DESCRIPTION
Title of the Invention: POLYLACTIC ACID COMPOSITION, FORMED
ARTICLE OBTAINED FROM POLYLACTIC ACID COMPOSITION, AND METHOD
FOR PRODUCING POLYLACTIC ACID COMPOSITION
Technical Field
The present invention relates to a polylactic acid
composition. More specifically, it relates to a polylactic
acid composition, a formed article obtained from a polylactic
acid composition, and amethod for producing a polylactic acid
composition.
Background Art
In recent years, from the viewpoint of global
environmental protection, biodegradable polymers, which
degrade in the natural environment, have been al-tracting
attention and studied all over the world. As biodegradable
polymers, polyhydroxyalkanoates, polycaprolactones,
polyglycolic acids, polybutylene succinates, polylactic acids,
and the like are known. Polylactic acids are obtained from
lactic acid, which is obtained from a biologically derived raw
material, or derivative sthereof, andthus have highbiological
safetyandserveas eco-friendlypolymermaterials. Therefore,
as formed articles made of a polylactic acid, the development
of fibers, films, and injection-molded products has been
advanced. In addition, applications in the medical field,
such as surgical sutures, sustained-release capsules, and
reinforcing materials for bone fracture, have also been
examined.
However, polylactic acids have low melting point, and
thus their use as fibers, films, or various molded articles
is limited. Moreover, the crystallization rate is also low,
and thus it is said that their forming processability is
inferior as compared with general plastics.
Meanwhile, it is known that by mixing a poly-L-lactic
acid and a poly-D-lactic acid in solution or melt form, a
polylactic acid having a stereocomplex crystal phase
(hereinafter sometimes referred to as stereocomplex
polylactic acid) is formed (PTL 1 and NPL 1). It is also known
that such a stereocomplex polylactic acid has a melting point
of 200to 230°C, which is higher as comparedwithpoly-L-lactic
acids or poly-D-lactic acids, and also shows higher
crystallinity. Therefore, stereocomplexpolylacticacidsmay
provide a wider range of usable applications than by the
low-melting-point, low-crystallinity polylactic acids
describedabove. Alsowith respect tothe low crystallization
rate, which is one of the drawbacks of polylactic acids, it
is known that use of a stereocomplex polylactic acid leads to
an improved crystallization rate
However, a stereocomplex polylactic acid does not show
single crystals but is a mixed composition composed of a
poly-L-lactic acid and poly-D-lactic acid crystal phase
(hereinafter sometimes referred to as homocrystal phase) and
a stereocomplex polylactic acid crystal phase (stereocomplex
crystal phase), and, usually, two peaks are observed: a
low-melting-point crystal melting peak having a peak
temperature of less than 190°C corresponding to the melting
of the homocrystal phase, and a high-melting-point crystal
melting peak having a peak temperature of 190°C or more
correspondingtothemeltingofthe stereocomplexcrystalphase.
Therefore, the heat resistance is on the same level as that
of ordinary polylactic acids, and, in addition, the
crystallinity or crystallization rate is not significantly
improved either. Thus, it cannot be said that the original
physical properties of stereocomplex polylactic acids have
been sufficiently exerted.
Meanwhile, in order for a stereocomplex polylactic acid
to sufficiently exert its heat resistance, PTL 2 describes a
polylactic acid composition using a crystallization nucleator,
suchas a phosphatemetal salt, and including not ahomocrystal
phase but only a stereocomplex crystal phase having a crystal
melting point of 20g°C.
Citation List
Patent Literature
PTL 1: JP-A-63-241024
PTL 2: JP-A-2003-192884
NPL 1: Macromolecules, 24, 5651 (1991)
Summary of Invention
Technical Problem
Incidentally, a poly-L-lactic acid and a poly-D-lactic
acid to serve as raw materials for producing a stereocomplex
polylactic acid usually contain certain kinds of
polymerization catalysts, and a phosphorus-based catalyst
deactivator may be added to deactivate them, or a
phosphorus-basedantioxidantmaybeaddedto suppress coloring,
for example. The present inventors have found that in such
a case, when a stereocomplex polylactic acid is produced using
themas rawmaterials, the stereocomplex crystallinitymaynot
be sufficient, or, even if the stereocomplex crystallinity is
high, it may happen that the melting point of stereocomplex
crystals itself is low or the molecular weight decreases;
therefore, it is difficult to produce a satisfactory
stereocomplex polylactic acid composition.
In order to deal with this problem, there has been a demand
for a method for stably producing a stereocomplex polylactic
acid having a high stereocomplex crystallinity and a high
stereocomplex crystal melting point, a small stereocomplex
melting point depression during remelting, a small decrease
inthemolecularweight, excellent formingprocessabillty, and
also heat resistance, even in the case where a poly-L-lactic
acid and a poly-I-lactic acid containing a phosphorus-based
catalyst deactivator, a phosphorus-based antioxidant, or like
additives are used as raw materials.
An object of the invention is to provide a novel
stereocomplex polylactic acid composition.
Another object of the invention is to provide a
stereocomplex polylactic acid composition having excellent
forming processability and excellent heat resistance.
Another object of the invention is to provide a formed
article obtained from a polylactic acid composition.
Still another object of the invention is to provide a
method for stablyproducingthe stereocomplex polylactic acid
composition described above.
Solution to Problem
The present inventors have conducted extensive research
to solve the above problems in the case where a tin-based
polymerization catalyst for producing a polylactic acid and
also a phosphorus-based compound, such as a phosphorus-based
catalyst deactivator for deactivating the catalyst or a
phosphorus-based antioxidant for suppressing the coloring of
the polylactic acid, are contained. As a result, they have
ascertained that it is important to use an organic acid metal
salt or an organic metal salt, or both of them, for
stereocomplex crystallization. They have found that when an
organic acid metal salt or an organic metal salt is used,
stereocomplex crystals grow preferentially, and, as a result,
a stereocomplex polylactic acid having a high stereocomplex
crystallinityanda high stereocomplexmelting point, inwhich
the stereocomplex crystal melting point depression durlng
remelting and a decrease in the molecular weighL can be
suppressed, can be suitably obtained, and thus accomplished
the invention.
That is, the invention is as follows.
[I] Apolylacticacidcompositioncontainingastereocomplex
polylactic acid,
the stereocomplex polylactic acid containing a
poly-L-lactic acid (A) and a poly-D-lactic acid (B) and having
a stereocomplex crystallinity (S) of 90% or more as defined
by the following equation (a):
S = AH,, x 100/ ( AHh, + AH,,) (a)
wherein AH,, represents the enthalpy (J/g) of stereocomplex
crystals in the polylactic acid composition, and AHh,
representstheenthalpy (J/g) ofhomocrystalsinthepolylactic
acid composition,
the content ratio between the poly-L-lactic acid (A) and
the poly-D-lactic acid ( E ) being within a range of 80/20 to
20/80 (mass ratio),
the polylactic acid composition containing a tin-based
compound, a phosphorus-based compound, and further at least
one of a metal organic acid metal salt of at least one member
selected from alkali metals and alkaline earth metals, and an
organic metal salt,
in the case where the kind of metal of the organic acid
metal salt is analkalimetal, themolar ratioofthephosphorus
(P) atom to the organic acid metal salt being within a range
of 0.5 to 1.5,
in the case where the kind of metal of the organic acid
metal salt is an alkaline earth metal, the molar ratio of the
phosphorus (P) atomtothe organic acidmetal salt being within
a range of 0.1 to 1.0,
in the case of the organic metal salt, the molar ratio
of the phosphorus (P) atom to the organic metal salt being
within a range of 0.5 to 2.2.
[2] The polylactic acid composition according to [I] above,
wherein the organic acid of the organic acid metal salt is a
C2-24 fatty acid.
[3] The polylactic acid composition according to [I] above,
wherein the organic acid of the organic acid metal salt is a
C7-12 aromatic acid.
[4] The polylactic acid composition according to [I] above,
wherein the organic metal salt is at least one kind of metal
alkoxide selected from the group consisting of Cl-ioa liphatic
alkoxides and c6-1~ aromatic alkoxides.
[5] The polylactic acid composition according to [I] above,
wherein the tin-based compound is at least one member selected
from the group consisting of tin octylate and tin alkoxides
containing a Cl-10 fatty alcohol as a constituent.
[6] The polylactic acid composition according to [I] above,
wherein the phosphorus-based compound is at least one kind of
phosphorus compound selected from the group consisting of
phosphorous acid, phosphoric acid, phosphonic acid,
phosphites, phosphates, and phosphonates.
[7] The polylactic acid composition according to any one of
[l] to [6] above, wherein the amount of Sn in terms of metal
is 0.02 parts by mass or less relative to 100 parts by mass
of the total of the poly-L-lactic acid and the poly-D-lactic
acid, and the mass ratio of the phosphorus atom from the
phosphorus-based compound to the tin atom from the t i-n-based
compound (P/Sn) is within a range of 0.15 to 5.0.
[8] The polylactic acid composition according to any one of
[l] to [7] above, wherein the polylactic acid composition has
a melting point (T,,) from stereocomplex crystals of 210°C or
more, and, in DSC measurement under the following conditions,
the difference between T,, measured after three cycles and T,,
measured after one cycle (AT,,) is 8°C or less:
DSC measurement conditions:
(i) heatlng from 30°C to 260°C (heating rate: 20°C/min);
(ii) holding at 260°C for 1 min;
(iii) cooling from 260°C to 30°C (cooling rate: 20°C/min) ;
and
(iv) the (i) to (iii) are taken as one cycle, and the
cycle is repeated three times as three cycles.
[9] The polylactic acid composition according to any one of
[1] to [8] above, wherein the stereocomplex polylactic acid
has a weight average molecular weight (Mw) of 100,000 or more.
[lo] The polylactic acid composition according to any one of
[I] to [9] above, containingO.1to10partsbyrnassofacompound
havingatleastone carbodiimide group inonemolecule relative
to 100 parts by mass of the polylactic acid composition.
[Ill The polylactic acid composition according to any one of
[I] to [lo] above, further containing an organic acid from the
organic acid metal salt.
[12] A formed article obtained from the polylacLic acid
composition according to any one of [I] to [Ill above.
[I31 A method for producing a polylactic acid composition
containing a stereocomplex polylactic acid,
the stereocomplex polylactic acid containing a
poly-L-lactic acid (A) and a poly-D-lactic acid (B) and having
a stereocomplex crystallinity (S) of 90% or more as defined
by the following equation (a) :
S = AH,, x 100/ (AHh, + AH,,) (a)
wherein AH,, represents the enthalpy ( J / g ) of stereocomplex
c r y s t a l s i n the p o l y l a c t i c a c i d composition, and AHho
r e p r e s e n t s t h e e n t h a l p y ( J / g ) ofhomocrystalsinthepolylactic
acid composition,
the content r a t i o between the poly-L-lactic acid (A) and
the poly-D-lactic acid ( B ) being within a range of 80/20 t o
20/80 (mass r a t i o ) ,
the method including a t l e a s t the following s t e p s :
(i) a step of preparing a mixture containing a
poly-L-lactic acid ( A ) , a poly-D-lactic acid ( B ) , a tin-based
compound, and a phosphorus-based compound;
(ii) a step of adding a t l e a s t one of an organic acid
metal s a l t of a t l e a s t one member s e l e c t e d from a l k a l i metals
and a l k a l i n e e a r t h metals, and an organic metal s a l t t o the
mixture of (i) i n such a manner t h a t the following conditions
a r e s a t i s f i e d : i n t h e c a s e w h e r e t h e k i n d o f m e t a l o f t h e o r g a n i c
acid metal s a l t is an a l k a l i metal, the molar r a t i o of the
phosphorus ( P ) atom t o the organic acid metal s a l t is within
a range of 0.5 t o 1.5; i n the case where the kind of metal of
the organic acid metal s a l t is an a l k a l i n e e a r t h metal, the
molar r a t i o ofthephosphorus ( P ) a t o m t o t h e organicacidmetal
s a l t is within a range of 0 . 1 t o 1 . 0 ; and i n the case of the
organic metal s a l t , the molar r a t i o of the phosphorus ( P ) atom
t o the organic metal s a l t is within a range of 0.5 t o 2.2; and
(iii) a s t e p of, a f t e r the step (ii),m elt-kneading the
mixture at a temperature of 260 to 300°C.
[14] The method for producing a polylactic acid composition
according to [I31 above, wherein in the step (i), themass ratio
of the phosphorus atom fromthe phosphorus-based compound to
the tin atom from the tin-based compound (P/Sn) is within a
range of 0.15 to 5.0.
Advantageous Effects of Invention
According to the invention, even when a tin-based
polymerization catalyst and a phosphorus-based compound are
present in the poly-L-lactic acid (A) and the poly-D-lactic
acid (B), by using a specific proportion of an organic acid
metal salt or an organic metal salt for stereocomplex
crystallization, a stereocomplex polylactic acid composition
having a high stereocomplex crystallinity and a high
stereocomplex crystal melting point, a small stereocomplex
crystalmelting point depression evenafter remeltiny, a small
decrease in the molecular weight, excellent forming
processability, andalsoheat resistance canbeprovided. The
stereocomplexpolylactic acidcomposition ofthe inventionhas
a small depression in the stereocomplex crystalmelting point,
and thus is extremely promising as injection-molded products,
films, fibers, and various formed products having excellent
heat resistance.
Description of Embodiments
Hereinafter, modes for carrying out the invention will
be described in detail. Incidentally, these descriptions and
examples are illustrative of the invention, and do not limit
the scope of the invention.

The polylactic acid in the invention is a
high-melting-point polylactic acid having stereocomplex
crystals (hereinafter sometimes referred to as stereocomplex
polylactic acid), and can be produced by solution-mixing or
melt-mixing a poly-L-lactic acid and a poly-D-lactic acid.
Hereinafter, polylactic acids (poly-L-lactic acid and
poly-D-lactic acid) will be described.
A polylactic acid is a polymer mainly containing an
L-lactic acid unit or D-lactic acid unit represented by the
following formula or a combination thereof. Polylactic acids
include poly-L-1.actic acids and poly-D-lactic acids.
A poly-L-lactic acid is a polymer mainly containing an
L-lactic acid unit. A poly-L-lactic acid contains the
L-lactic acidunitpreferablyinaproportionof 90to100mol%,
more preferably 95 to 100 mol%, and still more preferably 97
to 100 mol%. As other units, a D-lactic acid unit and units
other than lactic acid can be mentioned. The proportion of
the D-lactic acid unit and units other than lactic acid is
preferably 0 to 10 mol%, more preferably 0 to 5 mol%, and still
more preferably 0 to 3 mol%.
In addition, a poly-D-lactic acid is a polymer mainly
containing a D-lactic acid unit. A poly-D-lactic acid
contains the D-lactic acid unit preferably in a proportion of
90 to 100 mol%, more preferably 95 to 100 mol%, and still more
preferably 97 to 100 mol%. As other units, an L-lactic acid
unit and units other than lactic acid can be mentioned. The
p r o p o r t i o n o f t h e L - l a c t i c a c i d u n i t a n d ~ ~ n i t s o t h e r t h a n l a c t i c
acid is 0 to 10 mol%, preferably 0 to 5 mol%, and still more
preferably 0 to 3 mol%.
Examples of units other than lactic acid in a
poly-L-lactic acid or a poly-D-lactic acid include units
derived from dicarboxylic acids having two or more
ester-bond-forming functional groups, polyhydric alcohols,
hydroxycarboxylic acids, lactones, and the like, as well as
units derives from various polyesters, various polyethers,
various polycarbonates, and the like composed of these various
constituents.
Examples of dicarboxylic acids include succinic acid,
adipic acid, azelaic acid, sebacic acid, terephthalic acid,
andisophthalicacid. Examples ofpolyhydricalcoholsinclude
aliphatic polyhydric alcohols such as ethylene glycol,
propylene glycol, butanediol, pentanediol, dihydroxyhexane,
octanediol, glycerin, sorbitan, neopentyl glycol, diethylene
glycol, triethylene glycol, polyethylene glycol, and
polypropylene glycol, and also aromatic polyhydric alcohols
such as ethylene oxide-added bisphenol. Examples of
hydroxycarboxylic acids include glycolic acid and
hydroxybutyric acid. Examples of lactones include glycolide,
E-caprolactone glycolide, E-caprolactone, P-propiolactone,
6-butyrolactone, P- or y-butyrolactone, pivalolactone, and
6-valerolactone.
It is preferable that the poly-L-lactic acid and the
poly-D-lactic acid in the invention have an optical purity of
97% or more. When the optical purity is 97% or more, the
improvement of the melting point can be expected.
The optical purity of the poly-L-lactic acid and that
of the poly-D-lactic acid were determined as follows. In the
caseofapoly-L-lactic acid, the opticalpuritywas determined
from the ratio between the L-lactic acid unit, which is the
main structural unit, and the partial D-lactic acid unit.
First, 5 mL of 5 M sodium hydroxide and 2.5 mL of methanol were
added to 1 g of a sample, hydrolyzed with heating and stirring
at 40°C, and then neutralized with 1 M sulfuric acid. 1 mL of
the neutralized solution was diluted 25-fold to adjust the
concentration. The solution was subjected to high-speed
liquid chromatography (HPLC) to measure the detection peak
areas of L-lactic acid and D-lactic acid under UV light at 254
nm, and, from the mass proportion of the L-lactic acid unit
[L] ( % ) and the mass proportion of the D-lactic acid unit [Dl
( % ) forming the polylactic acid polymer, each optical purity
( % ) was calculated from the following equation.
Optical purity ( % of poly-L-lactic acid = 100 x [L] / ( [L]
+ [Dl)
Optical purity ( % ) o f p o l y - D - l a c t i c a c i d = 1 0 0 x [D]/([L]
+ [Dl)
Apolylactic acid canbeproducedby a knownmethod. For
example, it can be produced by subjecting L-lactide or
D-lactide to heating and ring-opening polymerization in the
presence of a metal-containing catalyst. It can also be
produced by crystallizing a low-molecular-weight polylactic
acid containing a metal-containing catalyst, followed by
heating and solid-phase polymerizationunder reducedpressure
or in an inert gas stream. Further, it can also be produced
by a direct polymerization method, in which lactic acid is
subjected to dehydration condensation in the presence or
absence of an organic solvent.
The polymerization reaction can be carried out in a
conventionallyknownreactionvessel. For example, avertical
reactionvesselequippedwithahigh-viscositystirringblade,
such as a helical ribbon blade, may be used alone, or it is
also possible to use such vessels in parallel. As a
polymerization initiator, an alcohol may be used. It is
preferable that such an alcohol does not inhrbit the
polymerization ofthepolylactic acid and is nonvolatile. For
example, decanol, dodecanol, tetradecanol, hexadecanol,
octadecanol, ethylene glycol, triethylene glycol, benzyl
alcohol, and the like may be preferably used.
In a solid-state polymerization method, a lactic acid
polyester having a relatively low molecular weight, which is
obtained by the ring-opening polymerization method or
lactic-acid direct polymerization method described above, is
usedasaprepolymer. It canbe saidthatintermsofpreventing
fusion, a mode in which the prepolymer is previously
crystallized in a temperature range not lower than its glass
transition temperature (Tg) and lower than its melting point
(Tm) is preferable. The crystallized prepolymer is placed in
a fixed vertical reaction vessel or in a reaction vessel which
itself rotates, such as a tumbler or a kiln, and heated to a
temperature range not lower than the glass transition
temperature (Tg) and lower than the melting point (Tm) of the
prepolymer. With respect to the polymerizatiori temperature,
there is no problem in increasing the temperature gradually
with the progress of polymerization. In addition, it is also
preferable to reduce the pressure inside the reaction vessel
forthe purpose of efficiently removingwater generatedduring
solid-state polymerization, or also use a method in which a
heated inert gas stream is circulated.
Generally, as metal-containing catalysts used for
producing a polylactic acid, catalysts containing at least one
member selected fromtin, aluminum, zinc, calcium, titanium,
germanium, manganese, magnesium, and rare earth elements are
known. In the invention, the metal-containing catalyst for
producing a poly-L-lactic acid or a poly-D-lactic acid is a
tin-containing catalyst containing tin (Sn). Specific
examplesthereof include tin-based compounds such as stannous
chloride, stannous bromide, stannous iodide, stannous sulfate,
stannic oxide, tin myristate, tin octylate, tin stearate,
tetraphenyltin, tinmethoxide, tinethoxide, andtinbutoxide.
The amount of tin-containing catalyst used is, in terms
of the Sn atom, preferably 0.02 parts by mass or less, more
preferably 0.0001 to 0.02 parts by mass, relative to 100 parts
by mass of the poly-L-lactic acid or the poly-D-lactic acid.
Further, considering the reactivity and also the color tone
and thermal stability of the resulting poly-L-lactic acid or
poly-D-lactic acid, the amount is stillmore preferably 0.0001
to 0.01 parts by mass, and particularly preferably 0.0001 to
0.005. theamount oftin-containingcatalystusedis, interms
of the Sn atom, preferably 0.01 parts by mass or less, more
preferably 0.0001 to 0.01 parts by mass, relative to 100 parts
by mass of the total of the poly-L-lactic acid and the
poly-D-lactic acid.
It is preferable that the tin-based compound is
deactivated with a deactivator composed of a phosphorus-based
compoundafterthecompletionoflactidepolymerization. Such
deactivation is advantageous in preventing a decrease in the
molecular weight of the polylactic acid.
As such deactivators, phosphorus-based compounds are
preferably used, for example. Examples thereof include
organic ligands consisting of chelate ligands having an imino
group and capzble of coordinating with a polymerization metal
catalyst; low-oxidation-number phosphoric acids having an
oxidation number of 5 or less, such as dihydridooxophosphoric
(I) acid, dihydridotetraoxodiphosphoric (I1,II) acid,
hydridotrioxophosphoric (111) acid,
dihydridopentaoxodiphosphoric (111) acid,
hydridopentaoxodiphosphoric (11, Iv) acid,
dodecaoxohexaphosphoric (111) acid,
hydridooctaoxotriphosphoric (111, IV, IV) acid,
octaoxotriphosphoric (IV, 111, IV) acid,
hydridohexaoxodiphosphoric (II1,V) acid, hexaoxodiphosphoric
(IV) acid, decaoxotetraphosphoric ( IV) acid,
hendecaoxotetraphosphoric (Iv) acid, and
enneaoxotriphosphoric (V, IV, IV) acid; acids represented by
the formula xH20. yP205, including orthophosphoric acid wherein
x/y = 3, polyphosphoric acids wherein 2 > x/y > 1, which are
calleddiphosphoric acid, triphosphoric acid, tetraphosphoric
acid, pentaphosphoric acid, and so forth depending on the
degree of condensation, as well as mixtures thereof,
metaphosphoric acids represented by x/y = 1, especially
trimetaphosphoric acid and tetrametaphosphoric acid, and
ultraphosphoric acids represented by 1 > x/y > 0 and having
a network structure with part of the phosphorus pentaoxide
structure remaining (these are sometimes collectively
referred to as metaphosphoric acid-based compounds), as well
as acidic salts of these acids; partial esters and complete
esters ofmonohydricandpolyhydricalcohols and polyalkylene
glycols; phosphites; and phosphono-substituted lower
aliphatic carboxylic acid derivatives.
In terms of catalyst deactivation ability, acids
represented by the formula xHzO. yP~05, including
orthophosphoric acid wherein x/y = 3, polyphosphoric acids
wherein 2 > x/y > 1, which are called diphosphori.~ acid,
triphosphoric acid, tetraphosphoric acid, pentaphosphoric
acid, and so forth depending on the degree of condensation,
as well as mixtures thereof, metaphosphoric acids represented
by x/y = 1, especially trimetaphosphoric acid and
tetrametaphosphoric acid, and ultraphosphoric acids
represented by 1 > x/y > 0 and having a network structure with
part of the phosphorus pentaoxide structure remaining (these
are sometimes collectively referred to as rnetaphosphoric
acid-based compounds), as well as acidic salts of these acids;
partial esters of monohydric and polyhydric alcohols and
polyalkylene glycols; phosphorus oxoacid and acidic esters
thereof; phosphono-substituted lower aliphatic carboxylic
acid derivatives; and the above metaphosphoric acid-based
compounds are preferably used.
Metaphosphoric acid-based compounds used in the
invention include a cyclic metaphosphoric acid having about
3 to 200 phosphoric acid units condensed, an ultra-region
metaphosphoric acid having a three-dimensional network
structure, and an alkali metal salt, an alkaline earth metal
salt, and an onium salt thereof.
Among them, cyclic sodium metaphosphate, ultra-region
sodium metaphosphate, dihexylphosphonoethyl acetate
(hereinafter sometimes abbreviated as DHPA) as a
phosphono-substituted lower aliphatic carboxylic acid
derivative can be mentioned. Examples of phosphites include
2,4,8,10-tetra-t-butyl-6-[3-(3-methyl-4-hydroxy-5-t-butylp
henyl) propoxy] dibenzo [d, f ] [l,3,2] dioxaphosphepine.
It is preferable that the content of the deactivator is,
in terms of the phosphorus (P) atom of the phosphorus-based
compound, withinarangeof0.001to0.05partsbymass relative
to 100 parts by mass of the poly-L-lactic acid or the
poly-D-lactic acid. When the content is less than 0.005 parts
by mass, the catalyst deactivation effect is small, causing
a decrease in the molecular weight. Further, when the content
is more than 0.05 parts by mass, decomposition is conversely
promoted, causing a decrease in the molecular weight.
It is preferable that the molar ratio of the phosphorus
atom ( P ) of the phosphorus-based compound to the tin atom (Sn)
of the tin-based compound (P/Sn ratio) is within a range of
0.15 to 5.0. The reason for this is as described above.
A stereocomplex polylactic acid obtained from a
poly-L-lactic acid and a poly-D-lactic acid is a polylactic
acid containing complex-phase crystals, whose main chain is
formed of a poly-L-lactic acid unit and a poly-D-lactic acid
unit. Such a polylactic acid having a stereocomplex crystal
phase shows a crystal melting peak at 190°C or more in
differential scanning calorimeter (DSC) measurement.
The stereocomplexcrystallinity (S) ofthe stereocomplex
polylactic acid in the invention is 90% or more, preferably
more than 97%, and more preferably loo%, as defined by the
following equation (a).
S = AH,, x 100/ (AHh, + AH,,) (a)
Here, AH,,representstheenthalpy (J/g) of stereocomplex
crystalsinthe stereocomplexpolylacticacidinthepolylactic
acid composition, and AHho represents the enthalpy (J/g) of
homocrystals in the stereocomplex polylactic acid in the
polylactic acid composition.
That is, when the stereocomplex polylactic acid has S
within the above range, formed products obtained using the
p o l y l a c t i c a c i d composition of the invention have e x c e l l e n t
heat r e s i s t a n c e and wet-heat r e s i s t a n c e .
It is p r e f e r a b l e t h a t the p o l y l a c t i c acid has
c r y s t a l l i n i t y , and it i s p r e f e r a b l e t h a t the stereocomplex
c r y s t a l content (Sc) i s 50% or more as defined by the following
equation (b) using the d i f f r a c t i o n peak i n t e n s i t y r a t i o
determined by wide-angle X-ray d i f f r a c t i o n (WAXD)
measurement.
Sc ( % ) = [CISCI/ (CISCI + IHM)] x 100 (b)
Here, CISCI = ISCl + ISC2 + ISC3, ISCI (I = 1 t o 3)
represents the i n t e g r a t e d i n t e n s i t i e s of d i f f r a c t i o n peaks
near 20 = 12.0°, 20.7O, and 24.0°, r e s p e c t i v e l y , and IHM
r e p r e s e n t s t h e i n t e g r a t e d i n t e n s i t y I H M o f t h e d i f f r a c t i o n p e a k
near 28 = 16.5' from homo-phase c r y s t a l s .
The p o l y l a c t i c acid used i n the invention is a mixture
ofapoly-L-1acti.cacidandapoly-D-lactic a c i d i n a m ~ l s rsa t i o
w i t h i n a rangeof 80/20to20/80. T h e r a t i o i s p r e f e r a b l y 3 0 / 7 0
t o 70/30, more preferably 60/40, and s t i l l more preferably
50/50. The mass r a t i o i s determined i n l i g h t of the melting
point or various physical p r o p e r t i e s .
The weight average molecular weight of t h e p o l y l a c t i c
acid is preferably 100,000 or more, more preferably within a
range of 100,000 t o 1,000,000, s t i l l more preferably 100,000
t o 500,000, yet more preferably 110,000 t o 350,000, and
particularly preferably 120,000 to 250,000. The weight
averagemolecular weight is a valuemeasuredby gel permeation
chromatography (GPC) and expressed in terms of standard
polystyrene.

The polylactic acid in the invention is a
high-melting-point polylactic acid containing stereocomplex
crystals, andcanbeproducedbysolution-mixingormelt-mixing
a poly-L-lactic acid and a poly-D-lactic acid.
As a method for mixing, solution-mixing performed with
the poly-L-lactic acid and the poly-D-lactic acid being
dissolved in a solvent or melt-mixing performed with the
poly-L-lactic acidandthepoly-D-lactic acidbeingmelted can
be employed. The mass ratio between the poly-L-lactic acid
andthepoly-D-lacticacidis, as former/latter, 80/20to 20/80.
The mass ratio js determined in light of the melting point or
various physical properties.
For example, as a method for melt-kneading, they are
kneaded using a tumbler, a V-shaped blender, a super mixer,
a Nauta mixer, a Banbury mixer, a kneading roll, or the like,
then melt-extruded, or, alternatively, they are directly
melt-kneaded and extrudedusing a single-screwmelt-extruder,
a vented twin-screw extruder, or the like, for example. In
any case, it is preferable that the melt-mixing temperature
is higher than the melting point of the resulting polylactic
acid containing stereocomplex crystals, preferably more than
260°C, andmorepreferably270°Cormore. Whenthemelt-mixing
temperature is too high, the poly-L-lactic acid and the
poly-D-lacticacidundergohydrolysis/pyrolysis, resultingin
the formation of low-molecular-weight substances, such as
lactide; therefore, this is undesirable. Fromthis point of
view, the temperature is preferably 300°C or less, and more
preferably 290°C or less. In addition, the screw rotation
speed of the extruder is determined in light of the desired
kneadability and the molecular weight of the resulting resin
composition, but is generally preferably 10 to 500 rpm, and
the melt-kneading time is preferably 1 to 20 minutes.

In the invention, as tin-based compounds, the
tin-containing catalysts used for producing a polylactic acid
described above can be mentioned. That is, examples thereof
include stannous chloride, stannous bromide, stannous iodide,
stannous sulfate, stannic oxide, tin myristate, tin octylate,
tin stearate, tetraphenyl tin, and tin alkoxides containing
a Cl-l0 fatty alcohol as a constituent, such as tin methoxide,
tin ethoxide, and tin butoxide. It is preferable that the
tin-based compound is at least one member selected from the
group consisting of tin octylate and tin alkoxides containing
a Cl-lo fatty alcohol as a constituent.

As phosphorus-based compounds in the invention, in
addition to the phosphorus-based compounds to serve as
deactivators for deactivating the tin-containing catalyst
described above, phosphorous acid, phosphoric acid,
phosphonic acid, phosphites, phosphate, andphosphondtes, for
example, can be mentioned. Specific examples thereof include
triphenyl phosphite, trisnonylphenyl phosphite, tricresyl
phosphite, triethylphosphite, tris(2-ethylhexyl) phosphite,
tributyl phosphite, tridecyl phosphite, trilauryl phosphite,
tris(tridecy1) phosphite, trioleyl phosphite, diphenyl
mono(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite,
diphenyl mono (tridecyl) phosphite, trilauryl
trithiophosphite, diethyl hydrogen phosphite,
bis(2-ethylhexyl) hydrogen phosphite, dilauryl hydrogen
phosphite, dilauryl hydrogen phosphite, dioleoyl hydrogen
phosphite, diphenyl hydrogen phosphite, tetraphenyl
dipropyleneglycol diphosphite, bis(decy1)pentaerythritol
diphosphite, bis(tridecy1)pentaerythritol diphosphite,
tristearylphosphite, distearyl pentaerythritoldiphosphite,
tris(2,4-di-tert-butylphenyl) phosphite, ethyl acid
phosphate, butyl acid phosphate, dibutyl pyrophosphate,
butoxyethyl acid phosphate, 2-ethylhexyl acid phosphate,
isotridecyl acid phosphate, oleyl acid phosphate, tetracosyl
acid phosphate, 2-hydroxyethyl methacrylate acid phosphate,
dibutyl phosphate, andbis(2-ethylhexyl) phosphate. A single
kind or two or more kinds of these compounds may be contained.

Inthe invention, anorganicacidmetal salt or anorganic
metal salt, oracombinationofthetwo, isused. Byuse thereof,
the stereocomplex crystallinity (S) of the stereocomplex
polylactic acid can be enhanced. As the organic acid metal
salt, at least one kind of metal selected from alkali metals
and alkaline earth metals is contained. As such organic acid
metal salts, fatty acid metal salts wherein the organic acid
is a CZ-24 fatty acid, aromatic acid metal salts wherein the
organic acid is a C7-12 aromatic acid, and carbonic acid metal
salts can be mentioned. In addition, as organic metal salts
for use in the invention, metal alkoxides can be mentioned.
As fatty acid metal salts, those having a CZ-18 fatty acid
are preferable. Specific examples thereof include lithium
acetate, potassium acetate, sodium acetate, calcium acetate,
magnesium acetate, barium acetate, lithium propionate,
potassium propionate, sodium propionate, calcium propionate,
magnesium propionate, barium propionate, lithium butanoate,
potassium butanoate, sodium butanoate, calcium butanoate,
magnesium butanoate, barium butanoate, lithium pentanoate,
potassium pentanoate, sodium pentanoate, calcium pentanoate,
magnesium pentanoate, barium pentanoate, lithium caproate,
potassium caproate, sodium caproate, calcium caproate,
magnesium caproate, barium caproate, lithium heptanoate,
potassium heptanoate, sodium heptanoate, calcium heptanoate,
magnesium heptanoate, barium heptanoate, lithium octanoate,
potassium octanoate, sodium octanoate, calcium octanoate,
magnesium octanoate, barium octanoate, lithium decanoate,
potassium decanoate, decane sodium, calcium decanoate,
magnesium decanoate, barium decanoate, lithium laurate,
potassiumlaurate, sodiumlaurate, calciumlaurate, magnesium
laurate, barium laurate, lithium myristate, potassium
myristate, sodium myristate, calcium myristate, magnesium
myristate, barium myristate, lithium- palminate, potassium
palminate, sodium palminate, calcium palminate, magnesium
palminate, barium palminate, lithium margarate, potassium
margarate, sodjilm margarate, calcium margarate, ~nagnesium
margarate, barium margarate, lithium stearate, potassium
stearate, sodium stearate, calcium stearate, magnesium
stearate, barium stearate, potassium oleate, sodium oleate,
calcium oleate, magnesium oleate, barium oleate, lithium
linoleate, potassium linoleate, sodium linoleate, calcium
linoleate, magnesium linoleate, barium linoleate, lithium
linolenate, potassiumlinolenate, sodiumlinolenate, calcium
linolenate, magnesium linolenate, barium linolenate, lithium
lactate, potassium lactate, sodium lactate, calcium lactate,
magnesium lactate, barium lactate, lithium glycolate,
potassium glycolate, sodium glycolate, calcium glycolate,
magnesium glycolate, and barium glycolate.
As aromatic acidmetal salts, thosehavingaC7.12 aromatic
acid are preferable. Specific examples thereof include
lithium benzoate, potassium benzoate, sodium benzoate,
calcium benzoate, magnesium benzoate, barium benzoate,
lithium toluate, potassium toluate, sodium toluate, calcium
toluate, magnesiumtoluate, barium toluate, lithium gallate,
potassium gallate, sodium gallate, calcium gallate, magnesium
gallate, barium gallate, lithium cinnamate, potassium
cinnamate, sodium cinnamate, calcium cinnamate, magnesium
cinnamate, barium cinnamate, lithium phthalate, potassium
phthalate, sodium phthalate, calcium phthalate, magnesium
phthalate, bariumphthalate, lithiumterephthalate, potassium
terephthalate, sodium terephthalate, calcium terephthalate,
magnesium terephthalate, barium terephthalate, lithium
isophthalate, potassium isophthalate, sodium isophthalate,
calcium isophthalate, magnesium isophthalate, barium
isophthalate, lithium salicylate, potassium sallcylate,
sodium salicylate, calcium salicylate, magnesium salicylate,
barium salicylate, lithium naphthoate, potassium naphthoate,
sodium naphthoate, calcium naphthoate, magnesium naphthoate,
barium naphthoate, lithium naphthalenedicarboxylate,
potassium naphthalenedicarboxylate, sodium
naphthalenedicarboxylate, calcium naphthalenedicarboxylate,
magnesium naphthalenedicarboxylate, and barium
naphthalenedicarboxylate.
Specific examples of carbonic acid metal salts include
sodium carbonate, potassium carbonate, lithium carbonate,
calcium carbonate, magnesium carbonate, andbarium carbonate.

As organicmetal salts, metalalkoxides canbementioned.
As metal alkoxides, Cl-loa liphatic alkoxides and C6-15a romatic
alkoxides are preferable. It is also possible to use a
combination of two or more kinds of them. Specific example
of aliphatic alkoxides include lithium methoxide, sodium
methoxide, lithium ethoxide, sodium ethoxide, calcium
ethoxide, barium ethoxide, potassium tert-butoxide, and
aluminum triisopropoxide.
In addition, specific examples of aromatic alkoxides
include sodiumphenoxide, sodium-3,5-dimethoxyphenoxide, and
sodium-2-phenyl phenoxide.

The polylactic acid composition of the invention
contains the tin-based compound, the phosphorus-based
compound, the organicacidmetal salt or the organicmetal salt,
and the polylactic acid having a stereocomplex crystallinity
(S) of 90% or more. It is also possible that both the organic
acid metal salt and the organic metal salt are present.
Here, it is preferable that the content of the
phosphorus-based compound in terms of the phosphorus (P) atom
is within a range of 0.001 to 0.05 parts by mass relative to
100 parts by mass of the polylactic acid composition. The
content is further 0.003 to 0.04 parts by mass, and still more
preferably 0.005 to 0.03 parts by mass.
In addition, it is preferable that the content of the
organic acid metal salt or the organic metal salt is within
a range of 0.01 to 20.0 parts by mass relative to 100 parts
by mass of the polylactic acid composition. When the content
is within this range, a stereocomplex polylactic acid
composition having a high stereocomplex crystallinity and a
high stereocomplex crystal melting point, a small
stereocomplex crystal melting point depression evt.:n after
remelting, a small decrease in the molecular weight, excellent
forming processability, and also heat resistance can be
obtained. The content is further 0.01 to 5.0 parts by mass,
and still more preferably 0.01 to 1.5 parts by mass. In the
case where both the organic acid metal salt and the organic
metal salt are present, it is preferable that the total of the
two is within the above range.
In the polylactic acid composition of the invention, in
the case where the kind of metal of the organic acid metal s a l t
is an a l k a l i metal, the molar r a t i o of phosphorus ( P ) t o the
organic acid metal s a l t is within a range of 0.5 t o 1.5. The
reason for t h i s is t h a t i n the case where the r a t i o of P to
themetal s a l t is small, it i s difficulttomaintainamolecular
weightof100,OOO ormoretomaintainthemechanicalproperties,
while i n the case where the r a t i o of P t o the metal s a l t i s
l a r g e , the stereocomplex proportion is l e s s Lhan 90%. It is
p r e f e r a b l e the r a t i o is within a range of 0.8 t o 1.3.
In t h e p o l y l a c t i c a c i d composition of the invention, in
the case where the kind of metal of the organic acid metal s a l t
is an a l k a l i n e e a r t h metal, the molar r a t i o of phosphorus ( P )
t o the organic acid metal s a l t is within a range of 0 . 1 t o 1 . 0 .
The reason f o r t h i s is t h a t i n the case where the r a t i o of P
t o the metal s a l t is small, it i s d i f f i c u l t t o maintain a
molecular weight of 100,000 or more t o m a i n t a i n the mechanical
p r o p e r t i e s , while i n the case where the r a t i o of P t o the metal
s a l t is l a r g e , the stereocomplex proportion is l e s s than 90%.
It is p r e f e r a b l e the r a t i o is within a range of 0.2 t o 0 . 6 .
In the case where t h e p o l y l a c t i c a c i d composition of the
invention contains an organic metal s a l t , the molar r a t i o of
phosphorus ( P ) t o the organic metal s a l t is w i t h i n a range of
0.5 t o 2 . 2 . The reason for t h i s is t h a t i n the case where the
r a t i o o f P t o t h e m e t a l s a l t i s small, it is d i f f i c u l t tomaintain
amolecularweightof100,0.0O ormoretomaintainthemechanical
properties, while in the case where the ratio of P to the metal
salt is large, the stereocomplex proportion is less than 90%.
It is preferable the ratio is within a range of 0.5 to 1.0.
Considering the content ratio between the
phosphorus-based compound and the tin-based compound, it is
preferable that the ratio of the phosphorus-based compound to
the tin-based compound (P/Sn) in the polylactic acid
composition is 0.15 to 5.0. This is because when the ratio
is within this range, a stereocomplex polylactic acid
composition having a high stereocomplex crystallinity and a
high stereocomplex crystal melting point, a small
stereocomplex crystal melting point depression even after
remelting, a small decrease in the molecular weight, excellent
forming processability, and also heat resistance can be
obtained.
Incidentally, the polylactic acid composition of the
invention may also contain an organic acid resulting from the
partialreactionbetweenthephosphorus-basedcompoundandthe
organic acid metal salt, such as lauric acid or benzoic acid.
It is preferable that in DSC measurement satisfying the
following conditions, the polylactic acid composition of the
invention has a melting point T from stereocomplex crystals
of 210°C or more, and the Tm,, depression (ATsc) measured after
three cycles is 8°C or less; this is because the resulting heat
resistance and thermal stability are excellent. AT,, is more
preferably 5'C or l e s s , s t l l l more preferably 4'C or l e s s , yet
more preferably 3OC or l e s s , and most preferably 2'C or l e s s .
DSC Measurement Conditions:
( I ) Heating from 30°C t o 260°C (heating r a t e : 20°C/min) ;
(11) holding a t 260°C for 1 min;
(111) ~ o o l i n g f r o m 2 6 0 ~ C t o 3 0(~c oCo l i n g r a t e : 20°C/min);
and
( I V ) the above ( I ) t o (111) are taken as one cycle, and
the cycle i s repeated three times as t h r e e cycles.
The c r y s t a l melting enthalpy of the p o l y l a c t i c acid
composition of the invention determined by DSCmeasurement is
preferably 20 J/g or more, more preferably within a range of
20 t o 80 J/g, and s t i l l more preferably 30 t o 80 J/g.
The l a c t i d e content i n the p o l y l a c t i c acid composition
of the invention is preferably 0 t o 0.1 p a r t s by mass, more
p r e f e r a b l y 0 t o 0.07 p a r t s by mass, and s t i l l more preferably
0 t o 0.05 p a r t s by mass, r e l a t i v e t o 100 p a r t s by ma:js of the
p o l y l a c t i c a c i d composition.
The molecular weight d i s t r i b u t i o n (Mw/Mn) of the
stereocomplex p o l y l a c t i c a c i d i n t h e p o l y l a c t i c acid
composition of the invention is p r e f e r a b l y w i t h i n a range of
1.5 t o 2.4, more preferably 1.6 t o 2.4, and s t i l l more
preferably 1.6 t o 2 . 3 .
The polylactic acid composition of the invention may
containadditives. For example, examples ofadditivesinclude
antihydrolysis agents, crystal nucleators, plasticizers, UV
absorbers, antistatic agents, hue regulators, flame
retardants, antibacterial agents, and foaming agents.
Among them, antihydrolysis agents are useful as
hydrolysis regulators. Specific examples thereof include
addition-reaction-type compounds such as carbodiimide
compounds, isocyanate compounds, epoxy compounds, oxazoline
compounds, oxazine compounds, and aziridine compounds. In
addition, although two or more of these compounds may be used
in combination, not all of them are usable, and it is important
toselect compoundsthat areeffectiveashydrolysis regulators
in the invention.
In addition, of the above compounds, in terms of water
resistance and reactivitywiththe acidic group, carbodiimide
compounds are preferable, for example. However, as above, not
all carbodiimide compounds are effective as hydrolysis
regulators in the invention, and it is important to select,
from carbodiimide compounds, compounds that are effective in
the invention.
Examples of carbodiimide compounds effective in the
invention include those having a basic structure of the below
formula (I) or (11).
W-NEC'N-R"
(1)
(In the formula, R and R' are each independently a C1-20
aliphatic group, a C3-20a licyclic group, a c5-1a~r omatic group,
or a combination thereof, optionally containing a heteroatom.
R and R' may be linked together to form a cyclic structure or
twoormorecyclicstructuresinaspirostructure, forexample.
(In the formula, R" is a CI-20 aliphatic group, a C3-20
alicyclicgroup, aC5.15ar~maticgroup,o r acombinationthereof,
optionally containing a heteroatom. n is an integer of 2 to
1,000.)
In terms of stability or ease of use, aromatic
carbodiimide compounds are more preferable. For example,
aromatic carbodi~imide compounds of the following Formulae
(111) and (IV) can be mentioned.
(In the formula, RI to Rq are each independently a CI-20
aliphatic group, a C3-20 alicyclic group, a Cs-1, aromatic group,
or a combination thereof, optionally containing a heteroatom.
XandYare eachindependentlya hydrogen atom, a C1-20a liphatic
group, a C3-z0 alicyclic group, a C5-15 aromatic group, or a
combination thereof, optionally containing a heteroatom. The
aromatic rings may be linked together through a substituent
to form a cyclic structure or two or more cyclic structures
in a spiro structure, for example.
(In the formula, Rs to R7 are each independently a C1p20
aliphatic group, a C3-Zo alicyclic group, a C5-15 aromatic group,
or a combination thereof, optionally containing a heteroatom.
n is an integer of 2 to 1,000.)
Specific examples of such aromatic carbodiimide
compounds include bis(2,6-diisopropylphenyl)carbodiimide,
polycarbodiimides synthesized by the decarboxylation
condensation reaction o f
1,3,5-triisopropylbenzene-2,4-diisocyanate and having five
or less carbodiimide groups, and combinations thereof.
It is preferable that the content of the carbodiimide
compound is 0.1 to 10 parts by mass relative to 100 parts by
mass of the polylactic acid composition of the invention.

A method for producing the polylactic acid composition
of the invention is not particularly limited. Examples
thereof include (I) a method in which the phosphorus-based
compound, the organic acidmetal saltand/orthe organic metal
salt, andthepolylactic acidare simultaneouslymelt-kneaded;
(11) a method in which the polylactic acid containing the
phosphorus-based compound is melt-kneaded, and then the
organic metal salt is added, followed by melt-kneading again;
and (111) a method in which the phosphorus-based compound is
added during the production of a poly-L-lactic acid or a
poly-D-lacticacid, orbothofthem, followedbymelt-kneading,
and then the organic metal salt is added, followed by
melt-kneading again. It is preferable that melt-kneading is
performed at a temperature of 260 to 300°C. The mass mixing
r a t i o b e t w e e n t h e p o l y - ~ - l a c t i c a c i d a n d t h e p o l y - D - l a c t i c a c i d
is 80/20 to 20/80 in order to enhance the stereocomplex
crystallinity (S) of the polylactic acid.
Thus, according to the invention, the polylactic acid
composition ofthe invention canbe produced as follows. That
is, the production can be achieved by a method for producing
a polylactic acid composition containing a stereocomplex
polylactic acid,
the stereocomplex polylactic acid containing a
p0ly-L-lactic acid (A) and a poly-D-lactic acid (B) and having
a Stereocomplex crystallinity (S) of 90% or more as defined
by the following equation ( a ) :
s = AH,, x ~ o o / ( A Mt ~A~H,, ) ( a )
wherein AH,, represents the enthalpy ( J / g ) of stereocomplex
c r y s t a l s i n the p o l y l a c t i c acid composition, and AHh,
r e p r e s e n t s t h e e n t h a l p y ( J / g ) ofhomocrystalsinthepolylactic
acid composition,
the content r a t i o between the poly-L-lactic acid (A) and
the poly-D-lactic acid ( B ) being within a range of 80/20 t o
20/80 (mass r a t i o ) ,
the method including a t l e a s t the following s t e p s :
(i) a s t e p of preparing a mixture containing a
poly-L-lactic acid ( A ) , a poly-D-lactic acid (B) , a tin-based
compound, and a phosphorus-based compound;
(ii) a step of adding a t l e a s t one of an organic acid
metal s a l t of a t l e a s t one member s e l e c t e d from a l k a l i metals
and a l k a l i n e e a r t h metals, and an organic metal s a l t t o the
mixture of (i) i n such a manner t h a t the following conditions
a r e s a t i s f i e d : i n t h e casewhere the kindofmetal o f t h e o r g a n i c
acid metal s a l t is an a l k a l i metal, the molar r a t i o of the
phosphorus ( P ) atom i n terms of metal t o t h e organic acidmetal
s a l t is within a range of 0.5 t o 1.5; i n the case where the
kind of metal of the organic acid metal s a l t is an a l k a l i n e
e a r t h m e t a l , themolar r a t i o o f t h e phosphorus ( P ) atominterms
of metal t o the organic acid metal s a l t i s within a range of
0 . 1 t o 1 . 0 ; and i n the case of the organic metal s a l t , the molar
ratiooftllephosphorus (P) atomintermsofmetaltotheorganic
metal salt is within a range of 0.5 to 2.2; and
(iii) a step of, after the step (ii) , melt-kneading the
mixture at a temperature of 260 to 300°C.
In the step (i), as the poly-L-lactic acid (A), the
poly-D-lactic acid (B), the tin-based compound, and the
phosphorus-based compound, those same as described above are
usable. Amixture containingthemcanbeprepared, for example,
by allowing a predetermined amount of monomer capable of
forming an L-lactic acid unit, such as L-lactide, and a
predetermined amount of monomer capable of forming a D-lactic
acid unit, such as D-lactide, to react with a predetermined
amount of tin-based compound, which is a polymerization
catalyst, then adding the phosphorus-based compound as a
polymerization catalyst deactivator or a coloring inhibitor,
andfurtherallowingthemixtureto react, followedby temoving
the lactide as necessary.
As described above, it is preferable that in the step
(i), the mass ratio of the phosphorus atom from the
phosphorus-based compound to the tin atom from the trn-based
compound (P/Sn) is within a range of 0.15 to 5.0.
In the case where the kind of metal of the organic acid
metal salt is an alkali metal, the organic acid metal salt is
addedsuchthatthemolar ratio of phosphorus (P) tothe organic
acid metal salt is within a range of 0.5 to 1.5, preferably
within a range of 0.8 to 1.3. In the case where the kind of
metal ofthe organic acidmetal salt is an alkaline earthmetal,
the organic acid metal salt is added such that the molar ratio
of phosphorus ( P ) to the organic acid metal salt is within a
range of 0.1 to 1.0, preferably within a range of 0.2 to 0.6.
In the case of the organic metal salt, the organic metal salt
is added such that the molar ratio of phosphorus (P) to the
organic metal salt is within a range of 0.5 to 2.2, preferably
within a range of 0.5 to 1.0. As a result, the stereocomplex
crystallinity (S) is enhanced, leading to excellent heat
resistance. In addition, the polylactic acid composition of
the invention can be stably produced.
In the step (iii), in terms of the stability of the
polylactic acid during melting and also of improving the
stereocomplex crystallinity (S), the melt-kneading
temperature is within a range of 260 to 300°C, preferably 260
to 280°C, and more preferably 260 to 275OC.
When melt-kneading is performed in such a mixing ratio
at such a temperature, the stereocomplex crystallinity (S) of
thepolylactic acidcanbemade 90% ormore. The crystallinity
(S) of the polylactic acid is preferably 90% to loo%, more
preferably 95% to loo%, still more preferably 97% to loo%, and
particularly preferably 100%.
The above melt-kneading method can be performed using
a conventionally known batch-type or continuous melt-mixer.
For example, it is possible t o use a m e l t - s t i r r i n g tank, a
single-screw or twin-screw extruder, a kneader, a non-screw
basket-shaped s t i r r i n g tank ( f i n i s h e r ) , BIVOLAK manufactured
by Sumitomo Heavy I n d u s t r i e s , N-SCRmanufacturedbyMitsubishi
Heavy I n d u s t r i e s , the spectacle blade, l a t t i c e blade, or
Kenix-type s t i r r e r manufactured by Hitachi, a tubular
polymerizer equipped with a Sulzer SMLX-type s t a t i c mixer, or
the l i k e . However, i n terms of p r o d u c t i v i t y and the q u a l i t y ,
p a r t i c u l a r l y color tone, of the p o l y l a c t i c acid, a non-screw
basket-shapedmixingtankwhichis a self-cleaningpolymerizer,
N-SCR, atwin-screw extruder, andthe l i k e a r e p r e f e r a b l y u s e d .
Althoughthe p o l y l a c t i c a c i d composition canbe d i r e c t l y
meltedandprocessedinto a f o r m e d a r t i c l e , it is a l s o possible
t h a t , a s one of preferred embodiments, t h e p o l y l a c t i c acid
composition is once s o l i d i f i e d , p e l l e t i z e d , andthen processed
i n t o a formed a r t i c l e . With respect t o the shape o t p e l l e t s ,
those having a shape s u i t a b l e f o r processing the p e l l e t s i n t o
a f o r m e d a r t i c l e b y v a r i o u s formingmethods, s p e c i f i c a l l y t h o s e
having a p e l l e t length of about 1 t o 7 mm, a major axis of about
3 t o 5 mm, and a minor axis of about 1 t o 4 mm, a r e p r e f e r a b l e .
I n a d d i t i o n , it is p r e f e r a b l e t h a t the p e l l e t s do not varymuch
i n shape.
I n a d d i t i o n t o t h e hydrolysis r e g u l a t o r s describedabove,
as desired, the p o l y l a c t i c a c i d composition of the invention
mayalsocontainthe followingcompoundswithoutdeparting from
the gist of the invention. For example, the polylactic acid
composition may contain a single kind or two or more kinds of
thermoplastic resins other than polylactic acids,
thermosetting resins, flexible thermoplastic resins, impact
resistance improvers, crystallization promoters,
crystallization nucleators, improvers for film formabilityby
electrostaticadhesion, plasticizers, lubricants, oryanicand
inorganic lubricants, organic and inorganic fillers,
antioxidants, light stabilizers, UV absorbers, heat
stabilizers, release agents, antistatic agents, flame
retardants, foaming agents, antibacterial/antifungal agents,
colorants containing an organic or inorganic dye or pigment,
and the like.
For the application of the above additives to the
polylactic acid composition of the invention, the agents may
beincorporatedatthe stage after the startofpolylactic acid
polymerization and before processing into a formed article.
In the case where the agents are added between the start and
end of polymerization, an ordinary agent-adding method may be
used to allow for the production of a polylactic acid
composition. In addition, for adding the agents to a
stereocomplex polylactic acid, conventionally known various
methods may be preferably used. As such various methods, for
example, mixing methods using a tumbler, a V-shaped blender,
a super mixer, a Nauta mixer, a Banbury mixer, a kneading roll,
a single-screw or twin-screw extruder, and the like are
suitably used.
Examples
Values in the examples were determined by the following
methods.
(1) Weight Average Molecular Weight (Mw):
The value was determined from comparison with a
polystyrene standard sample by gel permeation chromatography
(GPC) .
The GPC measuring instrument used was as follows, and
a chloroform eluent was used. The eluent was passed through
the column at a column temperature of 40°C and a flow rate of
l.OmL/min, anda10-pL samplehavinga concentrationof 1mg/mL
(1% hexafluoroisopropanol-containing chloroform) was
injected.
Detector: Differential refractometer, RID- 6A
manuractured by Shimadzu Corporation
Pump: LC-9A manufactured by Shimadzu Corporation
Column: TSKgeLG3000HXL, TSKgeLG4000HXL, TSKgeLG5000HXL,
andI'SKguaRdcoLuMnHXL-L (Tosoh Corporation) were connected in
series.
(2) Crystal Melting Point (Tho, Tsc), Crystal Melting Heat (AHho,
AH,,), Melting Point Depression, and Stereocomplex
Crystallinity (S) :
Using a polylactic acid composition, the values were
measured with a differential scanning calorimeter (DSC)
manufactured by PerkinElmer Co., Ltd. That is, in a nitrogen
atmosphere, 10 mg of a ample was heated from 30°C to 260°C at
aheating r a t e o f 2 0 ~ ~ / m i n i n t h ealn~dt~h~e ~cr~ys,t almelting
temperatures (Tho, Tsc) were measured.
The stereocomplex crystal melting point depression
A T ; hereinafter sometimes simply referred to as melting
point depression) was defined as a difference in temperature
between the stereocomplex crystalmelting point (melting point
T of the polylactic acid from stereocomplex crystals;
hereinafter sometimes simply referred to as melting point)
after one cycle and that after three cycles in the above DSC
measurement under the following measurement conditions.
DSC Measurement Conditions:
(I) Heating from 30°C to 260°C (heating rate: 20°C/min);
(11) holding at 260°C for 1 min;
(111) cooling from 260°C to 30°C (cooling rate: 2O0C/min) ;
and
(IV) the above (I) to (111) are taken as one cycle, and
the cycle is repeated three times as three cycles.
The stereocomplex crystallinity (S) was determined by
the following equation (a) from the low-temperature-phase
crystal melting heat (AHho) at less than 190°C and
high-temperature-phase crystal melting heat (AH,,) at 190°C or
more of the polylactic acid composition.
S = AH,, x 100/ (AHh, + AH,,) (a)
(In the above equation (a), AH,, represents the crystal
melting enthalpy (J/g) of the crystal melting peak at 190°C
or more corresponding to the melting of the stereocomplex
crystal phase in the DSCmeasurement, whileAHho represents the
crystal melting enthalpy (J/g) of the crystal melting peak at
lessthan190°C corresponding tothemelting ofthe homocrystal
phase in the DSC measurement.)
(3) Optical Purity
The optical purity of a poly-L-lactic acid and that of
a poly-D-lactic acid were determined as follows. In the case
of apoly-L-lactic acid, the opticalpuritywas determined from
the ratio between the L-lactic acid unit, which is the main
structural unit, and the partial D-lactic acid unit. First,
5 mL of 5 M sodiiim hydroxide and 2.5 mL of methanol wore added
to 1 g of a sample, hydrolyzed with heating and stirring at
40°C, and then neutralized with 1 M sulfuric acid. 1 mL of the
neutralized solution was diluted 25-fold to adjust the
concentration. The solution was subjected to high-speed
liquid chromatography (HPLC) to measure the detection peak
areas of L-lactic acid and D-lactic acid under UV light at 254
nm, and, from the mass proportion of the L-lactic acid unit
[L] ( % ) and the mass proportion of the D-lactic acid unit [Dl
( % ) forming the polylactic acid polymer, each optical purity
( % ) was calculated from the following equation.
Incidentally, the HPLC apparatus used was as follows:
pump: Shimadzu LC-GA, UV detector: Shimadzu SPD-GAV, column:
SUMICHIRAL OA-5000 (Sumika Chemical Analysis Service, Ltd.).
A 1 mM aqueous copper sulfate solution was used as the eluent,
and measurement was performed at a flow rate of 1.0 mL/min at
40°C.
Optical purity ( % ) of poly-L-lactic acid = 100 x [L] / ( [L]
+ [Dl)
Optical purity ( % ) of poly-D-lactic acid = 100 x [Dl / ( [Ll
+ [Dl)
(4) P and Sn Amounts in Terms of Metal:
The amounts of P and Sn in terms of metal were determined
by ICP-AES. 7 mL of nitric acid was added to 0.5 mg of a sample
placedinaquarts glass container, andtreatedusingMultiwave
3000 manufactured by PerkinElmer Co., Ltd., at an output of
200 W for 5 min and then at an output of 500 W for 45 min. At
this time, the final reaction temperature was 190°C, and the
internal pressure was 45 bar. The obtained sample was diluted
withpure water to 50 mLand subjectedto emission spectrometry
with VISTA-PRO manufactured by Varian Medical Systems, Inc.
The polylactic acids usedinthe following examples were
produced by the followinq production methods.
[Production Example 11 Production of Poly-L-Lactic Acid:
0.014 partsbymassoftinoctylatewas addedto100parts
by mass of L-lactide (manufactured by Musashino Chemical
Laboratory, optical purity: loo%), and, in a nitrogen
atmosphere, allowed to react in a reactor equipped with a
stirring blade at 180°C for 2 hours. 0.095 parts by mass of
trilauryl phosphite was added, then the remaining lactide was
removed at 13.3 Pa, and the mixture was formed into pellets,
thereby giving a poly-L-lactic acid.
MwandT,,,ofthe obtainedpoly-L-lactic acidwere193,OOO
and 176.4OC, respectively. The amount of P in terms of metal
was 0.00503 parts by mass relative to 100 parts by mass of the
obtained poly-L-lactic acid, and the amount of Sn in terms of
metal was 0.00403 parts by mass relative to 100 parts by mass
of the obtained poly-L-lactic acid. The optical purity was
99.8%.
[Production Example 2 to 161
The same operations as in Production Example 1 were
performed, except for changing the kind of lactide, the kind
of phosphorus-based compound, the amount of tin octylate, and
the amount of phosphorus-based compound.
Table 1 shows a summary of the obtained poly-L-lactic
acids orpoly-D-lactic acids. In the table, "DHPA" stands for
dihexylphosphonoethyl acetate.

[Example 11
The poly-L-lactic acid and the poly-D-lactic acid
produced in Production Examples 1 and 8, respectively, were
taken each in an amount of 50 parts by mass, dried at 80°C for
5 hours, and then, while adding 0.020 parts by mass of sodium
octanoate, melt-kneaded in a twin-screw kneader at a cylinder
temperature of 27OoC and a feed of 5 kg/h. Next, the mixture
was pelletized with a chip cutter, thereby producing a
polylactic acid composition.
The obtained polylactic acid composition was subjected
to DSC measurement. As a result, the stereocomplex
crystallinity (S) was 100.0%, the stereocomplex crystal
melting point T,, was 218. O°C, and the stereocomplex crystal
melting point depression (AT,,) was 3.2OC. In addition, Mw was
139,000. The formabilityinto fibers and films was excellent.
[Examples 2 to 291
The same operations as in Example 1 were performed,
except for changingthe kindandamountofpolylactic acidused
and the kind and amount of organic acid metal salt or organic
metal salt
Table 2 shows a summary of the obtained polylactic acid
compositions.
[Example 301
The polylactic acid composition obtained in Example 1
was taken in an amount of 200 parts by mass, dried at 80°C for
5 hours, and then, while adding 9.0 parts by mass of
bis(2,6-diisopropylphenyl)carbodiimide as a carbodiimide
compound, melt-kneaded in a twin-screw kneader at a cylinder
temperature of 230°C and a feed of 5 kg/h. Next, the mixture
was pelletizedwith a chip cutter, thereby giving a polylactic
acid composition.
The obtained polylactic acid composition was subjected
to DSC measurement. As a result, the stereocomplex
crystallinity (S) was 100.0%, the stereocomplex crystal
melting point T,, was 210.9°C, and the stereocomplex crystal
melting point depression (AT,,) was 1. 1°C. In addition, Mw was
136,000.
[Comparative Examples 1 to 91
The same operations as in Example 1 were performed,
except for changingthe kindandamountofpolylactic acidused
and the kind and amount of organic acid metal salt or organic
metal salt.
Table 3 shows a summary of the obtained polylactic acid
compositions. Incidentally, "ADK STAB NA-11" in the table is
2,4,8,10-tetra-tert-butyl-6- (sodiooxy) - 1 - d b n z o d, g [I,
3,3]dioxaphosphocin-6-oxide. "ADK STAB" is a registered
trademark.
Industrial applicability
The stereocomplex polylactic acid composition provided
by the invention contains a phosphorus-based compound and a
tin-based compound, but has excellent stability and high heat
resistance. Therefore, it is usable for various
injection-molded products, films, fibers, and various formed
products, which are required to have stability and high heat
resistance.

Table 3
I I I I I
Comparative
I I I I I
Comparative 1 9 50150 1.25
ADK STAB
Example 1 NA-11
Poly-L-Lactic
Acid Production
Example
Example 2
Example 3
Comparative
I ~oly-L-~actic
Example 4 I
Comparative
Example 5
1
Comparative
PlSn
(mass%)
Poly-D-Lactic
Acid Production
Example
Example 7
Kind of Organic
Acid Metal Salt
or Organic Metal
Salt
AcidlPoly-D-Lactic
Acid
(mass ratio)
Sodium i: 1 octanoate
Sodium
methoxide
Calcium
stearate
A OF Calcium
I .L3 / stearate
Sodium 1 octanoate
Sodium
octanoate
1.25 Sodium laurate
Comparative 1 9 50150 1.25 Sodium iaurate
Example 9
Added Amount
of Organic Acid
Metal Salt or
Organic Metal
Salt
(mass%)
0.300
JIOrganicAcid
Metal Salt or
Organic Metal
Salt
(molar ratio)
Kneading
Temperature
Yc)
S (%)
1. Apolylacticacidcompositioncomprisingastereocomplex
p o l y l a c t i c acid,
the stereocomplex p o l y l a c t i c a c i d containing a
poly-L-lactic acid (A) and a poly-D-lactic acid (B) and having
a stereocomplex c r y s t a l l i n i t y (S) of 90% or more as defined
by the following equation ( a ) :
S = AH,, x 1001' (AH,, + AH,,) ( a )
wherein AH,, r e p r e s e n t s the enthalpy ( J / g ) of stereocomplex
c r y s t a l s i n the p o l y l a c t i c a c i d composition, and AHh,
r e p r e s e n t s t h e e n t h a l p y ( J / g ) ofhomocrystalsinthepolylactic
acid composition,
the contentratiobetweenthepoly-L-lactic acid (A) and
the poly-D-lactic acid (B) being w i t h i n a range of 80/20 t o
20/80 (mass r a t i o ) ,
the p o l y l a c t i c acid composition containing a t i n-based
compound, a phosphorus-based compound, and f u r t h e r a t l e a s t
one of a metal organic acid metal s a l t of a t l e a s t one member
selected from a l k a l i metals and a l k a l i n e e a r t h metals, and an
organic metal s a l t ,
in the case where the kind of metal of the organic acid
metal s a l t is a n a l k a l i m e t a l , themolar r a t i o o f t h e phosphorus
( P ) atom t o the organic acid metal s a l t being within a range
of 0 . 5 t o 1.5,
in the case where the kind of metal of the organic acid
metal salt is an alkaline earth metal, the molar ratio of the
phosphorus (P) atomtothe organic acidmetal salt beingwithin
a range of 0.1 to 1.0,
in the case of the organic metal salt, the molar ratio
of the phosphorus ( P ) atom to the organic metal salt being
within a range of 0.5 to 2.2.
2. The polylactic acid composition according to claim 1,
wherein the organic acid of the organic acid metal salt is a
C2-24 fatty acid.
3. The polylactic acid composition according to claim 1,
wherein the organic acid of the organic acid metal salt is a
C 7 -a~r~om atic acid.
4. The polylactic acid composition according to claim 1,
wherein the organic metal salt is at least one kind of metal
alkoxide selected from the group consisting of Cl-Ioa liphatic
alkoxides and Cs-15 aromatic alkoxides.
5. The polylactic acid composition according to claim 1,
wherein the tin-basedcompoundis at least onemember selected
from the group consisting of tin octylate and tin alkoxides
containing a ClpIo fatty alcohol as a constituent.
6. The polylactic acid composition according to claim 1,
wherein the phosphorus-based compound is at least one kind of
phosphorus compound selected from the group consisting of
phosphorous acid, phosphoric acid, phosphonic acid,
phosphites, phosphates, and phosphonates.
7. The polylactic acid composition according to any one of
claims 1 to 6, wherein the amount of Sn in terms of metal is
0.02 parts by mass or less relative to 100 parts by mass of
thetotalofthepoly-L-lactic acidandthepoly-D-lactic acid,
and the mass ratio of the phosphorus atom from the
phosphorus-based compound to the tin atom fromthe tin-based
compound (P/Sn) is within a range of 0.15 to 5.0.
8. The polylactic acid composition according to any one of
claims 1 to 7, wherein the polylactic acid composition has a
meltingpoint ( T ) fromstereocomplexcrystals of 210°Cormore,
and, in DSC measurement under the following conditions, the
difference between T,, measured after three cycles and T,,
measured after one cycle (AT,,) is 8'C or less:
DSC measurement conditions:
(i) heating from 30°C to 26OoC (heating rate: 20°C/min) ;
(ii) holding at 260°C for 1 min;
(iii) cooling from 260°C to 30°C (cooling rate: 20°C/min) ;
and
(iv) the (i) to (iii) are taken as one cycle, and the
cycle is repeated three times as three cycles.
9. The polylactic acid composition according to any one of
claims 1 to 8, wherein the stereocomplex polylactic acid has
a weight average molecular weight (Mw) of 100,000 or more.
10. The polylactic acid composition according to any one of
claims 1 to 9, comprising 0.1 to 10 parts by mass of a compound
havingatleastonecarbodiimidegroupinonemolecule relative
to 100 parts by mass of the polylactic acid composition.
11. The polylactic acid composition according to any one of
claims 1 to 10, further comprising an organic acid from the
organic acid metal salt.
12. A formed article obtained from the polylactic acid
composition according to any one of claims 1 to 11.
13. A method for producing a polylactic acid composition
comprising a stereocomplex polylactic acid,
the stereocomplex polylactic acid containing a
poly-L-lactic acid (A) and a poly-D-lactic acid (B) and having
a stereocomplex crystallinity (S) of 90% or more as defined
by the following equation ( a ) :
s = AH,, x 1001 (AH,, t AH,,) ( a )
wherein AH,, r e p r e s e n t s the enthalpy ( J / g ) of stereocomplex
c r y s t a l s i n the p o l y l a c t i c acid composition, and AHh,
r e p r e s e n t s t h e e n t h a l p y ( J / g ) ofhomocrystalsinthepolylactic
acid composition,
the content r a t i o between the poly-L-lactic acid (A) and
the poly-D-lactic acid (B) being within a range of 80/20 t o
20/80 (mass r a t i o ) ,
the method including a t l e a s t the following s t e p s :
(i) a step of preparing a mixture containing a
poly-L-lactic acid ( A ) , a poly-D-lactic acid ( B ) , a tin-based
compound, and a phosphorus-based compound;
(ii) a s t e p of adding a t l e a s t one of an organic acid
metal s a l t of a t l e a s t one member s e l e c t e d from a l k a l i metals
and a l k a l i n e e a r t h metals, and an organic metal s a l t t o the
mixture of (i) in such a manner t h a t the following conditions
a r e s a t i s f i e d : i n t h e casewhere the k i n d o f m e t a l o f t h e o r g a n i c
acid metal s a l t is an a l k a l i metal, the molar r a t i o of the
phosphorus (P) atom t o the organic acid metal s a l t is within
a range of 0.5 t o 1.5; In the case where the kind of metal of
the organic acid metal s a l t is an a l k a l i n e e a r t h metal, the
molar r a t i o ofthephosphorus (P) a t o m t o t h e o r g a n i c a c i d m e t a l
s a l t is within a range of 0 . 1 t o 1.0; and i n the case of the
organic metal s a l t , the molar r a t i o of the phosphorus ( P ) atom
to the organic metal salt is within a range of 0.5 to 2.2; and
(iii) a step of, after the step (ii), melt-kneading the
mixture at a temperature of 260 to 300°C.
14. The method for producing a polylactic acid composition
according to claim 13, wherein in the step (i), the mass ratio
of the phosphorus atom fromthe phosphorus-based compound to
the tin atom from the tin-based compound (P/Sn) is within a
range of 0.15 to 5.0.