Biodegradable resin composition and molded article

Abstract

To provide a biodegradable resin composition capable of yielding a molded product that offers superior handleability, as well as a well-balanced combination of rigidity and impact strength, and also to provide a molded product with a well-balanced combination of rigidity and impact strength.SOLUTION: A biodegradable resin composition according to the present invention comprises a biodegradable resin, basic magnesium sulfate, and an acrylic compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biodegradable resin composition and a molded article. [Background technology]

[0002] There is a demand for biodegradable resin compositions that have excellent mechanical properties while maintaining biodegradability. A polylactic acid-based thermoplastic resin composition that improves compatibility by blending an olefin-based resin and reduces environmental impact has been proposed (see, for example, Patent Document 1). It is described that by using the resin composition of Patent Document 1, molded articles that are excellent in appearance and mechanical properties such as impact strength can be obtained.

[0003] Furthermore, a resin composition in which trans-polyisoprene is blended with a polylactic acid resin has been proposed (for example, Patent Document 2). It is described that the resin composition in Patent Document 2 forms a matrix-domain structure, which results in excellent foaming properties and allows the production of a resin foam with excellent strength (especially toughness). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-167403 [Patent Document 2] Patent Publication No. 2021-155654 Summary of the Invention [Problem to be solved by the invention]

[0005] Resin compositions used to produce molded articles are also required to have excellent handleability. However, a biodegradable resin composition that is excellent in handleability and can give molded articles with a good balance between rigidity and impact strength has not yet been obtained. Therefore, an object of the present invention is to provide a biodegradable resin composition that is easy to handle and that can give a molded article having a good balance between rigidity and impact strength, and to provide a molded article having a good balance between rigidity and impact strength. [Means for solving the problem]

[0006] The biodegradable resin composition according to the present invention contains a biodegradable resin, basic magnesium sulfate, and an acrylic compound.

[0007] The molded article according to the present invention is a molded product of the biodegradable resin composition described above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a biodegradable resin composition that is excellent in handleability and that can give a molded article having a good balance between rigidity and impact strength, and a molded article having a good balance between rigidity and impact strength. DETAILED DESCRIPTION OF THE INVENTION

[0009] As a result of extensive research, the present inventors have found that a resin composition obtained by blending a biodegradable resin with basic magnesium sulfate and an acrylic compound as a hydrolysis inhibitor has excellent handleability, and that the use of such a resin composition makes it possible to obtain a molded article having a good balance between rigidity and impact strength, thereby completing the present invention. Hereinafter, embodiments of the present invention will be described in detail.

[0010] <Biodegradable resin> The biodegradable resin is selected from the group consisting of aliphatic polyester biodegradable resins and aromatic-aliphatic polyester biodegradable resins. The weight-average molecular weight of the biodegradable resin is preferably within the range of 10,000 to 3,000,000, and more preferably within the range of 50,000 to 1,000,000. The weight-average molecular weight of the biodegradable resin can be determined, for example, by GPC (gel permeation chromatography).

[0011] Aliphatic polyester biodegradable resins include polymers of polylactic acid and hydroxycarboxylic acids. The hydroxycarboxylic acids can be selected from L-lactic acid, D-lactic acid, and DL-lactic acid. Copolymers of lactic acid and hydroxycarboxylic acids can also be used as biodegradable resins in the present invention.

[0012] Furthermore, polycondensates of aliphatic dicarboxylic acids and glycols are also known as aliphatic polyester biodegradable resins. Examples of aliphatic dicarboxylic acids include succinic acid and adipic acid, and aliphatic polyester biodegradable resins synthesized by polycondensation of these with glycols are suitable for use.

[0013] Examples of succinic acid-based biodegradable resins include polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), and polybutylene succinate lactate (PBSL), as well as polybutylene succinate hydrocaproate (PBSLC), polybutylene succinate carbonate (PBSC), polybutylene succinate terephthalate (PBST), polybutylene succinate diethylene glycol succinate (PBS-co-DEGS), polybutylene succinate butylene (PBS-co-BDGA), and polybutylene succinate fluonate (PBSF).

[0014] Adipic acid-based biodegradable resins include polybutylene adipate (PBA), polybutylene adipate terephthalate (PBAT), and polyethylene adipate terephthalate (PEAT).

[0015] The biodegradable resins described above may be used singly or in combination of two or more. Among the biodegradable resins described above, polylactic acid (PLA) is preferred as the biodegradable resin in the present invention because of its excellent alkali resistance.

[0016] <Basic magnesium sulfate> Basic magnesium sulfate is represented by the formula MgSO4·5Mg(OH)2·3H2O and can be obtained by hydrothermal synthesis using alkaline substances such as sodium hydroxide, magnesium hydroxide, magnesium oxide, and calcium hydroxide as raw materials and magnesium sulfate.

[0017] The shape of the basic magnesium sulfate is not particularly limited, and basic magnesium sulfate of any shape, such as fibrous or fan-shaped, can be used. For example, in the case of fibrous basic magnesium sulfate, the average fiber length is generally in the range of 2 to 100 μm, preferably 5 to 50 μm, and the average fiber diameter is generally in the range of 0.1 to 2.0 μm, preferably 0.1 to 1.0 μm. The average aspect ratio (average fiber length / average fiber diameter) of basic magnesium sulfate is generally 2 or more, preferably 3 to 1000, more preferably 3 to 100, and particularly preferably 5 to 50. The average fiber length and average fiber diameter of basic magnesium sulfate can be calculated from the number-average values ​​of the fiber length and fiber diameter measured by image analysis of enlarged images taken with a scanning electron microscope (SEM).

[0018] The content of basic magnesium sulfate is preferably 1 to 50 parts by mass, and more preferably 3 to 30 parts by mass, when the total mass of the biodegradable resin and basic magnesium sulfate is taken as 100. By changing the content of basic magnesium sulfate, it is possible to obtain a biodegradable resin composition having a soft or hard texture.

[0019] Wollastonite and other inorganic fillers are known to be blended into biodegradable resins to improve their physical properties. Because wollastonite does not dissolve in seawater, it is released into the ocean as a decomposition residue of biodegradable resins. In this case, the accumulation of the released wollastonite can cause unexpected problems.

[0020] In contrast, basic magnesium sulfate decomposes in seawater without leaving any residue, avoiding such problems. Basic magnesium sulfate decomposes in seawater into magnesium sulfate (MgSO4) and magnesium hydroxide (Mg(OH)2). It is presumed that magnesium sulfate dissolves in seawater, and magnesium hydroxide reacts with acidic components present in the atmosphere to dissolve as Mg salts.

[0021] <Hydrolysis inhibitor> The hydrolysis inhibitor is a compound that inhibits the hydrolysis of the biodegradable resin, and examples thereof include compounds that are reactive with the active hydrogen in the biodegradable resin. By adding such a compound, the amount of active hydrogen in the biodegradable resin is reduced, and it is possible to prevent the active hydrogen from catalytically hydrolyzing the polymer chains that constitute the biodegradable resin.

[0022] In the present invention, an acrylic compound is used as the hydrolysis inhibitor. Acrylic compounds have a high melting point of 140°C, which allows for the production of resin compositions that are easy to handle during melt-kneading. When the resin composition of the present invention containing an acrylic compound is used, kneaded pellets can be obtained without the hydrolysis inhibitor melting under the raw material hopper, even at temperatures of 200°C or higher during melt-kneading. Furthermore, resin molded articles can be stably produced even at temperatures of 180°C or higher during injection molding.

[0023] The acrylic compound is preferably a styrene acrylate polymer having a reactive epoxy group. Commercially available polymers include JONCRYL ADR4368, JONCRYL ADR4300, JONCRYL ADR4468, and JONCRYL ADR4400 (all manufactured by BASF), ARUFON UG4035, ARUFON UG4040, and ARUFON UG4070 (all manufactured by Toagosei), and LOTADER AX8840 (manufactured by Arkema).

[0024] The content of the acrylic compound is preferably 0.1 to 100 parts by mass, and more preferably 30 to 60 parts by mass, when the mass of the basic magnesium sulfate is taken as 100. When the total mass of the biodegradable resin and basic magnesium sulfate is taken as 100, the content of the acrylic compound is preferably 0.1 to 100 parts by mass, and more preferably 0.3 to 10 parts by mass.

[0025] The biodegradable resin composition of the present invention may contain other components as long as the effects of the present invention are not impaired.

[0026] The biodegradable resin composition of the present invention can be produced by mixing the components and then melt-kneading them. For example, the biodegradable resin, fibrous basic magnesium sulfate, and hydrolysis inhibitor are first mixed together. Mixing can be performed using a tumbler, blender, Henschel mixer, or the like.

[0027] During mixing, the remaining components can be added to the biodegradable resin in any order. Adding the fibrous basic magnesium sulfate and the hydrolysis inhibitor simultaneously is advantageous in terms of cost reduction due to process simplification. Adding the hydrolysis inhibitor to the biodegradable resin and then adding the fibrous basic magnesium sulfate increases the remaining fiber length of the fibrous basic magnesium sulfate after kneading, resulting in a higher reinforcing effect. The resulting mixture is melt-kneaded at 180 to 220°C using a twin-screw extrusion kneader or the like to obtain the biodegradable resin composition of the present invention.

[0028] That is, the method for producing a biodegradable resin composition of the present invention is a method comprising either the following steps (1) or (2): (1) A simultaneous addition step of adding basic magnesium sulfate and a hydrolysis inhibitor to a biodegradable resin. (2) A sequential addition step of adding a hydrolysis inhibitor to a biodegradable resin and then adding basic magnesium sulfate.

[0029] Various molded articles can be produced by molding the biodegradable resin composition of the present invention. For molding the resin composition, for example, a rolling molding machine (such as a calendar molding machine), a vacuum molding machine, an extrusion molding machine, an injection molding machine, a blow molding machine, a press molding machine, etc. can be used.

[0030] As described above, the biodegradable resin composition of the present invention contains basic magnesium sulfate and an acrylic compound as a hydrolysis inhibitor, and therefore, molded articles having excellent rigidity and high mechanical properties can be obtained. The flexural modulus of the biodegradable resin composition of the present invention can be adjusted by the content of basic magnesium sulfate, and therefore, molded articles for a variety of uses can be obtained.

[0031] For example, the molded article of the present invention can be suitably used in a wide range of applications, such as packaging materials for packaging liquids, powders, and solids, such as various foods, medicines, and miscellaneous goods, agricultural materials, and construction materials. Specific applications include injection-molded products (e.g., trays for fresh food, coffee capsules, fast food containers, outdoor leisure products, etc.), extrusion-molded products (films, e.g., fishing lines, fishing nets, vegetation nets, water-retaining sheets, etc.), and blown-molded products (bottles, etc.).

[0032] Further examples include agricultural films, coating materials, fertilizer coating materials, laminated films, plates, stretched sheets, monofilaments, nonwoven fabrics, flat yarns, staples, crimped fibers, creased tapes, split yarns, composite fibers, blown bottles, shopping bags, garbage bags, compost bags, cosmetic containers, detergent containers, bleach containers, ropes, binding materials, sanitary cover stock materials, cooler boxes, cushioning films, multifilaments, synthetic paper, and medical applications such as surgical thread, sutures, artificial bones, artificial skin, drug delivery systems (DDS) such as microcapsules, and wound dressings.

[0033] Furthermore, the composition can also be used in information and electronics materials such as toner binders and thermal transfer ink binders, automobile interior parts such as electrical appliance casings, instrument panels, seats, and pillars, and automobile exterior structural materials such as bumpers, front grilles, and wheel covers. Among these, more preferred are packaging materials such as packaging films, bags, trays, capsules, bottles, cushioning foams, and fish boxes, as well as agricultural materials. Examples of agricultural materials include mulching films, tunnel films, greenhouse films, sunshades, weed control sheets, ridge sheets, germination sheets, vegetation mats, seedling beds, and flower pots. [Example]

[0034] Specific examples of the present invention will be shown below, but the present invention is not limited to these.

[0035] The raw materials used are summarized below. <Basic magnesium sulfate> A: Fibrous basic magnesium sulfate, MOS-HIGE A-1, manufactured by Ube Material Industries, Ltd., average major axis 15 μm, average minor axis 0.5 μm <Polylactic acid> B: Polylactic acid Terramac TE-2000, manufactured by Unitika Ltd. <Hydrolysis inhibitor> C1: Joncryl ADR-4468 manufactured by BASF C2: 4,4'-methylenediphenyl diisocyanate Reagent

[0036] Example 1 First, 1 part by mass of basic magnesium sulfate (A), 99 parts by mass of polylactic acid (B), and 0.3 parts by mass of hydrolysis inhibitor (C1) were mixed together, and the resulting mixture was melt-kneaded at 200°C using a twin-screw melt-kneading extruder (L / D=25, manufactured by Imoto Machinery Co., Ltd.) to obtain a resin composition of Example 1.

[0037] <Example 2> A resin composition of Example 2 was obtained in the same manner as in Example 1, except that 5 parts by mass of basic magnesium sulfate (A), 95 parts by mass of polylactic acid (B), and 1.5 parts by mass of hydrolysis inhibitor (C1) were used.

[0038] Example 3 A resin composition of Example 3 was obtained in the same manner as in Example 1, except that 10 parts by mass of basic magnesium sulfate (A), 90 parts by mass of polylactic acid (B), and 3 parts by mass of hydrolysis inhibitor (C1) were used.

[0039] Example 4 A resin composition of Example 4 was obtained in the same manner as in Example 1, except that 5 parts by mass of basic magnesium sulfate (A), 95 parts by mass of polylactic acid (B), and 3 parts by mass of hydrolysis inhibitor (C1) were used.

[0040] <Example 5> A resin composition of Example 5 was obtained in the same manner as in Example 1, except that 10 parts by mass of basic magnesium sulfate (A), 90 parts by mass of polylactic acid (B), and 6 parts by mass of hydrolysis inhibitor (C1) were used.

[0041] Example 6 A resin composition of Example 6 was obtained in the same manner as in Example 1, except that 15 parts by mass of basic magnesium sulfate (A), 85 parts by mass of polylactic acid (B), and 9 parts by mass of hydrolysis inhibitor (C1) were used.

[0042] <Comparative Example 1> A resin composition of Comparative Example 1 was obtained in the same manner as in Example 1, except that 10 parts by mass of basic magnesium sulfate (A), 90 parts by mass of polylactic acid (B), and 3 parts by mass of hydrolysis inhibitor (C2) were used.

[0043] <Comparative Example 2> A resin composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that 15 parts by mass of basic magnesium sulfate (A), 85 parts by mass of polylactic acid (B), and 3 parts by mass of hydrolysis inhibitor (C2) were used.

[0044] <Comparative Example 3> Polylactic acid (B) alone was used as Comparative Example 3.

[0045] <Comparative Example 4> A resin composition of Comparative Example 4 was obtained in the same manner as in Example 3, except that the hydrolysis inhibitor (C1) was not added.

[0046] <Comparative Example 5> A resin composition of Comparative Example 5 was obtained in the same manner as in Example 6, except that the hydrolysis inhibitor (C1) was not added.

[0047] Table 1 below shows the blending compositions of the resin compositions of the examples and comparative examples.

[0048] [Table 1]

[0049] <Preparation of test specimens> Each resin composition was molded using a small electric injection molding machine (C.Mobile0813, manufactured by Shinko Selvic Co., Ltd.) to obtain strip test pieces (length 50 mm, width 5 mm, thickness 2 mm) for evaluating mechanical properties.

[0050] <Flexural modulus> A three-point bending test was performed using a universal mechanical testing machine (manufactured by Imada Co., Ltd.) in accordance with JIS K7171. The distance between supports was 40 mm, and the loading rate was 10 mm / min. The flexural modulus was evaluated from the obtained load-deflection curve.

[0051] <Weight average molecular weight> The weight-average molecular weight of the resin composition after melt-kneading corresponds to the weight-average molecular weight of polylactic acid. The weight-average molecular weights of polylactic acid and the resin composition were calculated in terms of polystyrene by gel permeation chromatography (GPC) using HLC-8320GPC (manufactured by Tosoh Corporation). Columns used were KG, K-805L, and K-800d (manufactured by Shodex), and chloroform was used as the eluent.

[0052] <Charpy impact strength> The Charpy impact strength was evaluated using a Charpy impact tester (manufactured by Mize Testing Instruments Co., Ltd.) in accordance with JIS K7111. The hammer force was 2.75 J.

[0053] <Handling> As an index showing the handling property, those which could stably obtain kneaded pellets and resin molded articles were marked with "Good", and those which could not be obtained were marked with "Poor".

[0054] Table 2 below shows the flexural modulus, weight average molecular weight, Charpy impact strength and handleability of the molded articles produced using each resin composition.

[0055] [Table 2]

[0056] In the above table, the weight average molecular weight of Comparative Example 3 represents the molecular weight of the polylactic acid itself used as the raw material. Comparative Example 3 uses polylactic acid alone, and does not contain basic magnesium sulfate or a hydrolysis inhibitor, so the flexural modulus of the resulting molded article cannot be increased. The resin compositions of Examples 1 to 6 contain an acrylic compound as a hydrolysis inhibitor together with basic magnesium sulfate, which inhibits hydrolysis of polylactic acid caused by basic magnesium sulfate and provides excellent handleability. Therefore, Examples 1 to 6 can maintain a weight-average molecular weight at the same level as the raw material (Comparative Example 1). Furthermore, by using the resin compositions of these Examples, molded articles with excellent handleability and a good balance between rigidity and impact strength can be obtained.

[0057] In contrast, Comparative Examples 1 and 2, which contained a hydrolysis inhibitor but were not an acrylic compound, had poor handleability, and Comparative Examples 4 and 5, which contained no hydrolysis inhibitor, hydrolysis occurred in the polylactic acid when melt-kneaded with basic magnesium sulfate, resulting in a significant decrease in weight-average molecular weight, making it impossible to obtain a resin composition suitable for producing a molded article.

Claims

1. A biodegradable resin composition containing a biodegradable resin, basic magnesium sulfate, and an acrylic compound, the acrylic compound is a styrene acrylate polymer having a reactive epoxy group, When the total mass of the biodegradable resin and the basic magnesium sulfate is taken as 100, the content of the biodegradable resin is 85 to 99 parts by mass, the content of the basic magnesium sulfate is 1 to 15 parts by mass, and the content of the acrylic compound is 0.1 to 100 parts by mass, When the mass of the basic magnesium sulfate is taken as 100, the content of the acrylic compound is 30 to 60 parts by mass. A biodegradable resin composition comprising:

2. 2. The biodegradable resin composition according to claim 1, wherein the biodegradable resin is selected from the group consisting of aliphatic polyester biodegradable resins and aromatic-aliphatic polyester biodegradable resins.

3. 3. The biodegradable resin composition according to claim 2, wherein the aliphatic polyester-based biodegradable resin contains a polymer of a hydroxycarboxylic acid.

4. 4. The biodegradable resin composition according to claim 3, wherein the hydroxycarboxylic acid comprises L-lactic acid, D-lactic acid, or DL-lactic acid.

5. A molded article which is a molded article of the biodegradable resin composition of claim 1.

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