Polylactic acid resin composition

Abstract

To provide a polylactic acid resin composition.SOLUTION: The lactic acid resin composition includes a polylactic acid resin and a solid base. In one aspect, the average particle size of the solid base is about 1 μm or more and about 1000 μm or less, and the content of the solid base in the composition is about 0. 3wt% or more and about 20wt% or less. In another aspect, the average particle diameter is about 1 μm or more and about 300 μm or less. In another aspect, the average particle diameter is about 1 μm or more and about 100 μm or less. In yet another aspect, the solid base comprises at least one selected from the group consisting of shell calcined calcium, calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a soil conditioner and a method for producing the same, and more particularly to a soil conditioner in which lactic acid monomers or oligomers neutralized with a solid base are slowly released into soil, suppressing the growth inhibition of soil microorganisms, particularly fungi, caused by lactic acid and promoting plant growth, and a method for producing the same. [Background technology]

[0002] A variety of plastics are used in agricultural fields, including weed control sheets, insect control sheets, and vinyl greenhouse sheets. However, collecting these agricultural sheets after use requires a great deal of effort, and manual collection and removal work is extremely hard work. Furthermore, since the collected sheets contain soil components and moisture, they are difficult to recycle, and most of them are disposed of as industrial waste, for which a fee is charged.

[0003] For this reason, methods have been proposed that use biodegradable polymers to solve the problems of the prior art and replace conventional agricultural sheets, thereby reducing the labor required for laying and collecting them (for example, Patent Documents 1 and 2). These methods achieve the above objectives by spraying biodegradable aliphatic polyesters, particularly polylactic acid, in a molten or dissolved state. Furthermore, it has been reported that the decomposition intermediates of polylactic acid in these methods promote plant growth (Non-Patent Document 1), making them preferable from the perspective of crop growth.

[0004] In addition, lactic acid or lactic acid oligomer may also be sprayed to promote plant growth. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 11-092304 [Patent Document 2] Patent Publication No. 2000-45164 [Non-patent literature]

[0006] [Non-Patent Document 1] Alan M. Kinnersley, Taylor C. Scott III, John H. Yopp and George H. Whitten, "Promotion of plant growth by polymers of lactic acid" Plant Growth regulation (1990) Vol. 9, pp.137~146 Summary of the Invention [Problem to be solved by the invention]

[0007] However, while polylactic acid alone can hydrolyze quickly in a high-temperature, high-humidity environment like a composting environment, the actual usage environment is colder and less humid than a composting environment. Therefore, in such an environment, polylactic acid hydrolysis is slower, and it takes time for lactic acid oligomers to elute. Therefore, it is necessary to accelerate hydrolysis, for example, by adding a polylactic acid degrading enzyme. Furthermore, there is a concern that even if lactic acid or lactic acid oligomers are sprayed, they can easily be washed away by rain or other factors.

[0008] Furthermore, the leached lactic acid and lactic acid oligomers are acidic and therefore antibacterial, raising concerns that they may inhibit the growth of soil microorganisms that are useful for growing agricultural crops. [Means for solving the problem]

[0009] Polylactic acid sheets mixed with solid bases (calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide) are used as agricultural materials such as agricultural mulch sheets, and then buried in the soil, which causes lactic acid, lactic acid oligomers, and metal ions to leach into the soil.

[0010] This means: (1) During use as an agricultural material, the hydrolysis of polylactic acid is accelerated by solid bases, and when buried in soil, lactic acid, lactic acid oligomers, and metal ions are gradually eluted. (2) The metal ions eluted from the solid base, as well as the neutralized lactic acid and lactic acid oligomers, promote the growth of soil microorganisms and plants, leading to improved agricultural productivity. (3) After use as an agricultural mulch sheet, there is no need to collect it or dispose of it as industrial waste, which reduces disposal costs and labor.

[0011] The present invention provides the following items. (Item 1) A polylactic acid resin composition comprising a polylactic acid resin and a solid base, A composition, wherein the average particle size of the solid base is from about 1 μm to about 1000 μm, and the content of the solid base in the composition is from about 0.3 wt % to about 20 wt %. (Item 2) The composition according to any one of the preceding items, wherein the average particle size is from about 1 μm to about 300 μm. (Item 3) The composition according to any one of the preceding items, wherein the average particle size is from about 1 μm to about 100 μm. (Item 4) The composition according to any one of the preceding items, wherein the average particle size is from about 3 μm to about 75 μm. (Item 5) The composition according to any one of the preceding items, wherein the solid base comprises at least one selected from the group consisting of calcined shell calcium, calcium oxide, calcined dolomite, calcium hydroxide, magnesium oxide, and magnesium hydroxide. (Item 6) Item 10. The composition of any one of the preceding items, wherein the solid base comprises calcined shell calcium, calcium oxide, or calcium hydroxide. (Item 7) The composition according to any one of the preceding items, wherein when the solid base is calcined shell calcium, calcium oxide, or magnesium oxide, the content of the calcined shell calcium, calcium oxide, or magnesium oxide in the composition is from about 3 wt% to about 10 wt%. (Item 8) The composition according to any one of the preceding items, wherein when the solid base is calcium hydroxide or magnesium hydroxide, the content of the calcium hydroxide or magnesium hydroxide in the composition is from about 8 wt% to about 15 wt%. (Item 9) The composition according to any one of the preceding items, further comprising at least one additive selected from the group consisting of an ultraviolet absorber, an antioxidant, a plasticizer, a compatibilizer, and a surfactant. (Item 10) A resin molded article comprising the composition according to any one of the above items. (Item 11) The resin molded body according to any one of the preceding items, wherein when the resin molded body is left standing for about three months in an environment of about 40°C and a relative humidity of about 90%, the weight average molecular weight of the resin molded body in terms of polystyrene decreases by about 80% or more. (Item 12) The resin molded article according to any one of the preceding items, which is an agricultural material.

[0012] The present invention also provides the following: Item A-1 Solid base-mixed polylactic acid molded product, in which a solid base with an average particle size of 2 μm to 1000 μm is mixed with polylactic acid resin at a ratio of 0.3 wt% to 20 wt%. However, the mixing ratio of polylactic acid varies depending on the type of solid base.

[0013] Item A-2 The solid base-mixed polylactic acid molded product according to item A-1, characterized in that the solid base contains at least one of calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide.

[0014] Item A-3 A solid base-mixed polylactic acid molded product according to Item A-1, characterized in that after a step of exposing the solid base-mixed polylactic acid molded product according to Item A-1 outdoors, the product is buried in soil, compost, fertilizer, or waste mushroom bed to gradually release lactic acid, lactic acid oligomers, and metal ions (see Figure 1). [Effects of the Invention]

[0015] According to the present invention, the hydrolysis rate of polylactic acid can be controlled by kneading with a solid base. Furthermore, according to the present invention, the growth of soil microorganisms and plants can be promoted by the sustained release of lactic acid, lactic acid oligomers, and metal ions. This is expected to reduce the labor of agricultural workers, reduce waste disposal costs, and improve agricultural productivity. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 outlines the application process of the solid base-mixed polylactic acid molded product and the effects of the present invention. [Figure 2] FIG. 2 is a schematic diagram of the decomposition of a solid base-mixed polylactic acid molded product. [Figure 3] FIG. 3 is a graph showing the time course of the amount of Ca (A) and lactic acid (B) eluted into soil from a solid base-mixed polylactic acid molded product. [Figure 4] Figure 4 is a bar graph showing the evaluation of the viable cell count of soil microorganisms when PLA sheets and solid base-mixed polylactic acid sheets were buried in culture soil (A) and waste mushroom beds (B). [Figure 5] FIG. 5 shows an exemplary injection molding machine and its temperature settings for producing the solid base-blended polylactic acid molded article of the present invention. [Figure 6] FIG. 6 shows a schematic diagram of an exemplary press molding machine for producing a molded article of polylactic acid kneaded with a solid base according to the present invention, and a photograph of the actual machine. [Figure 7A] 7A and 7B show a typical example of the growth status of spinach grown outdoors using a solid base-mixed polylactic acid sheet of the present invention, with Fig. 7A showing a photograph of the entire plant. [Figure 7B]Figures 7A and 7B show typical examples of the growth status of spinach grown outdoors using the solid base-mixed polylactic acid sheet of the present invention, and Figure 7B shows a photograph arranging the results under each cultivation condition. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following describes embodiments of the present invention. The embodiments described below are examples of preferred embodiments of the invention, and do not limit the constituent elements of the present invention described in the claims.

[0018] As used herein, the term "about" is meant to cover a range of ±10% of the stated value.

[0019] Application examples of the present invention and the mechanism of action of the present invention (1) When solid base-mixed polylactic acid molded products are used in agricultural materials such as weed control sheets, greenhouse spreading sheets, seedling pots, absorbent sheets for bottom irrigation, attractant strings, and binding strings, and then buried in the soil, lactic acid, lactic acid oligomers, and metals are slowly released, as shown in Figures 2 and 3. Furthermore, the uses of solid base-mixed polylactic acid molded products are not limited to agricultural materials, but can also be used in a variety of applications, including building materials, container packaging, and textile materials.

[0020] (2) Lactic acid monomers and oligomers produced by hydrolysis of polylactic acid often inhibit the growth of soil microorganisms (bacteria and fungi) that are beneficial for plant growth. However, in the present invention, the lactic acid monomers and oligomers are neutralized by a solid base, and metal ions necessary for growth are also eluted, promoting the growth of soil microorganisms (Figure 4) and plants, which ultimately leads to improved agricultural productivity.

[0021] (3) In the case of solid base-mixed polylactic acid moldings, the solid base is also used as a soil conditioner, so it does not cause soil pollution. Furthermore, polylactic acid decomposes and disappears in the soil, which not only reduces the labor required by farmers but also reduces CO2 emissions from disposal.

[0022] (Resin used in the present invention) In the present invention, polylactic acid is used as the resin, but other biodegradable resins such as polybutylene succinate (PBS), polyhydroxybutyrate (PHB), or polycaprolactone (PCL), which are also biodegradable resins and have acidic monomers, can also be used. In general, any biodegradable resin that is rapidly hydrolyzed by contact with alkali can be used.

[0023] (Type of solid base) The solid base is preferably calcium oxide, calcium hydroxide, magnesium oxide, or magnesium hydroxide, with calcium oxide, calcined dolomite, or calcium hydroxide being most preferred. Calcium oxide and calcium hydroxide are easily available because they can be prepared from limestone, shells, or eggshells. They are classified as strong bases, which can moderately promote the hydrolysis of polylactic acid. Furthermore, they are required in large quantities for plant growth. As commonly known in the art, "quicklime" is a colloquial term for "calcium oxide," and these terms are used interchangeably herein. Similarly, "slaked lime" is synonymous with "calcium hydroxide," and these terms are also used interchangeably herein. As used herein, "calcined shell" or "calcined shell calcium" refers to shells (e.g., scallop shells) that have been calcined at high temperatures and pulverized (95% or more through a 300-mesh filter), and the component is 91% or more calcium oxide (65% or more in terms of calcium).

[0024] (particle size of solid base) In one embodiment, the particle size of the solid base is preferably 1 μm or more and 1000 μm or less, more preferably 1 μm or more and 300 μm or less, even more preferably 1 μm or more and 100 μm or less, and most preferably 3 μm or more and 75 μm or less. In another embodiment, the particle size of the solid base is particularly preferably 4 μm or more and 15 μm or less. In one embodiment, the median diameter of the solid base is approximately 10 μm. If the particle size of the solid base is less than 1 μm, significant scattering occurs, resulting in reduced production efficiency. Furthermore, if the particle size is greater than 1000 μm, it becomes difficult to knead the solid base with good dispersibility into polylactic acid, resulting in a reduced molding yield. The particle size here can be measured, for example, by electron microscope observation or dry laser diffraction / scattering method. In this example, several tens of particles were randomly selected using an electron microscope, and the particle sizes of these particles were measured to calculate the average particle size.

[0025] (Solid base mixing ratio in solid base mixed polylactic acid) When calcined shell calcium, calcium oxide, or magnesium oxide is used as the solid base, the proportion of the solid base mixed with polylactic acid is preferably 0.3 wt% to 20 wt%, more preferably 3 wt% to 10 wt%, and most preferably 4.5 wt% to 5.5 wt%. If the proportion of the solid base mixed with polylactic acid is less than 0.3 wt%, the alkaline hydrolysis of polylactic acid is slow, and even if the solid base is used in agricultural applications and buried in soil, the amount of lactic acid monomer, lactic acid oligomer, and metal elution is low, which may result in a lack of soil microorganism and plant growth promotion effects. If the proportion of the solid base mixed with polylactic acid is greater than 20 wt%, the strength of the solid base-mixed polylactic acid molded product may be significantly reduced, making it difficult to use. Without wishing to be bound by theory, the alkaline hydrolysis of polylactic acid depends on the contact area between the solid base and polylactic acid and the basic strength of the solid base. This contact area is governed by the specific surface area and pore volume of the solid base and the size distribution of the polylactic acid. Considering the basic strength of the solid base, the specific surface area and the pore volume of the solid base, the preferable mixing ratio of various alkaline earth metal oxides to polylactic acid is thought to be approximately 0.3 wt% to 20 wt%.

[0026] When calcium hydroxide or magnesium hydroxide is used as the solid base, the mixing ratio with polylactic acid is preferably 0.5 wt% to 25 wt%, more preferably 8 wt% to 15 wt%, and most preferably 10 wt% to 12 wt%. If the mixing ratio with polylactic acid is less than 0.5 wt%, the alkaline hydrolysis of polylactic acid is slow, and even if it is buried in the soil after use in agricultural applications, the amount of lactic acid monomer, lactic acid oligomer, and metal elution is small, so there is a concern that the effect of promoting soil microorganisms and plant growth will not be observed. On the other hand, if the mixing ratio is more than 20 wt%, the strength of the polylactic acid molded product mixed with the solid base will decrease significantly, making it difficult to use in agricultural applications. Furthermore, although we do not wish to be bound by theory, as in the case of the various alkaline earth metal oxides described above, taking into consideration the basic strength of the solid base, the specific surface area and pore volume of the solid base, it is believed that the preferred mixing ratio of various alkaline earth metal hydroxides to polylactic acid is generally between 0.5 wt% and 25 wt%.

[0027] (molecular weight of polylactic acid) When producing a solid base-mixed polylactic acid molded product, the weight-average molecular weight of polylactic acid is 1.0 × 10 5 Over 2.0 x 10 5 Less than 1.2 x 10 is preferable. 5 Over 1.8 x 10 5 Less than 1.4 x 10 is preferable. 5 Over 1.5 x 10 5 The most preferred weight average molecular weight is 1.0×10 5 If the ratio is less than 2.0 × 10, the strength of the solid base mixed polylactic acid molded product will be low, and it may be difficult to use it for agricultural purposes. 5 If the molecular weight is larger, moldability is poor, and there is a concern that the yield rate of molded products will decrease. The value obtained by dividing the weight average molecular weight of polylactic acid by the number average molecular weight (dispersity) is preferably 1 or more and 2 or less.

[0028] (Shape of solid base mixed polylactic acid molded product) The solid base-kneaded polylactic acid molded product can be used in any shape, but a sheet or string shape is more preferable because the hydrolysis of the polylactic acid proceeds uniformly.

[0029] (Method for molding solid base-mixed polylactic acid molded products) The solid base-mixed polylactic acid molded article can be preferably molded by any of injection molding, insert molding, compression molding, vacuum molding, extrusion molding, rotational molding, blow molding, T-die molding, and inflation molding.

[0030] (molding temperature) The molding temperature for the solid base-mixed polylactic acid molded product is preferably 160° C. or higher and 220° C. or lower, more preferably 170° C. or higher and 200° C. or lower, and most preferably 180° C. or higher and 190° C. or lower. At temperatures higher than 220° C., the thermal decomposition of polylactic acid becomes significant, which may reduce moldability, and at temperatures lower than 160° C., the polylactic acid does not dissolve sufficiently, which may result in uneven mixing of the solid base.

[0031] (Additive for solid base kneaded polylactic acid molded products) When producing solid base-mixed polylactic acid molded articles, UV absorbers, antioxidants, plasticizers, compatibilizers, and surfactants, or combinations thereof, can be added as needed to improve physical properties, prevent discoloration, improve moldability, and improve durability. Surface treatment of the solid base with a surfactant can also be considered to facilitate the mixing process. Furthermore, adding next-generation polylactic acid, a copolymer of lactic acid (LA) and 3-hydroxybutanoic acid (HB) (LAHB), to the solid base-mixed polylactic acid molded articles can be considered as a means to maintain biodegradability while improving durability. For details on next-generation polylactic acid, see S. Taguchi et al., Proc. Natl. Acad. Sci. USA (2008) 105(45) 17323-7; Y. Imai et al., Int. J. Biol. Macromol. (2024) 266(Part 1) 130990, and related literature.

[0032] (Additive addition ratio) The addition ratio of each of these additives is preferably 10 wt% or less, more preferably 5 wt% or less, and most preferably 2 wt% or less, because if more than 10 wt% is added, there is a concern that the strength of the solid base-mixed polylactic acid molded product may be significantly reduced.

[0033] (Hydrolysis conditions for solid base mixed polylactic acid molded products) Solid base-mixed polylactic acid molded products are expected to be used in a variety of applications, both indoors and outdoors, in addition to agricultural applications. During use, polylactic acid undergoes moderate hydrolysis, which facilitates the elution of lactic acid monomers, lactic acid oligomers, and metal ions. To address this issue, temperatures during use should preferably be between 20°C and 60°C, more preferably between 30°C and 45°C, and most preferably between 37°C and 40°C. If temperatures during use are below 20°C, hydrolysis of polylactic acid may not proceed sufficiently, potentially resulting in a lack of growth-promoting effects for soil microorganisms and plants even if the product is buried in soil after use. Furthermore, temperatures above 60°C may significantly change the physical properties of polylactic acid, making it difficult to use.

[0034] In particular, when using the solid base-mixed polylactic acid molded article of the present invention outdoors, if you want to accelerate the rate of hydrolysis, you can use a molding color (e.g., black) that easily absorbs light (e.g., sunlight), and conversely, if you want to slow down the rate of hydrolysis, you can use a molding color (e.g., white) that easily reflects light. Furthermore, if you want to adjust (accelerate or slow down) the rate of hydrolysis after molding or during use, you can paint the molded article with a black or white paint or a heat-shielding paint.

[0035] Regarding humidity, when the temperature is below 30°C, a humidity of 80% to 95% R.H. (relative humidity) is preferred, with 85% to 90% R.H. being more preferred. When the temperature is below 30°C, if the humidity is less than 80% R.H., hydrolysis of polylactic acid does not proceed sufficiently, and there is a concern that burying the product in soil after use will not be effective in promoting the growth of soil microorganisms and plants. On the other hand, if the humidity is 95% or higher, there is no significant change in hydrolysis of polylactic acid. Furthermore, when the temperature is 30°C or higher, a humidity of 60% to 95% R.H. is preferred, with 75% to 92% R.H. being more preferred, and 85% to 90% R.H. being most preferred. This is because when the temperature is 30°C or higher and the humidity is less than 60R.H.%, the hydrolysis of polylactic acid does not proceed sufficiently, and there is a concern that the growth-promoting effect of soil microorganisms and plants will not be observed even if the product is buried in the soil after use, and when the humidity is 95R.H.% or higher, there is no significant change in the hydrolysis of polylactic acid.

[0036] In this specification, the degree of hydrolysis of polylactic acid can be evaluated by the decrease in weight-average molecular weight. For example, when a solid base-mixed polylactic acid molded article of the present invention is left standing for about three months in an environment of about 40°C and a relative humidity of about 90%, the weight-average molecular weight of the polylactic acid molded article, calculated as polystyrene, decreases by about 80% or more. In another embodiment, the weight-average molecular weight decreases by about 80% to about 93%. In another embodiment, the weight-average molecular weight decreases by 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, or 93% or more. Examples of methods for measuring molecular weight include gel permeation chromatography, size exclusion chromatography, field-flow fractionation, electrophoresis, hydrodynamic chromatography, MTF (Molecular Topology Fractionation), and temperature-rising elution fractionation. A preferred method for determining molecular weight is gel permeation chromatography, as described in the Examples herein.

[0037] (Soil type) The types of soil in which the solid base-mixed polylactic acid molded product can be buried include gray lowland soil, gray plateau soil, gley soil, gley plateau soil, humid black soil, yellow soil, brown lowland soil, black gley soil, black mud soil, waste mushroom beds (for example, crushed or composted), leaf mold, sand, peat moss, and compost. [Example]

[0038] The present inventors conducted the following experiments to investigate the effects of the present invention. The outline and results of the experiments are shown below. The present invention will be explained in more detail below by showing experimental examples, examples, and comparative examples, but the present invention is not limited to the following examples.

[0039] Example 1 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) 95 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika) were mixed with 5 parts by weight of calcined seashell calcium (calcined seashell calcium, manufactured by NC Corporation, median diameter: approximately 10 μm), the main component of which is calcium oxide. The mixture was then stirred and mixed at 50 rpm for 10 minutes using a rotary mixer to obtain solid base-mixed polylactic acid pellets.

[0040] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid pellets were introduced into the hopper of an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., owned by the Center) as shown in Figure 5 and molded into a sheet. At this time, the heater temperatures of the cylinder and nozzle of the injection molding machine were set to 180, 185, 185, 185, and 180°C, respectively, the injection speed was 100 mm / s, and the back pressure was 70 MPa.

[0041] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of the polylactic acid in the solid base-mixed polylactic acid sheet was measured using a gel permeation chromatograph (DGU-20A3 / LC-20AD / CBM-20A / SIL-20AHT / CTO-20AC / SPD-M20A / RID-10A / FRC-10A, manufactured by Shimadzu Corporation). The polylactic acid was dissolved in 10 mL of chloroform (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and filtered through a membrane filter (PTFE, 0.50 μm) before analysis. The measurement conditions are shown in Table 1. [Table 1]

[0042] The weight average molecular weight (hereinafter referred to as molecular weight) was calculated in polystyrene equivalent terms using polystyrene (Shodex STANDARD Type: SM-105, manufactured by Showa Denko K.K.) as a standard substance. As a result, the molecular weight at the time of manufacturing the solid base-mixed polylactic acid sheet was 1.4 × 10 5 For comparison, the molecular weight of a polylactic acid sheet prepared under similar conditions was 1.8 × 10 5 It was.

[0043] (Penetration strength measurement) The penetration test for the solid base-mixed polylactic acid sheet was performed as follows. A test specimen measuring approximately 4 cm in length, 4 cm in width, and 0.8 mm in thickness was fixed to a sample holder (No. 103) with the convex side facing downwards if the specimen was curved. Measurements were made using a creep meter (model RE2-33005C, Yamaden Co., Ltd.) with a 1.5 mm diameter plunger at a penetration rate of 1 mm / sec. The penetration strength of the solid base-mixed polylactic acid sheet was 52.2 N. For comparison, a polylactic acid sheet produced under similar conditions had a penetration strength of 85.9 N. The acceptable penetration strength was 2 N or greater, which allowed the sheet to retain its shape when held and lifted with tweezers or similar.

[0044] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded product was left standing for three months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the solid base-mixed polylactic acid sheet was measured, and it was found to be 2.5 × 10 4 The penetration strength was measured and found to be 5.1 N. For comparison, the molecular weight of a polylactic acid sheet that had been similarly treated was 1.2 × 10 5 The penetration strength was 65.7N.

[0045] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) One gram of solid base-modified polylactic acid sheet was immersed in 100 ml of distilled water and stirred at 500 rpm for 1 hour. The amounts of lactic acid and calcium in the supernatant were then quantified using an ion chromatograph (Thermo Fisher Scientific, ICS-1600). These amounts were used as the amounts of lactic acid and calcium eluted from the solid base-modified polylactic acid sheet. The detector used was a conductivity detector, the anion separation column was an IonPac AS22, and the eluent was a mixture of Na2CO3 and NaHCO3. The sample volume used for analysis was 25 μL. The amounts of lactic acid and calcium eluted from 1 g of solid base-modified polylactic acid sheet were 22.4 and 35.4 mg, respectively. For comparison, the amounts of lactic acid and calcium eluted from a similarly treated polylactic acid sheet were 0.1 and 0.0 mg (not detected), respectively.

[0046] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) 600 g of potting soil containing 100 g of thermo- and humidity-treated solid base-kneaded polylactic acid sheet was mixed with 10 kg of seedling soil (nitrogen: 247 mg / L, phosphorus: 510 mg / L, potassium: 70 mg / L) and then placed in a transparent container (420 x 265 x 328 mm) with light-shielding protection. Sixteen spinach plants were then sown and cultivated for six months (from October 24, 2023 (sown) to April 24, 2024 (harvested)). Organic compound fertilizer was added at the time of sowing, and a chemical fertilizer was added three months later. Watering was performed twice daily, in the morning and evening, when the weather was fine and the temperature was above 25°C, and once daily in the morning otherwise.

[0047] When evaluating soil microorganisms, 1g of soil near the solid base-kneaded polylactic acid sheet was collected three months after cultivation, and the number of viable bacteria in the soil was evaluated using the ATP method. For the evaluation of spinach cultivation, 20 days after germination, the plants were thinned from 16 to 6, 40 days after germination, and then from 6 to 4 again after 80 days. Growth conditions were evaluated according to Table 2. The pass criterion for the growth index was 4 or higher.

[0048] As a result, the cell-derived ATP concentration in the soil suspension was 18.6 × 10 -10 For comparison, the viable bacterial count in the culture medium was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the sample suspension was 4.4 × 10 -10 mol / L, and when no solid base-mixed polylactic acid sheet or polylactic acid was added, the cell-derived ATP concentration in the sample suspension was 4.8 × 10 -10 mol / L. Thus, while the number of viable bacteria in the culture soil decreased when the polylactic acid sheet was used, the number of viable bacteria increased when the solid base mixed polylactic acid sheet was buried, demonstrating the effect of promoting the growth of soil microorganisms. On the other hand, the growth evaluation index for spinach was 5. [Table 2]

[0049] The results of growing spinach using the solid base-mixed polylactic acid sheet are shown in Figures 7A and 7B. Spinach grown in potting soil or waste mushroom beds containing the solid base-mixed polylactic acid sheet (shown as "CaO mixed" in the figures) tended to have longer roots than those grown in potting soil alone. The number of leaves also tended to be greatest in the following order: potting soil alone, potting soil (CaO mixed), and waste mushroom bed (CaO mixed).

[0050] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0051] Example 2 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that quicklime (manufactured by Fujifilm / Wako Pure Chemical Industries) was added in an amount of 6 parts by weight to 94 parts by weight of polylactic acid pellets (Terramac manufactured by Unitika).

[0052] (Forming of solid base mixed polylactic acid sheet) 70 g of solid base-mixed polylactic acid pellets were placed in a compression mold measuring 300 mm in length, 300 mm in width, and 1.3 mm in thickness, and pressed at 185°C and 10 MPa for 4 minutes using a press molding machine (Mini Test Press, MP-WCL, manufactured by Toyo Seiki Seisakusho) as shown in Figure 2, followed by pressing at 15 MPa for 5 minutes and cooling for 4 minutes to obtain a solid base-mixed polylactic acid sheet.

[0053] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.4 × 10 5 For comparison, the molecular weight of a polylactic acid sheet prepared under similar conditions was 1.8 × 10 5It was.

[0054] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example was 50.6 N. For comparison, the penetration strength of a polylactic acid sheet produced under similar conditions was 84.4 N.

[0055] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 37°C and 85% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 2.1 × 10 4 The penetration strength was measured and found to be 4.5 N. For comparison, the molecular weight of a polylactic acid sheet that had been similarly treated was 1.2 × 10 5 The penetration strength was 66.0N.

[0056] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 23.7 and 39.6 mg, respectively. For comparison, the amounts of lactic acid and calcium eluted from a polylactic acid sheet treated in the same manner were 0.1 and 0.0 (undetectable) mg, respectively.

[0057] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying the constant temperature and humidity treated solid base mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 18.2 × 10 -10For comparison, the viable bacterial count in the culture medium was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the sample suspension was 4.4 × 10 -10 mol / L, and when no solid base-mixed polylactic acid sheet or polylactic acid was added, the cell-derived ATP concentration in the sample suspension was 4.8 × 10 -10 mol / L. Thus, while the number of viable bacteria in the culture soil decreased when the polylactic acid sheet was used, the number of viable bacteria increased when the solid base mixed polylactic acid sheet was buried, demonstrating the effect of promoting the growth of soil microorganisms. On the other hand, the growth evaluation index for spinach was 5.

[0058] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0059] Example 3 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 10 parts by weight of calcium hydroxide (manufactured by Fujifilm / Wako Pure Chemical Industries) was added to 90 parts by weight of polylactic acid pellets (Terramac manufactured by Unitika).

[0060] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0061] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.5 × 10 5 It was.

[0062] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 45.7 N.

[0063] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for two months in an environment of 40°C and 60% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 6.2 × 10 4 The penetration strength was measured and found to be 22.9 N. For comparison, the molecular weight of a polylactic acid sheet that had been similarly treated was 1.3 × 10 5 The penetration strength was 76.4N.

[0064] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 15.4 and 149.6 mg, respectively. For comparison, the amounts of lactic acid and calcium eluted from a polylactic acid sheet treated in the same manner were 0.1 and 0.0 (undetectable) mg, respectively.

[0065] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying the constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 14.9 × 10 -10 For comparison, the viable bacterial count in the culture soil was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the soil suspension was 4.4 × 10 -10 mol / L, and when no solid base-mixed polylactic acid sheet or polylactic acid was added, the cell-derived ATP concentration in the soil suspension was 4.8 × 10-10 mol / L. Thus, while the number of viable bacteria in the culture soil decreased when the polylactic acid sheet was used, the number of viable bacteria increased when the solid base mixed polylactic acid sheet was buried, demonstrating the effect of promoting the growth of soil microorganisms. On the other hand, the growth evaluation index for spinach was 4.

[0066] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0067] Example 4 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 0.3 parts by weight of baked seashells (median diameter: approximately 10 μm) were added to 99.7 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika).

[0068] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 2.

[0069] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.4 × 10 5 It was.

[0070] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 76.3 N.

[0071] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left to stand for one month in an environment of 30°C and 75% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 8.9 × 10 4 The penetration strength was measured and found to be 55.1 N. For comparison, the molecular weight of a polylactic acid sheet that had been similarly treated was 1.4 × 10 5 The penetration strength was 78.2N.

[0072] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 10.7 mg and 2.0 mg, respectively. For comparison, the amounts of lactic acid and calcium eluted from a polylactic acid sheet treated in the same manner were 0.1 mg and 0.0 mg (not detected), respectively.

[0073] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 13.1 × 10 -10 For comparison, the viable bacterial count in the culture soil was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the soil suspension was 4.5 × 10 -10 mol / L, and when no solid base-mixed polylactic acid sheet or polylactic acid was added, the cell-derived ATP concentration in the soil suspension was 4.8 × 10 -10 mol / L. Thus, while the number of viable bacteria in the culture soil decreased when the polylactic acid sheet was used, the number of viable bacteria increased when the solid base mixed polylactic acid sheet was buried, demonstrating the effect of promoting the growth of soil microorganisms. On the other hand, the growth evaluation index for spinach was 4.

[0074] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0075] Example 5 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) In the same manner as in Example 1, solid base-mixed polylactic acid pellets were prepared.

[0076] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0077] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.5 × 10 5 It was.

[0078] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 52.2 N.

[0079] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 20°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 6.9 × 10 4 The penetration strength was measured and found to be 18.1 N. For comparison, the molecular weight of a polylactic acid sheet that had been similarly treated was 1.6 × 10 5The penetration strength was 75.7N.

[0080] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of solid base-mixed polylactic acid sheet were 15.9 and 24.1 mg, respectively. For comparison, the amounts of lactic acid and calcium eluted from a polylactic acid sheet treated in the same manner were 0.1 and 0.0 (undetectable) mg, respectively.

[0081] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying a solid base-mixed polylactic acid sheet that had been subjected to constant temperature and humidity treatment was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 14.3 × 10 -10 For comparison, the viable bacterial count in the culture soil was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the soil suspension was 4.6 × 10 -10 mol / L, and when no solid base-mixed polylactic acid sheet or polylactic acid was added, the cell-derived ATP concentration in the soil suspension was 4.8 × 10 -10 mol / L. Thus, while the number of viable bacteria in the culture soil decreased when the polylactic acid sheet was used, the number of viable bacteria increased when the solid base mixed polylactic acid sheet was buried, demonstrating the effect of promoting the growth of soil microorganisms. On the other hand, the growth evaluation index for spinach was 4.

[0082] (comprehensive evaluation) When the solid base-mixed polylactic acid sheet used in this example was buried in soil, the amount of lactic acid eluted was greater than that of the polylactic acid sheet alone, and the growth promotion effect of soil microorganisms and plants was also observed, so it was evaluated as suitable. Furthermore, although the solid base-mixed polylactic acid sheet of this example cannot be used for applications such as agricultural mulch, it was shown that burying the solid base-mixed polylactic acid sheet itself in the soil promoted the growth of soil microorganisms and plants. Therefore, since these growth promotion effects were also observed, it was evaluated as suitable.

[0083] Example 6 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 10 parts by weight of baked seashells (median diameter: approximately 10 μm) were added to 90 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika).

[0084] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1. (Properties of solid base mixed polylactic acid sheet during manufacturing)

[0085] (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.2 × 10 5 It was.

[0086] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 46.7 N.

[0087] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 1.4 × 10 4 The measured penetration strength was 3.9N.

[0088] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 32.6 mg and 69.5 mg, respectively.

[0089] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying the constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 18.1 × 10 -10 For comparison, the viable bacterial count in the culture soil was evaluated using a polylactic acid sheet, and the cell-derived ATP concentration in the soil suspension was 4.5 × 10 -10 mol / L, and the growth evaluation index for spinach was 5.

[0090] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0091] Example 7 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 20 parts by weight of baked seashells (median diameter: approximately 10 μm) were added to 80 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika).

[0092] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0093] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.1 × 10 5 It was.

[0094] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 36.5 N.

[0095] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 7.9 × 10 3 The measured penetration strength was 2.1N.

[0096] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 41.2 mg and 122.7 mg, respectively.

[0097] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by burying a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 18.0 × 10 -10 mol / L. The growth evaluation index for spinach was 5.

[0098] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this example was evaluated as suitable for agricultural use, and when buried in soil, it eluted more lactic acid than the polylactic acid sheet alone, and also showed an effect of promoting the growth of soil microorganisms and plants.

[0099] (Comparative Example 1) (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 10 parts by weight of calcium carbonate (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 90 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika Co., Ltd.).

[0100] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0101] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.6 × 10 5 It was.

[0102] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 58.4 N.

[0103] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 1.0 × 10 5 The measured penetration strength was 49.4N.

[0104] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 2.9 mg and 4.6 mg, respectively.

[0105] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by embedding a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 4.4 × 10 -10 mol / L. The growth evaluation index for spinach was 3.

[0106] (comprehensive evaluation) Although the solid base-mixed polylactic acid sheet used in this comparative example was suitable for agricultural use, when buried in soil, the amount of lactic acid eluted was insufficient, and no effect of promoting the growth of soil microorganisms and plants was observed, so it was evaluated as unsuitable. This is thought to be because the calcium carbonate used as the solid base in this comparative example is weakly basic compared to calcium oxide or calcium hydroxide, and hydrolysis of polylactic acid was slow.

[0107] (Comparative Example 2) (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 0.1 parts by weight of baked seashells (median diameter: approximately 10 μm) were added to 99.9 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika).

[0108] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0109] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.8 × 10 5 It was.

[0110] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 82.6 N.

[0111] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 1.2 × 10 5 The measured penetration strength was 62.5N.

[0112] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 0.1 mg and 0.4 mg, respectively.

[0113] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by embedding a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 4.1 × 10 -10 mol / L. The growth evaluation index for spinach was 3.

[0114] (comprehensive evaluation) Although the polylactic acid sheet kneaded with a solid base used in this comparative example was suitable for agricultural use, when buried in soil, the amount of lactic acid and calcium eluted was insufficient, and no effect of promoting the growth of soil microorganisms and plants was observed. Therefore, it was evaluated as unsuitable. This is thought to be because the amount of baked shells, which is a solid base, kneaded into the sheet was small, and the hydrolysis of the polylactic acid was slow.

[0115] (Comparative Example 3) (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) The solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1.

[0116] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 2.

[0117] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.4 × 10 5 It was.

[0118] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 82.6 N.

[0119] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 5°C and 10% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 1.2 × 10 5 The measured penetration strength was 37.1N.

[0120] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 9.1 mg and 9.5 mg, respectively.

[0121] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by embedding a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 8.7 × 10 -10 mol / L. The growth evaluation index for spinach was 3.

[0122] (comprehensive evaluation) Although the solid base-mixed polylactic acid sheet used in this comparative example was suitable for agricultural use, when buried in soil, the amount of lactic acid and calcium released was insufficient, and the growth-promoting effect on soil microorganisms and plants was not observed. Therefore, it was evaluated as unsuitable. This is thought to be due to the low temperature and humidity during the constant temperature and humidity treatment in this comparative example, which slowed the hydrolysis of polylactic acid.

[0123] Comparative Example 4 (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 5 parts by weight of quicklime (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 95 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika Co., Ltd.).

[0124] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 1.

[0125] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 1.4 × 10 5 It was.

[0126] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 53.1 N.

[0127] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left to stand for 0.1 month in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 1.3 × 10 5 The measured penetration strength was 45.2N.

[0128] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 1.5 mg and 2.3 mg, respectively.

[0129] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by embedding a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 4.7 × 10 -10 mol / L. The growth evaluation index for spinach was 3.

[0130] (comprehensive evaluation) Although the solid base-mixed polylactic acid sheet used in this comparative example was suitable for agricultural use, when buried in soil, the amount of lactic acid and calcium eluted was insufficient, and the growth-promoting effect on soil microorganisms and plants was not observed. Therefore, it was evaluated as unsuitable. This is thought to be due to the short constant temperature and humidity treatment period in this comparative example, which resulted in insufficient hydrolysis of polylactic acid due to the constant temperature and humidity treatment.

[0131] (Comparative Example 5) (Production of solid base mixed polylactic acid molded products) (Preparation of solid base-mixed polylactic acid pellets) Solid base-mixed polylactic acid pellets were prepared in the same manner as in Example 1, except that 25 parts by weight of baked seashells (median diameter: approximately 10 μm) were added to 75 parts by weight of polylactic acid pellets (Terramac, manufactured by Unitika).

[0132] (Forming of solid base mixed polylactic acid sheet) The solid base-mixed polylactic acid sheet of this example was produced in the same manner as in Example 2.

[0133] (Properties of solid base mixed polylactic acid sheet during manufacturing) (Molecular weight measurement method) The molecular weight of polylactic acid was measured in the same manner as in Example 1. As a result, the molecular weight of the polylactic acid sheet kneaded with a solid base in this example was 9.2 × 10 4 It was.

[0134] (Penetration strength measurement) The penetration strength of the solid base-mixed polylactic acid sheet used in this example was measured in the same manner as in Example 1. As a result, the penetration strength of the solid base-mixed polylactic acid sheet produced in this example at the time of production was 29.3 N.

[0135] (Molecular weight and penetration strength of solid base-mixed polylactic acid sheets left at constant temperature and humidity) The solid base-mixed polylactic acid molded article prepared in this example was left standing for 3 months in an environment of 40°C and 90% RH, assuming its use in agricultural applications. After that, the molecular weight of the polylactic acid was measured and found to be 4.9 × 10 3 The measured penetration strength was 1.1N.

[0136] (Amount of lactic acid and calcium eluted from a solid base-mixed polylactic acid sheet left in a constant temperature and humidity environment) The amounts of lactic acid and calcium eluted from the solid base-mixed polylactic acid sheet after standing in a constant temperature and humidity environment were measured in the same manner as in Example 1. As a result, the amounts of lactic acid and calcium eluted per gram of the solid base-mixed polylactic acid sheet were 55.9 mg and 164.9 mg, respectively.

[0137] (Promotion of soil microorganisms and plant growth by burying constant temperature and humidity treated solid base-kneaded polylactic acid sheets) The promotion of soil microorganisms and plant growth by embedding a constant temperature and humidity treated solid base-mixed polylactic acid sheet was evaluated in the same manner as in Example 1. As a result, the cell-derived ATP concentration in the soil suspension was 18.5 × 10 -10 mol / L. The growth evaluation index for spinach was 5.

[0138] (comprehensive evaluation) The solid base-mixed polylactic acid sheet used in this comparative example was found to have the effect of promoting the growth of soil microorganisms and plants when buried in soil after constant temperature and humidity treatment, but it was evaluated as unsuitable for agricultural use because it had low strength and was considered difficult to use for agricultural purposes.

[0139] (summary) Table 3 shows the type of solid base, the mixing ratio of the solid base in the solid base-mixed polylactic acid molded product, the molding method and conditions for the solid base-mixed polylactic acid molded product, the shape of the solid base-mixed polylactic acid molded product, the temperature and humidity conditions for the constant temperature and humidity treatment, and the constant temperature and humidity treatment period for Examples 1 to 7 and Comparative Examples 1 to 5. Table 4 also shows the penetration strength, weight-average molecular weight, lactic acid and calcium elution amounts when stirred in distilled water, and the results of the viable cell count evaluation of soil microorganisms and plant growth index for the solid base-mixed polylactic acid molded products produced in Examples 1 to 7 and Comparative Examples 1 to 5. [Table 3] [Table 4]

Claims

1. A polylactic acid resin composition comprising a polylactic acid resin and a solid base, The solid base has an average particle size of about 1 μm or more and about 1000 μm or less, and the content of the solid base in the composition is about 0.3 wt % or more and about 20 wt % or less.

2. 2. The composition of claim 1, wherein the average particle size is from about 1 μm to about 300 μm.

3. 2. The composition of claim 1, wherein the average particle size is from about 1 μm to about 100 μm.

4. 2. The composition of claim 1, wherein the average particle size is from about 3 μm to about 75 μm.

5. 2. The composition of claim 1, wherein the solid base comprises at least one selected from the group consisting of calcined shell calcium, calcium oxide, calcined dolomite, calcium hydroxide, magnesium oxide, and magnesium hydroxide.

6. 10. The composition of claim 1, wherein the solid base comprises calcined shell calcium, calcium oxide, or calcium hydroxide.

7. 2. The composition according to claim 1, wherein when the solid base is calcined shell calcium, calcium oxide, or magnesium oxide, the content of the calcined shell calcium, calcium oxide, or magnesium oxide in the composition is from about 3 wt % to about 10 wt %.

8. 2. The composition according to claim 1, wherein when the solid base is calcium hydroxide or magnesium hydroxide, the content of the calcium hydroxide or magnesium hydroxide in the composition is from about 8 wt % to about 15 wt %.

9. 10. The composition of claim 1, further comprising at least one additive selected from the group consisting of ultraviolet absorbers, antioxidants, plasticizers, compatibilizers, and surfactants.

10. A resin molded article comprising the composition according to any one of claims 1 to 9.

11. 11. The resin molded body according to claim 10, wherein when the resin molded body is left standing for about three months in an environment of about 40°C and a relative humidity of about 90%, the weight average molecular weight of the resin molded body in terms of polystyrene decreases by about 80% or more.

12. The resin molded article according to claim 10, which is an agricultural material.

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