JP2007063360A - Biodegradable crosslinked product and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a biodegradable crosslinked product that has an improved hardness, is flexible and bent at the glass transition temperature of polylactic acid or below, improves the defect of reduction in strength at the glass transition temperature or above and keeps a shape. <P>SOLUTION: The biodegradable crosslinked product comprises a polylactic acid and a polybutylene adipate terephthalate copolymer in which both are integrated by crosslinking. The method for producing the biodegradable crosslinked product comprises a process for preparing a composition containing at least a lactic acid, a polybutylene adipate terephthalate copolymer and a crosslinkable monomer, a process for forming the composition obtained by the process, and a process for irradiating the formed material obtained by the process with ionizing radiation and crosslinking the polylactic acid and the polybutylene adipate terephthalate to integrate them. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a biodegradable crosslinked body and a biodegradable crosslinked body produced by the method, and the biodegradable crosslinked body is a plastic product such as a structure or a part such as a film, a container, or a casing. Is used as a biodegradable product or component useful for solving the problem of disposal treatment after use.

Petroleum synthetic polymer materials currently used for many films and containers are used for the global warming caused by heat and exhaust gas from heat treatment and the food and health caused by toxic substances in combustion gases and residues after combustion. Various social problems are concerned about the disposal process alone, such as adverse effects on the environment and securing of landfill sites.
Biodegradable polymer materials typified by starch and polylactic acid have been attracting attention as materials for solving such problems of disposal of petroleum synthetic polymer materials. Biodegradable polymer materials have a negative impact on the global environment, including ecosystems, such as the amount of heat generated by combustion is less than petroleum synthetic polymer materials and the cycle of decomposition and resynthesis in the natural environment is maintained. Don't give. Among biodegradable polymer materials, aliphatic polyester resins have characteristics comparable to petroleum synthetic polymer materials in terms of strength and processability, and are recently attracting particular attention. Among the aliphatic polyester resins, polylactic acid is especially made from starch supplied from plants, and it is becoming cheaper than other biodegradable polymer materials due to cost reduction due to mass production in recent years. Therefore, many studies are currently being made on its application.

However, polylactic acid is very hard at a glass transition temperature of 60 ° C. or lower, and has virtually no elongation. On the other hand, at a glass transition temperature of 60 ° C. or higher, the polylactic acid becomes so soft that the shape cannot be maintained. It is an obstacle. The temperature of 60 ° C. is a temperature that cannot be easily reached as the air temperature and water temperature in nature, but is a temperature that can be reached, for example, in the interior of automobiles and window materials that are closed in midsummer. Therefore, a significant change in the property that it is hard and brittle at 60 ° C. or lower, whereas it becomes weak at 60 ° C. or higher and the formed shape cannot be maintained is a fatal defect.
Such a remarkable change in properties is derived from the crystal structure of polylactic acid. That is, at a normal cooling speed after melt molding, the polylactic acid hardly crystallizes and is mostly amorphous. Polylactic acid has a high melting point of 160 ° C., and the crystalline portion does not melt easily, but the non-crystalline portion occupying the majority starts to move out of the restriction at around 60 ° C. of the glass transition temperature. Therefore, an extreme characteristic change occurs near the glass transition temperature of 60 ° C.

Non-Patent Document 1 describes that a specific plasticizer is kneaded with polylactic acid in order to improve hardness and brittleness at a glass transition temperature of 60 ° C. or lower and improve impact resistance to the same level as general-purpose plastics.
On the other hand, in order to solve the problem that when the glass transition temperature is 60 ° C. or higher, the strength becomes too low and the strength is lowered, polylactic acid is crosslinked using ionizing radiation or a chemical initiator. No. -313214 (Patent Document 1).

However, each of these techniques cannot solve both the problem at a glass transition temperature of 60 ° C. or lower and the problem at a temperature of 60 ° C. or higher at the same time. Further, even when these techniques are simply combined and a composition obtained by kneading a plasticizer with polylactic acid is crosslinked by irradiation with ionizing radiation or the like, crosslinking does not proceed completely.
This is because polylactic acid molecules need to contact and bond with each other in order for polylactic acid to crosslink, but when the plasticizer is kneaded first, the plasticizer penetrates between the polylactic acid molecules, and the polylactic acid molecules This is because the connection between each other is prevented.

JP 2003-313214 A Issued by Arakawa Chemical Industries, Ltd., “Arakawa NEWS”, issued in July 2004, No. No.326 Page 2-7

An object of the present invention is to provide a biodegradable cross-linked product with little change in strength around 60 ° C., which is the glass transition temperature of polylactic acid, and a method for producing the same.
More specifically, the hardness of the polylactic acid at a temperature below the glass transition temperature is improved and it can be bent with a soft shape. On the other hand, the shape is improved by improving the defect that the strength decreases at a temperature above the glass transition temperature. It is an object of the present invention to provide a biodegradable crosslinked product capable of maintaining the above and a method for producing the same.

In order to solve the above problems, as a first invention, there is provided a biodegradable crosslinked product comprising polylactic acid and a polybutylene adipate terephthalate copolymer, and the two are integrated by crosslinking. ing.
As a second invention, a step of producing a composition containing at least a polylactic acid, a polybutylene adipate terephthalate copolymer, and a crosslinkable monomer;
Molding the composition obtained in the step,
The biodegradable crosslinked product comprising the step of irradiating the molded product obtained in the step with ionizing radiation to integrate the polylactic acid and the polybutylene adipate terephthalate copolymer by crosslinking. The manufacturing method is provided.

As a result of intensive studies to solve the above problems, the present inventors have found that polybutylene adipate terephthalate copolymer (hereinafter referred to as “PBAT”), which is a kind of biodegradable polyester, imparts plasticity to polylactic acid. Focused on being able to. However, simply mixing polylactic acid and PBAT improves the hardness at temperatures below the glass transition temperature of polylactic acid and makes it possible to bend it softly. Can not.
Therefore, the present inventors made further studies and found that PBAT can be crosslinked by irradiation with ionizing radiation in the same manner as polylactic acid.
FIG. 1 shows the relationship between the electron beam irradiation amount and gel fraction in PBAT. However, triallyl isocyanurate which is a crosslinkable monomer is kneaded with PBAT at a ratio of 5% by mass.
Based on this knowledge, it was found that by integrating polylactic acid and PBAT by crosslinking, strength reduction at the glass transition temperature or higher can be effectively prevented and heat resistance can be improved, and the present invention has been completed.

The polylactic acid used in the present invention includes polylactic acid composed of L-lactic acid, polylactic acid composed of D-lactic acid, polylactic acid obtained by polymerizing a mixture of L-lactic acid and D-lactic acid, or two or more of these. A mixture is mentioned. Note that L-lactic acid or D-lactic acid, which is a monomer constituting polylactic acid, may be chemically modified.
The polylactic acid used in the present invention is preferably a homopolymer as described above, but a polylactic acid copolymer in which a lactic acid monomer or lactide and other components copolymerizable therewith are copolymerized may be used. Examples of the “other components” forming the copolymer include hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid; succinic acid, adipic acid, and sebacic acid Dicarboxylic acids typified by glutaric acid, decanedicarboxylic acid, terephthalic acid or isophthalic acid; polyhydric alcohols typified by ethylene glycol, propanediol, octanediol, dodecanediol, glycerin, sorbitan or polyethylene glycol; glycolide, Examples include lactones represented by ε-caprolactone or δ-butyrolactone.

PBAT used in the present invention is a random copolymer of butanediol, adipic acid, and terephthalic acid, and the glass transition temperature differs depending on the ratio of the three monomer components, but any of them can be used in the present invention. It is.
Among these, as PBAT used in the present invention, as described in JP-T-10-508640,
(A) Mainly adipic acid or an ester-forming derivative thereof or a mixture thereof 35 to 95 mol%, terephthalic acid or an ester-forming derivative thereof or a mixture thereof 5 to 65 mol% (the total of individual mol% is 100 mol%) To a mixture consisting of
(B) PBAT obtained by reaction of a mixture containing butanediol in an amount selected from a molar ratio of (a) to (b) in the range of 0.4: 1 to 1.5: 1. Is preferred.
Examples of commercially available PBAT include “Ecoflex” manufactured by BASF.

  In the present invention, the mixing ratio of polylactic acid and PBAT is not particularly limited. Even if it is somewhat hard, polylactic acid is increased when shape maintenance is particularly required, and conversely when more flexibility is required, PBAT is increased. However, in order to exert the effects peculiar to each component, it is preferable that each of polylactic acid and PBAT is contained at least 5% by mass with respect to the total mass of polylactic acid and PBAT. That is, the mixing ratio of polylactic acid and PBAT is polylactic acid: PBAT = 19: 1 to 1:19, preferably 9: 1 to 1: 9, more preferably 9: 1 to 1: 4. More preferably, it is 9: 1 to 1: 1.

  In the present invention, the method for integrating polylactic acid and PBAT by crosslinking is not particularly limited, and a known method may be used, for example, a method of irradiating ionizing radiation, a method of using a chemical initiator, or the like. . Among these, in the present invention, it is preferable to use a method of irradiating ionizing radiation.

The biodegradable crosslinked product of the present invention is preferably produced by the following method.
That is, a step of producing a composition containing at least polylactic acid, PBAT, and a crosslinkable monomer;
Molding the composition obtained in the step,
The biodegradable cross-linked product of the present invention can be produced by a method comprising a step of irradiating ionized radiation to the molded product obtained in the above step and integrating polylactic acid and PBAT by cross-linking.

  The crosslinkable monomer is not particularly limited as long as it is a monomer that can be crosslinked by irradiation with ionizing radiation, and examples thereof include an acrylic or methacrylic crosslinkable monomer and a polyfunctional monomer having an allylic crosslinkable monomer. It is done.

  Examples of acrylic or methacrylic crosslinkable monomers include 1,6-hexanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and ethylene oxide-modified trimethylolpropane. Tri (meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate, diethylene glycol di (meth) acrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, caprolactone Modified dipentaerythritol hexaacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol te La (meth) acrylate, polyethylene glycol di (meth) acrylate, tris (acryloyloxyethyl) isocyanurate, tris (methacryloxyethyl) isocyanurate.

  Examples of allylic crosslinking monomers include triallyl isocyanurate, trimethallyl isocyanurate, triallyl cyanurate, diallylamine, triallylamine, diacrylic chlorate, allyl acetate, allyl benzoate, allyl dipropyl. Isocyanurate, allyl octyl oxalate, allyl propyl phthalate, bityl allyl malate, diallyl adipate, diallyl carbonate, diallyldimethylammonium chloride, diallyl fumarate, diallyl isophthalate, diallyl malonate, diallyl oxalate, diallyl phthalate, diallyl propyl Isocyanurate, diallyl sebacate, diallyl succinate, diallyl terephthalate, diallyl tartrate, dimethyl Rirufutareto, ethyl allyl malate, methyl allyl fumarate, methyl meta-allyl maleate, diallyl monoglycidyl isocyanurate.

  The crosslinkable monomer used in the present invention is preferably an allylic crosslinkable monomer because a high degree of crosslinking can be obtained at a relatively low concentration. Of these, triallyl isocyanurate (hereinafter referred to as TAIC) is particularly preferable because it has a high crosslinking effect on polylactic acid and also has a crosslinking effect on PBAT as shown in FIG. Further, even when triallyl cyanurate, which can be structurally converted by TAIC and heating, is used, the effect is substantially the same.

The crosslinkable monomer is preferably blended at a ratio of 4 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of polylactic acid and PBAT. The amount of the crosslinkable monomer is 4 parts by mass or more. If the amount of the crosslinkable monomer is less than 4 parts by mass, the crosslinking effect of the mixture of polylactic acid and PBAT by the crosslinkable monomer is not sufficiently exhibited. This is because the strength of the biodegradable crosslinked product decreases at a high temperature of 60 ° C. or higher, and in the worst case, the shape may not be maintained. On the other hand, the blending amount of the crosslinkable monomer is 15 parts by mass or less because when the blending amount of the crosslinkable monomer exceeds 15 parts by mass, the entire amount of the crosslinkable polymer is uniformly mixed with the mixture of polylactic acid and PBAT. This is because it becomes difficult and a significant difference in cross-linking effect does not appear.
The amount of the crosslinkable monomer is more preferably 5 parts by mass or more in order to ensure the shape maintaining effect at a high temperature of 60 ° C. or higher, and the biodegradability can be increased by increasing the content of polylactic acid and PBAT. In order to raise, it is more preferable that it is 10 mass parts or less.

In addition to the polylactic acid, PBAT, and crosslinkable monomer, other components may be added to the composition prepared in the first step as long as the object of the present invention is not adversely affected.
For example, biodegradable resins other than polylactic acid and PBAT may be blended. Examples of biodegradable resins other than polylactic acid and PBAT include natural biodegradable resins such as lactone resins, synthetic biodegradable resins such as aliphatic polyesters and polyvinyl alcohol, and natural linear polyester resins such as polyhydroxybutyrate and valerate. Degradable resins can be mentioned.

  Moreover, you may mix the synthetic polymer and / or natural polymer which have biodegradability in the range which does not impair a melt characteristic. Examples of synthetic polymers having biodegradability include cellulose acetate, cellulose butyrate, cellulose propionate, cellulose nitrate such as cellulose nitrate, cellulose sulfate, cellulose acetate butyrate or cellulose nitrate acetate, or polyglutamic acid, polyaspartic acid or Examples include polypeptides such as polyleucine. Examples of the natural polymer include starch, raw starch such as corn starch, wheat starch or rice starch, or processed starch such as acetate esterified starch, methyl etherified starch or amylose.

  Further, the composition includes a resin component other than a biodegradable resin, a curable oligomer, various stabilizers, a flame retardant, an antistatic agent, an antifungal agent or a viscosity imparting agent, glass fiber, glass beads, Metal powders, inorganic and organic fillers such as talc, mica or silica, and colorants such as dyes or pigments can also be added.

The above-mentioned polylactic acid, PBAT, crosslinkable monomer and other components as required are mixed together by a known method such as a Banbury mixer, a kneader, or an open roll.
Specifically, polylactic acid and PBAT are heated to a temperature equal to or higher than the melting points of polylactic acid and PBAT and softened, and then a crosslinkable monomer and other ingredients are added thereto and kneaded therein, or polylactic acid such as chloroform or cresol is mixed. An example is a method in which polylactic acid and PBAT are dissolved or dispersed in a solvent in which both lactic acid and PBAT can be dissolved, and then a crosslinkable monomer and other components are added thereto as desired and kneaded. In the present invention, the former is preferred because there is no need to remove the solvent.
The kneading time may be appropriately selected depending on the kind of the crosslinkable monomer and the temperature at the time of kneading. Moreover, the mixing order is not particularly limited, and all the components may be mixed at once, or a part of them may be mixed in advance, and other components may be mixed into the obtained kneaded product.

  Next, the composition obtained in the above step is formed into a desired shape. A shaping | molding method is not specifically limited, You may use a well-known method. For example, known molding machines such as an extrusion molding machine, a compression molding machine, a vacuum molding machine, a blow molding machine, a T-die molding machine, an injection molding machine, and an inflation molding machine are used.

The biodegradable crosslinked product of the present invention can be obtained by irradiating ionizing radiation to the obtained molded product and crosslinking polylactic acids, PBATs, and polylactic acid and PBAT.
As ionizing radiation, γ-rays, X-rays, β-rays or α-rays can be used. However, for industrial production, γ-ray irradiation with cobalt-60 or electron beam irradiation with an electron beam accelerator is preferable.
The irradiation with ionizing radiation is preferably performed in an inert atmosphere or air except for air. This is because when the active species generated by the irradiation with ionizing radiation are combined with oxygen in the air and deactivated, the crosslinking efficiency is lowered.

The dose of ionizing radiation is preferably 10 kGy or more and 200 kGy or less.
Depending on the amount of crosslinkable monomer, polylactic acid and PBAT may be crosslinked even when the irradiation dose of ionizing radiation is 1 kGy or more and less than 10 kGy, but the strength decreases at a temperature of 60 ° C. or more, which is the glass transition temperature of polylactic acid. In order to crosslink the polylactic acid molecule to such an extent that it can be prevented, it is preferable that the dose of ionizing radiation is 10 kGy or more. Further, in order to crosslink almost 100% of polylactic acid and PBAT molecules, it is more preferable that the irradiation dose of ionizing radiation is 50 kGy or more. And in order to perform bridge | crosslinking integration completely, it is more preferable that the irradiation amount of ionizing radiation is 80 kGy or more.
On the other hand, the irradiation dose of ionizing radiation is 200 kGy or less because polylactic acid and PBAT have the property of being disintegrated by radiation when the resin is used alone. Therefore, when the irradiation dose of ionizing radiation exceeds 200 kGy, it decomposes contrary to crosslinking. It is because it will advance. The upper limit of the ionizing radiation dose is preferably 150 kGy, and more preferably 100 kGy.

As described above, the method for producing the biodegradable crosslinked product of the present invention by irradiation with ionizing radiation has been described. However, the biodegradable crosslinked product of the present invention can also be produced by the following method using a chemical initiator. Can do.
That is, a step of producing a composition containing at least polylactic acid, PBAT, a crosslinkable monomer, and a chemical initiator;
Molding the composition obtained in the step,
Heating the molded product obtained in the above step to a temperature at which the chemical initiator is thermally decomposed, and integrating the polylactic acid and PBAT by crosslinking.

Examples of the chemical initiator include dicumyl peroxide that generates peroxide radicals by thermal decomposition, propionitrile peroxide, benzoyl peroxide, di-t-butyl peroxide, diacyl peroxide, pelargonyl peroxide, myristoyl peroxide, Any catalyst that initiates polymerization of a monomer, such as a peroxide catalyst such as t-butyl perbenzoate or 2,2′-azobisisobutyronitrile, may be used.
The temperature conditions for crosslinking can be appropriately selected depending on the type of chemical initiator. Crosslinking is preferably performed in an inert atmosphere or air except for air, as in the case of irradiation with radiation.
Other items are the same as those in the above embodiment.

  The biodegradable crosslinked product of the present invention can be reliably maintained in shape by the crosslinked network of polylactic acid and PBAT even at a high temperature exceeding 60 ° C. which is the glass transition temperature of polylactic acid. At temperatures below the glass transition temperature of polylactic acid, PBAT is dispersed in the polylactic acid cross-linking network and integrated with polylactic acid, thereby preventing interaction between polylactic acid molecules, resulting in excellent flexibility. It will exhibit the properties and elongation, and also improve the impact resistance, which is a drawback of polylactic acid. In addition, since the processability is greatly improved, it can be expected to be applied to general uses where plastics are currently used. It is also suitable to use as a shape memory product that requires both flexibility and shape memory.

  Since the biodegradable cross-linked product of the present invention has biodegradability, it has very little influence on the ecosystem in nature, and can solve various problems related to disposal treatment that conventional plastics have. Moreover, since the biodegradable crosslinked product of the present invention has both unprecedented flexibility and heat resistance, it can be expected to be applied to fields where polylactic acid has not been available so far. In addition, since it does not affect the living body, it is a material that can be applied to medical instruments such as syringes and catheters used inside and outside the living body.

Hereinafter, embodiments of the present invention will be described.
In the present invention, a polylactic acid homopolymer is used. The polylactic acid used in the present invention preferably has a melting point measured by DSC method of 150 ° C. or higher, more preferably 160 ° C. or higher. Furthermore, it is preferable that MFR in 190 degreeC measured by ASTM D-1238 is 1-5 g / 10min.

The PBAT used in the present invention has a density measured by ISO 1183 of 1 to 1.5 g / cm ³ , preferably 1.2 to 1.3 g / cm ³ and an MVR measured by ISO 1133 of 2 to ⁵ ml / cm 2. It is preferably 10 minutes, the melting point measured by the DSC method is preferably 100 to 130 ° C., the shear D hardness measured by ISO 868 is preferably 30 to 35, and the Picat measured by ISO 306 The softening point is 70 to 90 ° C, preferably 75 to 85 ° C.

First, the pellets of polylactic acid and PBAT are mixed in advance at a desired mass ratio, particularly preferably at a mass ratio of polylactic acid: PBAT = 9: 1 to 2: 1.
Next, the mixed pellet is heated and softened, or the mixed pellet is poured into a solvent in which both polylactic acid such as chloroform and cresol and PBAT can be dissolved and dissolved or dispersed. In the present invention, since it is not necessary to remove the solvent, it is preferable to heat and soften the mixed pellets. The heating temperature at this time is preferably a temperature equal to or higher than the melting points of polylactic acid and PBAT, specifically 160 ° C. or higher, more preferably about 180 ° C.

Next, a crosslinkable monomer is added. TAIC is particularly preferred as the crosslinkable monomer. The addition amount of the crosslinkable monomer is preferably 5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total of polylactic acid and PBAT.
After the addition, the mixture is stirred and mixed so that the crosslinkable monomer is uniform.
Subsequently, the solvent may be further removed by drying.
In this way, a composition containing at least polylactic acid, PBAT, and a crosslinkable monomer is prepared.

  The composition is softened again by heating or the like and formed into a desired shape such as a sheet, film, fiber, tray, container or bag. This molding may be performed after preparing the composition, for example, in a state dissolved in a solvent, or may be performed after cooling or removing the solvent by drying.

Next, the resulting molded product is irradiated with ionizing radiation to crosslink polylactic acid and PBAT to obtain a biodegradable crosslinked product.
The ionizing radiation is preferably electron beam irradiation by an electron beam accelerator.
The radiation irradiation amount is appropriately selected from the range of 80 kGy or more and 150 kGy or less according to the blending amount of the crosslinkable monomer.

In the biodegradable crosslinked product of the present invention thus obtained, it is preferable that substantially all of polylactic acid and PBAT contained therein are crosslinked.
That is, when the biodegradable crosslinked product of the present invention contains only polylactic acid, PBAT, and a crosslinkable monomer, the gel fraction of the biodegradable crosslinked product is preferably substantially 100%.
On the other hand, when the biodegradable crosslinked product of the present invention contains other components other than polylactic acid, PBAT, and a crosslinkable monomer, the other components are mixed with chloroform as a solvent for measuring the gel fraction. Judging whether or not it is soluble, the gel fraction value of the biodegradable crosslinked product is corrected based on the following formula, and the corrected gel fraction indicating the degree of crosslinking between polylactic acid and PBAT is substantially 100%. It is preferable.
Corrected gel fraction (%)
= {(Dry content of gel -α) / (Dry mass of biodegradable crosslinked product−α−β)} × 100
α: other components than polylactic acid, PBAT, and crosslinkable monomer,
The total mass of components insoluble or hardly soluble in chloroform β; other components other than polylactic acid, PBAT, and crosslinkable monomer,
Total mass of ingredients soluble in chloroform

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited only to these Examples.

As polylactic acid, pellet-shaped polylactic acid lacia (LACEA) H-400 manufactured by Mitsui Chemicals, Inc. was used. As PBAT, a pellet-shaped Ecoflex manufactured by BASF was used. These were mixed at a ratio of polylactic acid: PBAT = 4: 1.
TAIC, which is a kind of allylic crosslinkable monomer, is prepared. When an extruder (Ikegai Iron Works Co., Ltd., PCM30 type) is used to melt and extrude a mixture of polylactic acid and PBAT at a cylinder temperature of 180 ° C., TAIC was added to polylactic acid and PBAT by dropping TAIC at a constant speed with a peristaltic pump into the pellet supply section. At that time, the ratio of the dropping speed of TAIC and the extrusion speed of the extruder was adjusted so that the blending amount of TAIC was 7 parts by mass with respect to 100 parts by mass of polylactic acid and PBAT. The extruded product was cooled with water and pelletized with a pelletizer to obtain a pellet-like composition containing polylactic acid, PBAT, and a crosslinkable monomer.

This composition was hot-pressed into a sheet at 180 ° C. and then rapidly cooled with water to produce a 500 μm thick sheet.
This sheet was irradiated with an electron beam at 100 kGy by an electron accelerator (acceleration voltage: 10 MeV, current amount: 12 mA) in an inert atmosphere excluding air to obtain a biodegradable crosslinked product of the present invention.

(Example 2)
A biodegradable crosslinked product of the present invention was obtained in the same manner as in Example 1 except that the mixing ratio of polylactic acid: PBAT was 9: 1.

(Comparative Examples 1-5)
Comparative Examples 1 and 2 were made in the same manner as Examples 1 and 2, respectively, except that TAIC was not blended.
Further, Comparative Examples 3 and 4 were made in the same manner as Examples 1 and 2 except that the electron beam irradiation was not performed.
Further, Comparative Example 5 was made in the same manner as Example 1 except that PBAT was not mixed.

In Examples and Comparative Examples, the gel fraction of the biodegradable crosslinked product was evaluated by the following method, a bendability test was conducted to investigate flexibility, and a hot water immersion test was conducted by the following method to investigate heat resistance. It was.
(1) Evaluation of gel fraction After accurately measuring the dry mass of each biodegradable cross-linked product, wrapped in 200 mesh stainless steel wire, boiled in chloroform solution for 48 hours, and then dissolved in chloroform. The remaining gel content was obtained. After drying at 50 ° C. for 24 hours, chloroform in the gel was removed, and the dry mass of the gel was measured. Based on the obtained value, the gel fraction was calculated based on the following formula.
Gel fraction (%) = (dry weight of gel content / dry weight of biodegradable crosslinked product) × 100

(2) Bendability test The sheet is cut into a stick with a width of 1 cm and a length of 15 cm, bent at both ends with hands to a bending angle of 90 °, rested for a few seconds, and then released, the sample breaks or breaks. We observed whether there were any eyes or creases.

(3) Warm water immersion test The sheet was cut into a stick having a width of 1 cm and a length of 5 cm, and it was observed whether or not it was deformed by being immersed in water at 90 ° C. for 5 minutes.

The results of the evaluation are summarized in Table 1 below together with the differences in production conditions.

(Evaluation results)
In Examples 1 and 2 and Comparative Example 5 using only polylactic acid without blending PBAT, the gel fraction was almost 100%, and most of the constituent molecules in the biodegradable crosslinked body were integrated by crosslinking. On the other hand, no cross-linking was observed in Comparative Examples 1 and 2 in which TAIC was not mixed and in Comparative Examples 3 and 4 in which electron beam irradiation was not performed.
Examples 1 and 2 and Comparative Examples 1 to 4 blended with PBAT were rich in flexibility, bent without problems in the bendability test, and returned to their original shapes elastically. On the other hand, the comparative example 5 which did not mix | blend PBAT was hard and it broke as a result of bending at 90 degrees in a bendability test.
In the warm water immersion test, Examples 1 and 2 and Comparative Example 5 in which most of the constituent molecules were crosslinked maintained the shape even in warm water, whereas Comparative Examples 1 to 4 in which no crosslinking was observed contracted. Deformed into a round lump.
As is clear from the above evaluation results, Examples 1 and 2 have both flexibility and heat resistance, but it was confirmed that there was a problem with any of the properties in the comparative example.

It is a graph which shows the relationship between the electron beam irradiation amount and gel fraction in PBAT which knead | mixed 5 mass% TAIC.

Claims (5)

  A biodegradable crosslinked product comprising polylactic acid and a polybutylene adipate terephthalate copolymer, wherein the two are integrated by crosslinking.   The biodegradable crosslinked product according to claim 1, wherein the mixing ratio of polylactic acid and polybutylene adipate terephthalate copolymer is 19: 1 to 1:19. Producing a composition comprising at least polylactic acid, polybutylene adipate terephthalate copolymer, and a crosslinkable monomer;
Molding the composition obtained in the step,
The method includes the step of integrating the polylactic acid and the polybutylene adipate terephthalate copolymer by irradiating ionizing radiation to the molded product obtained in the step and crosslinking the polylactic acid and the polybutylene adipate terephthalate copolymer. 2. A method for producing a biodegradable crosslinked product according to 2.   The method for producing a biodegradable crosslinked product according to claim 3, wherein an allyl crosslinking monomer, an acrylic or methacrylic crosslinking monomer is used as the crosslinking monomer.   The method for producing a biodegradable crosslinked product according to claim 3 or 4, wherein the irradiation dose of ionizing radiation is 10 kGy or more and 200 kGy or less.

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