JP2008308571A - Method for producing biodegradable aromatic polyester of which biodegradability is controlled - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve biodegradability of biodegradable aromatic polyester represented by a polyethylene terephthalate-adipate copolymer. <P>SOLUTION: An ionization radiation is irradiated to the polyethylene terephthalate-adipate copolymer, and molecular structure is made to cause decomposition reaction prior to crosslinking reaction. More concretely, in vacuum, the ionization radiation is irradiated to the polyethylene terephthalate-adipate copolymer, and the molecular structure is made to cause decomposition reaction, and thus, the biodegradable aromatic polyester is produced. Alternatively, in the air, γ ray is irradiated to the polyethylene terephthalate-adipate copolymer, and the molecular structure is made to cause decomposition reaction, and thus, the biodegradable aromatic polyester is produced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an aromatic polyester having a high level of biodegradability that is environmentally friendly and does not cause semi-permanent accumulation in soil or the ocean.

  Currently produced petroleum synthetic plastics are indispensable materials in our daily life. On the other hand, it has a demerit that directly leads to environmental problems, such as its semi-permanent accumulation in the soil and ocean due to its stable and difficult to decompose nature. Against this background, biodegradable plastics have been developed and put to practical use as environmentally friendly materials. Biodegradable plastics have been researched and developed mainly for aliphatic polyesters, but recently, biodegradable aromatic polyesters mainly composed of terephthalic acid, which is the raw material of polyethylene terephthalate, have been developed. As representative biodegradable aromatic polyesters, polyethylene terephthalate adipate copolymer (trade name: Biomax (registered trademark), manufactured by Du Pont), polybutylene terephthalate adipate copolymer (trade name: Eco) Flex (registered trademark), manufactured by BASF). Among them, the polyethylene terephthalate / adipate copolymer is thermally stable because it has an aromatic ring, and has excellent heat resistance (melting point 200 ° C.) and durability.

“Biodegradable Aromatic Polyester: About Biomax” Monthly Eco-Industry, 12 pages, written by Shuji Sakai, September 25, 2003

  Polyethylene terephthalate / adipate copolymer with polyethylene terephthalate as the basic skeleton and biodegradability in its molecular structure has excellent heat resistance and durability. It is expected as a next-generation degradable material that combines strength. However, since the polyethylene terephthalate-adipate copolymer has an aromatic ring, the biodegradation rate is slower than that of the aliphatic polyester, and control of biodegradability is an important technical issue.

  So far, regarding the biodegradability control of biodegradable aliphatic polyester, it has been shown that a decomposition reaction or a crosslinking reaction by irradiation is effective. In other words, it has been found that biodegradability is improved by the degradation reaction due to radiation irradiation, and that biodegradability is reduced by the cross-linking reaction due to the presence of cross-linked sites, making it difficult for the enzyme to penetrate into the sample. We have already publicly reported that degradability can be controlled freely both in Japan and overseas. This method is effective as a method that does not require an additive or an initiator and that does not select the shape and size of a material to be processed such as liquid or solid. However, the control of biodegradability of aromatic polyesters by irradiation is still unsolved, and there are no published documents. In addition, the irradiation behavior of aromatic polyester is completely unknown.

  Accordingly, an object of the present invention is to provide a method for producing a biodegradable aromatic polyester having excellent biodegradability and controlled biodegradability. More specifically, it is to further improve the biodegradability of a biodegradable aromatic polyester represented by a polyethylene terephthalate adipate copolymer (Biomax (registered trademark), manufactured by Du Pont).

  In order to achieve the above object, the radiation irradiation behavior of the polyethylene terephthalate / adipate copolymer was examined in detail, and the biodegradability of the irradiated polyethylene terephthalate / adipate copolymer was evaluated. As a result, it was confirmed that when the polyethylene terephthalate / adipate copolymer was irradiated with ionizing radiation, the decomposition reaction occurred in preference to the crosslinking reaction in the molecular structure. Therefore, the method for producing the biodegradable aromatic polyester of the present invention is to cause the molecular structure to undergo a decomposition reaction by irradiating the polyethylene terephthalate-adipate copolymer with ionizing radiation.

  In a more preferable method, the above-described decomposition reaction is caused by irradiating the polyethylene terephthalate / adipate copolymer with an electron beam or by irradiating the polyethylene terephthalate / adipate copolymer with γ rays. A biodegradable aromatic polyester is produced. In an even more preferred method, a biodegradable aromatic polyester is produced by irradiating a polyethylene terephthalate / adipate copolymer with γ rays in the air accompanied by an oxidative decomposition reaction.

  According to the present invention, a biodegradable aromatic polyester, for example, a biodegradable aromatic polyester that is much more biodegradable than before without deteriorating the inherent properties of a polyethylene terephthalate-adipate copolymer. Can do.

A preferred embodiment of the present invention will be described with reference to FIGS.
Before describing specific examples, the contents of samples and reagents used in the examples, the method of radiation irradiation, and the method of measuring the sample after irradiation will be described.
(1) Samples and reagents

Polyethylene terephthalate-adipate copolymer was produced by using Biomax (registered trademark) (WA101A type) provided by DuPont Co., Ltd., using a hot press machine (Ikeda Machine Industry Co., Ltd.). A strip (20 × 150 × 0.5 mm) was used. Moreover, m-cresol [Wako Pure Chemical Industries, Ltd.] for dissolving the polyethylene terephthalate / adipate copolymer used a commercial product as it was.
(2) Radiation irradiation

  When the polyethylene terephthalate / adipate copolymer was irradiated with an electron beam, four polyethylene terephthalate / adipate copolymer films (20 × 150 × 0.5 mm) were placed in a polyethylene / nylon bag, degassed and heat-sealed. The sample is then irradiated with an electron beam (maximum acceleration voltage: 2 MeV, current: 2 mA) at room temperature (25 ° C) at a predetermined dose (100, 200, 500, 700, 1000 kGy) using a Cockcroft-Walton electron accelerator. did.

On the other hand, γ-ray irradiation is performed at room temperature in vacuum and in air, and in the same way as in the case of electron beam irradiation, four films (20 × 150 × 0.5 mm) are placed in a polyethylene / nylon bag, After degassing, γ-rays (dose rate: 10 kGy / h) with Co-60 as a radiation source were irradiated at 200 kGy in the 6th cell of Cobalt 2nd irradiation building of the same laboratory. In air, the film was irradiated with gamma rays (dose rate 10 kGy / h) at a predetermined dose (100, 200, 500, 900 kGy).
(3) Measurement

The viscosity of the irradiated polyethylene terephthalate / adipate copolymer was measured using an Ostwald viscometer at a concentration of 0.5 g / dL and 30 ° C. using m-cresol as a solvent. Differential scanning calorimetry (DSC) [manufactured by Shimadzu Corporation, DSC-60] was performed with the following temperature program. Under a nitrogen atmosphere, the sample was first heated from 30 ° C. to 250 ° C. at 10 ° C./min and held for 5 minutes, then cooled to 30 ° C. at 20 ° C./min and held for 20 minutes. Thereafter, the process was again heated from 30 ° C to 250 ° C at 10 ° C / min, and this process was observed. Thermogravimetric analysis (TGA) [manufactured by Shimadzu Corp., TGA-60] was carried out under a nitrogen atmosphere at a heating rate of 10 ° C./min, and a 10% weight loss temperature (T _d10 ) was measured.
(4) Biodegradability test

LB medium with pH 7.5 [NaCl 5.0 g / L, Yeast Extract 5.0 g / L, Polypepton 10 using 0.6 g of soil in Takasaki City, Gunma Prefecture and 3 g of swine manure as the microbial inoculum. 0 g / L)], a polyethylene terephthalate / adipate copolymer film (10 × 10 × 0.5 mm) was placed and shaken at 50 ° C. for 14 to 28 days. The decomposed film was washed with methanol and distilled water and freeze-dried. The weight reduction rate was calculated by subtracting the weight of the film after decomposition from the initial weight of the film. In addition, as a control experiment, a non-microorganism intake was treated in the same manner.
(5) Observation with a scanning electron microscope (SEM)

The polyethylene terephthalate / adipate copolymer film surface before and after biodegradation was vapor-deposited in vacuum using an ion sputtering device (JEOL, Quick auto coater JFC-1500), and the sample surface was SEM (JEOL, JSM- 6700FS) and observed at an acceleration voltage of 20 kV.
(Concrete example)
1. Irradiation behavior of polyethylene terephthalate-adipate copolymer

  The polyethylene terephthalate / adipate copolymer prepared as described above was irradiated with an electron beam or γ-ray. The sample thus obtained was dissolved in m-cresol and the viscosity was measured. FIG. 1 shows the intrinsic viscosity (ηinh (g / dL)) of the irradiated sample. As a result, the viscosity of the polymer decreased as the absorbed dose of the electron beam increased. On the other hand, when γ-rays were irradiated in the air, a large decrease in viscosity was observed compared to the case in vacuum. Therefore, it was revealed that the decomposition reaction proceeds by irradiating the polyethylene terephthalate / adipate copolymer with radiation.

The difference in the degree of decomposition between the sample irradiated in vacuum and air is considered to be related to the oxidative decomposition reaction by oxygen in the air. Moreover, the number of methylene chains in the glycol part is cited as the reason why the decomposition reaction preferentially progresses upon irradiation of the polyethylene terephthalate / adipate copolymer. Since the number of methylene chains, which are sites where active species (radicals) can be formed, is as small as two, it is considered that the decomposition reaction proceeded preferentially.
2. Thermal properties of irradiated polyethylene terephthalate-adipate copolymer.

  DSC measurement was performed to evaluate the thermal properties of the irradiated polyethylene terephthalate-adipate copolymer. As a result, it was confirmed that the melting point (Tm) and heat of fusion (ΔHm) decreased as the irradiation dose increased. The sample irradiated in air tended to have a lower melting point and heat of fusion than the sample irradiated in vacuum. From these facts, it can be seen that the decomposition reaction due to irradiation reduces the crystallinity of the polyethylene terephthalate-adipate copolymer.

In order to confirm the effect of the degradation reaction of polyethylene terephthalate-adipate copolymer upon irradiation on the thermal stability of polyethylene terephthalate-adipate copolymer, the temperature when pyrolysis was performed by 10% by thermogravimetric analysis (TGA) measurement. (T _d10 ) was _calculated and T _d10 was the same at 418 ° C for both unirradiated polyethylene terephthalate / adipate copolymer and irradiated sample. It can be seen that the sex is maintained.
3. Biodegradability test of irradiated polyethylene terephthalate-adipate copolymer

From the above results, it was found that the molecular weight and crystallinity were reduced by irradiating the polyethylene terephthalate / adipate copolymer with radiation. This suggests an improvement in the flexibility of the polyethylene terephthalate / adipate copolymer by irradiation, and an improvement in biodegradability can be expected. Biodegradability tests of polyethylene terephthalate / adipate copolymer (0, 200, 900 kGy) irradiated with γ-rays in air were conducted for 14 to 28 days using soil and swine feces in Takasaki City, Gunma Prefecture as a microbial inoculum. As can be seen in FIG. 2, the weight reduction rate of the unirradiated polyethylene terephthalate-adipate copolymer was less than 1%, whereas the weight reduction rate due to biodegradation increased as the absorbed dose increased, The kGy-irradiated polyethylene terephthalate-adipate copolymer showed a maximum weight loss rate of 8.3% in 28 days. From these results, it was clarified that the biodegradability is improved by irradiating the polyethylene terephthalate / adipate copolymer with radiation.
4). Observation of sample surface by SEM

  The film surface of the sample before decomposition and 28 days after decomposition was observed by SEM. It was observed that the surface of the film before decomposition was relatively smooth, but the surface became rough as the irradiation dose increased and eroded to the inside of the film. This result also supported that the biodegradability increased as the irradiation dose increased, and it was found that the degradation progressed from the film surface in all cases.

  As a result of detailed examination of the radiation irradiation behavior of the polyethylene terephthalate-adipate copolymer, it was found that the decomposition reaction proceeded preferentially, and it was found that the degree of decomposition improved as the irradiation dose increased. It was also found that the oxidative decomposition reaction by oxygen in the air is accelerated when the irradiation is performed in the air rather than the irradiation in the vacuum. As a result of evaluating the thermal properties of the irradiated polyethylene terephthalate-adipate copolymer by DSC measurement, it was confirmed that the crystallinity decreased as the irradiation dose increased. Furthermore, the results of the biodegradability test of irradiated polyethylene terephthalate-adipate copolymer show that biodegradability improves as the irradiation dose increases, and the biodegradability is improved by irradiating the polyethylene terephthalate-adipate copolymer with radiation. It became clear that degradability could be controlled.

  The biodegradable aromatic polyester whose biodegradability can be controlled as described above can be used in a wide range of fields such as industrial, agricultural, medical and food. Examples thereof are given below, but are not limited thereto. The biodegradable aromatic polyester produced by the production method according to the present invention is an environmentally friendly material that is extremely excellent in biodegradability. Currently, the materials used for agricultural multi-film are petroleum-synthetic vinyl chloride materials that are not biodegradable and are incinerated by individual treatment, but the biodegradable aromatics produced by the present invention By using polyester for them, it becomes possible to dispose of them directly in the soil without incineration.

It is a figure which shows the intrinsic viscosity of the polyethylene-terephthalate-adipate copolymer sample irradiated with the electron beam in vacuum, and the intrinsic viscosity of the polyethylene-terephthalate-adipate copolymer sample irradiated with the gamma ray in the vacuum and air. . It is a figure which shows the result of the biodegradability test of the polyethylene terephthalate adipate copolymer irradiated with the gamma ray in the air.

Explanation of symbols

Dose absorbed dose
Weight loss Weight loss

Claims (2)

  A method for producing a biodegradable aromatic polyester with controlled biodegradability by irradiating an aromatic biodegradable polyester with ionizing radiation to cause a decomposition reaction accompanied by molecular chain breakage.   The method for producing a biodegradable aromatic polyester with controlled biodegradability, wherein the decomposition reaction is caused to occur in air.

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