Polylactic acid composite resin and method for producing polylactic acid composite resin

Abstract

This invention provides a new polylactic acid composite resin and a method for producing the polylactic acid composite resin. [Solution] The polylactic acid composite resin is formed by compounding polylactic acid and cellulose fiber via a surfactant represented by Formula 1. The method for producing the polylactic acid composite resin includes the steps of: dissolving polylactic acid and the surfactant represented by Formula 1 in a solvent to obtain a polylactic acid solution; adding cellulose fiber to the polylactic acid solution to obtain a mixed turbidity; and drying the mixed turbidity to obtain a polylactic acid composite resin in which polylactic acid and cellulose fiber are compounded via the surfactant. In Formula 1, R 1 This is a maintenance of alcohol compounds, R 2 Here, m represents a residue of the diisocyanate compound, and n represents a positive real number. JPEG2026048155000010.jpg23170

Description

[Technical Field]

[0001] This invention relates to polylactic acid composite resins and methods for producing polylactic acid composite resins. [Background technology]

[0002] Polylactic acid (PLA) is a biodegradable and biocompatible polymer derived from renewable natural resources such as corn and sugarcane. Because PLA is thermoplastic, it has excellent processability and is one of the most widely used biopolymers. Therefore, PLA is suitable for applications in biomedicine, tissue engineering, and industrial packaging.

[0003] However, polylactic acid has drawbacks such as brittleness, a low crystallization rate, and poor heat resistance, which limits its applications.

[0004] To improve the properties of polylactic acid, one method involves mixing in fine particles such as silica, clay, and talc. However, since these particles are inorganic, complete biodegradation is not achieved. As a way to improve the properties of polylactic acid without compromising its complete biodegradability, polylactic acid composite resins incorporating cellulose fibers are being investigated.

[0005] Cellulose is a naturally occurring polymer found in large quantities in nature, possessing high mechanical strength and biodegradability, and can be used as a filler in polymer composites. A composite polymer of polylactic acid and cellulose is expected to improve upon the shortcomings of polylactic acid without compromising its complete biodegradability. Furthermore, cellulose nanofibers and cellulose nanowhiskers, which are made by mechanically or chemically processing cellulose fibers such as pulp fibers to create nanoscale fibers, exhibit even more pronounced strength characteristics because the defective parts have been removed.

[0006] Various polylactic acid composite resins have been reported, which are composites of polylactic acid and cellulose (e.g., Non-Patent Documents 1-5). Non-Patent Document 1 discloses poly-L-lactic acid blended with CLN-ICN, which is obtained by treating cellulose nanowhiskers (CLN) with n-octadecyl isocyanate (ICN). Non-Patent Document 2 discloses the treatment of cellulose nanofibers with various carboxylic acid anhydrides and their compounding with poly-L-lactic acid. Non-Patent Document 3 discloses that a composite of cellulose nanocrystals and poly-L-lactic acid can be obtained by polymerizing L-lactide in the presence of cellulose nanocrystals (CNC). Non-Patent Documents 4 and 5 disclose the use of decylamine, cetyltrimethylammonium bromide, and sodium lauryl sulfate as surfactants for compounding with poly-L-lactic acid, and the use of cellulose nanocrystals. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Etzael Espino-Perez, et al., "Influence of chemical surface modification of cellulose nanowhiskers on thermal, mechanical, and barrier properties of poly(lactide) based bionanocomposites", European Polymer Journal, 49 (2023), 3144-3154. [Non-Patent Document 2] Naharullah Jamaluddin, et al., "Effects of Acid-Anhydride-Modified Cellulose Nanofiber on Poly(Lactic Acid) Composite Films", Nanomaterials, 11 (2021), 753. [Non-Patent Document 3] Chuanwei Miao, et al., "In-situ polymerized cellulose nanocrystals (CNC)-poly(l-lactide)(PLLA) nanomaterials and applications in nanocomposite processing" Carbohydrate Polymers, 153 (2016), 549-558. [Non-Patent Document 4] Jose Luis Orellana, et al., "Mechanical and Optical Properties of Polylactic Acid Films Containing Surfactant-Modified Cellulose Nanocrystals", Journal of Nanomaterials, 2018 (2018), 7124260. [Non-Patent Document 5] Ragab E. Abou-Zeid, et al., "Surfactant-Assisted Poly(lactic acid) / Cellulose Nanocrystal Bionanocomposite for Potential Application in Paper Coating", Journal of Renewable Materials, 6 (2018), 394-401. [Overview of the project] [Problems that the invention aims to solve]

[0008] Polylactic acid composite resins are still materials that have room for improvement, and further development of polylactic acid composite resins is desired.

[0009] The present invention has been made in view of the above matters, and its object is to provide a new polylactic acid composite resin and a method for producing a polylactic acid composite resin. [Means for solving the problem]

[0010] The polylactic acid composite resin according to the first aspect of the present invention is such that polylactic acid and cellulose fiber are compounded through a surfactant represented by Formula 1 [Chemical formula] (In Formula 1, R , represents a residue of an alcohol compound, R 2 represents a residue of a diisocyanate compound, m represents a positive real number, and n represents a positive real number.) It is characterized by this.

[0011] Also, in Formula 1, R 1 may represent a benzyl group, and R 2 may represent a hexamethylene group.

[0012] The method for producing a polylactic acid composite resin according to the second aspect of the present invention is a step of dissolving polylactic acid and a surfactant represented by Formula 1 in a solvent to obtain a polylactic acid solution, [Chemical formula] (In Formula 1, R 1 represents a residue of an alcohol compound, R 2 represents a residue of a diisocyanate compound, m represents a positive real number, and n represents a positive real number.) a step of adding cellulose fiber to the polylactic acid solution to obtain a mixed suspension, a step of drying the mixed suspension to obtain a polylactic acid composite resin in which the polylactic acid and the cellulose fiber are compounded through the surfactant, including It is characterized by this.

[0013] ed Also, it is preferable to add the cellulose fiber to the polylactic acid solution after filtering the polylactic acid solution.

[0014] Also, it is preferable to disperse the cellulose fiber by subjecting the mixed suspension to ultrasonic treatment. [Effects of the Invention]

[0015] According to the present invention, a novel polylactic acid composite resin and a method for producing the polylactic acid composite resin can be provided. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows the manufacturing scheme for polylactic acid composite resin film in the examples. [Figure 2] This is a photograph of the polylactic acid composite resin film used in the example. [Modes for carrying out the invention]

[0017] <Polylactic acid composite resin> Polylactic acid composite resin is formed by compounding polylactic acid and cellulose fibers via a surfactant.

[0018] (Surfactants) The surfactant is represented by formula 1.

[0019] [ka]

[0020] In formula 1, R 1 R represents a residue of an alcohol compound. Also, in formula 1, 2represents a residue of a diisocyanate compound. The alcohol compound residue is, for example, a monovalent residue of an alcohol compound used as an initiator for ring-opening polymerization of L-lactide, such as a benzyl group. The diisocyanate compound residue is, for example, a divalent residue of a diisocyanate compound used when synthesizing the surfactant represented by formula 1, such as a hexamethylene group. Details of the alcohol compound and diisocyanate compound will be described later. In formula 1, m represents the degree of polymerization and is a real number from 2 to 10000, preferably from 2 to 1000. In formula 1, n represents the degree of polymerization and is a real number from 10 to 1000, preferably from 20 to 200.

[0021] As shown in Formula 1, the surfactant is a state in which one isocyanate group of the diisocyanate compound is bonded to the terminal hydroxyl group of polylactic acid by a urethane bond, and the other isocyanate group is bonded to the hydroxyl group of polyvinyl alcohol by a urethane bond.

[0022] (Polylactic acid) Commercially available polylactic acid can be used. Examples of polylactic acid include polymers of L-lactide, polymers of D-lactide, and random or block copolymers of L-lactide and D-lactide.

[0023] (Cellulose fiber) Cellulose fiber is a natural material that possesses properties such as high strength and resistance to thermal expansion. It is preferable that the cellulose fiber is a fiber obtained by defibrating pulp raw material, specifically cellulose nanofibers defibrated to the nanometer scale.

[0024] There are no restrictions on the pulp raw materials; in addition to wood pulp extracted from hardwoods and softwoods, non-wood pulp extracted from grass, straw, bamboo, etc. may also be used. Furthermore, examples of chemical pulps obtained by chemical processing from the above pulp raw materials include kraft pulp (KP), sulfide pulp (SP), and alkali pulp (AP), and mechanical pulps obtained by mechanical processing include ground pulp (GP), refiner ground pulp (RGP), thermomechanical pulp (TMP), and chemi-thermo-mechanical pulp (CTMP). One or more of these may be used.

[0025] There are no restrictions on the average fiber diameter of the cellulose fibers, but it is preferably 3 to 1000 nm, more preferably 4 to 500 nm, and even more preferably 5 to 100 nm. If the average fiber diameter is large, the homogeneity of the polylactic acid composite resin may be impaired. If the average fiber diameter is small, it may decompose during the manufacturing process of the polylactic acid composite resin, which may lead to a decrease in the mechanical strength of the polylactic acid composite resin.

[0026] Furthermore, there is no limit to the average fiber length of the cellulose fibers, but it is preferably 0.1 to 1000 μm, more preferably 0.2 to 500 μm, and even more preferably 0.3 to 100 μm. If the average fiber length is long, there is a risk of fiber aggregation occurring in the polylactic acid composite resin. On the other hand, if the average fiber length is short, there is a risk of a decrease in the mechanical strength of the polylactic acid composite resin.

[0027] As described above, the surfactant represented by Formula 1 has a residue of a diisocyanate compound sandwiched therebetween, and has a polylactic acid site and a polyvinyl alcohol site. Therefore, it has excellent affinity with polylactic acid that is complexed with the polylactic acid site of the surfactant represented by Formula 1. Further, it is considered that a hydroxyl group of the polyvinyl alcohol site of the surfactant represented by Formula 1 forms a hydrogen bond with cellulose fiber. Thereby, in the polylactic acid composite resin, polylactic acid and cellulose fiber are homogeneously dispersed and complexed through the surfactant represented by Formula 1.

[0028] Since the polylactic acid composite resin is complexed with cellulose fiber having excellent mechanical strength, its mechanical strength such as tensile strength is improved as compared with a single polylactic acid. Further, since cellulose fiber is derived from plant fiber and has biodegradability, it has an advantage of low environmental load regarding disposal. That is, the polylactic acid composite resin in which both polylactic acid and cellulose fiber having biodegradability are complexed has an advantage of low environmental load.

[0029] <Production method of polylactic acid composite resin> The polylactic acid composite resin can be produced as follows. First, as shown in Scheme 1, a surfactant (PVA-graft-PLLA) is synthesized. In Scheme 1, R 1 and R 2 are synonymous with R 1 and R 2 in Formula 1 described above, respectively.

[0030]

Chemical formula

[0031] <Synthesis of surfactant (copolymer (PVA-graft-PLLA) in which polylactic acid is bonded as a graft chain to polyvinyl alcohol)> Poly-L-lactic acid (PLLA) is obtained by ring-opening polymerization of L-lactide (LLA). Ring-opening polymerization of LLA can be carried out by reacting it at 100°C for about 24 hours in the presence of a catalyst such as tin 2-ethylhexanoate (Sn(Oct)2) and an alcohol compound as an initiator. Examples of alcohol compounds include monools with a boiling point of 100°C or higher, such as benzyl alcohol, 1-butanol, 1-pentanol, and 1-hexanol.

[0032] Next, the terminal ends of the obtained poly-L-lactic acid are modified with isocyanate groups to synthesize isocyanate-modified poly-L-lactic acid (PLLA-NCO). Modification with isocyanate groups can be carried out by treating poly-L-lactic acid with an excess amount of diisocyanate compound in the presence of a catalyst such as Sn(Oct)2, reacting the terminal hydroxyl groups of polylactic acid with the isocyanate groups of the diisocyanate compound, and then washing with hexane to remove unreacted diisocyanate. This allows the terminal ends of poly-L-lactic acid to be modified with isocyanate groups via urethane bonds.

[0033] Examples of diisocyanate compounds include aliphatic diisocyanates and aromatic diisocyanates. Specifically, examples include ethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, cyclohexylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, 1,5-diisocyanatonaphthalene, p-phenylene diisocyanate, isophorone diisocyanate, norbornane diisocyanate, m-xylylene diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane.

[0034] Next, a solution of PLLA-NCO is added to a solution of polyvinyl alcohol (PVA) dissolved in dimethyl sulfoxide, and a catalyst is added and the mixture is heated. The heating temperature should be 60-70°C and the heating time should be approximately 12-24 hours. Sn(Oct)2 can be used as the catalyst. The hydroxyl group of polyvinyl alcohol reacts with the isocyanate group at the end of PLLA-NCO to synthesize PVA-graft-PLLA, in which poly-L-lactic acid is urethane-bonded as a graft chain to polyvinyl alcohol.

[0035] <Method for manufacturing polylactic acid composite resin> A method for producing a polylactic acid composite resin includes the steps of: dissolving polylactic acid and a surfactant represented by formula 1 in a solvent to obtain a polylactic acid solution; adding cellulose fiber to the polylactic acid solution to obtain a mixed turbidity; and drying the mixed turbidity to obtain a polylactic acid composite resin in which polylactic acid and cellulose fiber are compounded via the surfactant.

[0036] It is preferable to separate the polylactic acid solution into solid and liquid components using separation methods such as filtration, and then add cellulose fibers to the polylactic acid solution. By removing the insoluble portion of the surfactant from the polylactic acid solution, it is possible to suppress the aggregation of solvent-insoluble surfactants in the polylactic acid composite resin.

[0037] Furthermore, in the process of obtaining the mixed turbidity, it is preferable to sufficiently disperse the cellulose fibers in the mixed turbidity. The method for dispersing the cellulose fibers can be any known method, for example, by ultrasonic treatment of the mixed turbidity. By dispersing the cellulose fibers in the mixed turbidity, homogenization of the polylactic acid composite resin can be achieved.

[0038] Furthermore, any solvent capable of dissolving polylactic acid and surfactants may be used, such as CHCl3.

[0039] Regarding the mixing ratios of polylactic acid, cellulose fiber, and surfactant, they may be appropriately adjusted at a weight ratio of about 50 to 150:2 to 20:0.2 to 2.

[0040] A polylactic acid composite resin can be obtained by drying the mixed solution. The obtained polylactic acid composite resin can be used as a molding material, and molded products can be obtained by known molding means such as injection molding, extrusion molding, blow molding, etc. These molded products can be used for various purposes as parts in the fields of biomedical, tissue engineering, industrial packaging, etc.

Example

[0041] As follows, a surfactant (PVA-graft-PLLA) was synthesized, and a polylactic acid composite resin film in which poly-L-lactic acid (PLLA) and cellulose nanofiber (CNF) were compounded through the synthesized PVA-graft-PLLA was produced, and the properties of the polylactic acid composite resin film were evaluated.

[0042] <Synthesis of PVA-graft-PLLA> PLLA was synthesized by ring-opening polymerization of LLA using benzyl alcohol (BnOH) as an initiator in the presence of a tin 2-ethylhexanoate (Sn(Oct)2) catalyst. Next, PLLA was treated with an excess of hexamethylene diisocyanate (HDI) to synthesize PLLA modified with an isocyanate group at the terminal (PLLA-NCO). The number average molecular weight M n of the obtained PLLA-NCO was 1.0×10 4 , and the molecular weight distribution M w / M n was 1.1. [The OH groups in PVA]0:[PLLA-NCO]0 = 100:2 charging ratio, a DMSO solution of PLLA-NCO was added to a DMSO solution of PVA. A catalyst (Sn(Oct)2) was added thereto and reacted at 60 °C overnight. After the reaction, an excess of MeOH was added, and the precipitated polymer was recovered and dried to obtain PVA-graft-PLLA (yield 39%).

[0043] <Manufacturing of polylactic acid composite resin film> Using the synthesized PVA-graft-PLLA, polylactic acid composite resin (hereinafter referred to as PLLA-CNF composite resin) films were fabricated by solution casting according to the scheme shown in Figure 1. The weight ratio of PLLA:CNF:PVA-graft-PLLA was 100:5:0.5. The PLLA used was purchased from Musashino Chemical Research Institute (Mn=4.9×10⁻⁶). 4 Furthermore, the CNF used was lignocellulose nanofiber produced from cedar waste wood from Hiroshima Prefecture using a grinding method.

[0044] (A) PLLA was added to CHCl3. (B) Furthermore, PVA-graft-PLLA was added. (C) This solution was stirred at 50°C. (D) Subsequently, the PVA-graft-PLLA that did not completely dissolve in CHCl3 was removed by filtration. (E) CNF was added to this solution. (F) Subsequently, the CNF was dispersed by ultrasonic treatment. (G) The mixture was cast onto a PFA (perfluoroalkoxyalkane) petri dish, air-dried under atmospheric pressure for 3 days, and then vacuum-dried for another day to produce a PLLA-CNF composite resin film. This PLLA-CNF composite resin film is denoted as film (d).

[0045] Furthermore, a PLLA-CNF composite resin film was prepared in the same manner as above, except that PVA-graft-PLLA was not added and ultrasonic treatment was not performed, that is, steps (B), (D), and (F) above were not performed. This PLLA-CNF composite resin film will be referred to as film (a).

[0046] Furthermore, a PLLA-CNF composite resin film was prepared in the same manner as described above, except that filtration was not performed, i.e., the process in (D) above was not performed. This PLLA-CNF composite resin film is referred to as film (b).

[0047] Also, a PLLA-CNF composite resin film was produced in the same manner as above, except that PVA-graft-PLLA was not added, that is, except that the steps (B) and (D) were not performed. This PLLA-CNF composite resin film is referred to as film (c).

[0048] A film of PLLA alone was produced in the same manner as above, except that PVA-graft-PLLA and CNF were not added, that is, except that the steps (B), (D) to (F) were not performed. This film is referred to as film PLLA.

[0049] Photographs of the produced films are shown in Fig. 2. Aggregation of CNF occurred in film (a) to which no PVA-graft-PLLA was added and no ultrasonic treatment was performed. Insoluble PVA-graft-PLLA appeared as lumps in film (b) in which filtration was not performed. In films (c) and (d) to which both ultrasonic treatment and filtration were performed, there was little difference in appearance, and both were semi-transparent films similar to film PLLA.

[0050] <Evaluation of PLLA-CNF Composite Resin Film> The tensile modulus, tensile strength, and elongation at break of each of the prepared films are shown in Table 1. The measurement was performed three times for each sample at a tensile speed of 50 mm / min using a tensile testing machine.

[0051]

Table 1

[0052] From Table 1, films (a) in which filtration was not performed and film (b) in which ultrasonic treatment was not performed showed lower physical properties compared to PLLA. Films (c) and (d) to which filtration and ultrasonic treatment were performed showed better mechanical strength compared to films (a) and (b). Film (d) with added PVA-graft-PLLA had a tensile strength of 38.9 MPa, which was a significant improvement over film (c) (29.0 MPa) without added PVA-graft-PLLA, and nearly 10% higher than PLLA (36.2 MPa). The elastic modulus was about 24% lower, suggesting that the brittleness of PLLA had been improved. These results clearly show that adding PVA-graft-PLLA can result in a PLLA-CNF composite resin with improved physical properties.

[0053] Table 2 shows the thermal properties of the fabricated films, evaluated by DSC (Differential Scanning Calorimetry) measurements. Measurements were performed at 10°C / min from 30°C to 200°C.

[0054] [Table 2]

[0055] In all films with added CNF, the melting point (T m The glass transition temperature (T) is similar to that of PLLA, indicating that the effect of compounding with CNF on heat resistance is small. In addition, both films have a glass transition temperature (T) of about the same as PLLA. g ) was not detected. [Industrial applicability]

[0056] Polylactic acid composite resins are expected to have applications in fields such as biomedicine, tissue engineering, and industrial packaging due to their excellent processability, biocompatibility, biodegradability, and mechanical properties.

Claims

1. Polylactic acid and cellulose fiber are compounded via a surfactant represented by formula 1. 【Chemistry 1】 (In formula 1, R １ R is a residue of an alcohol compound. ２ (where m represents a residue of the diisocyanate compound, and n represents a positive real number.) A polylactic acid composite resin characterized by the following features.

2. In the above formula 1, R １ represents a benzyl group, R ２ This represents a hexamethylene group. The polylactic acid composite resin according to feature 1.

3. A step of dissolving polylactic acid and a surfactant represented by formula 1 in a solvent to obtain a polylactic acid solution, 【Chemistry 2】 (In formula 1, R １ R is a residue of an alcohol compound. ２ (where m represents a residue of the diisocyanate compound, and n represents a positive real number.) The process involves adding cellulose fiber to the polylactic acid solution to obtain a mixed turbidity, The process includes drying the mixed turbidity to obtain a polylactic acid composite resin in which the polylactic acid and the cellulose fiber are compounded via the surfactant. A method for producing a polylactic acid composite resin characterized by the above.

4. After filtering the polylactic acid solution, the cellulose fiber is added to the polylactic acid solution. A method for producing a polylactic acid composite resin according to feature 3.

5. The mixed turbidity is subjected to ultrasonic treatment to disperse the cellulose fibers. A method for producing a polylactic acid composite resin according to feature 3.

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