboxylic acids; and</li><li>(4) C_3-6 ethylenically unsaturated aldehydes;</li></ul></li></ul>

0018Such polymers are typically called nitrile rubbers or caboxylated nitrile rubbers. Preferably the polymers comprise from 60 to 95% of one or more C_4-6 conjugated diolefins, form 40 to 5% of one or more C_1-4 alkenyl nitriles. The polymer need not contain a functional coup such as a carboxylic acid, an anhydride of a carboxylic acid, or an amide of a carboxylic acid. However, if one or more of such functional groups are present then they are preferably present in an amount from about 0.5 to 3 weight % and typically the amount of conjugated diolefin would decrease correspondingly. Some functional monomers have been discussed above. Suitable C_4-6 conjugated diolefins include those discussed above and chloroprene. Suitable C_2-4 alkenyl nitriles include acrylonitrile and methacrylonitrile.

0019The lactide polymer may be alloyed with copolymers of isoprene and isobutylene in a molar ratio from 1:99 to 3:97. Such polymers may be unhalogenated or halogenated with up to about 3 weight % of chlorine or bromine. Such polymers are commercially available and are commonly referred to as butyl rubbers.

0020The lactide polymer may be alloyed with a polyurethane thermoplastic elastomer. The polyurethane may be a polyether urethane or a polyester urethane. A preferred polyurethane or a polyester urethane. A preferred polyurethane is a polyester urethane most preferably based on adipic acid or caprolactone. The polyester urethane may have a molecular weight from about 10,000 to about 150,000.

0021The polymers detailed above may additionally be alloyed with a copolymer of a vinyl aromatic monomer and a conjugated diene and optionally one or more functional monomers. Such a polymer may be a random polymer, a linear block, or a radial block polymer. The vinyl aromatic-conjugated diene polymer may comprise from 80 to 20 weight % of one or more C_8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C_1-4 alkyl radical and from 20 to 80 weight % of one or more C_4-6 conjugated diolefins and from 0 to 5 weight % of one or more functional monomers selected from : <ul id="ul0007" list-style="none" compact="compact"><li>(a) C_3-6 ethylenically unsaturated carboxylic acids;</li><li>(b) C_4-6 ethylenically unsaturated dicarboxylic acids and anhydrides of such acids;</li><li>(c) amides of C_3-6 ethylenically unsaturated carboxylic acids; and</li><li>(d) C_3-6 ethylenically unsaturated aldehydes which polymers are unhydrogenated or hydrogenated to not less than 80%.</li></ul>

0022Preferably the polymer of vinyl aromatic monomer and conjugated diolefin comprises: from 60 to 40 weight % of one or more C_8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C_1-4 alkyl radical and from 40 to 60 weight % of one or more C_4-6 conjugated diolefins and from 0 to 3 weight % of one or more functional monomers selected from : <ul id="ul0008" list-style="none" compact="compact"><li>(a) C_3-6 ethylenically unsaturated carboxylic acids;</li><li>(b) C_4-6 ethylenically unsaturated dicarboxylic acids and anhydrides of such acids;</li><li>(c) amides of C_3-6 ethylenically unsaturated carboxylic acids; and</li><li>(d) C_3-6 ethylenically unsaturated aldehydes.</li></ul>

0023The polymer of vinyl aromatic monomer and conjugated diolefin need not comprise any functional monomer. That is it may comprise only vinyl aromatic monomer and conjugated diolefin.

0024The vinyl aromatic and conjugated diene copolymer may be unhydrogenated or it may be hydrogenated to at least 80, preferably 90, most preferably greater than 95 weight %. An hydrogenated vinyl aromatic and conjugated diene polymer may be a linear or radial, preferably linear, block copolymer comprising from 40 to 60 weight % of vinyl aromatic monomer, from 60 to 40 weight % of conjugated diolefin and from 0.5 to 3 weight % of an anhydride of a C_4-6 ethylenically unsaturated carboxylic acid which polymer has been hydrogenated to at least 90 weight %.

0025Suitable vinyl aromatic monomers include styrene, alpha methyl styrene, and tertiary butyl styrene. A particularly suitable vinyl aromatic monomer is styrene. Suitable conjugated diolefin monomers include 1,4 butadiene, and isoprene.

0026The alloys of the present invention may be prepared by conventional processing techniques. That is the polymeric components may be blended in a tumble blender at a suitable weight ratio. The dry blend may be extruded using conventional techniques known to those skilled in the art. The dwell time, temperature and shear rate in the exruder are selected so that the alloy and particularly the lactide polymer will not undergo significant degradation during the extrusion process. Generally the temperatures in the extruder should not exceed 20, preferably less than 10, degrees above the melting temperature of the lactide polymer. For example, in a single screw extruder having a D to L ratio of 1:24 the operating temperature should not exceed about 200 degrees Centigrade and the operating rate should be from about 50 to 150, preferably from about 75 to 120 RPMs.

0027Of course, if a suitable common solvent can be found the alloy could be prepared by solution blending. However, the requirement to use and remove solvents which are typically organic is less desirable due to environmental regulation.

0028The alloys may be prepared by reactive blending. That is the lactide may be used in monomer or partially or fully polymerized form. The resulting mass is then reacted preferably in the presence of a catalyst at atmospheric pressure at temperatures up to about 10 degrees above the melting to polylactide homopolymer.

0029A catalyst may comprise metallic ester(s) of C_2-10, preferably C_6-10 carboxylic acids. Suitable metals include tin and zinc.

0030The catalyst concentration may be in the range from 0.01 to about 1, preferably from 0.01 to 0.3 weight % of the reactive mixture. The reaction time will vary depending on the type of reactor, mixing conditions and heat transferability of the reactor. Typically the residence times for the reaction/mixing will range from about 1 to 60 minutes.

0031The resulting base alloy may then be further compounded with suitable processing aids and other additives e.g. antioxidants, flame retardants and fillers. Typically these additives will not form more than about 50, preferably less than 25, most preferably less than about 15 weight % of the polymer alloy.

0032The resulting alloy may be converted into useful products using known techniques such as blow, injection and compression molding, and extrusion, and blow extrusion for thin films and relatively thin sheets. Extrusion techniques followed by thermoforming may be used to produce various products. The alloy my be injection or compression molded.

0033The alloy may be formed into thin sheets or films useful in packaging applications such as bags and blister packaging.

0034As noted in the specification the alloys may have a high degree of translucence or may even be transparent while at the same time having good flexibility.

0035The present invention will now be illustrated by the following non-limiting examples in which unless otherwise specified parts by weight and % is weight %. In the table the ratio of lactide polymer (BP) to alloy polymer (X) is a weight ratio.

<b>Example 1</b>

0036A sample of polylactide polymer (L polylactide) was charged to a Brabender mixer under a 10 kg ram weight. The bowl of the Brabender was heated to 180 degrees C. The mixing continued until a constant torque. Then a sample of alloy polyer was added to the Brabender and the torque initially fell then mixing continued until a constant torque was obtained. The sample was allowed to cool to about 20 degrees C and the sample was then removed from the Brabender. The resulting sample was then compression molded as a thin sheet. The exudence of the alloy (e.g. the tendency of the soft phase to migrate to the surface of the alloy), transparency, flexibility and crazing of the resulting sheet were then subjectively measured. The results and the scale for measuring results are set forth in Table 1. <tables id="tabl0001" num="0001"><img file="EP0748846A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0748846A2_D0002.tif" /></tables> The results show that the alloys of the present invention have good flexibility and may be compounded to obtain high translucence or even transparent sheets or films.

0037In the present application's disclosure of the present invention, any numerical value includes the precise value and any value "about" or "essentially" or "substantially" the same as the precise value. The wording of the appended claims and abstract is incorporated into the present description.