JP2002256142A - Polylactate resin composition with controlled degradability and method for degradation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biodegradable resin composition which can be degraded more rapidly in the natural environment or in an accelerated degradation apparatus and to provide a method for degrading the resin composition. SOLUTION: The polylactate resin composition contains 99.99-95 pts.mass polylactate polymer and 0.01-5 pts.mass organic carboxylic acid compound and/or organic carboxylate compound. The method comprises allowing an organic carboxylic acid compound and/or an organic carboxylate compound to act on a polylactate polymer as a biodegradable resin composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a biodegradable resin composition which decomposes faster in a natural environment or in a decomposition promoting device. The present invention also relates to a method for decomposing a biodegradable resin by reacting an organic carboxylic acid compound and / or an organic carboxylate compound.

[0002]

2. Description of the Related Art Conventionally, paper, plastics, etc. have been used in a wide range of fields, such as packaging materials for liquids, powders and granules, solids such as various foods, beverages, medicines, miscellaneous goods, agricultural materials, and building materials. Films, aluminum foils and the like are used. In particular, plastic films have strength, water resistance, moldability,
It has excellent properties such as transparency and cost, and is used in many applications as bags and thermoformed containers. Current,
Plastics used in these applications include:
Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. However, films made of plastic as described above
It does not biodegrade or hydrolyze in the natural environment, or its decomposition rate is extremely slow.If it is buried after use, it will remain in the soil. May destroy the environment. In addition, even when incinerated, there is a problem in that harmful gases such as dioxin are generated, and the incinerator is deteriorated due to high calorie incineration.

[0003] With the increasing social demands for environmental preservation, biodegradable resins that are enzymatically decomposed by microorganisms or hydrolyzed by the action of water have attracted attention. Specific examples of the biodegradable resin, polybutylene succinate, polybutylene succinate adipate, polycaprolactone, aliphatic polyesters such as polylactic acid,
Or an aliphatic / aromatic copolymerized polyester such as a butanediol / adipic / terephthalic acid copolymer.

Among the above biodegradable resins, polylactic acid in which monomers are widely distributed in nature and which is harmless to animals, plants and humans has a melting point of around 170 ° C. and a glass transition point of 60 ° C.
Since it is near, has sufficient heat resistance, and is relatively inexpensive, it is expected as a biodegradable resin excellent in practicality.

[0005] Under such circumstances, various polylactic acid resin compositions have been developed for use in the above applications. In particular, when used for packaging materials and agricultural materials, various end-users handle the materials, so it is expected that they will be rapidly decomposed when disposed after use. But,
In fact, polylactic acid did not always decompose at a satisfactory rate when it was treated with a decomposition accelerating device such as a commercially available composting device or a drying treatment device, or when plowed into soil.

[0006] Since high molecular weight polylactic acid did not originally exist in nature, bacteria that enzymatically decompose high molecular weight compounds do not generally exist in nature. The decomposition mechanism of polylactic acid is divided into two stages, the first stage is hydrolysis,
Only when the weight-average molecular weight is degraded to about 60,000 or about 20,000, the second-stage microbial enzymatic degradation starts. Therefore, how to increase the hydrolysis rate affects the overall biodegradation rate.

As a method for increasing the biodegradation rate of polylactic acid, for example, Japanese Patent Application Laid-Open No. 4-168149 proposes a method of blending a hydrolase such as lipase, but the enzyme is a relatively large molecule. Therefore, only the contact part can work, and the cost of the film is high because the enzyme is expensive, and the thermostability of the enzyme is low, so that general thermoforming methods cannot be used when packaging films and other agricultural materials. There was a problem.

Japanese Patent Application Laid-Open No. 10-219088 proposes a method of accelerating the biodegradation rate by mixing inorganic particles. However, the effect is low unless a large amount of inorganic particles is added. In such a case, there is a problem that the practicability is lowered, for example, mechanical properties such as tensile strength and impact resistance are lowered, and thermal stability during molding is lowered.

Further, Japanese Patent Application Laid-Open Nos. 10-323810, 11-241008 and 241009 propose a method of controlling the rate of biodegradation by blending with a component based on natural resources. Practical use, such as deterioration of the appearance of the product surface, and in particular, when molded into fibers, films, sheets, etc., the mechanical properties such as tensile strength and impact strength are reduced, and the thermal stability during molding is reduced. There is a problem that the property is reduced.

On the other hand, polyethylene terephthalate (PE)
Carboxylic acid (CO) in polyester polymers such as T)
It has been reported that when the concentration of (OH group) is increased, the decomposition rate of the polymer is increased by the catalytic action of the COOH group.
However, in the prior art, only the results of long-term model tests under very severe conditions have been reported for non-biodegradable resins. In resin, the extent to which the COOH group concentration quantitatively affects biodegradability has hardly been investigated, and what kind of adverse effects are practically unknown.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and does not impair the excellent properties of polylactic acid and increases the biodegradability at the time of disposal. It is intended to provide a resin composition and a method for decomposing a biodegradable resin.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a polylactic acid-based polymer containing a specific amount of an organic carboxylic acid and / or an organic carboxylate compound. The present inventors have found that the coalesced composition does not decrease the mechanical properties and the thermal stability at the time of melting, and that it is easy to control the decomposition rate at the time of disposal, and have reached the present invention.

That is, the gist of the present invention is as follows. (1) A polylactic acid resin composition containing 0.01 to 5 parts by mass of an organic carboxylic acid compound and / or an organic carboxylate compound per 99.99 to 95 parts by mass of a polylactic acid-based polymer. (2) The polylactic acid resin composition according to (1), wherein the molecular weight retention A in the treatment at 200 ° C. for 5 minutes satisfies the following formula: (Molecular weight retention A): Mn (A, t) / Mn (A, 0) ≧ 0.90 where Mn (A, t) represents a number average molecular weight after treatment at 200 ° C. × 5 minutes, and Mn (A , 0) represents the number average molecular weight before treatment. (3) The polylactic acid resin composition according to the above (1) or (2), wherein the molecular weight retention B after treatment in an environment of 80 ° C. × 90% RH for 8 hours satisfies the following formula: (Molecular Weight Retention B): Mn (B, t) / Mn (B, 0) ≦ 0.85 where Mn (B, t) is the number average molecular weight after treatment at 80 ° C. × 90% RH for 8 hours. And Mn (B, 0) represents the number average molecular weight before the treatment. (4) A packaging material using the polylactic acid resin composition according to any one of (1) to (3). (5) An agricultural material using the polylactic acid resin composition according to any one of (1) to (3). (6) A method for decomposing a biodegradable resin, in which an organic carboxylic acid compound and / or an organic carboxylate compound is allowed to act on a polylactic acid-based polymer.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polylactic acid resin composition of the present invention contains an organic carboxylic acid compound and / or an organic carboxylate compound in an amount of 0.01 to 95 parts by mass based on the polylactic acid-based polymer in order to enhance biodegradability. It is necessary to include 5 parts by mass.
Further, 0.5 to 1 part by mass is particularly preferred. If these compounds are less than 0.01 part by mass, the effect of increasing the decomposition rate is low, and if they are added in excess of 5 parts by mass, thermal stability and mechanical properties are undesirably deteriorated.

In particular, when an organic carboxylic acid compound is added, the preferred range of the addition amount is determined by the COOH group concentration (COOH group concentration of the polylactic acid polymer and COOH group concentration of the organic carboxylic acid compound) in the resin composition. And the number average molecular weight of the polylactic acid polymer. That is, the number average molecular weight Mn of the polylactic acid-based polymer
And the COOH group concentration C contained in the polylactic acid resin composition
When the following formula is satisfied between (mol / ton), the effect of accelerating the decomposition rate is particularly high, which is preferable. Therefore, it is preferable to add an organic carboxylic acid compound so as to satisfy the formula. (Decomposition acceleration index D): {C} (2 × 10 ⁶ g / Mn) ≧≧ 3

Further, as for the properties of the biodegradable resin composition, it is desirable that the properties change little during molding and decompose as quickly as possible during disposal. Thermal stability during molding and biodegradability during disposal can be confirmed by changes in molecular weight before and after each treatment. Examples of the method for measuring the molecular weight include GPC, NMR, osmotic pressure method, viscosity method, light scattering method and the like. The polylactic acid resin composition of the present invention contains 20
The ratio of the molecular weight before and after the treatment when the treatment was performed at 0 ° C. × 5 minutes,
That is, the molecular weight retention A is desirably 0.90 or more, and particularly desirably 0.95 or more. When it is less than 0.90, it means that the molecular weight is reduced when the biodegradable resin composition is melted and molded into various forms such as films, sheets, fibers, and non-woven fabrics. Storage stability and mechanical properties are undesirable. Furthermore, the polylactic acid resin composition of the present invention has a temperature of 80 ° C. × 9.
The ratio of the molecular weight before and after the treatment for 8 hours in a 0% RH environment and the molecular weight retention B are desirably 0.85 or less, and particularly desirably 0.8 or less. If it exceeds 0.85, the decomposition cannot be performed within an assumed processing time at the time of disposal treatment by the decomposition accelerating device or the like, and undecomposed molded products are accumulated in the decomposition accelerating device, which is not desirable.

When the storage stability of the polylactic acid resin is particularly emphasized, the polylactic acid resin composition itself does not contain an organic carboxylic acid compound and / or an organic carboxylic acid salt compound, and the polylactic acid-based polymer is When it is desired to carry out the waste treatment, the decomposition rate can be increased by allowing these organic carboxylic acid compounds and / or organic carboxylate compounds to act.

As a method of allowing an organic carboxylic acid compound and / or an organic carboxylic acid salt compound to act on a polylactic acid-based polymer, these compounds are brought into direct contact with a molded article of a polylactic acid-based polymer, and then a solution is prepared. A method of adhering, dipping into a solution, soaking the solution in sawdust, starch, or the like, and bringing the solution into contact with a molded body can be used. The amount to act is preferably at least 5 parts by mass, more preferably at least 10 parts by mass, particularly preferably at least 50 parts by mass, based on 100 parts by mass of the polylactic acid-based polymer. . Although depending on the method of acting, if the amount of these compounds acting is less than 5 parts by mass, the effect of increasing the decomposition rate is low, which is not desirable.

In the present invention, the organic carboxylic acid compound is an organic compound whose terminal group is a carboxylic acid, such as adipic acid, succinic acid, stearic acid, tricarballylic acid,
Examples include aliphatic carboxylic acids such as sebacic acid and aromatic carboxylic acids such as terephthalic acid and isophthalic acid. Further, a biodegradable oligomer obtained by condensing an aliphatic / aromatic dicarboxylic acid such as adipic acid or terephthalic acid with an aliphatic diol such as ethylene glycol or butanediol may be used. The organic carboxylate compound is a metal salt of these organic carboxylic acid compounds, and among them, a sodium salt is particularly desirable in view of the balance between the effect and the thermal stability.

In the present invention, the polylactic acid-based polymer may be any one having polylactic acid or a lactic acid component as a main component, such as polylactic acid, lactic acid or lactide and other hydroxycarboxylic acids, dicarboxylic acids, diols, and the like. Copolymers and blends with cyclic lactones are mentioned. In these, a urethane bond, an amide bond, an ether bond, or the like may be introduced as long as the biodegradability is not affected. The D / L ratio of the polylactic acid is not particularly limited.
Any of L-form, DL-form and a mixture thereof may be used. The number average molecular weight of polylactic acid is desirably from 20,000 to 300,000. If it is less than 20,000, mechanical properties are inferior, and if it is more than 300,000, molding becomes difficult.

In order to increase the molecular weight of polylactic acid, a small amount of a chain extender such as a bisoxazoline compound, a diisocyanate compound, a carbodiimide compound,
Epoxy compounds, acid anhydrides and the like may be used. These additives may be added at any stage during the polymerization, or may be added during melt-kneading for the purpose of molding after the polymerization.

If necessary, the polylactic acid-based polymer may contain other biodegradable resins, such as aliphatic polyester-based resins, aliphatic / aromatic polyester-based resins, and biodegradable compounds based on natural resources. It may be added / copolymerized. Specifically, lactic acid, glycolic acid, hydroxybutyric acid, hydroxycarboxylic acids such as hydroxycaproic acid, caprolactone, butyrolactone, lactide, cyclic lactones such as glycolide, ethylene glycol, butanediol,
Diols such as cyclohexanedimethanol, bis-hydroxymethylbenzene, and toluenediol; dicarboxylic acids such as succinic acid, adipic acid, suberic acid, sebacic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid; cyclic acid anhydrides; oxirane And their polymers, blends and copolymers. In addition, a urethane bond, an amide bond, an ether bond, or the like can be introduced into these as long as the biodegradability is not affected.

The method of polymerizing the polylactic acid-based polymer and other biodegradable resin is not particularly limited, and examples thereof include a condensation polymerization method and a ring-opening polymerization method. It is also possible to add one or more subcomponents such as another polymer, monomer, or oligomer component during or immediately after the polymerization to further increase the degree of polymerization.

In order to control the flexibility of the polylactic acid resin composition of the present invention, a plasticizer may be used. The plasticizer is not particularly limited, but preferably has excellent compatibility with the polylactic acid resin composition of the present invention, and specifically, an aliphatic polycarboxylic acid ester derivative, an aliphatic polyhydric alcohol ester derivative, Single or multiple mixtures selected from aliphatic oxyacid ester derivatives, aliphatic polyether derivatives, aliphatic polyether polycarboxylic acid ester derivatives, and the like. As aliphatic polycarboxylic acid ester derivatives, dimethyl adipate, dibutyl adipate, diisobutyl adipate, etc., as aliphatic polyhydric alcohol ester derivatives, triethylene glycol diacetate, polypropylene glycol dibutyrate, etc., as aliphatic oxyacid ester derivatives Are aliphatic polyether derivatives such as methyl acetyl ricinoleate and acetyl tributyl citric acid; and aliphatic polyether derivatives such as polyethylene glycol, polypropylene glycol, and copolymerized polyalkylene glycol such as ethylene glycol and propylene glycol or butylene glycol. Acid ester derivatives include dibutyl diglycol succinate, dimethyl diglycol succinate, dibutyl diglycol succinate. Pies, dimethyl diglycol adipate.

The polylactic acid resin composition of the present invention contains a lubricant, an anti-blocking agent, an ultraviolet ray inhibitor, a light stabilizer, an anti-fogging agent, an anti-fog agent, an antistatic agent, as long as the effects of the present invention are not impaired. Additives such as a flame retardant, a coloring inhibitor, an antioxidant, a hydrolysis inhibitor, a filler and a pigment can be used alone or in combination. The lubricant is not particularly limited, but is preferably an aliphatic carboxylic acid amide. Examples of such an aliphatic carboxylic acid amide include stearic acid amide, oleic acid amide, erucic acid amide, and behenic acid amide. The inorganic filler is not particularly limited, but is preferably a natural or synthetic silicate compound, titanium oxide, barium sulfate, calcium phosphate, calcium carbonate, sodium phosphate and the like. Examples of the silicate compound include layered silicates such as kaolinite, halloysite, talc, smectite, vermiculite, and mica. These layered silicates may be swellable or non-swellable, and may be surface-treated.

[0026]

In the present invention, the polylactic acid-based polymer 99.9
By adding 0.01 to 5 parts by mass of an organic carboxylic acid compound and / or an organic carboxylate compound to 9 to 95 parts by mass, biodegradability whose degradability is controlled so as to decompose more rapidly. A resin composition is obtained. By adding a specific amount of these organic carboxylate and / or organic carboxylate compound, it is possible to achieve both the effect of accelerating the decomposition and the thermal stability at the time of molding. Also, it does not lower the mechanical properties or deteriorate the appearance of the molded product. When the storage stability is particularly important, the organic carboxylic acid compound and / or the organic carboxylate compound are not directly added to the polylactic acid resin composition itself, and these compounds act when it is desired to perform a disposal treatment. By doing so, the decomposition rate can be increased.

[0027]

Next, the present invention will be described more specifically with reference to examples. The raw materials used in the examples and comparative examples and methods for measuring respective physical property values are as follows.

(1) Raw material (a) Polylactic acid: D, manufactured by Cargill Dow Polymers
(B) Plasticizer: acetyl tributyl citric acid (ATB)
C, manufactured by Kyowa Hakko) (c) Lubricant: silica (manufactured by Fuji Devison, Cyria),
Particle size: 1.6 μm (d) Organic carboxylic acid: adipic acid (manufactured by Nacalai Tesque), tricarballylic acid (1,2,3-propanetricarboxylic acid, manufactured by Tokyo Kasei Kogyo), stearic acid (manufactured by Nacalai Tesque) , L─lactide (Nacalai Tesque) (e) Organic carboxylate: sodium stearate (Nacalai Tesque)

(2) Measuring method (a) Molecular weight Mn The number average molecular weight was measured in terms of styrene using LC-VP type GPC manufactured by Shimadzu Corporation using THF as a mobile phase. (B) COOH group concentration About 0.1 g of a sample is precisely weighed, the sample is dissolved at room temperature using 20 ml of methylene chloride, and phenolphthalein is used as an indicator, and titration is performed with a 0.1 N KOH solution. went. (C) Molecular weight retention A kneader (Labo Plastmill R-60 manufactured by Toyo Seiki Seisaku-sho, Ltd.)
Using (10-150)), the polylactic acid resin composition was
After melt-kneading at 00 ° C. for 5 minutes, the molecular weight Mn was measured to determine Mn (A, t). Molecular weight Mn before melt kneading
The ratio of Mn (A, t) to (A, 0) (Mn (A,
t) / Mn (A, 0)) was taken as the molecular weight retention A. (D) Molecular Weight Retention B Using a constant temperature and humidity chamber SH-220 manufactured by Tabai Espec Co., a film-shaped sample piece was treated for 8 hours in an environment of 80 ° C. × 90% RH, and the molecular weight Mn was measured. (B,
t) was determined. Molecular weight Mn (B, 0) before constant temperature and humidity treatment
(Mn (B, t) / Mn)
(B, 0)) was taken as the molecular weight retention B. (E) Tensile strength Measured according to ASTM D882. (F) Compost treatment test Using a compost treatment tester, 1
The state of the sample piece after a week was visually observed. ：: The sample was fragmented. X: No change in appearance of the sample was observed.

Example 1 85 parts by mass of polylactic acid having a number average molecular weight of 110,000, 15 parts by mass of ATBC as a plasticizer, 0.2 parts by mass of silica as a lubricant, and 1 part by mass of adipic acid as an organic carboxylic acid compound were prepared by using a cylinder having an inner diameter of 30 mm. Screw extruder (Ikegai Iron Works,
Using PCM # 45), the mixture was melt-kneaded at a temperature of 220 ° C. Subsequently, after being extruded into a strand shape, it was cut to obtain a pellet. Next, the pellets are melt-extruded at a temperature of 200 ° C. from a round die (200 mmφ, lip interval 1 mm) using an extruder (L / D = 28, single screw extruder) having a cylinder inner diameter of 50 mm, and then blow-up inflation. By the method, an inflation film having a film thickness of 50 μm and a weave width of 450 mm was obtained. These films were treated with a thermo-hygrostat, and their hydrolytic properties were examined assuming disposal. Table 1 shows the physical property values of the obtained film.

Examples 2-4, Comparative Examples 1-3 Organic carboxylic acid compounds / organic carboxylate compounds are shown in Table 1.
Except that the resin, plasticizer and lubricant were changed as in Example 1.
A blown film was obtained in the same manner as described above. These films were treated with a thermo-hygrostat, and their hydrolytic properties were examined assuming disposal. Table 1 shows the physical property values of the obtained film.

In Examples 1 to 4, the resin composition has a high value of the molecular weight retention A of 0.95 or more, so that it has excellent thermal stability and is decomposed by heat during molding. No adverse effects were observed. Furthermore, the film obtained from this resin also showed excellent mechanical properties in terms of tensile strength. On the other hand, it is preferable that hydrolysis progresses quickly at the time of disposal treatment, so that the molecular weight retention B is desirably a low value. In Examples 1 to 4, the molecular weight retention B was 0.85 or less, indicating high degradability in the compost treatment. In Comparative Example 1, the organic carboxylic acid and / or the organic carboxylate compound was not added, the molecular weight retention B was a high value near 1, and the decomposition rate was low in the compost treatment. In Comparative Example 2, as a result of adding an excessive amount of the organic carboxylic acid, the thermal stability of the resin composition was lowered, and the mechanical properties (tensile strength) of the obtained film were low. In Comparative Example 3, the thermal stability of the resin composition was not good, and
The degree of improvement in the hydrolyzability at the time of disposal treatment is smaller than that of Comparative Example 1.

Example 5 Sample of Comparative Example 1 (molecular weight retention B is 1.05) 0.1
g was immersed in 1 ml of a 5% aqueous solution of tricarballylic acid (corresponding to 50 parts by mass of organic carboxylic acid with respect to 100 parts by mass of the resin), left at room temperature for 3 minutes, pulled up, and then treated with a thermo-hygrostat. Was. As a result, the molecular weight retention B of the sample dropped from 1.05 to 0.44, and improvement in the decomposability in the compost treatment was observed.

[0034]

[Table 1]

[0035]

According to the present invention, at the time of disposal, an improved decomposability can be obtained as compared with the conventional polylactic acid resin composition, and the heat stability, appearance, and cost during molding can be maintained. It is a resin composition excellent in practicality.
In addition, since this resin composition is biodegradable, it can be used in packaging fields such as vegetable packaging, food packaging, newspaper / magazine packaging, garbage bags, compost bags, fertilizer bags, rice bags and other bags, and lining for greenhouses. For lining, for tunnel house,
It can be applied to agricultural films such as multi-cultivation films, hanging strings for fruits and vegetables, bundling strings, packing bands, and other industrial uses. It is extremely useful as a simple resin composition.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Nishimura 31-3 Uji Hinojiri, Uji City, Kyoto Prefecture Unitika Uji Plastic Factory F-term (reference) 4F301 AA25 CA09 CA23 4J002 CF181 EF056 EF066 EF116 EG017 EG027 EG057 EG107 FD010 FD020 FD170 GA01 GG02

Claims (6)

[Claims] 1. A polylactic acid resin composition comprising 0.01 to 5 parts by mass of an organic carboxylic acid compound and / or an organic carboxylate compound per 99.99 to 95 parts by mass of a polylactic acid-based polymer. 2. The polylactic acid resin composition according to claim 1, wherein the molecular weight retention A in the treatment at 200 ° C. for 5 minutes satisfies the following formula. (Molecular weight retention A): Mn (A, t) / Mn (A, 0) ≧ 0.90 where Mn (A, t) represents a number average molecular weight after treatment at 200 ° C. × 5 minutes, and Mn (A , 0) represents the number average molecular weight before treatment. 3. The molecular weight retention ratio B after treatment for 8 hours in an environment of 80 ° C. × 90% RH satisfies the following expression.
The polylactic acid resin composition according to the above. (Molecular weight retention B): Mn (B, t) / Mn (B, 0) ≦ 0.85 where Mn (B, t) is the number average molecular weight after 8 hours of treatment at 80 ° C. × 90% RH. And Mn (B, 0) represents the number average molecular weight before the treatment. 4. A packaging material using the polylactic acid resin composition according to claim 1. An agricultural material using the polylactic acid resin composition according to any one of claims 1 to 3. 6. A method for decomposing a biodegradable resin, wherein an organic carboxylic acid compound and / or an organic carboxylate compound is allowed to act on a polylactic acid-based polymer.