Starch composite material

Abstract

To provide a starch composite material capable of kneading at low temperature and having high biodegradability.SOLUTION: A starch composite material contains low crystalline starch and glycerin.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to starch composite materials. [Background technology]

[0002] In recent years, mass production and mass consumption of plastics have become a problem. Since plastics do not decompose in the natural world, if they drift in the ocean, they turn into microplastics, becoming unrecoverable man-made objects and polluting the environment. Therefore, biodegradable resins that are highly biodegradable and decompose under natural conditions have been proposed. Patent Document 1 discloses a resin composition containing starch, glycerin, and a thermoplastic resin that is a biodegradable resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2009-120651 Summary of the Invention [Problem to be solved by the invention]

[0004] Starch, glycerin, and a thermoplastic resin are kneaded while being heated, and then molded by any known technique (e.g., extrusion molding) to produce a resin composition. In the technique of Patent Document 1, the heating temperature when kneading starch, glycerin, and a thermoplastic resin is high, ranging from 100°C to 200°C. Kneading at high temperatures causes thermal degradation of starch, which causes the resin composition to become brittle. The present invention has been made in view of the above circumstances, and aims to provide a starch composite material that can be kneaded at low temperatures and is highly biodegradable. [Means for solving the problem]

[0005] In order to solve the above problems, the starch composite material of the present invention comprises low-crystalline starch and glycerin. Effect of the Invention

[0006] According to the present invention, it is possible to provide a starch composite material which can be kneaded at a low temperature and has high biodegradability. [Brief description of the drawings]

[0007] [Figure 1] 13 is a table showing evaluation results of properties according to comparative examples. [Diagram 2] FIG. 13 is a diagram showing evaluation results of properties according to an embodiment. [Diagram 3] 13 is a SEM image of a comparative example after kneading and an example after kneading. [Figure 4] 1 shows the results of wide-angle X-ray diffraction measurement of CS alone and a comparative example after molding. [Diagram 5] 1 shows the results of wide-angle X-ray diffraction measurement of the ACS alone and the example after molding. [Figure 6] FIG. 1 is a schematic diagram showing the composite of starch and glycerin. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The starch composite material of the present invention is a composite material of low crystalline starch (gelatinized starch) and glycerin. The starch composite material of the present invention is highly biodegradable and is used for various applications such as food packaging, agricultural films, and cushioning materials. For example, the starch composite material of the present invention is used as a master batch in resin molding.

[0009] The low-crystalline starch used in the present invention is a starch having a lower degree of crystallinity than crystalline starch (beta-starch). The degree of crystallinity of the low-crystalline starch is, for example, 20% or less, and preferably 10% or less.

[0010] Low crystalline starch is produced from raw materials such as plants, such as cereals and pseudocereals, whose main component is starch. Examples of raw materials include plants such as rice, potato, wheat, soybean, red bean, buckwheat, potatoes, beans, and corn. Crystalline starch produced from these plants may also be used as the raw material. For example, tapioca produced from cassava rhizomes may also be used as the raw material. The type of low crystalline starch of the present invention is appropriately changed depending on the type of raw material. For example, low crystalline starch includes one or both of amylose and amylopectin.

[0011] The low-crystalline starch may be produced by any known method, for example, the method proposed in Japanese Patent No. 4767128, Japanese Patent No. 5503885, or Japanese Unexamined Patent Publication No. 2009-213472.

[0012] Specifically, the above-mentioned raw materials are fed into a mortar-type grinder, and the raw materials are pulverized under shearing conditions while being heated at 80°C or higher (e.g., 100 to 200°C), to produce low-crystalline starch. That is, low-crystalline starch is produced by simultaneously carrying out heating and shearing. Therefore, low-crystalline starch can be produced instantaneously. The above-mentioned production method has the advantage that low-crystalline starch with a high degree of low crystallinity can be easily produced without adding water. The low-crystalline starch produced by the above-mentioned method is contained in the starch composite material.

[0013] The crystallinity of the low crystalline starch can be appropriately controlled according to the grinding conditions in the above manufacturing method. The crystallinity of the starch is calculated by any known technique. For example, the crystallinity of the starch is determined according to the result of X-ray diffraction intensity. Specifically, a peak representing an amorphous portion and a peak representing a crystalline portion are extracted from the result of X-ray diffraction intensity. A known peak separation technique is used arbitrarily to extract each peak. Although multiple peaks representing a crystalline portion can be extracted, only multiple peaks whose peak values ​​exceed a predetermined value are used to determine the crystallinity. The crystallinity is determined from the ratio of the peak representing the amorphous portion to the peak representing the crystalline portion. For example, the crystallinity is calculated by inserting the area A of the peak representing the crystalline portion (the total area of ​​multiple peaks) and the area B of the peak representing the amorphous portion into the following formula (1). Crystallinity (%) = 100 x Area A / (Area A + Area B)…(1) The peak angle used in formula (1) is adjusted appropriately depending on the raw material and the grinding method used when grinding the raw material.

[0014] The mass ratio of the low crystalline starch to the total mass of the low crystalline starch and glycerin is, for example, 50 to 95 mass%, and preferably 60 to 80 mass%. According to the above configuration, a starch composite material having high biodegradability and excellent moldability can be provided.

[0015] The starch composite material of the present invention is produced by kneading low crystalline starch and glycerin while heating. The temperature when kneading low crystalline starch and glycerin is, for example, 30°C to 200°C. Therefore, the thermal deterioration of the low crystalline starch is suppressed, and it becomes possible to produce a strong starch composite material. The composite material may be molded into a molded product by any known method such as extrusion molding, blow molding, or injection molding.

[0016] In addition to the low crystalline starch and glycerin, other materials may be contained in the starch composite material. For example, the starch composite material may contain a thermoplastic resin. As the thermoplastic resin, an olefin resin such as polyethylene or polypropylene is used. As the thermoplastic resin, a biodegradable thermoplastic resin having biodegradability is also considered. As the biodegradable thermoplastic resin, for example, an aliphatic polyester, polylactic acid, polyvinyl alcohol, polycaprolactone, acetyl cellulose, or polyhydroxybutyrate-valerate copolymer is used. By containing a biodegradable thermoplastic resin in the starch composite material, a starch composite material with high biodegradability can be provided. In addition, the starch composite material containing a biodegradable thermoplastic resin is suitably used for various products such as films and sheets. In addition, a compatibilizer, a surfactant, etc. may be contained in the starch composite material.

[0017] When the starch composite material is molded into a body, wide-angle X-ray diffraction shows a peak in the diffraction angle (2θ) range of 20 degrees to 22 degrees, and no peak is shown in the range exceeding 22 degrees. However, depending on the material contained in the starch composite material, a peak may be shown in the range exceeding 22 degrees. The measurement conditions for wide-angle X-ray diffraction will be described later. EXAMPLES

[0018] Examples of the present invention will be described in detail below, although the present invention is not limited to the following examples.

[0019] Various evaluations were performed on the sample of Comparative Example 1-2 and the sample of Example 1-3 (starch composite material). In the following description, crystalline cornstarch is abbreviated as "CS", low crystalline cornstarch is abbreviated as "ACS", and refined glycerin is abbreviated as "Gly". CS is a type of crystalline starch, ACS is a type of low crystalline starch, and Gly is a type of glycerin.

[0020] The materials contained in the sample of Comparative Example 1-2 and the sample of Example 1-3 are as follows. Materials for Comparative Example 1-2: CS (manufactured by Showa Sangyo Co., Ltd.), Gly (manufactured by Kao Corporation) Materials for Examples 1-3: ACS (prepared by pulverizing the same CS as in Comparative Example 1 using a heat shear type mortar-type pulverizer), Gly (manufactured by Kao Corporation)

[0021] Table 1 shows the property evaluation of CS and ACS. [Table 1] As shown in Table 1, the degree of crystallinity of ASC prepared by crushing CS is significantly lower than that of CS. The degree of crystallinity was calculated using the method described above.

[0022] The above materials were mixed to prepare a sample of Comparative Example 1-2 and a sample of Example 1-3. Specifically, Gly was mixed with CS and ASC using Labo Plastomill 10c100-01 (manufactured by Toyo Seiki Seisakusho). The amount of Gly added was 25 wt%, and the rotation speed of the Labo Plastomill was 40 rpm. The mixing temperatures used to prepare Examples 1-2 and 1-3 were as follows: Comparative Example 1: 90°C Comparative Example 2: 100°C Example 1: 50°C Example 2: 90°C Example 3: 100°C

[0023] Next, the samples (samples after kneading) of Comparative Example 1-2 and Example 1-3 were each molded into a molded body. Comparative Example 1-2 and Example 1-3 were molded into a molded body by using a hot press heating machine mini TEST PRESS10 (manufactured by Toyo Seiki Seisakusho). The molding pressure was 15 MPa, and the molding time was 10 minutes. The molding temperature was the same as the kneading temperature.

[0024] FIG. 1 shows the evaluation results of the properties of Comparative Example 1-2 after kneading and after molding. The sample of Comparative Example 2 after kneading was composited, so it was possible to mold it into a molded body. On the other hand, the sample of Comparative Example 1 after kneading was not composited and was in a powder form, so it was not possible to mold it into a molded body.

[0025] FIG. 2 shows the evaluation results of the properties after kneading and after molding for Examples 1-3. In all of Examples 1-3, Gly and ASC were complexed after kneading. Therefore, the samples of Examples 1-3 could be molded into molded bodies. In particular, it was found that complexation was possible not only in Example 2, where the kneading temperature was 90° C., but also in Example 1, where the kneading temperature was as low as 50° C.

[0026] FIG. 3 shows SEM images of Comparative Example 1 after kneading and Example 2 after kneading. The SEM images were taken using a 3D real surface view microscope VE-9800 (manufactured by KEYENCE). The accelerating voltage was 1 kV and the magnification was 150 times. It is clear from the SEM images that Example 2 is composited and Comparative Example 1 is not composited.

[0027] As can be understood from the above explanation, the starch composite material of the present invention, which is made of low crystalline starch and glycerin, can be composited at a lower kneading temperature compared to a sample made of crystalline starch and glycerin. That is, it becomes possible to produce a starch composite material at a low temperature. Furthermore, the thermal degradation of the low crystalline starch is suppressed. Therefore, it is possible to provide a strong starch composite material.

[0028] FIG. 4 shows the results of wide-angle X-ray diffraction measurement of CS alone and Comparative Example 1-2 after molding. FIG. 5 shows the results of wide-angle X-ray diffraction measurement of ACS alone and Example 2-3 after molding. Wide-angle X-ray diffraction measurement was performed using an Ultima IV (manufactured by Rigaku). The measurement conditions were as follows: X-ray source: Cu-Kα radiation, wavelength: 1.54 Å, tube voltage: 40 kV, tube current: 40 mA, scan range: 5° to 35°, scan speed: 10° / min.

[0029] As can be seen from FIG. 4 and FIG. 5, in the molded bodies of the composite samples (Comparative Example 2, Example 2-3), peaks were observed in both the diffraction angle (2θ) range of 13 degrees to 15 degrees and the diffraction angle (2θ) range of 20 degrees to 22 degrees. In addition, as can be seen from FIG. 4 (Comparative Example 2), when CS was used, a peak was also present in the range where the diffraction angle (2θ) exceeded 22 degrees. On the other hand, as can be seen from FIG. 5 (Example 2-3), when ACS was used, no peak was observed in the range where the diffraction angle (2θ) exceeded 22 degrees. This shows the characteristics of the case where ASC was used. It is known that the peaks near 13 degrees and near 20 degrees are derived from amylose-lipid complexes. Amylose-lipid complexes are formed when lipids enter the helices of amylose in starch. The formation of amylose-lipid complexes indicates that ACS (CS) and Gly are mixed on the scale of molecular chains.

[0030] FIG. 6 is a schematic diagram showing conjugation of CS and ACS with Gly. As mentioned above, ACS produced by grinding CS has a lower degree of crystallinity than CS. A decrease in crystallinity means destabilization of hydrogen bonds. As can be seen from Figure 6, in ACS with destabilized hydrogen bonds, it is considered that Gly can easily penetrate between starch molecular chains even at low temperatures. In other words, ACS has a high affinity for Gly.

[0031] As can be understood from the above description, the starch composite material of the present invention is highly biodegradable and can be kneaded at low temperatures. As a result, the thermal degradation of low crystalline starch is suppressed, making it possible to provide a stronger starch composite material.

Claims

1. A composite material of low-crystalline starch that does not show a peak in the range of diffraction angles (2θ) of 20 degrees to 22 degrees in wide-angle X-ray diffraction measurement using CuKα radiation (wavelength 1.54 Å), and glycerin, In the molded body, In wide-angle X-ray diffraction measurements using CuKα radiation (wavelength 1.54 Å), a peak is observed in the diffraction angle (2θ) range of 20 degrees to 22 degrees, and no peak is observed in the range exceeding 22 degrees. Starch composite material.

2. The mass ratio of the low crystalline starch to the total mass of the low crystalline starch and the glycerin is 50 to 95% by mass. The starch composite material of claim 1 .

3. The low crystallinity starch contains amylose or amylopectin. The starch composite material according to claim 1 or claim 2.

4. The low crystalline starch has a crystallinity of 20% or less. A starch composite material according to any one of claims 1 to 3.

5. Masterbatch for resin molding 5. The starch composite material according to claim 1 .

6. Contains thermoplastic resin 6. A starch composite material according to any one of claims 1 to 5.

Images