Biodegradable resin composition, fiber thereof, and nonwoven fabric

Abstract

To provide a fiber with significantly enhanced biodegradability of polylactic acid and a resin composition used as a material thereof.SOLUTION: A resin composition comprises polylactic acid (component A), a copolyester of lactic acid and hydroxycarboxylic acid (component B), and polyhydroxyalkanoate (component C), wherein the lactic acid monomer fraction in the copolymer of the component B is 9 mol% or more and 44 mol% or less. Also provided are a fiber and / or nonwoven fabric composed of the resin composition, as well as products comprising these.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biodegradable resin composition obtained by modifying the biodegradability of polylactic acid (hereinafter also referred to as PLA), as well as fibers and nonwoven fabrics thereof. [Background technology]

[0002] In recent years, various biomass-based resins based on polylactic acid have been proposed, and spunbond nonwoven fabrics produced by melt-spinning these resins into fibers are now widely available. However, at present, polylactic acid is not biodegradable at room temperature, and because of its high glass transition temperature (Tg around 60°C), it is necessary to use industrial composting facilities that operate at high temperatures of 60°C or higher. Therefore, various studies are being conducted to make polylactic acid biodegradable in environments around room temperature.

[0003] Patent Document 1 below discloses a method for modifying polylactic acid by blending polylactic acid with a random copolymer polyester (hereinafter referred to as multi-component polylactic acid or multi-component PLA) of polylactic acid and polyhydroxyalkanoate (hereinafter referred to as PHA). The purpose of this method is to provide a polylactic acid resin-containing resin composition that is plasticized and softened without impairing the biodegradability of polylactic acid by blending the multi-component polylactic acid with polylactic acid. Furthermore, Patent Document 2 below proposes blending polyhydroxyalkanoate, which has higher biodegradability than polylactic acid, in order to improve the biodegradability of polylactic acid. Furthermore, Patent Document 3 below provides a resin composition and a molded article thereof that are heat-resistant and impact-resistant and have a high biomass content, which are obtained by blending polylactic acid with polyhydroxyalkanoate and a block copolymer of polylactic acid and polyhydroxyalkanoate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7383264 [Patent Document 2] International Publication No. 2019 / 122191 [Patent Document 3] Patent No. 5212183 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the resin composition of polylactic acid and multi-component polylactic acid described in Patent Document 1, the polylactic acid is plasticized and softened, so crystallization does not proceed during fiberization, causing shrinkage and making it difficult to obtain fibers. As mentioned above, Patent Document 2 proposes blending polyhydroxyalkanoate to improve the biodegradability of polylactic acid, but increasing the blending ratio of polyhydroxyalkanoate to enhance biodegradability causes the problem of shrinkage of the yarn during fiberization. On the other hand, increasing the blending ratio of polylactic acid to reduce shrinkage causes the problem of insufficient biodegradability. Furthermore, the blend of polylactic acid with polyhydroxyalkanoate and a block copolymer of polylactic acid and polyhydroxyalkanoate described in Patent Document 3 had the problem that the block copolymer of polylactic acid and polyhydroxyalkanoate was not biodegradable at room temperature because of the high glass transition temperature (Tg around 60°C) inherent to lactic acid polymers. Furthermore, such copolymers were chemically synthesized block copolymers, and required the use of organic solvents and harmful heavy metal catalysts, which posed problems from the perspective of green processes. In view of the above state of the art, the problem to be solved by the present invention is to provide a fiber of polylactic acid with significantly improved biodegradability, and a resin composition that is the raw material for the fiber. [Means for solving the problem]

[0006] In order to solve the above problems, the inventors of the present application conducted extensive research and experiments, and as a result, unexpectedly discovered that by blending polylactic acid with polyhydroxyalkanoate and a specific copolyester, fibers with significantly improved biodegradability of polylactic acid could be obtained, leading to the completion of the present invention.

[0007] That is, the present invention is as follows. [1] A resin composition comprising polylactic acid (component A), a copolymer polyester of lactic acid and a hydroxycarboxylic acid (component B), and a polyhydroxyalkanoate (component C), wherein the lactic acid monomer fraction in the copolymer of component B is 9 mol% or more and 44 mol% or less. [2] Fibers made from the resin composition described in [1] above. [3] A nonwoven fabric made from the resin composition described in [1] above. [4] A product containing the fiber described in [2] above. [5] A product comprising the nonwoven fabric described in [3] above. [Effects of the Invention]

[0008] The resin composition according to the present invention can be spun stably into fibers and has higher biodegradability than conventional PLA. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a photograph of the fiber of Example 1. [Figure 2] 1 is a photograph of the fibers of Example 2. [Figure 3] 1 is a photograph of the fibers of Example 3. [Figure 4] 1 is a photograph of the fiber of Comparative Example 1. [Figure 5] 1 is a photograph of the fiber of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the present invention will be described in detail based on an embodiment. One embodiment of the present invention is a resin composition comprising the following polylactic acid (component A), a copolymer polyester of lactic acid and a hydroxycarboxylic acid (component B), and a polyhydroxyalkanoate (component C), wherein the lactic acid monomer fraction in the copolymer of component B is 9 mol % or more and 44 mol % or less.

[0011] The polylactic acid component A may be a polymer selected from the group consisting of a polymer of D-lactic acid, a polymer of L-lactic acid, a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and a hydroxycarboxylic acid, a copolymer of L-lactic acid and a hydroxycarboxylic acid, and a copolymer of D-lactic acid, L-lactic acid, and a hydroxycarboxylic acid, or a blend of two or more of these polymers. The D / L ratio of the polylactic acid polymer can be set within a range that does not impair spinnability or nonwoven fabric properties. The D-isomer ratio of the total polylactic acid weight is preferably 0% to 15%; more preferably 0.1% to 10%; and even more preferably 0.1% to 6%. A D-isomer ratio within these ranges provides good spinnability, enabling stable production of nonwoven fabrics. Furthermore, the melting point, crystallinity, and other properties are within appropriate ranges, making it easy to obtain nonwoven fabrics with the desired properties. The copolymer polyester, component B, is a copolymer of lactic acid and another hydroxycarboxylic acid. In the present invention, the use of a random copolymer is preferred from the viewpoint of biodegradability. The lactic acid-derived monomer unit in the copolymer polyester may be either an L-lactic acid-derived monomer unit or a D-lactic acid-derived monomer unit, and is not particularly limited, but is generally a D-lactic acid-derived monomer unit.

[0012] The other hydroxycarboxylic acid is preferably a 3-hydroxyalkanoic acid, specifically 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxypentadecanoic acid, 3-hydroxyhexadecanoic acid, etc. These may be used alone or in combination of two or more. Of these, it is preferable to include 3-hydroxybutanoic acid as the other hydroxycarboxylic acid. As the copolymer polyester, P(LA-co-3HB), a copolymer polyester of lactic acid and 3-hydroxybutanoic acid, can be most preferably used.

[0013] The ratio of lactic acid to other hydroxyalkanoic acids constituting the copolymer polyester is not particularly limited. However, because of its high effect of softening PLA, the monomer fraction of lactic acid relative to the total moles of lactic acid and other hydroxyalkanoic acids constituting the copolymer polyester is preferably 9 mol% or more and 44 mol% or less. More preferably, it is 15 mol% or more and 40 mol% or less, and even more preferably, it is 20 mol% or more and 35 mol% or less. The value of the monomer fraction of lactic acid can be determined using HPLC.

[0014] There are no particular restrictions on the molecular weight of the copolymer polyester, but the weight average molecular weight may be, for example, from 1 to 1,000,000, and preferably from 1 to 500,000. The weight-average molecular weight was determined based on standard polystyrene using gel permeation chromatography (GPC) (Shimadzu Corporation) equipped with a tandem TSKgel Super HZM-H column (Tosoh Corporation).

[0015] The method for producing the copolymer polyester is not particularly limited and may be a conventionally known method. Among them, examples of the method for producing P(LA-co-3HB) include production methods using recombinant microorganisms such as those described in WO 2009 / 131186 and WO 2006 / 126796.

[0016] The polyhydroxyalkanoate, component C, is preferably a 3-hydroxyalkanoate copolymer (abbreviated as 3HA copolymer) produced by a microorganism using biomass as a raw material. The P3HA used in the present invention is a polymer containing 3-hydroxyalkanoic acid (3HA) as an essential monomer component. Among these, the P3HA is preferably a P3HA (aliphatic polyester) containing a repeating unit represented by formula (1): [-CHR-CH2-CO-O-] {wherein R is an alkyl group represented by CnH2n+1, and n is an integer of 1 to 15.}

[0017] As the 3HA, P3HA containing a 3-hydroxybutyrate unit is preferred. Examples of such PHA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), which are preferred because they can be easily produced industrially. Among these, P3HB, P3HB3HV, P3HB3HV3HH, P3HB3HH, and P3HB4HB are particularly preferred, with P3HB3HH being even more preferred. When P3HA is P3HA containing a 3-hydroxybutyrate unit structure, the average composition ratio of the repeating units (monomer structural units) is not particularly limited, but from the viewpoint of the balance between flexibility and strength, the composition percentage of poly(3-hydroxybutyrate) is preferably 80 mol % or more and 99 mol % or less, more preferably 85 mol % or more and 97 mol % or less.

[0018] P3HA can be produced by known methods. When P3HA is produced by a microorganism, the microorganism used to produce the P3HA is not particularly limited as long as it is a microorganism capable of producing P3HAs. For example, the first P3HB-producing bacterium was Bacillus megaterium, discovered in 1925. Other known natural microorganisms include Cupriavidus necator (formerly classified as Alcaligenes eutrophus or Ralstonia eutropha) and Alcaligenes latus, and these microorganisms accumulate P3HB intracellularly.

[0019] Known bacteria that produce copolymers containing hydroxybutyrate units and other hydroxyalkanoate units include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligeneseutrophus, which produces P3HB4HB. In particular, for P3HB3HH, Alcaligeneseutrophus AC32 (FERMBP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), which has been introduced with genes encoding P3HA synthases, is preferred for increasing P3HB3HH productivity. These microorganisms are cultured under appropriate conditions to accumulate P3HB3HH within the cells. In addition to the above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may be used depending on the PHA to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0020] Because microbial production is easy and the resin composition of the present invention has good moldability, heat resistance, and impact strength, the content of 3HB units in the PHA resin is preferably 70 mol% or more and 95 mol% or less. Furthermore, the weight-average molecular weight Mw of the PHA resin, calculated as a standard polystyrene equivalent by GPC analysis, is preferably 2 to 3,000,000, and more preferably 5 to 1,500,000. Within the above range, microbial production is possible, and there are no problems when fiberizing the resin composition of the present embodiment.

[0021] The resin composition of this embodiment may contain a thermoplastic resin other than polylactic acid, copolymer polyester, and PHA. Such resins are not particularly limited, and conventionally known resins can be used. Specific examples include biodegradable aliphatic polyesters and aromatic polyesters. The resin composition of the present invention may also contain other additives as appropriate, provided that the effects of the present invention are not impaired. Examples of such additives include, but are not limited to, plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, UV absorbers, processing aids, antistatic agents, colorants, crystal nucleating agents, inorganic or organic particles, lubricants, mold release agents, water repellents, inorganic fillers, mildew inhibitors, antibacterial agents, foaming agents, and flame retardants. The content of each additive can be determined appropriately depending on the purpose. Only one type of additive may be blended, or two or more types may be blended. As the plasticizer, any plasticizer generally used as a plasticizer for polymers can be used, and specific examples thereof include polyester-based plasticizers, glycerin-based plasticizers, polycarboxylic acid ester-based plasticizers, polyalkylene glycol-based plasticizers, and epoxy-based plasticizers.

[0022] Other embodiments of the present invention are fibers made from the resin composition, and nonwoven fabrics made from the resin composition. The biodegradable fiber of this embodiment can be obtained by melt-extruding a resin composition obtained by blending Components A, B, and C in the desired ratio in an extruder, discharging the extruded resin from a spinneret, and pulling the extruded resin with a pulling device. The cross-sectional shape of the fiber is not particularly limited, and may be circular, triangular, polygonal, flat, hollow, or the like.

[0023] The spinning temperature when melt-spinning the biodegradable fiber of the present invention is preferably 165°C or higher and 200°C or lower, and more preferably 175°C or higher and 195°C or lower. If the spinning temperature is lower than 165°C, the temperature is too low to achieve a stable molten state, resulting in variations in fiber diameter. If the spinning temperature exceeds 200°C, the fiber obtained by pyrolysis will be discolored and satisfactory spinnability will not be obtained.

[0024] The spinning speed when melt spinning the biodegradable fiber of this embodiment is preferably in the range of 100 m / min to 5500 m / min. If the spinning speed is less than 100 m / min, the filaments are not sufficiently drawn, and sufficient strength cannot be obtained. If the spinning speed exceeds 5500 m / min, thread breakage occurs during melt spinning, making it impossible to obtain a fiber.

[0025] Alternatively, the biodegradable resin may be extruded from multiple spinnerets and deposited on a collection device to form a web. The formed web may be bonded using a bonding means such as thermocompression bonding to obtain the nonwoven fabric of this embodiment. The means for joining the nonwoven fabric webs includes, but is not limited to, a heat pressing method using a calendar roll, a hot air blowing method, a needle punching method, and a hydroentanglement method. When a thermocompression bonding method is selected, it is preferable that the thermocompression bonding area ratio is 3% or more under heating at 80° C. or more and 160° C. or less, and the thermocompression bonding treatment can achieve good adhesion between the fibers. As a processing method, a heated plate can be used, but a method in which the web is passed between a pair of calender rolls for compression bonding is preferable because it has excellent productivity.

[0026] The calender roll may have a smooth surface or may have an engraved pattern (for example, a rectangular, pinpoint, woven, Y-pattern, dappled, herringbone, square, diamond ikat, or diagonal ikat pattern), or a combination of the same type of rollers or a combination of different types of rollers may be used. When an embossing roll with an engraved pattern is used, the compression area ratio is preferably 3% or more and 30% or less from the viewpoint of strength and flexibility. [Example]

[0027] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples.

[0028] 1. Evaluation of spinnability In the examples and comparative examples, the resin compositions were air-pulled using an ejector to thin them to a predetermined fineness (stretched filaments), and the spinnability (whether or not they could be made into a spunbond nonwoven fabric) was evaluated according to the following evaluation criteria. 〇 (Good spinnability): Can be pulled for 30 minutes without thread breakage at a spinning speed of 100 m / min or more × (poor spinnability): Yarn breakage occurs within 30 minutes at a spinning speed of 100 m / min or more, resulting in poor spinning.

[0029] 2.Biodegradability evaluation The biodegradability of the fibers was evaluated in accordance with ASTM D-7081. The biodegradation test of the fibers was carried out in environmental water (collected from a pond) at 25°C, and the biodegradability was calculated using the following formula: Biodegradability (%)=BOD×100 / ThOD where BOD is the amount of oxygen consumed in microbial decomposition, and ThOD is the amount of oxygen required to completely decompose an analyte into inorganic matter. It was calculated as follows.

[0030] <Sample 1> A polymer prepared by the method described in Patent Document 2 was used as a blend of polylactic acid and PHA. A copolymer polyester was prepared according to the description in Journal of Biotechnology, 154 (2011), pp. 255-260, and P(LA-co-3HB):lactic acid monomer fraction of 9 mol% was mixed in a ratio of 30:70 to obtain Sample 1, a biodegradable resin composition that is a random copolymer polyester.

[0031] <Sample 2> Sample 2 was obtained in the same manner as Sample 1, except that a copolymerized polyester having a lactic acid monomer fraction of 29 mol % was used.

[0032] <Sample 3> Sample 3 was obtained in the same manner as Sample 1, except that a copolymerized polyester having a lactic acid monomer fraction of 44 mol % was used.

[0033] <Sample 4> As a blend of polylactic acid and PHA, a polymer prepared by the method described in Patent Document 2 was used.

[0034] <Sample 5> Polylactic acid (6202D) manufactured by NatureWorks was used.

[0035] [Example 1] Sample 1 was melted and kneaded in a single-screw extruder, and spun at a discharge rate of 0.9 g / min·hole, a spinning temperature of 186°C, and a spinning speed of 800 m / min to obtain fibers. The results of the obtained fibers are shown in Table 1 below, and the obtained fibers are shown in Figure 1.

[0036] [Example 2] Fibers were obtained in the same manner as in Example 1, except that Sample 2 was used. The results for the obtained fibers are shown in Table 1 below. The obtained fibers are also shown in Figure 2.

[0037] [Example 3] Fibers were obtained in the same manner as in Example 1, except that Sample 3 was used. The results for the obtained fibers are shown in Table 1 below. The obtained fibers are also shown in Figure 3.

[0038] [Comparative Example 1] Fibers were obtained in the same manner as in Example 1, except that Sample 4 was used. The results for the obtained fibers are shown in Table 1 below. The obtained fibers are also shown in FIG.

[0039] Comparative Example 2 Fibers were obtained in the same manner as in Example 1, except that Sample 5 was used. The results for the obtained fibers are shown in Table 1 below. The obtained fibers are also shown in FIG.

[0040] [Table 1] [Industrial Applicability]

[0041] The resin composition of the present invention is composed of biomass-based polylactic acid (PLA) resin, polyhydroxyalkanoate (PHA) resin, and copolymerized polyester derived from these. This composition can be melt-spun to produce fibers and nonwoven fabrics composed of the fibers. Therefore, the present invention provides highly biodegradable fibers and nonwoven fabrics. Therefore, the present invention can be used in a variety of products and applications including the fibers and / or nonwoven fabrics.

Claims

1. A resin composition comprising polylactic acid (component A), a copolymer polyester of lactic acid and a hydroxycarboxylic acid (component B), and a polyhydroxyalkanoate (component C), wherein the lactic acid monomer fraction in the copolymer of component B is 9 mol% or more and 44 mol% or less.

2. A fiber made from the resin composition according to claim 1.

3. A nonwoven fabric made from the resin composition according to claim 1.

4. 3. An article comprising the fiber of claim 2.

5. 4. An article of manufacture comprising the nonwoven fabric of claim 3.

Images