JP5285834B2 - Method for producing polylactic acid - Google Patents

Description

  The present invention relates to a method for producing high molecular weight polylactic acid. The present invention also relates to a method for producing polylactic acid having a high molecular weight and a high stereocomplex crystal content. Furthermore, the present invention relates to a polylactic acid and a molded article excellent in mechanical strength, heat resistance, thermal stability and the like.

  In recent years, bioplastics made from plants have attracted attention as biodegradable polymers that decompose in the natural environment from the standpoint of protecting the natural environment and as environmentally friendly plastics that effectively use renewable resources. In particular, the polylactic acid polymer is a melt-decomposable biodegradable polymer having a relatively high melting point of around 170 ° C. and excellent transparency. For example, the melting point and glass transition temperature of poly-L-lactic acid are 175 ° C. and 60 ° C., respectively, and the injection-molded product is glassy and hard and brittle. However, poly-L-lactic acid fibers and films that are molecularly oriented by stretching have sufficient strength. Therefore, in addition to products that are discarded in a short period of time, such as food trays and packaging, and that do not require much mechanical strength, they are also being used in engineering applications such as automobiles and home appliances that require a long life and high performance. ing.

On the other hand, as a polylactic acid polymer having a relatively high melting point, a method is known in which poly (L-lactide) and poly (D-lactide) are blended to improve thermal properties (Patent Document 1). In this method, poly (L-lactide) obtained by ring-opening polymerization of L-lactide and poly (D-lactide) obtained from D-lactide in the same manner are blended in a solution. In this method, a new crystal structure (hereinafter referred to as a stereocomplex structure) that is completely different from the crystal phase formed by the high-melting point homopolymer appears.
Further, a polymer composition comprising a poly (R-lactide) portion and a poly (S-lactide) portion is disclosed (Patent Document 2). According to this, it is reported that a stereocomplex structure appears even when the mixing ratio and the molecular weight ratio of poly (S-lactide) and poly (R-lactide) are different.
Also disclosed is a polylactic acid fiber formed from a blend of poly-L-lactic acid and poly-D-lactic acid (Patent Document 3). For the fibers, a mixed solution of 1 to 50% by weight containing poly-L-lactic acid and poly-D-lactic acid having a weight average molecular weight of 20,000 to 1,000,000 is prepared, and this is spun with a coagulating liquid. It is manufactured by doing.

On the other hand, all of the above Patent Documents 1 to 3 are those in which polylactic acid is dissolved in a solvent, but a technique relating to a polylactic acid resin composition obtained by melt-mixing poly-L-lactic acid and poly-D-lactic acid is also disclosed. (Non Patent Literature 1, Patent Literature 4, Patent Literature 5). Patent Document 4 discloses that the heat resistance is improved when the weight-average molecular weight ratio of poly-D-lactic acid or poly-L-lactic acid is 3 or more in poly-L-lactic acid / poly-D-lactic acid. .
Also, a polylactic acid stereocomplex fiber composed of poly-L-lactic acid and poly-D-lactic acid, wherein the high-temperature crystal dissolution phase accounts for 90% or more of the entire crystal phase, and the melting start temperature of the high-temperature crystal melt phase is A fiber that is 190 ° C. and has a texture that is not hardened by ironing is also disclosed (Patent Document 6). In this technology, the phenomenon that polylactic acid fibers are hardened by heat treatment is closely related to the melting start temperature of the high-temperature crystal melt phase, the existence ratio of the high-temperature crystal melt phase is within a specific range, and the melt start of the high-temperature crystal melt phase is started. By setting the temperature to a specific temperature, the curing phenomenon due to heat treatment is prevented.

There is also a technique of using a phosphoric ester metal salt as a crystal nucleating agent in forming such a polylactic acid stereocomplex (Patent Document 7). This technique is a technique that does not make a crystallization peak a double peak by adding a phosphoric ester metal salt as a nucleating agent, increases a crystallization temperature and a crystallization speed, and shortens an injection molding cycle.
Furthermore, a polylactic acid block copolymer produced by mixing poly-L-lactic acid and poly-D-lactic acid into a mixture and solid-phase polymerization at a temperature lower than the melting point of the mixture is also disclosed (patent). Reference 8). As described above, various studies have been conducted on the technology applying the stereo complex structure.
JP-A-61-36321 JP 63-24014 A JP-A 63-264913 JP 2003-96285 A JP 2000-17163 A JP 2003-105629 A JP 2003-192894 A JP 2003-238672-A Macromolecules, 24, 5651-5655 (1991)

  Stereocomplex polylactic acid is an equimolar mixture of poly-L-lactic acid (L component) and poly-D-lactic acid (D component). The melting point of the L component or D component is about 180 ° C., but the melting point of stereocomplex polylactic acid is about 230 ° C., which is known to be higher than that of the L component or D component.

When mixing the L component and the D component, if either one of the components has a low molecular weight, a good mixed state is formed and a stereo complex is easily formed. However, once a stereocomplex has been formed, it has been difficult to increase its molecular weight.
In addition, when both the L component and the D component have a high molecular weight, it is difficult to mix them, resulting in a non-uniform mixed state, easily forming a large number of single crystals of the L component or D component, and the ratio of stereocomplex crystals being low. Therefore, the mechanical strength and heat resistance are inferior, and it is not sufficient for use in electronic devices and machine parts.
Thus, in stereocomplex polylactic acid, it was difficult to achieve both high molecular weight and high stereocomplex crystal content.

An object of the present invention is to provide a method for producing polylactic acid (II) having a high molecular weight, a high stereocomplex crystal content, and excellent mechanical strength, heat resistance and thermal stability.
Another object of the present invention is to provide a method for producing polylactic acid (I), which can easily produce the polylactic acid (II) simply by melting.
Another object of the present invention is to provide a polylactic acid (II) having a high molecular weight, a high stereocomplex crystal content, and a high temperature-falling crystallization degree, and a molded article comprising the same.

As a result of intensive studies to achieve the above object, the present inventors have conducted mixing under the conditions of non-uniform mixing rather than mixing them completely to the molecular level when mixing the L and D components. A polymer blend (polylactic acid blend) of poly-L-lactic acid and poly-D-lactic acid having a stereocomplex crystal content (Fs) of 0.6 or less is prepared, and this is subjected to solid-phase polymerization. The present inventors have found that polylactic acid (I) with a high molecular weight can be obtained under various conditions.
Moreover, when polylactic acid (I) obtained by solid phase polymerization is melted, surprisingly, a stereocomplex crystal is easily formed, and polylactic acid (II) having a high molecular weight and a high stereocomplex crystal content can be obtained. As a result, the present invention has been completed.
That is, in the present invention, (i) poly-L-lactic acid (L component) and poly-D-lactic acid (D component) satisfying the following formula (2) or (3) are represented by the following formula (1). Mixing at a temperature T (° C.) to prepare a polylactic acid blend having a stereocomplex crystal content (Fs) of 0.6 or less; and
ts ≦ T <Te (1)
However, the melting start temperature of the component with the lower melting point of the L component and the D component is ts (° C.), and the melting end temperature of the component with the higher melting point of the L component and the D component is Te (° C.) .
7 ≦ M _WD / M _WL ≦ 30 (2)
7 ≦ M _WL / M _WD ≦ 30 (3)
_However, the weight average molecular weight of _{M WL} is the L _{component, M WD} is Ri weight average molecular weight der of component D, the case of formula _(2), the _{M WL} is _{4,000~40,000, M WD} 100,000~ In the case of Formula (3), M _WL is 100,000 to 300,000, and M _WD is 4,000 to 40,000.
(Ii) solid-phase polymerization of the polylactic acid blend;
Is a method for producing polylactic acid (I).

Moreover, this invention is a manufacturing method of polylactic acid (II) which melt | dissolves polylactic acid (I) obtained by the said method.
Further, the present invention is a molded product obtained by melt-molding polylactic acid (I) obtained by the above method and crystallizing it.
Furthermore, the present invention comprises an L lactic acid unit and a D lactic acid unit as polylactic acid (II) obtained by the above method , has a weight average molecular weight of 150,000 or more, and a stereocomplex crystal content (Fs) of 0.00. It includes 95 or more and polylactic acid having a cooling crystallization temperature (Tcd) of 160 ° C. or more.

According to the present invention, a polylactic acid blend consisting of an L component and a D component and having a stereocomplex crystal content (Fs) of 0.6 or less is subjected to solid phase polymerization, so that a high molecular weight can be obtained under mild solid phase polymerization conditions. Polylactic acid (I) is obtained.
That is, according to the present invention, when the L component and the D component are melt-mixed, the stereocomplex crystal content (Fs) is not obtained by mixing them under conditions that partially melt them instead of completely melting them. A polylactic acid blend having an A of 0.6 or less is prepared, and this is solid-phase polymerized to obtain high molecular weight polylactic acid (I) under mild solid-state polymerization conditions.

Although the stereocomplex crystal content (Fs) in polylactic acid (I) is low, by melting this, polylactic acid (II) having a high stereocomplex crystal content (Fs) and a high molecular weight can be obtained.
Since the polylactic acids (I) and (II) of the present invention are composed only of L-lactic acid and D-lactic acid, they are excellent in transparency, safety, low irritation, and biodegradability.
A molded product obtained by melt-molding the polylactic acid (II) and the polylactic acid (I) of the present invention has a high molecular weight, a narrow molecular weight distribution (Mw / Mn), and is excellent in mechanical strength, heat resistance, and thermal stability.

Hereinafter, the present invention will be described in detail.
(Poly-L-lactic acid, poly-D-lactic acid)
The poly-L-lactic acid (L component) used in the present invention is a polymer mainly containing L-lactic acid units, and the poly-D-lactic acid (D component) is a polymer mainly containing D-lactic acid units. It is a coalescence.

  The L component is preferably composed of 90 to 100 mol%, more preferably 95 to 100 mol%, and still more preferably 98 to 100 mol% of L-lactic acid units. Examples of other units include D-lactic acid units and copolymer component units other than lactic acid. The D-lactic acid unit and the copolymer component unit other than lactic acid are preferably 0 to 10 mol%, more preferably 0 to 5 mol%, and still more preferably 0 to 2 mol%.

  The component D is composed of 90 to 100 mol%, preferably 95 to 100 mol%, more preferably 98 to 100 mol% of D-lactic acid units. Examples of other units include L-lactic acid units and copolymer component units other than lactic acid. L-lactic acid units and copolymer component units other than lactic acid are 0 to 10 mol%, preferably 0 to 5 mol%, more preferably 0 to 2 mol%.

  The copolymer component unit is a unit derived from dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, etc. having a functional group capable of forming two or more ester bonds, and various polyesters, various polyethers composed of these various components, Examples are derived from various polycarbonates and the like.

  Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of polyhydric alcohols include aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol. Or aromatic polyhydric alcohol etc., such as what added ethylene oxide to bisphenol, etc. are mentioned. Examples of the hydroxycarboxylic acid include glycolic acid and hydroxybutyric acid. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.

  The L component and D component-lactic acid used in the present invention is a ring-opening polymerization method of lactide, which is a cyclic dimer of lactic acid (see JP-A Nos. 7-118259 and 7-138253), and direct lactic acid. Known methods such as a polycondensation method (JP-A-9-31180), a melt polymerization method or a solid-phase polymerization method (JP-A-2001-139672, JP-A-2001-297143), a combination of two or more of these However, it is more preferable to use a product produced by a method of dehydrating and condensing lactic acid in terms of quality and cost.

The optical purity of the L component and D component used in the present invention is preferably 92% or more, more preferably 95% or more, and still more preferably 96% or more. When the optical purity is less than 92%, the helical structure of the L component and the D component is broken, making it difficult to form a stereo complex structure of the L component and the D component, and the crystallinity is lowered, resulting in heat resistance and mechanical properties. A polylactic acid block copolymer having excellent strength may not be obtained. The optical purity (%) is a value calculated by the following formula from the weight ratio [L] (%) of L-lactic acid constituting the polylactic acid and the weight ratio [D] (%) of D-lactic acid.
Optical purity (%) = 100 × [L] / ([L] + [D]), or Optical purity (%) = 100 × [D] / ([L] + [D])

(Polylactic acid blend)
The polylactic acid blend is obtained by mixing the L component and the D component, and the stereocomplex crystal content (Fs) is 0.6 or less.
The polylactic acid blend can be prepared by bringing the L component and the D component into contact with each other at a temperature T (° C.) represented by the following formula (1). Preferably, it can be prepared by contacting at a temperature T (° C.) represented by the following formula (1-a). More preferably, it can be prepared by contacting at a temperature T (° C.) represented by the following formula (1-b).
ts ≦ T <Te (1)
Ts ≦ T <Te (1-a)
Ts ≦ T ≦ Tm (1-b)
Here, the melting start temperature of the low melting point component of the L component and the D component is ts (° C.), the melting start temperature of the high melting point component of the L component and the D component is Ts (° C.), and the melting point is Tm. (° C.), and the melting end temperature is Te (° C.).

The reason why the L component and the D component are brought into contact with each other at the temperature T represented by the above formula (1) is not a state where both the L component and the D component are melted, but a state where at least a part of one component is not melted This is to make it contact with each other. When a polylactic acid blend is prepared in a state where both the L component and the D component are melted, a stereocomplex is formed, and it is difficult to increase the molecular weight even after solid phase polymerization.
When the melting start temperature of the component having a low melting point among the L component and the D component is ts (° C.) and the melting end temperature is te (° C.), when the relationship of ts <Ts <te <Tm holds, the following formula ( It is preferable to prepare a polylactic acid blend by contacting at a temperature T (° C.) represented by 1-c). When the relationship of ts <Ts <Tm <te is satisfied, it is preferable to prepare a polylactic acid blend by contacting at a temperature T (° C.) represented by the following formula (1-d).
Ts ≦ T ≦ te (1-c)
Ts ≦ T ≦ Tm (1-d)

  In preparing the polylactic acid blend, preferred combinations of the molecular weights of the L component and the D component are as follows. It is preferable that the weight average molecular weight of L component is 4,000-60,000, and the weight average molecular weight of D component is 4,000-60,000. More preferably, the L component has a weight average molecular weight of 5,000 to 60,000, and the D component has a weight average molecular weight of 5,000 to 60,000. More preferably, the L component has a weight average molecular weight of 6,000 to 60,000, and the D component has a weight average molecular weight of 6,000 to 60,000.

Also, among the L component and the D component, we use a high weight average molecular weight only one. Immediate Chi, weight average molecular weight of the L component _{(M WL)} and a weight average molecular weight of component D ratio of _{(M WD),} satisfies the following formula (2) or (3).
7 ≦ M _WD / M _WL ≦ 30 (2)
7 ≦ M _WL / M _WD ≦ 30 (3)
In the case of the above formula (2), M _WL is preferably 4,000 to 40,000, and M _WD is preferably 100,000 to 300,000. Further, when the above equation _{(3), M WL} is 100,000 to _{300,000, M WD} is preferably 4,000～40,000.
In this case, the obtained polylactic acid (I) becomes a polylactic acid (II) having a high molecular weight, a high stereocomplex crystal content (Fs), and a high temperature-falling crystallization temperature (Tcd) by melting.

The weight ratio of the D component and the L component is preferably D component / L component = 10/90 to 90/10. More preferably, D component / L component = 40/60 to 60/40.
The mixing time is preferably 2 to 60 minutes, more preferably 5 to 10 minutes. The heating temperature is preferably gradually increased to such an extent that the polylactic acid blend is not completely melted.
In the present invention, the atmosphere at the time of mixing is not particularly limited, and it can be carried out under any conditions of normal pressure and reduced pressure. In the case of normal pressure, it is preferably carried out under an inert gas flow such as nitrogen. Moreover, in order to remove the monomer which decomposes | disassembles at the time of melting, it is preferable to carry out under reduced pressure.

There is no limitation on the order of introduction of each component into the apparatus or the like when blending the L component and the D component. Accordingly, the two components may be charged simultaneously into the blending apparatus. For example, the L component may be charged and mixed after the D component is melted. At this time, each component may have any shape such as powder or granule. The mixing may be performed by heating and kneading using a mill roll, a mixer, a single or twin screw extruder, a heatable batch container, and the like.
At the time of mixing the L component and the D component, a polymerization catalyst can be added for the next solid phase polymerization. Examples of such a catalyst include metal halides such as stannous chloride and zinc chloride, metal oxides such as tin oxide, antimony oxide, and zinc oxide, and organic carboxylic acid metal salts such as tin octylate and zinc acetate. be able to. The amount of these used is 0.0001 to 0.2 parts by weight, more preferably 0.0005 to 0.1 parts by weight with respect to 100 parts by weight of the total amount of the L component and the D component.

  In addition, metal alkoxides such as aluminum, titanium, and germanium, and organic sulfonic acids such as toluenesulfonic acid, methanesulfonic acid, and ethylsulfonic acid may be used as a cocatalyst. These usage-amounts are 0.01-0.1 weight part with respect to 100 weight part of total amounts of L component and D component, More preferably, it is 0.03-0.1 weight part. These can be used alone or in combination. In addition, when such a polymerization catalyst and a cocatalyst are contained in D component and L component which are raw material compounds, it is not necessary to add further.

During mixing, a solvent capable of swelling or dispersing the L component and the D component may be used. For example, when the L component and the D component are separately swelled or dispersed in a solution, and after mixing them, the solvent is removed to form a polylactic acid blend.
At the time of mixing, a method of mixing the L component and the D component in a powder or solid state and fixing them may be used. At the time of mixing, the L component and the D component may be brought into contact with each other in a nano film state and fixed. The size of the powders and particles of the L component and D component during mixing is preferably 2 mm or less, more preferably 1 mm or less.

  The weight average molecular weight of the polylactic acid blend is preferably 10,000 to 100,000, more preferably 20,000 to 90,000. In addition, the weight average molecular weight of the polylactic acid blend is a numerical value measured by a method described later. The stereocomplex crystal content (Fs) of the polylactic acid blend is 0.6 or less, preferably 0.4 or less, more preferably 0.2 to 0.4. The polylactic acid blend is cooled and solidified, preferably pulverized, and subjected to solid phase polymerization.

(Solid phase polymerization)
The solid phase polymerization is preferably performed at 130 to 160 ° C. According to the present invention, the molecular weight can be increased even when solid phase polymerization is performed under mild conditions. The time for solid phase polymerization is preferably 5 to 50 hours, more preferably 20 to 40 hours.
In the present invention, it is preferable to increase the solid-state polymerization temperature in accordance with the degree of polymerization. For example, for example, it is preferable to perform the solid-state polymerization temperature (T _n : ° C.) and the time for maintaining the temperature (t _n : time) in n stages satisfying the following formula.
130 ≦ T _n ≦ 160
T _n <T _{n + 1}
1 ≦ t _n ≦ 15
n = 1-10
That is, between 130 ° C. and 160 ° C., maintained at a temperature T ₁ for t ₁ hour, then maintained at a temperature T ₂ higher than T ₁ for t ₂ hours, and further at a temperature T ₃ higher than T ₂ at t _3. It is preferable to raise the polymerization temperature step by step so as to maintain the time. The total polymerization time (Σt _n ) is preferably 5 to 50 hours, more preferably 20 to 40 hours. When the polymerization temperature is raised stepwise in this way, the weight average molecular weight (Mw) of the obtained polylactic acid (I) is improved. This is probably because the crystal growth is promoted by gradually increasing the temperature to increase the crystal size.

The solid phase polymerization is preferably performed under an inert gas flow or under reduced pressure, for example, 1 to 2,000 Pa, preferably 10 to 200 Pa. Since the L component and the D component are chemically bonded by an ester reaction or a dehydration condensation reaction, H ₂ O is by-produced as the reaction proceeds. Polymerization under reduced pressure is preferable because this by-product water can be efficiently removed out of the system and the reaction equilibrium can be shifted to the polymerization side. When the pressure exceeds 2,000 Pa, such dehydration becomes insufficient. On the other hand, even if the pressure is lower than 1 Pa, no further dehydration effect can be obtained, and at the same time, the by-product lactide is distilled off and the yield is reduced. Therefore, it is not preferable.

In the present invention, the apparatus for solid phase polymerization is not particularly limited, but a batch type concentration drying apparatus, a continuous type solid state polymerization apparatus, or the like can be used. Moreover, a conical dryer, a drum-type heater, etc. can also be used.
The weight average molecular weight of polylactic acid (I) obtained by solid phase polymerization is preferably 100,000 or more, more preferably 100,000 to 200,000. The stereocomplex crystal content is 0.1 to 0.3.

(Melting)
By melting polylactic acid (I) obtained by solid phase polymerization, polylactic acid (II) having a high stereocomplex crystal content can be produced. The melting is preferably performed by maintaining at 220 to 300 ° C. The melting temperature is preferably 230 to 250 ° C. If it exceeds 300 ° C., it is difficult to suppress the decomposition reaction, which is not preferable. The melting time is not particularly limited as long as the polylactic acid is completely melted, and is 0.2 to 20 minutes, preferably 1 to 5 minutes. As an atmosphere at the time of melting, any of an atmospheric pressure atmosphere, an inert atmosphere, or reduced pressure can be applied.
The stereocomplex crystal content (Fs) of the polylactic acid (II) obtained by melting is preferably 0.95 or more, more preferably 0.98 or more, and further preferably 1.0. The weight average molecular weight (Mw) is preferably 100,000 or more, more preferably 100,000 to 200,000.

Polylactic acid (II) obtained by melting has a high stereocomplex crystal content (Fs) and is excellent in mechanical strength, heat resistance, and thermal stability. This melting generally coincides with the molding conditions, and by molding the polylactic acid after solid phase polymerization, a stereocomplex crystal content (Fs) is high, and a molded product having a high molecular weight can be obtained.
(Polylactic acid (II))
According to the present invention, when the molecular weight of the L component and the D component satisfies the above formula (2) or (3), a polylactic acid blend is prepared, solid-phase polymerized, and melted, II) is composed of L lactic acid units and D lactic acid units, has a weight average molecular weight of 150,000 or more, a stereocomplex crystal content (Fs) of 0.95 or more, and a cooling crystallization temperature (Tcd) of 160 ° C. The above polylactic acid is obtained.
The polylactic acid is a polymer substantially composed of L lactic acid units and D lactic acid units represented by the following formula.

  The ratio of the D lactic acid unit and the L lactic acid unit is D lactic acid unit / L lactic acid unit = 10/90 to 90/10, preferably 40/60 to 60/40. Polylactic acid is a multi-block polymer in which poly-L-lactic acid blocks and D component blocks are randomly arranged. The average chain length (ν) of the L-lactic acid block and the D-lactic acid block is 20 to 60, preferably 20 to 50.

Polylactic acid has a weight average molecular weight of 150,000 or more, preferably 150,000 to 180,000. The stereocomplex crystal content (Fs) is preferably 0.95 or more, more preferably 0.98 or more, and still more preferably 1.0. The cooling crystallization temperature (Tcd) is 160 ° C. or higher, preferably 160 to 180 ° C. or higher.
The polylactic acid preferably has a melting peak in the temperature range of 200 ° C. or higher, more preferably 200 to 220 ° C.
Polylactic acid contains normal additives such as UV absorbers, antioxidants, heat stabilizers, lubricants, mold release agents, dyes, pigments, antibacterial and antifungal agents, as long as the purpose is not impaired. can do. Polylactic acid can be widely used as a molded article. Molded products include films, sheets, fibers, fabrics, non-woven fabrics, injection molded products, extrusion molded products, vacuum pressure air molded products, blow molded products, agricultural materials, horticultural materials, fishery materials, civil engineering and construction materials. Stationery, medical supplies, electrical and electronic parts.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. In addition, the measurement of the characteristic value etc. in a manufacture example, an Example, and a comparative example was performed with the following method.

(1) Weight average molecular weight (Mw) and number average molecular weight (Mn)
This was performed by gel permeation chromatography (GPC) and converted to standard polystyrene. The GPC measuring equipment is as follows.
Detector: differential refractometer, Shimadzu RID-6A
Pump: Shimadzu LC-9A
Column: Toso-TSKgelG3000HXL, TSKgelG4000HXL, TSKgelG5000HXL and TSKguardcocumnHXL-L connected in series, Toso-TSKgelG2000HXL, TSKgelG3000HXL and TSKguardLum40 The sample was poured at a flow rate of 1.0 ml / min at 10 ° C., and 10 μl of a sample having a concentration of 1 mg / ml (chloroform containing 1% hexafluoroisopropanol) was injected.

(2) Measurement of average chain length of block (ν)
¹³ CNMR apparatus: BURKER ARX-500 manufactured by Nippon Bruker
Sample: 50 mg / 0.7 ml Measurement solvent Measurement solvent: Deuterated chloroform containing 10% HFIP Internal standard: Tetramethylsilane (TMS) 1% (v / v)
Measurement temperature: 27 ° C (300K)
Measurement frequency: 125 MHz
Measurement method: According to ¹³ C-NMR measurement, among carbon peaks attributed to carbonyl carbon (C═O), peak (a) (around 170.1-170.3 MHz) is a homo sequence (LLLLLL or DDDDDD). Peak (b) (around 170.0-169.8 MHz) belongs to the racemic chain (LLLDDD...), And the average chain length was calculated from the integrated value of these peaks according to the following formula.
ν = integral value of peak (a) / integral value of peak (b)

(3) Thermal characteristics (Ts, ts, Tm, Te, te, ΔHmh, ΔHms, Tcd)
Shimadzu DSC-60 differential scanning calorimeter DSC was used. The measurement was performed by a method in which 10 mg of a sample was heated from room temperature to 250 ° C. at a rate of temperature increase of 10 ° C./min in a nitrogen atmosphere, allowed to cool for 20 minutes, and then again heated to 250 ° C. at 10 ° C./min. In the first scan, crystal melting start temperature (Ts, ts), crystal melting temperature (Tm), crystal melting end temperature (Te, te), homocrystal melting heat (ΔHmh), stereo complex crystal melting heat (ΔHms) are measured. did. Moreover, the temperature-falling crystallization temperature (Tcd) was measured by the method of raising the temperature to 240 ° C. at 20 ° C./min and lowering the temperature to 40 ° C. at 5 ° C./min.

(4) Crystallinity (χ _h , χ _S )
The degree of crystallinity was determined as follows. From DSC, 100% crystallized polylactic acid has a homocrystal melting heat (ΔHmh ⁰ ) of −203.4 J / g, 100% crystallized polylactic acid has a stereocomplex crystal heat of fusion (ΔHms ⁰ ) of −142 J / g. The homocrystallinity (χ _h ) and stereocomplex crystallinity (χ _S ) were calculated from the following formulas from the actually obtained homocrystal fusion heat (ΔHmh) and stereocomplex crystallization heat of fusion (ΔHms).
χ _h (%) = 100 × (ΔHmh / ΔHmh ⁰ )
χ _S (%) = 100 × (ΔHms / ΔHms ⁰ )

(5) Stereocomplex crystal content (Fs)
The stereocomplex crystal content was calculated by the following formula.
Fs = χ _S / (χ _h + χ _S )

(6) Optical purity (%)
The optical purity was determined from the constituent ratio of L-lactic acid and D-lactic acid constituting polylactic acid. To 1 g of the sample, 5 ml of 5M sodium hydroxide and 2.5 ml of isopropanol were added, hydrolyzed while heating and stirring at 40 ° C., and then neutralized with 1M sulfuric acid. The concentration was adjusted by diluting 1 ml of the neutralized solution 25 times. The detection peak area of L-lactic acid and D-lactic acid at UV light UV 254 nm was measured by HPLC, and the weight ratio [L] (%) of L-lactic acid constituting polylactic acid and the weight of D-lactic acid. The optical purity (%) was calculated from the ratio [D] (%) by the following formula.
As an HPLC apparatus, a pump; Shimadzu LC-6A, UV detector; Shimadzu SPD-6AV, column; SUMICHIRAL OA-5000 (Sumitomo Chemical Analysis Center) was used, and 1 mM copper sulfate aqueous solution was used as an eluent. Measurement was performed at a flow rate of 1.0 ml / min and 40 ° C.
Optical purity (%) = 100 × [L] / ([L] + [D]), or Optical purity (%) = 100 × [D] / ([L] + [D])

(Production Example 1) Preparation of poly-L-lactic acid (PL1) 1 kg of 90% by weight L-lactic acid aqueous solution (manufactured by Musashino Chemical Laboratory Co., Ltd.) was stirred at 150 ° C./4,000 Pa for 6 hours while distilling water. And oligomerized. To this oligomer, 0.2 g of stannous chloride and 0.2 g of p-toluenesulfonic acid were added and melt polymerized at 180 ° C./1300 Pa / 6 hours. Thereafter, the solid was pulverized to obtain an L component (PL1). Table 1 shows the weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), crystal melting start temperature (Ts or ts), crystal melting temperature (Tm), crystal melting end temperature (Te or te), and optical purity of PL1. Show.

(Manufacture example 2) Preparation of poly-L-lactic acid (PL2) Except having performed melt polymerization for 5 hours, operation similar to manufacture example 1 was performed and L component (PL2) was obtained. Table 1 shows the physical properties of PL2.

(Production Example 3) Preparation of poly-L-lactic acid (PL3) In the same manner as Production Example 1, after melt polymerization, the solid was pulverized and subjected to solid phase polymerization at 140 ° C for 30 hours. The same operation was performed to obtain an L component (PL3). Table 1 shows the physical properties of PL3.

(Production Example 4) Preparation of poly-D-lactic acid (PD1) The same procedure as in Production Example 2 was carried out except that a 90% by weight D-lactic acid aqueous solution (manufactured by Musashino Chemical Laboratory Co., Ltd.) was used. (PD1) was obtained. Table 1 shows the physical properties of PD1.

(Production Example 5) Preparation of poly-D-lactic acid (PD2) A component D (PD2) was obtained in the same manner as in Production Example 4 except that melt polymerization was carried out for 4 hours. Table 1 shows the physical properties of PD2.

(Production Example 6) Preparation of poly-D-lactic acid (PD3) A component D (PD3) was obtained in the same manner as in Production Example 4 except that melt polymerization was performed in 3 hours. Table 1 shows the physical properties of PD3.

< Reference Example 1>
(Preparation of polylactic acid blend)
30 g of PL1 and 30 g of PD1 were heated at normal pressure while blending in a 200 cc flask, and the temperature was raised from room temperature to 165 ° C. over 10 minutes. Some melting was confirmed at 150 ° C. during the temperature raising process. Thereafter, the temperature was lowered to obtain a polylactic acid blend (MB1). MB1 was cooled, solidified and pulverized into particles. Table 2 shows Mw, Tm, and other physical properties of MB1.

(Solid phase polymerization)
Then, under reduced pressure (60 Pa), it was heated at 130 ° C. for 5 hours, 140 ° C. for 5 hours, and 150 ° C. for 15 hours (total 30 hours) to perform solid phase polymerization to obtain polylactic acid (FSB1). Mw, Mw / Mn, and other physical properties of FSB1 were measured. The results are shown in Table 3.

< Reference Example 2>
(Preparation of polylactic acid blend)
30 g of PL2 and 30 g of PD2 were heated at normal pressure while blending in a 200 cc flask, and the temperature was raised from room temperature to 160 ° C. over 10 minutes. Some melting was confirmed at 145 ° C. during the temperature raising process. Thereafter, the temperature was lowered to obtain a polylactic acid blend (MB2). MB2 was cooled to solidify and pulverized into particles. Table 2 shows Mw, Tm and other physical properties of MB2.

(Solid phase polymerization)
Subsequently, under reduced pressure (0.5 mmHg), heating was performed at 140 ° C. for 10 hours, 150 ° C. for 10 hours, and 160 ° C. for 10 hours (total 30 hours) to perform solid phase polymerization to obtain polylactic acid (FSB1). Mw, Mw / Mn, and other physical properties of FSB2 were measured. The results are shown in Table 3.

<Example 3>
(Preparation of polylactic acid blend)
30 g of PL3 and 30 g of PD3 were heated at normal pressure while blending in a 200 cc flask, and the temperature was raised from room temperature to 190 ° C. over 10 minutes. Part of melting was confirmed at 160 ° C. during the temperature raising process. Thereafter, the temperature was lowered to obtain a polylactic acid blend (MB3). MB3 was cooled, solidified and pulverized into particles. Table 2 shows Mw, Tm and other physical properties of MB3.

(Solid phase polymerization)
Next, after heat treatment at 110 ° C. for 2 hours under reduced pressure (0.5 mmHg), the mixture was heated at 130 ° C. for 5 hours and at 140 ° C. for 25 hours (total 30 hours) to perform solid phase polymerization to obtain polylactic acid (FSB3). It was. Mw, Mw / Mn, and other physical properties of FSB3 were measured. The results are shown in Table 3.

<Comparative Example 1>
(Preparation of polylactic acid blend)
30 g of PL1 and 30 g of PD1 were heated at normal pressure while blending in a 200 cc flask, and the temperature was raised from room temperature to 175 ° C. over 10 minutes. It was confirmed that PL1 and PD1 were uniformly melted at 175 ° C. Thereafter, the temperature was lowered to obtain a polylactic acid blend (MB0). MB0 was cooled and solidified and pulverized into particles. Table 2 shows Mw, Tm, and other physical properties of MB0.

(Solid phase polymerization)
Subsequently, solid-phase polymerization was performed under reduced pressure (60 Pa) at 160 ° C. for 30 hours to obtain polylactic acid (FSB0). Table 3 shows Mw, Tm and other physical properties of FSB0.

< Reference Example 4>
(Melting)
FSB1 obtained in Reference Example 1 was gradually heated from room temperature to 240 ° C. and melted to obtain polylactic acid (SSB1). Mw, Mw / Mn, and other physical properties of SSB1 were measured. The results are shown in Table 4.

< Reference Example 5>
(Melting)
FSB2 obtained in Reference Example 2 was gradually heated from room temperature to 250 ° C. and melted to obtain polylactic acid (SSB2). Mw, Mw / Mn, and other physical properties of SSB2 were measured. The results are shown in Table 4.

<Example 6>
(Melting)
FSB3 obtained in Example 3 was gradually heated from room temperature to 250 ° C. and melted to obtain polylactic acid (SSB3). Mw, Mw / Mn, and other physical properties of SSB3 were measured. The results are shown in Table 4.

<Comparative example 2>
(Melting)
FSB0 obtained in Comparative Example 1 was gradually heated from room temperature to 240 ° C. and melted to obtain polylactic acid (SSB0). Mw, Mw / Mn, and other physical properties of SSB0 were measured. The results are shown in Table 4.

According to the present invention, polylactic acid is provided that is excellent in mechanical strength, heat resistance, and thermal stability, and also excellent in transparency, safety, and biodegradability. This polylactic acid is expected to be used for engineering applications such as foods, packaging, automobiles and home appliances.

Claims (8)

(I) Poly-L-lactic acid (L component) and poly-D-lactic acid (D component) satisfying the following formula (2) or (3) at a temperature T (° C.) represented by the following formula (1) Mixing to prepare a polylactic acid blend having a stereocomplex crystal content (Fs) of 0.6 or less, and
ts ≦ T <Te (1)
However, the melting start temperature of the component with the lower melting point of the L component and the D component is ts (° C.), and the melting end temperature of the component with the higher melting point of the L component and the D component is Te (° C.) .
7 ≦ M _WD / M _WL ≦ 30 (2)
7 ≦ M _WL / M _WD ≦ 30 (3)
_However, the weight average molecular weight of _{M WL} is the L _{component, M WD} is Ri weight average molecular weight der of component D, the case of formula _(2), the _{M WL} is _{4,000~40,000, M WD} 100,000~ In the case of Formula (3), M _WL is 100,000 to 300,000, and M _WD is 4,000 to 40,000.
(Ii) solid-phase polymerization of the polylactic acid blend;
A process for producing polylactic acid (I) comprising In the polylactic acid blend, an L component and a D component are represented by the following formula (1-a):
Ts ≦ T <Te (1-a)
However, the melting start temperature of the component having the higher melting point among the L component and the D component is Ts (° C.), and the melting end temperature is Te (° C.).
The manufacturing method according to claim 1, wherein the contact is made at a temperature T (° C.) represented by the formula: A method for producing polylactic acid (II), comprising melting polylactic acid (I) obtained by the method according to claim 1 or 2. The weight ratio of D component and L component is D component / L component = 10 / 90-90 / 10, The manufacturing method as described in any one of Claims 1-3. The production method according to any one of claims 1 to 4, wherein solid phase polymerization is performed at 130 to 160 ° C. The production method according to claim 3, wherein the melting after the solid-phase polymerization is performed at 220 to 300 ° C. Claims comprising an L lactic acid unit and a D lactic acid unit, having a weight average molecular weight of 150,000 or more, a stereocomplex crystal content (Fs) of 0.95 or more, and a cooling crystallization temperature (Tcd) of 160 ° C or more. Polylactic acid obtained by the production method according to any one of 3 to 6. A molded article obtained by melt-molding and crystallizing polylactic acid (I) obtained by the production method according to claim 1.