Polylactic acid and cellulose nanocrystal mixture

Abstract

[Problem] The present invention provides a PLA and CNC mixture which is improved to have physical properties required for general purposes without increasing environmental issues while keeping biodegradability that is intrinsically necessary for PLA. [Solution] A PLA and CNC mixture according to the present invention is obtained by adding only CNC which are not chemically modified with a biodegradable substance and has a crystallinity of 90% or more to PLA. Since the CNC dispersed in the PLA serve as crystal nuclei and innumerable crystals are formed, tie molecules extending over a plurality of crystals are formed, thereby forming a PLA crystal network structure, and the structure improves the physical properties of the PLA. Instead of improving PLA by modifying the PLA through crosslinking or polymerization of a substance that has an environmental load or another chemical substance to the PLA, or improving PLA through addition of a chemical substance which has an environmental load, this PLA and CNC mixture improves the physical properties of PLA by modifying the PLA through crystallization and crystal structure change of the PLA itself by adding CNC, which are biodegradable and nontoxic and do not have an environmental load, to the PLA, thereby maintaining the biodegradability of the PLA without degradation.

Description

Polylactic acid, cellulose nanocrystal mixture

[0001] The present invention relates to biodegradable plastics. More specifically, it relates to a PLA / CNC mixture that maintains the biodegradability that is the greatest feature of PLA, a biodegradable resin, while improving its physical properties depending on the intended use.

[0002] Traditionally, synthetic resins made from petroleum have become indispensable in our daily lives due to their versatility and wide range of uses and applications. Typical examples include polypropylene and polyethylene used in hotel amenities, shopping bags, straws and forks, polypropylene and vinyl chloride used in medical equipment such as disposable syringes, polystyrene used in instant ramen and seasoning packets used in processed foods, nylon and polyethylene terephthalate (PET), and PET used in most beverage bottles.

[0003] Furthermore, petroleum-based synthetic fibers are widely used in textile products that are indispensable to our daily lives, such as clothing, carpets, curtains, etc. In particular, polyester-based synthetic fibers, including PET, cationic dyeable PET, polybutylene terephthalate, polytrimethylene terephthalate, etc., have extremely excellent properties as clothing materials, such as dimensional stability, wrinkle resistance, and strength, and account for 65% of clothing materials used worldwide.

[0004] Although synthetic resins are widely used, they are used in large quantities and are discarded in large quantities, which poses many disposal problems.

[0005] When disposing of plastic by incineration, depending on the type of plastic, it must be incinerated at a high temperature of over 800°C, otherwise harmful environmental hormones such as dioxins will be released, resulting in high energy costs for incineration. In addition, the fuel used for combustion and the synthetic resin products being incinerated release large amounts of carbon dioxide, which contributes to global warming.

[0006] When disposed of by landfilling, synthetic resin products are not biodegradable, so they will remain in the soil in the same state as when they were buried, even after nearly 100 years.

[0007] Furthermore, synthetic resin products that are not collected and dumped are degraded and broken down by ultraviolet rays, becoming a source of environmental pollution. The current problem of microplastics in the ocean is a good example of this.

[0008] The use of biodegradable resins has been proposed as a material that can overcome this situation. Biodegradable resin is a general term for resins that are literally broken down and disappear by the bacteria that live in soil and water. The energy cost of incineration is low, and even if buried in the ground, they will disappear within a few months to a few years. Furthermore, if the raw materials are made from plants, the carbon dioxide absorbed by the plants during their growth period is released when they are incinerated or decomposed, making them carbon-neutral materials that do not contribute to the increase or decrease of carbon dioxide in the global environment.

[0009] In particular, PLA is a polyester-based biodegradable resin made from corn starch and sugarcane molasses, which are lactic acidized through lactic acid fermentation and then polymerized with ester bonds. Among biodegradable resins, it has a high melting point, is highly versatile, and is environmentally friendly. The manufacturing process for PLA involves extracting sugar from plant-derived raw materials, lactic acid fermenting it using microorganisms to produce lactic acid, and then polymerizing that lactic acid. The commonly known manufacturing process from corn is as follows: Corn ⇒ Extraction of sugar from starch ⇒ Lactic acid fermentation ⇒ Polymerization ⇒ PLA

[0010] Of these processes, the polymerization step, which takes place at 200-220°C, requires the most energy and generates the most CO2. Other steps are carried out at temperatures below 100°C, and in some cases even below 50°C. This makes it an environmentally friendly resin in terms of the shortness of the process, the amount of CO2 generated, and the amount of energy used. Its environmental impact is clear when compared to the manufacturing process of PET resin, the most widely used in the world. For comparison, the general PET manufacturing process, from raw materials such as naphtha and natural gas to polymerization, is as follows: <When synthesized entirely from petroleum> Petroleum (naphtha) ⇒ ethylene, xylene refinement ⇒ ethylene glycol, terephthalic acid synthesis ⇒ polymerization ⇒ PET <When synthesized from petroleum and natural gas> Petroleum (naphtha) ⇒ xylene refinement ⇒ terephthalic acid synthesis Natural gas ⇒ ethylene refinement ⇒ ethylene glycol synthesis Terephthalic acid + ethylene glycol ⇒ polymerization ⇒ PET

[0011] Each step in PET manufacturing requires heat of over 200°C, resulting in significant amounts of energy consumption and CO2 emissions.Compared to the polymerization process that requires the most energy in PLA, the polymerization temperature for PET is 280-300°C, which is significantly higher than the polymerization temperature for PLA.

[0012] In recent years, biomass PET, which uses plant-based raw materials, has been proposed, but its manufacturing process is as follows, and it takes longer than manufacturing from petroleum or natural gas, and the amount of energy used and CO2 emitted is significantly greater. <When synthesizing from petroleum and corn> Petroleum (naphtha) ⇒ xylene purification ⇒ terephthalic acid synthesis Corn (starch) ⇒ fermentation ⇒ distillation + dehydration (ethanol extraction) ⇒ ethylene purification ⇒ ethylene glycol synthesis Terephthalic acid + ethylene glycol ⇒ polymerization ⇒ PET

[0013] In recent years, methods have been developed to manufacture terephthalic acid from plant-derived raw materials, just like ethylene glycol, and the development of 100% biomass PET is anticipated, but this requires more processes than PET made from biomass ethylene glycol alone, and will require more energy consumption and generate more CO2. Because the raw materials are plant-derived, biomass PET is considered a carbon-neutral material, but there are concerns that the process load, energy consumption, and CO2 emissions may exceed the amount of CO2 consumed by the plants that are the raw materials, resulting in more CO2 emissions than PET made from petroleum or natural gas.

[0014] Taking the above into consideration, a life cycle assessment (LCA) of PLA and PET made from petroleum based on the manufacturing process and conditions yields the following results: PLA: Energy consumption 92MJ / Kg, CO2 emissions 4.1-6.5Kg / Kg PET: Energy consumption 142MJ / Kg, CO2 emissions 8.9-12.2Kg / Kg

[0015] As such, PLA consumes approximately 60% of the energy and emits approximately 50% of the CO2 compared to commonly used PET, making it a much more environmentally friendly resin than polyester. Furthermore, PLA is made from renewable plant-based raw materials, and its manufacturing process does not generate more CO2 than the plants it is made from, making it a carbon-neutral material. Therefore, it is likely to become an indispensable material in today's sustainable society.

[0016] For this reason, PLA has been investigated for various applications since its development up until now. However, compared to widely used synthetic resins, especially the commonly used PET, PLA has a lower strength and melting point, which limits the applications in which it can be used, and it has not yet been widely adopted in society.

[0017] To address these issues, methods have been proposed for modifying PLA to use it as a general-purpose resin. These methods include modifying the crystalline form of PLA to a stereocomplex form to improve its strength and heat resistance (melting point) (e.g., Patent Document 1), polymerizing other substances with PLA to increase its heat resistance (e.g., Patent Documents 2 and 3), and modifying PLA to create a crystalline core structure by adding an inorganic filler (e.g., Patent Document 4). In recent years, research has focused on modifying PLA by adding organic fillers from a sustainability perspective, with modification methods using cellulose nanofibers being a prime example (e.g., Patent Document 5 and Reference 6).

[0018] However, modification to a stereocomplex form results in almost no biodegradability, while modification methods involving the polymerization of other substances only increase heat resistance without increasing strength, resulting in a significant decrease in biodegradability due to the influence of other polymerized substances. Furthermore, the addition of inorganic fillers results in poor compatibility with PLA and larger particle sizes than PLA crystals, making it possible to use it in molded products. However, when considering fiber or film applications, the inorganic fillers clog the nozzle, preventing spinning or film casting. Even if this were possible, it would cause manufacturing problems by inhibiting the oriented crystallization of PLA during the subsequent stretching process. Furthermore, the use of inorganic fillers can leave residue during biodegradation, especially during incineration, which, depending on the inorganic filler's composition, could potentially pollute the environment. In this sense, PLA with inorganic fillers cannot be considered a biodegradable material. In other words, all modification methods result in significant decreases in biodegradability or high environmental toxicity.

[0019] When adding cellulose nanofibers, a sustainable organic filler, they cannot be made small enough to be used as a filler unless they are chemically modified after being defibrated and extracted. Unmodified cellulose nanofibers are too coarse to be used as a filler. Furthermore, cellulose nanofibers contain not only cellulose but also hemicellulose and lignin, making them heat-resistant. Heating them above 200°C can cause discoloration due to the Maillard reaction, making them unsuitable for use in molten resins. Furthermore, while organic fillers emit combustion gases such as carbon dioxide when burned, cellulose nanofibers are chemically modified, potentially emitting harmful gases due to the effects of modifiers and matching agents.

[0020] Therefore, there is a current demand for the development of a biodegradable resin, PLA, that does not reduce biodegradability, does not increase environmental load, and yet has improved mechanical properties such as strength.

[0021] JP 2005-023512 A JP 2009-024058 A JP 2008-255500 A JP 2003-327803 A JP 2022-062595 A

[0022] "Cellulose Nanofiber Research and Practical Applications" NTS Publishing, November 2021, ISBN: 978-4-86043-751-0, Part 1, Chapters 4-5 and Part 3, Chapters 4-6

[0023] The present invention was made in consideration of this current situation, and aims to provide a PLA / CNC mixture that has been improved to have physical properties required for general use, while maintaining the biodegradability inherently required of PLA, a biodegradable resin, without increasing the environmental burden.

[0024] The present inventors have conducted extensive research to solve the above problems, and as a result have arrived at and completed the present invention.

[0025] That is, the gist of the present invention is as follows.

[0026] The PLA / CNC mixture of the present invention is a PLA / CNC mixture that has been improved to have properties required for general purposes, while maintaining biodegradability and reducing environmental impact, by adding only CNC that has never been chemically modified with a biodegradable substance to PLA, and the CNC dispersed within the PLA acts as a crystalline nucleus to promote crystallization and form a crystalline network structure through the formation of tie molecules.

[0027] Here, "not chemically modified" means that no other functional groups (e.g., sulfo groups, phosphate groups, etc.) have been added to the cellulose, and that the cellulose has the same structural units as the original cellulose structural units (Chemical Formula 1). Furthermore, "never chemically modified" excludes cellulose that has undergone some kind of chemical modification and then undergoes an operation to return it to the original structural unit of Chemical Formula 1. The structural units of the following formula are preferably used as structural units of cellulose.

[0028]

[0029] In the present invention, the preferred cellulose content in CNC is 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more, with the higher the content being the more preferable. The raw material for producing CNC is not particularly limited, but for example, seed hair fibers such as cotton, bast or vein fibers such as hemp, etc. are preferably used.

[0030] Tie molecules are polymer chains that exist between the crystals formed within the resin. In this invention, a large number of crystals are formed using CNC as the crystal nucleus, and the tie molecules that span these crystals are spread throughout the resin, forming a network-like structure. This structure improves physical properties such as strength and heat resistance, which are important for improving versatility.

[0031] Rather than modifying PLA by crosslinking or polymerizing environmentally harmful chemicals to denature PLA or by adding environmentally harmful chemicals, the present invention modifies PLA by adding a biodegradable, environmentally friendly, natural, highly crystalline CNC to alter the crystallization and crystalline structure of PLA. This results in a PLA / CNC mixture that maintains the biodegradability of polylactic acid while improving its properties for general use. Furthermore, the CNC used in the present invention is unmodified and therefore safe enough to be consumed. Only safe PLA suitable for food packaging is used, resulting in a PLA / CNC mixture that remains safe in soil after biodegradation and in combustion gases, without increasing environmental impact.

[0032] The present invention is a PLA / CNC mixture characterized by the fact that the improved physical properties obtained vary depending on the particle size, amount, and addition method of the CNC added to the PLA.

[0033] The detailed gist of the present invention is as follows:

[0034] The polylactic acid and cellulose nanocrystal mixture of the present invention is characterized in that only chemically unmodified cellulose nanocrystals are uniformly dispersed in the polylactic acid, and the amount of cellulose nanocrystals uniformly dispersed in the polylactic acid is 0.01 to 60.0 wt % of the total weight of the mixture produced.

[0035] The method for producing a mixture of polylactic acid and cellulose nanocrystals according to the present invention includes a step of adding chemically unmodified cellulose nanocrystals to polylactic acid and mixing them, and is characterized in that the amount of cellulose nanocrystals added to the polylactic acid is 0.01 to 60.0% by weight of the total weight of the mixture produced.

[0036] The PLA / CNC mixture of the present invention is a mixture that maintains the biodegradability of PLA and has been improved to have physical properties required for general use without increasing the environmental burden.

[0037] According to the present invention, it is possible to obtain a PLA / CNC mixture that has been improved to have properties required for general use while maintaining biodegradability and without increasing the environmental burden.Furthermore, it is possible to obtain a PLA / CNC mixture that can be used for general purposes and that can be improved to have properties required for specific applications more than conventional PLA or modified PLA.

[0038] FIG. 1 is a chart graph obtained by DSC measurement of Example 1. FIG. 2 is a chart graph obtained by DSC measurement of Comparative Example 1. FIG. 3 is a chart graph obtained by DSC measurement of Example 10. FIG. 4 is a chart graph obtained by DSC measurement of Comparative Example 2. FIG. 5 is a chart graph obtained by DSC measurement of Example 11. FIG. 6 is a chart graph obtained by DSC measurement of Comparative Example 3. FIG. 7 is a photograph of Example 13 observed under a polarizing microscope at 5x magnification. FIG. 8 is a photograph of Example 13 observed under a polarizing microscope at 40x magnification. FIG. 9 is a photograph of Example 15 observed under a polarizing microscope at 5x magnification. FIG. 10 is a photograph of Example 15 observed under a polarizing microscope at 40x magnification. FIG. 11 is a photograph of Comparative Example 4 observed under a polarizing microscope at 5x magnification. FIG. 12 is a photograph of Comparative Example 4 observed under a polarizing microscope at 40x magnification. FIG. 13 is a photograph of Example 13 observed under a phase contrast microscope at 40x magnification. FIG. 14 is a photograph of Example 13 observed under differential interference contrast at 40x magnification. FIG. 15 is a photograph of Example 15 observed under phase contrast contrast at 40x magnification. FIG. 16 is a photograph of Example 15 observed under differential interference contrast at 40x magnification. FIG. 17 is a photograph of Comparative Example 4 observed under phase contrast contrast at 40x magnification. FIG. 18 is a photograph of Comparative Example 4 observed under differential interference contrast at 40x magnification. FIG. 19 is a photograph of the stretched film of Example 13 observed under a polarizing microscope. FIG. 20 is a photograph of the stretched film of Example 15 observed under a polarizing microscope. FIG. 21 is a photograph of the stretched film of Comparative Example 4 observed under a polarizing microscope. FIG. 22 is a photograph of the stretched film of Example 13 observed under phase contrast contrast. FIG. 23 is a photograph of the stretched film of Example 15 observed under phase contrast contrast. FIG. 24 is a photograph of the stretched film of Comparative Example 4 observed under phase contrast contrast. Fig. 25 is a photograph obtained by differential interference observation of the stretched film of Example 13. Fig. 26 is a photograph obtained by differential interference observation of the stretched film of Example 15. Fig. 27 is a photograph obtained by differential interference observation of the stretched film of Comparative Example 4. Fig. 28 is a photograph obtained by polarizing microscope observation under crossed Nicols of the stretched film of Example 20. Fig. 29 is a photograph obtained by polarizing microscope observation under open Nicols of the stretched film of Example 20. Fig. 30 is a photograph obtained by polarizing microscope observation under crossed Nicols of the stretched film of Example 21. Fig. 31 is a photograph obtained by polarizing microscope observation under open Nicols of the stretched film of Example 21.FIG. 32 is a photograph of the stretched film of Example 22 observed under a polarizing microscope with crossed Nicols. FIG. 33 is a photograph of the stretched film of Example 22 observed under a polarizing microscope with open Nicols. FIG. 34 is a photograph of the stretched film of Comparative Example 9 observed under a polarizing microscope with crossed Nicols. FIG. 35 is a photograph of the stretched film of Comparative Example 9 observed under a polarizing microscope with open Nicols. FIG. 36 is a photograph of the multifilament of Example 18 observed under a polarizing microscope with crossed Nicols. FIG. 37 is a photograph of the multifilament of Example 19 observed under a polarizing microscope with crossed Nicols. FIG. 38 is a photograph of the multifilament of Comparative Example 7 observed under a polarizing microscope with crossed Nicols. FIG. 39 is a measurement chart graph of the multifilaments of Example 19 and Comparative Example 7 measured with a TMA device. FIG. 40 is a measurement chart graph of the stretched films of Example 20 and Comparative Example 9 measured with a TMA device.

[0039] Hereinafter, embodiments of the present invention will be described in detail.

[0040] The present invention is a PLA / CNC mixture in which only non-chemically modified CNC is added to PLA.

[0041] (1) PLA The PLA used in the present invention may be any commonly used PLA. Depending on the intended use of the PLA and CNC mixture of the present invention, appropriate PLA resins may be selected based on the mixing ratio of the L- and D-isomers, molecular weight, and product grades designated for fiber, film, injection molding, extrusion molding, etc. The mixing ratio of the L- and D-isomers is not particularly limited. However, for fiber applications, for example, a mixture or copolymer of L- and D-isomers containing the L-isomer as the main component is preferred from the perspective of biodegradability and spinnability. The content of the D-isomer is preferably 0 to 0.7 mol%, more preferably 0.1 to 0.6 mol%, and even more preferably 0.1 to 0.5 mol%, based on the total monomer units polymerized into PLA. A D-isomer content greater than 0.7 mol% based on the total monomer units polymerized into PLA may result in reduced spinnability, heat resistance, and fiber strength, making it unsuitable for use in the present invention. Of course, in the present invention, even if the purity of the D-isomer is high and the content of the L-isomer is low, the same effect as that of PLA mainly composed of L-isomer can be obtained, so PLA mainly composed of either the L-isomer or the D-isomer can be appropriately selected and used depending on the intended use of the PLA and CNC mixture of the present invention.The molecular weight of the PLA used can also be appropriately selected and used depending on the intended use, and is not particularly limited.

[0042] The PLA used may be made from any raw material, such as corn, sugarcane, beets, or cassava, and may be polymerized using any method, such as the lactide method, direct polymerization method, or melt polymerization method.

[0043] (2) CNC The CNC used in the present invention is a type of nanostructured cellulose, which is made by finely disaggregating cellulose, the main component of plants, to the nano-level. CNC is obtained by acid hydrolysis using strong acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid to dissolve non-cellulose components such as lignin and hemicellulose, as well as amorphous components, from cellulose raw materials such as plants, and extracting and purifying only the crystalline cellulose. In the present invention, CNC purified by acid hydrolysis is used that has not been chemically modified.

[0044] The cellulose raw materials used include natural cellulose raw materials and regenerated cellulose raw materials.

[0045] Examples of natural cellulose raw materials that can be used include wood pulp obtained from broad-leaved or coniferous trees, non-wood pulp obtained from bamboo, cotton-based fibers, hemp-based fibers, bagasse, kenaf, and linters, as well as purified pulps of both (e.g., purified linters). Examples of animal-derived natural cellulose include the tunic (exoskeleton) of sea squirts. Examples of non-wood pulp include cotton-derived pulp, including cotton linter pulp and cotton lint pulp, hemp-derived pulp made from abaca (e.g., Ecuadorian or Philippine-grown abaca) and zaisal, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp. Purified pulp obtained from cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp through purification processes such as delignification by cooking, bleaching, and the like, can also be used as natural cellulose raw materials.

[0046] As the raw material for the CNC of the present invention, a CNC that can more effectively exhibit the crystal nucleation effect within PLA is preferred, and a raw material that can extract a large amount of high-crystallinity, strong CNC is preferred. The higher the crystallinity of the CNC raw material used in the present invention, the more desirable it is, but at least 85% or more, 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more is desirable. As the raw material for the CNC used in the present invention, pulp made from cotton fiber or hemp fiber, which has a higher crystallinity than wood pulp and is expected to be in stable supply, is preferred. It is even more preferable to use unused (discarded) resources such as discarded clothing or cutting scraps generated during processes such as spinning, weaving, knitting, and sewing, as this will result in an environmentally friendly CNC. The use of aquatic plants and discarded agricultural crops is also preferred from an environmental perspective.

[0047] The inventors discovered that adding the above-mentioned CNC to PLA improves the physical properties required for general use, and further discovered that using CNC that has never been chemically modified can suppress the increase in environmental load caused by modification.As a result of extensive research, they arrived at and completed the present invention.

[0048] The term "chemically unmodified CNC" used in the present invention refers to CNC that is not chemically modified when added to PLA. For example, CNC that has been acid hydrolyzed with hydrochloric acid is desirable because it is a CNC that is not chemically modified during the purification process of acid hydrolysis. The term "natural CNC that has never been chemically modified" used in the present invention refers to CNC that has been acid hydrolyzed with hydrochloric acid and purified. CNC that has never been chemically modified not only maintains its crystallinity, thereby enhancing the crystal nucleation effect, but is also highly safe enough to be used in food. This not only reduces the environmental impact but also ensures high safety for the human body.

[0049] Furthermore, when cellulose raw materials are hydrolyzed with sulfuric acid, sulfate esterification occurs simultaneously during hydrolysis, resulting in modification of the CNC surface. The purified CNC is chemically modified by sulfate esterification, but can be returned to its unmodified state through subsequent chemical reactions. The CNC of the present invention also includes CNC that has been returned to its unmodified state in this manner. However, since CNC that has been returned to its unmodified state has lower crystallinity than CNC that has never been modified, it becomes difficult to obtain a sufficient crystal nucleation effect to improve physical properties. In the present invention, it is desirable to use CNC that has never been chemically modified, as it has high crystallinity and exhibits a sufficient crystal nucleation effect.

[0050] In the present invention, CNC is added so as to be uniformly dispersed within the PLA. "Uniformly dispersed" here refers to a state in which PLA and CNC particles are uniformly dispersed. However, 100% uniform dispersion is not necessarily required. It may be uniformly dispersed by 60% or more, 70% or more, more preferably 85% or more, even more preferably 90% or more, even more preferably 95% or more, and particularly preferably 98% or more. Furthermore, even dispersion achieved by kneading with a twin-screw kneader (or twin-screw kneader / extruder) is considered "uniformly dispersed." The uniformly dispersed CNC accelerates the crystallization rate of PLA through the crystal nucleation effect, forming fine, uniformly dispersed PLA crystals. The uniformly dispersed PLA crystals cause mutual interference, forming tie molecules between the crystals, resulting in a crystalline network-like structure in which the fine crystals are connected by tie molecules. This structure gives PLA toughness after crystallization, and controlling the crystalline network structure that forms with the amount of CNC added can improve physical properties such as strength, elongation, and elastic modulus. Furthermore, the tie molecules formed between the crystals suppress the thermal flow of the amorphous region of PLA, resulting in improved heat resistance. This invention makes it possible to improve physical properties tailored to specific applications by controlling the crystalline network structure of the fine crystals and tie molecules formed by the nucleation effect of the added CNC.

[0051] The PLA / CNC mixture of the present invention is a mixture in which CNC is uniformly dispersed in an amount of 0.01 to 60.0 wt% of the total weight of the mixture. If the amount of CNC added is less than 0.01 wt%, the amount of CNC uniformly dispersed within the PLA is low, causing no inter-crystalline interference and the formation of a crystalline network structure, resulting in no PLA modification. Furthermore, if the amount of CNC added is less than 0.01 wt%, uniform mixing is difficult, resulting in insufficient dispersion and the formation of a crystalline network structure. If the amount of CNC added is greater than 60.0 wt%, the PLA and CNC cannot be uniformly mixed, resulting in aggregation of the CNC, making it difficult to achieve stable physical properties. Furthermore, when using the mixture for molding, such as injection molding, the viscosity increases too much, making it difficult to deliver the mixture to every corner of the mold, making molding difficult.

[0052] The amount of CNC added in the present invention may be appropriately selected depending on the form of the product produced from the mixture, the intended use of the product, etc. For example, when forming fibers, the amount of CNC added can be selected taking into account the fineness and diameter of the fibers to be produced, and the amount of CNC added is preferably in the range of 0.01 to 3.0 wt %, more preferably 0.1 to 1.2 wt %, and even more preferably 0.3 to 1.0 wt % of the total weight of the mixture to be produced. When forming films or sheets, the amount of CNC added can be selected taking into account the film thickness and transparency of the film or sheet to be produced, and the amount of CNC added can be selected taking into account the film thickness and transparency of the film or sheet to be produced, and the amount of CNC added is preferably in the range of 0.01 to 1.5 wt %, more preferably 0.03 to 1.0 wt %, and even more preferably 0.05 to 0.7 wt % of the total weight of the mixture to be produced. When forming a molded product, the amount of CNC to be added can be selected taking into consideration the molding method, intended use, required performance, etc., and the amount of CNC to be added is preferably in the range of 0.1 to 60.0 wt % of the total weight of the mixture to be produced, more preferably 0.5 to 55.0 wt %, and even more preferably 1.0 to 50.0 wt %.

[0053] CNC is obtained by further finely disaggregating hydrolyzed cellulose, which is purified by acid hydrolysis in a dispersed state in a strong acid solution, filtered from the strong acid solution, washed, and then repeatedly filtered from the washings. Therefore, hydrolyzed cellulose purified by acid hydrolysis contains nano-sized spindle-shaped crystals at the smallest unit, mixed with particles of various sizes ranging from nanometers to millimeters. If the cellulose is in a wet state after filtration, it can be disaggregated to the same size as immediately after acid hydrolysis by dissolving it in water again. However, once dried, hydrogen bonding via the hydroxyl groups in the cellulose results in the formation of strong aggregates that are difficult to completely disaggregate. In this invention, CNC must be added to PLA melted at high temperatures, so it must be dried and added in a powder state from which the moisture has been thoroughly removed. When drying CNC, the hydrolyzed cellulose is further disaggregated, but if it is not completely disaggregated, secondary aggregation occurs during drying, resulting in a powder containing a fairly wide range of particles, from nanometers to millimeters. The PLA and CNC mixture of the present invention can be improved to have the properties required for general use depending on the intended use, and is a mixture that can be used for general purposes such as fibers, films / sheets, and molded products, so it is essential that the particle size of the CNC is controlled.

[0054] Therefore, the CNC used in the present invention is a powder product containing a mixture of nano- to micron-sized spindle-shaped cellulose crystal aggregates, with a maximum particle size of 60 μm or less as measured using a particle size distribution analyzer with 2-propanol as a dispersion solvent. The inventors conducted extensive research in light of the CNC manufacturing conditions described above and discovered that the maximum particle size can be used to estimate the particle size distribution of the CNC used, providing a basis for determining whether or not it can be used for a particular application. The PLA / CNC mixture of the present invention, using CNC selected using the criteria discovered by the inventors, can be used to produce products that can be improved to achieve the physical properties required for general use depending on the application.

[0055] The maximum particle size of the CNCs used in the present invention may be appropriately selected depending on the form of the product produced from the mixture, the intended use of the product, etc. For example, when fiberizing, the maximum particle size of the CNCs may be selected taking into account the fineness and diameter of the fibers to be produced, etc., with the maximum particle size of the CNCs being preferably 12 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. When forming films or sheets, the maximum particle size of the CNCs to be used may be selected taking into account the film thickness and transparency of the film or sheet to be produced, with the maximum particle size of the CNCs being preferably 12 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. When forming molded products, the maximum particle size of the CNCs to be used may be selected taking into account the molding method, intended use, required performance, etc., and may be, for example, 100 μm or less depending on the intended use, but the maximum particle size of the CNCs is preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less.

[0056] (3) Mixing of PLA and CNC In the present invention, a PLA / CNC mixture is prepared by dispersing and mixing CNC in PLA.

[0057] The PLA and CNC blending method of the present invention may be any known blending method. When blending fillers such as CNC with polymers that are melted and spun, film-cast, or molded using resin pellets such as polypropylene, nylon, PET, or PLA, the blending is typically performed using one of the following methods: "1. Blending the filler at any stage between the polymerization of the molten polymer and the pellet formation process" or "2. Melting and blending the molten polymer and filler using a kneader." The PLA and CNC blend of the present invention may be blended using either method. Of course, in addition to blending method 1, blending may also be performed using known methods, such as blending the polymerized PLA directly into a product manufacturing process such as spinning without pelletizing it, or blending during a thermal flow process prior to product manufacturing. Furthermore, blended pellets prepared by blending method 2 may be used as 100% blended pellets, or they may be used as master chips and mixed with 100% PLA pellets during product manufacturing to adjust the CNC blending ratio.

[0058] The kneader used for the mixing method in 2 is typically a known twin-screw extrusion kneader, and this kneader may also be used for the mixing in the present invention. When using this kneader, fillers such as CNC are mixed in either by mixing them simultaneously with PLA from a resin pump or by mixing them into molten PLA using a powder feeder from a separate block. Either method may be used for the mixing in the present invention. However, when mixing CNC at a high mixing ratio, it is preferable to mix the CNC using a powder feeder from a separate block, taking into consideration uniform dispersion and mixing of the CNC.

[0059] When mixing the PLA / CNC mixture of the present invention, the mixing temperature must be considered. The mixing temperature can be set appropriately, taking into account the melting point of PLA and the thermal decomposition temperature of CNC. However, if the mixing temperature is too high, the thermal decomposition of PLA will be accelerated, resulting in a decrease in molecular weight, which may lead to a decrease in product strength and insufficient improvement in physical properties. Furthermore, the CNC will also begin to thermally decompose, causing discoloration due to the Maillard reaction, resulting in a brown-colored mixture. This coloration persists even with bleaching or other color-changing treatments, resulting in poor design and a lack of versatility as a product. Careful temperature setting and other factors are required when mixing the PLA / CNC mixture of the present invention to prevent these phenomena from occurring.

[0060] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The performance of the PLA and CNC mixture in the examples was evaluated by the following method.

[0061] [1] Evaluation test and evaluation method (1) Crystallization rate Using the PLA and CNC kneaded pellets obtained in the examples and comparative examples, a PerkinElmer power-compensated double furnace DSC8500 differential scanning calorimeter (hereinafter referred to as DSC) was used to measure the temperature drop recrystallization peak temperature in the temperature range from 0°C to 210°C at a heating rate of 2°C / min, after which the temperature was held at 210°C for 10 minutes.

[0062] (2) Observation of the Crystallization State of PLA and CNC Mixtures The PLA and CNC mixed pellets obtained in the Examples and Comparative Examples were used to form films, as light sources would not pass through them as they were. The crystallization state was observed using a polarizing microscope BX51 manufactured by Olympus Corporation. The films were then stretched uniaxially three times using a biaxial film stretching machine IMC-1AA6 manufactured by Imoto Manufacturing Co., Ltd., and the changes in the crystallization state during stretching were observed. Furthermore, the crystallization state of the multifilaments manufactured from the PLA and CNC mixtures in the Examples and Comparative Examples was also observed.

[0063] (3) Physical Properties of Products Made from PLA and CNC Blends (3)-1 Physical Properties of Multifilaments (3)-1-1 Tensile Strength and Elongation Using the multifilaments of the Examples and Comparative Examples made from the PLA and CNC blended pellets obtained in the Examples and Comparative Examples, the apparent fineness was measured using the correct fineness method B in accordance with JIS L-1013, and then measured using a Shimadzu AG-10kNX Plus tensile tester by the constant rate of extension method. (3)-1-2 Apparent Young's Modulus Calculated from the values ​​measured in (3)-1-1 above. (3)-1-3 Tensile Strength and Elongation Using the multifilaments of the Examples and Comparative Examples made from the PLA and CNC blended pellets obtained in the Examples and Comparative Examples, the elongation modulus was measured using a Shimadzu AG-10kNX Plus tensile tester by the elongation modulus method A in accordance with JIS L-1013. (3)-2 Physical Properties of Stretched Films (3)-2-1 Tensile Strength and Elongation Measurements were carried out using the stretched films of the Examples and Comparative Examples produced using the PLA and CNC kneaded pellets obtained in the Examples and Comparative Examples, in accordance with JIS L-1096 tensile strength and elongation method A, using a tensile testing machine AG-10kNX plus manufactured by Shimadzu Corporation. (3)-3 Physical Properties of Injection-Molded Rectangular Test Pieces (3)-3-1 Flexural Modulus Measurements were carried out using the injection-molded rectangular test pieces of the Examples and Comparative Examples, in accordance with JIS K-7171 flexural test method A, using a precision universal testing machine Autograph AGS-kNX manufactured by Shimadzu Corporation, at a test speed of 2 mm / min.

[0064] (4) Heat resistance of products made from PLA and CNC mixtures (4)-1 Heat resistance of multifilaments Using the multifilaments of the examples and comparative examples made using the PLA and CNC kneaded pellets obtained in the examples and comparative examples, measurements were carried out using a thermomechanical analyzer TMA / SS7100 (hereinafter referred to as TMA) manufactured by Hitachi High-Tech Science Corporation, with a load of 50 mN applied to a multifilament sample of 20 mm in length, at a heating rate of 10°C / min, and in a measurement temperature range of 25°C to 150°C, and the temperature at which the fiber changes from relaxation shrinkage to elongation, the load-softening temperature, was calculated from the measurement graph. (4)-2 Heat resistance of stretched films Using the stretched films of the examples and comparative examples produced using the PLA and CNC kneaded pellets obtained in the examples and comparative examples, measurements were carried out using a thermomechanical analyzer TMA / SS7100 (hereinafter referred to as TMA) manufactured by Hitachi High-Tech Science Corporation, with a load of 10 mN applied to a stretched film sample of 20 mm in length, at a heating rate of 10°C / min, and in a measurement temperature range of 30°C to 140°C, and the temperature at which relaxation shrinkage changes to elongation, and the load-softening temperature, were calculated from the measurement graph. (4)-3 Heat resistance of rectangular injection-molded test pieces The rectangular injection-molded test pieces of the examples and comparative examples, which were produced using the PLA and CNC kneaded pellets obtained in the examples and comparative examples, were used to measure the deflection temperature under load in accordance with Method A of JIS K-7191-1, 2, using an HDT testing machine S6-MH manufactured by Toyo Seiki Seisaku-sho, Ltd., under the conditions of a bending pressure of 1.8 MPa applied to the test pieces and a heating rate of 120°C / hour.

[0065] Example 1: PLA was used as high-heat-resistant PLA pellets "Luminy L-105" manufactured by TotalEnergies Corbion (weight-average molecular weight (MW) of 99,248 as determined by gel permeation chromatography (GPC) analysis). CNC was used as cotton-derived CNC "AirCryst CC01S" manufactured by Filler Bank Co., Ltd. The maximum particle size of this grade measured by a particle size distribution analyzer was 8 μm. A twin-screw extruder HK25D-41 manufactured by Parker Corporation, equipped with a Micron Feeder TF-70-EC(L) manufactured by Aisin Nano Technologies Co., Ltd. in the third block, was used. Each melt block was set to a minimum temperature of 180°C and a maximum temperature of 240°C, and the CNC was added to the molten PLA to a mixing ratio of 0.5 wt% (wt%). After the molten mixed resin flowed for 10 minutes from the start of CNC addition, the extruded strand was cooled with water and cut with a pelletizer to obtain pellets of the PLA and CNC mixture. The obtained pellets were then recrystallized at 110°C for 8 hours using a resin dryer DP-63P manufactured by Yamato Scientific Co., Ltd., to obtain the pellets of Example 1.

[0066] Examples 2 to 5 Pellets of Examples 2 (0.01 wt%), 3 (0.2 wt%), 4 (1.0 wt%), and 5 (10.0 wt%) were obtained in the same manner as in Example 1, except that the CNC mixing ratio in Example 1 was changed to 0.01 wt%, 0.2 wt%, 1.0 wt%, and 10.0 wt%.

[0067] Example 6 Pellets of Example 6 were obtained in the same manner as in Example 1, except that the CNC used in Example 1 was changed to "AirCrystCC03L," a cotton-derived CNC manufactured by Filler Bank Co., Ltd., with a maximum particle size of 60 μm as measured by a particle size distribution analyzer, the weighing feeder used was changed to a twin screw feeder K-CL-SFS-KT20 manufactured by Coperion K-Tron, and the CNC mixing ratio was changed to 40.0 wt%.

[0068] Examples 7 to 9 Pellets of Examples 7 (30.0 wt%), 8 (50.0 wt%), and 9 (60.0 wt%) were obtained in the same manner as in Example 6, except that the CNC mixing ratio in Example 6 was changed to 30.0 wt%, 50.0 wt%, and 60.0 wt%.

[0069] Example 10 Pellets of Example 10 were obtained in the same manner as in Example 7, except that the PLA used in Example 6 was changed to high-heat-resistant PLA pellets "Luminy L-130" manufactured by Total Energies Corbion (MW of 144,387 by GPC analysis).

[0070] Example 11 Pellets of Example 11 were obtained in the same manner as in Example 6, except that the PLA used was changed to high heat-resistant grade PLA pellets "Luminy L-175" manufactured by Total Energies Corbion (Mw 175,000 according to the catalog).

[0071] Example 12 Pellets of Example 12 were obtained in the same manner as in Example 1, except that the PLA used in Example 1 was changed to PLA pellets "FY-601" manufactured by HighChem Co., Ltd. (Mw of 149,992 by GPC analysis).

[0072] Examples 13 to 15 Pellets of Examples 13 (0.7 wt%), 14 (1.0 wt%), and 15 (3.0 wt%) were obtained in the same manner as in Example 1, except that in Example 12, the CNC mixing ratio was changed to 0.7 wt%, 1.0 wt%, and 3.0 wt%.

[0073] Examples 16 and 17 Pellets of Examples 16 (30.0 wt%) and 17 (50.0 wt%) were obtained in the same manner as in Example 1, except that in Example 6, the PLA used was changed to PLA pellets "FY-601" manufactured by HighChem Co., Ltd., the CNC used was changed to cotton-derived CNC "AirCrystCC02M" manufactured by Filler Bank Co., Ltd., of a grade with a maximum particle size of 12 μm as measured by a particle size distribution analyzer, and the CNC mixing ratio was changed to 30.0 wt% and 50.0 wt%.

[0074] Comparative Example 1 Pellets of Comparative Example 1 were obtained in the same manner as in Example 1, except that CNC was not used.

[0075] Comparative Example 2 For comparison with Example 10, the high heat-resistant PLA pellets "Luminy L-130" (Mw of 144,387 by GPC analysis) manufactured by TotalEnergies Corbion, which were used in Example 10, were used as pellets in Comparative Example 2.

[0076] Comparative Example 3 As a comparative example with Example 11, the highly heat-resistant PLA pellets "Luminy L-175" (Mw 175,000 according to the catalog) manufactured by TotalEnergies Corbion, which were used in Example 11, were used as pellets in Comparative Example 3.

[0077] Comparative Example 4 Pellets of Comparative Example 4 were obtained in the same manner as in Example 12, except that CNC was not used.

[0078] Comparative Example 5 In Example 1, the amount of CNC added from the weighing feeder was adjusted so that the CNC mixing ratio was 0.008 wt%, and an attempt was made to produce pellets for Comparative Example 5 using the same method as in Example 1. However, it was confirmed that a constant amount could not be added from the feeder and the material was not kneaded uniformly. Furthermore, clumps of CNC that were thought to have aggregated during kneading were confirmed in the extruded strands, so pellet production was discontinued.

[0079] Comparative Example 6 In Examples 16 and 17, the amount of CNC added from the weighing feeder was adjusted so that the CNC mixing ratio was 65.0 wt%, and an attempt was made to produce pellets for Comparative Example 6 using the same method as in Example 6. However, the extruded strands aggregated to form strands with many CNCs floating on the surface, so pellet production was discontinued.

[0080] Example 18: Using a resin dryer DP-63P manufactured by Yamato Scientific Co., Ltd., residual moisture was removed from the pellets previously prepared in Example 1 by vacuum drying at 90°C for 12 hours. Using a melt-spun multifilament production device manufactured by Musashino Kikai Co., Ltd. equipped with a 24-hole nozzle, the extruder cylinder temperature, head and pump section temperature, and nozzle temperature were set one by one with a minimum temperature of 180°C and a maximum temperature of 240°C. The above vacuum-dried pellets prepared in Example 1 were then introduced, and spinning was carried out while maintaining a constant screw rotation speed in the extruder and a constant amount of resin supplied. Next, the yarn spun from the nozzle was cooled by air cooling, and then a 15% aqueous solution of Delion PLA-1001, a spinning oil for PLA manufactured by Takemoto Yushi Co., Ltd., was applied to it, and the yarn was wound around a Nelson roller. After observing the condition of the yarn, the yarn was wound around a preheating roller and a stretching roller adjusted to 70 to 90°C and hot-stretched at a draw ratio of 4. After observing the condition of the yarn, the yarn was wound around a heat-setting roller adjusted to 110 to 130°C to heat-set it, and then wound on a winding machine to obtain the multifilament of Example 18.

[0081] Example 19 A multifilament of Example 19 was obtained in the same manner as in Example 18, except that the heat draw ratio was changed to 4.5 times.

[0082] Comparative Example 7 A multifilament of Comparative Example 7 was obtained in the same manner as in Example 18, except that the pellets produced in Comparative Example 1 were used.

[0083] Comparative Example 8 An attempt was made to obtain a multifilament of Comparative Example 8 by the same method as in Comparative Example 7, except that the heat draw ratio was changed to 4.5 times. However, frequent yarn breakage occurred at the drawing rollers, heat setting rollers, and winding device, and it was not possible to obtain a multifilament, so the production was discontinued.

[0084] Example 20: Using a resin dryer DP-63P manufactured by Yamato Scientific Co., Ltd., residual moisture was removed from the pellets previously prepared in Example 1 by drying at 90°C for 12 hours. Using a T-die film / sheet molding machine GT-20-A manufactured by Plastics Engineering Research Institute Co., Ltd. equipped with a T-die set to a die width of 150 mm and a clearance of 750 μm, the minimum temperature was set to 170°C and the maximum temperature to 190°C for each melt block, and then the dried pellets prepared in Example 1 were added. An unstretched film of this example having a film thickness of 240 to 260 μm was obtained at a resin discharge speed of 0.3 m / min and a film take-up speed of 1 m / min. Next, the unstretched film obtained above was stretched using a film biaxial stretching machine IMC-1AA6 manufactured by Imoto Machinery Co., Ltd., with the preheating temperature adjusted to 70-90°C based on the state of the film. The film was stretched at a stretching speed of 120 mm / min, with the stretch ratio set to 3.5 times in the film casting direction and 1.5 times in the film width direction, for a total stretch ratio of 5.25 times, to obtain the stretched film of Example 20.

[0085] Examples 21 to 24 Stretched films of Examples 21 (0.01 wt%), 22 (0.2 wt%), 23 (1.0 wt%), and 24 (10.0 wt%) were obtained in the same manner as in Example 20, except that the pellets used in Example 20 were changed to the pellets of Examples 2 to 5.

[0086] Comparative Example 9 A stretched film of Comparative Example 9 was obtained in the same manner as in Example 20, except that the pellets produced in Comparative Example 1 were used.

[0087] Example 25: Using a resin dryer DP-63P manufactured by Yamato Scientific Co., Ltd., residual moisture was removed from the pellets previously prepared in Example 10 by drying at 90°C for 12 hours. An injection molding machine SE18DUZ-C30 manufactured by Sumitomo Heavy Industries, Ltd., equipped with a mold for rectangular molded test pieces measuring 80 mm in length, 10 mm in width, and 4 mm in thickness, was used, and each melt block was set at a minimum temperature of 180°C and a maximum temperature of 230°C. After that, the injection conditions were changed to an injection pressure of 266 MPa and an injection rate of 101 cm. 3 / sec, theoretical injection volume; 11cm 3The molding was repeated under these conditions, the state of the test piece was checked, and injection molding was carried out after adjusting the conditions, to obtain a rectangular injection-molded test piece of Example 25.

[0088] Example 26 The rectangular injection-molded test piece prepared in Example 25 was annealed at 90°C for 3 minutes using a resin dryer DP-63P manufactured by Yamato Scientific Co., Ltd., to obtain the rectangular injection-molded test piece of Example 26.

[0089] Example 27: A rectangular injection-molded test piece of this example was obtained in the same manner as in Example 25, except that the pellets used in Example 25 were changed to those of Example 11. Next, an annealing treatment was carried out in the same manner as in Example 26, and a rectangular injection-molded test piece of Example 27 was obtained.

[0090] Comparative Example 10 A rectangular injection-molded test piece for Comparative Example 10 was obtained in the same manner as in Example 25, except that the pellets produced in Comparative Example 2 were used.

[0091] Comparative Example 11 A rectangular injection-molded test piece for Comparative Example 11 was obtained in the same manner as in Example 26, except that the rectangular injection-molded test piece produced in Comparative Example 10 was used.

[0092] Comparative Example 12 A rectangular injection-molded test piece for Comparative Example 12 was obtained in the same manner as in Example 27, except that the pellets produced in Comparative Example 3 were used.

[0093] (1) Crystallization Rate Table 1 shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the obtained PLA and CNC kneaded pellets of Examples 1 to 5 and the PLA pellet of Comparative Example 1.

[0094]

[0095] As is clear from Table 1, the PLA and CNC mixed pellets of Examples 1 to 5 according to the present invention all have a temperature-reducing recrystallization peak temperature that is shifted to the higher temperature side compared to the PLA pellets without CNC of Comparative Example 1. This shows that the crystallization rate is accelerated by the CNC.

[0096] The measurement chart of Example 1 using the DSC meter is shown in FIG. 1, and the measurement chart of Comparative Example 1 is shown in FIG.

[0097] Comparing the behavior of the temperature-reducing recrystallization in Figures 1 and 2, the peak areas in both Figures 1 and 2 are almost the same, but the rise is sharper and the time from the recrystallization start temperature to the end temperature is shorter in Figure 1. It is clear that the crystallization rate is accelerated and crystallization is completed in a short time, so it is clear that many small crystals are formed in Example 1 according to the present invention compared to Comparative Example 1, and that the mixed CNCs act as nuclei to form crystals.

[0098] Furthermore, the cooling rate was changed from 1° C. / min to 2° C. / min, and the cooling recrystallization peak temperatures of Example 1 and Comparative Example 1 measured with a DSC meter are shown in Table 2.

[0099]

[0100] As is clear from Table 2, the PLA and CNC blended pellets of Example 1 according to the present invention exhibit less variation in the peak recrystallization temperature due to changes in the cooling rate compared to the PLA pellets of Comparative Example 1 that do not contain CNC. This indicates that the crystallization rate of PLA is accelerated by the action of CNC. It is clear that the crystallization rate of PLA and CNC blends is accelerated according to the present invention, regardless of the applied thermal behavior.

[0101] Table 3 shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the PLA and CNC kneaded pellets obtained in Examples 6 to 9 and the PLA pellets in Comparative Example 1.

[0102]

[0103] As is clear from Table 3, the PLA and CNC mixed pellets of Examples 6, 7, 8, and 9 according to the present invention all have a temperature-reducing recrystallization peak temperature that is shifted to the higher temperature side compared to the PLA pellets of Comparative Example 1 that do not contain CNC. It can be seen that the crystallization rate is also accelerated in PLA and CNC mixed pellets with a high CNC mixing rate. It is clear that the crystallization rate of PLA is accelerated according to the present invention, regardless of the CNC mixing rate.

[0104] Table 4 shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the obtained PLA and CNC kneaded pellets of Example 10 and the PLA pellets of Comparative Example 2.

[0105]

[0106] Table 5 also shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the obtained PLA and CNC kneaded pellets of Example 11 and the PLA pellets of Comparative Example 3.

[0107]

[0108] Next, the measurement chart of Example 10 using the DSC meter is shown in FIG. 3, the measurement chart of Comparative Example 2 in FIG. 4, the measurement chart of Example 11 in FIG. 5, and the measurement chart of Comparative Example 3 in FIG.

[0109] As is clear from Tables 1, 4, and 5, the PLA and CNC blended pellets of the present invention have a higher temperature-recrystallization peak temperature than the PLA pellets of the comparative example that do not contain CNC. This shows that the crystallization rate is accelerated by CNC even when the molecular weight of the PLA resin used changes. It is clear that the crystallization rate of the PLA used is accelerated regardless of the molecular weight of the PLA used according to the present invention.

[0110] Comparing the temperature-reducing recrystallization behavior in Figures 3 and 4, and Figures 5 and 6, crystallization is so slow that a peak can barely be seen in Figure 4 and the rise of the peak cannot be seen in Figure 6, whereas the rise of the peak appears sharper in Figures 3 and 5, and the time from the start temperature to the end temperature of recrystallization is short. It is clear that the crystallization rate is accelerated and crystallization is completed in a short time, so it is clear that many small crystals are formed in Example 10 according to the present invention compared to Comparative Example 2, and in Example 11 according to the present invention compared to Comparative Example 3, indicating that the mixed CNCs act as nuclei to form crystals.

[0111] Table 6 shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the obtained PLA and CNC kneaded pellets of Examples 12, 15, and 16 and the PLA pellet of Comparative Example 4.

[0112]

[0113] Table 7 shows the temperature-reducing recrystallization peak temperatures measured with a DSC meter for the PLA and CNC kneaded pellets obtained in Examples 16 and 17 and the PLA pellets in Comparative Example 4.

[0114]

[0115] As is clear from Tables 6 and 7, the PLA and CNC blended pellets of the present invention have a higher temperature-reducing peak recrystallization temperature than the PLA pellets of the comparative example without CNC. It can be seen that the crystallization rate is accelerated by CNC regardless of the manufacturer of the PLA resin used or the CNC blend ratio. It is clear that the crystallization rate of the PLA used is accelerated regardless of the manufacturer of the PLA used.

[0116] (2) Observation of the Crystallization State of the PLA and CNC Mixture The obtained PLA and CNC mixed pellets of Examples 13 and 15 and the PLA pellet of Comparative Example 4 were made into thin films so that they could be observed under a polarizing microscope, and the crystallization state of the PLA was observed under a polarizing microscope. Phase contrast observation and differential interference observation were also performed.

[0117] Figure 7 shows a photograph of Example 13 observed under a polarizing microscope at 5x magnification, Figure 8 shows a photograph of Example 13 observed under a polarizing microscope at 40x magnification, Figure 9 shows a photograph of Example 15 observed under a polarizing microscope at 5x magnification, Figure 10 shows a photograph of Example 15 observed under a polarizing microscope at 40x magnification, Figure 11 shows a photograph of Comparative Example 4 observed under a polarizing microscope at 5x magnification, and Figure 12 shows a photograph of Comparative Example 4 observed under a polarizing microscope at 40x magnification.

[0118] As is clear from comparing Figures 7 and 9 with Figure 11, and Figures 8, 10 with Figure 12, the photographs of the examples according to the present invention show shadows that are presumably Maltese cross-shaped PLA spherulites, which are not visible in the comparative examples. The shadows become more clearly visible when the magnification is increased.

[0119] Phase contrast observation and differential interference observation were carried out to confirm that the irregularities or distortions observed in the photographs were not caused by the production of the film.

[0120] Figure 13 shows a photograph of Example 13 observed under phase contrast at 40x magnification, Figure 14 shows a photograph of Example 13 observed under differential interference contrast at 40x magnification, Figure 15 shows a photograph of Example 15 observed under phase contrast at 40x magnification, Figure 16 shows a photograph of Example 15 observed under differential interference contrast at 40x magnification, Figure 17 shows a photograph of Comparative Example 4 observed under phase contrast at 40x magnification, and Figure 18 shows a photograph of Comparative Example 4 observed under differential interference contrast at 40x magnification.

[0121] 13 and 15 with Fig. 17, and Fig. 14, 16 with Fig. 18, respectively, the photographs of the examples according to the present invention show shadows that are presumed to be Maltese-cross shaped PLA spherulites, which are not visible in the comparative examples. As with the polarizing microscope photographs described above, shadows that are presumed to be Maltese-cross shaped PLA spherulites can be seen in the images, and mixing CNC results in a structure in which crystallized PLA is present throughout.

[0122] The PLA and CNC kneaded pellets of Examples 13 and 15 and the PLA pellets of Comparative Example 4 were formed into thin films so that they could be observed under a polarizing microscope, and the films were uniaxially stretched and observed under a polarizing microscope.

[0123] FIG. 19 shows a polarizing microscope photograph of the stretched film of Example 13, FIG. 20 shows a polarizing microscope photograph of the stretched film of Example 15, and FIG. 21 shows a polarizing microscope photograph of the stretched film of Comparative Example 4.

[0124] As is clear from comparing Figures 19 and 20 with Figure 21, the photographs of the examples of the present invention, like the unstretched film, show overlapping shadows that are presumed to be Maltese-cross spherulites of PLA, which are rare in the comparative examples. Also, in Figures 19 and 20, vertical and horizontal streaky shadows that are presumed to be shish-kebab-shaped oriented crystals caused by stretching can be seen in the images. Comparing Figures 19 and 20, it can be seen that as the CNC mixing ratio increases, these streaky shadows become finer and denser.

[0125] As with the unstretched film, phase contrast observation and differential interference observation were carried out to confirm that the irregularities observed in the photograph were not due to unevenness during film production or distortion during stretching.

[0126] FIG. 22 shows a photograph of the retardation observation of the stretched film of Example 13, FIG. 23 shows a photograph of the retardation observation of the stretched film of Example 15, and FIG. 24 shows a photograph of the retardation observation of the stretched film of Comparative Example 4.

[0127] In addition, Figure 25 shows a differential interference observation photograph of the stretched film of Example 13, Figure 26 shows a differential interference observation photograph of the stretched film of Example 15, and Figure 27 shows a differential interference observation photograph of the stretched film of Comparative Example 4.

[0128] 22 and 23 with Figure 24, and Figures 25, 26 and 27, respectively, the photographs of the examples according to the present invention show shadows that are presumed to be Maltese-cross shaped PLA spherulites, which are not visible in the comparative examples. As with observations using a polarizing microscope, the images show vertical and horizontal striped shadows that are thought to be oriented crystals created by stretching, which indicates that mixing CNC results in a structure in which crystallized PLA is present throughout.

[0129] Next, we actually observed the crystallization state of the product made from the PLA and CNC mixture. First, we demonstrated the polarized microscope observation of the product made from the mixture pellets made by kneading and then forming a film.

[0130] The crystallization state of the PLA was observed using a polarizing microscope for the stretched films produced from the PLA and CNC kneaded pellets obtained in Examples 20 to 22 and the stretched film produced from the PLA pellets in Comparative Example 9. To confirm whether what was visible in the photographs was distortion or unevenness caused by stretching, observation was performed using crossed Nicols (dark field observation) and open Nicols (bright field observation).

[0131] Figure 28 shows a photograph of the stretched film of Example 20 observed under a polarizing microscope with crossed Nicols, Figure 29 shows a photograph of the stretched film of Example 20 observed under a polarizing microscope with open Nicols, Figure 30 shows a photograph of the stretched film of Example 21 observed under a polarizing microscope with crossed Nicols, Figure 31 shows a photograph of the stretched film of Example 21 observed under a polarizing microscope with open Nicols, Figure 32 shows a photograph of the stretched film of Example 22 observed under a polarizing microscope with crossed Nicols, Figure 33 shows a photograph of the stretched film of Example 22 observed under a polarizing microscope with open Nicols, Figure 34 shows a photograph of the stretched film of Comparative Example 9 observed under a polarizing microscope with crossed Nicols, and Figure 35 shows a photograph of the stretched film of Comparative Example 9 observed under a polarizing microscope with open Nicols.

[0132] As is clear from comparing Figures 28, 30, and 32 with Figure 34, and Figures 29, 31, 33, and 35, respectively, the photographs of the examples according to the present invention show shadows presumably representing Maltese-cross-shaped PLA spherulites, which are not visible in the comparative examples. It is speculated that the incorporation of CNC promotes PLA crystallization. In Figure 30, shadows presumably resulting from CNC crystallization can be seen in the image. Combined with the results of the DSC measurement of the peak recrystallization temperature during cooling, it is speculated that crystallization is promoted at a CNC content of 0.01 wt%. Furthermore, comparing Figures 28, 30, and 32, the shadows presumably representing Maltese-cross-shaped PLA spherulites appear to overlap as the CNC content increases, suggesting that the promotion of PLA crystallization is due to CNC.

[0133] Furthermore, to observe the crystallization state of products made from PLA and CNC mixtures, the crystallization state of the PLA was observed by polarizing microscope for the multifilament produced from the PLA and CNC kneaded pellets of Example 18 with a draw ratio of 4, the multifilament produced from the PLA and CNC kneaded pellets of Example 19 with a draw ratio of 4.5, and the multifilament produced from the PLA pellets of Comparative Example 7 with a draw ratio of 4. As is clear from Comparative Example 8, it was not possible to obtain a multifilament drawn 4.5 times from PLA pellets not mixed with CNC, but it was possible to obtain a multifilament drawn 4.5 times from the PLA and CNC kneaded pellets mixed with CNC. This suggests that multifilaments with a high draw ratio could be obtained due to the crystalline network structure formed by the CNC acting as a crystal nucleus. This was verified by observing the crystallization state using a polarizing microscope.

[0134] Figure 36 shows a photograph of the multifilament of Example 18 drawn at a draw ratio of 4 times, observed under a polarizing microscope with crossed Nicols. Figure 37 shows a photograph of the multifilament of Example 19 drawn at a draw ratio of 4.5 times, observed under a polarizing microscope with crossed Nicols. Figure 38 shows a photograph of the multifilament of Comparative Example 7 drawn at a draw ratio of 4 times, observed under a polarizing microscope with crossed Nicols.

[0135] As is clear from comparing Figures 36 and 38, the photographs of the Example of the present invention show more clearly the vertical and horizontal streaks, which are thought to be shish kebab-like oriented crystals, confirming that the Example is more crystallized than the Comparative Example. Both Figures 36 and 38 confirm oriented crystallization due to drawing, confirming that the crystalline network structure formed by CNCs as crystal nuclei does not inhibit oriented crystallization of the fiber but promotes the crystallization of the fiber itself. Furthermore, comparing Figures 36 and 37, crystallization is more promoted in Figure 37 than in Figure 36, and the fiber appears to have a dense crystalline structure covered with crystals. Because the crystalline network structure of the mixed CNCs further promotes crystallization, we believe that a higher draw ratio can be achieved than in multifilaments made from PLA pellets without mixed CNCs, resulting in the production of multifilaments with higher strength.

[0136] (3) Physical properties of products made from PLA and CNC mixtures (3)-1 Physical properties of multifilaments The physical properties of the multifilaments made from the PLA and CNC kneaded pellets of Examples 18 and 19 and the physical properties of the multifilament made from the PLA pellets of Comparative Example 7 are shown in Table 8.

[0137]

[0138] As is clear from Table 8, the multifilament produced from the PLA and CNC kneaded pellets of Example 18 according to the present invention has improved tensile strength compared to the multifilament produced from the PLA pellets not mixed with CNC of Comparative Example 7. Furthermore, multifilament Example 19, which was not able to be produced in Comparative Example 8 with a draw ratio of 4.5 times, shows a further improvement in strength.

[0139] Comparing the elongation rates of Examples 18 and 19 with those of Comparative Example 7, the results for the Examples are lower. This is thought to be because, in addition to oriented crystallization due to stretching, many fine crystals are formed with CNC as the crystal nucleus in the Examples, and the crystalline network structure formed by the tie molecules connecting these crystals affects the elongation of the filament.

[0140] However, since the apparent Young's modulus and elongation modulus of elasticity of Examples 18 and 19 are improved compared to Comparative Example 7, it is clear that the toughness is improved and the toughness is higher than that of Comparative Example 7.

[0141] (3)-2 Physical Properties of Stretched Films The physical properties of the stretched films produced from the PLA and CNC kneaded pellets of Examples 20 to 24 and the physical properties of the multifilament produced from the PLA pellets of Comparative Example 9 are shown in Table 9.

[0142]

[0143] As is clear from Table 9, the stretched films produced from the PLA and CNC blended pellets of Examples 20-24 according to the present invention all have improved tensile strength compared to the stretched film produced from the PLA pellets without CNC blends of Comparative Example 9. As with the multifilaments of Examples 18 and 19, the addition of CNC to the stretched film promotes PLA crystallization, thereby improving strength. Since the tensile strength is improved even at 0.01 wt% in Example 21, it is believed that concerns about film opacity due to the addition of CNC can be resolved by adjusting the CNC blending ratio. The PLA and CNC blends of the present invention are highly versatile blends that can modify physical properties depending on the intended use.

[0144] Comparing the elongation rates of Examples 20 to 24 and Comparative Example 9, the results for the Examples are lower. This is thought to be because the Examples contain many fine crystals with CNC as the crystal nucleus, and the crystalline network structure formed by the tie molecules connecting these crystals affects the elongation of the film.

[0145] (3)-3 Physical Properties of Injection-Molded Strip Test Pieces The physical properties of the injection-molded strip test pieces made from the PLA and CNC kneaded pellets of Examples 25, 26, and 27, and the physical properties of the injection-molded strip test pieces made from the PLA pellets of Comparative Examples 10, 11, and 12 are shown in Table 10.

[0146]

[0147] As is clear from Table 10, the rectangular injection-molded test piece made from the PLA and CNC kneaded pellets of Example 25 according to the present invention has an improved flexural modulus compared to the rectangular injection-molded test piece made from PLA pellets not mixed with CNC of Comparative Example 10. Improvements in flexural modulus were also observed between Example 26 and Comparative Example 11, and between Example 27 and Comparative Example 12, with the examples according to the present invention showing an improvement of about 1.5 times that of the comparative examples. It can be seen that even molded products cured with a high CNC mixing ratio have improved toughness, resulting in high toughness.

[0148] (4) Heat resistance of products made from PLA and CNC mixtures (4)-1 Heat resistance of multifilaments Figure 39 shows a measurement chart of the multifilament made from the PLA and CNC mixed pellets of Example 19, measured with a TMA device, and a measurement chart of the multifilament made from the PLA pellets of Comparative Example 7, measured with a TMA device.

[0149] As is clear from Figure 39, the thermal behavior of the multifilament produced from the PLA and CNC blended pellets of Example 19 according to the present invention is higher than the thermal behavior of the multifilament produced from the PLA pellets not mixed with CNC of Comparative Example 7. Both the multifilaments of Example 19 and Comparative Example 7 shrink with a force stronger than the load applied to the filament due to entropy relaxation of the strained molecular chains when stretched by drawing. Then, the crystals begin to melt due to the continued heat applied beyond the glass transition point, and they begin to stretch when they soften to the point where they cannot withstand the constant load. When the onset temperatures of this behavior were confirmed using TMA measurement data, Comparative Example 7 had a shrinkage onset temperature of 26.4°C and an elongation onset temperature (softening temperature under load) of 85.5°C, while Example 19 had a shrinkage onset temperature of 53.5°C and an elongation onset temperature (softening temperature under load) of 97.8°C, both of which were higher by 10°C or more. The physical property results for Example 19 confirmed that crystallization was promoted by CNC, and the difference in physical properties between Example 19 and Comparative Example 7 is thought to be due to the promotion of crystallization by CNC. Therefore, it can be seen that the temperature difference confirmed by TMA measurement is also due to the number of PLA crystals formed using CNC as a crystal nucleus in Example 19 and the crystalline network structure of tie molecules.

[0150] (4)-2 Heat resistance of stretched film Figure 40 shows a measurement chart of the stretched film produced from the PLA and CNC kneaded pellets of Example 20, measured with a TMA device, and a measurement chart of the stretched film produced from the PLA pellets of Comparative Example 9, measured with a TMA device.

[0151] As is clear from Figure 40, the thermal behavior of the stretched film produced from the PLA and CNC kneaded pellets of Example 20 according to the present invention slides to the higher temperature side compared to the thermal behavior of the stretched film produced from the PLA pellets not mixed with CNC of Comparative Example 9. As with the thermal behavior of the multifilaments of Example 19 and Comparative Example 7, it can be seen that the elongation start temperature (load-softening temperature) of Comparative Example 9 is 70.2 ° C, and the elongation start temperature (load-softening temperature) of Example 20 is 71.5 ° C, which is 1.3 ° C higher. As with the multifilaments of Example 19 and Comparative Example 7, it can be seen that the heat resistance is improved by the number of PLA crystals formed using CNC as a crystal nucleus and the crystalline network structure of tie molecules.

[0152] (4)-3 Heat resistance of rectangular injection-molded test pieces The results of measuring the deflection temperature under load of rectangular injection-molded test pieces made from the PLA and CNC kneaded pellets of Examples 25, 26, and 27, and the results of measuring the deflection temperature under load of rectangular injection-molded test pieces made from the PLA pellets of Comparative Examples 10, 11, and 12 are shown in Table 11.

[0153]

[0154] As is clear from Table 11, the rectangular injection-molded test piece produced from the PLA and CNC mixed pellets of Example 25 according to the present invention has a higher deflection temperature under load than the rectangular injection-molded test piece produced from the PLA pellets not mixed with CNC of Comparative Example 10. The deflection temperature under load is higher in both Example 26 and Comparative Example 11, and Example 27 and Comparative Example 12, and it is clear that the examples according to the present invention have improved heat resistance compared to the comparative examples.

[0155] The PLA / CNC mixture of the present invention is a versatile biodegradable material that can reduce environmental impact while maintaining biodegradability and can have its physical properties improved depending on the intended use.

[0156] The present invention can be widely used in the chemical industry, such as the textile industry, film and sheet industry, and plastic molding industry.

Claims

1. A polylactic acid / cellulose nanocrystal mixture in which only chemically unmodified cellulose nanocrystals are uniformly dispersed in polylactic acid, and the amount of cellulose nanocrystals uniformly dispersed in the polylactic acid is 0.01 to 60.0% by weight of the total weight of the mixture.

2. The polylactic acid / cellulose nanocrystal mixture described in claim 1, characterized in that the cellulose nanocrystals uniformly dispersed in the polylactic acid are cellulose nanocrystals that have never been chemically modified and are produced by hydrolysis with hydrochloric acid, and have a crystallinity of 90% or more.

3. A polylactic acid and cellulose nanocrystal mixture as described in claim 1 or claim 2, characterized in that the crystal nucleation effect of the cellulose nanocrystals uniformly dispersed in the polylactic acid improves the crystallinity and crystallization rate of the polylactic acid, and forms a crystalline network structure due to the formation of tie molecules spanning multiple crystals.

4. A polylactic acid and cellulose nanocrystal mixture described in either one of claims 1 or 2, characterized in that the maximum particle size of the cellulose nanocrystals uniformly dispersed in the polylactic acid is 60 μm or less when measured by particle size distribution using 2-propanol as the dispersion solvent.

5. A polylactic acid / cellulose nanocrystal mixture described in either one of claims 1 or 2, characterized in that the improved physical properties of the polylactic acid / cellulose nanocrystal mixture are heat resistance and / or toughness.

6. A polylactic acid and cellulose nanocrystal mixture described in either one of claims 1 or 2, characterized in that the physical property of the polylactic acid and cellulose nanocrystal mixture that is improved is one of strength, elongation, and elastic modulus.

7. A polylactic acid / cellulose nanocrystal mixture according to any one of claims 1 or 2, characterized in that the polylactic acid / cellulose nanocrystal mixture is used for fibers.

8. A polylactic acid / cellulose nanocrystal mixture according to any one of claims 1 or 2, characterized in that the polylactic acid / cellulose nanocrystal mixture is used as a film or sheet.

9. A polylactic acid and cellulose nanocrystal mixture according to any one of claims 1 and 2, characterized in that the polylactic acid and cellulose nanocrystal mixture is used as a molded product formed by any of injection molding, extrusion molding, blow molding, and press molding.

10. A method for producing a polylactic acid / cellulose nanocrystal mixture, comprising the step of adding non-chemically modified cellulose nanocrystals to polylactic acid and mixing them, wherein the amount of cellulose nanocrystals added to the polylactic acid is 0.01 to 60.0% by weight of the total weight of the mixture produced.

11. A method for producing a polylactic acid / cellulose nanocrystal mixture as described in claim 10, characterized in that the cellulose nanocrystals added to the polylactic acid are cellulose nanocrystals that have never been chemically modified and are produced by hydrolyzing cellulose raw materials with hydrochloric acid.

12. A method for producing a polylactic acid and cellulose nanocrystal mixture as described in claim 10 or 11, in which the crystal nucleation effect of the cellulose nanocrystals added to the polylactic acid improves the crystallinity and crystallization rate of the polylactic acid, and improves physical properties by forming a crystalline network structure through the formation of tie molecules spanning multiple crystals.

13. A method for producing a polylactic acid and cellulose nanocrystal mixture as described in claim 10 or 11, characterized in that the maximum particle size of the cellulose nanocrystals added to the polylactic acid is 60 μm or less when measured by particle size distribution using 2-propanol as the dispersion solvent.

14. A method for producing a mixture of polylactic acid and cellulose nanocrystals as described in claim 10 or 11, characterized in that the physical properties improved by the method for producing a mixture of polylactic acid and cellulose nanocrystals are heat resistance and / or toughness.

15. A method for producing a polylactic acid and cellulose nanocrystal mixture as described in claim 10 or 11, characterized in that the physical property improved by the method for producing a polylactic acid and cellulose nanocrystal mixture is one of strength, elongation, and elastic modulus.

16. A method for producing a mixture of polylactic acid and cellulose nanocrystals according to claim 10 or 11, characterized in that the method for adding cellulose nanocrystals to polylactic acid satisfies the following requirement (1), and the cellulose nanocrystals are uniformly dispersed within the polylactic acid: (1) A method in which the cellulose nanocrystals are added in an amount of 0.01 to 60.0% by weight of the total weight of the mixture to be produced during any step from polymerization of polylactic acid to pellet formation.

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