JP2005350503A - Highly efficient crosslinking method for biodegradable polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient crosslinking method for biodegradable polyesters, able to improve physical properties depending on application without spoiling biodegradability of the biodegradable polyesters, and crosslinked products prepared by the method. <P>SOLUTION: The highly efficient crosslinking method for the biodegradable polyesters comprises a process for mixing and kneading a polyfunctional monomer having two or more double bonds in one molecule with at least one species of biodegradable polyesters and a process for irradiating radioactive rays by heating the kneaded product at a temperature equal to or higher than the glass transition temperature of the biodegradable polyesters and equal to or lower than the heat degradation temperature of the biodegradable polyesters. Preferably, the biodegradable polyester is a polylactic acid and the polyfunctional monomer is a triallyl isocyanurate or a triallyl cyanurate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a highly efficient crosslinking method of a biodegradable polyester and a crosslinked body thereof. More specifically, the present invention relates to a high-efficiency crosslinking method and a crosslinked body capable of improving physical properties according to the use without impairing the biodegradability of the biodegradable polyester.

  The plastic used in Japan reaches about 14 million tons per year, and about 8.4 million tons, about 60% of which is processed as waste plastic. This waste plastic is usually disposed of by incineration and landfilling, but various social problems are concerned about plastic disposal. For example, in the incineration process, there are concerns about the impact on food and the human body due to the global warming caused by heat and exhaust gas and the generation of harmful dioxins as environmental hormones. There is a risk of staying in the soil for a long period of time, and there is a risk that additives such as plasticizers will flow out with deterioration, and there are problems such as securing a disposal site for disposal.

  In response to these problems, there is a need for plastic materials that can be easily processed after use without impacting the environment. Biodegradable polymers, such as starch and polylactic acid, have a lower calorific value due to combustion than general-purpose petroleum-synthetic polymers, and can also be composted and discarded by decomposition and digestion by microorganisms in the soil. Therefore, it is an environmentally friendly material that is expected to be developed in future applications. In particular, biodegradable aliphatic polyesters have attracted attention in recent years because they have properties comparable to petroleum synthetic polymers in physical properties such as strength. However, since biodegradable aliphatic polyester has low processability and heat resistance, its practical use is currently delayed. Accordingly, there is a need for a process for modifying biodegradable aliphatic polyesters that can achieve the desired properties required for the application.

  As one of the useful modification techniques for plastics, there is a method of improving physical properties such as heat resistance by crosslinking molecular chains by radiation treatment. Cross-linking technology by radiation treatment is used to improve the workability of radial tires, heat-resistant electric wire covering materials, and processing and manufacturing foams. These materials include natural rubber, styrene / butadiene rubber, polyethylene, polypropylene, polyvinyl chloride, polyurethane, and the like. In particular, techniques for crosslinking polyethylene and polypropylene are performed mainly for the purpose of improving heat resistance. However, in the crosslinking modification technique using a polymer alone, depending on the type and form of the material, generally, a large dose of irradiation is required for the crosslinking reaction to occur.

  On the other hand, when the present inventors added a polyfunctional monomer that accelerates the crosslinking reaction to the biodegradable polymer, it can be crosslinked by irradiation with a relatively low dose of radiation. A method has been developed (see, for example, Patent Document 1). Specifically, it is a method in which about 3% by weight of a polyfunctional monomer is added and irradiated at room temperature. However, according to this method, the polyfunctional monomer and the homopolymer may be cross-linked and partially become non-biodegradable. In consideration of the residual in the natural environment and the use in the in vivo environment, Some are not preferred. In particular, when the bridging material is applied to plastic products such as films, containers, housings, and other structures and parts, it is embedded in the soil after use, or composted and disposed of by decomposing into carbon dioxide and water. When applied to regenerative medical materials such as scaffolds for regenerating bones and tendons, and regenerating living tissue cells by absorbing in vivo, particularly excellent biodegradability is required.

Therefore, there is a need for a method for modifying a biodegradable aliphatic polyester that can improve the physical properties according to the application without impairing the biodegradability of the original material. In the process of crosslinking in the presence of polyfunctional monomers, it is necessary to reduce the amount of polyfunctional monomers.
JP 2003-313214 A

  The present invention has been made in view of the above problems, and an object of the present invention is a high-efficiency crosslinking method for biodegradable polyester, depending on the application without impairing the biodegradability of the biodegradable polyester. It is to provide a highly efficient crosslinking method capable of improving physical properties and to provide a crosslinked body crosslinked by the method.

Such an object is achieved by the present invention described below.
The highly efficient crosslinking method of the biodegradable polyester of the present invention includes a step of kneading a polyfunctional monomer having two or more double bonds in one molecule with at least one biodegradable polyester, and the kneaded product. And irradiating with radiation while heating to a temperature not lower than the glass transition temperature of the biodegradable polyester and not higher than the thermal decomposition temperature.

Thereby, the highly efficient bridge | crosslinking method which can improve a physical property according to a use can be provided, without impairing the biodegradability of biodegradable polyester.
The highly efficient crosslinking method of the biodegradable polyester of the present invention includes a step of kneading a polyfunctional monomer having two or more double bonds in one molecule with at least one biodegradable polyester, A step of rapidly cooling after molding the kneaded product under heat and pressure, and a step of irradiating the molded kneaded product while heating the molded kneaded product to a temperature not lower than the glass transition temperature of the biodegradable polyester and not higher than the thermal decomposition temperature. It is characterized by including.

  This provides a high-efficiency cross-linking method capable of improving the physical properties according to the application without impairing the biodegradability of the biodegradable polyester, and providing a method capable of forming the polyester material into a desired form. Can do.

In the highly efficient crosslinking method of the biodegradable polyester of the present invention, the radiation is preferably γ rays or electron rays, and the dose is preferably 5 to 50 kGy.
Thereby, the irradiation dose required for bridge | crosslinking biodegradable polyester can be reduced.

In the highly efficient crosslinking method of the biodegradable polyester of the present invention, the radiation is preferably γ rays or electron rays, and the dose is preferably 10 kGy.
Thereby, the irradiation dose required for bridge | crosslinking biodegradable polyester can be reduced.

In the highly efficient crosslinking method of the biodegradable polyester of the present invention, it is preferable to knead the polyfunctional monomer at a concentration of 0.1 to 3% by weight.
Thereby, the density | concentration of a polyfunctional monomer can be reduced and the obtained crosslinking material can be applied to the use which requires high biodegradability.

In the highly efficient crosslinking method of the biodegradable polyester of the present invention, the biodegradable polyester is preferably polylactic acid.
As a result, the obtained bridging material can be suitably used as an alternative material for general-purpose plastic products that are manufactured and discarded in large quantities, or as a regenerative medical material such as a scaffold base material that regenerates bones and tendons. Can do.

In the highly efficient crosslinking method of the biodegradable polyester of the present invention, the polyfunctional monomer is preferably triallyl isocyanurate or triallyl cyanurate.
Thereby, a bridging material having a high gel fraction can be obtained at a low monomer concentration and a low dose.

  According to the present invention, a high-efficiency crosslinking method for biodegradable polyester, which can improve physical properties according to the application without impairing the biodegradability of the biodegradable polyester. It is also possible to provide a crosslinked body that is crosslinked by the method.

Hereinafter, the highly efficient crosslinking method of the biodegradable polyester of this invention is demonstrated.
Here, “high efficiency” in the present specification means that a high degree of crosslinking (gel fraction) can be obtained with a low monomer concentration and a low dose.

[Biodegradable polyester]
The biodegradable polyester that can be used in the present invention is a biodegradable aliphatic polyester, and is not particularly limited, but includes polylactic acid, polyglycolic acid, polycaprolactone, polybutylene succinate, poly (butylene succinate, Adipate) copolymer, poly (butylene succinate / carbonate) copolymer, poly (ethylene succinate), poly (3-hydroxybutyrate) and its copolymer, poly (butylene succinate / terephthalate) copolymer Etc. These may be used by blending a plurality of kinds, or may be used by blending with other biodegradable polymers such as starch and cellulose.

  The biodegradable polyester that can be used in the present invention is preferably polylactic acid. Polylactic acid is a carbon-neutral plant-derived plastic, so it has little impact on the ecosystem in the global environment and has good biocompatibility, so it can be used as a substitute for general-purpose plastic products that are manufactured and discarded in large quantities. It can be suitably used as a material or a regenerative medical material such as a scaffold base material for regenerating bones and tendons. The polylactic acid may have an L-form, a D-form, or a mixture as a molecular structure unit, or may be a single or a mixture of two or more of these.

[Multifunctional monomer]
The polyfunctional monomer that can be used in the present invention is a monomer having two or more double bonds in one molecule. By using such a monomer, the crosslinking efficiency of the biodegradable polyester can be improved when the biodegradable polyester kneaded material containing this monomer is irradiated with radiation.

  The polyfunctional monomer is not particularly limited, and examples thereof include acrylic monomers such as 1,6 hexanediol diacrylate, methacrylic monomers such as trimethylolpropane trimethacrylate, and allyl monomers.

  The polyfunctional monomer is preferably an allylic monomer because a high crosslinking degree can be obtained at a very low concentration and a low dose. The allyl monomer is not particularly limited, but triallyl isocyanurate, trimethallyl isocyanurate, triallyl cyanurate, trimethallyl cyanurate, diallylamine, triallylamine, allyl acetate, allyl benzoate, allyl dipropyl isocyanurate Allyl octyl oxalate, allyl propyl phthalate, bityl allyl malate, diallyl adipate, diallyl carbonate, diallyl fumarate, diallyl isophthalate, diallyl malonate, diallyl propyl isocyanurate, diallyl sepacate, diallyl succinate, diallyl terephthalate, Diallyl tartrate, dimethallyl phthalate, ethyl allyl malate, methyl allyl fumarate, methyl metaallyl malate, diac Rukurorenteto, diallyl dimethyl ammonium chloride. A preferred allylic monomer is triallyl isocyanurate (hereinafter referred to as TAIC), and the structure can be converted to TAIC by heating. Therefore, triallyl cyanurate (hereinafter referred to as TAC) also has a substantially bridging effect. The same.

  The polyfunctional monomer is at a concentration of 0.1 to 3 wt%, preferably 0.1 to 1 wt%, most preferably 1 wt%, based on the total weight of the biodegradable polyester and polyfunctional monomer. use.

[radiation]
The radiation that can be used in the present invention is not particularly limited, and examples thereof include ionizing radiation such as α rays, β rays, γ rays, and X rays, or ultraviolet rays.

  In order to initiate the crosslinking reaction, radical initiators such as organic oxides and azo compounds may be added or heated. However, according to these methods, unreacted polyfunctional monomer remains. For the purpose of completing the crosslinking reaction, it is desirable to use radiation, with ionizing radiation being preferred.

  The ionizing radiation is preferably a gamma ray from cobalt-60 or an electron beam by an accelerator for industrial production. The electron accelerator is not limited as long as it can generate an electron beam having energy that passes through the thickness of the irradiated sample. When the thickness of the irradiated sample is 1 mm or more, the electron accelerator has a medium energy to high acceleration voltage of 1 MeV or higher. An energy electron accelerator is preferable. When the thickness of the irradiated sample is less than 1 mm and thin, a low energy electron accelerator of 1 MeV or less may be used.

[Kneading process]
In the present invention, the polyfunctional monomer is kneaded into the biodegradable polyester by the kneading step. By this step, the biodegradable polyester and the polyfunctional monomer can be uniformly dispersed and mixed, and crosslinking can be performed efficiently. Kneading can be performed by any means known in the art, but preferably a mixer having a temperature maintaining function is used.

  The kneading temperature is not particularly limited, but is preferably a temperature at which the biodegradable polyester is softened. By kneading at a temperature at which the biodegradable polyester is softened, the degree of dispersion and mixing with the polyfunctional monomer can be increased.

  In one preferred embodiment of the present invention, the biodegradable polyester and the polyfunctional monomer are mixed well in advance, and the mixture is melt blended in a mixer heated to a temperature at which the biodegradable polyester is softened or softened. A polyfunctional monomer is added to the biodegradable polyester heated up to and melt blended.

  In another preferred embodiment of the present invention, the biodegradable polyester and the polyfunctional monomer are dissolved and dispersed and mixed in a solvent such as chloroform in which the biodegradable polyester is dissolved.

The kneaded product obtained after kneading may be softened by heating or the like and formed into a desired shape.
[Molding process]
Following the kneading step, in some cases, in the molding step, the kneaded product is molded under heat and pressure and then rapidly cooled. Thereby, a polyester material can be shape | molded in a desired form.

  Molding can be done by any means known in the art. There are no particular limitations on the heating and pressing conditions at the time of molding, and the conditions can be appropriately determined depending on the properties of the biodegradable polyester and the polyfunctional monomer and the molding conditions.

  The rapid cooling can be performed by any means known in the art such as water cooling, ice cooling, and air cooling. By rapidly cooling the kneaded product to the recrystallization temperature or lower after molding, the amorphous portion can be retained, and the crosslinking efficiency can be increased.

  In one embodiment of the present invention, a kneaded product of polylactic acid and triallyl isocyanurate is pressed at a temperature of 160 ° C. to 200 ° C., which is the melting point of polylactic acid, and formed into a film, and then cooled to 60 ° C. or less with water. .

[Radiation irradiation process]
The kneaded product is irradiated with radiation while being heated to a predetermined temperature by the radiation irradiation step following the kneading step or, optionally, the molding step. Crosslinking can be performed by irradiating a biodegradable polyester kneaded material containing a polyfunctional monomer with radiation. Further, by irradiating with radiation at a predetermined temperature, a high degree of crosslinking can be achieved with a low monomer concentration and a low dose as compared with the conventional method.

  The irradiation temperature is not particularly limited, but is preferably not less than the glass transition temperature of the biodegradable polyester and not more than the thermal decomposition temperature. At temperatures above the glass transition temperature, the micro-Brownian motion of the biodegradable polyester is active and bridging is likely to occur, and at temperatures above the melting point, the structural form of the biodegradable polyester itself changes and becomes amorphous. It is desirable when the state is increased, but polylactic acid is not desirable because it is easily thermally decomposed. Since the polyester itself decomposes at a temperature higher than the thermal decomposition temperature, it is not desirable.

Specifically, the irradiation temperature can be determined depending on the type of biodegradable polyester.
When polylactic acid (glass transition temperature: 60 ° C., recrystallization temperature: 100 ° C.) is used as the biodegradable polyester, the irradiation temperature is not particularly limited, but is 25 ° C. to 170 ° C., preferably 70 ° C. It is -100 degreeC, Most preferably, it is 70 degreeC. In modification of a polymer by radiation, a crosslinking reaction generally tends to occur at an amorphous part in the polymer. At a temperature near the recrystallization temperature, the crystallization of the non-crystalline portion of polylactic acid proceeds, and the portion that can react with the polyfunctional monomer decreases. Therefore, in order to achieve a high degree of crosslinking, it is preferable that the irradiation temperature is lower than the recrystallization temperature.

  When polycaprolactone (glass transition temperature: −65 ° C., melting point: 60 ° C.) is used, the irradiation temperature is not particularly limited, but is −65 ° C. to 60 ° C., preferably 45 ° C. to 60 ° C., Most preferably, the temperature is 45 ° C. on the assumption that polycaprolactone is melted at a temperature equal to or higher than the melting point.

  When polybutylene succinate (glass transition temperature: −32 ° C., heat distortion temperature: 95 ° C., melting point: 115 ° C.) is used, the irradiation temperature is not particularly limited, but is −32 ° C. to 120 ° C., preferably 25 ° C to 120 ° C, most preferably 95 ° C to 120 ° C.

  The irradiation dose is not particularly limited, but is 1 to 200 kGy, preferably 5 to 50 kGy, and most preferably 10 kGy. In the present invention, it is significant that the dose required at least 50 kGy in the conventional method can be reduced to 50 kGy or less. On the other hand, if the dose exceeds 200 kGy, it is not preferable because radiation-degradable polyester such as polylactic acid is decomposed.

  At the time of irradiation, there is almost no influence on the crosslinking due to oxygen in the ambient atmosphere, but in order to suppress a decrease in the crosslinking density, the irradiation region including the irradiated sample is vacuum sealed with a suitable means such as a polyester film. It is desirable to irradiate after that.

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

(Example 1-4)
Weigh 40g of polylactic acid (fine powdered polylactic acid Lacia H-100 made by Mitsui Chemicals) and melt it at 180 ° C with Labo Plast Mill (Toyo Seiki Co., Ltd.). 1% by weight of lactic acid was added and kneaded in a molten state for 10 minutes. The mixture was finely cut into pellets, placed in a glass ampule tube, and sealed using a vacuum line until the pressure was reduced to 10 ⁻³ Pa. The ampoule tube was heated to a predetermined temperature with a block heater, and while maintaining the temperature, γ rays using cobalt-60 as a radiation source were irradiated with 5 kGy, 10 kGy, 20 kGy, 30 kGy, and 50 kGy, respectively, and a crosslinking reaction was performed. . Predetermined temperatures at the time of irradiation were 25 ° C. (room temperature), 70 ° C., 100 ° C., and 170 ° C., and Examples 1 to 4, respectively.

(Example 5-6)
Except that the concentration of TAIC is 0.5% by weight, 1.0% by weight, 1.5% by weight, 2.0% by weight, 3.0% by weight, and the irradiation temperature is 70 ° C., 100 ° C. The crosslinking reaction was carried out in the same manner as in Example 1-4. Irradiation temperatures of 70 ° C. and 100 ° C. were taken as Examples 5 and 6, respectively.

(Comparative Example 1-2)
The crosslinking reaction was carried out in the same manner as in Example 1-4, except that TAIC was not mixed and the temperature during irradiation was changed to 25 ° C. and 70 ° C. The irradiation temperature of 25 ° C. and 70 ° C. were set as Comparative Examples 1 and 2, respectively.

(Example 7)
After mixing polylactic acid and TAIC in the same manner as in Example 1-4 above, it was molded using a heating and pressing machine at the same temperature (180 ° C.) and immediately cooled to maintain the amorphous state of polylactic acid. A 0.5 mm thick sheet was prepared. The sheet is an irradiation container whose temperature can be controlled, heated to 70 ° C. and maintained at a temperature in a nitrogen atmosphere, while using a Cockcroft-Walton type electron accelerator (acceleration voltage 2 MeV, current 0.1 mA), respectively. Irradiation with electron beams of 4 kGy, 26.8 kGy, 40.2 kGy, and 67 kGy was performed to perform a crosslinking reaction.

(Example 8-9)
Bridging in the same manner as in Example 7 except that the concentration of TAIC was 0.5 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, and the irradiation dose was 26.8 kGy, 67 kGy. Reaction was performed. Irradiation doses of 26.8 kGy and 67 kGy were taken as Examples 8 and 9, respectively.

(Comparative Example 3-4)
A crosslinking reaction was carried out in the same manner as in Example 7 except that TAIC was not mixed and the temperature at irradiation was 25 ° C. and 70 ° C. The irradiation temperature of 25 ° C. and 70 ° C. were set as Comparative Examples 3 and 4, respectively.

(Evaluation of Examples and Comparative Examples)
The following gel fraction evaluation (1) and mechanical property evaluation (2) of the sheet were performed on the cross-linked materials obtained in the examples and comparative examples.

The gel fraction, which is a measure of the degree of crosslinking, was determined as follows.
(1) Evaluation of gel fraction A predetermined amount of the obtained crosslinking material was accurately measured and wrapped in a 200 mesh stainless steel wire mesh. Next, this is immersed in chloroform solvent for 48 hours or boiled for 24 hours, so that the uncrosslinked dissolved component (sol content) is transferred to the chloroform solvent side, and only the crosslinked insoluble component (gel content) is transferred. It remained in the wire mesh. In order to remove the attached sol, the wire mesh containing the gel was washed with cold chloroform, and further washed with a large amount of methanol. Subsequently, it dried until it became constant weight for 24 hours or more in a 50 degreeC vacuum dryer. The gel fraction is determined by the following formula.

Gel fraction (%) = (gel content dry weight) / (initial dry weight) × 100
The gel fraction obtained by the above method is shown in FIGS. 1 shows the results of Example 1-4 and Comparative Example 1-2, FIG. 2 shows the results of Example 5-6, FIG. 3 shows the results of Example 7, and FIG. 4 shows the results of Example 8. ing.

  As shown in FIG. 1, in Comparative Example 1-2, the gel fraction was not obtained and was not bridged regardless of the temperature and dose at the time of γ-ray irradiation. When the temperature at the time of γ-ray irradiation of Example 1 was 25 ° C., which was room temperature, even when irradiated up to 30 kGy, it was not cross-linked, and when irradiated with 50 kGy, the gel fraction increased only to 42%. In the case of 70 ° C., which is in the vicinity of the glass transition temperature of Example 2, the gel fraction suddenly increases to about 45% at a low dose of 5 kGy compared to that at room temperature, and the gel fraction reaches 70% at 10 kGy. did. When irradiated with higher doses of 20 kGy, 30 kGy, and 50 kGy, the gel fraction became about 80%, and it bridged very efficiently and maintained transparency. In the case of 100 ° C., which is the crystallization temperature of Example 3, it is easier to crosslink than at room temperature, but it is difficult to crosslink compared to 70 ° C., and the gel fraction is about 29% at 5 kGy and about 42 at 10 kGy. %, About 48% at 20 kGy, and it was cloudy. Moreover, in the case of 170 degreeC which is more than melting | fusing point of Example 4, a gel fraction was not obtained at any dose, and it did not bridge.

  As shown in FIG. 2, in the relationship between the temperature at the time of irradiation and the TAIC concentration, the γ-ray irradiation dose was fixed at 10 kGy. As a result, in the case of 70 ° C. in Example 5, the TAIC concentration was up to 1% by weight. The gel fraction reached 70%, and even at higher concentrations, the gel fraction was approximately 55-69%, maintaining transparency. In the case of Example 6 at 100 ° C., the gel fraction tended to be lower than that at 70 ° C. at any concentration as in FIG. Since recrystallization proceeded at 100 ° C., and polylactic acid and TAIC became difficult to mix, there was a tendency for the gel fraction to increase as the concentration increased.

  As shown in FIG. 3, at 25 ° C. and 70 ° C. in Comparative Examples 3 and 4, no gel fraction was obtained and crosslinking did not occur regardless of the dose even when irradiated with an electron beam. When irradiated at 70 ° C. in Example 7, the gel fraction was about 47% at 13.4 kGy, about 66% at 26.8 kGy, and about 66% at 40.2 kGy, and the gel fraction was about It reached 70% and retained transparency.

As shown in FIG. 4, in the case of Example 8 in which the electron beam irradiation dose was kept constant at 26.8 kGy, the gel fraction tended to increase as the TAIC concentration increased.
(2) Evaluation of mechanical properties of sheet The sheets prepared in Examples 7-9 and Comparative Examples 2 and 3 were punched into JIS standard 1 (1/2) dumbbell molds, and the tensile speed was measured using TENSILON manufactured by TOYO BALDWIN. Was measured at 2 mm / min, and the distance between the marked lines was 25 mm. The average value measured five times was used as the measurement value.

  Table 1 shows the results of elongation at break obtained by the above method, and Table 2 shows the results of tensile strength.

  The results of the above mechanical properties are shown in FIGS. 5 and 6 as the rate of change when the unirradiated sample is taken as 100%. The sheet irradiated at a temperature of 70 ° C. prepared in Example 7-9 improved by about 20 to 80% in breaking elongation from the unirradiated sample up to 40 kGy compared with Comparative Example 3-4, and the tensile strength was about Improved by 20%.

  The high-efficiency cross-linked biodegradable polyester material of the present invention is intended to solve disposal problems after use in fields where plastic products such as films, containers, housings, and other structures and parts are used. Before being used in the field of regenerative medical materials used as biodegradable products or parts that decompose into carbon dioxide and water by composting, as well as scaffold base materials that regenerate bones and tendons, etc. Application to a polymer bioabsorbable regenerative medical material having heat resistance that can withstand heat sterilization is expected. In particular, since the polylactic acid material of the present invention is a plant-derived plastic, it can be applied as a substitute for general-purpose plastic products such as agricultural multi-films and packaging materials.

It is a graph which shows the relationship between the dose and gel fraction by the difference in the temperature at the time of (gamma) irradiation about Example 1-4 of this invention, and Comparative Examples 1-2. It is a graph which shows the relationship between TAIC density | concentration in the temperature at the time of (gamma) irradiation 70 degreeC, and 10 kGy irradiation about Examples 5-6 of this invention, and a gel fraction. It is a graph which shows the relationship between the dose in the temperature at the time of the electron beam irradiation of Example 7 of this invention at 70 degreeC, and a gel fraction. It is a graph which shows the relationship between TAIC density | concentration and gel fraction in the electron beam irradiation temperature 70, 100 degreeC, and 26.8kGy irradiation about Examples 8-9 of this invention. It is a graph which shows the relationship between the irradiation dose of the polylactic acid sheet which irradiated the electron beam about Example 7-9 of this invention, and Comparative Examples 3-4, and the breaking elongation of a sheet | seat. It is a graph which shows the relationship between the irradiation dose of the polylactic acid sheet which irradiated the electron beam about Examples 7-9 and Comparative Examples 3-4 of this invention, and the tensile strength of a sheet | seat.

Claims (7)

  A highly efficient crosslinking method for biodegradable polyester, a step of kneading a polyfunctional monomer having two or more double bonds in one molecule with at least one biodegradable polyester; Irradiating with radiation while heating to a temperature not lower than the glass transition temperature of the biodegradable polyester and not higher than the thermal decomposition temperature.   A highly efficient crosslinking method for biodegradable polyester, a step of kneading a polyfunctional monomer having two or more double bonds in one molecule with at least one biodegradable polyester; A step of rapid cooling after molding under heat and pressure, and a step of irradiating the molded kneaded product while heating to a temperature not lower than the glass transition temperature of the biodegradable polyester and not higher than the thermal decomposition temperature. Said method.   The method according to claim 1 or 2, wherein the radiation is gamma rays or electron rays, and the dose thereof is 5 to 50 kGy.   The method according to any one of claims 1 to 3, wherein the radiation is gamma rays or electron rays, and the dose thereof is 10 kGy.   The crosslinking method according to claim 1, wherein the polyfunctional monomer is kneaded at a concentration of 0.1 to 3% by weight.   The method according to any one of claims 1 to 5, wherein the biodegradable polyester is polylactic acid. The method according to any one of claims 1 to 6, wherein the polyfunctional monomer is triallyl isocyanurate or triallyl cyanurate.

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