JP3367577B2 - Acid-blocked polylactic acid - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polylactic acid which is substantially capped with an acid terminal and is excellent in hydrolysis resistance. Further, the present invention relates to polylactic acid, which has both acid and hydroxyl terminal groups blocked and is excellent in stability at high temperatures.

[0002]

2. Description of the Related Art In recent years, due to the problem of environmental destruction caused by plastic waste, research and development of biodegradable plastics that are decomposed by enzymes and microorganisms have been actively conducted, and among them, aliphatic polyesters have attracted attention. ing. As the biodegradable polyester, poly [(R) -3
-Hydroxybutyrate], polycaprolactone, or a polyester comprising a glycol such as ethylene glycol or 1,4-butanediol and a carboxylic acid such as succinic acid or adipic acid is known. Poly [(R) -3-hydroxybutyrate] -based polyester is expensive because it is mainly produced by microbial synthesis. In addition, other polyesters have a low melting point, which makes it difficult to expand their applications.

Polylactic acid resins have good biodegradability and are used as bioabsorbable materials such as surgical sutures and microcapsules for injections. In recent years, various problems caused by plastic waste have become a social concern, and as one of the solutions, attention has been paid to biodegradable plastics that are expected to be decomposed by enzymes and microorganisms, and R & D It is being advanced. Polylactic acid resin is excellent in various properties such as thermal properties, mechanical properties, and biodegradability,
Furthermore, it has a number of remarkable features such as complete degradability such that there is almost no residue after decomposition, and the safety of the decomposed product has been established, and its use is highly expected.

However, the stability in water or in humidity is not sufficient, which is a big problem. Such low hydrolysis resistance is extremely disadvantageous in using the polylactic acid resin as a biodegradable plastic, and the development of general-purpose applications is currently hindered. In addition, polylactic acid has low stability when melted and causes a decrease in molecular weight during melt molding. This not only causes deterioration of the physical properties of the molded product, but also causes deterioration of molding stability.

[0005]

Although polylactic acid having excellent hydrolysis resistance and stability upon melting as described above has been earnestly desired, such polylactic acid has not been obtained yet. Has not been done. For this reason, the present invention provides a polylactic acid resin having good hydrolysis resistance that can stably exist in water or in a humidity atmosphere, and further provides polylactic acid that also has stability when melted. The purpose is to

[0006]

[Means for Solving the Problems] Therefore, as a result of intensive studies to obtain a polylactic acid-based resin having good hydrolysis resistance, the present inventors have found that there is a correlation between the acid terminal and the hydrolyzability. After finding out, the present invention was finally completed. That is, the present invention provides a polylactic acid (provided that the acid terminal represented by the following general formula (I) is substantially blocked (however,
By permeation chromatography (GPC)
Polylactic acid having a weight average molecular weight of 50,000 or less measured by
2% based on the total weight of compounds with a number average molecular weight of 1000 or less
The following is excluded) . (Up
Compounds having a number average molecular weight of 1,000 or less in polylactic acid
The ratio of the product is 2.0 g (W ₁ ) of the sample and 10 parts of chloroform.
After dissolving in 100 ml, pour into 100 ml of methanol,
After separating the precipitated polymer precipitate by filtration, reduce the pressure at 50 ° C for 24 hours.
Dried and the amount obtained polymer (W ₂₎ than Wlow value (here
Calculate Wlow = {(W ₁ −W ₂ ) / W ₁ } × 100)
It is something that is requested. )

[0007]

[Chemical 2] (In the formula, X represents a hydrogen atom or a hydrocarbon group, Y represents a monovalent or more polyvalent aliphatic hydrocarbon group having 1 to 50 carbon atoms, and n represents a positive integer of 10 or more and 1 or more. .)

The hydrolysis resistance of polylactic acid has a correlation with the number of acid terminal groups, and as the number of acid terminal groups increases, the hydrolysis resistance tends to decrease. Therefore, low-molecular-weight polylactic acid has significantly lower hydrolysis resistance than high-molecular-weight polylactic acid. In order to improve the hydrolysis resistance of the polymer regardless of its molecular weight, it is important to block the acid end group. If the acid terminal group is not sufficiently blocked, the desired good hydrolysis resistance will not be exhibited. It is necessary to block at least 50% of the total number of acid terminal groups. Furthermore,
It is preferable to block by 80% or more.

The polylactic acid referred to in the present invention means a condensate of lactic acid units such as L-lactic acid and D-lactic acid, or a mixed condensate thereof. When it is produced by the lactide method, any of L-lactide, D-lactide, DL-lactide and meso-lactide may be used.

In order to block the acid terminal as described above, a lactide or lactic acid is polymerized in the presence of a saturated and / or unsaturated monohydric or higher polyhydric aliphatic alcohol having 1 to 50 carbon atoms to produce it. Should be done. Specific examples of the aliphatic alcohol used include methanol, ethanol, propanol, isopropanol, butanol, pentanol, nonanol, decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, methyl lactate, ethyl lactate, and butyl lactate. Dialcohols such as alcohol, ethylene glycol, propanediol, butanediol, hexamethylene glycol, nonanediol, tetramethylene glycol, glycerol, sorbitol, xylitol, ribitol,
Examples thereof include polyhydric alcohols such as erythritol, but are not limited thereto.

These alcohols can be used alone or in combination of two or more. In particular, long-chain alcohols such as decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, and stearyl alcohol are suitable. When the boiling point of the alcohol used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure. The amount of alcohol used varies depending on the purpose, but if it is too large, the molecular weight is difficult to increase, and the amount of low molecular weight compounds increases, which is not preferable. It is used in a proportion of 0.001 to 1 mol% based on all monomers.

Further, in order to further improve the melt stability,
The end of the hydroxyl group may be blocked with a hydrocarbon group, preferably 70% or more, more preferably 80% or more, of X in the formula (I) should be blocked with an acyl group having 2 to 50 carbon atoms. When producing such a polylactic acid having a hydroxyl group end blocked, a saturated and / or unsaturated aliphatic acid having 2 to 50 carbon atoms is used. In the case of production by the lactide method, the ring-opening polymerization reaction may be carried out in the presence of these aliphatic acids, or the polymer may be polymerized and then treated with an aliphatic acid anhydride to block the ends.

Specific examples of the aliphatic acid used include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, capric acid,
Pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, aragic acid, behenic acid, linoleic acid, oleic acid, succinic acid, adipic acid, suberic acid,
Examples thereof include azelaic acid, sebacic acid, undecanedioic acid, dimer acid, fumaric acid, etc., but are not limited thereto. Further, it is possible to add these acid anhydrides.

These aliphatic acids can be used alone or in combination of two or more. In particular, stearic acid, palmitic acid, myristic acid, linoleic acid, oleic acid are flavoring agents,
Emulsifier, vitamin enhancer, fumaric acid, succinic acid,
Adipic acid is also mentioned as a seasoning, an acidulant, or a food additive as a raw material thereof, and is preferable because safety is established. More preferably, stearic acid, which is a raw material of calcium stearate used as an auxiliary agent for bread making, can be mentioned. When the boiling point of the aliphatic acid used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure. The amount of the aliphatic acid used varies depending on the purpose, but if it is too large, the molecular weight is difficult to increase and the amount of the low molecular weight compound increases, which is not preferable. 0.001 to all monomers
It is used in a proportion of 1 mol%.

The polylactic acid of the present invention may be copolymerized with a second component and the like, and a component having biodegradability is preferable.
Specifically, it is an oxyacid component composed of an alkylene group having 1 to 20 carbon atoms, and when a polymer is produced by the lactide method, a corresponding lactone may be allowed to coexist. Examples of the copolymerization component include β-butyrolactone, γ-butyrolactone, ε-caprolactone, propiolactone and δ.
-Valerolactone, 4-valerolactone, glycolide, etc. can be mentioned, but not limited thereto.

A catalyst is generally used when producing the polylactic acid resin of the present invention, and a known catalyst is used for these. When it is produced by the lactide method, specific examples thereof include tin, antimony, zinc, titanium, iron and aluminum compounds, but the invention is not limited thereto. Among these, tin-based catalysts and aluminum-based catalysts are particularly preferable, and tin octylate and aluminum acetylacetonate are particularly preferable.

The polylactic acid resin of the present invention may be added with additives such as pigments, antioxidants, deterioration inhibitors, plasticizers, matting agents, antistatic agents, and ultraviolet absorbers, if necessary. Absent. When it is added, it is preferable to reduce the amount of the low molecular weight compound and then add the low molecular weight compound from the viewpoint of the amount remaining in the polymer.

The polylactic acid-based resin of the present invention can be molded into fibers, films, sheets and various molded products from a molten / solution state, and has better hydrolysis resistance than conventional products. Therefore, it can be used over a wide range. Specifically, for fibers and non-woven fabrics, fishing lines, fishing nets, non-woven fabrics for plant roots, non-woven fabrics for nursery beds, mulching materials, agricultural and horticultural non-woven fabrics for weed-proof sheets, etc. , Shopping bags, garbage bags, tapes, fertilizer bags, separation membranes, etc., for molded products such as beverages and cosmetics bottles, disposable cups, trays, knives, forks, spoons and other tableware, agricultural and garden garden pots, nursery beds Building materials such as pipes that are not dug up and temporary fixing materials.

[0019]

EXAMPLES Examples will be described below to more specifically describe the present invention, but the present invention is not limited thereto. The characteristic values in the examples were measured by the following methods. Reduced specific viscosity (η _SP / C) Dissolve 0.5 g of polymer in 100 ml of chloroform,
It was measured at 25 ° C. Hydrolysis resistance test A 3.50 cm x 1.75 cm x 500 µm sheet-shaped test piece was immersed in a phosphate buffer solution at 90 ° C and pH 7.0 for 12 hours, and the weight and reduced specific viscosity before and after immersion were measured. From the obtained results, the weight retention rate (WR) and the viscosity retention rate (VR) were calculated by the following formulas.

[0020]

[Equation 1]

[0021]

[Equation 2] Melt Stability Test After the polymer was completely dried, it was stirred at 200 ° C. for 1 hour in a nitrogen atmosphere, and the reduction specific viscosity change was measured. From the obtained results, the viscosity retention during melting (VMR) was calculated by the following formula.

[0022]

[Equation 3]

Example 1 A toluene solution of 20.0 g of L-lactide, 32 mg of 1-decanol and 6 mg of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen inlet tube, dried under reduced pressure for 2 hours, and then a nitrogen stream was passed. It was heated to 200 ° C. below and ring-opening polymerization was performed. After the reaction was completed in 1 hour, the polymer was taken out. The reduced specific viscosity of the obtained polymer was 1.67 dL / g. The hydrolysis resistance was good as shown in Table 1. Also, V
The MR was 75%.

Example 2 A toluene solution of 20.0 g of L-lactide, 58 mg of stearic acid, 32 mg of 1-decanol and 6 mg of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen introducing tube,
After drying under reduced pressure for 2 hours, it was heated to 200 ° C. under a nitrogen stream to carry out ring-opening polymerization. After the reaction was completed in 1 hour, the polymer was taken out. The reduced specific viscosity of the obtained polymer was 1.
It was 26 dl / g. The hydrolysis resistance was good as shown in Table 1. The VMR was 91%, and the melt stability was good.

Example 3 17.0 g of L-lactide, 114 mg of stearic acid, ε-
A toluene solution of 3.0 g of caprolactone, 32 mg of 1-decanol and 6 mg of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen introducing tube, dried under reduced pressure for 2 hours, and then heated to 200 ° C. under a nitrogen stream, Ring-opening polymerization was performed. 1.
After the reaction was completed in 5 hours, the polymer was taken out. The polymer obtained had a reduced specific viscosity of 1.01 dl / g. The hydrolysis resistance was good as shown in Table 1. The VMR was 89%, and the melt stability was good.

Examples 4 and 5 Polymers were obtained in the same manner as in Example 1 except for the composition shown in Table 1. The results of the hydrolysis resistance evaluation are shown in Table 1.

Comparative Example 1 A toluene solution of 20.0 g of L-lactide and 6 mg of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen introducing tube, dried under reduced pressure for 2 hours, and then heated to 200 ° C. under a nitrogen stream. It was heated and subjected to ring-opening polymerization. After the reaction was completed in 1 hour, the polymer was taken out. The reduced specific viscosity of the obtained polymer was 2.19 dl / g. The hydrolysis resistance was poor as shown in Table 1. The VMRha was 0%.

Comparative Example 2 A toluene solution of 20.0 g of L-lactide, 114 mg of stearic acid and 6 mg of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen introducing tube, dried under reduced pressure for 2 hours, and then under a nitrogen stream. Then, the mixture was heated to 200 ° C. to carry out ring-opening polymerization. After the reaction was completed in 1 hour, the polymer was taken out. The reduced specific viscosity of the obtained polymer was 1.88 dl / g. The results of the hydrolysis resistance evaluation are shown in Table 1. Also, VMR is 8
It was 7%.

[0029]

[Table 1]

[0030]

As is clear from the above examples, the polylactic acid-based resin of the present invention has good hydrolysis resistance, so that the polylactic acid-based resin of the present invention has a problem in the prior art such as water or humidity. The stability is significantly improved. Further, the stability at the time of melting can be further improved, so that a wide range of applications can be expected. The polymer of the present invention greatly contributes to solving industrial and environmental problems.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minako Ariji, Minako Ariji, 1-1 1-1 Katata, Otsu, Shiga Prefecture, Toyo Spinning Co., Ltd. (72) Inventor Kiyofumi Horita 2-1-1, Katata, Otsu, Shiga No. Toyo Boshoku Research Institute (56) Reference JP-A-7-278277 (JP, A) JP-A-7-316272 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) C08G 63/00-63/91

Claims (2)

(57) [Claims] 1. An acid end-capped polylactic acid characterized by being substantially capped at an acid end represented by the following general formula (I) (provided that gel permeation chromatography is used).
Weight average molecular weight of 50,000 or more measured by (GPC)
Compounds with lower polylactic acid and number average molecular weight of 1000 or less
Excluding polylactic acid whose content is 2% or less based on the total weight).
(The number average molecular weight of the polylactic acid is 1000 or less.
The ratio of the compound is 2.0 g (W ₁ ) of the sample and chloroform.
Dissolve in 10 ml, then add to 100 ml of methanol
Then, the precipitated polymer precipitate is separated by filtration and then at 50 ° C. for 24 hours.
The polymer was dried under reduced pressure, and the obtained polymer amount (W ₂ ) was used to obtain a low value
(Here Wlow = {(W ₁ −W ₂ ) / W ₁ } × 100)
It is what you seek by putting it out. ) [Chemical 1] (In the formula, X represents a hydrogen atom or a hydrocarbon group, Y represents a monovalent or more polyvalent aliphatic hydrocarbon group having 1 to 50 carbon atoms, and n represents a positive integer of 10 or more and 1 or more. .) 2. 70% of X represented by the general formula (I)
The acid end-capped polylactic acid according to claim 1, wherein the above is an acyl group having 2 to 50 carbon atoms.