Biodegradable packaging thermoplastics from lactides

Environmentally biodegradable compositions of poly(lactic acid) plasticized with lactic acid, D-lactide, L-lactide, meso D,L-lactide, racemic D,L-lactide, oligomers of lactic acid, oligomers of lactide, derivatives of oligomers of lactic acid, or various mixtures thereof; the compositions are suitable replacements of thermoplastic polymer compositions; the compositions are useful for pliable films and other packaging applications conventionally served by polyethylene and other nondegradable thermoplastics; homopolymers or copolymers of D-lactic acid, L-lactic acid, D-lactide, L-lactide, meso D,L-lactide, and/or racemic D,L-lactide having properties similar to other known polymers may be prepared by varying the ratios of monomer and polymerization conditions, the amount and type of plasticizer in the polymer and process conditions; additives and subsequent treatment are also used to modify properties.

FIELD OF THE INVENTION 
The present invention relates to plasticized biodegradable polymers of 
L-lactide, D-lactide, D,L-lactide and mixtures thereof suitable for 
packaging applications conventionally served by nondegradable plastics 
(e.g. polyethylene). The invention further relates to a method for 
producing pliable films and other packaging items from such polymers and 
to the unique product thereof. The invention has utility in producing a 
product that has the physical characteristics of the usual film forming 
plastics, yet is biodegradable. 
The present application is related to the application entitled 
BIODEGRADABLE REPLACEMENT OF CRYSTAL POLYSTYRENE, having Ser. No. 
07/579,465, the application entitled BLENDS OF POLYLACTIC ACID, having 
Ser. No. 07/579,000, and the application entitled DEGRADABLE IMT 
MODIFIED POLYLACTIC ACID, having Ser. No. 07/579,460, all having the same 
assignee and filing date as the present application, the disclosures of 
which are incorporated by reference herein. 
BACKGROUND OF THE INVENTION 
There is a need for an environmentally biodegradable packaging 
thermoplastic as an answer to the tremendous amounts of discarded plastic 
packaging materials. U.S. plastic sales in 1987 were 53.7 billion pounds 
of which 12.7 billion pounds were listed as plastics in packaging. A 
significant amount of this plastic is discarded and becomes a plastic 
pollutant that is a blot on the landscape and a threat to marine life. 
Mortality estimates range as high as 1-2 million seabirds and 100,000 
marine mammals per year. 
A further problem with the disposal of plastic packaging is the concern for 
dwindling landfill space. It has been estimated that most major cities 
will have used up available landfills for solid waste disposal by the 
early 1990's. Plastics comprise approximately 3 percent by weight and 6 
percent of the volume of solid waste. 
One other disadvantage of conventional plastics is that they are ultimately 
derived from petroleum, which leaves plastics dependent on the 
uncertainties of foreign crude oil imports. A better feedstock would be 
one that derives from renewable, domestic resources. 
However, there are good reasons for the use of packaging plastics. They 
provide appealing aesthetic qualities in the form of attractive packages 
which can be quickly fabricated and filled with specified units of 
products. The packages maintain cleanliness, storage stability, and 
desirable qualities such as transparency for inspection of contents. These 
packages are known for their low cost of production and chemical 
stability. This stability, however leads to very long life of plastic, so 
that when its one time use is completed, discarded packages remain on, and 
in, the environment for incalculably long times. 
The polymers and copolymers of lactic acid have been known for some time as 
unique materials since they are biodegradable, biocompatible and 
thermoplastic. These polymers are well behaved thermoplastics, and are 100 
percent biodegradable in an animal body via hydrolysis over a time period 
of several months to a year. In a wet environment they begin to show 
degradation after several weeks and disappear in about a year's time when 
left on or in the soil or seawater. The degradation products are lactic 
acid, carbon dioxide and water, all of which are harmless. 
In practice, lactic acid is converted to its cyclic dimer, lactide, which 
becomes the monomer for polymerization. Lactic acid is potentially 
available from inexpensive feedstocks such as cornstarch or corn syrup, by 
fermentation, or from petrochemical feedstocks such as ethylene. Lactide 
monomer is conveniently converted to resin by a catalyzed, melt 
polymerization, a general process well-known to plastics producers. By 
performing the polymerization from an intermediate monomer, versatility in 
the resin composition is permitted. Molecular weight can be easily 
controlled. Compositions can be varied to introduce specific properties. 
Homopolymers and copolymers of various cyclic esters such as glycolide, 
lactide, and the lactones have been disclosed in numerous patents and 
scientific publications. Early patents disclosed processes for 
polymerizing lactic acid, lactide, or both, but did not achieve high 
molecular weight polymers with good physical properties, and the polymer 
products were frequently tacky, sticky materials. See, for example, U.S. 
Pat. Nos. 1,995,970; 2,362,511; 2,683,136; and 3,565,869. The Lowe patent, 
U.S. Pat. No. 2,668,162, teaches the use of pure glycolide and lactide to 
achieve high molecular weight polymers and copolymers of lactide. 
Copolymerization of lactide and glycolide imparted toughness and improved 
thermoplastic processability as compared to the homopolymers. Emphasis was 
placed on orientable, cold-drawable fibers. Films are described as 
self-supporting, or stiff, tough, and either clear or opaque. The polymers 
were high melting and stiff. U.S. Pat. No. 3,565,869 discloses the typical 
attitude to the presence of monomer in polyglycolide--the removal of the 
monomer from the product. In U.S. Pat. No. 2,396,994, Filachione et al 
disclose a process for producing poly(lactic acids) of low molecular 
weights from lactic acid in the presence of a strong mineral acid 
catalyst. In U.S. Pat. No. 2,438,208, Filachione et al disclose a 
continuous process for preparing poly(lactic acid) with an acidic 
esterification catalyst. In U.S. Pat. No. 4.683,288, Tanaka et al disclose 
the polymerization or copolymerization of lactic and/or glycolic acid with 
a catalyst of acid clay or activated clay. The average molecular weight of 
the polymer is at least 5,000 and preferably 5,000-30,000. In U.S. Pat. 
No. 4,789,726, Hutchinson discloses a process for production of 
polylactides or poly (lactide-co-glycolide) of specified low-medium 
molecular weight, by controlled hydrolysis of a higher molecular weight 
polyester. 
Similar disclosures in the patent and other literature developed the 
processes of polymerization and copolymerization of lactide to produce 
very strong, crystalline, orientable, stiff polymers which were fabricated 
into fibers and prosthetic devices that were biodegradable and 
biocompatible, sometimes called absorbable. The polymers slowly 
disappeared by hydrolysis. See, for example, U.S. Pat. Nos. 2,703,316; 
2,758,987; 3,297,033; 3,463,158; 3,498,957; 3,531,561; 3,620,218; 
3,636,956; 3,736,646; 3,797,499; 3,839,297; 3,982,543; 4,243,775; 
4,438,253; 4,496,446; 4,621,638; European Patent Application EP0146398, 
International Application WO 86/00533, and West German Offenlegungsschrift 
DE 2118127 (1971). U.S. Pat. Nos. 4,539,981 and 4,550,449 to Tunc teach 
high molecular weight materials suitable for prosthetic devices, while in 
EP 321,176 (1989) Tunc discloses a process for orienting resorbable 
thermoplastic members made from polylactides disclosed in the U.S. 
patents. U.S. Pat. No. 4.603,695 discloses sheet surgical adhesion 
preventatives. U.S. Pat. No. 4,534,349 discloses molded medical devices 
for nerve repair. R. G. Sinclair et al in, Preparation and Evaluation of 
Glycolic and Lactic Acid-Based for Implant Devices Used in Management of 
Maxillofacial Trauma, I; AD748410. National Technical Information Service, 
prepares and evaluates polymers and copolymers of L-lactide and glycolide, 
the polymers were light brown in the case of the polyglycolide with 
increasing color in the case of the polymers incorporating more lactide, 
in a second series of polymers the homopolymer of lactide was a snow white 
crystalline solid. 
Other patents teach the use of these polymers as stiff surgical elements 
for biomedical fasteners, screws, nails, pins, and bone plates. See, for 
example, U.S. Pat. Nos. 3,739,773; 4,060,089; and 4,279.249. 
Controlled release devices, using mixtures of bioactive substances with the 
polymers and copolymers of lactide and/or glycolide, have been disclosed. 
See, for example, U.S. Pat. Nos. 3,773,919; 3,887,699; 4,273,920; 
4,419,340; 4,471,077; 4,578,384; in 4,728,721, Yamamoto et al disclose the 
treatment of biodegradable high molecular weight polymers with water or a 
mixture of water and water soluble organic solvents so as to remove 
unreacted monomer or monomers and polymers of low polymerization degree. 
Poly(lactic acid) and copolymers of lactic and glycolic acid of 2,000 to 
50,000 molecular weight are prepared by direct condensation for use as an 
excipient for microcapsules; R. G. Sinclair, in Environmental Science & 
Technology, 7 (10), 955 (1973). R. G. Sinclair, Proceedings, 5th 
International Symposium on Controlled Release of Bioactive Materials, 5.12 
and 8.2, University of Akron Press, 1978. These applications of lactide 
polymers and copolymers required tough, or glassy materials, that were 
grindable and did not disclose physical properties for obvious use in 
thermoplastic packaging materials. R. G. Sinclair in, Lactic Acid 
Polymers--Controlled Release Applications for Biomedical Use and Pesticide 
Delivery; Proc. of the First Annual Corn Util. Conf., p. 211, Jun. 11-12, 
1987, discusses some of the advantages of lactides as homopolymers and as 
copolymers with glycolide and caprolactones. 
Some mention has been disclosed in the prior art for use of lactide 
copolymers for packaging applications. Thus, in the aforementioned patent 
to Lowe, clear, self-supporting films are noted of a copolymer of lactide 
and glycolide. In U.S. Pat. No. 2,703,316 lactide polymers are described 
as film formers, which are tough and orientable. "Wrapping tissue" was 
disclosed that was tough, flexible, and strong, or pliable. However, to 
obtain pliability the polylactide must be wet with volatile solvent, 
otherwise, stiff and brittle polymers were obtained. This is an example of 
the prior art which teaches special modifications of lactide polymers to 
obtain pliability. Thus, in U.S. Pat. No. 3,021,309, lactides are 
copolymerized with delta valerolactone and caprolactone to modify lactide 
polymers and obtain tough, white, crystalline solids. Soft, solid 
copolymer compositions are mentioned only with the copolymer of 
caprolactone and 2,4-dimethyl-4-methoxymethyl-5-hydroxypentanoic acid 
lactone, not with lactide compositions. U.S. Pat. No. 3,284,417 relates to 
the production of polyesters which are useful as plasticizers and 
intermediates for the preparation of elastomers and foams. This patent 
excludes lactides and uses compositions based on 7 to 9 membered ring 
lactones, such as epsilon caprolactone, to obtain the desired 
intermediates. No tensile strength, modulus, or percent elongation data 
are given. U.S. Pat. No. 3,297,033 teaches the use of glycolide and 
glycolide-lactide copolymers to prepare opaque materials, orientable into 
fibers suitable for sutures. It is stated that "plasticizers interfere 
with crystallinity, but are useful for sponge and films". Obvious in these 
disclosures is that the lactide polymers and copolymers are stiff unless 
plasticized. This is true also of U.S. Pat. No. 3.736,646, where 
lactide-glycolide copolymers are softened by the use of solvents such as 
methylene chloride, xylene, or toluene. In U.S. Pat. No. 3,797,499 
copolymers of L-lactide and D,L-lactide are cited as possessing greater 
flexibility in drawn fibers for absorbable sutures. These fibers have 
strengths greater than 50.000 psi with elongation percentages of 
approximately 20 percent. Moduli are about one million psi. These are 
still quite stiff compositions compared to most flexible packaging 
compositions, reflecting their use for sutures. U.S. Pat. No. 3,844,987 
discloses the use of graft and blends of biodegradable polymers with 
naturally occurring biodegradable products, such as cellulosic materials, 
soya bean powder, rice hulls, and brewer's yeast, for articles of 
manufacture such as a container to hold a medium to germinate and grow 
seeds or seedlings. These articles of manufacture are not suitable for 
packaging applications. 
U.S. Pat. No. 4,620,999 discloses a biodegradable, disposable bag 
composition comprised of polymers of3-hydroxybutyrate and 
3-hydroxybutyrate/3-hydroxyvalerate copolymer. Lactic acid, by comparison, 
is 2-hydroxy propionic acid. U.S. Pat. No. 3,982,543 teaches the use of 
volatile solvents as plasticizers with lactide copolymers to obtain 
pliability. U.S. Pat. Nos. 4,045,418 and 4,057,537 rely on 
copolymerization of caprolactone with lactides, either L-lactide, or 
D,L-lactide, to obtain pliability. U.S. Pat. No. 4,052,988 teaches the use 
of poly (p-dioxanone) to obtain improved knot tying and knot security for 
absorbable sutures. U.S. Pat. Nos. 4,387,769 and 4,526,695 disclose the 
use of lactide and glycolide polymers and copolymers that are deformable, 
but only at elevated temperatures. European Patent Application 0108933 
using a modification of glycolide copolymers with polyethylene glycol to 
obtain triblock copolymers which are taught as suture materials. As 
mentioned previously, there is a strong consensus that pliability is 
obtained in lactide polymers only by plasticizers which are fugitive, 
volatile solvents, or other comonomer materials. 
Copolymers of L-lactide and D,L-lactide are known from the prior art, but 
citations note that pliability is not an intrinsic physical property. The 
homopolymers of L-lactide and D,L-lactide, as well as the 75/25, 50/50, 
and 25/75, weight ratio, of L-/D,L-lactide copolymers are exampled in U.S. 
Pat. No. 2,951,828. The copolymers have softening points of 
110.degree.-135.degree. C. No other physical property data are given 
relating to stiffness and flexibility. The 95/5, 92.5/7.5, 90/10, and 
85/15, weight ratio, of L-lactide/D,L-lactide copolymers are cited in U.S. 
Pat. Nos. 3,636,956 and 3,797,499. They are evaluated as filaments from 
drawn fibers and have tensile strengths in excess of 50,000 psi, moduli of 
about one million psi, and percent elongations of approximately 20 
percent. Plasticizers, the same as in U.S. Pat. No. 3,636,956, above, were 
used to impart pliability. A snow-white, obviously crystalline polymer, is 
cited in Offenlegungsschrift 2118127 for a 90/10, L-lactide/D,L-lactide 
copolymer. No physical properties were given for this copolymer. The 
patent teaches the use of surgical elements. 
Canadian Patent 808,731 cites the copolymers of L- and D,L-lactide where a 
divalent metal of Group II is part of the structure. The 90/10, 
L-/D,L-lactide copolymer (Example 2) and the L-lactide homopolymer were 
described as "suitable for films and fibers". The 90/10 copolymer is 
described as a snow-white copolymer and the homopolymer of L-lactide can 
be molded to transparent films. (The more crystalline polymer should be 
the opaque, or snow-white material, which is the homopolymer.) The patent 
discloses "the fact that the novel polylactides of the present invention 
contain the metallic component of the catalyst in the form of a lactate is 
believed to be of significance". Furthermore, "the polylactides find 
utility in the manufacture of films and fibers which are prepared by 
conventional thermoplastic resin manufacturing methods". No physical 
property data are given on the strength and flexibility of the films. 
Canadian Patent 863,673 discloses compositions of L-lactide and D,L-lactide 
copolymers in the ratios of 97/3, 95/5, 92.5/7.5, 90/10, and 85/15 ratios 
of L-/D,L-lactide, respectively. These were all characterized as drawn 
filaments for surgical applications. Tensile strength, approximately 
100,000 psi, was high, elongation was approximately 20 percent and 
plasticizers were mentioned to achieve pliability. D,L-lactide 
compositions of less than 15 weight percent are claimed. 
Canadian Patent 923,245 discloses the copolymers of L- and D,L-lactide 
(Example 15). The 90/10 copolymer is described as a snow white 
polylactide. The polylactides prepared by the methods of the patent are 
stated to have utility in the manufacture of films or fibers prepared by 
conventional thermoplastic resin fabricating methods. 
U.S. Pat. No. 4,719,246 teaches the use of simple blending of poly L-and 
poly (D-lactide), referred to as poly (S-lactide) and poly (R-lactide). 
The examples are all physical mixtures. The special properties of the 
"interlocking" stem from racemic compound formation (cf. "Stereochemistry 
of Carbon Compounds", E. L. Eliel, McGraw-Hill, 1962, p. 45). Racemic 
compounds consist of interlocked enantiomers, that is, the D and L forms 
(or R and S) are bonded to each other by polar forces. This can cause a 
lowering, or raising, of the crystalline melting points, depending on 
whether the D to D (or L to L) forces are less, or greater, than the D to 
L forces. Required of polymer racemic compounds to enhance the effect (and 
stated in U.S. Pat. No. 4,719,246, Column 4, line 48) are homopolymers, or 
long chain lengths, of both D and L. The great symmetry or regularity of 
these structures permit them to fit together, or interlock, by very 
regular polar forces, either because they are the same, or mirror images. 
This leads to considerable crystallinity. The art of racemic compounds has 
a long history that goes back to classical chemistry. 
Additional related art includes: Low molecular weight poly D,L-lactide has 
been recently added to high molecular weight D,L-lactide along with a drug 
such as caffeine, salicylic acid, or quinidine, see R. Bodmeier et al, 
International J. of Pharm. 51, pp. 1-8, (1989). Chabot et al in 
polymerizing L-lactide and racemic D,L-lactide for medical applications 
removed residual monomer and lower oligomers, see Polymer, Vol. 24, pp. 
53-59, (1983). A. S. Chawla and Chang produced four different molecular 
weight D,L-lactide polymers but removed monomer for in vivo degradation 
studies, see Biomat., Med. Dev. Art. Org., 13(3&4), pp. 153-162, 
(1985-86). Kleine and Kleine produce several low residual monomer, 
poly(lactic acids) from D,L-lactide while determining lactide levels 
during the polymerization, see Macromolekulare Chemie, Vol. 30, pp. 23-38, 
(1959); Kohn et al also makes a low residual monomer product while 
monitoring the monomer content over time, see Journ. Appl. Polymer 
Science, Vol. 29, pp. 4265-4277, (1984). M. Vert et al teaches high 
molecular weight polylactides with elimination of residual monomer, see 
Makromol. Chem., Suppl. 5, pp. 30-41, (1981). M. Vert, in Macromol. Chem., 
Macromol. Symp. 6, pp.109-122, (1986), discloses similar 
poly(L-/D,L-lactide) polylactides, see Table 6, p. 118. In EP 311,065 
(1989) poly D,L-lactide is prepared as an implant material for drug 
delivery as the material degrades, the material contains drugs, low 
molecular weight polylactide, and other additives; EP 314,245 (1989) 
teaches a polylactide having a low amount of residual monomer, the polymer 
is prepared by polymerization of meso D,L-lactide or other monomers; West 
German Offenlegungsschrift DE 3,820,299 (1988) teaches the polymerization 
of meso D,L-lactide with lactides, however, the advantages of the present 
invention are not obtained. 
Nowhere in the prior art is it disclosed that lactic acid or lactide 
polymers, can be the source of pliable, highly-extensible compositions by 
the use of lactide monomers, or lactic acid, or oligomers of lactic acid, 
or derivatives of oligomers of lactic acid, or oligomers of lactide as the 
plasticizer. None of the prior compositions are suitable for well-defined 
packaging needs. 
BRIEF DESCRIPTION OF THE INVENTION 
The general teaching of the invention is that poly(lactic acids) derived 
from lactic acid (homopolymers or copolymers of L-lactic acid or D-lactic 
acid) or lactides (homopolymers or copolymers of L-lactide, D-lactide, 
meso D,L-lactide, and racemic D,L-lactide) that have been intimately 
plasticized with a plasticizer such as lactic acid, lactide, oligomers of 
lactic acid, oligomers of lactide, derivatives of oligomeric lactic acid 
(as used herein this term includes derivatives of oligomeric lactide), and 
various mixtures thereof, have utility as well behaved thermoplastics 
which can mimic properties of the usual environmentally very slowly 
degradable plastics, (e.g., the properties of polyethylene and the like). 
The term, intimately dispersed, as used herein means the material is 
homogeneously and intimately mixed with the polymer. Since both lactic 
acid and lactide can achieve the same repeating unit, the general term 
poly(lactic acid) as used herein refers to polymers having the repeating 
unit of formula I without any limitation as to how the polymer was made 
(e.g. from lactides, lactic acid, or oligomers), and without reference to 
the degree of polymerization or level of plasticization. 
In general, a first embodiment of the invention provides for an 
environmentally biodegradable composition useful as a replacement for 
thermoplastic polymer compositions comprising a poly(lactic acid), and a 
plasticizer selected from the groups below, wherein the plasticizer is 
intimately dispersed within the polymer. The poly(lactic acid) polymer has 
the repeating units of the formula, 
##STR1## 
wherein n is the number of repeating units and n is an integer equal to at 
least about 150. Preferably the unoriented composition has the physical 
properties of: 150.ltoreq.n.ltoreq.20,000, a tensile strength of about 300 
to about 20,000 psi, an elongation to failure of about 50 to about 1,000 
percent, and a tangent modulus of about 20,000 to about 250,000 psi. The 
intimate dispersion of the plasticizer can yield a substantially 
transparent composition, although, transparency may not be obtained with 
certain processes as when the composition is foamed. 
In a further embodiment the composition can be a replacement for 
polyethylene when the unoriented composition has a tensile strength of 
about 1,200 to about 4,000 psi, an elongation to failure of about 100 to 
about 800 percent, and a tangent modulus of about 20,000 to about 75,000 
psi. The composition can be a replacement for polypropylene when the 
unoriented composition has a tensile strength of about 4,500 to about 
10,000 psi, an elongation to failure of about 100 to about 600 percent, a 
tangent modulus of about 165,000 to about 225,000 psi, and a melting point 
of about 150.degree. C. to about 190.degree. F. 
A further embodiment of the invention provides a process for producing an 
environmentally biodegradable composition useful as a replacement for 
thermoplastic polymer compositions having the steps (a) polymerizing a 
lactide monomer selected from the group consisting of D-lactide, 
L-lactide, meso D,L-lactide, racemic D,L-lactide, and mixtures thereof, in 
the presence of a suitable catalyst; (b) controlling the polymerization to 
allow the reaction to be stopped prior to complete polymerization; (c) 
monitoring the level of remaining monomer; (d) stopping the polymerization 
prior to complete reaction so that unreacted monomer in a predetermined 
amount is trapped in association with the polymer; and (e) treating the 
polymer and unreacted monomer to obtain an intimately plasticized 
composition. The polymerization reaction is preferably stopped at a 
monomer level up to about 40 weight percent. If desired, additional 
plasticizer may be incorporated into the composition prior to, during, or 
after the treating step, wherein the plasticizer is selected from the 
group of plasticizers discussed below. The sum of remaining monomer and 
additional plasticizer is preferably below about 40 weight percent, and is 
most preferably between about 10 and about 40 weight percent for a pliable 
composition. 
A yet further embodiment includes a process for producing a plasticized 
polymer of poly(lactic acid) that comprises mixing, heating, and melting 
one or more lactide monomers and a catalyst; polymerizing the monomers of 
the solution to form a polymer without stopping the reaction; and 
incorporating plasticizer as described below into the formed polymer. 
A yet further embodiment includes a process for providing a poly(lactic 
acid) to which the described plasticizers may be added to obtain the 
desired properties. 
A yet further embodiment includes a process for the preparation of a 
biodegradable blown film through the inclusion of the below listed 
plasticizers in poly(lactic acid) to achieve desired properties followed 
by extrusion of the plasticized poly(lactic acid) as a blown film. 
Plasticizers useful with the invention include lactic acid, lactide, 
oligomers of lactic acid, oligomers of lactide, and mixtures thereof. The 
preferred oligomers of lactic acid, and oligomers of lactide are defined 
by the formula: 
##STR2## 
where m is an integer: 2.ltoreq.m.ltoreq.75. Preferably m is an integer: 
2.ltoreq.m.ltoreq.10. 
Further plasticizers useful in the invention include oligomeric derivatives 
of lactic acid, selected from the group defined by the formula: 
##STR3## 
where R=H, alkyl, aryl, alkylaryl or acetyl, and R is saturated, where 
R'=H, alkyl, aryl, alkylaryl or acetyl, and R' is saturated, where R and 
R' cannot both be H, where q is an integer: 2.ltoreq.q.ltoreq.75; and 
mixtures thereof. Preferably q is an integer: 2.ltoreq.q.ltoreq.10. 
For pliability, lactic acid or lactide monomer plasticizer is present in an 
amount of from about 10 to about 40 weight percent of the polymer, while 
plasticizers such as oligomers of lactide, or oligomers of lactic acid, 
and derivatives of oligomers of lactic acid may be present in an amount 
from about 10 to about 60 weight percent. This composition allows many of 
the desirable characteristics of nondegradable polymers, e.g. 
polyethylene, such as pliability, transparency, and toughness. In 
addition, the presence of plasticizer facilitates melt processing, 
prevents discoloration, and enhances the degradation rate of the 
compositions in contact with the environment. 
The intimately plasticized composition should be processed into a final 
product in a manner adapted to retain the plasticizer as an intimate 
dispersion in the polymer. The treatments to obtain an intimate dispersion 
include: (1) quenching the composition at a rate adapted to retain the 
plasticizer as an intimate dispersion; (2) melt processing and quenching 
the composition at a rate adapted to retain the plasticizer as an intimate 
dispersion; and (3) processing the composition into a final product in a 
manner adapted to maintain the plasticizer as an intimate dispersion. 
The composition may comprise from about 2 to about 60 weight percent 
plasticizer. When a lactide is selected, the composition preferably 
comprises from about 10 to about 40 weight percent lactide plasticizer 
selected from the group consisting of lactic acid, D-lactide, L-lactide, 
meso D,L-lactide, racemic D,L-lactide, and mixtures thereof. 
If desired, the plasticizer can be selected from the group of lactides 
consisting of D-lactide, L-lactide, meso D,L-lactide, racemic D,L-lactide 
and mixtures thereof so that at least part of the lactide plasticizer is 
stereochemically different from the monomer used to prepare the polymer. 
Similarly the plasticizer may comprise oligomers of lactide, or oligomers 
of lactic acid, or mixtures thereof, having the formula II, that are not 
produced during the production of the polymer. 
Particularly advantageous is the sequential incorporation of plasticizer 
into poly(lactic acid) to obtain a blended composition by melt blending 
with the poly(lactic acid), a first plasticizer selected from the group 
consisting of oligomers of lactic acid, oligomers of lactide, and mixtures 
thereof; and melt blending with the blend a second plasticizer selected 
from the group consisting of lactic acid, L-lactide, D-lactide, meso 
D,L-lactide, racemic D,L-lactide, and mixtures thereof. If desired, a 
first plasticizer defined by the formula III may be used alone or in 
admixture with an oligomer of formula II. This procedure allows the 
blending of the first plasticizer at a first temperature and the blending 
of the second plasticizer at a second temperature lower than the first 
temperature.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
The environmentally biodegradable compositions disclosed herein are 
completely degradable to environmentally acceptable and compatible 
materials. The intermediate products of the degradation, lactic acid, and 
short chain oligomers of lactide or lactic acid are widely distributed 
naturally occurring substances that are easily metabolized by a wide 
variety of organisms. Their natural end degradation products are carbon 
dioxide and water. Contemplated equivalents of these compositions such as 
those that contain minor amounts of other materials, fillers, or extenders 
can also be completely environmentally degradable by proper choice of 
materials. The compositions herein provide environmentally acceptable 
materials because their physical deterioration and degradation is much 
more rapid and complete than the conventional nondegradable plastics that 
they replace. Further, since all or a major portion of the composition 
will be poly(lactic acid), and/or a lactic acid derived lactide or 
oligomer, no residue or only a small portion of more slowly degrading 
residue will remain. This residue will have a higher surface area than the 
bulk product and an expected faster degradation rate. 
The general application of the invention results in the first and general 
embodiment of the invention. The homopolymers of D-lactide, L-lactide, 
D,L-lactide as well as copolymers of D-lactide, L-lactide; D-lactide, 
D,L-lactide; L-lactide, D,L-lactide; and D-lactide, L-lactide, and 
D,L-lactide all produce materials useful in the invention when plasticized 
by lactide monomers, lactic acid, oligomers of lactide, oligomers of 
lactic acid, derivatives of oligomeric lactic acid and mixtures thereof 
that are intimately dispersed in the polymer. A plasticizer may be 
produced by stopping the reaction before polymerization is completed. 
Optionally additional plasticizer consisting of lactide monomers 
(D-lactide, L-lactide, D,L-lactide, or mixtures thereof), lactic acid, 
oligomers lactide or oligomers of lactic acid or its derivatives including 
all L-, D-, and DL- configurations and mixtures thereof can be added to 
the formed polymer. While aspects of the invention can be applied to 
various polylactides in general, one preferred polymer is defined by the 
formula: 
##STR4## 
where n is the degree of polymerization (number of repeating units), 
plasticized with a plasticizer derived from incomplete polymerization of 
the monomers used to produce the polymer. The more intimately the 
plasticizer is integrated within the polymer the better are its 
characteristics. In fact very intimate integration is needed to obtain the 
advantages of the invention further discussed below. If desired, 
additional monomer or oligomer plasticizer can be added to any residual 
monomer or oligomer remaining in the composition after polymerization. The 
preferred oligomers of lactic acid, and oligomers of lactide including all 
L-, D-, DL- configurations and mixtures thereof, both random and block 
configurations, useful for a plasticizer are defined by the formula: 
##STR5## 
where m is an integer: 2.ltoreq.m.ltoreq.75. Preferably m is an integer: 
2.ltoreq.m.ltoreq.10. The oligomers of lactic acid and its derivatives 
including all L-, D-, DL- configurations and mixtures thereof, both random 
and block configurations, useful for a plasticizer are defined by the 
formula III: 
##STR6## 
where R=H, alkyl, aryl, alkylaryl or acetyl, and R is saturated, and where 
R'=H, alkyl, aryl, alkylaryl or acetyl, and R' is saturated, where R and 
R' cannot both be H, where q is an integer: 2 .ltoreq.q.ltoreq.75; and 
mixtures thereof. Preferably q is an integer: 2.ltoreq.q.ltoreq.10. 
The plasticizers added to the polymer compositions have the following 
functions: 
(a) They act as plasticizers introducing pliability and flexibility into 
the polymer compositions not found in polymer-only composition. 
(b) Addition of these plasticizers to the poly(lactic acid) reduces the 
melt viscosity of the polymers and lowers the temperature, pressure, and 
shear rate required to melt form the compositions. 
(c) The plasticizers prevent heat build up and consequent discoloration and 
molecular weight decrease during extrusion forming of poly(lactic acid). 
(d) The plasticizers add impact resistance to the compositions not found in 
the polymer alone. 
In addition, the plasticizers may act as compatibilizers for melt-blends of 
polylactides and other degradable and nondegradable polymers. That is, 
molten mixtures of two different polymers can more intimately associate 
and mix into well dispersed blends in the presence of the plasticizers. 
The plasticizers may also improve performance in solution blending. 
The subscripts n, m, and q above refer to the average number of mers (the 
repeating unit) of the polymer or oligomer. Number average molecular 
weight M.sub.n as used herein is related to the mers by multiplying n, m, 
or q by the molecular weight of the individual mer, for poly(lactic acid) 
this number is 72. The number of mers present in a polymer is also called 
the degree of polymerization. The reader is referred to the following 
texts where this subject is discussed further Polymer Chemistry an 
Introduction, 2nd Edition, R. Seymour et al, Marcel Dekker, Inc., 1988 and 
Introduction to Polymer Chemistry, R. Seymour, McGraw-Hill, New York, 
1971. 
The proportions of L-lactide, D-lactide, and D,L-lactide in the polymer are 
not critical to obtaining flexible thermoplastics; however, the 
proportions of D,L-lactide may vary certain properties as further 
discussed below. The parts of L-lactide, D-lactide, and D,L-lactide can 
vary over a wide, weight-ratio to form a homopolymer or copolymer. The 
lactide monomers employed in accordance with the invention are available 
commercially so that neither the monomeric reactant per se nor the method 
by which it is prepared constitute any portion of the invention. 
D-lactide is a dilactone, or cyclic dimer, of D-lactic acid. Similarly, 
L-lactide is a cyclic dimer of L-lactic acid. Meso D,L-lactide is a cyclic 
dimer of D- and L-lactic acid. Racemic D,L-lactide comprises a mixture of 
D-lactide and L-lactide. When used alone herein, the term "D,L-lactide" is 
intended to include meso D,L-lactide or racemic D,L-lactide. 
One of the methods reported in the literature for preparing a lactide is to 
dehydrate lactic acid under high vacuum. The product is distilled at a 
high temperature and low pressure. Lactides and their preparation are 
discussed by W. H. Carothers, G. L. Dorough and M. J. Johnson (J. Am. 
Chem. Soc. 54, 761-762 [1932]); J. Gay-Lussac and J. Pelouse (Ann. 7, 43 
[1833]); C. A. Bischoff and P. Walden (Chem. Ber. 26, 263 [1903]; Ann. 
279, 171 [1984]); and Heinrich Byk (Ger. Pat. 267,826 [1912]); through 
Chem. Abstr. 8, 554, 2034 [1914]). 
The optically active acids can be prepared by direct fermentation of almost 
any nontoxic carbohydrate product, by-product or waste, utilizing numerous 
strains of the bacterial genus Lactobacillus. e.g. Lactobacillus 
delbrueckii, L. salivarius. L. casei, etc. The optically active acids can 
also be obtained by the resolution of the racemic mixture through the zinc 
ammonium salt, or the salt with alkaloids, such as morphine. L-lactide is 
a white powder having a molecular weight of 144. If an impure, 
commercially-available product is employed in accordance with the present 
invention, it is preferable to purify it by recrystallization from 
anhydrous methyl isobutyl ketone. The snow-white crystals of L-lactide 
melt at 96.degree.-98.degree. C. As used herein the symbol C denotes 
degrees Centigrade and replaces the symbol .degree.C., similarly the 
symbol F denotes degrees Fahrenheit and replaces the symbol .degree.F. 
D,L-lactic acid which is used in the preparation of D,L-lactide is 
available commercially. The D,L-lactic acid can be prepared synthetically 
by the hydrolysis of lactonitrile (acetaldehyde cyanohydrin) or by direct 
fermentation of almost any nontoxic carbohydrate product, by-product or 
waste, utilizing numerous strains of the bacterial genus Lactobacillus. 
D,L-lactide is a white powder having a molecular weight of 144. If an 
impure, commercially-available product is employed in accordance with the 
present invention, it is preferable to purify it by recrystallization from 
anhydrous methyl isobutyl ketone. One such commercially available product 
comprising a mushy semisolid melting at 90.degree.-130.degree. C. was 
recrystallized from methyl isobutyl ketone and decolorized using charcoal. 
After three such recrystallizations, the product was tumble-dried in vacuo 
under a nitrogen bleed for 8 to 24 hours at room temperature. The snow 
white crystals thus obtained comprise a D,L-lactide mixture melting from 
115.degree.-128.degree. C. 
In preparing the compositions in accordance with the invention, it is 
preferred to carry out the reaction in the liquid phase in a closed, 
evacuated vessel in the presence of a tin ester of a carboxylic acid 
containing up to 18 carbon atoms. The compositions however, can also be 
prepared at atmospheric pressure with the polymerization system blanketed 
by an inert gas such as, for example, nitrogen. If polymerization is 
conducted in the presence of oxygen or air, some discoloration occurs with 
a resulting decrease in molecular weight and tensile strength. The process 
can be carried out at temperatures where the polymerization is sluggish in 
its later stages so as to trap residual monomer in the viscous polymer 
melt. Preferred temperatures for this purpose are generally between the 
melting points of pure L-lactide and pure D,L-lactide, or between 
95.degree. to 127.degree. C. While in no way wishing to limit the scope of 
the invention it is presently believed that below about 129.degree. C., 
the following occurs: 
1. The reactant lactide monomer mixture of L- and D,L-lactide monomers melt 
to form a eutectic mixture, which melts to a mobile fluid that is an 
intimate solution of one, two, or three monomers. 
2. The fluid melt is polymerized by catalyst to form an increasingly 
viscous solution and eventually unreacted monomer is trapped in 
association with the polymer as a solution, rather than as a distinct 
heterogeneous phase. The monomer no longer can react since the reaction is 
extremely diffusion controlled and cannot efficiently contact the low 
concentration of active end-groups of the polymer. 
3. The polymerization ceases or slows considerably so that at room 
temperature the blend of monomer and polymer are a solid solution that 
imparts plasticization, clarity, and flexibility to the composition. 
4. The catalyst deactivates so that subsequent melt-fabrication does not 
reinitiate the polymerization. 
5. The plasticized composition is quite stable since the residual monomer 
is very high boiling, e.g., lactide has a boiling point of 142.degree. C. 
at 8 torr, and is tightly associated with its open-chain tautomer, 
polylactide. 
Alternatively, the process can be carried out at any temperature between 
the melting point of the L-lactide and 200.degree. C. and lactic acid or 
lactide is subsequently melt or solvent-blended into the polymer as a 
further processing step. Temperatures above 200.degree. C. are undesirable 
because of the tendency of the copolymer to be degraded. Increasing the 
temperature within the range of 95.degree. to 200.degree. C. generally 
increases the speed of the polymerization. Good results are obtained by 
heating a mixture of L-lactide and D,L-lactide at a temperature between 
about 110.degree. C. and 160.degree. C. 
The catalysts employed in accordance with the invention are tin salts and 
esters of carboxylic acids containing up to 18 carbon atoms. Examples of 
such acids are formic, acetic, propionic, butyric, valeric, caproic, 
caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic and 
benzoic acids. Good results have been obtained with stannous acetate and 
stannous caprylate. 
The catalyst is used in normal catalytic amounts. In general, a catalyst 
concentration in the range of about 0.001 to about 2 percent by weight, 
based on the total weight of the L-lactide and D,L-lactide is suitable. A 
catalyst concentration in the range of about 0.01 to about 1.0 percent by 
weight is preferred. Good results were obtained when the catalyst 
concentration is in the range of about 0.02 to about 0.5 percent by 
weight. The exact amount of catalyst in any particular case depends to a 
large extent upon the catalyst employed and the operating variables 
including time and temperature. The exact conditions can be easily 
determined by those skilled in the art. 
The reaction time of the polymerization step, per se, is governed by the 
other reaction variables including the reaction temperature, the 
particular catalyst, the amount of catalyst and whether a liquid vehicle 
is employed. The reaction time can vary from a matter of minutes to a 
period of hours, or days, depending upon the particular set of conditions 
which are employed. Heating of the mixture of monomers is continued until 
the desired level of polymerization is detected. The level of 
polymerization can be determined by analysis for residual monomers. As 
discussed previously, the reaction temperature can be chosen to enhance 
the incorporation of monomer and provide plasticized compositions coming 
directly out of the polymerization reactor. The reaction can be halted at 
such time that the composition has attained the conversion of monomer to 
polymer that is desired to achieve the desired plasticization. In the 
preferred embodiment of the invention, approximately 2 to 30 percent 
lactide is left unreacted, depending on the degree of plasticization to be 
achieved. 
In general it is preferred to conduct the polymerization in the absence of 
impurities which contain active hydrogen since the presence of such 
impurities tends to deactivate the catalyst and/or increase the reaction 
time. It is also preferred to conduct the polymerization under 
substantially anhydrous conditions. 
The copolymers of the invention can be prepared by bulk polymerization, 
suspension polymerization or solution polymerization. The polymerization 
can be carried out in the presence of an inert normally-liquid organic 
vehicle such as, for example, aromatic hydrocarbons, e.g.. benzene, 
toluene, xylene. ethylbenzene and the like; oxygenated organic compounds 
such as anisole, the dimethyl and diethyl esters of ethylene glycol; 
normally-liquid saturated hydrocarbons including open chain, cyclic and 
alkyl-substituted cyclic saturated hydrocarbons such as hexane, heptane, 
cyclohexane, alkylcyclohexanes, decahydronaphthalene and the like. 
The polymerization process can be conducted in a batch, semi-continuous, or 
continuous manner. In preparing the lactide monomeric reactants and 
catalyst for subsequent polymerization, they can be admixed in any order 
according to known polymerization techniques. Thus, the catalyst can be 
added to either of the monomeric reactants. Thereafter, the 
catalyst-containing monomer can be admixed with the other monomer. In the 
alternative, the monomeric reactants can be admixed with each other. The 
catalyst can then be added to the reactant mixture. If desired, the 
catalyst can be dissolved or suspended in an inert normally-liquid organic 
vehicle. If desired, the monomeric reactants either as a solution or a 
suspension in an inert organic vehicle can be added to the catalyst, 
catalyst solution or catalyst suspension. Still further, the catalyst and 
the monomeric reactants can be added to a reaction vessel simultaneously. 
The reaction vessel can be equipped with a conventional heat exchanger 
and/or a mixing device. The reaction vessel can be any equipment normally 
employed in the art of making polymers. One suitable vessel, for example, 
is a stainless steel vessel. 
The environmentally biodegradable compositions produced in accordance with 
the present invention depending upon the L-lactide, D-lactide, meso 
D,L-lactide ratios, find utility in articles of manufacture, such as 
films, fibers, moldings and laminates, which are prepared by conventional 
fabricating methods. These articles of manufacture are contemplated for 
nonmedical uses i.e. outside the body where they can substitute for the 
common environmentally nondegradable plastics. 
Filaments, for example, are formed by melt-extruding the copolymer through 
a spinneret. Films are formed by casting solutions of the biodegradable 
compositions and then removing the solvent, by pressing solid 
biodegradable compositions in a hydraulic press having heated platens, or 
by extrusion through a die, including Blown Film techniques. 
Various techniques including melt blending, slow cooling, and rapid cooling 
(quenching) can be employed in preparing products e.g. moldings from the 
polymers and copolymers of the invention. 
Quenching as used herein indicates that the temperature is dropped rapidly 
to prevent extensive crystallization of the polymer. Crystallization of 
polymers is a slow process, requiring minutes to hours to fully 
accomplish. When this is desired, the temperature is held above the 
glass-transition temperature, Tg, for some time to allow the molecules to 
order themselves into extensive crystalline lattices. This is called 
annealing. When cooled rapidly from an amorphous melt, the polymer does 
not have the time required and remains largely amorphous. The time 
required to quench depends on the thickness of the sample, its molecular 
weight, melt viscosity, composition, and its Tg, where it is frozen-in as 
a glassy state. Note that melt viscosity and Tg are lowered by 
plasticization and favor quenching. Thin films obviously cool very quickly 
because of their high surface-to-volume ratio while molded items cool more 
slowly with their greater thicknesses and time spent in a warm mold before 
removal. Regular structures such as poly (L-lactide) order more easily and 
crystallize more quickly than more random structures such as a copolymer. 
With the polylactides the melting points are approximately 
150.degree.-190.degree. C. depending on the L-lactide content and, 
therefore, the regularity of structure. The Tg of all the polylactides, 
including various L and D,L homopolymers and copolymers is 60.degree. C. 
The Tg decreases when residual lactide is intimately dispersed with the 
polymer. Quenching to an amorphous state requires that the polymer or 
copolymer in an amorphous melt is rapidly cooled from its molten state to 
a temperature below its Tg. Failure to do so allows spherulitic 
crystallinity to develop, that is, crystalline domains of submicron to 
micron size. The latter scatters light and the polymer specimens become 
opaque. These crystalline forms have improved stability to heat 
distortion. This spherulitic crystallinity is often called short range 
order-long range disorder since the crystallites are separated by 
amorphous regions. However, the crystallites act as pseudo crosslinks to 
maintain dimensional stability above the Tg but below their melting 
points. Alternatively stability to heat distortion can be obtained by 
orienting an amorphous polymer above its Tg but below its melting point. 
Here, the polymer molecules are stretched to allow some long range 
ordering, then "heat set" to permit the ordering to complete, that is, 
given some time to anneal. The amorphous polymer is thereby crystallized 
into a different order, called long-range order, short range disorder. 
Transparency and resistance to heat distortion are favored. 
A detailed discussion can be found in textbooks, for example, "Structural 
Polymer Properties", by Robert J. Samuels, Wiley Publications, New York, 
N.Y. 1974. 
Contemplated equivalents of the compositions of the invention are those 
that contain minor amounts of other materials. The copolymers produced in 
accordance with the present invention can be modified, if desired, by the 
addition of a cross-linking agent, other plasticizers, a coloring agent, a 
filler and the like, or minor amounts of other lactone monomers such as 
glycolide or caprolactone. 
Cross-linking can be effected by compounding the compositions with 
free-radical initiators such as cumene hydroperoxide and then molding at 
elevated temperatures. This can improve heat-and solvent-resistance. 
Curing can also be effected by compounding the copolymers with 
multifunctional compounds such as polyhydric alcohols and molding, or 
thermoforming under heat and vacuum. Graft-extruder reactions to effect 
curing of the polyesters is an obvious method of cross-linking and 
chain-extending the copolymers. 
In preparing moldings, a filler can be incorporated in the compositions 
prior to curing. A filler has the function of modifying the properties of 
a molding, including hardness, strength, temperature resistance, etc. 
Known filler materials include aluminum powder, powdered calcium 
carbonate, silica, kaolinite (clay), magnesium silicate and the like. Of 
particular advantage is starch, which blends well with the compositions to 
obtain a blend which is totally environmentally biodegradable. Other 
property modifications can be effected by melt blending the compositions 
with other polymers and copolymers of the lactides, glycolides, and 
caprolactones. 
The compositions prepared according to the present invention can be used in 
producing reinforced laminates according to known procedures. In general, 
laminates are made from a fibrous mat or by assembling a multiplicity of 
sheets of material to form a matrix which is consolidated into a unitary 
structure by flowing molten precursor or composition through the fibrous 
material and curing it while in a mold or hydraulic press to form the 
polymer. Fibers which are used in forming the matrix include natural and 
synthetic fibers such as cellulose derived from wood, cotton, linen, hemp, 
and the like, glass, nylon, cellulose acetate and the like. 
The compositions of the invention and their preparation are further 
illustrated by the following specific examples. 
EXAMPLE 1 
80/20, L-lactide/racemic D,L-lactide 
160 grams of L-lactide and 40 grams of racemic D,L-lactide, both of high 
purity (Purac, Inc., triply recrystallized), were charged into a 500 ml, 
round-bottom flask and purged with dry nitrogen overnight. 10 ml of 
stannous octoate is dissolved in 60 ml of anhydrous toluene, and 10 ml of 
the solvent is distilled to a Dean-Stark trap to effect dryness of this 
catalyst solution by azeotropic distillation. From the 10 ml of stannous 
octoate in 50 ml of dry toluene a 0.20 ml portion is removed with a 
syringe and injected into the lactides in the reaction flask. The nitrogen 
purge is continuous via a syringe needle connection that enters the 
reaction flask through a rubber septum and vents via a piece of tubing 
that connects to a bubbler. The nitrogen flow is maintained at 1-3 bubbles 
per second. The flask was heated in an oil bath maintained at 
123.degree.-127.degree. C. During the first part of the heating the 
lactides melt and are mixed thoroughly by swirling. Thereafter, the 
products become quite viscous. After 20 hours of heating, the flask and 
the colorless, transparent products are removed from the heating bath, 
cooled, the flask broken, and shocked with liquid nitrogen to remove glass 
from the product. The copolymer was molded in a heated hydraulic press. 
Compression molding to 5 to 10 mil thick films was possible at 20,000 lb 
pressure, at 170.degree. C., in a time period of 2 minutes. The films were 
evaluated for their tensile properties on a Instron tester, and the 
results are listed in Table 1. Samples 1/8 inch thick were also molded for 
impact strength testing. A thermogravimetric analysis of the product was 
performed, noting the weight loss upon heating the sample to 150.degree. 
C. in 4 minutes and holding the temperature at 150.degree. C. for 60 
minutes. The weight loss of the sample was 19.5 percent and nearly 
complete in 60 minutes. The weight loss is attributed to loss of lactide 
monomer. Results of differential scanning calorimetry reveal that the 
composition has an endotherm beginning about 110.degree. C., becoming 
more pronounced as the temperature increases to 200.degree. C. No melting 
point was observed. Specimens were annealed at 185.degree. F. overnight 
and reexamined. They remained transparent, colorless and pliable. Samples 
of the copolymer could not be remolded 6 times without any discoloration 
or obvious loss of strength. Thin films were clear, transparent, 
colorless, and quite flexible, despite the repeated molding. 
TABLE 1 
______________________________________ 
PROPERTIES OF COPOLYMERS.sup.(a) OF L-LACTIDE AND 
D,L-LAcTIDE WHEN PLASTICIZED BY LACTIDE 
Example No. 1 2 3 
______________________________________ 
Film thickness, mil 
8 8 10 
Tensile strength, 1000 psi, 
3.9 1.7 7.9 
ASTM D638 
Elongation, percent 
280 806 3.5 
100 percent modulus, 1000 psi 
0.74 -- -- 
200 percent modulus, 1000 psi 
1.20 -- -- 
Tangent modulus, 1000 psi 
36.6 -- 289 
Izod impact strength, ft-lb./in..sup.(b) 
0.63 -- 0.4 
M.sub.w, 1000's 540 281 341 
M.sub.n, 1000's 270 118 97.5 
Residual lactide,.sup.(c) percent 
19.5 27.8 2.7 
______________________________________ 
.sup.(a) 80/20, weight ratio, of L/racemic D,Llactide. 
.sup.(b) 1/8 inch, notched samples. 
.sup.(c) By isothermal thermogravimetric analysis weight loss at 150 C. 
EXAMPLE 2 
In a 3-liter, round-bottom flask was charged 1.84 Kg of L-lactide, 0.46 Kg 
of racemic D,L-lactide and 2.3 ml of the stannous octoate solution, 
similar to Example 1. The mixture was purged with argon for 3 hours, then 
heated isothermally in a 125.degree. C. oil bath. The mixture melts, was 
mixed thoroughly by swirling, and forms a homogeneous, transparent, 
colorless fluid whose viscosity increases substantially after several 
hours. After 64 hours the flask was removed from the heating bath, cooled, 
and the glass removed from the clear, transparent, solid product. The 
rubbery composition was guillotined into slices and ground to 1/8 inch, or 
smaller, size in a grinder with dry ice. The grind was dried in an air 
circulating oven at 100.degree. F. for several hours, then vacuum dried 
overnight at ambient temperature. Compression-molded films were prepared 
as described in Example 1 and the films were examined for their tensile 
properties and weight loss by thermogravimetric analysis as shown in Table 
1. 
EXAMPLE 3 
In a 250-ml, round bottom flask was placed 79.98 g of L-lactide, 20.04 g of 
racemic D,L-lactide, and 0.20 ml of stannous octoate solution, similar to 
Example 1. The flask was swept by nitrogen through inlets and outlets and 
heated in a 125.degree. C. oil bath. The mixture melted to a colorless and 
fluid liquid that was thoroughly mixed by swirling the flask. After 2 
hours, the oil bath temperature was increased to 147.degree. C., and after 
14 hours total heating time, the temperature was decreased to 131.degree. 
C. Total heating time was 18 hours. The product is transparent, colorless, 
and glassy. It was evaluated, similar to the preceding examples and the 
results are recorded in Table 1. 
Examples 1 to 3 reveal the effect of reaction temperature on the properties 
of the copolymers as occasioned by the resulting composition. 
EXAMPLE 4 
Films of the copolymers of Examples 1 and 3 were immersed in water for 
several months. After 3 weeks, the copolymer of Example 1 became hazy 
while that of Example 3 remained clear for approximately 2 months; after 3 
months the film of Example 3 became noticeably hazy and the film of 
Example 1 is white and opaque. The water that had been in contact with the 
film of Example 1 tastes acidic while that of Example 3 is tasteless. 
Inspection of the data of Table 1 reveals that the copolymer of Example 1 
is an environmentally biodegradable replacement for polyethylene. Those 
skilled in the art will recognize that the physical properties of the 
copolymer are an excellent combination useful for many packaging 
applications. Its tensile strength and initial tangent modulus compare 
favorably with polyethylene compositions used, for example, in plastic 
trash bags, general film wrap, plastic shopping bags, sandwich wrap, six 
pack yokes and the like. The shape of the stress-strain curves are 
approximately the same for both the copolymer and that for a linear low 
density polyethylene composition commonly used in trash bag compositions. 
A comparison of properties are shown in Table 2. 
TABLE 2 
______________________________________ 
COMISON OF POLYETHYLENE 
TO POLYLACTIC ACID 
LDPE-.sup.(a) Lactide 
Property NA 272 LLDPE.sup.(b) 
Copolymer.sup.(c) 
______________________________________ 
Tensile strength, 
2.18 2.9 3.90 
1000 psi, 
ASTM Standard C 
Elongation, % 
261 500 280 
Tangent modulus, 
54.9 51.0 36.6 
1000 psi 
100% modulus, 
1.77 -- 0.74 
1000 psi 
200% modulus 
1.82 -- 1.20 
HDT,.sup.(d) 264 psi, F 
95 99 122 
______________________________________ 
.sup.(a) Linear low density polyethylene, 5-10 mil, 2in./min., our 
experiments. 
.sup.(b) Linear low density polyethylene, data from computer file. 
.sup.(c) Copolymer of Llactide/racemic D,Llactide, Example 1. 
.sup.(d) Heat deflection temperature. 
The lactide polymerization can be stopped at incomplete monomer-to-polymer 
conversion in a controllable fashion. This is illustrated in Examples 1 
and 2. The lactide monomer binds very intimately with polymers of 
lactides. Alternatively, the compositions can be derived by mixing of 
lactide with preformed polymer. In that case, the lactide added can be the 
same or different with respect to stereochemistry, i.e., L-, D-, or 
D,L-lactide to that used to make the polymer. 
The compounding can be accomplished by blending the molten polymer with 
lactide monomer in conventional processing equipment such as a mill roll 
or a twin screw compounder. The normally stiff, glassy, lactide polymers 
are flexibilized by the lactide and remain transparent, colorless, and 
very nearly odorless. The lactide is not very fugitive, requiring heating, 
and a nitrogen sweep, typically, 170.degree.-200.degree. C. for 20-60 
minutes to remove the lactide in a gravimetric analysis. Neither is the 
lactide visible in films under an optical microscope. The lactide domains 
are submicron in size. This flexibilizing of the poly(lactic acid) 
suggests its use as a environmentally biodegradable replacement for 
polyolefin, disposable, packaging films. 
EXAMPLES 5-16 
A series of experiments were performed in which copolymers of L- and 
racemic D,L-lactide were prepared, melt blended with variable amounts of 
lactide, and the physical properties of the blends evaluated as a function 
of the lactide composition. Monomer lactide content was assayed by a 
previously developed isothermal, thermogravimetric analysis. The lactide 
contents were measured before and after compounding and molding into 
films. 
It was observed that open roll, 2 roll, milling tended to volatilize the 
lactide at temperatures required for the very high, molecular weight 
lactide copolymers. These losses could be minimized by masterbatching or 
by using lower molecular weight lactide copolymers (and their lower 
attendant mixing temperatures). A better mixing and blending method was a 
conventional, twin screw extruder, which minimized volatile losses. Some 
results are shown in Table 3. 
Alternatively, a mixture of oligomeric lactic acid, or a derivative of an 
oligomer of lactic acid, oligomeric lactic acid and lactide can be used to 
prepare a flexible film, whereby the oligomers or their derivatives are 
added first, allowing the lactide to be mixed in the melt later at lower 
temperature. By adding oligomers first the melt viscosity decreases very 
significantly, allowing the temperature to be lowered, and the lactide can 
then be mixed in at a lower temperature without significant 
volatilization. This is demonstrated in Example 16A. 
EXAMPLE 16A 
A 90/10, L/D,L-lactide copolymer prepared by methods previously described, 
and analyzed by gel permeation chromatography to have a weight-average 
molecular weight of 480,000, a number average molecular weight of 208,000, 
was banded, that is, melted and mixed on an open 2-roll mill preheated to 
350.degree. F. The copolymer will not melt and band well on the mill below 
350.degree. F. To 25 grams of this melted copolymer was added 10 grams of 
oligomeric lactic acid of a degree of polymerization of 2.34. After all of 
the oligomeric lactic acid mixed in, the temperature was dropped to 
300.degree. F., where the mixing was still quite good. With the roll 
temperature at 300.degree. F., 10 grams of L-lactide was added slowly and 
mixed. The mix was stripped from the roll and pressed into a thin film in 
a press at 300.degree. F. The 5-10 mil thick film was colorless, 
transparent and very flexible. Without the lactide the resulting film 
would have been stiff. Without first adding the oligomeric lactic acid the 
lactide could not have been added on a mill without being lost to 
volatilization. 
The blends of polylactide and lactide plasticizer are quite pliable, 
becoming increasingly so with increasing lactide content. They are 
colorless and transparent. Only a very faint (pleasant) odor of lactide is 
detectable and no discernable taste of lactide was noticeable. The Table 3 
plasticized film samples were tear resistant, easily foldable, and can be 
punctured without shattering or tearing. They stiffen somewhat when placed 
in a cooler (5.degree. C., 40.degree. F.), but remain flexible and 
creasible without breaking. These films noticeably soften in the hand, 
indicating a glass transition temperature below 37.degree. C. When the 
lactide content is less than 20 percent, the films will have a rattle 
typical of a polyolefin film. At greater lactide contents the films have 
the drape and "warm" feel of a plasticized poly(vinyl chloride) (PVC). In 
fact, the compositions of the invention are also a replacement for 
plasticized PVC in many applications. 
As shown in Table 3, the elastic moduli (initial tangent moduli) can be 
relatively high, similar to a linear low density polyethylene (LLDPE). 
This is an indication of potential form stability. Lower moduli and 
tensile strengths are similar to low density polyethylene (LDPE). Physical 
properties, as a function of lactide content, were plotted as shown in 
FIGS. 1 and 2. Referring to Table 3, at approximately 17-20 percent 
lactide content, the tensile properties are similar to polyethylenes used 
in trash bags and shopping bags. 
At lower lactide contents, the blends have a similarity to polypropylene. 
Some data can be compared in Table 3. Table 4 defines the conventional 
plastics used in the comparisons. 
TABLE 3 
__________________________________________________________________________ 
TENSILE PROPERTY COMISONS OF PLASTICIZED PLA.sup.(a) 
Elastic 
1% Secant 
Yield 
Strain 
Break 
Strain 
Ex. Lactide 
Modulus 
Modulus 
Strength 
at Strength 
at 
No. 
Composition 
% TGA 
1000 psi 
1000 psi 
1000 psi 
Yield % 
1000 psi 
Break % 
__________________________________________________________________________ 
5 90/10, L-/D,L- 
1.3 289 291 0 0 7.5 3 
Lactide 
Copolymer 
6 90/10, L-/D,L- 
17.3 119 119 2.23 4 2.29 288 
Lactide 
Copolymer 
7 90/10, L-/D,L- 
19.2 95.5 90.3 1.97 5 4.24 536 
Lactide 
Copolymer 
8 90/10, L-/D,L- 
19.6 88.7 88.7 1.72 4 2.12 288 
Lactide 
Copolymer 
9 90/10, L-/D,L- 
20.5 50.3 50.3 1.21 5 2.16 338 
Lactide 
Copolymer 
10 90/10, L-/D,L- 
25.5 33.7 22.9 0.32 4 2.44 546 
Lactide 
Copolymer 
11 LPDE.sup.(b) 
-- 41.3 40.6 1.51 17 1.60 365 
12 LLPDE.sup.(c) 
-- 44.4 42.7 1.66 16 1.66 599 
13 Biaxially.sup.(d) 
-- 38.9 41.1 1.69 16 4.78 838 
oriented PE 
14 Biaxially.sup.(e) 
-- 35.6 38.5 1.68 16 5.20 940 
oriented PE 
15 HDPE.sup.(f) 
-- 127.8 
120.9 3.48 9 1.95 216 
16 pp.sup.(g) 
-- 174 174 5.08 5 7.34 6 
__________________________________________________________________________ 
.sup.(a) ASTM 882; all samples were compression molded 5-10 mil films 
except Examples 13 and 14; strain rate 1.0 in/in min for all; D,Llactide 
is racemic. 
.sup.(b) USI low density polyethylene (petrothene No. 213). 
.sup.(c) Exxon linear low density polyethylene (LLPE 6202,57). 
.sup.(d) Machine direction. 
.sup.(e) Cross machine direction. 
.sup.(f) Phillips high density polyethylene (HMN 5060). 
.sup.(g) Chisso polypropylene (XF 1932, melt index 0.52). 
TABLE 4 
__________________________________________________________________________ 
MANUFACTURERS' DATA 
Recommended Elastic 
Trade Name Melt Tensile 
Modulus in 
and/or Density, 
Temperature, 
Strength 
Flexure, 
Melt Index 
Supplier Grade gm/cu cm 
F. at Yield 
10.sup.5 psi 
gm/10 min 
__________________________________________________________________________ 
LDPE (USI) Petrothene 
0.924 360-550 1820 0.37 8.0 
LLDPE (Exxon) 
6202.57 
0.926 425 1700 0.53 12.0 
HDPE (Phillips) 
HMN 5060 
0.950 425-525 3600 1.75 6.0 
80% LLDPE (Exxon) 
LPX 86 0.927 260 -- -- 0.8 
20% HDPE (Proces- 
(Octene 
sing oil) base) 
Polypropylene 
XF1932 0.91 450-500 5872 3.05 0.52 
(PP-Chisso) 
Polystyrene 
RI 1.05 400 7900 4.50 1.8 
(Amoco) 
__________________________________________________________________________ 
Table 3 reveals some data for lactide and polylactide mixtures. The results 
do not differ remarkably from similar compositions of Examples 1 and 2, 
prepared by other means. However, those skilled in the art will recognize 
that the precise physical properties will vary somewhat depending on the 
intimacy of the mixture, the tensile testing conditions, and the 
fabrication technique for preparing the films. Comparisons from Table 3 
reveal that the lactide-polymer mixtures have a broad range of 
controllable compositions that mimic many conventional, nondegradable 
plastic types. 
EXAMPLE 17 
An oligomeric poly(lactic acid) (OPLA) was prepared for mixing with 
polylactides as follows. An 88 percent solution of L-lactic acid (956 g) 
was charged to a 3-neck flask (1 liter) fitted with a mechanical stirrer 
and a pot thermometer. The reaction mixture was concentrated under a 
nitrogen purge at 150.degree.-190.degree. C. at 200 mm Hg for 1 hour until 
the theoretical water of dilution was removed. No catalyst was used except 
for lactic acid and its oligomers. This temperature and vacuum were 
maintained and distillation continued for 2 hours until 73 percent of the 
theoretical water of dehydration was removed. 
The total time required was 3 hours. At this time the reaction was stopped. 
The water samples and the pot oligomer were titrated with 0.5N NaOH. Some 
lactic acid, 26.2 g, was found in the water distillate. The pot oligomer 
(OPLA) was also refluxed with excess 0.5N NaOH, then back titrated with 
standard H.sub.2 SO.sub.4. The data are recorded in Table 5. The 
oligomeric poly(lactic acid) flows well when hot, and shows some cold 
flow. It has a degree of polymerization of 3.4. It was used in Example 20 
where it was melt blended with the polymer of Example 19. 
TABLE 5 
______________________________________ 
CHARACTERIZATION OF OPLA OF EXAMPLE 1 
Total Degree 
Percent Titratable 
Titratable 
Expressed as 
of 
Dehydrated, 
Acid, Ester, Lactic Acid 
Polymer- 
Theoretical 
percent percent percent ization 
______________________________________ 
58 34.4 82.4 116.8 3.4 
______________________________________ 
EXAMPLE 18 
The procedure of Example 17 was repeated except the distillation was 
conducted more slowly. After 8 hours of heating during which the 
temperature was slowly advanced from 63.degree. to 175.degree. C. at 200 
mm Hg, a sample of the pot was titrated to reveal 62.2 percent of 
theoretical water removal. Titration revealed a degree of polymerization 
of 4.3. The molecular weight of the oligomeric poly(lactic acid) was 
further advanced over 2 hours by heating at 179.degree. C. and using a 
vacuum pump. The oligomeric poly(lactic acid) was no longer soluble in 
0.1N NaOH, was water white, and would cold flow. This material is a second 
example of an oligomeric poly(lactic acid) preparation with somewhat 
higher degree of polymerization as compared to Example 1. It was mixed 
with polylactide in Examples 22 and 25. It is estimated that the degree of 
polymerization was about 6-10. 
EXAMPLE 19 
A polymer of lactide was prepared by methods similar to Example 3. A 90/10. 
weight percent L-/racemic D,L-lactide copolymer was melt polymerized using 
0.02 parts per hundred, anhydrous stannous octoate catalyst. In a similar 
manner a 100 percent L-lactide homopolymer (L-PLA) was prepared. The 
copolymer was melt blended with the homopolymer at 350.degree. F. in a 
twin-screw extruder at a weight ratio of 90/10, copolymer/homopolymer. Gel 
permeation chromatography of the blend reveals a weight-average molecular 
weight (M.sub.w) of 182,000 and a number-average molecular weight 
(M.sub.n) of 83,000. Residual lactide monomer by thermogravimetric 
analysis was 1.7 weight percent. This blend was mixed with the oligomeric 
poly(lactic acid) of Example 17 to provide material for Example 20. The 
tensile properties are listed in Table 6. 
EXAMPLE 20 
The polymer of Example 19 was melt blended with the oligomeric poly(lactic 
acid) of Example 17 on an open, 2-roll, mill for 20 minutes at 325.degree. 
F. The mix was compression molded into films and tested as shown in Table 
6. The gel permeation chromatography molecular weights were smooth, 
monomodal distributions (M.sub.w /M.sub.n =2.6) with M.sub.w =192,000 and 
M.sub.n =73,000. 
TABLE 6 
__________________________________________________________________________ 
PROPERTIES OF MELT BLENDS OF 90/10 
POLYLACTIDES AND OLIGOMERIC POLYLACTIC ACID 
Elastic 
Break 
Modulus, 
Strength, 
Strain at 
Tg, 
Example 
Composition, wt. % 
Lactide, 
1000 psi 
psi Break, % 
C 
Number 
Polymer 
Oligomer 
%, TGA 
(a) (a) (a) (b) 
__________________________________________________________________________ 
19 100.sup.(c) 
0.sup.10 
1.7 298 7500 3 55 
20 91.sup.(c) 
9.sup.(d) 
1.8 275 6113 2 -- 
21 100.sup.(e) 
0.sup. 
1.6 308 7478 3 58 
22 70.sup.(e) 
30.sup.(f) 
0.4 254 5052 3 42 
23 60.sup.(e) 
40.sup.(f) 
0.0 202 3311 2 38 
24 50.sup.(e) 
50.sup.(f) 
0.0 106 2334 25 35 
25 40.sup.(e) 
60.sup.(f) 
0.0 36 1180 129 35 
__________________________________________________________________________ 
(a) ASTM 882; 5-10 mil, compressionmolded films; strain rate 1.0 
in./in./min. 
(b) Glass transition temperature by differential scanning calorimetry. 
.sup.(c) A blend of 90% of a 90/10, L/D,L-lactide* copolymer with 10% 
poly(Llactide), Example 19. 
.sup. (d) Oligomeric PLA of Example 17. 
.sup.(e) A blend of 80% of a 90/10, L/D,L-lactide* copolymer with 20% 
poly(Llactide). 
.sup.(f) Oligomeric PLA of Example 18. 
*racemic 
EXAMPLE 21-25 
The copolymer of Example 19 was melt blended with 20 percent of the L-PLA 
described in Example 19. The blend is listed as Example 21 in Table 6, 
where its analyses and tensile properties are listed. Example 21 was, in 
turn, melt blended with various amounts of the oligomeric poly(lactic 
acid) of Example 18 and these were tested as before and listed in Table 6, 
Examples 22 to 25. Table 7 lists the gel permeation chromatography 
molecular weights of these compositions. The tensile strengths and moduli 
are compared to the weight percentages of oligomeric poly(lactic acid) in 
FIGS. 3 and 4 (Lower Curves). 
TABLE 7 
__________________________________________________________________________ 
MOLECULAR WEIGHTS AND GLASS TRANSITION TEMPERATURES 
OF 90/10 POLYLACTIDES AND OLIGOMERIC POLYLACTIC ACID 
Res..sup.(a) 
Example 
Composition, wt % 
Mon., 
GPC .times. 10.sup.-3(b) 
Tg,.sup.(c) 
Number 
Copolymer 
Oligomer 
% M.sub.n 
N.sub.w 
M.sub.z 
M.sub.w /M.sub.n 
C 
__________________________________________________________________________ 
21 100.sup.(d) 
0.sup. 
1.6 76.sup. 
175 
410 2.3 58 
22 70.sup.(e) 
30.sup.(f) 
0.4 67.sup.(g) 
136 
299 2.0 42 
23 60.sup.(e) 
40.sup.(f) 
0.0 61.sup.(g) 
112 
211 1.8 38 
24 50.sup.(e) 
50.sup.(f) 
0.0 62.sup.(g) 
114 
223 1.8 35 
25 40.sup.(e) 
60.sup.(f) 
0.0 69.sup.(g) 
120 
207 1.7 35 
__________________________________________________________________________ 
.sup.(a) Residual monomer by TGA. 
.sup.(b) Molecular weight by GPC. 
.sup.(c) Glass transition temperature by DSC. 
.sup.(d) A blend of 90% of 90/10, L/racemic D,Llactide copolymer with 10% 
LPla. 
.sup.(e) Example 21. 
.sup.(f) Example 18. 
.sup.(g) After blending; meltblending on an open mill roll at 325 F. 
All D,Llactide is racemic, not meso. 
EXAMPLES 26-30 
A second series of copolymers was blended with the oligomeric poly(lactic 
acid). A 92.5/7.5, L-/racemic D, L-lactide copolymer was prepared by 
methods similar to Examples 19 and 21. This is Example 26 of Tables 8 and 
9. It was melt blended with the oligomeric poly(lactic acid) of Example 18 
on an open, 2-roll mill at 325.degree. F. for approximately 20 minutes. 
The blends were compression molded into 3-5 mil thick films and their 
tensile properties and gel permeation chromatography molecular weights 
measured. The properties are recorded in Tables 8 and 9, and plotted in 
FIGS. 3 and 4. The second series of blends revealed significantly higher 
values for the tensile properties although the molecular weights were 
lower. This may be due to lower residual lactide monomer and/or the change 
in high polymer composition. All of the oligomeric poly(lactic acid) 
polylactide blends could be easily molded into tack free, transparent 
films. 
TABLE 8 
__________________________________________________________________________ 
PROPERTIES OF MELT BLENDS OF 92.5/7.5 POLYLACTIDES 
AND OLIGOMERIC POLYLACTIC ACID 
Elastic 
Break 
Strain 
Composition, wt. % Modulus, 
Strength, 
at 
Example 
Polymer 
Oligomer 
Lactide, 
1000 psi, 
psi Break, % 
Tg.sup.(b) 
Number 
(c) (d) %, TGA 
(a) (a) (a) C 
__________________________________________________________________________ 
26 100 0 0.2 338 10,527 
4 61 
27 80 20 0.3 346 9,144 
4 52 
28 70 30 0.2 346 5,675 
2 46 
29 60 40 0.6 249 5,617 
3 36 
30 50 50 1.5 112 1,984 
119 36 
__________________________________________________________________________ 
(a) ASTM 882; 3-5 mil compressionmolded films; strain rate 1.0 
in./in./min. 
(b) Glass transition temperature by differential scanning calorimetry. 
(c) 92.5/7.5, L/racemic D,Llactide copolymer. 
(d) Example 18. 
All D,Llactide is racemic, not meso. 
TABLE 9 
______________________________________ 
MOLECULAR WEIGHTS OF 9.25/7.5, 
L-/RACEMIC D,L-LACTIDE COPOLYMERS 
% GPC .times. 10.sup.-3(a) 
Example No. 
OPLA M.sub.n 
M.sub.w 
M.sub.z 
M.sub.w /M.sub.n 
______________________________________ 
26 0 63 124 228 1.95 
27 20 60 108 189 1.81 
28 30 48 80 125 1.66 
29 40 59 96 151 1.65 
30 50 56 92 141 1.64 
______________________________________ 
.sup.(a) Gel permeation chromatography (GPC) molecular weights as referre 
to monodisperse polystyrene standards. 
EXAMPLES 31 AND 32 
Film specimens with, and without plasticizer were exposed to seawater at 
Daytona, Fla. from March through May. The pH of the water varied from 7.3 
to 7.6 and the salinity from 33.2 to 38.4 ppt. The water gradually warmed 
in the test from 15.degree. to 27.degree. C. The specimens were cut into 
strips and tensile tested before, and after, periodic intervals in the 
seawater. The results are shown in Table 10. All of the samples showed 
whitening and physical degradation, which became progressive with time. 
Without plasticizer the samples showed whitening and degradation after six 
weeks in the seawater. The oligomeric poly(lactic acid) polylactide blend 
degraded faster, revealing clear evidence of degradation after 3 weeks. 
The incorporation of 20 percent lactide provoked immediate whitening and 
obvious degradation after one week of exposure. 
TABLE 10 
__________________________________________________________________________ 
PHYSICAL PROPERTIES AFTER SEAWATER EXPOSURE 
Seawater 
Tensile Properties, 1000 psi.sup.(a) 
Example Exposure 
Elastic 
1% Secant 
Yield 
Break 
Strain, % 
Number 
Composition 
Weeks 
Modulus 
Modulus 
Strength 
Strength 
Yield 
Break 
__________________________________________________________________________ 
31 90/10 copolymer 
0 305 292 -- 7.6 -- 4.7 
5% L-PLA 3.sup.(b) 
315 301 -- 7.1 -- 3.1 
6.sup.(c) 
317 317 -- 7.3 -- 3.0 
9.sup.(d) 
228 230 -- 6.2 -- 3.0 
12.sup.(e) 
355 343 -- 3.9 -- 1.0 
20 90/10 copolymer 
0 275 275 -- 6.1 -- 2.0 
with 10% 3.sup.(b) 
291 281 -- 6.8 -- 2.9 
oligomer 6.sup.(c) 
246 246 -- 3.9 -- 2.0 
9.sup.(d) 
211 105 2.2 1.4 3 2.0 
12.sup.(e) 
103 103 -- 1.7 -- 1.0 
32 90/10 copolymer 
0 300 298 -- 7.0 -- 3.0 
with 1% fumaric 
3.sup.(b) 
292 291 -- 6.5 -- 2.5 
acid 6.sup.(c) 
318 318 -- 6.9 -- 2.0 
9.sup.(d) 
226 223 -- 6.1 -- 3.0 
12.sup.(e) 
70 122 -- 0.8 -- 1.0 
9 92.5/7.5 co- 
1.sup.(e) 
Too brittle to test 
polymer with 
20% lactide 
__________________________________________________________________________ 
.sup.(a) 0.5 .times. 5 in. strips of film, 12-17 mil; strain rate 1 
in./in./min. 
.sup.(b) 15-21 C, saline seawater, regularly exchanged. 
.sup.(c) 20-22 C, saline seawater, regularly exchanged. 
.sup.(d) 22-23 C, saline seawater, regularly exchanged. 
.sup.(e) 22-27 C, saline seawater, regularly exchanged. 
EXAMPLE 33 
Examples 33 to 51 teach the use of incorporating lactide in conjunction 
with quenching to obtain pliability and transparency. Alternatively, the 
polymers can be annealed to improve stability against heat distortion. 
Poly L-(lactide) was prepared by methods previously described. Thus 300 g 
of triply recrystallized and thoroughly dried L-lactide was loaded into a 
clean, flame-dried, argon-cooled, 500 ml round-bottom flask. The flask was 
fitted with a rubber septum and inlet and outlet syringe needles that 
admitted a continuous argon purge. Stannous octoate solution was prepared 
by dissolving 20 g in 110 ml of toluene, previously dried over molecular 
sieves, then distilling 10 ml toluene in order to azeotropically dry the 
solution. The final concentration was 0.2 g/ml stannous octoate in 
toluene. A 0.3 ml quantity was injected through the septum onto the 
L-lactide. The flask and its contents were placed in a 150.degree. C. oil 
bath, and when melted, swirled vigorously to obtain a homogeneous mix. The 
argon purge continued and a thermocouple was fitted through the septum 
into the melt. The melt was 143.degree. C. The temperature of the oil bath 
was advanced to 200.degree. C. and heating and light purge continued for 
20 hours. The temperature of the melt advances to 170.degree. -174.degree. 
C. in the first two hours of heating. The final temperature was 
170.degree. C. After 20 hours of heating the flask was cooled in air to 
room temperature and the solid polymer was transparent. 
Polymer was recovered by shocking the flask with dry ice to free it from 
the glass. The residual monomer was analyzed by thermogravimetric analysis 
and the molecular weights by gel permeation chromatography. Differential 
scanning calorimetry reveals a glass transition temperature (T.sub.g) at 
53.degree. C. and two melting point endotherms with peaks at approximately 
170.degree. and 190.degree. C. The gel permeation chromatography molecular 
weights: M.sub.n =129,000; M.sub.w =268,000; M.sub.z =462,000; M.sub.w 
/M.sub.n =2.08. Residual monomer by thermogravimetric analysis was 2.3 
percent, (Example 33, Table 11.) The experiment shows that L-lactide can 
be polymerized above, or near, its melting point and the products remain 
transparent and more amorphous. 
EXAMPLE 34 
By methods similar to Example 33, 104.0 g of L-lactide was polymerized 
using 0.10 ml of stannous octoate catalyst solution. However, the reaction 
temperatures were 155.degree.-165.degree. C. for 72 hours. The polymer 
(No. 34 of Table 11) slowly crystallizes upon forming and is a white 
opaque solid at reaction or room temperature. Since the sample was smaller 
than the preceding experiment the polymer cooled more quickly, but it did 
still not quench to a transparent solid. In comparison to Example 33, the 
lower reaction temperature permits the poly(L-lactide) to crystallize and 
become opaque, thus an intimate dispersion of plasticizer does not form. 
The temperature is slowly advanced in many of these experiments to 
accommodate the polymerization exotherm. The reaction temperature must 
reach at least 170.degree.-175.degree. C. before there is substantial 
monomer-to-polymer conversion, otherwise the poly(L-lactide) crystallizes 
and is difficult to remelt. 
In Examples 36-42 the polymerization of L-lactide was repeated varying the 
conditions to obtain poly(L-lactides) with different residual lactide 
contents and crystallinities. The results are shown in Table 11, where it 
is seen that pliability and toughness were obtained only when the product 
has been quenched from the melt, is transparent at room temperature, and 
contained approximately 10 percent or more residual lactide. It is 
believed that the L-lactide homopolymer must be polymerized in the melt, 
and quenched from the monomer-polymer melt temperatures, to a transparent 
material as evidence of its homogeneous and intimately plasticized 
properties. When the poly(L-lactide) crystallizes during polymerization 
because the polymerization temperature is well below the polymer's melting 
point, the residual monomer is no longer effective as a plasticizer. If 
the polymer crystallizes upon cooling to room temperature, it also loses 
its plasticization. Annealing at elevated temperatures will restore 
crystallinity to amorphous samples. 
TABLE 11 
__________________________________________________________________________ 
POLYMERIZATION OF L-LACTIDE 
Catalyst Residual 
Sample 
Ex. Amount 
Temp Time, 
Polymer Monomer 
Size 
No. pph C. hours 
Appearance 
Percent 
g 
__________________________________________________________________________ 
33 0.02 156-201.sup.(a) 
20 clear 2.30 300 
150-174.sup.(b) 
transparent, 
2.30 300 
hard, glassy 
34 0.02 155-165.sup.(a) 
72 crystalline, 
-- 104 
opaque, hard 
brittle 
35 0.005 
120-200.sup.(a) 
24 crystalline, 
-- 100 
111-200.sup.(b) 
opaque, hard, 
brittle 
36 0.02 135-145.sup.(a) 
22 crystalline.sup.(d), 
1.1 500 
135-152.sup.(b) 
37 0.02 117-185.sup.(a) 
24 crystalline 
1.74 100 
120-175.sup.(b,c) 
opaque, hard, 
brittle 
38 0.02 160-170.sup.(a) 
8 crystalline 
2.18 2,000 
opaque, hard, 
brittle 
39 0.02 145.sup.(a) 
15 crystalline 
3.6 25 
137-144.sup.(b) 
opaque, hard, 
brittle 
40 0.0553 
190.sup.(a) 
0.3 clear, pliable 
10.1 25 
160-215.sup.(b) 
tough, trans- 
parent 
41 0.0553 
188-193.sup.(a) 
0.28 
clear, trans- 
22.9 25 
147-200.sup.(b) 
parent, pliable 
except at edge 
of polymerizate 
42 0.02 145.sup.(a) 
2.75 
crystalline.sup.(d), 
52.5 25 
150-133.sup.(b) 
opaque, hard 
brittle 
__________________________________________________________________________ 
.sup.(a) Oil bath temperature. 
.sup.(b) Polymer melt temperature. 
.sup.(c) This polymer crystallized at 160-169.degree. as the temperature 
was advanced and it did not remelt. 
.sup.(d) Transparent at reaction temperature, crystallizes upon cooling. 
This transparency and intimacy of association between polymer and monomer 
is also affected by the ratio of L/D,L-lactide. At approximately 95/5 
ratio the copolymer easily quenches to a transparent solid. The 90/10 
ratio, L/D,L-lactide copolymer quenches quite easily. The 100 percent 
L-lactide polymer quenches with difficulty from thick sections of the 
polymer to a transparent material. Some comparisons are shown by Examples 
43-47 of Table 12. Thinner cross sections, i.e., films of the L-lactide 
polymer can be plasticized and quenched to pliable and transparent 
materials. The 80/20 copolymer quenches very easily to a transparent 
solid. The latter has only a trace of crystallinity as seen by 
differential scanning calorimetry. 
TABLE 12 
__________________________________________________________________________ 
TRANSENCY OF LACTIDE POLYMERS 
Lactide Residual 
Ex. L/D,L- 
Temp., Time, Monomer, 
No. Ratio C.sup.(a) 
hours 
O/T.sup.(b) 
GPC M.sub.w 
percent 
__________________________________________________________________________ 
43 95/5 145-160 
67 SO 385,000 
2.64 
44 100 135-152 
22 O 322,000 
1.1 
45 90/10 150-157 
45 T 821,000 
4.95 
46 90/10 150-170 
48 T 278,000 
1.37 
47 80/20 .sup. 135-175.sup.(c) 
23 T -- -- 
__________________________________________________________________________ 
.sup.(a) Melt temperature (polymerization temperature). 
.sup.(b) Opaqueness/Transparency (O/T) after aircooling of polymerizates; 
opaque (O), slightly opaque (SO), transparent (T). 
.sup.(c) Slowcooled for 1 hour. 
All D,Llactide is racemic. 
All of the lactide polymers thermoform easily, that is, when heated by a 
radiant heater until soft, then sucked down on an intricate mold, they all 
form the pattern of the mold easily. However, the poly(L-lactide) becomes 
partially cloudy and hazy upon cooling. The 95/5, 90/10, and 80/20 
copolymers are quite clear and transparent throughout their thermoforms. 
EXAMPLE 48 
The poly(L-lactide) from Example 33 was melted and mixed on an open 2-roll 
mill for 5 minutes at 375.degree. F. (190.degree. C.), then compression 
molded at 375.degree. C. for 2 minutes, then air-quenched to room 
temperature in approximately 30 seconds. Both 7-and 20-mil thick films 
were prepared. Both were clear and transparent without trace of haze or 
opacity. Residual monomer in the film was 0.79 percent. The films are very 
stiff. 
EXAMPLE 49 
The experiment was repeated except that the milling was continued for 10 
minutes instead of 5 minutes. The films were analyzed by thermogravimetric 
analysis again and found to have 0.38 percent lactide. The films were 
clear, transparent, and stiff. 
EXAMPLE 50 
The mill-rolled polymer was also compression molded into a 
1/4.times.178.times.1 inch plaque. This plaque required 5-10 minutes to 
cool in the press by turning on the cooling water to the press. The plaque 
was white, opaque, and crystalline except for the extreme edges, which 
were transparent. 
The above Examples 48-50 teach the quenching of films of poly L-lactide to 
maintain transparency. When cooled more slowly, they crystallize and lose 
their transparency. 
As D,L-lactide is introduced as a comonomer, quenching can be replaced by 
ordinary cooling to retain transparency. Spherulitic crystallinity can be 
introduced into these films by annealing and the 100 percent L-lactide 
polymer is the fastest to crystallize. Where transparency is not required 
the higher L-lactide polymers can be annealed to greatly improve their 
resistance to thermal distortion. Conversely, where transparency is 
required, such as in a polystyrene offset, great care must be taken to 
avoid this type of opaque crystallinity. 
EXAMPLE 51 
The poly(L-lactide) film samples were annealed on a hot plate at 
240.degree. F. (115.degree. C.). The film turned hazy in approximately 1 
minute and completely cloudy in approximately 2 minutes. By way of 
comparison, a 90/10, L/D,L-lactide copolymer film required 10 minutes to 
turn hazy, 15 minutes to become completely cloudy. When suspended by one 
end horizontally in an oven and advancing the temperature slowly, the 
annealed poly(L-lactide) sample remained straight until a temperature of 
295.degree. F. (146.degree. C.) was obtained. The film then bent over. The 
annealed 90/10 copolymer bent over at a temperature of 185.degree. F. 
(85.degree. C.). The results show that the amount of crystallinity of 
polylactides can increase their form-stability at elevated temperatures to 
a temperature that is well above their T.sub.g. 
EXAMPLES 52-55 
The following examples illustrate the beneficial effects of adding lactide 
during compounding. The examples show that without lactide as modifier, 
the lactide polymer degrades during compounding. With the addition of 
lactide both discoloration and molecular weight decrease are prevented or 
substantially reduced during compounding. 
Thus, in Example 52, a 90/10, L-/D,L-lactide copolymer prepared as 
described by previous methods using 0.02 pph SnCl.sub.2.2H.sub.2 O 
catalyst was ground and extruded into pellets from a twin screw 
compounder, adding 5 weight percent lactide. The melt zone temperature of 
the extruder rose to 390.degree. F., the polymer discolored, and the 
weight average molecular weight (M.sub.w, by gel permeation 
chromatography) decreased by approximately 40 percent. The results 
indicated that insufficient lactide was added for this very high M.sub.w 
copolymer. The results are shown in Table 13. The pellets from this 
compounding were recompounded adding a further 10 weight percent lactide 
(Example 54). The melt zone temperature was 375.degree. F., and the 
results were much better: further discoloration did not occur, molecular 
weight decreased slightly, or within experimental error, and a pliable 
composition was obtained. 
TABLE 13 
______________________________________ 
EFFECT OF LACTIDE AS MODIFIER 
DURING COMPOUNDING 
Lactide.sup.(b) 
Ex. weight 
No. Color M.sub.w.sup.(a) 
M.sub.w /M.sub.n.sup.(a) 
percent 
______________________________________ 
Before Compounding 
52 light yellow 
513 2.15 0.78 
53 light yellow 
278 1.80 1.37 
After Compounding 
52 dark yellow 
322 2.05 5.56.sup.(c) 
53 yellow 184 1.90 2.26 
54 dark yellow 
307 2.00 14.4.sup.(d) 
55 colorless.sup.(e) 
324 1.99 14.6 
______________________________________ 
.sup.(a) GPC .times. 10.sup.-3. 
.sup.(b) By thermogravimetric analysis, at 200 C. 
.sup.(c) Five weight percent lactide added during compounding. 
.sup.(d) Further 10 weight percent lactide added during compound. 
.sup.(e) Thin film. 
To ascertain that the second compounding and extrusion were facilitated due 
to the lactide modifier and not the decreased molecular weight, another 
compounding (Example 53) was performed starting with a similar-M.sub.w 
copolymer of 90/10, L-/D,L-lactide. In this case, no lactide was added 
back in during the compounding. The melt zone temperature was 382.degree. 
F., the copolymer was discolored, and the M.sub.w decreased by 
approximately 66 percent. In addition, approximately 5 percent more torque 
was required to compound the mix of M.sub.w 278,000 as compared to the one 
of M.sub.w of 322,000 with added lactide. 
After compounding twice with lactide, Example 54 was analyzed by 
thermogravimetric analysis and found to have a lactide content of 14.4 
percent. The material of Example 54 was converted to a blown film by means 
of a Haake-Brabender extruder in Example 55. Thin films of this 
composition are colorless, highly transparent, and very pliable and 
extensible as described below in Examples 60-64. The Mw by gel permeation 
chromatography was 324,000 (cf. Mw=307,000 before compounding and 
extrusion). The Tg of this plasticized material is 42.degree. C. and 
differential scanning calorimetry reveals a very small amount of 
crystallinity melting at approximately 138.degree. C. The amount of 
lactide present is 14.6 percent as estimated by thermogravimetric 
analysis. 
EXAMPLES 56 AND 57 
The compounded polylactides, Example 52 and 53, were mixed together in the 
twin-screw compounder with extra lactide to raise the lactide level to 
approximately 20 percent. The compounding temperature was 347.degree. F. 
(175.degree. C.), much reduced from the previous 375.degree. to 
385.degree. F. The compounding proceeded smoothly without further 
discoloration. 
The above results clearly show the beneficial effects of added lactide as 
modifier. The required torque to compound the compositions, the 
discoloration, and the working temperature are decreased when adding 
lactide. Further evidence of plasticization is seen in the lowered Tg and 
the pliability of the compositions. In addition, molecular weight 
decreases are avoided and stable compositions are obtained. It will be 
obvious to those skilled in the art that the amount of lactide employed 
depends on many factors, including the desired amount of plasticization 
sought, the type of compounder that is used, and the molecular weight of 
the polylactides. 
EXAMPLES 58 AND 59 
Examples 58 and 59 illustrate blown film extrusion of polylactides. These 
pliable films mimic polyolefins. The plasticized compounds of Examples 56 
and 57 were adjusted to approximately 20 percent lactide in the twin-screw 
extruder. They were converted to blown films using a Haake-Brabender 
extruder. This consists of a 3/4-inch extruder with a blown-film die and 
take-up device. The blown-film was achieved using a 12.7 mm outside 
diameter orifice and a pin to establish an extrusion gap of 0.483 mm. An 
extrudate temperature of 187.degree. C. was maintained. A stable bubble 
was blown at this temperature with the inflation air at 3 oz/in..sup.2 
gauge pressure. Cooling air was blown against the exterior of the bubble 
at 18 psi. Since the final average film thickness was 0.158 mm (6.2 mil), 
the blow-up ratio was 3:1. When the extruder gap was reduced from 0.483 to 
0.254 mm, or the temperature raised, the polymer quenched readily to a 
crystalline, cloudy extrudate that would not expand. The larger orifice 
die produced an extrudate that was thicker and more viscous, cooled more 
slowly, and expanded in a consistent manner. The extruded film exhibited 
some elastic memory when stretched. The film also was resistant to tear 
and puncture and was very difficult to break by stretching. The blown film 
had an average elastic modulus of 117,000 psi, an average tensile strength 
of 3,735 psi, and an average elongation to break of 370 percent. This 
modulus is slightly higher than that of linear low density polyethylene, 
but the strength and elongation to break are comparable. The Elmerdorf 
Tear Strength (ASTM 1922) was 424 g in the cross machine direction and 183 
g in the machine direction. The Tg of the material was 36.degree. C., 
M.sub.w by gel permeation chromatography was 229,000, the residual lactide 
by thermogravimetric analysis was 19.7 percent, and the differential 
scanning calorimetry curves showed a weak endotherm centered at 
approximately 135.degree. C. 
EXAMPLES 60 TO 64 
These examples illustrate plasticization with oligomeric esters of 
poly(lactic acid). Copolymers of 90/10, L-/D,L-lactide were melt blended 
with added lactide, esters of oligomeric/lactic acid, and mixtures 
thereof. They were characterized by tensile and thermal properties. 
In Example 60, a control copolymer of 90/10, L-/D,L-lactide was assayed by 
thermogravimetric analysis to be 6.74 percent lactide. This was mixed with 
30 percent by weight oligomeric polymethyllactate (Mella) in Example 61, 
which was prepared by heating 2,500 g of (S)-methyllactate in an autoclave 
at 210.degree. C. for 3 hours, then collecting the Mella which 
fractionally distilled at 81 to 85.degree. C./1.25 torr. The mixture was 
melt blended on an open 2-roll mill at approximately 350.degree. F. The 
blend was compression molded in a press at approximately 350.degree. F. 
into clear, pliable films. The tensile properties, before and after, 
adding the Mella are recorded in Table 14. The glass transition 
temperature (Tg) was reduced by the Mella plasticizer. 
For Example 62, the 90/10, L-/D,L-lactide copolymer was melt blended with 
added L-lactide in a twin screw extruder to adjust the L-lactide content 
to 20 percent by weight. The blend was further mixed with oligomeric 
polyethyllactate (Ella) (Example 63) and Mella (Example 64). The 
properties of these blends are also recorded in Table 14. 
TABLE 14 
__________________________________________________________________________ 
CHARACTERISTICS OF POLYLACTIDES.sup.(a) PLASTICIZED 
WITH OLIGOMERIC ESTERS OF LACTIC ACID 
Elastic 
Break 
Ex. Modulus 
Strength 
Strain at 
No. Plasticizer 
psi psi Break, % 
T.sub.g.sup.(b) 
T.sub.m.sup.(c) 
__________________________________________________________________________ 
60 6.74%.sup.(d) L-lactide 
370,000 
6,903 2 51 141 
61 6.74%.sup.(d) L-lactide 
154,000 
2,012 100 30 141 
and 30% Mella.sup.(e) 
62 20% L-lactide 
101,000 
2,637 278 -- -- 
63 20% L-lactide 
7,316 
2,561 339 -- -- 
64 20% L-lactide 
3,620 
495 83 -- -- 
and 30% Mella.sup.(e) 
__________________________________________________________________________ 
.sup.(a) 90/10, L/racemic D,Llactide copolymer. 
.sup.(b) Glass transition temperature. 
.sup.(c) Melting point. 
.sup.(d) Analyzed by thermogravimetric analysis. 
.sup.(e) Methyllactate oligomer. 
.sup.(f) Ethyllactate oligomer. 
EXAMPLES 65 TO 81 
Comparative Examples 65 to 81 were selected from the patent literature that 
presented conditions most likely to result in materials of the present 
invention. The materials produced in these patents were not completely 
characterized, thus experiments were needed to allow a more complete 
characterization of the examples and provide meaningful comparisons that 
would demonstrate that the materials of the present invention are indeed 
novel. With regard to the present invention, compositions were sought that 
had residual lactide or lactic acid contents of about 0.1 to about 60 
weight percent and in addition may have the lactide or lactic acid 
intimately dispersed within the polymer. The results fall into obvious 
categories. Thus, products with number-average molecular weights, M.sub.n, 
less than 10,800 do not have the physical properties required in the 
present invention. In fact films from these low M.sub.n compositions were 
too brittle to be handled for tensile measurements. 
It is known from the teachings herein that lactic acid, lactide, or 
oligomers of lactide or lactic acid, or derivatives of lactic acid must be 
present to provide plasticization and some pliability. The lactide must be 
present in amounts greater than about 10 weight percent while the 
oligomers of lactic acid, oligomers of lactide and the derivatives of 
lactic acid must generally be present above about 40 percent to provide 
obvious plasticization and pliability to polylactides. However, any amount 
of plasticizer as taught herein when added to the composition will change 
properties and can be used to obtain specialty formulated compositions. 
Thus, if lactide is intimately dispersed and effectively mixed as 
plasticizer, the mix of lactide and polylactide is completely transparent. 
The heterogeneous domain size of the lactide is small enough, generally 
less than one micron, so that it will no longer scatter light, i.e., it is 
intimately dispersed. Conversely, white opaque samples are always hard 
because they have crystallized under the test conditions. Crystallization 
squeezes the lactide out of the polymer mass, resulting in hard stiff 
compositions that are a gross mixture of monomer and polymer. This is also 
obvious from differential scanning calorimetry (DCS). Monomeric lactide 
that has segregated reveals itself with a separate melting point at 
95.degree. to 100.degree. C., whereas well-plasticized samples do not show 
a distinct monomer melting point. 
One very important point is that the cited patents frequently specify 
L-lactide homopolymer ("100 percent L-" in Tables 15A and 15B). The 
homopolymer of L-lactide easily crystallizes because of its high melting 
point. At lower reaction temperatures, the homopolymer can retain 
appreciable quantities of monomer, but the composition freezes during 
polymerization. At higher reaction temperatures, the L-lactide polymerizes 
so quickly that it is very difficult to stop the polymerization with 
substantial monomer left in the product. 
Inspecting the results listed in Table 15A and 15B reveals that the 
comparative examples obtain either products with low residual lactide or 
else the polymerizations did not work or worked so poorly that greater 
than 40 percent lactide was left at the end of the specified 
polymerizations. Thus, Examples 65, 66 (very similar also to the work of 
Schneider), 67, 69, 73, 74, and 75 obtain low residual lactide. The 
Examples 70, 71, 72, 76, 77, and 78 examples did not work well as written 
in the patent examples. The best known laboratory techniques were added to 
the procedures, described in the footnotes, on these examples, from a 
historical standpoint (monomer purity, for example) in an effort to make 
the procedures work, with indifferent success. In no examples were pliable 
products found. Either glassy, or hard, crystalline, opaque products were 
obtained. It should be noted that only those examples using tin compounds 
as catalysts appear to be acceptable for many packaging applications. 
It appeared particularly that the Tunc methods would provide the materials 
of the present invention. To ascertain this, it was necessary to do the 
listed experiments on the teachings of Tunc in laborious detail as shown 
in Examples 79 to 81. FIG. 5 is a differential scanning calorimetry of one 
of the polylactides of the present invention. There is no detectable 
melting point for residual lactide monomer in the vicinity of 95.degree. 
to 100.degree. C. Only the polymer melting is seen. This material was 
analyzed separately by thermogravimetric analysis and shown to be 18.4 
percent monomer lactide. 
By way of contrast, preparations according to the exact replication of the 
Tunc methods were performed. Thermogravimetric analysis reveals 20.2 
percent residual lactide for one such preparation. Example 80. The 
differential scanning calorimetry of this material is shown in FIG. 6, 
where a very distinct monomer melting point is seen. This corresponds to 
segregated lactide with a melting point within its own heterogeneous 
domain. Whereas this polymer is white, opaque, very hard and stiff, the 
composition of the present invention preparation is clear, transparent, 
and very pliable. 
A similar result was obtained repeating the teachings of Tunc in Example 
81. This analyzed as 32.2 percent lactide and revealed a monomer melting 
point (FIG. 7). The material was very white, crystalline, and hard. The 
results are reviewed in Table 15A and 15B. 
TABLE 15A 
__________________________________________________________________________ 
RELATED ART POLYMERIZATIONS OF LACTIDE CONDITIONS 
Ex. Pat. Lactide 
Catalyst Polymerization 
No. 
Patent Ex. Monomer(s) 
Type pph Temp. C. 
hours 
__________________________________________________________________________ 
65 2,758,987 
1 L- PbO 0.30 150 42 
66 2,758,987 
3 50/50 PbO 3.00 150 89 
L-/D,L 
67 3,982,543 
3 L- PbO 0.30 150 31 
68 DD 14548 
2 L- SnO.sup.(a) 
0.009 
193 3 
69 4,137,921 
4 90/10 Sn(Oct).sub.2, 
0.0553 
180 0.33 
L-/DL GA/dioxane.sup.(b) 
190 0.33 
210 0.33 
70 GB 755,447 
4 D,L ZnO.sup.(c) 
0.02 150 24 
71 GB 755,447 
2 D,L Zn Powder.sup.(d) 
0.02 140 25.5 
72 GB 755,447 
6 D,L Zn Carbonate 
0.02 140 2 
Hydroxide.sup.(c) 
150 3 
73 CA 932,382 
1 D,L Tetraphenyl 
0.02 165 20 
Tin 
74 CA 923,245 
1,7 & 8 
L- Et.sub.2 Zn 
0.167 
105-110 
2 
75 DE 946,664 
2 D,L.sup.(e) 
ZnCl.sub.2 
0.25 140 48 
76 DE 1,112,293 
1 L- Sn Stearate 
0.0087 
205-210 
0.5 
as Sn 
77 2,951,828 
1 L-.sup.(f) 
SnCl.sub.4 
0.30 160 5 
suspension.sup.(g) 
78 3,268,487 
2 D,L Tris(2- 0.88 80 24 
chloroethyl) 
amine.sup.(h) 
79 EP Applic. 
6, L- Sn(Oct).sub.2 
0.00108 
165 93 
108,635(1984) 
Polymer 8 
4,550,449; 
4,539,981 
80 4,539,981 & 
Polymer 33 
L- Sn(Oct).sub.2 
0.00119 
136-139 
64 
4,550,449 
81 4,539,981 & 
Polymer 37 
L- Sn(Oct).sub.2 
0.00324 
115 64.5 
4,550,449 
__________________________________________________________________________ 
.sup.(a) No reaction until recipe was changed by adding 0.75 pph of 88 
percent lactic acid. Product was white, opaque, very hard and brittle; 
film too brittle to handle. 
.sup.(b) Included was glycolic acid as chain transfer agent. 
.sup.(c) Insoluble. 
.sup.(d) Insoluble after 24 hours plus additional 1.5 hours with 700 .mu. 
88 percent lactic acid and 100 .mu.l H.sub.2 O. 
.sup.(e) In toluene; product colorless and very viscous. 
.sup.(f) In mineral spirits, Stoddard solvent No. R66. 
.sup.(g) Agglomerated. 
.sup.(h) In dioxane containing 0.517 pph KOH; no polymerization. 
TABLE 15B 
__________________________________________________________________________ 
RELATED ART POLYMERIZATIONS OF LACTIDE RESULTS 
Residual 
Ex. 
Monomer, 
GPC .times. 10-3 
Polymerizate 
No. 
Percent 
M.sub.n 
M.sub.w 
M.sub.z 
M.sub.w M.sub.n 
Appearance 
__________________________________________________________________________ 
65 0 254 454 
717 1.79 
Light yellow, crystalline, 
opaque 
66 0 97 187 
322 1.94 
Light yellow, transparent 
67 0.85 95 195 
325 2.06 
Partially opaque crystalline, 
partial transparent 
68 17.5(a) 
5 7 9 1.47 
White, crystalline, opaque 
7.1;7.7 
7 8 10 1.25 
69 4.6 116 218 
356 1.88 
Light yellow, transparent 
70 47.7 -- -- -- -- White, crystalline (monomer), 
opaque 
71 65.3 -- -- -- -- White, crystalline (monomer), 
opaque 
72 79.6 -- -- -- -- White, crystalline (monomer), 
opaque 
73 1.4 116 214 
340 1.84 
Yellow, transparent 
74 1.9 80 150 
235 1.87 
Orange, crystalline, opaque 
75 5.4.sup.(i) 
164 377 
657 2.30 
Hard, colorless 
2.5;1.9.sup.(j) 
307 527 
808 1.72 
76 43.3 30 35 
41 1.17 
Hard, crystalline, opaque 
77 8.6;9.6 
219 343 
504 1.57 
Hard, crystalline, opaque 
78 100 -- -- -- -- All crystalline monomer 
79 5.0 14 26 
35 1.88 
White, crystalline, opaque 
film.sup.(k) 
14 26 
35 1.82 
Some transparency at edges 
80 20.2.sup.(l) 
greater than 1,000,000 
White, crystalline opaque 
81 32.2.sup.(m) 
greater than 1,000,000 
White, crystalline opaque 
__________________________________________________________________________ 
.sup.(i) Sample heated at 140 C, then 5 minutes in 60 C vacuum oven to 
remove solvent. 
.sup.(j) Sample heated overnight in 60 C vacuum oven to remove solvent. 
.sup.(k) Transparent, very stiff and brittle. 
.sup.(l) Tunc obtains 17.1 percent, very high molecular weight. 
.sup.(m) Tunc obtains 28.0 percent, very high molecular weight. 
The above examples establish that an all-lactic acid composition can be a 
pliable thermoplastic useful for flexible, plastic packaging films and 
containers. By way of comparison, nonplasticized homopoly (L-lactide) is a 
highly crystalline polymer with a tensile strength of about 7000 psi with 
an elongation of 1 percent and an initial modulus of 500,000 psi. It is 
very brittle, opaque, and crazes easily. It is not a well behaved 
thermoplastic, nor is it transparent. Poly (racemic D,L-lactide) is an 
amorphous, glassy, polymer with a glass transition temperature of 
approximately 50.degree. C., a tensile strength of about 6300 psi, an 
elongation of approximately 12 percent, and an initial modulus of 160,000 
psi. It is also very brittle although transparent. In stark contrast, a 
copolymer of L-lactide/racemic D,L-lactide that is plasticized with 
lactide monomer is remarkably different. For example, the plasticized 
polymers can have a tensile strength of approximately 3900 psi, an 
elongation of 431 percent, and an initial modulus of 56,000 psi. The 
plasticized polymer is clear and colorless, and the blend must be heated 
to above 100.degree. C. to remove the plasticizer. 
Although theory would predict a more amorphous structure as a result of 
plasticization, what is surprising is the pliable, transparent, stable 
compositions that can arise, and, secondly, the nearly exact fit of 
properties needed for certain packaging applications, such as 
polyethylene. This invention comes at a time when there is a need for such 
initial properties in a material that is slowly environmentally 
biodegradable since it could alleviate plastic pollution problems. 
It will be apparent to those skilled in the art that extremely intimate 
blends of high polymers and plasticizers are a rarity. Intimate 
plasticization allows a wide latitude in the initial physical properties 
and the time for environmental biodegradation. 
The amount of plasticizer in the polymer depends on the compositional 
characteristics desired. If lactide is used as plasticizer the range is 
preferably 10 to 40 weight percent whereas if only oligomers of lactide or 
lactic acid are used the range may be from 10 to 60 weight percent. 
Surprisingly, oligomer may be added at up to 30 weight percent without 
substantially affecting the tensile strength or modulus. See FIGS. 3 and 
4. Addition of 30 to 60 weight percent oligomers produces significant 
plasticization and attenuation of physical properties. This adds great 
economy to the composition since oligomeric lactic acid is cheaper than 
the high molecular weight polylactide. Oligomer may be prepared from 
lactic acid or any lactide. It is important to note that the oligomer of 
lactic acid normally contains significant amounts of lactic acid unless 
removed. This is an important consideration in tailoring compositions 
having specific properties. Those skilled in the art and knowing the 
teachings of this invention will be able to select reaction conditions to 
obtain appropriate chain lengths for the polymer, and the proportions of 
polymer and plasticizer so as to obtain fabricated compositions having 
physical properties similar to commonly used packaging thermoplastics and 
yet degrade comparatively rapidly. For example, higher amounts of 
plasticizer result in polymers having increased flexibility and 
increasingly tough physical properties, however, an increasing degradation 
rate will also be obtained. Further, shorter chain lengths for the polymer 
will require less plasticizer to obtain the same properties as with longer 
lengths. 
Preferably polymerization of the monomers is at a temperature less than 
129.degree. C. Further processing of the plasticized polymer into a final 
product is preferably at a temperature sufficiently low to retain the 
plasticizer in the polymer. This temperature may be above 129.degree. C. 
If additional monomer and/or oligomer are added after polymerization the 
retention of monomer during processing is of course not as critical. 
The unoriented compositions of the invention should have a tensile strength 
of 300 to 20,000 psi, an elongation to failure of 50 to 1,000 percent and 
a tangent modulus of 20,000 to 250,000 psi. Preferably for a polyolefin 
replacement the compositions have a tensile strength of at least 3000 psi, 
an elongation to failure of at least 250 percent, and a tangent modulus of 
at least 50,000 psi. 
A composition for the replacement of polyethylene is adjusted so that the 
unoriented composition has a tensile strength of about 1,200 to about 
4,000 psi, an elongation to failure of about 100 to about 800 percent, and 
a tangent modulus of about 20,000 to about 75,000 psi, while a composition 
for the replacement polypropylene, is adjusted so that the unoriented 
composition has a tensile strength of about 4,500 to about 10,000 psi, an 
elongation to failure of about 100 to about 600 percent, a tangent modulus 
of about 165,000 to about 225,000 psi, and a melting point of about 
150.degree. to about 190.degree. F. 
The homopolymers and copolymers of the present invention are insoluble in 
water but upon constant contact with water are slowly degradable. However, 
degradation is fast when compared to polyolefin compositions that are 
replaced by the invention. Thus, throwaway objects made from the polymers 
are environmentally attractive in that they slowly degrade to harmless 
substances. If objects made from polymers of the invention are 
incinerated, they burn with a clean, blue flame. 
The compositions herein are useful for replacement of polyolefin 
compositions and particularly polyethylene and polypropylene as well as 
polyvinyl chlorides and polyethylene terephthalate. In addition to the 
above list, the method is useful for replacement of polymers of styrene, 
vinyl acetate, alkyl methacrylate, alkyl acrylate. It is understood that 
copolymers made from mixtures of the monomers in the listed group and 
physical mixtures of the polymers and copolymers of the above group are 
likewise replaceable. Those skilled in the art will recognize that minor 
amounts of lactide and lactic acid can be replaced by contemplated 
equivalents such as glycolide, glycolic acid, and caprolactone. 
While the invention has been described above with reference to various 
specific examples and embodiments, it will be understood that the 
invention is not limited to such illustrated examples and embodiments and 
may be variously practiced within the scope of the claims hereinafter 
made.