Thermoplastic resin composition for biodegradable agricultural material, biodegradable agricultural material, and method for manufacturing the same

Abstract

The present disclosure aims to provide a thermoplastic resin composition for biodegradable agricultural materials, which not only has suitable toughness, good stretchability and flexibility, and high biodegradability, but also has a soil-improving effect after being turned into soil. The present embodiment is a thermoplastic resin composition for biodegradable agricultural materials, which includes an aliphatic polyester resin having biodegradability, an aliphatic / aromatic polyester resin having biodegradability, and trehalose.

Description

Technical Field

[0001] This disclosure relates to a thermoplastic resin composition for use in biodegradable agricultural materials, biodegradable agricultural materials, and a method for manufacturing the same. Background Technology

[0002] In recent years, driven by considerations of sustainable development, there has been a particular demand for the development of biodegradable agricultural materials (such as agricultural mulch films and sheets) for practical agricultural applications. Because biodegradable agricultural materials degrade naturally after use, they can reduce adverse impacts on soil and water quality, thus lessening the environmental burden. Furthermore, biodegradable agricultural materials can be buried in the soil after use, providing valuable organic matter to the soil during the degradation process.

[0003] Agricultural materials can include, for example, agricultural mulch film or seedling pots. Since biodegradable agricultural materials can be incorporated into the soil after use to promote their degradation, they are expected to alleviate the waste problems of recent years and the manpower required for agricultural material recycling.

[0004] Public literature on biodegradable agricultural materials can be found in, for example, Patent Document 1 or Patent Document 2.

[0005] Patent document 1 discloses a cellulose biodegradable sheet with cellulose microfibers and trehalose as the main components.

[0006] Patent document 2 discloses a biodegradable mulch film whose degradation rate is controlled by at least one of an additive and a resin component. The biodegradable mulch film consists of at least a first layer and a second layer, the first layer and the second layer being made of biodegradable resin. At least one of the first layer and the second layer has a different degradation rate than the second layer due to the addition of the additive or the selection of the resin component. The first layer and the second layer are the surface layers of the biodegradable mulch film, and one of the first layer and the second layer is laid on the soil in a manner that is in contact with the soil surface.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Patent Application with Publication No. JP2001279016

[0010] Patent Document 2: Patent Application Publication No. JP2012205552 Summary of the Invention

[0011] The problem to be solved by the present invention

[0012] However, while the biodegradable agricultural materials in Patent Documents 1 and 2 are biodegradable, they fail to fully provide the required properties when used as agricultural materials. For example, when used as agricultural materials, for ease of processing and handling, the product needs not only appropriate toughness but also good elasticity and flexibility. However, Patent Documents 1 and 2 completely fail to consider this factor. Furthermore, since biodegradable agricultural materials are sometimes treated by being turned into the soil after use, they need to have good biodegradability in the soil. However, research on the soil improvement effect of biodegradable agricultural materials after being turned into the soil is not discussed in Patent Documents 1 and 2, nor in any other literature.

[0013] Therefore, the purpose of this disclosure is to provide a thermoplastic resin composition for biodegradable agricultural materials, which not only has good toughness, elasticity, flexibility and high biodegradability, but also has the effect of improving soil when turned into the soil.

[0014] Problem Solving Methods

[0015] In order to solve the above problems, the inventors discovered after in-depth research that by using aliphatic polyester resin and aliphatic / aromatic polyester resin as biodegradable resin and making them contain trehalose, a thermoplastic resin composition for biodegradable agricultural materials can be provided. This composition not only has good toughness, elasticity, flexibility and high biodegradability, but also has the effect of improving soil after being turned into the soil. Based on this, the present disclosure is made.

[0016] Accordingly, various aspects of this embodiment are, for example:

[0017] (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;

[0018] (2) The thermoplastic resin composition as described in (1), wherein the content of aliphatic polyester resin in the composition is more than 10% by weight and less than 45% by weight, and the content of aliphatic / aromatic polyester resin in the composition is more than 45% by weight and less than 80% by weight.

[0019] (3) The thermoplastic resin composition as described in 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 weight or more.

[0020] (4) The thermoplastic resin composition according to any one of (1) to (3), wherein the ratio of the content of aliphatic polyester resin in the composition to the content of aliphatic / aromatic polyester resin in the composition is 1:1 to 1:5;

[0021] (5) The thermoplastic resin composition as described in any one of (1) to (4), wherein the content of trehalose in the composition is more than 5% by weight and less than 30% by weight;

[0022] (6) The thermoplastic resin composition of any one of (1) to (5), wherein the aliphatic polyester resin includes polylactic acid (PLA) and the aliphatic / aromatic polyester resin includes polybutylene adipate / terephthalate (PBAT).

[0023] (7) The thermoplastic resin composition according to any one of (1) to (6), wherein the proportion of the D-isomer of polylactic acid is 4% or more;

[0024] (8) The thermoplastic resin composition according to any one of (1) to (7), wherein the melting point of polylactic acid is below 160°C;

[0025] (9) The thermoplastic resin composition of any one of (1) to (8), wherein the weight-average molecular weight (Mw) of polylactic acid is 150,000 or more;

[0026] (10) The thermoplastic resin composition according to any one of (1) to (9), wherein the thermoplastic resin composition has an elongation at break of 150% or more, a flexural modulus of 500 MPa or more, and a melt tension of 8.0 mN or more.

[0027] (11) A biodegradable agricultural material comprising a thermoplastic resin composition as described in any one of (1) to (10);

[0028] (12) The biodegradable agricultural material as described in any one of (1) to (11), wherein the biodegradable agricultural material is an agricultural mulch film;

[0029] (13) A method for manufacturing a thermoplastic resin composition as described in any one of (1) to (12), comprising the following steps:

[0030] Aliphatic polyester resin, aliphatic / aromatic polyester resin, and trehalose are blended at a temperature that melts the aliphatic polyester resin and the aliphatic / aromatic polyester resin without melting the trehalose to obtain an extrudate.

[0031] Invention Effects

[0032] According to this disclosure, a thermoplastic resin composition for use in biodegradable agricultural materials can be provided, which not only has good toughness, elasticity, flexibility and high biodegradability, but also has the effect of improving soil when turned into the soil. Attached Figure Description

[0033] Figure 1 The images shown are SEM photographs taken in Experiment 4 to demonstrate the degradation status of various plastic films.

[0034] Figure 2 The images shown are SEM photographs taken in Experiment 4 to demonstrate the degradation of various plastic films after they are turned into the soil. Detailed Implementation

[0035] This embodiment is a thermoplastic resin composition for biodegradable agricultural materials, the composition comprising aliphatic polyester resin (hereinafter referred to as aliphatic polyester resin), aliphatic / aromatic polyester resin (hereinafter referred to as aliphatic / aromatic polyester resin), and trehalose.

[0036] According to this embodiment, a thermoplastic resin composition for biodegradable agricultural materials can be provided. This composition not only possesses good toughness, elasticity, flexibility, and high biodegradability, but also improves soil quality when incorporated into the soil. Specifically, an aliphatic polyester resin with high flexural modulus and good toughness is blended with an aliphatic / aromatic polyester resin with high elongation and good elasticity and flexibility in a manner that allows each polymer to exert its advantages. The combined product of these two polyester resins is used as a biodegradable resin. Thus, a thermoplastic resin composition possessing the toughness, elasticity, and flexibility required for agricultural materials can be obtained. When the thermoplastic resin composition of this embodiment is used in agricultural materials, it exhibits high damage resistance due to its suitable toughness, and high resistance to elastic deformation due to its good elasticity and flexibility. Good elasticity and flexibility mean that, for example, when used as agricultural mulch, it can easily conform to the shape of field ridges, reducing tearing during expansion and contraction. Furthermore, in this embodiment, trehalose is also compounded into the thermoplastic resin composition. By compounding with trehalose, higher biodegradability can be obtained than when trehalose is not present. The reason is speculated to be as follows: When the agricultural material made with the thermoplastic resin composition of this embodiment (i.e., the agricultural material of this embodiment) is plowed into the soil, trehalose will be leached from the agricultural material by the action of water and other substances in the soil, so that the biodegradable resin will begin to degrade from the leached site, thereby achieving higher biodegradability compared to the case without trehalose. In addition, when the agricultural material of this embodiment is plowed into the soil, it can produce a soil improvement effect. Specifically, in this embodiment, a surprising point is that the soil after the agricultural material of this embodiment is plowed into not only obtains sites with high phosphorus cycling activity, but also obtains a high evaluation result in the pattern classification of SOFIX (Soil Fertility Index) soil analysis.

[0037] The thermoplastic resin composition for agricultural materials according to this embodiment will be described in detail below.

[0038] <Thermoplastic Resin Compositions for Biodegradable Agricultural Materials>

[0039] This embodiment discloses a thermoplastic resin composition for use in biodegradable agricultural materials. The composition comprises a biodegradable aliphatic polyester resin, a biodegradable aliphatic / aromatic polyester resin, and trehalose. Biodegradable agricultural materials may include, for example, agricultural mulch films or seedling pots.

[0040] (Biodegradable resin)

[0041] In the thermoplastic resin composition of this embodiment, a combination of a biodegradable aliphatic polyester resin and a biodegradable aliphatic / aromatic polyester resin is used as a biodegradable resin. Both types of biodegradable polyester resins are polyester resins that possess the property of natural degradation under the action of microorganisms, enzymes, etc., in the environment; they can be degraded by various microorganisms and enzymes present in soil and water. The biodegradable polyester resin used in this embodiment can, for example, be a polyester resin that meets the biodegradability requirements specified in any one of ISO 14851, ISO 14855, ISO 9408, ISO 9439, ISO 10707, JISK 6950, JISK 6951, JISK 6953, and JISK 6955.

[0042] Aliphatic polyester resins possess a high flexural modulus. Flexural modulus is an indicator of a material's hardness and toughness. Materials with a high flexural modulus tend to quickly return to their original shape after deformation, and the resin exhibits strong resistance to flexural stress. Conversely, materials with a low flexural modulus tend to take some time to return to their original shape after deformation or permanently retain their deformed shape.

[0043] Furthermore, aliphatic / aromatic polyester resins exhibit high elongation at break. Elongation at break is an indicator of a material's ductility, representing, for example, the degree of deformation a material can undergo under tensile stress. High elongation at break represents high material flexibility and extensibility. Materials with high elongation at break are easily stretched and can withstand large displacements during deformation without breaking. This is particularly important for applications and product designs requiring extensibility and flexibility. When elongation at break is high, the resin possesses the property of easily maintaining its stretched state even after significant deformation. Conversely, materials with low elongation at break are brittle and tend to have limited extensibility.

[0044] After in-depth research, the inventors discovered that when the flexural modulus of the thermoplastic resin composition is 500 MPa or higher and the elongation at break is 150% or higher, an agricultural material that combines suitable toughness with good elasticity and flexibility required for agricultural applications can be provided. Accordingly, a flexural modulus of 500 MPa or higher and an elongation at break of 150% or higher were used as indicators for subsequent research. The flexural modulus can be measured according to ISO 178, while the elongation at break can be measured according to ISO 527. It should be noted that these indicators are only reference standards and do not limit the scope of this embodiment.

[0045] Aliphatic polyester resins can be, for example, polyester resins composed of lactic acid, i.e., polylactic acid (PLA). Furthermore, aliphatic polyester resins can also be, for example, polyester resins composed of aliphatic and / or alicyclic diol compounds and alicyclic dicarboxylic acid compounds. Aliphatic polyester resins can be used alone or in combination of two or more. Diol compounds can also be used alone or in combination of two or more. Although aliphatic polyester resins have a high flexural modulus and exhibit strong resistance to flexural stress, they tend to have a lower elongation at break.

[0046] The aforementioned diol compounds can be, for example, substances with a carbon number of 2 to 10 or less, specifically ethylene glycol, 1,3-propanediol, 1,4-butanediol, or 1,4-cyclohexanediol. Ethylene glycol or 1,4-butanediol is preferred, and 1,4-butanediol is more preferred. The diol compound can be used alone or in combination of two or more.

[0047] The aforementioned dicarboxylic acid compounds can be, for example, compounds with a carbon number of 2 to 10 or less, specifically succinic acid, oxalic acid, adipic acid, octanoic acid, sebacic acid, or dodecanoic acid. Succinic acid or adipic acid is preferred. A dicarboxylic acid compound can be used alone or in combination of two or more.

[0048] Aliphatic polyester resins include, for example, polylactic acid (PLA), polybutylene succinate (PBS), polyhydroxyaliphatic carboxylic acid ester (PHA), polybutylene succinate-adipate (PBSA), polycaprolactone (PCL), polyethylene succinate (PES), or polyethylene succinate-adipate, etc. For instance, polybutylene succinate (PBS) is an aliphatic polyester resin composed of succinic acid and 1,4-butanediol. PBS uses butylene succinate-based (C8H...) 12The polymer consists of repeating units (O4) as polymerization units. Furthermore, polyhydroxyaliphatic carboxylic acids (PHAs) use hydroxyaliphatic carboxylic acids as raw materials as polymerization components and contain at least repeating units derived from hydroxyaliphatic carboxylic acids. Polyhydroxyaliphatic carboxylic acids (PHAs) can be, for example, compounds produced by microorganisms using sugars, oils, etc., as nutrients within the body. Polyhydroxyaliphatic carboxylic acids can be synthesized artificially or by microbial biosynthesis. Examples of hydroxyaliphatic carboxylic acids include glycolic acid, 3-hydroxybutyric acid, 3-hydroxypropionic acid, 3-hydroxyvalerate, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, 3-hydroxyoctadecanoic acid, 4-hydroxybutyric acid, 4-hydroxyvalerate, 5-hydroxyvalerate, or 6-hydroxyhexanoic acid. The number of carbon atoms in the hydroxyaliphatic carboxylic acid can be 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, preferably 3 or more. The number of carbon atoms in hydroxyaliphatic carboxylic acids can 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 especially preferably 6 or less. Hydroxyaliphatic carboxylic acids can be used alone or in combination of two or more. Polyhydroxyaliphatic carboxylic acid esters are preferably poly(3-hydroxyaliphatic carboxylic acid ester) or poly(3-hydroxybutyrate / 3-hydroxyhexanoate).

[0049] Aliphatic / aromatic polyester resins, in addition to including aliphatic and / or alicyclic diols and alicyclic dicarboxylic acids as constituent components (polymerization components), also include aromatic dicarboxylic acid compounds as constituent components. The molar amount of aromatic dicarboxylic acid units in the total molar amount of aliphatic and / or alicyclic dicarboxylic acid units and aromatic dicarboxylic acid units is, for example, 5% to 95%, preferably 35% to 65%. Although aliphatic / aromatic polyester resins have high tensile elongation and good elasticity and flexibility, they tend to have a low flexural modulus.

[0050] The diol compound providing the diol unit can be, for example, a compound having 2 to 10 carbon atoms, specifically such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, or 1,4-cyclohexanediol. Ethylene glycol or 1,4-butanediol is preferred. The dicarboxylic acid compound providing the dicarboxylic acid unit can be, for example, a compound having 2 to 10 carbon atoms, specifically such as succinic acid, oxalic acid, adipic acid, octanoic acid, sebacic acid, or dodecanoic acid. Succinic acid or adipic acid is preferred. The aromatic dicarboxylic acid compound providing the aromatic dicarboxylic acid unit can be, for example, terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid. Terephthalic acid or isophthalic acid is preferred. Such compounds can be used alone or in combination of two or more.

[0051] Representative aliphatic / aromatic polyester resins include, for example, polybutylene adipate / terephthalate (PBAT), polybutylene sebacic acid / terephthalate, or polybutylene succinic acid / terephthalate. Among these, polybutylene adipate / terephthalate is preferred. Although polybutylene adipate / terephthalate has a high elongation at break and good elasticity and flexibility, it tends to have a low flexural modulus. PBAT is an enzyme-degradable biodegradable resin. Its degradation process mainly involves: first, enzymes secreted by soil microorganisms cleaving the polymer bonds; then, enzymatic degradation into oligomers; and finally, further degradation into 1,4-butanediol, adipic acid, and terephthalic acid, which are the resin components.

[0052] To enable aliphatic / aromatic polyester resins to exhibit biodegradability, it is preferable to insert aliphatic chains between aromatic rings. For this purpose, in aliphatic / aromatic polyester resins, the molar amount of aromatic dicarboxylic acid units in the total molar amount of aliphatic and / or alicyclic dicarboxylic acid units and aromatic dicarboxylic acid units is generally preferably 5% to 50%, more preferably 10% to 48%, and even more preferably 15% to 45%.

[0053] The thermoplastic resin composition of this embodiment includes an aliphatic polyester resin and an aliphatic / aromatic polyester resin as biodegradable resins; that is, an aliphatic polyester resin and an aliphatic / aromatic polyester resin are combined as a biodegradable polyester resin. While aliphatic polyester resins have a high flexural modulus, they tend to have a low elongation at break. Meanwhile, while aliphatic / aromatic polyester resins have a high elongation at break, they tend to have a low flexural modulus. Therefore, by appropriately combining aliphatic polyester resins and aliphatic / aromatic polyester resins, this embodiment allows the elongation at break and flexural modulus to be appropriately adjusted to a range suitable for agricultural materials.

[0054] 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 PBAT are combined as a biodegradable resin. While polylactic acid has a high flexural modulus, it tends to have a low elongation at break. Meanwhile, PBAT, while having a low flexural modulus, has a high elongation at break. Therefore, by appropriately combining polylactic acid and PBAT, a suitable range of elongation at break and flexural modulus can be achieved for agricultural materials.

[0055] Generally, aliphatic polyester resins have higher melting points than aliphatic / aromatic polyester resins. However, while there is no specific limitation on the melting point of the aliphatic polyester resin in this embodiment, it is, for example, below 180°C, preferably below 170°C, more preferably below 160°C, further preferably below 155°C, and even more preferably below 150°C. By using a low-melting-point aliphatic polyester resin, a lower temperature can be set during molding, thereby reducing the thermal decomposition of trehalose.

[0056] Specifically, while there are no specific limitations on the melting point of polylactic acid (PLA), it can be, for example, below 180°C, preferably below 160°C, more preferably below 155°C, and even more preferably below 150°C. By using PLA with a melting point below 160°C, a lower temperature can be effectively set during molding to reduce the thermal decomposition of trehalose under heating during the molding process, thereby allowing trehalose to be efficiently retained in the thermoplastic resin composition or agricultural material. The melting point of PLA is, for example, above 100°C. The melting point can be measured, for example, by differential scanning calorimetry (DSC).

[0057] Polylactic acid (PLA) is a lactic acid polymer whose melting point varies considerably, for example, within the range of approximately 120°C to approximately 180°C. The melting point of PLA depends on the proportion of D-lactic acid (D-isomer) in the polymer (hereinafter referred to as the D-isomer ratio). In other words, the melting point of PLA can be adjusted, for example, by regulating its D-isomer ratio. PLA contains lactic acid in either the D-isomer or the L-isomer form; however, a higher D-isomer content results in a more disordered crystal lattice structure and a lower melting point. The D-isomer ratio can be calculated using the formula: D-isomer ratio = {(D-isomer content / (D-isomer content + L-isomer content)} × 100 (%). The D-isomer ratio of polylactic acid (PLA) is preferably 4% or more. The D-isomer ratio of PLA is preferably 20% or less, more preferably 18% or less, even more preferably 16% or less, even more preferably 14% or less, even more preferably 12% or less, and even more preferably 10% or less. When the D-isomer ratio of PLA is 4% or more, the melting point of PLA decreases, thus allowing for the effective setting of a lower temperature during molding. PLA with a D-isomer ratio of 4% or more can be, for example, Ingeo Biopolymer sold by NatureWorks. Examples of polylactic acid (PLA) grades include 2003D, 2002D, 4043D, 4044D, and 7071D. Additionally, PLA grades without a specific melting point can also be used. Examples of PLA grades without a specific melting point include Ingeo Biopolymer 4060D, sold by NatureWorks.

[0058] The melt mass flow rate (MFR) of polylactic acid is preferably 5 to 11, more preferably 6 to 10. When the MFR value is above 5 and below 11, the viscosity increases, making it easier to achieve gas-blown molding. The MFR of the copolymer can be measured according to JIS K 7210, at a measurement temperature of 210°C and a measurement load of 2.16 kg, in units of g / 10 min.

[0059] The proportion of D-isomers of polylactic acid (PLA) can be measured, for example, by high-performance liquid chromatography (HPLC). Specifically, PLA is first frozen and pulverized into powder. This powder is then circulated in a 1N sodium hydroxide aqueous solution to hydrolyze it into lactic acid (monomer). After neutralization, the resulting solution is analyzed by HPLC to obtain HPLC chromatograms of D-isomer lactic acid and L-isomer lactic acid. The proportion of D-isomer lactic acid is calculated based on the peak areas of the D-isomer lactic acid and L-isomer lactic acid in the chromatograms.

[0060] While there is no specific limitation on the weight-average molecular weight (Mw) of polylactic acid (PLA), it can be, for example, from 50,000 to 1,000,000, preferably from 100,000 to 750,000. Considering melt viscosity, the weight-average molecular weight of PLA is preferably 150,000 or higher, more preferably 160,000 or higher, and even more preferably 170,000 or higher. When the weight-average molecular weight of PLA is 150,000 or higher, it can improve the mechanical properties and melt viscosity of the thermoplastic resin composition, thereby facilitating film formation. This allows for the efficient production of thin-film products such as agricultural mulch films (e.g., agricultural mulch films with a thickness of 50 μm or less). Specifically, when the weight-average molecular weight of PLA is 150,000 or higher, good molding performance can be achieved during air-expansion molding, making it easy to form film thicknesses suitable for agricultural mulch films. The weight-average molecular weight (Mw) of PLA is determined, for example, by gel permeation chromatography (GPC) through comparison with a standard with a known molecular weight (e.g., polystyrene).

[0061] Polybutylene adipate / terephthalate (PBAT) is a biodegradable aliphatic / aromatic polyester resin whose main constituent units are adipic acid-derived units, terephthalic acid-derived units, and 1,4-butanediol-derived units. Specifically, PBAT is a copolymer of adipic acid, terephthalic acid, and butanediol. Adipic acid, terephthalic acid, and butanediol do not necessarily need to be copolymerized simultaneously; they can also be copolymerized in multiple steps.

[0062] In the synthesis of poly(butylene adipate / terephthalate), in addition to adipic acid, terephthalic acid, and butanediol, trace amounts of other copolymerizing components may be added. These other copolymerizing components may be, for example, dicarboxylic acids other than terephthalic acid and adipic acid, or modifiers used for chain extension or end-capping purposes. These other copolymerizing components may be used alone or in combination of two or more.

[0063] Other dicarboxylic acids include, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, and octanoic acid. These other dicarboxylic acids can be used alone or in combination of two or more.

[0064] Poly(butylene adipate) terephthalate (PBAT) is a copolymer (such as a random copolymer) of 1,4-butanediol, adipic acid, and terephthalic acid, preferably (a) a mixture mainly composed of 35-95% adipic acid, adipic acid ester derivative, or a mixture thereof in molar percentage, and 5-65% terephthalic acid, a terephthalic acid ester derivative, or a mixture thereof in molar percentage (total molar percentage of 100%), and (b) a mixture containing butanediol (wherein the molar ratio of (a) to (b) is 0.4:1 to 1.5:1).

[0065] In all components of poly(butylene adipate / terephthalate) (total molar percentage of 100%), the total molar percentage content of adipic acid, terephthalic acid and butanediol is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, even more preferably 95% or more, and even more preferably 99% or more.

[0066] The melting point of poly(butylene adipate) is, for example, around 100-130°C. The preferred MFR of poly(butylene adipate) is around 2-8 g / 10 min, more preferably around 2-5 g / 10 min.

[0067] The weight-average molecular weight (Mw) of PBAT is preferably 35,000 or higher. This effectively increases the melt viscosity of the thermoplastic resin composition. The weight-average molecular weight (Mw) of PBAT is preferably 150,000 or lower. This effectively increases the flexibility of the thermoplastic resin composition. The weight-average molecular weight (Mw) is determined, for example, by gel permeation chromatography (GPC) through comparison with a standard (such as polystyrene) of known molecular weight.

[0068] Polybutylene adipate / terephthalate (PEG) can be, for example, Ecoflex manufactured by BASF Corporation of Japan. ® Origo-Bi manufactured by Novamont ® Or ECOPOND manufactured by Kingfa Science & Technology Co., Ltd. ® Etc. These types of poly(butylene adipate) / poly(terephthalate) can be used alone or in combination of two or more. Ecoflex, manufactured by BASF Corporation of Japan, is an example of such a product. ® F Blend C1200 (melting point: 110~120℃).

[0069] (Trehalose)

[0070] In addition to the biodegradable resins described above, the thermoplastic resin composition of this embodiment further contains trehalose.

[0071] Compared to agricultural materials without trehalose, those with trehalose exhibit higher biodegradability. The reason for this is presumably as follows: when the agricultural material is incorporated into the soil, the trehalose is leached out by moisture and other substances in the soil, allowing the biodegradable resin to degrade from the leached area, thus improving biodegradability compared to the case without trehalose. Furthermore, when the agricultural material of this embodiment, which further contains trehalose in addition to the biodegradable resin, is incorporated into the soil, a better soil improvement effect is achieved than when trehalose is not present. This is presumably because, in addition to the degradation products of the biodegradable resin, the trehalose leached into the soil also contributes to soil improvement through its action. Trehalose, for example, is TREHA manufactured by Nagase Microbiotechnology Co., Ltd. ® wait.

[0072] (composition)

[0073] While there is no specific limitation on the content of trehalose in the thermoplastic resin composition, it is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 15% by weight or more. When the trehalose content is 5% by weight or more, trehalose can effectively improve biodegradability and soil amendment. While there is no specific limitation on the content of trehalose in the thermoplastic resin composition, it is preferably 30% by weight or less, more preferably 25% by weight or less. When the trehalose content is 30% by weight or less, the decrease in the elongation at break of the thermoplastic resin composition due to the addition of trehalose can be reduced.

[0074] While there is no specific limitation on the content of aliphatic polyester resin in the thermoplastic resin composition, it is preferably 10% by weight or more, more preferably 15% by weight or more. When the content of aliphatic polyester resin is 10% by weight or more, it imparts good toughness. While there is no specific limitation on the content of aliphatic polyester resin in the thermoplastic resin composition, it is preferably 45% by weight or less, more preferably 40% by weight or less, further preferably 35% by weight or less, and even more preferably 30% by weight or less.

[0075] While there is no specific limitation on the content of aliphatic / aromatic polyester resin in the thermoplastic resin composition, it is preferably 45% by weight or more, more preferably 50% by weight or more, and even more preferably 55% by weight or more. When the content of aliphatic / aromatic polyester resin is 45% by weight or more, it can effectively impart good flexibility and extensibility. While there is no specific limitation on the content of aliphatic / aromatic polyester resin in the thermoplastic resin composition, it is preferably 80% by weight or less, more preferably 75% by weight or less, and even more preferably 70% by weight or less.

[0076] While there is no specific limitation on the content of aliphatic polyester resin and aliphatic / aromatic polyester resin in the thermoplastic resin composition, it is preferably 60% by weight or more, more preferably 65% ​​by weight or more, even more preferably 70% by weight or more, even more preferably 75% by weight or more, even more preferably 80% by weight or more, even more preferably 85% by weight or more, and even more preferably 90% by weight or more. When the content of aliphatic polyester resin and aliphatic / aromatic polyester resin is 60% by weight or more, it enables the thermoplastic resin composition to possess the toughness suitable for agricultural use and effectively obtain good extensibility and flexibility. While there is no specific limitation on the content of aliphatic polyester resin and aliphatic / aromatic polyester resin in the thermoplastic resin composition, it is preferably 95% by weight or less, more preferably 90% by weight or less.

[0077] The preferred ratio of aliphatic polyester resin to aliphatic / aromatic polyester resin is 1:1 to 1:5, more preferably 1:2 to 1:4.

[0078] In addition to aliphatic polyester resins and aliphatic / aromatic polyester resins, the thermoplastic resin composition of this embodiment may also include other resins. These other resins may include, for example, polyester resins other than the aforementioned aliphatic polyester resins and aliphatic / aromatic polyester resins, polystyrene resins, polyolefin resins, vinyl chloride resins, polycarbonate resins, polyamide resins, acrylic resins, or polyoxymethylene resins. These other resins are preferably biodegradable resins. Other resins may be used alone or in combination of two or more. When other resins are included, their content in the thermoplastic resin composition is, for example, 10% or less by weight, 5% or less by weight, 3% or less by weight, 1% or less by weight, or 0.1% by weight. In one embodiment, the thermoplastic resin composition does not contain other resins.

[0079] The thermoplastic resin composition of this embodiment may contain additives such as plasticizers, lubricants, fillers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, anti-caking agents, anti-fogging agents, flame retardants, colorants, fixing agents (alkaline earth metals), softeners, or compatibilizers, as long as they do not impair the effects of this embodiment. Additives may be used alone or in combination of two or more. Additives may be added in the form of a masterbatch containing colorants and other additives.

[0080] The additive content in the thermoplastic resin composition is, for example, less than 10% by weight, less than 5% by weight, less than 3% by weight, or less than 1% by weight. The additive content in the thermoplastic resin composition is, for example, more than 0.01% by weight, more than 0.1% by weight, or more than 0.5% by weight.

[0081] (Physical property values)

[0082] Considering the physical properties required for agricultural materials, the elongation at break of the thermoplastic resin composition, as measured according to ISO 527, is preferably 150% or more, more preferably 200% or more. Furthermore, while there is no specific limitation on the elongation at break of the thermoplastic resin composition, it is preferably 500% or less, more preferably 450% or less.

[0083] For consideration of the physical properties required for agricultural materials, the flexural modulus of the thermoplastic resin composition, as measured according to ISO 178, is preferably 500 MPa or more, more preferably 550 MPa or more, even more preferably 600 MPa or more, even more preferably 650 MPa or more, and even more preferably 700 MPa or more. Furthermore, the flexural modulus is preferably 1500 MPa or less, more preferably 1400 MPa or less, even more preferably 1300 MPa or less, and even more preferably 1200 MPa or less.

[0084] When the tensile elongation and flexural modulus are within the above range, the toughness, elasticity, and flexibility suitable for agricultural materials (such as agricultural mulch films) can be obtained.

[0085] For manufacturing considerations of agricultural materials (especially agricultural mulch films), the melt tension (melt temperature: 190°C, extrusion speed: 10 m / min, traction speed: 5 m / min) of the thermoplastic resin composition, as measured according to ISO 11443, is preferably 8.0 mN or more, more preferably 8.5 mN or more, further preferably 9.0 mN or more, even more preferably 9.5 mN or more, and even more preferably 10.0 mN or more. When the melt tension is within the above range, it is possible to produce agricultural mulch films with relatively thin thicknesses.

[0086] <Method for Manufacturing Thermoplastic Resin Compositions>

[0087] The method for manufacturing the thermoplastic resin composition in this embodiment includes the following steps: mixing aliphatic polyester resin, aliphatic / aromatic polyester resin and trehalose at a temperature that melts the aliphatic polyester resin and aliphatic / aromatic polyester resin without melting the trehalose, to obtain an extrudate.

[0088] The thermoplastic resin composition of this embodiment can be manufactured by kneading trehalose at a temperature at which aliphatic polyester resin and aliphatic / aromatic polyester resin are melted to form solids in the shape of granules or the like. Specifically, aliphatic polyester resin, aliphatic / aromatic polyester resin, and trehalose can be added, for example, in batch mixers such as kneaders, roller mills, super mixers, high-speed mixers, ball mills, sand mills, stirred mills, or internal mixers, as well as single-screw extruders, twin-screw extruders, and rotor-type twin-screw mixers, and various additives can be added as needed, followed by mixing and melt kneading to produce granular, powdered, granular, or bead-shaped extrudates. Among these, it is preferable to produce granular or other granular extrudates in a single-screw extruder or twin-screw extruder for the sake of strong mixing ability and ease of subsequent molding.

[0089] Thermoplastic resin compositions can be used in either the form of masterbatches or compound formulations. In the case of masterbatches, after the masterbatch is manufactured, it can be used as the main resin for agricultural materials, and aliphatic polyester resins and aliphatic / aromatic polyester resins can be mixed with the masterbatch as diluents to manufacture agricultural materials. In this case, the biodegradable resin used as the diluent can be the same as or different from the resin used in manufacturing the masterbatch. Since using the same biodegradable resin allows for good compatibility between the thermoplastic resin composition and the resin, it is preferred to use the same biodegradable resin. In the case of compound formulations, the compound formulation can be used directly in the manufacture of agricultural materials after its manufacture is completed.

[0090] <Biodegradable agricultural materials>

[0091] The thermoplastic resin composition of this embodiment can be used in biodegradable agricultural materials. Agricultural materials may include, for example, agricultural mulch film or seedling pots. Agricultural mulch film is a thin film (sheet) used to raise or maintain soil temperature and control pests. Seedling pots are specialized containers used for cultivating seedlings.

[0092] The agricultural material of this embodiment is a biodegradable agricultural material containing the thermoplastic resin composition of this embodiment. The agricultural material of this embodiment can be obtained by melting and molding the thermoplastic resin composition of this embodiment.

[0093] Furthermore, the agricultural material of this embodiment can also be obtained by directly feeding various raw materials into a film extruder or an air-expanding molding machine without using the thermoplastic resin composition of this embodiment. Accordingly, the agricultural material of this embodiment is a biodegradable agricultural material containing biodegradable aliphatic polyester resin, biodegradable aliphatic / aromatic polyester resin, and trehalose.

[0094] While there are no specific limitations on the thickness of agricultural mulch film, it is generally acceptable to use materials with a thickness of 8 μm to 50 μm, preferably 10 μm to 40 μm, and more preferably 12 μm to 30 μm. When the film thickness is 8 μm or more, it reduces the likelihood of voids forming during molding, thus ensuring stable molding. Furthermore, this thickness also improves soil temperature retention. Additionally, higher film strength reduces the likelihood of breakage during laying. When the film thickness is 50 μm or less, the amount of biodegradable resin and materials such as trehalose can be reduced.

[0095] <Methods for Manufacturing Biodegradable Agricultural Materials>

[0096] The manufacturing method of agricultural materials in this embodiment includes the following steps: the thermoplastic resin composition of this embodiment is melted and molded at a temperature that melts the aliphatic polyester resin and the aliphatic / aromatic polyester resin without melting the trehalose.

[0097] The thermoplastic resin composition of this embodiment can be thermoformed by extrusion, injection molding, or other processes using equipment such as extruders and injection molding machines used in conventional plastic molding processes. The heating during molding is preferably performed while melting the biodegradable resin, keeping the material temperature below the melting point of trehalose (e.g., 200°C). By performing heating molding under these conditions, the melting or decomposition of trehalose during molding can be reduced. It should be particularly noted that during molding, the melt temperature may exceed the target temperature of the equipment due to sliding heat or other reasons, and the heating effect caused by this excessively high temperature may cause the trehalose to melt or decompose. Specifically, the material (melt) temperature during heating is preferably between 150°C and 180°C. Furthermore, in this case, as described above, the aliphatic polyester resin is preferably polylactic acid with a high proportion of D-isomers (e.g., 4% or more).

[0098] In this embodiment, since at least two biodegradable resins are used, a twin-screw extruder is preferred. After the thermoplastic resin composition is melted in the extruder, it is molded into sheets, films, or other molded products under the action of a T-die, air inflation, etc. The film can be either a stretched film or an unstretched film. Furthermore, molded products for agricultural use can be obtained using equipment such as injection molding machines.

[0099] While there are no specific restrictions on the method of forming seedling pots, methods such as blow molding and vacuum forming are suitable. In blow molding, a heated and plasticized thermoplastic resin composition is extruded and fed directly into a mold without cooling and solidification, followed by blowing air in. In vacuum forming, a sheet or film of heated and plasticized thermoplastic resin composition is placed on a mold, and then vacuum is drawn from inside the mold.

[0100] While there are no specific restrictions on the forming method of the mulch film, methods such as extrusion molding or forming using an air-forming machine are suitable. In extrusion molding, the film is extruded from the T-die of the extruder and then cooled and solidified on a casting roll. The forming method can employ common film manufacturing methods, such as T-die forming, air-forming, and calendering. Furthermore, the formed film can be either unstretched or subjected to uniaxial or biaxial stretching.

[0101] In the method of manufacturing mulch film, either the compound material used as the thermoplastic resin composition of this embodiment can be fed into the film extruder or the air-forming machine, or various raw materials can be dry-mixed and directly fed into the film extruder or the air-forming machine.

[0102] Example

[0103] The present implementation will be described below through examples. It should be noted that the present implementation is not limited to all aspects of the examples, and appropriate modifications can be made without departing from the spirit of this disclosure.

[0104] (Materials used)

[0105] • Polylactic acid (PLA): Trade name "Luminy" ® L130 (manufactured by Total Corbion)

[0106] • Polylactic acid (PLA): Trade name "Ingeo Biopolymer 2003D" (manufactured by NatureWorks)

[0107] • Polybutylene succinate (PBS): Trade name "FORZEAS ZM9B02" (manufactured by Mitsubishi Chemical Corporation)

[0108] • Polybutylene succinate (PBS): Trade name "FORZEAS DA9005" (manufactured by Mitsubishi Chemical Corporation)

[0109] • Polyvinyl alcohol (PVA): Trade name "MOWFLEX C-500T" (manufactured by Kuraray Co., Ltd.)

[0110] • Polybutylene adipate / terephthalate (PBAT): Trade name "ecoflex" ®"F blend C1200" (manufactured by BASF Corporation, Japan)

[0111] Trehalose: Trade name "TREHA" ® (Manufactured by Nagase Microbiotechnology Co., Ltd.)

[0112] • Antioxidant: Trade name "Irganox 1010" (manufactured by BASF Corporation, Japan)

[0113] (Preparation of resin compound for forming dumbbell-shaped specimens)

[0114] The corresponding material is fed into a twin-screw extruder (manufactured by Shibaura Machinery Co., Ltd.; trade name: "TEM18SS"; extrusion temperature: 190℃; φ: 18mm) to produce a resin compound. The molding temperature is 180~190℃ and the rotation speed is 200rpm.

[0115] (Dumbbell-shaped specimens for measuring physical properties were prepared by injection molding)

[0116] Using an 80-ton injection molding machine (manufactured by Toyo Machinery & Metal Co., Ltd.; product name: "Sj-80IV"; molding temperature: 180~190℃; mold temperature: 50℃), the resin compound was molded into dumbbell-shaped specimens that meet ISO requirements.

[0117] (Elongation at break)

[0118] An 80-ton injection molding machine (manufactured by Toyo Machinery & Metal Co., Ltd.; product name: "Sj-80IV"; molding temperature: 180~190℃; mold temperature: 50℃) was used to prepare test samples conforming to ISO 20753 requirements, and the tensile elongation of the test samples was measured according to ISO 527. The test speed was 50 mm / min, and the distance between the fixtures was 114 mm.

[0119] It should be noted that although in this embodiment, a tensile elongation of 150% or more as measured according to ISO 527 is considered as one of the target material properties suitable for use as agricultural materials (especially agricultural mulch films), the thermoplastic resin composition of this embodiment is not limited to this evaluation criterion.

[0120] (Flexural modulus)

[0121] An 80-ton injection molding machine (manufactured by Toyo Machinery & Metal Co., Ltd.; product name: "Sj-80IV"; molding temperature: 180~190℃; mold temperature: 50℃) was used to prepare test samples conforming to ISO 20753 requirements, and the flexural modulus of elasticity of the test samples was measured according to ISO 178. The test speed was 2 mm / min, and the distance between the fixtures was 64 mm.

[0122] It should be noted that although in this embodiment a flexural modulus of elasticity of 500 MPa or more as measured according to ISO 178 is considered as one of the target material properties suitable for use as agricultural materials (especially agricultural mulch films), the thermoplastic resin composition of this embodiment is not limited to this evaluation criterion.

[0123] (Melt tension)

[0124] Melt tension was measured according to ISO 11443. Specifically, a certain amount of polymer was forcibly extruded from the extrusion orifice at a temperature of 190°C using a melt tension tester (trade name: Capilograph 1DPMD-C) manufactured by Toyo Seiki Co., Ltd., and the tension generated when it was stretched into a monofilament was detected by a strain gauge. The monofilament of molten polymer was pulled by a traction roller, and the tension was measured at various gradually increasing traction speeds. The maximum tension measured from the start of traction until the monofilament of molten polymer broke apart was taken as the melt tension (unit: mN).

[0125] The diameter of the extrusion orifice is 1mm, and the length of the extrusion orifice is 10mm.

[0126] <Experimental Example 1: Preparation of Thermoplastic Resin Composition>

[0127] (Experimental Example 1-1: Comparative Example)

[0128] Polylactic acid (Luminy L130 aliphatic polyester resin manufactured by Total Cobian, Ltd., melting point: 175°C, D-isomer ratio: less than 1%, weight average molecular weight: 130,000) and trehalose were compounded according to the composition shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the method described above. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the method described above, and then evaluated.

[0129] Table 1

[0130]

[0131] When only polylactic acid is used as the biodegradable resin, although the flexural modulus is high, the elongation at break is low.

[0132] In addition, the melt tension of sample 1 was measured according to ISO 11443. The melting temperature was 190℃ and the extrusion speed was 10 m / min. The measurement results are as follows: the melt tension was 1.7 mN at a traction speed of 5 m / min; the melt tension was 1.9 mN at a traction speed of 10 m / min; and the melt tension was 2.1 mN at a traction speed of 20 m / min.

[0133] (Experimental Examples 1-2: Comparative Examples)

[0134] Polybutylene succinate (an aliphatic polyester resin manufactured by Mitsubishi Chemical Corporation, trade name "FORZEAS ZM9B02") and trehalose were compounded according to the composition shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the method described above. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the method described above, and the specimens were evaluated.

[0135] Table 2

[0136]

[0137] When only polybutylene succinate (FORZEAS ZM9B02) is used as the biodegradable resin, although the flexural modulus is high, the elongation at break is low.

[0138] (Experimental Examples 1-3: Comparative Examples)

[0139] Polybutylene succinate (an aliphatic polyester resin manufactured by Mitsubishi Chemical Corporation, trade name "FORZEAS DA9005") and trehalose were compounded according to the composition shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the method described above. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the method described above, and the specimens were evaluated.

[0140] Table 3

[0141]

[0142] When only polybutylene succinate (FORZEAS DA9005) is used as the biodegradable resin, the elongation at low trehalose content (0%, 10%) is high, but the flexural modulus is low. However, when the trehalose content is high (20%, 30%), the elongation at high flexural modulus is high, but the elongation at high flexural modulus is low.

[0143] (Experimental Examples 1-4: Comparative Examples)

[0144] Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name "MOWFLEX C-500T") and trehalose were compounded according to the composition shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the method described above. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the method described above, and then evaluated.

[0145] Table 4

[0146]

[0147] In cases where only polyvinyl alcohol is used as the biodegradable resin, a lower trehalose content (10%) results in a higher elongation at stretching but a lower modulus of elasticity at flexural strength. However, a higher trehalose content (20%, 30%) results in a higher modulus of elasticity at stretching but a lower elongation at stretching.

[0148] (Experimental Examples 1-5: Comparative Examples)

[0149] Polybutylene adipate / terephthalate (an aliphatic / aromatic polyester resin manufactured by BASF Corporation, Japan, trade name "ecoflex") ® F blend C1200” was compounded with trehalose as shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the above method. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the above method, and then evaluated.

[0150] Table 5

[0151]

[0152] When only poly(butylene adipate) terephthalate is used as the biodegradable resin, although the elongation at break is high, the modulus of flexural elasticity is low.

[0153] In addition, the melt tension of sample No. 17 was measured according to ISO 11443. The melting temperature was 190℃ and the extrusion speed was 10 m / min. The measurement results are as follows: melt tension was 7.0 mN at a traction speed of 5 m / min; melt tension was 8.6 mN at a traction speed of 10 m / min; and melt tension was 8.8 mN at a traction speed of 20 m / min.

[0154] (Experimental Examples 1-6: Examples)

[0155] Polylactic acid (an aliphatic polyester resin manufactured by Total Cobian, trade name "Luminy") ® L130”, melting point: 175℃, D-isomer ratio: 1%, MFR: 10g / 10min, weight-average molecular weight: approximately 130,000; or aliphatic polyester resin manufactured by NatureWorks, trade name “Ingeo Biopolymer 2003D”, melting point: 150℃, D-isomer ratio: 4%, MFR: 6g / 10min, weight-average molecular weight: approximately 175,000; poly(butylene adipate) / poly(terephthalate) (aliphatic / aromatic polyester resin manufactured by BASF Corporation, trade name “ecoflex”). ®F blend C1200” and trehalose were blended according to the composition shown in the table below, and a resin compound for forming dumbbell-shaped specimens was prepared according to the above method. Subsequently, the compound was injection molded into dumbbell-shaped specimens for measuring physical properties according to the above method, and then evaluated.

[0156] Table 6

[0157]

[0158] By combining polylactic acid, an aliphatic polyester resin, and polybutylene adipate / terephthalate, an aliphatic / aromatic polyester resin, as biodegradable resins, resin compositions with high tensile elongation and flexural modulus that meet their respective target values ​​can be obtained.

[0159] In addition, the melt tension of samples 22 and 23 was measured according to ISO 11443. The melting temperature was 190°C and the extrusion speed was 10 m / min. The measurement results are as follows: the melt tension of sample 22 was 8.7 mN at a traction speed of 5 m / min, 9.2 mN at a traction speed of 10 m / min, and 9.3 mN at a traction speed of 20 m / min; the melt tension of sample 23 was 10.8 mN at a traction speed of 5 m / min, 12.3 mN at a traction speed of 10 m / min, and 12.8 mN at a traction speed of 20 m / min. Sample 23 (PLA molecular weight: approximately 175,000) exhibits a particularly high melt tension exceeding 10 mN. This may be due to the high molecular weight of the PLA (2003D) used, thus increasing the melt tension of the resin composition. Because higher melt tension allows for thinner film thickness, this sample can effectively form thin-film agricultural materials (such as agricultural mulch films). In practical applications, the film thickness is preferably below 100 μm, more preferably below 50 μm, even more preferably below 40 μm, and even more preferably below 30 μm.

[0160] Furthermore, the polylactic acid (2003D) used in sample 23 has a low melting point (approximately 150°C) due to its high D-isomer content (above 4%). For this reason, when molding this trehalose-containing resin composition, the molding temperature can be effectively set at a temperature lower than the melting point of trehalose (approximately 200°C), thereby reducing the melting or decomposition of trehalose during molding. It should be noted that during molding, the melt temperature may exceed the equipment's target temperature due to sliding heat generation, and the heating effect of this excessively high temperature may cause the trehalose to melt or decompose. In other words, by using polylactic acid with a high D-isomer content (e.g., above 4%), the melting point of the biodegradable resin can be lowered, allowing for a lower molding temperature to be set, thereby reducing the melting or decomposition of trehalose while melting the biodegradable resin. It should be noted that since the melting point of polybutylene adipate / terephthalate is approximately 110~120℃, which is lower than that of polylactic acid, there will be no specific problems regarding the melting point of polybutylene adipate / terephthalate.

[0161] <Experimental Example 2: Preparation of Thin Film Samples>

[0162] Following the composition of sample No. 23 in the aforementioned test example (Preparation of Thermoplastic Resin Composition), which achieved the corresponding target values ​​for both tensile elongation and flexural modulus, a film sample was prepared. Specifically, according to the composition shown in the table below, various materials were fed into a twin-screw extruder (manufactured by Shibaura Machinery Co., Ltd., trade name "TEM26SS", φ: 26mm), and the resin compound was prepared at an extrusion temperature of 160°C and a rotation speed of 200 rpm. It should be noted that "PBAT compound" in the table refers to "BDM OKC502 BLK" (Tokyo Ink Co., Ltd.) masterbatch containing PBAT and carbon black. Trehalose was top-fed, while the resin (PLA, PBAT, PBAT compound) was fed separately from the trehalose, but also top-fed. The trehalose and resin (PLA, PBAT, PBAT masterbatch) raw materials were fed through different weight feeders.

[0163] Table 7

[0164]

[0165] The resin temperature (actual temperature) inside the extruder is 167°C. Because the polylactic acid used has a higher proportion of D-isomers (2003D), the molding temperature can be set at a lower level, thus reducing the actual resin temperature. This allows for the melting of the biodegradable resin while minimizing the melting or decomposition of trehalose.

[0166] The resulting resin compound was fed into a short screw extruder (manufactured by GSI Corporation, φ: 40mm) and film-forming was performed at an extrusion temperature of 160°C. The resin temperature (actual temperature) inside the extruder was 145°C, and the traction speed during film formation was 10 m / min, thereby obtaining a film with a thickness of approximately 30 μm free of defects such as pores.

[0167] Furthermore, the DSC thermal analysis of the obtained film detected endothermic activity of trehalose, proving the presence of trehalose in the film. Thus, this experimental example demonstrates that it is possible to form a trehalose-containing film while minimizing the melting or decomposition of trehalose.

[0168] <Experimental Example 3: Preparation of Agricultural Mulch Film>

[0169] In order to conduct field trials, based on the film composition E1 shown in Experiment Example 2 above, a trial air-inflated molding mass production was carried out.

[0170] First, the resin composition was prepared by compounding components E1 and C1 as shown in Table 1 below.

[0171] Table 8

[0172]

[0173] The above compounding was carried out by Setsuna Chemical Co., Ltd. Specifically, the corresponding materials were fed into a twin-screw extruder (manufactured by Nippon Steel Co., Ltd., trade name "TEX44αII", φ: 44mm) and the resin compound was prepared at an extrusion temperature of 160°C. The resulting resin compound was then used to form a mulch film via air-expansion molding. Air-expansion molding was performed using a short-screw extruder (manufactured by PLACO Co., Ltd., φ: 600mm), with an extrusion temperature of 160°C and a production rate of 45 kg / hr.

[0174] Resin blends obtained from both E1 and C1 compositions were used to produce agricultural mulch films with a thickness of approximately 30 μm. Furthermore, after appropriately adjusting the air-expansion molding conditions, films with a thickness of approximately 18–20 μm were also produced. No defects such as pores were observed in the resulting films. Additionally, thermal analysis and scanning electron microscopy (SEM) observations of the films revealed the presence of trehalose both inside and on the surface of the films.

[0175] <Experimental Example 4: Field Trial of Trehalose-Containing Agricultural Mulch>

[0176] Field trials were conducted on the agricultural mulch film (thickness: 30 μm, length: 40 m) made according to compositions E1 and C1 in Experimental Example 3. In addition, as a reference, conventional mulch film (non-degradable polyethylene (PE) film manufactured by Iwatani Materials Co., Ltd., thickness: 20 μm, length: 40 m) and biodegradable mulch film without trehalose (manufactured by Sunplac Industry Co., Ltd., trade name "SUNBIO", thickness: 20 μm, length: 40 m) were also tested. The test site was located in Haruyama, Maniwa City, Okayama Prefecture, and the test crop was sweet corn (variety: Dolce Dream).

[0177] Four adjacent 40m-long ridges were created within the same field, and then leveled. On each ridge, one type of agricultural mulch film was laid: E1 (PBAT / PLA mulch film containing seaweed), C1 (PBAT / PLA mulch film without seaweed), a biodegradable mulch film without trehalose (biodegradable PBS / PBAT mulch film manufactured by Sunplac Industries, Ltd.), and a conventional mulch film (ordinary PE mulch film manufactured by Iwatani Materials Co., Ltd.). The edges of the mulch film were buried in the soil for fixation. After the mulch film was laid, two rows of equally spaced holes were made on its surface, and sweet corn seedlings were planted in these holes. The sweet corn was cultivated and harvested using conventional methods.

[0178] The evaluation criteria include: yield assessment; assessment of the degradation status of the plastic film; and soil analysis after the plastic film has degraded.

[0179] (Production Assessment)

[0180] Ten fruits were randomly collected from each of the following areas: E1 agricultural mulch film (containing trehalose), C1 agricultural mulch film (excluding trehalose), biodegradable mulch film (excluding trehalose), and ordinary mulch film. The average weight of each fruit was then determined. The results are shown in the table below.

[0181] Table 9

[0182]

[0183] As shown in the table above, the region where the E1 agricultural mulch film (containing trehalose) of this embodiment was used yielded the highest output. This indicates that when the agricultural material of this embodiment is used as agricultural mulch film, crop yield can be increased. The reason for this is that trehalose is leached from the agricultural material into the soil by atmospheric and soil moisture, rainwater, and dew.

[0184] (Degradation status of plastic film)

[0185] The degradation status of various mulch films was determined by observing the film surface using SEM at four time points: "at the start of the experiment" (during installation), "two months after installation," "before being turned into the soil after harvest," and "one month after being turned into the soil." SEM images are shown below. Figure 1 .

[0186] Conventional mulch film (ordinary mulch film) does not degrade in the soil. Therefore, at the time point "before being turned into the soil after harvest," after taking SEM images, it was not turned into the soil but directly removed. E1 agricultural mulch film ("trehalose-containing mulch film"), C1 agricultural mulch film ("trehalose-free mulch film"), and trehalose-free biodegradable mulch film ("biodegradable mulch film") all showed some degree of degradation before being turned into the soil, but no obvious breakage was observed, indicating that they retained their function as mulch film. Furthermore, the degradation of all three types of mulch film was accelerated after being turned into the soil. As a reference example, the residual film fragments of the trehalose-free biodegradable mulch film ("biodegradable mulch film"), as shown in its surface SEM image, became extremely thin and easily torn. Moreover, at the time point "one month after being turned into the soil," this mulch film was almost completely degraded.

[0187] The surface of E1 agricultural mulch film (containing trehalose) exhibits countless pores. These pores are believed to be caused by trehalose leaching, and degradation occurs from these pores outwards. This indicates that E1 agricultural mulch film (containing trehalose) has better biodegradability compared to C1 agricultural mulch film (without trehalose).

[0188] In addition, to further investigate the degradation status of various plastic films, soil samples of 30cm×30cm×10cm were collected from the location where the films were turned into the soil one and a half months after being turned in, and filtered through a sieve with a mesh size of 6mm to examine the degree of degradation. Figure 2 The image shows photographs of the recycled film fragments. As the photos show, compared to C1 agricultural mulch film (without trehalose), the largest fragments of E1 agricultural mulch film (containing trehalose) are smaller and there are more fragments, indicating that E1 agricultural mulch film (containing trehalose) is more easily degraded than C1 agricultural mulch film (without trehalose).

[0189] (Soil investigation after the degradation of plastic film)

[0190] Two weeks after being plowed into the soil, soil samples were collected after the mulch film degraded, and its SOFIX (Soil Fertility Index) was assessed using SOFIX soil analysis. In addition to conventional soil analysis (soil physicochemical property analysis), SOFIX soil analysis further scientifically analyzes the biological properties of the soil. Based on the results of this analysis, soil fertility can be assessed. SOFIX soil analysis includes measurements such as: nitrate nitrogen, ammonia nitrogen, exchangeable potassium, available phosphate, electrical conductivity (EC), pH, total carbon, total nitrogen, total phosphorus, total potassium, carbon-nitrogen ratio (C / N), carbon-phosphorus ratio (C / P), total bacterial count, ammonia oxidation activity, nitrite oxidation activity, phosphorus cycle activity, nitrogen cycle activity, phytic acid degradation activity, water content, and maximum water holding capacity.

[0191] The results are shown in Table 10. Specifically, after the E1 agricultural mulch film (containing trehalose) was incorporated into the soil, the phosphorus cycling active site of the soil was a high value of 21, while the total phosphorus content decreased. This indicates that phosphorus in the soil is in circulation and that plants are absorbing phosphorus. After the E1 agricultural mulch film (containing trehalose) was incorporated into the soil, the soil was rated "Special A" by SOFIX soil analysis model classification. "Special A" indicates "good organic soil environment", indicating that the E1 agricultural mulch film (containing trehalose) of this embodiment has a good soil improvement effect. In contrast, after the C1 agricultural mulch film (without trehalose), biodegradable mulch film (without trehalose), and ordinary mulch film were incorporated into the soil, the corresponding soils were all rated "A2" by SOFIX soil analysis model classification. "A2" indicates "generally good soil environment, but lacking proper phosphorus cycling". The above results indicate that the E1 agricultural mulch film (containing trehalose) of this embodiment is an agricultural mulch film with high biodegradability and can achieve soil improvement effect after being turned into the soil.

[0192] Table 10

[0193]

[0194] The upper and / or lower limits of the numerical ranges given in this specification can be arbitrarily combined to define the preferred numerical range. For example, the preferred numerical range can be defined by arbitrarily combining the upper and lower limits of each numerical range, by arbitrarily combining the upper limits of each numerical range, or by arbitrarily combining the lower limits of each numerical range.

[0195] The claims appended to this disclosure are explicitly incorporated into the disclosure of this specification as individual embodiments. This disclosure covers all solutions obtained by substituting the independent claim into the corresponding appended claims. Furthermore, this specification explicitly covers other embodiments derived from the independent claim and its appended claims.

[0196] Based on the foregoing description, those skilled in the art should be able to utilize this disclosure to the fullest extent. The claims and embodiments disclosed in this specification are for illustrative and exemplary purposes only and should not be construed as limiting the scope of this disclosure in any way. With the aid of this disclosure, modifications can be made to the details of the above embodiments without departing from the basic principles of this disclosure. In other words, various modifications and improvements to the above embodiments specifically disclosed in this specification also fall within the scope of this disclosure.

[0197] Although this embodiment has been described in detail above, the specific technical solution is not limited to this embodiment. All design changes made without departing from the spirit of this disclosure are covered within the scope of this disclosure.

[0198] This specification contains the disclosure of Japanese Patent Application No. JP2024-010682, which forms the basis of the priority claim of this application. All publications, patents, and patent applications referenced in this specification are incorporated herein by reference in their entirety.

Claims

1. A thermoplastic resin composition for use in biodegradable agricultural materials, characterized in that, This includes biodegradable aliphatic polyester resins, biodegradable aliphatic / aromatic polyester resins, and trehalose.

2. The thermoplastic resin composition according to claim 1, characterized in that, The aliphatic polyester resin in the composition is at a content of more than 10% by weight and less than 45% by weight, and the aliphatic / aromatic polyester resin in the composition is at a content of more than 45% by weight and less than 80% by weight.

3. The thermoplastic resin composition according to claim 1, characterized in that, The content of the aliphatic polyester resin in the composition and the sum of the content of the aliphatic / aromatic polyester resin in the composition are 60% or more by weight.

4. The thermoplastic resin composition according to claim 1, characterized in that, 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, characterized in that, The trehalose content in the composition is more than 5% by weight and less than 30% by weight.

6. The thermoplastic resin composition according to claim 1, characterized in that, The aliphatic polyester resin includes polylactic acid, and the aliphatic / aromatic polyester resin includes poly(butylene adipate / terephthalate).

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

8. The thermoplastic resin composition according to claim 7, characterized in that, The polylactic acid has a melting point below 160°C.

9. The thermoplastic resin composition according to claim 6, characterized in that, The polylactic acid has a weight-average molecular weight of over 150,000.

10. The thermoplastic resin composition according to claim 1, characterized in that, The thermoplastic resin composition has an elongation at break of 150% or more, a flexural modulus of elasticity of 500 MPa or more, and a melt tension of 8.0 mN or more.

11. A biodegradable agricultural material, characterized in that, It includes the thermoplastic resin composition as described in any one of claims 1 to 10.

12. The biodegradable agricultural material as described in claim 11, characterized in that, The biodegradable agricultural material is agricultural mulch film.

13. A method for manufacturing a thermoplastic resin composition as described in any one of claims 1 to 10, characterized in that, Includes the following steps: Aliphatic polyester resin, aliphatic / aromatic polyester resin, and trehalose are blended at a temperature that melts the aliphatic polyester resin and the aliphatic / aromatic polyester resin without melting the trehalose to obtain an extrudate.

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