JP4069282B2 - Biodegradable polylactic acid composition - Google Patents

Description

【００３３】
【表２】

【００３４】
表１から分かるように、分子量の異なる３種類のアタクチックＰＨＢが合成された。また、表２に示したＴｇの値から、２００℃で溶融したときの相溶性を判別したところ、ポリ乳酸と、分子量の低いアタクチックＰＨＢとのブレンドは、分子レベルで混ざりあっている相溶系であるが、重量平均分子量２１，０００のアタクチックＰＨＢとのブレンドでは、１部のアタクチックＰＨＢがポリ乳酸と混ざりあわない半相溶系、重量平均分子量が１４０，０００のアタクチックＰＨＢとのブレンドは、殆ど両者が混ざりあわない非相溶系であることが分かった。
【００３５】
ポリ乳酸／アタクチックＰＨＢのソルベントキャストフィルムを用いて、ポリ乳酸の球晶成長速度を調べた結果を図１に示した。非相溶系でのブレンド（ポリ乳酸と重量平均分子量１４０，０００とのブレンド）の球晶成長速度は、ポリ乳酸単独の球晶成長速度と同等であったが、半相溶系、相溶系のブレンドにおいては球晶成長速度は増加した。特に相溶系のブレンドにおいては、大きな増加がみられた。
【００３６】
ポリ乳酸／アタクチックＰＨＢの溶融結晶化フィルムの広角Ｘ回折測定（ＷＡＸＤ）から得られた結晶化度を図２に、ＤＳＣ測定から得られた融解熱（ΔＨｍ）を表３に示した。図２から、アタクチックＰＨＢの添加により、ポリ乳酸の結晶化度を減少させず、特に相溶系のブレンドにおいては、結晶化度が増加する現象が認められた。また、ΔＨｍと結晶化度は比例関係にあり、ΔＨｍより求めた結晶化度は、ＷＡＸＤから得られた結晶化度の値とよく一致した。
【００３７】
【表３】

【００３８】
【発明の効果】
本発明によれば、球晶成長速度を高めて成形加工性が改善され、また結晶化度を調節し、組成物の生分解速度を制御することのできる生分解性ポリ乳酸系組成物が提供される。
【００３９】
また、プラスチック公害が深刻化している現在、生分解生プラスチックの中で、特に注目されているポリ乳酸の成形加工性の改良および分解速度の制御を行うことの有用性は大きい。
【図面の簡単な説明】
【図１】ポリ乳酸／アタクチックＰＨＢのソルベントキャストフィルムを用いて、ポリ乳酸の球晶成長速度を調べた結果を示す図である。
【図２】ポリ乳酸／アタクチックＰＨＢの溶融結晶化フィルムの広角Ｘ回折測定（ＷＡＸＤ）から得られた結晶化度を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biodegradable polylactic acid composition that can be used for packaging materials, containers, medical materials, fishery materials, horticultural materials, agricultural films, and the like.
[0002]
[Prior art]
Plastic is light, strong, durable, and has excellent moldability, so it is used in large quantities in a wide range of fields, including packaging materials, light electrical parts, automotive parts, building materials, and household goods. General-purpose plastics such as polypropylene, polystyrene, and polyvinyl chloride are incinerated or landfilled as disposal methods after use.
[0003]
When landfilled, these general-purpose plastics are chemically stable, so they remain semi-permanently while remaining in their original form, which is one of the causes of the shortage of landfills. Thus, how to dispose of a large amount of plastic waste that has become unnecessary is a major social problem.
[0004]
Moreover, when it is discarded in the natural environment, the aesthetics are impaired, the living creatures accidentally eaten up, and the ecosystem under the natural environment is destroyed, which contributes to the destruction of the environment.
[0005]
As interest in environmental issues on a global scale has increased, biodegradable plastics that are biodegraded in the natural environment and incorporated into the natural carbon cycle have been actively studied. One of the biodegradable plastics is polylactic acid.
[0006]
Polylactic acid has a high glass transition point (60 ° C.), and crystalline one is a thermoplastic polymer having a high melting point (180 ° C.). It is known that lactic acid as a raw material can be efficiently obtained from fermentation of an inexpensive raw material such as corn starch. Polylactic acid is usually polymerized directly or via a cyclic dimer called lactide. Thus, since polylactic acid uses agricultural products as raw materials, it does not depend on petroleum resources, and has many excellent physical properties such as high strength and high elastic modulus.
[0007]
Polylactic acid degrades in a few weeks in compost, but in the natural environment, it degrades in 1 to 2 years under wet conditions. The decomposition products are lactic acid, water and carbon dioxide, which are completely harmless.
[0008]
[Problems to be solved by the invention]
However, polylactic acid has a disadvantage that the growth rate of spherulites is very slow and inferior in molding processability. In the prior art, there is an attempt to improve moldability by mixing a nucleating agent, but sufficient moldability is still not obtained, and it cannot be denied that it is disadvantageous in cost.
In addition, although there is a report that the biodegradation rate of polylactic acid greatly depends on the degree of crystallinity, the detailed degradation mechanism is not yet elucidated. As described above, polylactic acid has a slow degradation rate in the natural environment and is suitable for applications that require a long life of the molded article, but depending on the application, it is necessary to decompose quickly. That is, polymers that can have various biodegradation rates are desired depending on the application.
[0009]
Accordingly, an object of the present invention is to provide a biodegradable polylactic acid-based composition capable of improving the molding processability by increasing the spherulite growth rate, adjusting the crystallinity, and controlling the biodegradation rate of the composition. On offer.
[0010]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have been able to solve the conventional problems as described above.
That is, the present invention relates to poly [(R, S) -3-hydroxybutanoic acid having an atactic structure having an aliphatic polyester (A) of 40 to 97% by weight based on polylactic acid and a weight average molecular weight of 100,000 or less. ] The biodegradable polylactic acid type | system | group composition formed by containing 3-60 weight% of aliphatic polyester (B) containing 70 weight% or more is provided.
[0011]
The feature of the present invention is to improve the molding processability by increasing the spherulite growth rate of the aliphatic polyester (A) containing lactic acid as a main component, and also increasing the biodegradability rate by controlling the crystallinity. For this purpose, a specific aliphatic polyester (B) is combined with the aliphatic polyester (A) component. In general, when an amorphous polymer is added to a crystalline polymer, crystallization is suppressed and a spherulite growth rate and a decrease in crystallinity are caused. However, in the composition of the present invention, the spherulite growth rate is improved. However, no decrease in crystallinity is observed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The aliphatic polyester (A) containing polylactic acid as a main component is a component derived from lactic acid in a polymer of 50% by weight or more. For example, (1) polylactic acid homopolymer, (2) polylactic acid Examples include those obtained by block copolymerizing a small amount (50% by weight or less) of other polyester-forming raw materials, and (3) random copolymerization of other polyester-forming raw materials by a small amount (10% by weight or less) with polylactic acid.
[0013]
Examples of aliphatic polyester-forming raw materials that can be copolymerized with polylactic acid include (a) aliphatic hydroxycarboxylic acids such as glycolic acid and hydroxybutylcarboxylic acid, and (b) aliphatic lactones such as glycolide, butyrolactone, and caprolactone. (C) aliphatic diols such as ethylene glycol, propylene glycol, butanediol, hexanediol, etc., (d) diethylene glycol, triethylene glycol, ethylpropyl ether glycol, bishydroxyethylpropane, bishydroxypropylbutane, polyethylene glycol, Aliphatic polyether glycols such as polypropylene glycol, polybutylene ether, copolymers and oligomers thereof, (e) dihydroxybutyl carbonate, di Aliphatic polycarbonate glycols such as droxyhexyl carbonate, polybutylene carbonate (glycol), polyhexane carbonate (glycol), polyoctane carbonate (glycol), copolymers and oligomers thereof, (f) succinic acid, adipic acid, sebacine Examples thereof include aliphatic dicarboxylic acids such as acids.
Polymers obtained from the above polyester raw materials such as polycaprolactone, polyglycolic acid, polyethylene adipate, polyethylene sebacate, polybutylene succinate, polybutylene adipate, polybutylene sebacate, polyhexane adipate, polyhexane sebacate and the like Block copolymerization is easy. In addition to aliphatic raw materials, for example, phthalic acid, terephthalic acid, isophthalic acid and other aromatic polyester raw materials can be copolymerized in a small amount (for example, 20% by weight or less).
[0014]
The purpose of modifying polylactic acid by copolymerization, etc. is to reduce crystallinity, melting point (reduction of polymerization temperature, molding temperature, processing temperature), melt fluidity, toughness, improvement of flexibility and elastic recovery, friction Coefficient, surface roughness, adhesion, mixability, heat resistance and glass transition temperature decrease or increase, gas barrier properties, moisture permeability, hydrophilicity and water repellency improvement, dyeability improvement, degradability improvement or suppression, etc. The modified polylactic acid can be applied to the present invention depending on the purpose.
[0015]
The weight average molecular weight of the aliphatic polyester (A) containing polylactic acid as a main component is not particularly limited, but is preferably 50,000 or more, particularly preferably 70 to 700,000 from the strength of the molded product.
[0016]
Aliphatic polyesters (B) based on poly [(R, S) -3-hydroxybutanoic acid] having an atactic structure are (R) -3-hydroxybutanoic acid and (S) -3-hydroxybutanoic acid. Is a random copolymer (hereinafter abbreviated as atactic PHB). This atactic PHB is a kind of atactic polymer in which repeating units derived from R-form and S-form of 3-hydroxybutanoic acid are randomly bonded in one molecular chain. This atactic PHB can be synthesized by a chemical method.
[0017]
Next, an example of a method for synthesizing atactic PHB will be described. Atactic PHB is synthesized by ring-opening polymerization of a mixture (racemic β-butyrolactone) containing (R) -β-butyrolactone and (S) -β-butyrolactone in the presence of a catalyst.
[0018]
The molar ratio of (R) -β-butyrolactone to (S) -β-butyrolactone in the raw racemic β-butyrolactone is in the range of 100: 60 to 100: 160, particularly 100: 90 to 100: 110. It is preferable that the total amount of both in the raw material monomer is 70% by weight or more. Examples of other monomer components that can be present in the raw material in small amounts of less than 30% by weight include 3-hydroxypropionic acid, 5-hydroxypentanoic acid, 6-hydroxyhexanoic acid, glycolic acid, lactic acid, and the like. is there.
[0019]
The component (B) has a weight average molecular weight of 100,000 or less. When the molecular weight is higher than 100,000, the compatibility with the component (A) tends to be remarkably reduced.
[0020]
The catalyst used for the synthesis of atactic PHB is described in, for example, Macromolecules, Vol. 10, 275 (1977). According to this method, 0.6 mol of water is reacted with 1 mol of diethylzinc in an inert solvent such as dioxane in an inert gas atmosphere such as nitrogen or argon, and then the solvent is distilled under reduced pressure. Removal of the catalyst produces a catalyst.
[0021]
The catalyst thus obtained was added at a ratio of 1 to 5 parts by weight with respect to 100 parts by weight of racemic β-butyrolactone and reacted in a 1,2-dichloroethane solvent at a reaction temperature of about 60 ° C. for about 5 days. A crude product of atactic PHB is obtained. The crude product is dissolved in chloroform, poured into a mixed solvent of diethyl ether / distilled water, the solvent is removed, and the residue is dried under reduced pressure to obtain a purified product of atactic PHB. This synthesis method is an exemplification, and the atactic PHB used in the present invention is not limited to that synthesized by this method.
[0022]
The mixing ratio of component (A) and component (B) is 40 to 97% by weight of component (A) and 3 to 60% by weight of component (B).
Outside the range of this mixing ratio, there arises a problem that the compatibility is lowered and the strength is lowered due to the reduction of the polylactic acid component.
The mixing method of the components (A) and (B) is not particularly limited. For example, the components (A) and (B) are mixed by mechanical stirring such as a single-screw extruder, a twin-screw kneading extruder, a kneader, a gear pump, a kneading roll, and a tank having a stirrer. Alternatively, a static mixer that repeats diversion and merging by a flow guide device may be applied, or they may be used in combination. The mixing may be a batch method or a continuous method, but of course, a continuous method such as a single screw extruder, a twin screw kneading extruder, a static mixer or the like is preferable because of high efficiency. Further, the components (A) and (B) may be dissolved and mixed in a solvent.
[0023]
In the composition of the present invention, if necessary, colorants such as pigments and dyes, fillers such as inorganic or organic particles, glass fibers, whiskers and mica, crystal nucleating agents, antioxidants, UV absorbers Stabilizers, lubricants, mold release agents, water repellents, plasticizers, antibacterial agents and other secondary additives.
[0024]
The composition of the present invention can be formed into various fibers, yarns, ropes, knitted fabrics, woven fabrics, nonwoven fabrics, papers, films, sheets, tubes, plates, bars, containers, bags, parts and the like. It can also be processed into a biaxially stretched film. The molded product can be suitably used in agriculture, fishery, forestry, horticulture, medicine, hygiene, clothing, non-clothing, packaging, and other fields.
[0025]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
Poly (S) -lactic acid manufactured by Polyscience was used as polylactic acid as it was. Racemic β-butyrolactone is manufactured by Tokyo Chemical Industry Co., Ltd., a special grade product is dried with calcium hydride (Wako Pure Chemical Industries, Ltd., special grade product) for 1 day, and is distilled under reduced pressure in a nitrogen atmosphere (9 mmHg, 49- 50 ° C.). Diethyl zinc was manufactured by Tosoh Akzo Co., Ltd., diluted with 1,4-dioxane so that the amount of zinc was 1 mol. 1,2-Dichloroethane was used after being distilled in a nitrogen atmosphere after adding calcium hydride to a special grade product manufactured by Wako Pure Chemical Industries, Ltd. 1,4-Dioxane was manufactured by Wako Pure Chemical Industries, Ltd., and added to 14 liters of special grade product, 14 ml of concentrated nitric acid and 100 ml of distilled water, refluxed for 10 hours while flowing nitrogen, cooled, transferred to a separatory funnel, and slowly After adding potassium oxide and shaking until potassium hydroxide was not dissolved, the aqueous phase was separated, and then dioxane was taken out by decantation. Furthermore, after dehydrating by adding fresh potassium hydroxide, it was transferred to another flask and refluxed until it turned blue in the presence of metallic sodium and benzophenone, and then distilled and used.
[0026]
The atactic PHB synthesis catalyst was prepared by putting 50 ml of 1 mol of diethylzinc / 1,4-dioxane in a nitrogen-substituted 100 ml Schlenk flask under a nitrogen stream and cooling to 5 ° C. Next, 30 ml of 1,4-dioxane and 0.54 ml of degassed distilled water were placed in a dropping funnel with a pressure equalizing line purged with nitrogen, and added to a Schlenk flask over 1 hour at 5 ° C. with stirring. The reaction was completed by further stirring for 5 hours at room temperature. After completion of the reaction, the reaction solution was lyophilized and then dried under reduced pressure at room temperature for 10 hours to prepare a catalyst.
[0027]
Atactic PHB was prepared by adding the above catalyst and 1,2-dichloroethane to a 50 ml Schlenk flask purged with nitrogen under a nitrogen stream, cooling to 0 ° C., adding racemic β-butyrolactone under a nitrogen stream, and adding 5% at 60 ° C. Stirring was performed for days. After cooling, a small amount of methanol was added to stop the reaction, and chloroform was added to dissolve the product. After reprecipitation with about 10 times the amount of diethyl ether / distilled water (100/1, v / v), constant weight The solution was dried under reduced pressure at room temperature until a polymer was obtained. In addition, the polymer of various molecular weight was obtained by changing the preparation ratio of a monomer and a catalyst.
[0028]
A solvent cast film of polylactic acid / atactic PHB is prepared by dissolving a predetermined amount of polymer in chloroform to form a 2% (w / v) solution and using a glass petri dish by a solvent cast method at room temperature at normal pressure. did. The produced film was dried under reduced pressure until a constant weight was reached at room temperature. The obtained solvent cast film was used for measurement of thermal properties, spherulite growth rate, and preparation of a melt crystallized film.
[0029]
The melt crystallized film of polylactic acid / atactic PHB is set to 120 ° C in advance after the solvent cast film obtained by the above method is completely melted by heating in a hot press machine heated to 200 ° C for 1 minute. Immediately transferred to a constant temperature bath and left for 3 days. The obtained melt crystallized film was used for thermal properties and wide-angle X-ray diffraction measurement.
[0030]
The molecular weight of the polymer was measured using a Shimadzu 6A GPC system (manufactured by Shimadzu Corporation) equipped with a differential refractometer as a detector. The column was measured at a column temperature of 40 ° C. by connecting Shodex K-80M and K-802 (manufactured by Showa Denko) in series. Chloroform was used as the mobile phase, and analysis was performed at a flow rate of 0.8 ml / min. The molecular weight was calculated in terms of polystyrene. The thermal properties of the solvent cast film and the melt crystallized film were measured using a Shimadzu rapid cooling differential scanning calorimeter DSC-50Q (manufactured by Shimadzu Corporation) equipped with a cooling device. The melting point (Tm) and the heat of fusion (ΔHm) are measured by accurately measuring about 3 mg of a sample, putting it in an aluminum pan, and raising the temperature from room temperature to 200 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere. Went by. The glass transition point (Tg) is measured by raising the temperature up to 200 ° C. at 1 st run, melting it, quenching it quickly with liquid nitrogen, and raising the temperature from −100 ° C. to 200 ° C. at a rate of temperature rise of 20 ° C./min. Went by. The midpoint of the change in heat capacity was Tg. The spherulite growth rate was obtained by connecting a CCD camera (Ikegami IF-8500) to an optical microscope (Nikon OPTIPHOTO-2) equipped with a hot stage (Linkam TH-600PM) and a simple polarizing plate. The crystal image was processed by an image processing apparatus (OLYMPUS XL-10). First, about 2 mg of a solvent cast film was placed on a hot stage, and the temperature was raised from room temperature to 200 ° C. at a rate of temperature rise of 30 ° C./min in a nitrogen atmosphere. After the sample was completely melted at 200 ° C., it was rapidly cooled to 120 ° C. for isothermal crystallization, and spherulites were observed.
The spherulite growth rate was calculated from the slope of the spherulite radius plotted against time. The wide-angle X-ray diffraction pattern of the isothermal crystallized film was obtained by measuring at room temperature using a small-angle wide-angle measurement X-ray diffractometer (Rigaku ultraX18, RINT2500). CuKα rays (λ = 0.154 nm) were used as the X-ray source. The X-ray generation conditions were a fed voltage of 40 KV and a current of 200 mA. The scan range was 2θ = 6 ° to 40 ° width, and the scan speed was measured at 2 ° / min. The degree of crystallinity of the film was determined by using the method of Vonk calculated from the area ratio between the amorphous halo region and the crystal peak diffraction peak region in the X-ray diffraction diagram.
[0031]
The molecular weights of the polylactic acid used and the synthesized atactic PHB are shown in Table 1, and the glass transition temperature (Tg) of the solvent cast film is shown in Table 2.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
As can be seen from Table 1, three types of atactic PHBs with different molecular weights were synthesized. Further, when the compatibility when melted at 200 ° C. was determined from the Tg values shown in Table 2, the blend of polylactic acid and atactic PHB having a low molecular weight is a compatible system that is mixed at the molecular level. However, a blend with atactic PHB having a weight average molecular weight of 21,000 is a semi-compatible system in which 1 part of atactic PHB does not mix with polylactic acid, and a blend with atactic PHB having a weight average molecular weight of 140,000 is almost Was found to be incompatible with each other.
[0035]
The results of examining the polylactic acid spherulite growth rate using a polylactic acid / atactic PHB solvent cast film are shown in FIG. The spherulite growth rate of the blend (polylactic acid and weight average molecular weight 140,000) in the incompatible system was equivalent to the spherulite growth rate of the polylactic acid alone, but the semi-compatible and compatible blends. In spherulite growth rate increased. In particular, a large increase was observed in the compatible blend.
[0036]
The crystallinity obtained from the wide angle X diffraction measurement (WAXD) of the polylactic acid / atactic PHB melt crystallized film is shown in FIG. 2, and the heat of fusion (ΔHm) obtained from the DSC measurement is shown in Table 3. From FIG. 2, it was observed that the addition of atactic PHB did not decrease the crystallinity of polylactic acid, and in particular, in the case of a compatible blend, a phenomenon that the crystallinity increased. Further, ΔHm and the degree of crystallinity are in a proportional relationship, and the degree of crystallinity obtained from ΔHm was in good agreement with the value of the degree of crystallinity obtained from WAXD.
[0037]
[Table 3]

[0038]
【The invention's effect】
According to the present invention, there is provided a biodegradable polylactic acid-based composition that has an improved spherulite growth rate to improve molding processability, can control the degree of crystallinity, and can control the biodegradation rate of the composition. Is done.
[0039]
Moreover, at the present time when the pollution of plastics has become serious, it is highly useful to improve the molding processability of polylactic acid and control the degradation rate of biodegradable bioplastics, which are attracting particular attention.
[Brief description of the drawings]
FIG. 1 is a graph showing the results of examining the growth rate of polylactic acid spherulites using a polylactic acid / atactic PHB solvent cast film.
FIG. 2 is a graph showing the degree of crystallinity obtained from wide angle X diffraction measurement (WAXD) of a melt crystallized film of polylactic acid / atactic PHB.

Claims (1)

40% to 97% by weight of an aliphatic polyester (A) based on polylactic acid and 70% by weight of poly [(R, S) -3-hydroxybutanoic acid] having an atactic structure having a weight average molecular weight of 100,000 or less A biodegradable polylactic acid composition comprising 3 to 60% by weight of the aliphatic polyester (B) contained above .

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