Biodegradable resin composition and molded article

Abstract

Provided is a biodegradable resin composition which exhibits a high decomposition rate. The biodegradable resin composition exhibits water retention properties. The biodegradable resin composition contains a biodegradable resin and is preferably capable of retaining 0.007-15.0g, inclusive, of water per 1g of biodegradable resin. The biodegradable resin composition preferably contains a seaweed-derived polysaccharide, which is a hydrolysis promoter which promotes hydrolysis of the biodegradable resin and increases water retention. The seaweed-derived polysaccharide is preferably, for example, fucoidan, laminarin, alginic acid or alginate. In addition, the biodegradable resin composition preferably has a photocatalytically active substance which causes deterioration of the biodegradable resin.

Description

[Technical Field]

[0001] This disclosure relates to biodegradable resin compositions and molded articles. [Background technology]

[0002] In recent years, environmental pollution caused by the disposal of packaging and materials made from resin has become a problem, and biodegradable resins are being used in packaging and materials. Furthermore, in order to use biodegradable resins in packaging and materials, the decomposition rate is adjusted by additives so that they are decomposed by microorganisms after disposal while maintaining the mechanical strength of the resin molded product (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 3646193 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the decomposition rate of conventional biodegradable resins was not sufficient depending on the application. In particular, when biodegradable resins are used in lunch containers, agricultural materials, and gardening materials, food and soil contaminants adhere to them, making reuse or recycling difficult, and they often become waste. Therefore, faster decomposition after disposal is desired. This disclosure has been made in view of the above problems and aims to provide a biodegradable resin composition and molded article having a fast decomposition rate. [Means for solving the problem]

[0005] To solve the above-mentioned problems, a biodegradable resin composition according to one aspect of this disclosure is characterized by being a biodegradable resin composition that has water retention properties. Furthermore, a molded article according to one aspect of this disclosure is characterized by being formed from the biodegradable resin composition described above. [Effects of the Invention]

[0006] According to this disclosure, it is possible to obtain biodegradable resin compositions and molded articles having a faster decomposition rate compared to conventional methods. [Brief explanation of the drawing]

[0007] [Figure 1] This graph shows the test results from the accelerated degradation test in Example 1. [Figure 2A] This graph shows the molecular weight measurement results before and after the accelerated degradation test in Example 1. [Figure 2B] This graph shows the molecular weight measurement results before and after the accelerated degradation test in Example 1-1. [Figure 2C] This graph shows the molecular weight measurement results before and after the accelerated degradation test for Examples 1-2. [Figure 2D] This graph shows the molecular weight measurement results before and after the accelerated degradation test in Example 1-1. [Figure 2E] This graph shows the molecular weight measurement results before and after the accelerated degradation test for Examples 1-2. [Figure 2F] This graph shows the molecular weight measurement results before and after the accelerated degradation test for Comparative Example 1-1. [Figure 3] This graph shows the test results from the accelerated degradation test in Example 2. [Figure 4] This graph shows the test results from the weather resistance test in Example 2. [Figure 5A] These are scanning electron microscope images of the surface of each test specimen from Example 2-1 before the test. [Figure 5B] This is a scanning electron microscope image of the surface of the specimen after the accelerated degradation test in Example 2-1. [Figure 5C] This is a scanning electron microscope image of the surface of the test specimen after the weather resistance test in Example 2-1. [Figure 6A]It is a scanning electron microscope image observing the surface of the test piece before each test of Example 2-2. [Figure 6B] It is a scanning electron microscope image observing the surface of the test piece after the accelerated degradation test of Example 2-2. [Figure 6C] It is a scanning electron microscope image observing the surface of the test piece after the weather resistance test of Example 2-2. [Figure 7A] It is a scanning electron microscope image observing the surface of the test piece before each test of Comparative Example 2-1. [Figure 7B] It is a scanning electron microscope image observing the surface of the test piece after the accelerated degradation test of Comparative Example 2-1. [Figure 7C] It is a scanning electron microscope image observing the surface of the test piece after the weather resistance test of Comparative Example 2-1. [Figure 8] It is a graph showing the measurement results of the molecular weight of the biodegradable resin composition in the test piece before and after the accelerated degradation test of Example 2. [Figure 9A] It is a graph showing the molecular weight measurement results before the weather resistance test of Example 2. [Figure 9B] It is a graph showing the molecular weight measurement results before and after the weather resistance test of Example 2-1. [Figure 9C] It is a graph showing the molecular weight measurement results before the weather resistance test of Example 2-2. [Figure 9D] It is a graph showing the molecular weight measurement results before the weather resistance test of Comparative Example 2-1. [Figure 10A] It is a graph showing the molecular weight measurement results before the weather resistance test of Example 3. [Figure 10B] It is a graph showing the molecular weight measurement results before and after the weather resistance test of Example 3-1. [Figure 10C] It is a graph showing the molecular weight measurement results before and after the weather resistance test of Example 3-2. [Figure 10D] It is a graph showing the molecular weight measurement results before and after the weather resistance test of Example 3-3. [Figure 10E] It is a graph showing the molecular weight measurement results before and after the weather resistance test of Comparative Example 3-1. [Figure 11A]This is a scanning electron microscope image of the surface of the test specimen from Example 3-2 before the weather resistance test. [Figure 11B] This is a scanning electron microscope image of the surface of the test specimen after the weather resistance test in Example 3-2. [Figure 12A] This graph shows the measurement results of molecular weight measurement before the weather resistance test in Example 3-3. [Figure 12B] This is a scanning electron microscope image of the surface of the test specimen after the weather resistance test in Example 3-3. [Figure 13A] These are scanning electron microscope images of the surface of the test specimens from Examples 3-4 before the weather resistance test. [Figure 13B] These are scanning electron microscope images of the surface of the test specimens after the weather resistance test in Examples 3-4. [Figure 14] This graph shows the test results before and after the weather resistance test for Examples 4-3, 4-4, and Comparative Example 4-1. [Figure 15A] This is a scanning electron microscope image of the surface of the test specimen from Example 4-3 before the weather resistance test. [Figure 15B] This is a scanning electron microscope image of the surface of the test specimen after the weather resistance test in Example 4-3. [Figure 16A] This is a scanning electron microscope image of the surface of the test specimen from Example 4-4 before the weather resistance test. [Figure 16B] This is a scanning electron microscope image of the surface of the test specimen after the weather resistance test in Example 4-4. [Figure 17] This graph shows the molecular weight measurement results before and after the weather resistance test in Example 4. [Figure 18] This graph shows the water absorption rate of biodegradable resins or biodegradable resins to which various biodegradation accelerators have been added. [Figure 19] This graph shows the relationship between the hydrogen ion concentration (pH) of biodegradable resin or biodegradable resin to which various biodegradation accelerators have been added, and the amount of water absorbed by the biodegradable resin per 1 cm³ of molded material. [Figure 20]This graph shows the relationship between the hydrogen ion concentration (pH) of biodegradable resins or biodegradable resins to which various biodegradation accelerators have been added, and the amount of water absorbed per gram of resin. [Modes for carrying out the invention]

[0008] Embodiments of this disclosure will be described below with reference to the drawings. However, the embodiments described below are merely illustrative and are not intended to exclude various modifications or applications of techniques not explicitly stated below. This disclosure can be implemented in various ways (for example, by combining the embodiments) without departing from its spirit.

[0009] The biodegradable resin composition and molded articles relating to this disclosure will now be described. The biodegradable resin composition according to this embodiment can be applied to various products such as commonly used packaging, agricultural materials, and horticultural materials, and is particularly suitable for products that are prone to soiling, are difficult to reuse or recycle, and tend to become waste.

[0010] <Composition of biodegradable resin composition> The biodegradable resin composition contains a biodegradable resin and has water-retaining properties to promote the hydrolysis of the biodegradable resin. Preferably, the biodegradable resin composition can retain 0.007 g to 15.0 g of water per 1 g of biodegradable resin, more preferably 0.008 g to 15.0 g of water, and even more preferably 0.008 g to 0.5 g of water. Such biodegradable resin compositions preferably contain a biodegradation accelerator along with the biodegradable resin to promote the biodegradation of the biodegradable resin. The following provides a detailed explanation of biodegradable resins, biodegradation accelerators, and other additives.

[0011] (biodegradable resin) The biodegradable resin contained in the biodegradable resin composition according to this disclosure is preferably a biodegradable resin having ester bonds, which are broken down into low molecular weight resins by hydrolysis. Examples of such biodegradable resin compositions include polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene adipate terephthalate (PBAT).

[0012] (Biodegradation accelerator) A biodegradation accelerator is an additive that has the function of accelerating the hydrolysis of biodegradable resins. For this reason, it is preferable that the biodegradation accelerator is a material that enhances the water retention capacity of the biodegradable resin. Furthermore, when a biodegradable resin composition containing a biodegradation accelerator is disposed of in the soil, the biodegradable resin composition activates soil microorganisms. Therefore, by including a biodegradation accelerator in the biodegradable resin composition, not only is the hydrolysis of the biodegradable resin accelerated, but the biodegradability of the biodegradable resin can also be improved. In addition, from the viewpoint of environmental impact, it is preferable that the biodegradation accelerator is a naturally derived substance.

[0013] Such biodegradation accelerators are preferably, for example, polysaccharides derived from seaweed, and more preferably contain at least one of fucoidan, laminarin, alginic acid, and alginate. Mannitol may also be included along with at least one of fucoidan, laminarin, alginic acid, and alginate. Alginic acid or alginate is even more preferable as the biodegradation accelerator. Furthermore, the alginate is preferably at least one of sodium alginate, potassium alginate, and calcium alginate, with sodium alginate being more preferable. Here, fucoidan, mannitol, and laminarin are preferably used together with alginic acid or alginate. Furthermore, it is preferable that the biodegradation accelerator is not neutral, i.e., acidic or basic. Such biodegradation accelerators may be extracted from natural materials or produced industrially.

[0014] The biodegradation accelerator is preferably present in an amount of 0.01% by mass or more relative to the biodegradable resin, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. When the biodegradation accelerator is present within this range, the hydrolysis of the biodegradable resin is accelerated, and a higher content of the biodegradation accelerator is preferable because it increases the hydrolysis accelerating effect.

[0015] On the other hand, from the viewpoint of the strength of the resin molded article and the moldability of the resin using biodegradable resin, it is preferable to add a small amount of biodegradation accelerator to the biodegradable resin. For example, molded articles using biodegradable resin are expected to be formed by injection molding, blow molding, vacuum molding, inflation molding, or extrusion molding. In this case, it is preferable that the biodegradation accelerator is contained in an amount of 50% by mass or less relative to the biodegradable resin, more preferably 30% by mass or less, and even more preferably 10% by mass or less. In addition, various molding methods can be envisioned, such as increasing the melt flow rate (MFR) using a solvent and forming a film on the surface of a film or sheet with a die coater using a T-die. Thus, depending on the molding method, it is not necessarily required to limit the amount of biodegradation accelerator added to the biodegradable resin to 50% by mass or less, and it is possible to add an amount exceeding 50% by mass.

[0016] Based on the above, in order to enhance the effect of hydrolyzing the biodegradable resin, improve the strength of the resin molded article, and facilitate resin molding, the hydrolysis accelerator is preferably contained in an amount of 0.01% to 50% by mass relative to the biodegradable resin, more preferably in an amount of 0.1% to 30% by mass, and even more preferably in an amount of 0.5% to 10% by mass. Furthermore, the upper limit of the hydrolysis accelerator content can be adjusted as appropriate depending on the method used to mold the biodegradable resin. In a molded article formed from a biodegradable resin containing such a hydrolysis accelerator, it is preferable that the article can retain 0.007 g to 15.0 g of water per 1 g of biodegradable resin, more preferably 0.008 g to 15.0 g of water, and even more preferably 0.008 g to 0.5 g of water. 3 The biodegradable resin contained in each molded body is preferably capable of retaining 0.009 g to 15.0 g of water. Furthermore, the molded body is 1 cm 3 It is preferable that the container can retain between 0.009g and 15.0g of water per unit.

[0017] (Photocatalytic active substance) Photocatalytic active substances are catalysts that have the function of degrading biodegradable resins with light (photodegradation). Photocatalytic active substances accelerate the degradation of the parts of the biodegradable resin that are irradiated with light, leaving the parts that are not irradiated with light intact. This breaks down the biodegradable resin into multiple smaller pieces, increasing the surface area of ​​the remaining biodegradable resin and thus improving its biodegradability.

[0018] When light strikes the photocatalytic active substance contained in the biodegradable resin composition, it oxidizes water in the air or water, reduces oxygen to generate reactive oxygen species, and oxidatively decomposes the biodegradable resin. This photodecomposition of the biodegradable resin by the photocatalytic active substance occurs at an earlier stage than the biodecomposition of the biodegradable resin itself. Therefore, the photocatalytic active substance can further accelerate the biodegradation of the biodegradable resin by reducing its molecular weight and increasing its surface area before the biodegradable resin is biodegraded.

[0019] Examples of such photocatalytically active materials include titanium dioxide and tungsten oxide. The photocatalyst is preferably contained in an amount of 0.5% to 10% by mass of the total biodegradable resin composition, and more preferably in an amount of 1.0% to 5.0% by mass. When the photocatalyst is contained within this range, the photodegradability of the biodegradable resin can be exhibited. The upper limit of the photocatalytic active substance content can be appropriately adjusted depending on the method by which the biodegradable resin is molded.

[0020] (Other additives) The biodegradable resin composition may also contain other additives that promote the decomposition of the biodegradable resin. For example, it may further contain organic or inorganic materials that are mixed with the biodegradable resin and leave the biodegradable resin intact by corroding themselves. Such organic materials are preferably plant fibers or plant fragments, and more preferably rice bran, old rice, rice straw, rice hulls, wheat hulls, wheat bran, soybean hulls, coffee grounds, tea grounds, coconut shells, bagasse, wood flour, recycled paper, starch, etc. Furthermore, the inorganic material is preferably, for example, calcium carbonate. The organic and inorganic materials are preferably in the form of fillers. When the organic material is in the form of fillers, i.e., when the biodegradable resin composition contains organic fillers, each of the organic fillers becomes more susceptible to corrosion, which can easily create holes in the molded body of the biodegradable resin composition or cause it to lose its shape, thereby increasing its surface area. Similarly, when the inorganic material is in the form of fillers, i.e., when the biodegradable resin composition contains inorganic fillers, the biodegradable resin surrounding the inorganic fillers deteriorates, causing the inorganic fillers to fall out of the biodegradable resin, which can create holes in the molded body of the biodegradable resin composition or cause it to lose its shape, thereby increasing its surface area.

[0021] <Resin molded product> The biodegradable resin composition described above is preferably formed into processed products such as molded articles, films, or sheets. The molded body is formed into a desired shape by methods such as injection molding, blow molding, or vacuum forming. Furthermore, the film is formed to the desired thickness, for example, by inflation molding. Furthermore, the sheet is formed to the desired thickness, for example, by extrusion molding. Alternatively, a die coater or similar device can be used to form a desired thickness on the surface of a film or sheet made of a different material. [Examples]

[0022] The biodegradable resin compositions of this disclosure will be described in detail below with reference to various examples.

[0023] <Example 1> Biodegradable resin compositions were formed by changing the additives added to the biodegradable resin, and the tensile strength of test specimens using the biodegradable resin compositions was confirmed.

[0024] (Example 1-1) A biodegradable resin composition of Example 1-1 was obtained by adding an alginic acid mixture containing 30% by mass of alginic acid, 5% by mass of laminarin, 10% by mass of fucoidan, and 8% by mass of mannitol to polylactic acid (PLA), a biodegradable resin. In this case, the amount of alginic acid mixture added to the biodegradable resin composition was 0.5% by mass.

[0025] (Examples 1-2) A biodegradable resin composition of Example 1-2 was obtained in the same manner as in Example 1-1, except that alginic acid was used as an additive.

[0026] (Examples 1-3) The biodegradable resin composition of Example 1-3 was obtained in the same manner as in Example 1-1, except that sodium alginate was used as the additive.

[0027] (Examples 1-4) The biodegradable resin composition of Example 1-3 was obtained in the same manner as in Example 1-1, except that the additive was fucoidan.

[0028] (Comparative Example 1-1) A biodegradable resin composition of Comparative Example 1-1 was obtained in the same manner as in Example 1-1, except that no additives were added.

[0029] [evaluation] (Tensile test) Resin films were formed by extrusion molding using the biodegradable resin compositions described in each example and comparative example. The film thickness of the resin films in each example and comparative example was 0.4 mm for Examples 1-1 to 1-3 and Comparative Example 1-1, and 0.5 mm for Example 1-4. From these resin films, five rectangular test pieces were cut out for each example and comparative example, each with a length of 100 mm in the tensile direction and a length of 15 mm in the direction perpendicular to the tensile direction.

[0030] Next, the test specimen was fixed in a tensile testing machine (Shimadzu Corporation, AG-X 10kN) with a grip distance (chuck distance) of 50 mm. Under conditions of 23°C and 50% RH humidity, both ends of the test specimen were pulled at a tensile speed of 500 mm / min, and the tensile force at which the test specimen fractured was measured. Measurements were performed five times (five samples) for each example and comparative example, and the average value of the measurements for each example and comparative example was taken as the tensile force at fracture.

[0031] (Accelerated degradation test) The average value of the measurements obtained in the tensile tests for each example and comparison was taken as the tensile force at fracture (initial tensile force) before the test (when stored for 0 hours). Next, test specimens (5 samples each) obtained in the same manner as in the tensile test were stored for 96 hours in an environment of 60°C and 80% RH humidity. After this, measurements were taken five times (5 samples) for each example and comparative example under the same conditions as in the tensile test, and the average value of the measurements for each example and comparative example was taken as the tensile force at fracture after the test (tensile force after degradation).

[0032] (molecular weight measurement) Gel permeation chromatography (GPC) analysis was performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, before and after storage in a constant temperature and humidity chamber (accelerated degradation test) and before and after weather resistance testing (metal halide lamp irradiation), and the change in molecular weight of each test specimen was measured. The GPC analysis conditions at this time were as follows. Columns: Three high-performance analytical semi-micro columns (Shodex GPC KF-405LHQ, manufactured by Showa Denko Corporation) Flow rate: 0.30ml / min Detector: High-speed GPC device (manufactured by Tosoh Corporation, HLC-8220GPC) Detection condition: Differential refractive index (RI) Injection volume: 40μl Column temperature: 40℃ Eluent: Chloroform

[0033] Table 1 below shows the evaluation results of the tensile force at fracture relative to the film thickness of the test specimen before (0 hours of storage) and after the accelerated degradation test. Figure 1 is a graph showing the test results of the accelerated degradation test. Furthermore, Table 2 shows the evaluation results of the change in molecular weight before and after the accelerated degradation test. Figures 2A to 2F are graphs showing the change in molecular weight before and after the accelerated degradation test. Figure 2A shows the molecular weight of each example and comparative example before the accelerated degradation test, Figure 2B shows the molecular weight of Example 1-1 before and after the accelerated degradation test, Figure 2C shows the molecular weight of Example 1-2 before and after the accelerated degradation test, Figure 2D shows the molecular weight of Example 1-3 before and after the accelerated degradation test, Figure 2E shows the molecular weight of Example 1-4 before and after the accelerated degradation test, and Figure 2F shows the change in molecular weight of Comparative Example 1-1 before and after the accelerated degradation test.

[0034] [Table 1]

[0035] [Table 2]

[0036] As shown in Table 1 and Figure 1, test specimens formed from the biodegradable resin compositions of Examples 1-1 to 1-4, which have water-retaining properties due to the addition of alginic acid or alginate to the biodegradable resin, had lower breaking strength (tensile force at break per unit of film thickness) than test specimens formed from the biodegradable resin composition of Comparative Example 1-1, which did not contain any additives. In particular, test specimens formed from the biodegradable resin compositions of Example 1-1 (in which an alginic acid mixture was added to the biodegradable resin), Example 1-3 (in which sodium alginate was added), and Example 1-4 (in which fucoidan was added) each had lower breaking strength than test specimens formed from the biodegradable resin composition of Comparative Example 1-1 in both tensile tests and accelerated degradation tests.

[0037] Furthermore, the results of the accelerated degradation test showed that the test specimens formed from the biodegradable resin compositions of Examples 1-1 to 1-3, which contained alginic acid mixture, alginic acid, or sodium alginate, had lower breaking strength after the accelerated degradation test than the test specimen formed from the biodegradable resin composition of Comparative Example 1-1. Therefore, the test specimens formed from the biodegradable resin compositions of Examples 1-1 to 1-3 showed significant degradation under humid conditions. This is thought to be due to the water-retaining effect of alginic acid, which accelerated the degradation.

[0038] Furthermore, the results of the accelerated degradation test showed that the test specimens formed from the biodegradable resin composition of Example 1-2, which contained alginic acid, had higher initial tensile strength and lower tensile strength after the accelerated degradation test compared to the test specimens formed from the biodegradable resin composition of Comparative Example 1-1. This is particularly preferable because the resin product has high strength in the initial stages of formation (during use), and then degradation by hydrolysis progresses rapidly, making it easier for it to be decomposed by microorganisms.

[0039] Furthermore, as shown in Table 2 and Figure 2A, before the accelerated degradation test, the test specimens formed from the biodegradable resin compositions of Examples 1-1 to 1-4, which contained alginate mixture, alginate, alginate, and fucoidan, showed a shift in the peak top of the graph to the left and a decrease in molecular weight compared to the test specimen formed from the biodegradable resin composition of Comparative Example 1-1, which did not contain these additives. In addition, as shown in Figures 2B to E, the molecular weight of the test specimens formed from the biodegradable resin compositions of Examples 1-1 to 1-4 decreased before and after the accelerated degradation test, and as shown in Table 2, the rate of decrease in molecular weight was greater compared to Comparative Example 1-1.

[0040] <Example 2> Biodegradable resin compositions were formed by changing the amount of alginic acid mixture added to the biodegradable resin, and the tensile strength of test specimens using the biodegradable resin compositions was confirmed.

[0041] (Example 2-1) Similar to Example 1-1, the biodegradable resin composition of Example 2-1 was obtained by adding an alginate mixture in an amount of 0.5% by mass.

[0042] (Example 2-2) The biodegradable resin composition of Example 2-2 was obtained in the same manner as the biodegradable resin composition of Example 2-1, except that the amount of alginate mixture added was 1.0% by mass.

[0043] (Comparative Example 2-1) A biodegradable resin composition of Comparative Example 2-1 was obtained in the same manner as the biodegradable resin composition of Example 2-1, except that an alginic acid mixture was not added. Here, Comparative Example 2-1 has the same configuration as Comparative Example 1-1.

[0044] [evaluation] (Tensile test) In the same manner as in Example 1, tensile tests were performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, and the average value of the tensile force at fracture was obtained.

[0045] (Accelerated degradation test) In the same manner as in Example 1, accelerated degradation tests were performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, and the average value of the tensile force at fracture was obtained.

[0046] (Weather resistance test) Test specimens (before accelerated degradation testing) formed using the biodegradable resin compositions described in each example and comparative example were irradiated with a metal halide lamp under the following conditions. Afterward, a tensile test was performed under the same conditions as in Example 1, and the average tensile force at fracture of the test specimen after metal halide lamp irradiation was obtained. Subsequently, the fracture strength after metal halide lamp irradiation was calculated as a percentage of the test specimen's film thickness. Temperature: 60℃ Humidity: 50%RH Water spray cycle: 18 minutes / 2 hours Irradiance: 1.5kW / m 2 (Metal halide lamp wavelength: 295nm to 450nm) Irradiation time: 8 hours Furthermore, the surfaces of test specimens formed using the biodegradable resin compositions described in each example and comparative example were observed using a scanning electron microscope (SEM) after irradiation with a metal halide lamp.

[0047] (molecular weight measurement) Gel permeation chromatography (GPC) analysis was performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, before and after storage in a constant temperature and humidity chamber (accelerated degradation test) and before and after weathering tests (irradiation with a metal halide lamp), and the change in molecular weight of each test specimen was measured. The GPC analysis conditions at this time were the same as in Example 1.

[0048] Furthermore, the molecular weight of each test specimen was measured by performing gel permeation chromatography analysis on test specimens formed using the biodegradable resin compositions described in each example and comparative example, after irradiation with a metal halide lamp. The GPC analysis conditions were as described above. The metal halide lamp irradiation conditions were the same as those for the weather resistance test in Example 2. Furthermore, the test specimens formed using the biodegradable resin composition described in Comparative Example 1-1 were irradiated with a metal halide lamp for twice the time (i.e., 16 hours), and then gel permeation chromatography analysis was performed to measure the molecular weight of the test specimens.

[0049] Table 3 below shows the evaluation results of the accelerated degradation test and the weathering resistance test. Table 4 below shows the evaluation results of the change in molecular weight before and after the accelerated degradation test, and Table 5 below shows the evaluation results of the change in molecular weight before and after the weathering resistance test. Furthermore, Figure 3 shows the results of the accelerated degradation test in a graph, and Figure 4 shows the results of the weathering resistance test in a graph. In addition, Figures 5A to 7C show scanning electron microscope (SEM) images of the surface of the test specimens before each test, after the accelerated degradation test, and after the weathering resistance test. Figures 5A, 5B, and 5C are surface SEM images of test specimens formed using the biodegradable resin composition of Example 2-1, before each test (Figure 5A), after the accelerated degradation test (Figure 5B), and after the weathering resistance test (Figure 5C). Figures 6A, 6B, and 6C are surface SEM images of test specimens formed using the biodegradable resin composition of Example 2-2, before each test (Figure 6A), after the accelerated degradation test (Figure 6B), and after the weathering resistance test (Figure 6C). Figures 7A, 7B, and 7C show surface SEM images of test specimens formed using the biodegradable resin composition of Comparative Example 2-1 before the accelerated degradation test (Figure 7A), after the accelerated degradation test (Figure 7B), and after the weathering test (Figure 7C). Figure 8 shows a graph of the change in molecular weight measurement before and after the accelerated degradation test. Figures 9A to 9D show graphs of the change in molecular weight measurement before and after the weathering test. Figure 9A is a graph comparing the molecular weight measurement results before metal halide lamp irradiation for each example and comparative example, Figure 9B is a graph comparing the molecular weight before and after metal halide lamp irradiation for Example 2-1, Figure 9C is a graph comparing the molecular weight before and after irradiation for Example 2-1, Figure 9C is a graph comparing the molecular weight before and after irradiation for Example 2-2, and Figure 9D is a graph comparing the molecular weight before and after irradiation for Comparative Example 1-1.

[0050] [Table 3]

[0051] [Table 4]

[0052] [Table 5]

[0053] As shown in Table 3 and Figures 3 and 4, the test specimens formed from the biodegradable resin compositions of each example and comparative example showed improved breaking strength after metal halide lamp irradiation. This is thought to be because the polylactic acid crystallized upon irradiation with the metal halide lamp, improving its strength. However, the test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2, which had alginate mixture added, had lower breaking strength compared to Comparative Example 2-1, which did not have alginate mixture added, confirming that the biodegradable resin was more easily decomposed. Furthermore, the test specimens formed from the biodegradable resin composition of Example 2-2 showed a greater decrease in breaking strength before and after metal halide lamp irradiation compared to the test specimens formed from the biodegradable resin compositions of Examples 2-1 and Comparative Example 2-1, and the rate of decrease in breaking strength was also higher. This confirmed that a higher amount of alginate mixture added makes the biodegradable resin more easily decomposed.

[0054] As shown in Figures 5A and 5B, and Figures 6A and 6B, test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2, to which the alginate mixture was added, showed deterioration after the accelerated degradation test, specifically the formation of voids (dotted lines in Figure 5B and dashed lines in Figure 6B) and depressions (dashed lines in Figure 6B). These large, well-formed voids (see Figure 5B) and small, well-formed voids and depressions (see Figure 6B) that appear on the test specimens after the accelerated degradation test are thought to be voids caused by the alginate mixture. On the other hand, the test specimens formed from the biodegradable resin composition without the alginate mixture shown in Comparative Example 2-1 in Figures 7A and 7B differed from the test specimens of Examples 2-1 and 2-2 in that they had a clean shape and did not show large voids or small voids or depressions distributed evenly across the test specimens.

[0055] As shown in Figures 5A and 5C, and Figures 6A and 6C, test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2, to which the alginate mixture was added, showed void formation after the weathering test, indicating deterioration of the test specimens. These voids are thought to be caused by the alginate mixture. On the other hand, the test specimens formed from the biodegradable resin composition without the alginate mixture shown in Comparative Example 2-1 in Figures 7A and 7C showed small, irregularly shaped holes (voids due to resin degradation) all over the surface, but no large voids like those in the test specimens of Examples 2-1 and 2-2 were observed.

[0056] Figure 8 is a graph showing the molecular weight measurements of the biodegradable resin compositions in the test specimens of each example and comparative example before and after the accelerated degradation test. As shown in Figure 8 and Table 4, before the accelerated degradation test, the test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2, which contained the alginate mixture, showed a shift in the peak top of the graph to the left and a decrease in molecular weight compared to the test specimen formed from the biodegradable resin composition of Comparative Example 2-1, which did not contain the alginate mixture. Furthermore, as shown in Figure 8, the test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2 showed a decrease in molecular weight before and after the accelerated degradation test.

[0057] Figures 9A to 9D are graphs showing the molecular weight measurements of the biodegradable resin compositions in the test specimens of each example and comparative example before and after the weathering test. Figure 9A is a graph showing the molecular weight of the biodegradable resin compositions in the test specimens of Example 2-1, Example 2-2, and Comparative Example 2-1 before metal halide lamp irradiation. Figure 9B, Figure 9C, and Figure 9D show the molecular weight of the biodegradable resin compositions in the test specimens of Example 2-1, Example 2-2, and Comparative Example 2-1 before and after metal halide lamp irradiation.

[0058] As shown in Figure 9A and Table 5, before metal halide lamp irradiation (weather resistance test), the test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2, which had the alginate mixture added, showed a shift in the peak top of the graph to the left and a decrease in molecular weight compared to the test specimen formed from the biodegradable resin composition of Comparative Example 2-1, which did not have the alginate mixture added. Furthermore, as shown in Figures 9B and 9C, and Table 5, the molecular weight of the test specimens formed from the biodegradable resin compositions of Examples 2-1 and 2-2 decreased before and after irradiation with a metal halide lamp, and the molecular weight decreased particularly in the test specimen formed from the biodegradable resin composition of Example 2-2. In this case, the molecular weight decreased more significantly than in Comparative Example 2-1 shown in Figure 9D and Table 5 for the same irradiation time, and decreased to a similar extent as when the irradiation time was doubled. From the above, it was confirmed that the greater the amount of additives such as alginate mixtures added, the lower the tensile strength becomes, meaning that the biodegradable resin becomes more easily decomposed.

[0059] <Example 3> Biodegradable resin compositions were formed by changing the additives added to the biodegradable resin, and the tensile strength of test specimens using the biodegradable resin compositions was confirmed.

[0060] (Example 3-1) A biodegradable resin composition of Example 3-1 was obtained by adding an alginate mixture and titanium dioxide (rutile type), a photocatalyst, to PLA (polylactic acid), a biodegradable resin. At this time, the amount of alginate mixture added to the biodegradable resin composition was set to 0.5% by mass, and the amount of titanium dioxide added to the biodegradable resin composition was set to 3.0% by mass. Using this biodegradable resin composition, a resin film with a thickness of 0.4 mm was formed by extrusion molding to obtain the test piece of Example 3-1.

[0061] (Example 3-2) Test specimens using the biodegradable resin composition of Example 3-2 were obtained in the same manner as in Example 3-1, except that the thickness of the resin film was set to 0.2 mm.

[0062] (Example 3-3) Test specimens using the biodegradable resin composition of Example 3-2 were obtained in the same manner as in Example 3-2, except that alginic acid was used as an additive.

[0063] (Examples 3-4) Test specimens using the biodegradable resin composition of Example 3-2 were obtained in the same manner as in Example 3-2, except that sodium alginate was used as the additive.

[0064] (Comparative Example 3-1) Test specimens using the biodegradable resin composition of Comparative Example 3-1 were obtained in the same manner as in Example 3-1, except that no additives were added.

[0065] (Comparative Example 3-2) Test specimens using the biodegradable resin composition of Comparative Example 3-2 were obtained in the same manner as in Example 3-2, except that no additives were added.

[0066] [evaluation] (Tensile test) In the same manner as in Example 1, tensile tests were performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, and the average value of the tensile force at fracture was obtained.

[0067] (Weather resistance test) In the same manner as in Example 2, test specimens formed using the biodegradable resin compositions described in each example and comparative example were irradiated with a metal halide lamp, and then subjected to tensile tests to obtain the average value of the tensile force at fracture.

[0068] (molecular weight measurement) In the same manner as in Example 2, the molecular weight changes of test specimens formed using the biodegradable resin compositions described in each example and comparative example were measured before and after accelerated degradation testing (storage in a constant temperature and humidity chamber) and before and after weathering resistance testing (irradiation with a metal halide lamp).

[0069] Table 6 below shows the evaluation results of the tensile force at fracture relative to the film thickness of the test specimens for each example and comparative example before and after the weathering test. Table 7 below shows the evaluation results of the molecular weight of the test specimens for each example and comparative example before and after the weathering test. Furthermore, Figure 10A is a graph comparing the molecular weight measurements of the test specimens for each example and comparative example before metal halide lamp irradiation; Figure 10B compares the molecular weight before and after metal halide lamp irradiation for Example 3-2, Figure 10C for Example 3-3, Figure 10D for Example 3-4, and Figure 10E for Comparative Example 3-2. Figures 11A and 11B show surface SEM images of the test specimens before and after the weathering test for Example 3-2, Figures 12A and 12B for Example 3-3, and Figures 13A and 13B for Example 3-4.

[0070] [Table 6]

[0071] [Table 7]

[0072] As shown in Table 6, the test specimens formed from the biodegradable resin composition of Example 3-1, to which an alginic acid mixture and titanium dioxide were added to the biodegradable resin, showed higher breaking strength in the tensile test than the test specimens formed from the biodegradable resin composition of Comparative Example 1-1, which had the same film thickness (0.4 mm) but did not contain alginic acid. However, in the weathering test, they showed lower breaking strength than the test specimens formed from the biodegradable resin composition of Comparative Example 1-1. Similarly, the test specimens formed from the biodegradable resin composition of Example 3-2, to which alginic acid and titanium dioxide were added to the biodegradable resin, showed almost the same strength after the tensile test as the test specimens formed from the biodegradable resin composition of Comparative Example 1-2, which had the same film thickness (0.2 mm) but did not contain alginic acid. However, they showed lower breaking strength after the weathering test. In other words, the strength of the resin product was high in the initial stages of formation (during use), and then degradation by hydrolysis progressed rapidly, making it more susceptible to degradation by microorganisms. Furthermore, the degradation effect by hydrolysis was higher in test specimens with thinner film thicknesses. Furthermore, in particular, test specimens formed from the biodegradable resin compositions of Examples 3-4, in which sodium alginate and titanium dioxide were added to the biodegradable resin, exhibited significantly lower breaking strength in tensile tests.

[0073] Furthermore, as shown in Figure 10A and Table 7, before irradiation with a metal halide lamp, the test specimens formed from the biodegradable resin compositions of Examples 3-2 to 3-4, to which alginate mixture, alginate, and sodium alginate were added, respectively, showed a shift in the peak top of the graph to the left and a decrease in molecular weight compared to the test specimen formed from the biodegradable resin composition of Comparative Example 3-2, which did not contain a biodegradation accelerator. In particular, the biodegradable resin containing the alginate mixture in Example 3-2 had a particularly small molecular weight, confirming that the biodegradable resin was easily decomposed.

[0074] Furthermore, as shown in Figures 10B to 10D and Table 7, the test specimens formed from the biodegradable resin compositions of Examples 3-2 to 3-4 tended to show a decrease in molecular weight before and after irradiation with a metal halide lamp, and in particular, the test specimen formed from the biodegradable resin composition containing sodium alginate and titanium dioxide of Example 3-4 showed a significant decrease in molecular weight. From the above, it was confirmed that when a biodegradable resin composition contains titanium dioxide, the resin product has high strength in the initial stages of formation (during use), and thereafter the biodegradable resin becomes more easily decomposed due to the degradation effect of hydrolysis accelerators (especially sodium alginate).

[0075] As shown in Figures 11A to 13B, it was confirmed that the test specimens mixed with the hydrolysis accelerator and titanium dioxide deteriorated after the weathering test, with voids forming in the specimens.

[0076] <Example 4> Biodegradable resin compositions were formed by adding an alginate mixture and titanium dioxide to a biodegradable resin, and varying the amount of alginate mixture added. The tensile strength of test specimens with different film thicknesses using these biodegradable resin compositions was then confirmed.

[0077] (Example 4-1) Similar to Example 3-1, the biodegradable resin composition of Example 4-1 was obtained by adding 0.5% by mass of the alginate mixture and 3.0% by mass of titanium dioxide. Using this biodegradable resin composition, a resin film with a thickness of 0.4 mm was formed by extrusion molding to obtain the test specimen of Example 4-1.

[0078] (Example 4-2) A biodegradable resin composition of Example 4-2 was obtained in the same manner as the biodegradable resin composition of Example 4-1, except that the amount of alginate mixture added was 1.0% by mass. Using this biodegradable resin composition, a resin film with a thickness of 0.5 mm was formed by extrusion molding to obtain the test specimen of Example 4-2.

[0079] (Example 4-3) Test specimens using the biodegradable resin composition of Example 4-3 were obtained in the same manner as in Example 4-1, except that the thickness of the resin film was set to 0.2 mm.

[0080] (Example 4-4) Test specimens using the biodegradable resin composition of Example 4-4 were obtained in the same manner as in Example 4-2, except that the thickness of the resin film was set to 0.2 mm.

[0081] (Comparative Example 4-1) A biodegradable resin composition of Comparative Example 4-1 was obtained in the same manner as the biodegradable resin composition of Example 4-1, except that an alginic acid mixture was not added.

[0082] (Comparative Example 4-2) Test specimens using the biodegradable resin composition of Comparative Example 4-2 were obtained in the same manner as in Comparative Example 4-1, except that the thickness of the resin film was set to 0.2 mm.

[0083] [evaluation] (Tensile test) In the same manner as in Example 1, tensile tests were performed on test specimens formed using the biodegradable resin compositions described in each example and comparative example, and the average value of the tensile force at fracture was obtained.

[0084] (Weather resistance test) In the same manner as in Example 2, test specimens formed using the biodegradable resin compositions described in each example and comparative example were irradiated with a metal halide lamp, and then subjected to tensile tests to obtain the average value of the tensile force at fracture.

[0085] (molecular weight measurement) In the same manner as in Example 2, the change in molecular weight of each test specimen formed using the biodegradable resin compositions described in each example and comparative example was measured before and after the weathering test (irradiation with a metal halide lamp).

[0086] Table 8 below shows the evaluation results of the tensile force at fracture relative to the film thickness of the test specimens for each example and comparative example before and after the weathering test. Table 9 below shows the evaluation results of the molecular weight of the test specimens for each example and comparative example before and after the weathering test. Figure 14 is a graph showing the test results of the tensile force at fracture relative to the film thickness of the test specimens for Example 4-3, Comparative Example 4-4, and Comparative Example 4-1 before and after the weathering test. Figures 15A and 15B show surface SEM images of the test specimens for Example 4-3, and Figures 16A and 16B show surface SEM images of the test specimens for Example 4-4 before and after the weathering test. Furthermore, Figure 17 is a graph comparing the molecular weight of Example 4-3, Example 4-4, and Comparative Example 4-1 before and after metal halide lamp irradiation.

[0087] [Table 8]

[0088] [Table 9]

[0089] As shown in Table 8 and Figure 14, it was confirmed that test specimens formed from the biodegradable resin compositions of Examples 4-1 to 4-4, to which alginate mixture was added, exhibited lower breaking strength after metal halide lamp irradiation, meaning the biodegradable resin became more easily decomposed. In particular, before metal halide lamp irradiation, the breaking strength may improve depending on the amount of alginate mixture added (see Examples 4-1 and Comparative Example 4-1, Examples 4-3 and Comparative Example 4-2), but after metal halide lamp irradiation, the addition of alginate mixture reduced the breaking strength, confirming that the biodegradable resin became more easily decomposed. Furthermore, the test specimens formed from the biodegradable resin compositions of Examples 4-2 and 4-4 showed a greater decrease in breaking strength before and after metal halide lamp irradiation compared to the test specimens formed from the biodegradable resin compositions of Examples 4-1 and 4-3, and the rate of decrease in breaking strength increased with increasing amounts of alginate mixture added.

[0090] This can be confirmed by the fact that the SEM image of the test specimen after the weathering test of Example 4-4, shown in Figure 16B, shows that more pores have formed than the SEM image of the test specimen after the weathering test of Example 4-3, shown in Figure 15B. Furthermore, from the molecular weight of the biodegradable resin of the test specimens after the weathering test, shown in Figure 17, it was confirmed that the molecular weight peak of the test specimen of Example 4-4 is shifted to the left compared to Example 4-3, indicating a decrease in molecular weight and making the biodegradable resin more easily decomposed.

[0091] From the above, it was confirmed that the greater the amount of additives such as alginate mixtures added, the lower the tensile strength, meaning that the biodegradable resin becomes more easily decomposed. Furthermore, after irradiation with a metal halide lamp, the tensile strength of the test specimen decreased compared to before irradiation with a metal halide lamp, meaning the test specimen deteriorated. This confirmed that the biodegradable resin deteriorates due to the photodegradation of titanium dioxide.

[0092] <Example 5> Biodegradable resin (density 1.25g / cm 3Or, the water absorption rate and the relationship between the hydrogen ion index (pH) and the water absorption amount were confirmed when forming test pieces formed using a biodegradable resin composition obtained by adding 0.5% by mass or 1.0% by mass of each hydrolysis accelerator (alginate mixture, alginate, sodium alginate, fucoidan) used in Example 1 to this biodegradable resin.

[0093] [Evaluation] (Water absorption rate) After measuring the mass of a test piece of a predetermined size before water absorption, the test piece was immersed in water, and the mass of the test piece after water absorption was measured. At this time, the size of the test piece and the method of immersing the test piece in water were made to conform to the size and method according to JIS K7209. In addition, the immersion of the test piece in water was measured only for the biodegradable resin (PLA) containing 1.0% by mass of fucoidan by the measurement method (water absorption rate (number of samples n = 4)) shown in the method for obtaining the water absorption rate of plastics shown in JIS K7209, and the other test pieces were measured by the measurement method (water absorption rate (number of samples n = 3)) shown in the method for obtaining the water absorption rate of plastics shown in JIS K7209.

[0094] Subsequently, the amount of water retained in the test piece was calculated from the difference between the mass of the test piece after water absorption and the mass of the test piece before water absorption. Finally, the ratio of the amount of water retained in the test piece to the mass of the test piece before water absorption was calculated and taken as the water absorption rate [%].

[0095] (Water absorption amount) The water absorption amount of a test piece of a predetermined size calculated by the above method was divided by the volume of the test piece to calculate the water absorption amount per 1 cm 3 for the molded body per. For a test piece formed of a biodegradable resin not containing a hydrolysis accelerator, the water absorption amount per 1 cm 3 for the molded body per was taken as the water absorption amount per 1 cm 3 for the biodegradable resin per. Subsequently, the water absorption amount of the biodegradable resin contained in the molded body per 1 cm 3 per was calculated. The water absorption amount in the biodegradable resin contained in the molded body per 1 cm 3 per is as follows for the biodegradable resin contained in the molded body per 1 cm3 The amount of water absorbed per molded piece was calculated by multiplying the weight percentage of biodegradable resin in the test piece. Furthermore, the amount of water absorbed per gram of biodegradable resin in the molded body was calculated. The amount of water absorbed per gram of biodegradable resin is calculated per 1 cm 3 The amount of water absorbed by the biodegradable resin contained in each molded product and the density of the biodegradable resin (PLA) were used to calculate the result.

[0096] Table 10 below shows the 1 cm in each test specimen. 3 Water absorption per unit area of ​​the molded body, 1 cm 3 This shows the amount of water absorbed by the biodegradable resin contained in each molded product and the amount of water absorbed per gram of biodegradable resin in the molded product. Figure 18 is a graph showing the water absorption rate of each test piece, and Figure 19 shows the hydrogen ion concentration (pH) and 1 cm of the hydrolysis accelerator. 3 Figure 19 and Figure 20 show the relationship between the amount of water absorbed by the biodegradable resin contained in a single molded product and the amount of water absorbed by 1g of biodegradable resin. For the sake of comparison, the water absorption of biodegradable resin (PLA) without the hydrolysis accelerator is shown at the pH=0 position of the hydrolysis accelerator in Figures 19 and 20.

[0097] [Table 10]

[0098] As shown in Figure 18 and Table 10, the water absorption rate of molded articles made from biodegradable resin containing hydrolysis accelerators was 70% or more, while the water absorption rate of molded articles made from biodegradable resin without hydrolysis accelerators was less than 70%. Biodegradable resins (PLA) to which hydrolysis accelerators such as alginic acid mixture, alginic acid, sodium alginate, and fucoidan were added tended to have improved water absorption rates compared to biodegradable resin (PLA) alone. In particular, biodegradable resin mixed with 1.0% alginic acid mixture showed a significant improvement in water absorption rate. Furthermore, as shown in Figure 19 and Table 10, it is preferable that the hydrolysis accelerator is acidic or basic, and a molded body formed from a biodegradable resin to which the hydrolysis accelerator has been added is 1 cm 3 It was found that the amount of moisture absorbed by the biodegradable resin inside was 0.009g or more, and 0.01g or more was preferable. Furthermore, as shown in Figure 20 and Table 10, it is preferable that the hydrolysis accelerator is acidic or basic, and a molded body formed from a biodegradable resin to which the hydrolysis accelerator has been added is 1 cm 3 It was found that the amount of moisture absorbed by the biodegradable resin inside was 0.009g or more, and 0.01g or more was preferable.

[0099] While embodiments of the present disclosure have been described above, these embodiments are merely illustrative examples of devices and methods for realizing the technical concept of the present disclosure, and the technical concept of the present disclosure does not specify the material, shape, structure, arrangement, etc., of the components. The technical concept of the present disclosure can be modified in various ways within the technical scope defined by the claims described in the patent claims.

Claims

1. The invention comprises a biodegradable resin, a polysaccharide derived from seaweed which is a hydrolysis accelerator that promotes the hydrolysis of the biodegradable resin, and a photocatalytic active substance which degrades the biodegradable resin. The biodegradable resin is polylactic acid. The hydrolysis accelerator comprises fucoidan, mannitol, laminarin, and alginic acid. A biodegradable resin composition with water-retaining properties.

2. The biodegradable resin composition according to claim 1, which is capable of retaining 0.007 g to 15.0 g of water per 1 g of the biodegradable resin.

3. The aforementioned photocatalytic active substance is tungsten oxide. The biodegradable resin composition according to claim 1 or 2.

4. The hydrolysis accelerator is acidic or basic. A biodegradable resin composition according to any one of claims 1 to 3.

5. The hydrolysis accelerator is contained in an amount of 0.01% by mass or more and 50% by mass or less relative to the biodegradable resin. A biodegradable resin composition according to any one of claims 1 to 4.

6. Organic materials A biodegradable resin composition according to any one of claims 1 to 5.

7. The photocatalytic active substance is contained in the biodegradable resin composition in an amount of 1.0% by mass or more and 5.0% by mass or less of the total biodegradable resin composition. A biodegradable resin composition according to any one of claims 1 to 6.

8. A molded article formed from the biodegradable resin composition according to any one of claims 1 to 7.

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