JP4238113B2 - Heat-resistant crosslinked product having biodegradability and method for producing the heat-resistant crosslinked product - Google Patents

Description

  The present invention relates to a heat-resistant crosslinked product having biodegradability and a method for producing the same, and particularly in the field where plastic products such as a structure such as a film, a container, and a casing are used, and a solution for disposal treatment after use. It is suitably used as a biodegradable product or component for the purpose.

  Petroleum synthetic polymer materials currently used in many films and containers are depleted of their raw materials, global warming due to heat and exhaust gas from heat treatment, and toxicity in combustion gases and post-combustion residues. There are concerns about various social issues such as the effects of substances on food and health, and securing landfill sites.

In response to these problems, biodegradable polymers such as starch and polylactic acid have been attracting attention as materials for solving the problems of disposal of petroleum synthetic polymers.
Biodegradable polymers do not adversely affect the global environment, including ecosystems, as compared to petroleum synthetic polymers, the amount of heat associated with combustion is small and the cycle of decomposition and resynthesis in the natural environment is maintained. Among them, aliphatic polyester resins having properties comparable to petroleum synthetic polymers in terms of strength and processability are materials that have attracted attention in recent years. In particular, polylactic acid is made from starch supplied from plants, and is currently becoming much cheaper than other biodegradable polymers due to cost reduction due to mass production in recent years. Consideration has been made.

  Polylactic acid is a biodegradable resin that is closest to its substitute material because it has processability and strength comparable to general-purpose petroleum synthetic polymers in terms of its characteristics. In addition, it is expected to be applied to various uses such as substitution from transparency comparable to acrylic resin, and substitution of ABS resin such as a casing of electrical equipment from the viewpoint of high Young's modulus and shape retention.

However, polylactic acid has a glass transition point at a relatively low temperature of around 60 ° C., and the so-called glass plate suddenly becomes a vinyl table cloth before and after that temperature. It has a fatal defect that it is difficult to maintain the shape of time.
In addition, the polylactic acid crystal part that does not melt until it reaches a relatively high melting point of 160 ° C. is a microcrystal that does not show a large lump shape, and in a normal crystallinity, the crystal part alone supports the overall strength. Although it is a cause of this drastic change in Young's modulus, the change occurs before and after the glass transition temperature, which is the temperature at which the amorphous part can move freely. Thus, it can be said that there is a major reason for almost losing the interaction between molecules.

As a method of improving the disadvantages of lack of shape retention at high temperatures and poor heat resistance, reducing the non-crystalline portion and increasing the crystallinity of polylactic acid to 90-95% suppresses softening at 60 ° C or higher. And it becomes possible to hold | maintain the shape.
However, as a specific method for increasing the degree of crystallinity of polylactic acid, after the polylactic acid is once melted and molded into various shapes by injection molding or the like, crystallization proceeds at a temperature below the melting point and above the glass transition temperature. It is necessary to keep it as it is for a long time. Therefore, for example, in order to make a part with a thickness of only a few millimeters to less than 1 cm, it is necessary to maintain it in the mold while heating for several tens of minutes after injection molding. It is n’t.

In order to improve the heat resistance of the polylactic acid, “High Heat-resistant Polylactic Acid Injection Molding Grade Advanced Terramac” (Non-Patent Document 1) has been published in the magazine “Plastic Age”.
Non-Patent Document 1 discloses a technology in which a nano-sized fine particle mineral filler is mixed with polylactic acid and the degree of crystallization is increased in a relatively short time using the particle as a nucleus.

  In the method described in the above paper, it is possible to take out from the mold on the order of several tens of minutes to several minutes, and realistic manufacturing is becoming possible. However, although there is an improvement in terms of industrial production cost, since the opaque clay filler is mixed with 1 to 5% by weight or more of polylactic acid, the transparency inherent in polylactic acid is lost, and originally A glossy polylactic acid surface such as glass has a rough feel due to the filler, and has disadvantages such as poor appearance, and the usable products are limited.

Furthermore, since it is impossible to disperse the mineral filler beyond the original size, there is a tendency for strength variations to occur, and there is basically no bond between the mineral filler and the base resin. Since the reinforcing effect depends solely on the strength of the filler itself, it is necessary to increase the blending amount of the filler in order to increase the strength. If the blending amount of the filler is increased, the transparency and smoothness are impaired. Furthermore, when the filler is mixed and molded, there is a problem that the bleed phenomenon that the filler comes out from the base resin tends to occur with time.
"High heat-resistant polylactic acid injection molding grade Advanced Terramac" (Plastics Age, April 2003, pages 132-135)

  The present invention has been made in view of the above problems, is made of a biodegradable material, improves the shape retention that is drastically lowered above the glass transition point, imparts heat resistance, and has transparency, surface glossiness and It is an object of the present invention to provide a heat-resistant crosslinked product having biodegradability that does not impair smoothness and a production method that is practical in industrial production.

As a result of intensive studies on this problem, the present inventor has found that the above problem can be solved by integrating both the biodegradable aliphatic polyester and the hydrophobic polysaccharide derivative by crosslinking.
Furthermore, as a method for producing the above heat-resistant crosslinked product, three types of biodegradable aliphatic polyester, hydrophobic polysaccharide derivative and cross-linked polyfunctional monomer are used at a temperature equal to or higher than the melting point of the biodegradable aliphatic polyester. The present inventors have found a production method characterized by irradiating the mixture with ionizing radiation after uniform mixing.

The first invention made on the basis of the above findings is that a molded article comprising a mixture of a biodegradable aliphatic polyester, a hydrophobic polysaccharide derivative and a crosslinkable polyfunctional monomer is crosslinked by irradiation with ionizing radiation. Integrated,
The biodegradable aliphatic polyester is composed of polylactic acid or polybutylene succinate,
The hydrophobic polysaccharide derivative comprises acetate ester starch, fatty acid ester starch or acetate ester cellulose,
The cross-linked polyfunctional monomer is a monomer having an allyl group composed of triallyl isocyanurate or trimethallyl isocyanurate ,
The tensile strength is 30 to 70 g / mm ² at a high temperature of 150 ° C. or more and 200 ° C. or less which is the melting point of the biodegradable aliphatic polyester and the softening point of the hydrophobic polysaccharide derivative and the melt molding temperature , and the elongation rate. It consists of a heat-resistant crosslinked product having biodegradability characterized by being 50 to 20% .
The term “integrated” means that at least a part of both components is included as a component of a product insolubilized by crosslinking in a solvent in which both components can be originally dissolved.

Specifically, the heat-resistant crosslinked product of the present invention has a crosslinked structure with a gel fraction (gel content dry weight / initial dry weight) of 50% to 95%.
The gel fraction is measured by wrapping a predetermined amount of a sample sheet in a 200 mesh stainless steel wire net and boiling it in a chloroform solution for 48 hours, and then removing the sol dissolved in chloroform to obtain the remaining gel. Dry at 50 ° C. for 24 hours to remove chloroform in the gel, measure the dry weight of the gel, and calculate the gel fraction by the following formula.
Gel fraction (%) = (gel content dry weight) / (initial dry weight) × 100

  As described above, the heat resistant cross-linked product of the present invention has a main component of a polymer composed of a biodegradable aliphatic polyester having a gel fraction of 50% or more, preferably 65% or more, and the biodegradable aliphatic polyester is hydrophobic. Since it is crosslinked and integrated with the functional polysaccharide derivative to form an infinite number of three-dimensional network structures in the polymer, heat resistance that does not deform even at a temperature higher than the glass transition temperature of the polymer can be imparted. Therefore, it can improve the heat resistance, which was a disadvantage of biodegradable materials, has the same shape retention as conventional resin products made of petroleum synthetic polymers, can be used as an alternative, and has biodegradability. Therefore, the discard processing problem can be solved.

The original object of the present invention is to provide a heat-resistant cross-linked product having biodegradability that has various properties equivalent to those of general-purpose petroleum synthetic polymers and can be substituted for them. Thus, the biodegradable aliphatic polyester Le to be used for purposes of the present invention consists of the polylactic acid or port polybutylene succinate.

Furthermore, the hydrophobic polysaccharide derived material to integrate the crosslinked to the biodegradable aliphatic polyester is subjected to the purpose of the present invention is acetic acid ester starch, a fatty acid ester starch or acetate Sul loin.

The above hydrophobic polysaccharide derivatives can be used alone or in combination of two or more. However, in view of the purpose of mixing with an aliphatic polyester, the degree of substitution of hydroxyl groups is basically 1.5 or more, preferably 1. Derivatives sufficiently substituted with 8 or more, more desirably 2.0 or more, that is, those sufficiently hydrophobized can be suitably used.
The degree of substitution refers to the average value of the number of hydroxyl groups substituted by esterification or the like among the three hydroxyl groups of the polysaccharide in one constituent unit. Therefore, the maximum value of the degree of substitution is 3. The polysaccharide derivative is affected by the functional group introduced by substitution, but generally has a degree of substitution of 1.5 or less and is hydrophilic, and 1.5 or more is hydrophobic.

  Furthermore, as an additive to these, for the purpose of improving flexibility, polyglycolic acid or polyvinyl alcohol as a liquid plasticizer at room temperature such as glycerin, ethylene glycol or triacetylglycerin, or as a solid plasticizer at room temperature It is possible to add other biodegradable fatty acid polyesters such as addition of a biodegradable resin such as, for example, as a plasticizer for adding a small amount of polycaprolactone to polylactic acid. Not required.

A monomer having an allyl group composed of triallyl isocyanurate or trimethallyl isocyanurate is blended in the aliphatic polyester and the hydrophobic polysaccharide as a crosslinking polyfunctional monomer .

  The concentration ratio of the monomer to be added is 0.1% by weight or more with respect to 100% by weight of the fatty acid polyester, and an effect is confirmed. In view of the use as a functional plastic, it is desirable that the biodegradable aliphatic polyester and the hydrophobic polysaccharide derivative, which are surely decomposed, be 99% or more, and therefore the monomer content is in the range of 0.5 to 1% by weight. It is desirable that

The heat-resistant crosslinked product having biodegradability according to the present invention has a melting point of the biodegradable aliphatic polyester and a softening point of the hydrophobic polysaccharide derivative and a substantial melt molding temperature of 150 ° C to 200 ° C, The tensile strength at a high temperature in the vicinity of the temperature is 30 to 70 g / mm ² , the elongation is 50 to 20%, the elongation is small, and the tensile strength is large.
As mentioned above, at high temperatures, it has a low elongation and a high tensile strength, making it difficult to deform, so it has shape retention at high temperatures and improved heat resistance, so it can be widely used as an industrial product. It will be a thing.

  The second aspect of the present invention is a method for producing the heat-resistant crosslinked product of the present invention, wherein three types of biodegradable aliphatic polyester, hydrophobic polysaccharide derivative, and crosslinkable polyfunctional monomer are used as the biodegradable aliphatic. There is provided a method for producing a heat-resistant cross-linked product, characterized in that after mixing uniformly at a temperature equal to or higher than the melting point of polyester, the mixture is irradiated with ionizing radiation.

Specifically, first, both the aliphatic polyester and the hydrophobic polysaccharide derivative are heated to a temperature at which they are melted or softened by heating, or are dissolved and dispersed in a solvent capable of dissolving both chloroform and cresol. State. The monomer is then added thereto and the three components are mixed as uniformly as possible. These three components may be mixed simultaneously, or only two of them may be kneaded in advance for the purpose of sufficiently dispersing and mixing the hydrophobic polysaccharide derivative in two of them, for example, aliphatic polyester.
Next, it is heated and softened or dissolved in a solvent, or once cooled or dried to remove the solvent, it is heated and softened again, pressed, and then rapidly cooled to form a desired shape.
The molded article is irradiated with ionizing radiation to cause a crosslinking reaction.

  As the ionizing radiation to be irradiated, γ rays, X-rays, β rays or α rays can be used. However, for industrial production, γ ray irradiation by cobalt-60 and electron beams by an electron accelerator are preferable. Further, the irradiation dose necessary for generating the crosslinking reaction can be from 1 kGy to 300 kGy, preferably 30 to 100 kGy, and most preferably 30 to 50 kGy.

  In the production method of the present invention, an allyl monomer such as TAIC is used to irradiate ionizing radiation to crosslink and integrate the biodegradable fatty acid polyester and the hydrophobic polysaccharide derivative. It is intended to improve the shape retention at 60 ° C. or higher, which is a drawback.

The relationship between the biodegradable aliphatic polyester, the hydrophobic polysaccharide derivative, and the crosslinked polyfunctional monomer, which are the main components of the heat-resistant crosslinked product of the present invention, can be explained as follows.
When the above three types of kneaded materials are irradiated with ionizing radiation, the biodegradable aliphatic polyester molecules as the main components are kneaded with the hydrophobic polysaccharide derivative by the cross-linked polyfunctional monomer activated by the radiation. A cross-linked structure is formed between these molecules, and also between the biodegradable aliphatic polyester and the hydrophobic polysaccharide derivative molecules, resulting in an infinite number of three-dimensional network structures.
Hydrophobic polysaccharide derivatives can be heated and kneaded by selecting a hydrophobic polysaccharide derivative that softens near the melting point of the biodegradable aliphatic polyester to be integrated, but generally does not have a clear melting point, But it remains very hard. In the case of biodegradable aliphatic polyesters such as polylactic acid that are softened at a temperature above the glass transition temperature of 60 ° C., which is much lower than the melting point near 160 ° C., and lose their shape retention, they have a softening point above 160 ° C. The hydrophobic polysaccharide derivative that is hard and does not deform at temperatures below that effectively imparts a hard property to the entire kneaded product. That is, in the present invention, the hydrophobic polysaccharide derivative is not only kneaded into the biodegradable aliphatic polyester, but is also cross-linked with the cross-linked polyfunctional monomer activated by radiation irradiation. Since it is incorporated in the network structure, heat resistance that is hard above this glass transition temperature and is not easily deformed can be efficiently imparted to the entire polymer comprising biodegradable aliphatic polyester as a main component.

  The hydrophobic polysaccharide derivative to be blended with the biodegradable fatty acid polyester is similar to the method disclosed in the non-patent document in which a mineral filler is reinforced to be hard at high temperatures, but is excellent in the following points. .

  (1) While it is impossible to disperse the mineral filler beyond its original size, the hydrophobic polysaccharide derivative is once melted when mixed by heating or solvent dissolution, so the mixing condition is arbitrary. It is possible to mix with the aliphatic polyester at an arbitrary level from the particle size before mixing to the molecular size.

  (2) There is basically no bond between the mineral filler and the base resin, and the reinforcing effect depends solely on the strength of the filler itself, but the hydrophobic polysaccharide derivative is a base aliphatic polyester crosslinked with the same monomer. Cross-linking also occurs between the two. For this reason, the original hardness of the hydrophobic polysaccharide derivative is improved by its own hardness by cross-linking, the effect of cross-linking integration with the base resin, and by these three, the heat resistance exceeds the single reinforcing effect when viewed as a filler. Strength can be imparted to the base resin.

  (3) When filler is mixed and molded, the filler has a problem that the bleed phenomenon that goes out from the base resin occurs with time. For the same reason as in (2) above, the molecules are uncrosslinked during mixing. Despite being separated and easy to mix, the hydrophobic polysaccharide derivative crosslinks after irradiation and does not bleed at all because it is integrated with each other or with the aliphatic polyester to increase the molecular weight.

  (4) Mineral filler, for example, loses the transparency of polylactic acid and the gloss of the resin surface due to its mixing, and gives a rough texture. In the present invention, although the transparency is somewhat lost depending on the mixing condition, it is slight. And the surface texture is not impaired.

  (5) In terms of workability, the high temperature maintenance time for increasing the degree of crystallinity has been successfully shortened by a method using a nano-sized mineral filler. unnecessary. Therefore, the manufacturing time can be greatly shortened.

When using a chemical initiator instead of radiation to generate a crosslinking reaction, add a monomer having an allyl group and a chemical initiator at a temperature equal to or higher than the melting point of the biodegradable aliphatic polyester, knead well, and uniformly After mixing, the molded article made of this mixture is raised to a temperature at which the chemical initiator is thermally decomposed.
Chemical initiators that can be used in the present invention are dicumyl peroxide, propionitrile peroxide, pensoyl peroxide, di-t-butyl peroxide, diacyl peroxide, and verargonyl peroxide that generate peroxide radicals by thermal decomposition. , Peroxide catalyst such as myristoyl peroxide, t-butyl perbenzoate, 2,2′-azobisisobutylnitrile, or any other catalyst that initiates polymerization of monomers. The bridging action is preferably performed in an inert atmosphere or air, excluding air, as in the case of radiation irradiation.

As described above, the heat-resistant crosslinked product of the present invention can improve the shape retention of a biodegradable aliphatic polyester, particularly polylactic acid, at 60 ° C. or higher. Further, since the hydrophobic polysaccharide derivative blended in the polylactic acid for maintaining the strength at high temperature is used, the transparency and surface gloss of the polylactic acid generated when using the mineral filler are not greatly impaired. Moreover, although it is necessary to raise the set temperature to some extent in industrial production, it is possible to produce without lowering the productivity with conventional injection molding equipment.
In addition, since hydrophobic polysaccharide derivatives are also biodegradable, they have little impact on ecosystems in nature, and are expected to be used as alternative materials for plastic products in general that are manufactured and discarded in large quantities. In addition, since it does not affect the living body, it is a material suitable for application to medical instruments used inside and outside the living body.

Embodiments of the present invention will be described below.
The heat-resistant crosslinked product of the embodiment uses polylactic acid as a biodegradable aliphatic polyester, and uses acetic ester starch as a hydrophobic polysaccharide derivative in the polylactic acid. Furthermore, it consists of the composition which mix | blended 0.5 to 3 weight% with respect to 100 weight% of polylactic acid, using TAIC as a bridge | crosslinking type polyfunctional monomer.
The above three types are mixed, the mixture is formed into a sheet by injection molding, ionizing radiation is irradiated to the sheet at 30 to 100 kGy, crosslinking is promoted by TAIC, and polylactic acid and acetate ester starch are integrated by crosslinking. ing.

The heat-resistant crosslinked product has a crosslinked structure having a gel fraction of 50 to 95%, has a melting point of the biodegradable aliphatic polyester or higher, a softening point or higher of the hydrophobic polysaccharide derivative, and a substantial melt molding temperature of 150 ° C. The tensile strength is 30 to 70 g / mm ² and the elongation is 50 to 20% at a high temperature around −200 ° C. or lower. Therefore, in a high temperature environment, the elongation is reduced and the tensile strength is increased, and the shape retention force is increased.

  The present invention is not limited to the above-described embodiment, and the electron beam irradiation can be performed by changing the type of raw material of the biodegradable material, the type and amount of the hydrophobic polysaccharide derivative, the type and amount of the crosslinked polyfunctional monomer. The crosslinking structure (gel fraction) can be changed within the scope of the present invention by the amount and irradiation of the electron beam.

Example 1
As the aliphatic polyester, finely powdered polylactic acid (Lacia H-100J manufactured by Mitsui Chemicals) was used. Moreover, the powder of acetate ester starch (CP-1 by Nippon Corn Starch) was used as a hydrophobic polysaccharide derivative.
The polysaccharide derivative has a hydroxyl group substitution degree of about 2.0, is insoluble in water but dissolves in acetone, and is completely hydrophobic. Moreover, although it softens at 180 degreeC or more, it does not have clear melting point, but is resin with very high Young's modulus.

5 parts by weight of acetic ester starch was previously mixed with 100% by weight of polylactic acid. This mixture was melted at 190 ° C. in a substantially closed kneader Laboplast Mill, and sufficiently melt-kneaded until it became transparent. During this mixing, 3% by weight of TAIC (Nippon Kasei Co., Ltd.), which is one of allyl monomers, is added to the total of polylactic acid and acetate ester starch, and kneaded well for 10 minutes at a rotation speed of 20 rpm. did.
Thereafter, this kneaded product was subjected to hot pressing at 190 ° C., and then rapidly cooled at 100 ° C./min to normal temperature to produce a 1 mm thick sheet. This sheet was irradiated with an electron beam at 5 to 100 kGy by an electron accelerator (acceleration voltage 2 MeV, current amount 1 mA) under an inert atmosphere excluding air, and the obtained radiation cross-linked product was taken as Example 1.

(Examples 2 and 3)
The ratio of TAIC to aliphatic polyester and hydrophobic polysaccharide derivative was 10% by weight in Example 2 and 30% by weight in Example 3. The rest was the same as in Example 1.
(Example 4)
Example 4 uses cellulose diacetate having a substitution degree of about 2 as a hydrophobic polysaccharide derivative (manufactured by Daicel Corporation, cellulose acetate L-30), and the ratio of the hydrophobic polysaccharide derivative to the aliphatic polyester is 10% by weight. It was. The rest was the same as in Example 2.
(Example 5)
In Example 5, as the hydrophobic polysaccharide derivative, cellulose diacetate having the same substitution degree of about 2 as in Example 2 was used, and the ratio of the hydrophobic polysaccharide derivative to the aliphatic polyester was 30% by weight. Except this, it was the same as Example 3.
Except this, Example 4 and Example 5 were made in the same manner as Example 2 and 3, respectively.
(Example 6)
Polybutylene succinate (Bionor # 1020, Showa High Polymer) was used as the aliphatic polyester, and fatty acid ester starch (CP-5, Nippon Corn Starch) was used as the hydrophobic polysaccharide derivative. The fatty acid ester starch has a degree of substitution of about 2 and an average fatty acid length of about 10 fatty acids.
As in Example 3, the ratio of TAIC to the aliphatic polyester and the hydrophobic polysaccharide derivative was 3% by weight.
The aliphatic polyester and the hydrophobic polysaccharide derivative were kneaded at a softening temperature of 150 ° C. and pressed at 150 ° C. to obtain a sheet.

(Comparative Examples 1-6)
Except not performing electron beam irradiation, it was set as Comparative Examples 1-6 similarly to Examples 1-6, respectively.
(Comparative Example 7)
Comparative Example 7 was made in the same manner as in Example 1 except that only the polylactic acid was used as a raw material without kneading the hydrophobic polysaccharide derivative and the monomer.
(Comparative Example 8)
A comparative example 8 was obtained by using only the hydrophobic polysaccharide derivative.
(Comparative Example 9)
Example 3 was repeated except that 3% by weight of TMPT was used instead of TAIC.
(Comparative Example 10)
The procedure was the same as Example 6 except that no cross-linked multifunctional monomer was used.

  The differences between the above Examples 1 to 6 and Comparative Examples 1 to 10 are summarized in Table 1.

  In the table, ○ indicates that there was no change before and after the test, Δ indicates that there was some change such as bending, and × indicates that the shape was not completely collapsed and could not be maintained.

  About the above Examples 1-6 and Comparative Examples 1-10, in order to evaluate the heat resistant improvement effect in the temperature more than a glass transition point, the shape retainability in 80 degreeC and 150 degreeC was evaluated. Evaluation was performed on samples of electron beam irradiation amount of 50 kGy of each example and comparative example. The results are shown in Table 1.

Further, for the purpose of evaluating the degree of cross-linking of molecules by irradiation, the relationship between the irradiation amount and the gel fraction of the samples of each Example and Comparative Example was measured. The result is shown in FIG.
Furthermore, in order to see the improvement effect of the Young's modulus above the glass transition point, the strength elongation curve in a 100 ° C. tensile test was measured for the samples of Examples 1 to 3 and Comparative Examples 7 to 8 with an electron beam irradiation amount of 50 kGy, The result is shown in FIG.

  The evaluation methods for each evaluation are as follows.

(1) Shape retention evaluation Each sheet of each example and comparative example was cut into a rectangular shape having a length of 10 cm and a width of 1 cm, and the width was 1 mm equal to the thickness of the sheet and the depth was 1 cm. Stand in the groove almost vertically so that the long side of the sample is up and down. This was put into a constant temperature bath at 80 ° C. and evaluated whether or not the sample was self-supporting after 1 hour. Evaluation was also performed at 150 ° C. in addition to 80 ° C.

(2) Gel fraction evaluation The gel fraction measurement method described above is the same method, that is, a predetermined amount of each sheet is wrapped in a 200 mesh stainless steel wire, boiled in chloroform solution for 48 hours, and then dissolved in chloroform. The remaining sol content is obtained by removing the sol content. Dry at 50 ° C. for 24 hours to remove chloroform in the gel, measure the dry weight of the gel, and calculate the gel fraction by the following formula.
Gel fraction (%) = (gel content dry weight) / (initial dry weight) × 100

(3) Evaluation of high-temperature tensile test After molding a sample into a rectangle with a width of 1 cm and a length of 10 cm, the sample was pulled in a 100 ° C constant temperature bath at 2 cm between chucks and at a tensile rate of 10 mm / min. Was measured. The measurement was performed after the sample reached the same temperature in the thermostat.

(Evaluation results of Examples and Comparative Examples)
Regarding shape retention, as shown in Table 1, at 80 ° C., which exceeds 60 ° C., which is the glass transition point of polylactic acid, all of Examples 1 to 6 and Comparative Examples 8 to 10 were subjected to before and after heating. However, in Comparative Examples 1 to 7, the shape could not be maintained, for example, the sheet melted and fell down. Furthermore, at 150 ° C. near the melting point, only in Example 1 the sheet was bent and the shape was changed, but the other Examples 2 to 6 showed good shape retention.

As for the gel fraction, as shown in FIG. 1, in Examples 1 to 6, crosslinking proceeds by electron beam irradiation, and the mixed aliphatic polyester, hydrophobic polysaccharide derivative, and crosslinked polyfunctional monomer are integrated. The peak reached 68-95%. Examples 1 to 3 reached a peak at an irradiation dose of about 50 kGy, and Examples 4, 5, and 6 reached a peak at 100 kGy. When the irradiation amount exceeded 100 kGy, in particular, in the case of blending polylactic acid having electron beam decomposability, the decomposition started and the gel fraction tended to decrease.
Also in the comparative example, the comparative example 8 which mix | blended polylactic acid and TAIC crosslinked like the Example. In Comparative Example 9, it was found that TMPT caused crosslinking by heat during production, lost the crosslinking function when irradiated with an electron beam, and decomposed even when irradiated.

Regarding the tensile strength and elongation at high temperatures, as shown in FIG. 2, under the measurement condition of 100 ° C., in Comparative Example 7 using only polylactic acid, there is almost no tensile strength, but it can be extended as much as possible. Comparative Example 8, which was crosslinked with TAIC, showed some tensile strength, but was not sufficient.
On the other hand, in Examples 1 to 3, the tensile strength is 30 to 70 g / mm ² , the elongation is about 20 to 50%, the tensile strength increases as the blending amount of the hydrophobic polysaccharide derivative increases, and the elongation increases. A decrease was observed, that is, it was observed that the Young's modulus increased and the shape retention increased.

From the evaluation of the above examples and comparative examples, the polylactic acid has a Young's modulus drastically reduced at 60 ° C. or higher, and the material becomes extremely soft, so that it is difficult to maintain the shape. It was confirmed that the shape retention was slightly increased by crosslinking by addition of a monomer such as TAIC, but it was insufficient.
In addition, the hydrophobic polysaccharide derivatives acetate starch and cellulose acetate cellulose are similarly crosslinked by TAIC and exhibit a very high Young's modulus even above the glass transition point of polylactic acid. These did not show a clear melting point even near the melting point of polylactic acid, and it was confirmed that the Young's modulus did not decrease so much.

It is a graph which shows the relationship between electron beam irradiation amount and a gel fraction about Examples 1-6 of this invention and Comparative Examples 1-10. It is a graph which shows the relationship between tensile strength and elongation by the tension test in 100 degreeC about Examples 1-3 of this invention and Comparative Examples 7-8.

Claims (6)

A molded product composed of a mixture of a biodegradable aliphatic polyester, a hydrophobic polysaccharide derivative and a crosslinkable polyfunctional monomer is cross-linked and integrated by irradiation with ionizing radiation.
The biodegradable aliphatic polyester is composed of polylactic acid or polybutylene succinate,
The hydrophobic polysaccharide derivative comprises acetate ester starch, fatty acid ester starch or acetate ester cellulose,
The cross-linked polyfunctional monomer is a monomer having an allyl group composed of triallyl isocyanurate or trimethallyl isocyanurate ,
The tensile strength is 30 to 70 g / mm ² at a high temperature of 150 ° C. or more and 200 ° C. or less which is the melting point of the biodegradable aliphatic polyester and the softening point of the hydrophobic polysaccharide derivative and the melt molding temperature , and the elongation rate. A heat-resistant crosslinked product having biodegradability characterized by being 50 to 20% .   The heat-resistant crosslinked product having biodegradability according to claim 1, which has a crosslinked structure with a gel fraction (gel content dry weight / initial dry weight) of 50% to 95%.   The hydrophobic polysaccharide derivative is a derivative having a hydroxyl group substitution degree of 2.0 or more and 3.0 or less, and the hydrophobic polysaccharide derivative is 5% by weight to 30% with respect to 100 parts by weight of the biodegradable aliphatic polyester. The heat-resistant crosslinked product having biodegradability according to claim 1 or 2, which is blended in an amount of not more than% by weight. The said bridge | crosslinking type polyfunctional monomer is 0.5 weight% or more and 3 weight% or less with respect to 100 weight% of biodegradable aliphatic polyester, The description of any one of Claim 1 thru | or 3 A heat-resistant crosslinked product with biodegradability. A method for producing a heat-resistant crosslinked product having biodegradability according to any one of claims 1 to 4,
After mixing the biodegradable aliphatic polyester, the hydrophobic polysaccharide derivative, and the crosslinkable polyfunctional monomer at a temperature equal to or higher than the melting point of the biodegradable aliphatic polyester, the mixture is molded and the molded article is formed. A method for producing a heat-resistant crosslinked product having biodegradability, characterized by irradiating ionizing radiation. After blending 5 to 30% by weight of the hydrophobic polysaccharide derivative and 0.5 to 3% by weight of the crosslinked polyfunctional monomer with respect to 100% by weight of the biodegradable aliphatic polyester, The method for producing a heat-resistant crosslinked product having biodegradability according to claim 5, wherein the mixture is molded, and the molded product is irradiated with ionizing radiation at 30 to 100 kGy .

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