Biodegradable resin composition and molded article

Abstract

A biodegradable resin composition according to the present invention contains a biodegradable resin, basic magnesium sulfate, and a carbodiimide-based compound, wherein the amount of the carbodiimide-based compound included is 1-50% of the mass of the basic magnesium sulfate.

Description

Biodegradable resin composition and molded article

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

[0002] There is a demand for biodegradable resin compositions that have excellent mechanical properties while maintaining biodegradability. Polylactic acid-based thermoplastic resin compositions that incorporate an olefin-based resin to improve compatibility and reduce environmental impact have been proposed (see, for example, Patent Document 1). Patent Document 1 describes that the use of the resin composition allows for the production of molded articles that are excellent in appearance and mechanical properties such as impact strength.

[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 foamability and allows the production of a resin foam with excellent strength (especially toughness).

[0004] JP 2021-167403 A JP 2021-155654 A

[0005] Resin compositions used to produce molded articles are also required to have excellent handleability (moldability). Although it may be possible to achieve a biodegradable resin composition that can produce molded articles with a good balance between rigidity and impact strength by incorporating appropriate additives, there is a concern that the additives may increase the viscosity of the biodegradable resin composition, resulting in poor handleability. Depending on the type and amount of additives, this may also lead to increased manufacturing costs. A biodegradable resin composition that can produce molded articles with excellent handleability and a good balance between rigidity and impact strength has not yet been obtained.

[0006] 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.

[0007] The biodegradable resin composition according to the present invention contains a biodegradable resin, basic magnesium sulfate, and a carbodiimide compound, and the content of the carbodiimide compound is 1 to 50% by mass of the basic magnesium sulfate.

[0008] The molded article according to the present invention is a molded product of the biodegradable resin composition described above.

[0009] 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.

[0010] As a result of extensive research, the present inventors have found that a resin composition obtained by blending a biodegradable resin with a carbodiimide compound as a hydrolysis inhibitor together with basic magnesium sulfate has excellent handleability, and that the use of such a resin composition allows the production of molded articles with a good balance between rigidity and impact strength, thereby completing the present invention. Hereinafter, embodiments of the present invention will be described in detail.

[0011] <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 in the range of 10,000 to 3,000,000, and more preferably in 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).

[0012] Examples of aliphatic polyester-based 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.

[0013] 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.

[0014] Examples of succinic acid-based biodegradable resins include polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), and polybutylene succinate lactate (PBSL). Further examples include 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).

[0015] Examples of adipic acid-based biodegradable resins include polybutylene adipate (PBA), polybutylene adipate terephthalate (PBAT), and polyethylene adipate terephthalate (PEAT).

[0016] 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.

[0017] In the biodegradable resin composition of the present invention, the content of the biodegradable resin is preferably 1 to 50 parts by mass, more preferably 5 to 30 parts by mass, when the total mass of the biodegradable resin and the basic magnesium sulfate described below is 100 parts by mass.

[0018] <Basic magnesium sulfate> Basic magnesium sulfate is MgSO ４ ・5Mg(OH) ２ ・3H ２ O, and can be obtained by hydrothermal synthesis using, as raw materials, an alkaline substance such as sodium hydroxide, magnesium hydroxide, magnesium oxide, or calcium hydroxide, and magnesium sulfate.

[0019] 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).

[0020] 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 that is soft or hard.

[0021] 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.

[0022] In contrast, basic magnesium sulfate does not decompose in seawater to produce residue, so such problems can be avoided. Basic magnesium sulfate does not decompose in seawater to produce magnesium sulfate (MgSO ４ ) and magnesium hydroxide (Mg(OH) ２ Magnesium sulfate dissolves in seawater, and magnesium hydroxide is presumed to react with acidic components present in the atmosphere and dissolve as Mg salts.

[0023] <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.

[0024] In the present invention, a carbodiimide compound is used as the hydrolysis inhibitor. Various carbodiimide compounds can be used, and are not particularly limited as long as they have one or more carbodiimide groups in the molecule. Examples of carbodiimide compounds include aliphatic monocarbodiimides, aliphatic polycarbodiimides, alicyclic monocarbodiimides, alicyclic polycarbodiimides, aromatic monocarbodiimides, and aromatic polycarbodiimides. Furthermore, compounds having various heterocycles or various functional groups in the molecule may also be used.

[0025] The method for producing a carbodiimide compound is not particularly limited, and many methods can be used, such as a method using an isocyanate compound as a raw material. As the carbodiimide compound, both a carbodiimide compound having an isocyanate group in the molecule and a carbodiimide compound not having an isocyanate group in the molecule can be used without distinction.

[0026] Examples of the carbodiimide skeleton of the carbodiimide compound include N,N'-di-o-triylcarbodiimide, N,N'-dioctyldecylcarbodiimide, N,N'-di-2,6-dimethylphenylcarbodiimide, N-triyl-N'-cyclohexylcarbodiimide, N-triyl-N'-phenylcarbodiimide, N,N'-di-p-nitrophenylcarbodiimide, N,N'-di-p-hydroxyphenylcarbodiimide, and N,N'-di- Examples of carbodiimide skeletons include many carbodiimide skeletons such as cyclohexylcarbodiimide, N,N'-di-cyclohexylcarbodiimide, N,N'-di-p-triylcarbodiimide, p-phenylene-bis-di-o-triylcarbodiimide, 4,4'-dicyclohexylmethanecarbodiimide, tetramethylxylylenecarbodiimide, N,N'-dimethylphenylcarbodiimide, and N,N'-di-2,6-diisopropylphenylcarbodiimide.

[0027] Many specific examples of carbodiimide compounds can be mentioned. Specifically, for example, alicyclic monocarbodiimides include dicyclohexylcarbodiimide. Alicyclic polycarbodiimides include polycarbodiimides derived from 4,4'-dicyclohexylmethane diisocyanate. Aromatic monocarbodiimides include N,N'-diphenylcarbodiimide and N,N'-di-2,6-diisopropylphenylcarbodiimide. Aromatic polycarbodiimides include polycarbodiimides derived from phenylene-p-diisocyanate and polycarbodiimides derived from 1,3,5-triisopropyl-phenylene-2,4-diisocyanate. The above carbodiimide compounds can be used alone or in combination of two or more.

[0028] In polycarbodiimide, both ends of the molecule or any part of the molecule may have a functional group such as an isocyanate group, or the molecular chain may be branched, or the molecular structure may be different from that of other parts.

[0029] In the biodegradable resin composition of the present invention, the content of the carbodiimide compound is specified to be 1 to 50% by mass of the basic magnesium sulfate. Because a predetermined amount of the carbodiimide compound is contained, the biodegradable resin composition of the present invention has an appropriate viscosity and excellent handleability. Furthermore, it has the advantage of being able to be produced without increased costs due to additives. The content of the carbodiimide compound is preferably 5 to 30% by mass of the basic magnesium sulfate.

[0030] The content of the carbodiimide compound is preferably 0.1 to 10%, more preferably 0.5 to 5%, of the total mass of the biodegradable resin and basic magnesium sulfate.

[0031] The biodegradable resin composition of the present invention may contain other components as long as the effects of the present invention are not impaired.

[0032] 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.

[0033] 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 greater reinforcing effect. The biodegradable resin composition of the present invention can be obtained by melt-kneading the resulting mixture at 180 to 220°C using a twin-screw extrusion kneader or the like.

[0034] That is, the method for producing a biodegradable resin composition of the present invention is a method comprising either of the following steps (1) or (2): (1) a simultaneous addition step of simultaneously adding a hydrolysis inhibitor together with basic magnesium sulfate to a biodegradable resin, or (2) a sequential addition step of adding a hydrolysis inhibitor to a biodegradable resin and then adding basic magnesium sulfate.

[0035] 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.

[0036] As described above, the biodegradable resin composition of the present invention contains basic magnesium sulfate and a carbodiimide compound as a hydrolysis inhibitor, and therefore, molded articles having excellent rigidity and high mechanical properties can be obtained. The biodegradable resin composition of the present invention can adjust the flexural modulus by changing the content of basic magnesium sulfate, and therefore, molded articles for various uses can be obtained.

[0037] 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 liquid, powdered, and solid materials, 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 hollow-molded products (bottles, etc.).

[0038] 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, insulated 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.

[0039] 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.

[0040] Specific examples of the present invention will be shown below, but the present invention is not limited to these.

[0041] The raw materials used are summarized below. <Polylactic acid> A: Polylactic acid Terramac TE-2000, manufactured by Unitika Ltd. <Basic magnesium sulfate> B: 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 <Hydrolysis inhibitor> C1: Carbodiimide compound Carbodilite HMV-15CA, manufactured by Nisshinbo Chemical Co., Ltd. C2: Acrylic compound Joncryl ADR-4468, manufactured by BASF

[0042] Example 1 First, 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 1 part 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.

[0043] Example 2 A resin composition of Example 2 was obtained in the same manner as in Example 1, except that 95 parts by mass of polylactic acid (A), 5 parts by mass of basic magnesium sulfate (B), and 0.7 parts by mass of hydrolysis inhibitor (C1) were used.

[0044] Example 3 A resin composition of Example 3 was obtained in the same manner as in Example 1, except that 90 parts by mass of polylactic acid (A), 10 parts by mass of basic magnesium sulfate (B), and 1.3 parts by mass of hydrolysis inhibitor (C1) were used.

[0045] Example 4 A resin composition of Example 4 was obtained in the same manner as in Example 1, except that 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 2 parts by mass of hydrolysis inhibitor (C1) were used.

[0046] Example 5 A resin composition of Example 5 was obtained in the same manner as in Example 1, except that 95 parts by mass of polylactic acid (A), 5 parts by mass of basic magnesium sulfate (B), and 1 part by mass of hydrolysis inhibitor (C1) were used.

[0047] Example 6 A resin composition of Example 6 was obtained in the same manner as in Example 1, except that 90 parts by mass of polylactic acid (A), 10 parts by mass of basic magnesium sulfate (B), and 2 parts by mass of hydrolysis inhibitor (C1) were used.

[0048] Example 7 A resin composition of Example 7 was obtained in the same manner as in Example 1, except that 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 3 parts by mass of hydrolysis inhibitor (C1) were used.

[0049] Comparative Example 1 A resin composition of Comparative Example 1 was obtained in the same manner as in Example 1, except that 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 1 part by mass of hydrolysis inhibitor (C2) were used.

[0050] Comparative Example 2 A resin composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 2 parts by mass of hydrolysis inhibitor (C2) were used.

[0051] Comparative Example 3 A resin composition of Comparative Example 3 was obtained in the same manner as in Example 1, except that 85 parts by mass of polylactic acid (A), 15 parts by mass of basic magnesium sulfate (B), and 3 parts by mass of hydrolysis inhibitor (C2) were used.

[0052] Comparative Example 4 A resin composition of Comparative Example 4 was obtained in the same manner as in Example 1, except that 90 parts by mass of polylactic acid (A), 10 parts by mass of basic magnesium sulfate (B), and 0.7 parts by mass of the hydrolysis inhibitor (C2) were used.

[0053] Comparative Example 5 A resin composition of Comparative Example 5 was obtained in the same manner as in Example 1, except that 90 parts by mass of polylactic acid (A), 10 parts by mass of basic magnesium sulfate (B), and 1.3 parts by mass of the hydrolysis inhibitor (C2) were used.

[0054] Comparative Example 6 A resin composition of Comparative Example 6 was obtained in the same manner as in Example 1, except that 90 parts by mass of polylactic acid (A), 10 parts by mass of basic magnesium sulfate (B), and 2 parts by mass of hydrolysis inhibitor (C2) were used.

[0055] Comparative Example 7 A resin composition of Comparative Example 7 was obtained in the same manner as in Example 1, except that 95 parts by mass of polylactic acid (A), 5 parts by mass of basic magnesium sulfate (B), and 0.4 parts by mass of the hydrolysis inhibitor (C2) were used.

[0056] Comparative Example 8 A resin composition of Comparative Example 8 was obtained in the same manner as in Example 1, except that 95 parts by mass of polylactic acid (A), 5 parts by mass of basic magnesium sulfate (B), and 0.7 parts by mass of the hydrolysis inhibitor (C2) were used.

[0057] Comparative Example 9 In Comparative Example 9, polylactic acid (A) alone was used.

[0058] Table 1 below summarizes the formulations of the resin compositions of the examples and comparative examples.

[0059]

[0060] As shown in Table 1 above, in the biodegradable resin compositions of the examples, the content of the carbodiimide compound (C1) as a hydrolysis inhibitor is 7 to 20% by mass of the basic magnesium sulfate (B), and 0.7 to 3% by mass of the total mass of the biodegradable resin (A), basic magnesium sulfate, and (B).

[0061] The weight average molecular weights of the resin compositions of the examples and comparative examples were determined. Furthermore, test specimens were prepared using each resin composition, and the flexural modulus, Charpy impact strength, MVR, and handleability were examined. MVR is an index of the fluidity of a resin composition and affects handleability.

[0062] <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 as polystyrene equivalent molecular weights by gel permeation chromatography (GPC) using HLC-8320GPC (manufactured by Tosoh Corporation). Columns used were K-G, K-805L, and K-800d (manufactured by Shodex), and chloroform was used as the eluent.

[0063] <Preparation of Test Pieces> Each resin composition was molded using a small electric injection molding machine (C.Mobile 0813, manufactured by Shinko Selvic Co., Ltd.) to obtain strip test pieces (length 50 mm, width 5 mm, thickness 2 mm) for evaluating mechanical properties.

[0064] <Flexural modulus> A three-point bending test was performed using a universal mechanical testing machine (manufactured by Imada Co., Ltd.) according to JIS K 7171. 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.

[0065] <Charpy Impact Strength> A test was carried out in accordance with JIS K 7111 using a Charpy impact tester (manufactured by Mize Testing Instruments Co., Ltd.) to evaluate the Charpy impact strength. The hammer force was 2.75 J.

[0066] <MVR> MVR was determined using a melt flow indexer (G-01, manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K 7210. The measurement conditions were 190°C and 2.160 kgf.

[0067] <Handling Efficiency> As an index showing handling efficiency, those which could stably obtain kneaded pellets and resin molded products were marked with "Good", and those which could not were marked with "Poor". A resin composition with a large MVR and too low viscosity has poor handling efficiency.

[0068] The flexural modulus, Charpy impact strength, MVR and handleability of the molded articles produced using each resin composition are shown in Table 2 below, along with the weight average molecular weight of each resin composition.

[0069]

[0070] The resin compositions of Examples 1 to 7 contain a carbodiimide compound as a hydrolysis inhibitor along with basic magnesium sulfate, thereby inhibiting the hydrolysis of polylactic acid caused by basic magnesium sulfate. Therefore, the resin compositions of Examples 1 to 7 are able to maintain a weight-average molecular weight equivalent to that of the raw material (Comparative Example 9). In the table above, the weight-average molecular weight of Comparative Example 9 represents the molecular weight of the polylactic acid itself used as the raw material.

[0071] Moreover, the resin compositions of Examples 1 to 7 have an MVR of 40 cm ３ The resin compositions of Examples 1 to 7 have a flexural modulus of 4.0 GPa or more and a viscosity of 0.9 kJ / m or less. ２ It is possible to produce a molded article having the above Charpy impact strength.

[0072] In the resin compositions of the examples, the content of the carbodiimide compound as a hydrolysis inhibitor is 7 to 20% by mass of the basic magnesium sulfate. Even with such a low content of hydrolysis inhibitor, the desired effects described above are achieved. The biodegradable resin compositions of the examples were shown to be biodegradable resin compositions that are easy to handle and can produce molded articles with a good balance of rigidity and impact strength.

[0073] On the other hand, although the biodegradable resin compositions of Comparative Examples 1 to 8 also contain a hydrolysis inhibitor, it is a compound other than a carbodiimide compound (an acrylic additive). In the case of an acrylic additive, even when added in an amount of 7 to 20% by mass of basic magnesium sulfate, the MVR is 40 cm ３ It is difficult to obtain a resin composition with a hardness of 10 min or less. Therefore, the desired handling properties are not obtained. Comparative Examples 1 to 8 show that the biodegradable resin composition containing an acrylic additive does not have the desired handling properties and is unable to obtain a molded product with a good balance between rigidity and impact strength.

Claims

1. A biodegradable resin composition comprising a biodegradable resin, basic magnesium sulfate, and a carbodiimide compound, wherein the content of the carbodiimide compound is 1 to 50% by mass of the basic magnesium sulfate.

2. The biodegradable resin composition according to claim 1, wherein the basic magnesium sulfate has an average fiber length in the range of 2 to 100 μm and an average fiber diameter in the range of 0.1 to 2.0 μm.

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

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

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

6. A molded article made from the biodegradable resin composition of claim 1 or 2.

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