Thermoplastic resin composition for biodegradable agricultural material, biodegradable agricultural material, and method for producing same

Abstract

The purpose of the present disclosure is to provide a thermoplastic resin composition for a biodegradable agricultural material, which has moderate toughness, is excellent in stretchability and flexibility, has high biodegradability, and can exhibit a soil improvement effect after plowing.　This thermoplastic resin composition for a biodegradable agricultural material contains a biodegradable aliphatic polyester resin, a biodegradable aliphatic aromatic polyester resin, and trehalose.

Description

Thermoplastic resin composition for biodegradable agricultural materials, biodegradable agricultural materials, and method for producing the same

[0001] The present disclosure relates to a thermoplastic resin composition for biodegradable agricultural materials, a biodegradable agricultural material, and a method for producing the same.

[0002] In recent years, from the perspective of sustainability, there has been a strong demand for the development of biodegradable agricultural materials (e.g., agricultural mulch films and sheets), particularly in agricultural fields. Biodegradable agricultural materials decompose naturally after use, reducing adverse effects on soil and water quality and reducing the burden on the environment. Furthermore, biodegradable agricultural materials can be buried in the soil after use, and can also supply useful organic matter to the soil during decomposition.

[0003] Examples of agricultural materials include agricultural mulch films, seedling pots, etc. Biodegradable agricultural materials can be decomposed by plowing them into the soil after use, which could be a solution to the current waste problem and reduce the work required to recover agricultural materials.

[0004] Examples of documents disclosing biodegradable agricultural materials include Patent Document 1 and Patent Document 2.

[0005] Patent Document 1 discloses a cellulose-based biodegradable sheet containing fine cellulose fibers and trehalose as main components.

[0006] Patent Document 2 discloses a biodegradable mulch film whose decomposition rate is controlled by at least one of an additive or a resin component, the biodegradable mulch film being formed from at least a first layer and a second layer, the first layer and the second layer being made of a biodegradable resin, the decomposition rate of the first layer and the decomposition rate of the second layer being made different by adding the additive to at least one of the first layer and the second layer or by selecting the resin component, the first layer and the second layer being surface layers of the biodegradable film, and the biodegradable mulch film being spread on the soil so that either the first layer or the second layer is in contact with the soil surface.

[0007] JP 2001-279016 A JP 2012-205552 A

[0008] However, the biodegradable agricultural materials of Patent Documents 1 and 2, even though they are biodegradable, have the problem of not fully satisfying the characteristics required for agricultural materials. For example, agricultural materials are required to have moderate toughness as well as excellent elasticity and flexibility from the standpoint of product processability and ease of handling, but Patent Documents 1 and 2 do not consider these points at all. Furthermore, since biodegradable agricultural materials are sometimes disposed of by plowing them into the soil after use, it is desirable for them to have excellent biodegradability in soil. Furthermore, no study has been conducted, not only in Patent Documents 1 and 2, that takes into account the soil improvement effect of biodegradable agricultural materials after plowing them into the soil.

[0009] Therefore, an object of the present disclosure is to provide a thermoplastic resin composition for biodegradable agricultural materials that has excellent toughness, stretchability, and flexibility, is highly biodegradable, and can have a soil improvement effect after being plowed in.

[0010] The present inventors have conducted extensive research to solve the above problems and have found that by using an aliphatic polyester resin and an aliphatic aromatic polyester resin as biodegradable resins and further containing trehalose, it is possible to provide a thermoplastic resin composition for biodegradable agricultural materials that has excellent toughness, stretchability, and flexibility, is highly biodegradable, and can improve soil after being plowed in, thereby completing the present disclosure.

[0011] Therefore, an example of the present embodiment is as follows.

[0012] (1) A thermoplastic resin composition for biodegradable agricultural materials, comprising a biodegradable aliphatic polyester resin, a biodegradable aliphatic-aromatic polyester resin, and trehalose. (2) The thermoplastic resin composition according to (1), wherein the content of the aliphatic polyester resin in the composition is 10% by mass or more and 45% by mass or less, and the content of the aliphatic-aromatic polyester resin in the composition is 45% by mass or more and 80% by mass or less. (3) The thermoplastic resin composition according to any one of (1) to (2), wherein the sum of the content of the aliphatic polyester resin in the composition and the content of the aliphatic-aromatic polyester resin in the composition is 60% by mass or more. (4) The thermoplastic resin composition according to any one of (1) to (3), wherein the ratio of the content of the aliphatic polyester resin in the composition to the content of the aliphatic-aromatic polyester resin in the composition is 1:1 to 1:5. (5) The thermoplastic resin composition according to any one of (1) to (4), wherein the trehalose content in the composition is 5% by mass or more and 30% by mass or less. (6) The thermoplastic resin composition according to any one of (1) to (5), wherein the aliphatic polyester-based resin contains polylactic acid (PLA) and the aliphatic aromatic polyester-based resin contains polybutylene adipate terephthalate (PBAT). (7) The thermoplastic resin composition according to any one of (1) to (6), wherein the D-form ratio of the polylactic acid is 4% or more. (8) The thermoplastic resin composition according to any one of (1) to (7), wherein the melting point of the polylactic acid is 160°C or less. (9) The thermoplastic resin composition according to any one of (1) to (8), wherein the weight-average molecular weight (Mw) of the polylactic acid is 150,000 or more. (10) The thermoplastic resin composition according to any one of (1) to (9), which has a tensile elongation of 150% or more, a flexural modulus of 500 MPa or more, and a melt tension of 8.0 mN or more. (11) A biodegradable agricultural material comprising the thermoplastic resin composition according to any one of (1) to (10). (12) The biodegradable agricultural material according to any one of (1) to (11), which is an agricultural mulch film.(13) A method for producing the thermoplastic resin composition according to any one of (1) to (12), comprising the step of kneading an aliphatic polyester resin, an aliphatic-aromatic polyester resin, and trehalose at a temperature at which the aliphatic polyester resin and the aliphatic-aromatic polyester resin melt but the trehalose does not melt, to obtain an extrudate.

[0013] The present disclosure makes it possible to provide a thermoplastic resin composition for biodegradable agricultural materials that has excellent toughness, stretchability, and flexibility, is highly biodegradable, and can improve soil after being plowed in.

[0014] 10 is a SEM photograph showing the decomposition state of each mulch film in Test Example 4. 11 is a photograph showing the decomposition state of each mulch film after being plowed in in Test Example 4.

[0015] The present embodiment is a thermoplastic resin composition for biodegradable agricultural materials, which comprises a biodegradable aliphatic polyester resin (hereinafter also simply referred to as an aliphatic polyester resin), a biodegradable aliphatic-aromatic polyester resin (hereinafter also simply referred to as an aliphatic-aromatic polyester resin), and trehalose.

[0016] This embodiment provides a thermoplastic resin composition for biodegradable agricultural materials that has excellent toughness, elasticity, and flexibility, is highly biodegradable, and can improve soil after plowing. Specifically, a polymer alloy was prepared to take advantage of the advantages of each polymer: an aliphatic polyester resin with a high flexural modulus and excellent toughness, and an aliphatic aromatic polyester resin with a high tensile elongation and excellent elasticity and flexibility. These polyester resins were then combined to form a biodegradable resin. This resulted in a thermoplastic resin composition with the toughness, elasticity, and flexibility required for agricultural materials. The thermoplastic resin composition according to this embodiment has moderate toughness for agricultural use, resulting in high resistance to fracture, and excellent elasticity and flexibility, resulting in high resistance to elastic deformation. Excellent elasticity and flexibility allow the composition to easily conform to the shape of field ridges, for example, when used as an agricultural mulch film, and can suppress tearing during expansion and contraction. Furthermore, in this embodiment, trehalose is incorporated into the thermoplastic resin composition. The inclusion of trehalose results in higher biodegradability than that of materials not containing trehalose. This is presumably because, when agricultural materials made using the thermoplastic resin composition of this embodiment, i.e., the agricultural materials of this embodiment, are plowed into soil, trehalose elutes from the agricultural materials due to moisture in the soil, and decomposition of the biodegradable resin proceeds from the eluted area, resulting in higher biodegradability than those not containing trehalose. Furthermore, when the agricultural materials of this embodiment are plowed into soil, soil improvement effects can be achieved. Specifically, in this example, the soil after plowed into the agricultural materials of this embodiment surprisingly exhibited high phosphorus cycling active sites and was highly evaluated in the pattern classification of SOFIX soil analysis.

[0017] The thermoplastic resin composition for agricultural materials according to this embodiment will be described in detail below.

[0018] <Thermoplastic resin composition for biodegradable agricultural materials> This embodiment is a thermoplastic resin composition for biodegradable agricultural materials, which contains a biodegradable aliphatic polyester resin, a biodegradable aliphatic aromatic polyester resin, and trehalose. Examples of biodegradable agricultural materials include agricultural mulch films and seedling pots.

[0019] (Biodegradable Resin) In the thermoplastic resin composition according to this embodiment, a biodegradable aliphatic polyester resin and a biodegradable aliphatic aromatic polyester resin are used in combination as the biodegradable resin. These biodegradable polyester resins are polyester resins that are naturally decomposed by microorganisms, enzymes, etc. in the environment, and can be decomposed by the action of various microorganisms and enzymes present in soil and water. The biodegradable polyester resin used in this embodiment may be, for example, a polyester resin that satisfies the biodegradability specified in any of ISO 14851, ISO 14855, ISO 9408, ISO 9439, ISO 10707, JIS K 6950, JIS K 6951, JIS K 6953, or JIS K 6955.

[0020] Aliphatic polyester resins have a high flexural modulus, which is an indicator of a material's hardness and toughness. Materials with a high flexural modulus tend to return to their original shape quickly when deformed, and the resin has strong resistance to bending stress. On the other hand, materials with a low flexural modulus tend to take longer to return to their original shape after deformation, or the deformation tends to be permanent.

[0021] Aliphatic aromatic polyester resins also have high tensile elongation. Tensile elongation is an index of a material's ductility, e.g., how much a material can deform under tensile stress. A high tensile elongation indicates high flexibility and stretchability of the material. Materials with high tensile elongation are easily stretched and can tolerate large displacements without breaking during deformation, which is particularly important for applications and product designs that require stretchability and flexibility. When a resin has a high tensile elongation, it has the property of easily maintaining the stretched state even when subjected to large deformations. On the other hand, materials with a low tensile elongation tend to be brittle and have limited stretchability.

[0022] Through extensive research, the present inventors have found that when a thermoplastic resin composition has a flexural modulus of 500 MPa or more and a tensile elongation of 150% or more, it is possible to provide an agricultural material that has adequate toughness as an agricultural material and is excellent in stretchability and flexibility. The inventors conducted research using a flexural modulus of 500 MPa or more and a tensile elongation of 150% or more as indicators. The flexural modulus can be measured in accordance with ISO 178. The tensile elongation can be measured in accordance with ISO 527. Note that these indicators are merely guidelines and do not limit the scope of the present embodiment.

[0023] Examples of aliphatic polyester resins include polyester resins containing lactic acid as a constituent component, i.e., polylactic acid. Examples of aliphatic polyester resins also include polyester resins containing an aliphatic and / or alicyclic diol compound and an aliphatic and / or alicyclic dicarboxylic acid compound as constituent components. The aliphatic polyester resins may be used alone or in combination of two or more. Aliphatic polyester resins tend to have a high flexural modulus and high resistance to bending stress, but a low tensile elongation.

[0024] Examples of the diol compound include those having a carbon number of typically 2 or more and 10 or less, and specific examples include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Among these, ethylene glycol or 1,4-butanediol is preferred, and 1,4-butanediol is more preferred. One type of diol compound may be used alone, or two or more types may be used in combination.

[0025] Examples of the dicarboxylic acid compound include those having a carbon number of typically 2 to 10, specifically succinic acid, oxalic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. Among these, succinic acid or adipic acid is preferred. The dicarboxylic acid compound may be used alone or in combination of two or more.

[0026] Examples of aliphatic polyester resins include polylactic acid (PLA), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), polybutylene succinate adipate (PBSA), polycaprolactone (PCL), polyethylene succinate (PES), and polyethylene succinate adipate. Among these, for example, polybutylene succinate (PBS) is an aliphatic polyester resin composed of two raw materials, succinic acid and 1,4-butanediol. PBS is composed of butylene succinate as a polymerization unit, and C ８ H １２ O ４has a repeating structure. Furthermore, polyhydroxyalkanoate (PHA) contains hydroxyalkanoic acid, which is a raw material component, as a polymerization component, and has at least a repeating unit derived from hydroxyalkanoic acid. Polyhydroxyalkanoate (PHA) can be, for example, a compound produced in the body of a microorganism that feeds on carbohydrates, oils, fats, etc. Polyhydroxyalkanoate may be artificially synthesized or may be biosynthesized by a microorganism. Examples of hydroxyalkanoic acids include glycolic acid, 3-hydroxybutyrate, 3-hydroxypropionate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynanoate, 3-hydroxydecanoate, 3-hydroxytetradecanoate, 3-hydroxyhexadecanoate, 3-hydroxyoctadecanoate, 4-hydroxybutyrate, 4-hydroxyvalerate, 5-hydroxyvalerate, and 6-hydroxyhexanoate. The number of carbon atoms in the hydroxyalkanoic acid may be 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, or 8 or more, preferably 3 or more. The number of carbon atoms in the hydroxyalkanoic acid may be 15 or less, 12 or less, 10 or less, 8 or less, 6 or less, or 4 or less, preferably 10 or less, and particularly 6 or less. One type of hydroxyalkanoic acid may be used alone, or two or more types may be used in combination. Preferred examples of the polyhydroxyalkanoate include poly(3-hydroxyalkanoate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0027] Aliphatic aromatic polyester resins contain an aromatic dicarboxylic acid compound as a constituent component in addition to the aliphatic and / or alicyclic diol compound and the aliphatic and / or alicyclic dicarboxylic acid compound, which are constituent components (polymerization components) of aliphatic polyester resins. The content of the aromatic dicarboxylic acid unit is, for example, 5 to 95 mol %, preferably 35 to 65 mol %, based on the total of the aliphatic and / or alicyclic dicarboxylic acid unit and the aromatic dicarboxylic acid unit. Aliphatic aromatic polyester resins tend to have a high tensile elongation and excellent stretchability and flexibility, but a low flexural modulus.

[0028] Examples of diol compounds that provide diol units include those having 2 to 10 carbon atoms, and specific examples include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Of these, ethylene glycol or 1,4-butanediol is preferred. Examples of dicarboxylic acid compounds that provide dicarboxylic acid units include those having 2 to 10 carbon atoms, and specific examples include succinic acid, oxalic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. Of these, succinic acid or adipic acid is preferred. Examples of aromatic dicarboxylic acid compounds that provide aromatic dicarboxylic acid units include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid. Of these, terephthalic acid or isophthalic acid is preferred. These compounds may be used alone or in combination of two or more.

[0029] Representative examples of aliphatic aromatic polyester resins include polybutylene adipate terephthalate (PBAT), polybutylene sebacate terephthalate, and polybutylene succinate terephthalate. Of these, polybutylene adipate terephthalate is preferred. Polybutylene adipate terephthalate has a high tensile elongation and excellent stretchability and flexibility, but tends to have a low flexural modulus. PBAT is an enzymatically degradable biodegradable resin, and decomposition occurs primarily through enzymes secreted by microorganisms in the soil, cleaving the polymer bonds. After being decomposed into oligomers by the enzymes, PBAT is further decomposed into the components that make up the resin (1,4-butanediol, adipic acid, and terephthalic acid).

[0030] In order to impart biodegradability to an aliphatic aromatic polyester resin, it is desirable that an aliphatic chain be present between aromatic rings. Therefore, the amount of aromatic dicarboxylic acid units in the aliphatic aromatic polyester resin is usually preferably 5 mol % or more and 50 mol % or less, more preferably 10 mol % or more and 48 mol % or less, and even more preferably 15 mol % or more and 45 mol % or less, based on the total amount of aliphatic and / or alicyclic dicarboxylic acid units and aromatic dicarboxylic acid units.

[0031] The thermoplastic resin composition according to this embodiment contains an aliphatic polyester resin and an aliphatic aromatic polyester resin as biodegradable resins. That is, a combination of an aliphatic polyester resin and an aliphatic aromatic polyester resin is used as the biodegradable polyester resin. Aliphatic polyester resins tend to have a high flexural modulus but a low tensile elongation. On the other hand, aliphatic aromatic polyester resins tend to have a high tensile elongation but a low flexural modulus. Therefore, in this embodiment, by appropriately combining an aliphatic polyester resin and an aliphatic aromatic polyester resin, it is possible to appropriately adjust the tensile elongation and flexural modulus to be within a range suitable for agricultural materials.

[0032] In this embodiment, the aliphatic polyester resin preferably includes polylactic acid (PLA), and the aliphatic aromatic polyester resin preferably includes polybutylene adipate terephthalate (PBAT). That is, polylactic acid and polybutylene adipate terephthalate are used in combination as the biodegradable resin. Polylactic acid has a high flexural modulus but a low tensile elongation. Polybutylene adipate terephthalate has a low flexural modulus but a high tensile elongation. Therefore, by appropriately combining polylactic acid and polybutylene adipate terephthalate, it is possible to obtain a tensile elongation and flexural modulus within a range suitable for agricultural materials.

[0033] In general, aliphatic polyester resins have a higher melting point than aliphatic aromatic polyester resins, but in this embodiment, the melting point of the aliphatic polyester resin is not particularly limited, and is, for example, 180° C. or lower, preferably 170° C. or lower, preferably 160° C. or lower, preferably 155° C. or lower, and preferably 150° C. or lower. By using an aliphatic polyester resin with a low melting point, the molding temperature can be set low, and thermal decomposition of trehalose can be suppressed.

[0034] Specifically, for example, the melting point of polylactic acid is not particularly limited, but is, for example, 180°C or lower, preferably 160°C or lower, preferably 155°C or lower, and preferably 150°C or lower. By using polylactic acid with a melting point of 160°C or lower, the molding temperature can be effectively set low, and as a result, thermal decomposition of trehalose due to heating during molding can be suppressed, allowing trehalose to remain efficiently in the thermoplastic resin composition or agricultural material. The melting point of polylactic acid is, for example, 100°C or higher. The melting point can be measured by DSC.

[0035] Polylactic acid is a polymer of lactic acid, and its melting point varies widely, for example, from about 120°C to about 180°C. The melting point of polylactic acid is determined by the proportion of D-lactic acid (D-form) contained in the polymer (referred to as the D-form ratio). That is, the melting point of polylactic acid can be adjusted, for example, by the D-form ratio of polylactic acid. Lactic acid contained in polylactic acid can be in the form of either the D-form or the L-form, but if a large amount of D-form is contained, the crystalline structure will be disrupted, resulting in a lower melting point. The D-isomer ratio can be calculated by {(D-isomer content / (D-isomer content+L-isomer content)}×100(%). The D-isomer ratio of polylactic acid is preferably 4% or more. The D-isomer ratio of polylactic acid is preferably 20% or less, preferably 18% or less, preferably 16% or less, preferably 14% or less, preferably 12% or less, and preferably 10% or less. When the D-isomer ratio of polylactic acid is 4% or more, the melting point of polylactic acid decreases, and therefore the molding temperature can be effectively set low. Examples of polylactic acid having a D-isomer ratio of 4% or more include Ingeo Biopolymer, commercially available from NatureWorks. Examples of polylactic acids that can be used include Ingeo Biopolymer 4060D, Ingeo Biopolymer 4060D, and Ingeo Biopolymer 4060D.

[0036] The melt flow rate (MFR) of polylactic acid is preferably 5 to 11, and more preferably 6 to 10. When the MFR value is 5 or more and 11 or less, the viscosity increases, making it easier to achieve molding processing by inflation molding. The MFR of the copolymer can be measured in accordance with JIS K 7210 at 210°C under a load of 2.16 kg, and is expressed in g / 10 min.

[0037] The D-form ratio of polylactic acid can be measured, for example, by a method using HPLC. Specifically, polylactic acid is first freeze-pulverized to form a powder, and the powder is refluxed in a 1N aqueous solution of sodium hydroxide to hydrolyze it into lactic acid (monomer). After neutralizing the solution, it is analyzed by HPLC to obtain HPLC chromatograms of D- and L-lactic acid. The D-form ratio of lactic acid is calculated from the peak areas of the obtained D- and L-lactic acid.

[0038] The weight-average molecular weight (Mw) of polylactic acid is not particularly limited, but is, for example, 50,000 to 1,000,000, preferably 100,000 to 750,000. From the viewpoint of melt viscosity, the weight-average molecular weight of polylactic acid is preferably 150,000 or more, more preferably 160,000 or more, and even more preferably 170,000 or more. When the weight-average molecular weight of polylactic acid is 150,000 or more, the mechanical properties and melt viscosity of the thermoplastic resin composition can be improved, facilitating film formation. Therefore, film-like products such as agricultural mulch films (e.g., agricultural mulch films with a thickness of 50 μm or less) can be efficiently produced. Specifically, when the weight-average molecular weight of polylactic acid is 150,000 or more, excellent moldability during inflation molding is achieved, making it easy to form a film with a thickness suitable for agricultural mulch films. The weight average molecular weight (Mw) of polylactic acid can be determined, for example, by gel permeation chromatography (GPC) in comparison with a standard substance (such as polystyrene) of known molecular weight.

[0039] Polybutylene adipate terephthalate (PBAT) is a biodegradable resin and an aliphatic aromatic polyester resin containing, as main structural units, structural units derived from adipic acid, structural units derived from terephthalic acid, and structural units derived from 1,4-butanediol. Specifically, polybutylene adipate terephthalate is a copolymer of adipic acid, terephthalic acid, and butanediol. Adipic acid, terephthalic acid, and butanediol do not need to be copolymerized simultaneously, and may be copolymerized in multiple stages.

[0040] When synthesizing polybutylene adipate terephthalate, in addition to adipic acid, terephthalic acid, and butanediol, trace amounts of other copolymerization components may be added. Examples of other copolymerization components include dicarboxylic acids other than terephthalic acid and adipic acid, and modifiers for the purposes of chain extension, terminal blocking, etc. These may be used alone or in combination of two or more.

[0041] Other dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, etc. These may be used alone or in combination of two or more.

[0042] Polybutylene adipate terephthalate is a copolymer (e.g., a random copolymer) of 1,4-butanediol, adipic acid, and terephthalic acid, and is preferably a PBAT obtained by reacting (a) a mixture consisting mainly of 35 to 95 mol % of adipic acid or an ester-forming derivative thereof, or a mixture thereof, and 5 to 65 mol % of terephthalic acid or an ester-forming derivative thereof, or a mixture thereof (the sum of the individual mol % is 100 mol %) with (b) a mixture containing butanediol (wherein the molar ratio of (a) to (b) is 0.4:1 to 1.5:1).

[0043] Of all components constituting polybutylene adipate terephthalate (100 mol %), the total content of the adipic acid component, the terephthalic acid component, and the butanediol component is preferably 70 mol % or more, more preferably 80 mol % or more, more preferably 90 mol % or more, more preferably 95 mol % or more, and more preferably 99 mol % or more.

[0044] The melting point of polybutylene adipate terephthalate is, for example, about 100 to 130° C. The MFR of polybutylene adipate terephthalate is preferably about 2 to 8 g / 10 min, and more preferably about 2 to 5 g / 10 min.

[0045] The weight average molecular weight (Mw) of the PBAT is preferably 35,000 or more. This allows the melt viscosity of the thermoplastic resin composition to be effectively improved. The weight average molecular weight (Mw) of the PBAT is preferably 150,000 or less. This allows the flexibility of the thermoplastic resin composition to be effectively improved. The weight average molecular weight (Mw) can be determined, for example, by gel permeation chromatography (GPC) by comparison with a standard substance of known molecular weight (e.g., polystyrene).

[0046] Examples of polybutylene adipate terephthalate include Ecoflex (registered trademark) manufactured by BASF Japan Ltd., Origo-Bi (registered trademark) manufactured by Novamont, and ECOPOND (registered trademark) manufactured by Kingfisher Science & Technology Co., Ltd. These may be used alone or in combination of two or more. Examples of Ecoflex manufactured by BASF Japan Ltd. include "Ecoflex (registered trademark) F Blend C1200" (melting point: 110 to 120°C).

[0047] (Trehalose) The thermoplastic resin composition according to this embodiment contains trehalose in addition to the biodegradable resin.

[0048] Agricultural materials containing trehalose have higher biodegradability than agricultural materials without trehalose. This is presumably because, when agricultural materials are plowed into soil, trehalose elutes from the agricultural materials due to moisture in the soil, and decomposition of the biodegradable resin proceeds from the eluted area, resulting in higher biodegradability than those without trehalose. Furthermore, when agricultural materials according to this embodiment containing trehalose in addition to a biodegradable resin are plowed into soil, they can achieve a better soil improvement effect than those without trehalose. This is presumably because the soil improvement effect is achieved not only by the decomposition products of the biodegradable resin but also by the trehalose eluted into the soil. Examples of trehalose include Treha (registered trademark) manufactured by Nagase Vita Co., Ltd.

[0049] (Composition) The content of trehalose in the thermoplastic resin composition is not particularly limited, but is preferably 5% by mass or more, preferably 10% by mass or more, and preferably 15% by mass or more. When the trehalose content is 5% by mass or more, the biodegradability-improving effect and soil improvement effect of trehalose can be effectively obtained. The content of trehalose in the thermoplastic resin composition is not particularly limited, but is preferably 30% by mass or less, and preferably 25% by mass or less. When the trehalose content is 30% by mass or less, the decrease in tensile elongation of the thermoplastic resin composition due to the addition of trehalose can be suppressed.

[0050] The content of the aliphatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 10% by mass or more, and preferably 15% by mass or more. When the content of the aliphatic polyester resin is 10% by mass or more, excellent toughness can be effectively imparted. The content of the aliphatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 45% by mass or less, preferably 40% by mass or less, preferably 35% by mass or less, and preferably 30% by mass or less.

[0051] The content of the aliphatic aromatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 45% by mass or more, preferably 50% by mass or more, and preferably 55% by mass or more. When the content of the aliphatic aromatic polyester resin is 45% by mass or more, excellent flexibility and stretchability can be effectively imparted. The content of the aliphatic aromatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 80% by mass or less, preferably 75% by mass or less, and preferably 70% by mass or less.

[0052] The content of the aliphatic polyester resin and the aliphatic aromatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 60% by mass or more, preferably 65% ​​by mass or more, preferably 70% by mass or more, preferably 75% by mass or more, preferably 80% by mass or more, preferably 85% by mass or more, and preferably 90% by mass or more. When the content of the aliphatic polyester resin and the aliphatic aromatic polyester resin is 60% by mass or more, a thermoplastic resin composition having appropriate toughness and excellent stretchability and flexibility for agricultural materials can be effectively obtained. The content of the aliphatic polyester resin and the aliphatic aromatic polyester resin in the thermoplastic resin composition is not particularly limited, but is preferably 95% by mass or less, preferably 90% by mass or less.

[0053] The content ratio of the aliphatic polyester resin to the aliphatic aromatic polyester resin is preferably 1:1 to 1:5, and more preferably 1:2 to 1:4.

[0054] The thermoplastic resin composition according to this embodiment may contain other resins in addition to the aliphatic polyester resins and the aliphatic aromatic polyester resins. Examples of other resins in addition to the aliphatic polyester resins and the aliphatic aromatic polyester resins include polyester resins other than the aliphatic polyester resins and the aliphatic aromatic polyester resins, polystyrene resins, polyolefin resins, vinyl chloride resins, polycarbonate resins, polyamide resins, acrylic resins, and polyoxymethylene resins. The other resins are preferably biodegradable resins. These may be used alone or in combination of two or more. When other resins are contained, the content of the other resins in the thermoplastic resin composition is, for example, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.1% by mass. In one embodiment, the thermoplastic resin composition does not contain other resins.

[0055] The thermoplastic resin composition according to this embodiment may contain additives such as plasticizers, lubricants, fillers, heat stabilizers, antioxidants, UV absorbers, antistatic agents, antiblocking agents, antifogging agents, flame retardants, colorants, pinning agents (alkaline earth metals), softeners, or compatibilizers, as long as the effects of this embodiment are not impaired. The additives may be used alone or in combination of two or more. The additives may be added in the form of a masterbatch containing additives such as colorants.

[0056] The content of the additive in the thermoplastic resin composition is, for example, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less. The content of the additive in the thermoplastic resin composition is, for example, 0.01% by mass or more, 0.1% by mass or more, or 0.5% by mass or more.

[0057] (Characteristic Values) From the viewpoint of the physical properties required for agricultural materials, the tensile elongation of the thermoplastic resin composition measured in accordance with ISO 527 is preferably 150% or more, and more preferably 200% or more. Furthermore, the tensile elongation of the thermoplastic resin composition is not particularly limited, but is preferably 500% or less, and more preferably 450% or less.

[0058] From the viewpoint of the physical properties required for agricultural materials, the flexural modulus of the thermoplastic resin composition measured in accordance with ISO 178 is preferably 500 MPa or more, preferably 550 MPa or more, preferably 600 MPa or more, preferably 650 MPa or more, or preferably 700 MPa or more. In addition, the flexural modulus is preferably 1500 MPa or less, preferably 1400 MPa or less, preferably 1300 MPa or less, or preferably 1200 MPa or less.

[0059] When the tensile elongation and flexural modulus are within the above ranges, the film can have toughness, stretchability, and flexibility suitable for use as an agricultural material (for example, agricultural mulch film).

[0060] From the viewpoint of producing agricultural materials, particularly agricultural mulch films, the melt tension of the thermoplastic resin composition measured in accordance with ISO 11443 (melting temperature 190°C, extrusion speed 10 m / min, take-up speed 5 m / min) is preferably 8.0 mN or more, preferably 8.5 mN or more, preferably 9.0 mN or more, preferably 9.5 mN or more, preferably 10.0 mN or more. When the melt tension is within the above range, a thin agricultural mulch film can be successfully produced.

[0061] <Method for producing thermoplastic resin composition> The method for producing a thermoplastic resin composition according to this embodiment includes a step of kneading an aliphatic polyester resin, an aliphatic aromatic polyester resin, and trehalose at a temperature at which the aliphatic polyester resin and the aliphatic aromatic polyester resin melt but the trehalose does not melt, to obtain an extrudate.

[0062] The thermoplastic resin composition according to this embodiment can be produced by kneading trehalose at a temperature at which the aliphatic polyester resin and the aliphatic-aromatic polyester resin melt, and then forming a solid in the form of pellets or the like. Specifically, for example, an aliphatic polyester resin, an aliphatic-aromatic polyester resin, trehalose, and various additives, if necessary, are added, and the mixture is mixed and melt-kneaded using a batch mixer such as a kneader, roll mill, super mixer, high-speed mixer, ball mill, sand mill, attritor, or Banbury mixer, a single-screw extruder, a twin-screw extruder, or a rotor-type twin-screw kneader, to form an extrudate in the form of pellets, powder, granules, or beads. Because of their strong kneading power and ease of subsequent molding, forming into pellets or the like using a single-screw or twin-screw extruder is preferred.

[0063] The thermoplastic resin composition may be used in the form of either a masterbatch or a compound. In the case of a masterbatch, after producing the masterbatch, an aliphatic polyester resin and an aliphatic aromatic polyester resin are used as diluents as the main resin of the agricultural material, and the masterbatch is blended to produce the agricultural material. The biodegradable resin used as the diluent may be the same as or different from that used in producing the masterbatch, but using the same biodegradable resin is preferred because it provides excellent compatibility between the thermoplastic resin composition and the resin. In the case of a compound, after producing the compound, the agricultural material can be produced using the compound as is.

[0064] <Biodegradable Agricultural Materials> The thermoplastic resin composition according to this embodiment is used in biodegradable agricultural materials. Examples of agricultural materials include agricultural mulch films and seedling pots. Agricultural mulch films are films (sheets) used for purposes such as increasing or maintaining soil temperature and controlling pests. Seedling pots are a type of dedicated container for growing seedlings.

[0065] The agricultural material according to this embodiment is a biodegradable agricultural material containing the thermoplastic resin composition according to this embodiment. The agricultural material according to this embodiment can be obtained by melting the thermoplastic resin composition according to this embodiment and molding it.

[0066] Furthermore, the agricultural material according to this embodiment can also be obtained by dry-blending the raw materials and directly feeding the blend into a film extruder or an inflation molding machine for molding, without first going through the thermoplastic resin composition according to this embodiment. Thus, the agricultural material according to this embodiment is a biodegradable agricultural material comprising a biodegradable aliphatic polyester resin, a biodegradable aliphatic aromatic polyester resin, and trehalose.

[0067] The thickness of the agricultural mulch film is not particularly limited, but is, for example, 8 μm to 50 μm, preferably 10 μm to 40 μm, and preferably 12 μm to 30 μm. When the mulch film is 8 μm or thicker, holes are less likely to form during molding, resulting in stable moldability. The effect of maintaining soil temperature is also enhanced. Furthermore, the film strength is increased, making it less likely to break during spreading. When the mulch film is 50 μm or thicker, the amount of materials used, such as biodegradable resins and trehalose, can be reduced.

[0068] <Method for producing biodegradable agricultural material> The method for producing an agricultural material according to this embodiment includes the steps of melting the thermoplastic resin composition according to this embodiment at a temperature at which the aliphatic polyester resin and the aliphatic-aromatic polyester resin melt but the trehalose does not melt, and molding the resin.

[0069] The thermoplastic resin composition according to this embodiment can be thermoformed by extrusion, injection, or the like using an extruder, injection molding machine, or the like typically used for molding plastics. Heating during molding is preferably performed so that the material temperature is lower than the melting point of trehalose (e.g., 200°C), even though the biodegradable resin melts. By performing heat molding under these conditions, melting or decomposition of trehalose during molding can be suppressed. During molding, the temperature of the molten material may rise above the target temperature of the equipment due to factors such as sliding heat generation. Heating at an excessively high temperature can melt or decompose trehalose, so caution is required. Specifically, the temperature of the material (molten material) during heating is preferably 150°C or higher and 180°C or lower. Furthermore, as described above, it is preferable to use polylactic acid with a high D-isomer ratio (e.g., 4% or higher) as the aliphatic polyester resin.

[0070] In this embodiment, since at least two types of biodegradable resins are used, it is preferable to use a twin-screw extruder. The thermoplastic resin composition melted in the extruder is molded into a sheet, film, or other molded product using a T-die, inflation, or the like. The film may be stretched or unstretched. Molded products can also be obtained using an injection molding machine or the like and used as agricultural materials.

[0071] The method for molding the seedling pots is not particularly limited, but suitable methods include blow molding, in which a thermoplastic resin composition that has been plasticized by heating is extruded and then placed directly into a mold without being cooled and solidified, and air is blown into the extruded thermoplastic resin composition; and vacuum molding, in which a sheet or film of a thermoplastic resin composition that has been plasticized by heating is placed on a mold and vacuum-suctioned from the inside of the mold to form the extruded thermoplastic resin composition.

[0072] The molding method for the mulch film is not particularly limited, but suitable examples include extrusion molding, in which a film extruded through a T-die using an extruder is cooled and solidified using a cast roll, or molding using an inflation molding machine. The molding method can be any commonly used film manufacturing method. Examples include T-die molding, inflation molding, and calendar molding. Furthermore, the film can be unstretched or uniaxially or biaxially stretched.

[0073] In the method for producing the mulch film, a compound as the thermoplastic resin composition according to this embodiment may be fed into a film extruder or an inflation molding machine, or the respective raw materials may be dry blended and fed directly into the film extruder or the inflation molding machine.

[0074] The present embodiment will be described below using examples. Note that the present embodiment is not limited to the aspects of the examples, and the configuration can be appropriately changed within the scope of the gist of the present disclosure.

[0075] (Materials used) Polylactic acid (PLA): trade name "Luminy (registered trademark) L130" (manufactured by Total Corbion) Polylactic acid (PLA): trade name "Ingeo Biopolymer 2003D" (manufactured by NatureWorks) Polybutylene succinate (PBS): trade name "FORZEAS ZM9B02" (manufactured by Mitsubishi Chemical Corporation) Polybutylene succinate (PBS): trade name "FORZEAS DA9005" (manufactured by Mitsubishi Chemical Corporation) Polyvinyl alcohol (PVA): trade name "MOWFLEX C-500T" (manufactured by Kuraray Co., Ltd.) Polybutylene adipate terephthalate (PBAT): trade name "ecoflex (registered trademark) F blend" C1200 (manufactured by BASF Japan Ltd.) Trehalose: trade name "Treha (registered trademark)" (manufactured by Nagasevita Co., Ltd.) Antioxidant: trade name "Irganox 1010" (manufactured by BASF Japan Ltd.)

[0076] (Preparation of resin compound for forming dumbbells) The predetermined materials were fed into a twin-screw extruder (manufactured by Shibaura Machine Co., Ltd., product name "TEM18SS", extrusion temperature: 190°C, φ: 18 mm) to prepare a resin compound. The molding temperature was 180 to 190°C, and the rotation speed was 200 rpm.

[0077] (Injection molding of dumbbells for measuring physical properties) Using the resin compound, dumbbells for test pieces conforming to ISO were molded using an 80-ton injection molding machine (Toyo Machinery Metal Co., Ltd., product name "Sj-80IV", molding temperature: 180 to 190°C, mold temperature: 50°C).

[0078] (Tensile elongation) An 80-ton injection molding machine (manufactured by Toyo Machinery & Metal Co., Ltd., trade name "Sj-80IV", molding temperature: 180 to 190°C, mold temperature: 50°C) was used to prepare an evaluation sample in accordance with ISO 20753. The tensile elongation of the evaluation sample was measured in accordance with ISO 527. The test speed was 50 mm / min, and the distance between supports was 114 mm.

[0079] In this example, one of the physical property values ​​of a material suitable for agricultural materials (especially agricultural mulch films) was a tensile elongation of 150% or more measured in accordance with ISO 527. However, this criterion does not limit the thermoplastic resin composition according to this embodiment.

[0080] (Flexural Modulus) An evaluation sample was prepared in accordance with ISO 20753 using an 80-ton injection molding machine (manufactured by Toyo Machinery & Metal Co., Ltd., trade name "Sj-80IV", molding temperature: 180 to 190°C, mold temperature: 50°C). The flexural modulus of the evaluation sample was measured in accordance with ISO 178. The test speed was 2 mm / min, and the distance between supports was 64 mm.

[0081] In this example, one of the targets for the physical properties of a material suitable for agricultural materials (especially agricultural mulch films) was a flexural modulus of 500 MPa or more measured in accordance with ISO 178. However, this criterion does not limit the thermoplastic resin composition according to this embodiment.

[0082] (Melt Tension) The melt tension was measured in accordance with ISO 11443. Specifically, a melt tension tester (trade name: Capilograph 1DPMD-C) manufactured by Toyo Seiki Seisakusho, Ltd. was used, and a certain amount of polymer was forcibly extruded from an orifice hole at a temperature of 190°C, and the tension generated when the polymer was pulled into a monofilament was detected with a strain gauge. The tension was measured while increasing the take-up speed at a constant rate with a take-up roll until the monofilament-like molten polymer broke, and the maximum value of the tension measured from the start of take-up to the break was taken as the melt tension (unit: mN). Orifice: diameter 1 mm, length 10 mm

[0083] Test Example 1: Preparation of thermoplastic resin composition Test Example 1-1: Comparative Example Polylactic acid (aliphatic polyester resin, Luminy L130, manufactured by Total Corbion, melting point: 175°C, D-isomer ratio: 1% or less, weight-average molecular weight: 130,000) and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbells was prepared according to the method described above. Using this compound, dumbbells for measuring physical properties were injection molded according to the method described above, and the properties were evaluated.

[0084]

[0085] When only polylactic acid was used as the biodegradable resin, the flexural modulus was high but the tensile elongation was low.

[0086] The melt tension of Sample No. 1 was measured in accordance with ISO 11443. The melt temperature was 190°C and the extrusion speed was 10 m / min. The melt tension was 1.7 mN at a take-up speed of 5 m / min, 1.9 mN at a take-up speed of 10 m / min, and 2.1 mN at a take-up speed of 20 m / min.

[0087] Test Example 1-2: Comparative Example Polybutylene succinate (aliphatic polyester resin, trade name "FORZEAS ZM9B02", manufactured by Mitsubishi Chemical Corporation) and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbells was prepared according to the method described above. Using this compound, dumbbells for measuring physical properties were injection molded according to the method described above, and evaluated.

[0088]

[0089] When only polybutylene succinate (FORZEAS ZM9B02) was used as the biodegradable resin, the flexural modulus was high but the tensile elongation was low.

[0090] Test Example 1-3: Comparative Example Polybutylene succinate (aliphatic polyester resin, trade name "FORZEAS DA9005", manufactured by Mitsubishi Chemical Corporation) and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbells was prepared according to the method described above. Using this compound, dumbbells for measuring physical properties were injection molded according to the method described above, and evaluated.

[0091]

[0092] When polybutylene succinate (FORZEAS DA9005) alone was used as the biodegradable resin, the tensile elongation was high but the flexural modulus was low when the trehalose content was low (0%, 10%), whereas the flexural modulus was high but the tensile elongation was low when the trehalose content was high (20%, 30%).

[0093] Test Example 1-4: Comparative Example Polyvinyl alcohol (trade name "MOWFLEX C-500T", manufactured by Kuraray Co., Ltd.) and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbells was prepared according to the method described above. Using this compound, dumbbells for measuring physical properties were injection molded according to the method described above, and evaluated.

[0094]

[0095] When only polyvinyl alcohol was used as the biodegradable resin, the tensile elongation was high but the flexural modulus was low when the trehalose content was low (10%), whereas the flexural modulus was high but the tensile elongation was low when the trehalose content was high (20%, 30%).

[0096] Test Example 1-5: Comparative Example Polybutylene adipate terephthalate (aliphatic aromatic polyester resin, product name "ecoflex (registered trademark) F blend C1200", manufactured by BASF Japan Ltd.) and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbells was prepared according to the method described above. Using this compound, dumbbells for measuring physical properties were injection molded according to the method described above, and evaluated.

[0097]

[0098] When only polybutylene adipate terephthalate was used as the biodegradable resin, the tensile elongation was high but the flexural modulus was low.

[0099] The melt tension of Sample No. 17 was measured in accordance with ISO 11443. The melt temperature was 190°C, and the extrusion speed was 10 m / min. The melt tension was 7.0 mN at a take-up speed of 5 m / min, 8.6 mN at a take-up speed of 10 m / min, and 8.8 mN at a take-up speed of 20 m / min.

[0100] (Test Examples 1-6: Examples) Polylactic acid (aliphatic polyester resin, trade name "Luminy (registered trademark) L130", manufactured by Total Corbion, melting point: 175°C, D-body ratio: 1%, MFR: 10 g / 10 min, weight-average molecular weight: about 130,000) or polylactic acid (aliphatic polyester resin, trade name "Ingeo Biopolymer 2003D", manufactured by NatureWorks, melting point: 150°C, D-body ratio: 4%, MFR: 6 g / 10 min, weight-average molecular weight: about 175,000), polybutylene adipate terephthalate (aliphatic aromatic polyester resin, trade name ecoflex (registered trademark) F blend) A resin compound for forming dumbbells was prepared according to the method described above, using the compound to injection-mold dumbbells for measuring physical properties according to the method described above.

[0101]

[0102] By using a combination of polylactic acid, an aliphatic polyester resin, and polybutylene adipate terephthalate, an aliphatic aromatic polyester resin, as the biodegradable resin, it was possible to obtain a resin composition that has high tensile elongation and flexural modulus, and that can achieve the target values ​​for both.

[0103] The melt tensions of Samples No. 22 and 23 were measured in accordance with ISO 11443. The melt temperature was 190°C, and the extrusion speed was 10 m / min. The melt tensions of Sample No. 22 were 8.7 mN at a take-up speed of 5 m / min, 9.2 mN at a take-up speed of 10 m / min, and 9.3 mN at a take-up speed of 20 m / min. The melt tensions of Sample No. 23 were 10.8 mN at a take-up speed of 5 m / min, 12.3 mN at a take-up speed of 10 m / min, and 12.8 mN at a take-up speed of 20 m / min. The melt tension of Sample No. 23 (PLA molecular weight: approximately 175,000) exceeded 10 mN, demonstrating a particularly high value. This is thought to be due to the high molecular weight of the PLA (2003D) used, which resulted in a high melt tension of the resin composition. High melt tension allows the film thickness to be thin, which is effective for forming film-like agricultural materials (e.g., agricultural mulch films). In practice, the film thickness is preferably 100 μm or less, more preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less.

[0104] Furthermore, the polylactic acid (2003D) used in Sample No. 23 has a high D-isomer ratio (4% or more) and a low melting point of approximately 150°C. Therefore, when molding a resin composition containing trehalose, the molding temperature can be effectively set lower than the melting point of trehalose (approximately 200°C), thereby suppressing melting or decomposition of trehalose during molding. In particular, during molding, the temperature of the molten material may rise above the target temperature set by the device due to factors such as sliding heat generation, and heating at such an excessively high temperature may result in melting or decomposition of trehalose. Therefore, by using polylactic acid with a high D-isomer ratio (e.g., 4% or more), the melting point of the biodegradable resin can be lowered, allowing the molding temperature to be set lower, thereby melting the biodegradable resin while suppressing melting or decomposition of trehalose. The melting point of polybutylene adipate terephthalate is about 110 to 120° C., which is lower than the melting point of polylactic acid, so the melting point of polybutylene adipate terephthalate does not pose any particular problem.

[0105] Test Example 2: Preparation of Film-Like Samples In the above test example (preparation of thermoplastic resin compositions), a film-like sample was prepared based on the composition of Sample No. 23, which achieved both the tensile elongation and flexural modulus targets. Specifically, various materials were fed into a twin-screw extruder (Shibaura Machine Co., Ltd., product name "TEM26SS," φ: 26 mm) according to the composition shown in the table below, and a resin compound was prepared at an extrusion temperature of 160°C and a rotation speed of 200 rpm. The PBAT-based compound in the table is "BDM OKC502 BLK" (Tokyo Ink Co., Ltd.), a masterbatch containing PBAT and carbon black. Trehalose was added via a top feed. The resins (PLA, PBAT, and PBAT-based compounds) were fed separately from the trehalose via a top feed. Trehalose and resins (PLA, PBAT, PBAT-based masterbatch) were fed as raw materials from separate weight feeders.

[0106]

[0107] The resin temperature (actual temperature) in the extruder was 167°C. By using polylactic acid (2003D) with a high D-isomer ratio as the polylactic acid, the molding temperature could be set low, and as a result, the actual temperature of the resin could be lowered. Therefore, the biodegradable resin could be melted while suppressing the melting or decomposition of trehalose.

[0108] The obtained resin compound was then fed into a single-screw extruder (manufactured by GSI Creos Corporation, φ: 40 mm) and film formation was carried out at an extrusion temperature of 160° C. The resin temperature (actual temperature) inside the extruder was 145° C. At a take-up speed of 10 m / min during film formation, a film having a film thickness of approximately 30 μm and free of defects such as holes could be obtained.

[0109] Furthermore, thermal analysis of the obtained film by DSC confirmed endothermic reaction due to trehalose, confirming the presence of trehalose in the film. This demonstrates that in this test example, a film containing trehalose can be formed while suppressing the melting or decomposition of trehalose.

[0110] Test Example 3: Preparation of agricultural mulch film Based on the film composition E1 shown in Test Example 2 above, mass production trials were carried out by inflation molding in order to be suitable for field testing.

[0111] First, compounds were prepared according to the compositions E1 and C1 shown in Table 1 below to prepare resin compositions.

[0112]

[0113] The compounding was carried out at Setsunan Chemical Co., Ltd., where the specified materials were fed into a twin-screw extruder (manufactured by The Japan Steel Works, Ltd., trade name "TEX44αII", φ: 44 mm) and a resin compound was produced at an extrusion temperature of 160 ° C. The resulting resin compound was used to produce a multi-film by inflation molding. The inflation molding was carried out using a single-screw extruder (manufactured by Placo Co., Ltd., φ: 600 mm) at an extrusion temperature of 160 ° C. and a discharge rate of 45 kg / hr.

[0114] Both resin compounds E1 and C1 produced agricultural mulch films with a thickness of approximately 30 μm. Furthermore, by adjusting the inflation molding conditions appropriately, films with a thickness of approximately 18-20 μm were also produced. No holes or other defects were present. Furthermore, thermal analysis and scanning electron microscope (SEM) observation of the film confirmed the presence of trehalose in the film and on its surface.

[0115] Test Example 4: Field test using trehalose-containing agricultural mulch film A field test was conducted using agricultural mulch films (thickness 30 μm, length 40 m) with compositions E1 and C1 prepared in Test Example 3. For reference, a general mulch film (manufactured by Iwatani Materials Corporation, made of PE, non-degradable, thickness 20 μm, length 40 m) and a biodegradable mulch film not containing trehalose (manufactured by Sunplac Industrial Co., Ltd., product name: Sanbio, thickness 20 μm, length 40 m) were also tested. The test location was Hiruzen, Maniwa City, Okayama Prefecture, and the test crop was sweet corn (variety: Dolce Dream).

[0116] Four 40-m-long ridges were constructed adjacent to each other in the same field, and then the ridges were leveled. Each leveled ridge was covered with an agricultural mulch film of composition E1 (trehalose-containing mulch film, made of PBAT / PLA), an agricultural mulch film of composition C1 (trehalose-free mulch film, made of PBAT / PLA), a trehalose-free biodegradable mulch film (biodegradable mulch film, manufactured by Sunplac Industrial Co., Ltd., made of PBS / PBAT), and a general mulch film (general mulch film, manufactured by Iwatani Materials Corporation, made of PE). The bottoms of the mulch films were buried and fixed in the soil. Two equally spaced vertical rows of holes were drilled on the surface of the laid mulch film, and sweet corn seedlings were planted therein. The sweet corn was grown and harvested using conventional methods.

[0117] As part of the evaluation, we investigated the yield, checked the decomposition status of the mulch film, and investigated the soil after the mulch film was decomposed.

[0118] (Yield Investigation) The average weight of 10 fruits randomly harvested from each of the plots containing agricultural mulch film of composition E1 (containing trehalose), agricultural mulch film of composition C1 (not containing trehalose), biodegradable mulch film (not containing trehalose), and general mulch film was measured. The results are shown in the table below.

[0119]

[0120] The above table confirms that the yield was highest in the plot cultivated using the agricultural mulch film (containing trehalose) of composition E1 according to this embodiment. This indicates that the use of the agricultural material according to this embodiment as an agricultural mulch film can improve crop yields. This is presumably because trehalose leaches out of the agricultural material into the soil due to moisture in the air or soil, rainwater, dewwater, etc.

[0121] (Decomposition of mulch film) The decomposition of each mulch film was observed by SEM at the start (when laid), two months after installation, before plowing in after harvest, and one month after plowing in. SEM photographs are shown in Figure 1.

[0122] Because general mulch films (general mulch films) do not decompose in the soil, SEM photographs were taken after harvesting and before incorporation, and then the films were removed without incorporation. The agricultural mulch films of composition E1 (trehalose-containing mulch films), the agricultural mulch films of composition C1 (trehalose-free mulch films), and the trehalose-free biodegradable mulch films (biodegradable mulch films) all showed some degree of decomposition before incorporation, but no obvious tears or tears were observed, and they still functioned as mulch films. However, decomposition accelerated after incorporation. The trehalose-free biodegradable mulch film (biodegradable mulch film) shown as a reference example shows an SEM photograph of the surface of the remaining film fragments, but the film fragments were very thin and easily torn, and were almost completely decomposed within one month of incorporation.

[0123] The agricultural mulch film of composition E1 (containing trehalose) had numerous holes on its surface, which were presumably formed by the elution of trehalose, and it was confirmed that decomposition spread from these holes. Therefore, it was confirmed that the agricultural mulch film of composition E1 (containing trehalose) has superior biodegradability compared to the agricultural mulch film of composition C1 (not containing trehalose).

[0124] To further investigate the decomposition status of each mulch film, 1.5 months after incorporation, a 30 cm x 30 cm x 10 cm sample of soil was collected from the incorporation site and passed through a 6 mm mesh sieve to examine the degree of decomposition. Figure 2 shows a photograph of the recovered film fragments. As shown in the photograph, the agricultural mulch film of composition E1 (containing trehalose) had a smaller maximum fragment size and a larger number of fragments than the agricultural mulch film of composition C1 (not containing trehalose). This confirmed that the agricultural mulch film of composition E1 (containing trehalose) had accelerated decomposition compared to the agricultural mulch film of composition C1 (not containing trehalose).

[0125] (Soil Investigation After Mulch Film Decomposition) Two weeks after plowing, soil samples with decomposed mulch film were collected, and SOFIX, a soil fertility index, was evaluated using SOFIX soil analysis. SOFIX soil analysis scientifically analyzes the biological properties of soil in addition to conventional soil analysis (analysis of soil chemistry and physical properties). The analysis results can be used to evaluate soil fertility. SOFIX soil analysis includes, for example, the following measurement items: nitrate nitrogen, ammonium nitrogen, exchangeable potassium, available phosphate, EC value, pH, total carbon, total nitrogen, total phosphorus, total potassium, C / N ratio, C / P ratio, total bacterial count, ammonia oxidation activity, nitrite oxidation activity, phosphorus cycle activity, nitrogen cycle activity, phytic acid decomposition activity, moisture content, and maximum water holding capacity.

[0126] The results are shown in Table 10. In particular, the soil plowed with agricultural mulch film (containing trehalose) of composition E1 showed a high phosphorus cycling activity site value of 21, and the total phosphorus content was reduced. This indicates that phosphorus in the soil is circulating and that plants are absorbing phosphorus. The soil plowed with agricultural mulch film (containing trehalose) of composition E1 was classified as "Special A" in the SOFIX soil analysis pattern classification. Since "Special A" indicates a good organic soil environment, it was confirmed that the agricultural mulch film (containing trehalose) of this embodiment of the present invention also has excellent soil improvement effects. In addition, the soil plowed with agricultural mulch film (not containing trehalose) of composition C1, biodegradable mulch film (not containing trehalose), and general mulch film was classified as "A2" in the SOFIX soil analysis pattern classification. "A2" indicates a basically good soil environment, but the phosphorus cycling is not appropriate. From the above results, it was confirmed that the agricultural mulch film E1 (containing trehalose) of this embodiment is an agricultural mulch film that has high biodegradability and can improve soil after plowing.

[0127]

[0128] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range.

[0129] The claims that follow this written disclosure are expressly incorporated into this written disclosure herein, with each claim standing on its own as a separate embodiment. The present disclosure includes all instances in which an independent claim is replaced by its dependent claim. Furthermore, any additional embodiments derived from the independent claim and the subsequent dependent claims are also expressly incorporated into this written specification.

[0130] Those skilled in the art can use the above description to make the most of the present disclosure. The claims and embodiments disclosed herein are merely descriptive and exemplary and should not be construed as limiting the scope of the present disclosure in any way. With the aid of this disclosure, changes can be made to the details of the above embodiments without departing from the basic principles of the present disclosure. In other words, various modifications and improvements of the embodiments specifically disclosed in the above specification are within the scope of the present disclosure.

[0131] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure.

[0132] This specification includes the disclosure of Japanese Patent Application No. 2024-010682, from which the present application claims priority. All publications, patents, and patent applications cited in this specification are incorporated herein by reference in their entirety.

Claims

1. A thermoplastic resin composition for use in biodegradable agricultural materials, comprising a biodegradable aliphatic polyester resin, a biodegradable aliphatic aromatic polyester resin, and trehalose.

2. A thermoplastic resin composition as described in claim 1, wherein the content of the aliphatic polyester resin in the composition is 10% by mass or more and 45% by mass or less, and the content of the aliphatic aromatic polyester resin in the composition is 45% by mass or more and 80% by mass or less.

3. A thermoplastic resin composition according to claim 1, wherein the sum of the content of the aliphatic polyester resin in the composition and the content of the aliphatic aromatic polyester resin in the composition is 60 mass% or more.

4. The thermoplastic resin composition according to claim 1, wherein the ratio of the content of the aliphatic polyester resin in the composition to the content of the aliphatic-aromatic polyester resin in the composition is 1:1 to 1:

5.

5. The thermoplastic resin composition according to claim 1, wherein the trehalose content in the composition is 5% by mass or more and 30% by mass or less.

6. The thermoplastic resin composition according to claim 1, wherein the aliphatic polyester-based resin comprises polylactic acid (PLA) and the aliphatic-aromatic polyester-based resin comprises polybutylene adipate terephthalate (PBAT).

7. The thermoplastic resin composition according to claim 6, wherein the proportion of D-isomer in the polylactic acid is 4% or more.

8. The thermoplastic resin composition according to claim 7, wherein the melting point of the polylactic acid is 160°C or lower.

9. The thermoplastic resin composition according to claim 6, wherein the weight average molecular weight (Mw) of the polylactic acid is 150,000 or more.

10. The thermoplastic resin composition according to claim 1, which has a tensile elongation of 150% or more, a flexural modulus of 500 MPa or more, and a melt tension of 8.0 mN or more.

11. A biodegradable agricultural material comprising the thermoplastic resin composition according to any one of claims 1 to 10.

12. The biodegradable agricultural material according to claim 11, which is an agricultural mulch film.

13. A method for producing the thermoplastic resin composition according to any one of claims 1 to 10, comprising the step of kneading an aliphatic polyester resin, an aliphatic-aromatic polyester resin, and trehalose at a temperature at which the aliphatic polyester resin and the aliphatic-aromatic polyester resin melt but the trehalose does not melt, to obtain an extrudate.

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