Poly(lactic acid-b-3-hydroxypropionic acid) block copolymers having excellent tensile strength and articles containing the same

Abstract

The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is characterized by improving various physical properties of polylactic acid, such as tensile strength, by introducing a monomer derived from 3-hydroxypropionic acid into polylactic acid, thereby expanding its application fields.

Description

[Technical field]

[0001] [Cross-reference to related applications] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0024928 filed on February 24, 2021, and Korean Patent Application No. 10-2022-0024171 filed on February 24, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to poly(lactic acid-b-3-hydroxypropionic acid) block copolymers having excellent tensile strength and articles containing the same. [Background technology]

[0003] Polylactic acid (PLA) is a plant-derived resin obtained from plants such as corn, and is attracting attention as an excellent environmentally friendly material with biodegradable properties. Unlike conventionally used petroleum-based resins such as polystyrene resin, polyvinyl chloride resin, and polyethylene, polylactic acid has the effect of preventing the depletion of petroleum resources and suppressing carbon dioxide emissions, and therefore can reduce environmental pollution, which is a drawback of petroleum-based plastic products. Therefore, as the problem of environmental pollution caused by waste plastics and other materials has emerged as a social issue, efforts are being made to expand the scope of application of polylactic acid to product areas where general plastics (petroleum-based resins) are used, such as food packaging materials and containers and electronic product cases.

[0004] However, compared to existing petroleum-based resins, polylactic acid has inferior impact resistance and heat resistance, limiting its range of application.In addition, it has low tensile strength, poor elongation properties, and brittleness, which limits its use as a general-purpose resin.

[0005] In order to improve the above-mentioned shortcomings, research is being conducted on copolymers containing other repeating units in polylactic acid, and in particular, 3-hydroxypropionic acid has been attracting attention as a comonomer to improve elongation. However, the properties expressed vary depending on the degree of introduction of 3-hydroxypropionic acid, and if the degree of introduction is not controlled, there is a risk that the inherent properties of polylactic acid will be impaired.

[0006] Therefore, the present invention aims to provide a block copolymer having improved physical properties such as tensile strength while maintaining the inherent physical properties of polylactic acid by controlling the degree of introduction of the monomer derived from 3-hydroxypropionic acid. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a copolymer having improved physical properties such as tensile strength while maintaining the inherent properties of polylactic acid, and an article containing the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a poly(lactic acid-b-3-hydroxypropionic acid) block copolymer represented by the following chemical formula 1, wherein the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has a tensile strength of 30 MPa or more: [Chemical formula 1] [ka] In the above Chemical Formula 1, m is an integer from 100 to 1000; n is an integer from 500 to 4000.

[0009] The term "poly(lactic acid-b-3-hydroxypropionic acid) block copolymer" used in the present invention refers to a block copolymer in which a lactide-derived monomer and a 3-hydroxypropionic acid-derived monomer are polymerized as represented by Chemical Formula 1 above, and in particular, a block copolymer in which various physical properties such as the tensile strength of polylactic acid are improved by introducing a 3-hydroxypropionic acid-derived monomer.

[0010] When a monomer derived from 3-hydroxypropionic acid is introduced as a comonomer into polylactic acid, various physical properties of polylactic acid are improved, but the properties that are expressed vary depending on the degree of introduction. Therefore, in the present invention, the degree of introduction of the monomer derived from 3-hydroxypropionic acid is controlled to maintain the inherent physical properties of polylactic acid while improving physical properties such as tensile strength.

[0011] Preferably, m is 250 to 650. The m means the repeat number of the monomer derived from 3-hydroxypropionic acid, and by introducing it in the above range, it is possible to improve physical properties such as tensile strength while maintaining the inherent physical properties of polylactic acid. More preferably, m is 260 or more, 270 or more, or 280 or more; and 640 or less, 600 or less, 500 or less, or 400 or less.

[0012] Preferably, n is 600 to 1400. The n means the repeating number of a monomer derived from lactide. More preferably, n is 700 or more, 800 or more, 900 or more, or 1000 or more; and 1300 or less, or 1200 or less.

[0013] In addition, in the present invention, the relative ratio of the monomers is important, and preferably the m / n is 0.20 to 0.60. Within this range of m / n, the inherent physical properties of polylactic acid can be maintained while improving physical properties such as tensile strength. More preferably, the m / n is 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, or 0.25 or more; 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, or 0.30 or less.

[0014] The tensile strength of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 30 MPa or more. The method for measuring the tensile strength will be described in the Examples below. Preferably, the tensile strength of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 31 MPa or more, 32 MPa or more, 33 MPa or more, 34 MPa or more, 35 MPa or more, 36 MPa or more, 37 MPa or more, 38 MPa or more, 39 MPa or more, or 40 MPa or more. On the other hand, the higher the tensile strength, the better it is, but if the value is too high, the application field of the copolymer may be limited. From this viewpoint, the tensile strength of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is preferably 60 MPa or less. More preferably, the tensile strength of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 59 MPa or less, 58 MPa or less, 57 MPa or less, 56 MPa or less, 55 MPa or less, 54 MPa or less, 53 MPa or less, 52 MPa or less, 51 MPa or less, or 50 MPa or less.

[0015] Also, preferably, the elongation of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 30% to 250%. The method for measuring the elongation is embodied in the examples described below. Preferably, the elongation of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100% or more, 110% or more, 120% or more, 130% or more, 140% or more, 150% or more, 160% or more, 170% or more, 180% or more, 190% or more, or 200% or more. Also, preferably, the elongation of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention is 240% or less, 230% or less, 220% or less, or 210% or less.

[0016] Preferably, the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention has a tensile modulus of 1.0 to 2.0 GPa. The method for measuring the tensile modulus will be embodied in the examples described later.

[0017] Also, preferably, the weight average molecular weight of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer is 50,000 to 350,000. More preferably, the weight average molecular weight of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer is 60,000 or more, 70,000 or more, 80,000 or more, 90,000 or more, 100,000 or more, 110,000 or more, 120,000 or more, or 130,000 or more; 300,000 or less, 250,000 or less, 200,000 or less, 190,000 or less, 180,000 or less, or 170,000 or less.

[0018] The present invention also provides a method for producing the above-mentioned poly(lactic acid-b-3-hydroxypropionic acid) block copolymer, comprising the steps of: polymerizing a 3-hydroxypropionic acid polymer, lactide, and a catalyst.

[0019] The 3-hydroxypropionic acid polymer means a homopolymer of 3-hydroxypropionic acid, and is prepared by controlling the degree of polymerization in consideration of the above ranges of m and n.

[0020] Meanwhile, since the preparation method involves lactide ring-opening polymerization reaction, it is carried out in the presence of a lactide ring-opening catalyst. For example, the catalyst may be a catalyst represented by Chemical Formula 2.

[0021] [Chemical formula 2] MA 1 p A 2 2-p In the above Chemical Formula 2, M is Al, Mg, Zn, Ca, Sn, Fe, Y, Sm, Lu, Ti or Zr; p is an integer from 0 to 2; A 1 and A 2 are each independently an alkoxy or carboxyl group.

[0022] More specifically, the catalyst represented by Formula 2 may be tin(II) 2-ethylhexanoate (Sn(Oct)2).

[0023] Preferably, the amount of the catalyst used may be 0.001 to 10 mol %, 0.01 to 5 mol %, or 0.03 to 1 mol %, assuming that the total number of moles of lactide is 100 mol %.

[0024] Preferably, the production method is carried out at 150 to 200° C. Preferably, the production method is carried out for 5 minutes to 10 hours, more preferably 10 minutes to 1 hour. Preferably, the production method is carried out at 0.5 to 1.5 atm.

[0025] The present invention also provides an article comprising the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer described above. Effect of the Invention

[0026] As described above, the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to the present invention has the characteristic that it can improve various physical properties such as tensile strength of polylactic acid by introducing a monomer derived from 3-hydroxypropionic acid into polylactic acid, thereby expanding its application field. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the embodiments of the present invention will be described in more detail with reference to the following examples. However, the following examples are merely illustrative of the embodiments of the present invention, and the content of the present invention is not limited to the following examples.

[0028] Production Example: Production of Poly(3-hydroxypropionate) Oligomer In the biosynthesis of high molecular weight poly(3-hydroxypropionate) according to the present invention, fermentation was carried out under the following conditions to produce a fermentation liquid containing 3-hydroxypropionate as a fermentation substrate. Specifically, E. coli W3110 having GDH and ALDH enzyme genes was used as the strain for fermentation. M9 was used as the medium, and 70 g / L of glycerol was used as the substrate for fermentation to produce 3-hydroxypropionate.

[0029] Thereafter, poly(3-hydroxypropionic acid) (hereinafter, "P(3HP)") was produced by fermentation using the produced 3-hydroxypropionate as a substrate. Specifically, a 5L fermenter (internal volume: 3L) was used for fermentation, and the microorganism used for fermentation was a recombinant E. coli produced by transforming XL1-Blue E. coli with a recombinant vector in which the RecC gene, which is a polyhydroxyalkanoate synthase (PHA synthase) derived from Ralstonia eutropha, and the mutant 540 (CPPCT_540) gene of propionyl-CoA transferase derived from Clostridium propionicum were cloned into the pBLuescript II KS(+) vector.

[0030] The CPPCT_540 gene is an improved gene in which the base sequence has been substituted so that the 193rd amino acid, valine, is expressed as alanine (V194A), and three silent mutations (T669C, A1125G, T1158C) have been made without any other amino acid changes, i.e., DNA substitutions have been made (WO09 / 022797).

[0031] The medium was a modified Riesenberg (MR) medium containing glucose (20 g / L) and the fermentation liquid (2.0 g / L) containing the 3-hydroxypropionate produced above as a substrate. This was fermented under aeration conditions of 300 rpm and 1 vvm, and finally high molecular weight poly(3-hydroxypropionate) was produced (Mn: 136,645; Mw: 354,615; PDI: 2.60; measured using an Agilent 1200 series and calibrated with PC standard).

[0032] The prepared poly(3-hydroxypropionate) was placed in distilled water and hydrolyzed at 100°C for 18, 24, and 72 hours, respectively, to obtain poly(3-hydroxypropionate) oligomers with weight average molecular weights (measured using an Agilent 1200 series and calibrated with PC standard) of 30,000 g / mol, 60,000 g / mol, and 80,000 g / mol, respectively. EXAMPLES

[0033] Example 1: Preparation of poly(lactic acid-b-3-hydroxypropionic acid) block copolymer Into the reactor, lactide (25g), poly(3-hydroxypropionate) oligomer (5g) having a weight average molecular weight of 30,000g / mol produced in the previous production example, tin(II) ethylhexanoate (0.014g) as a catalyst, and toluene (100uL) were added and dried for about 30 minutes to 1 hour. Next, the reactor was placed in an oil bath pre-heated to 180°C and polymerization was carried out for 1.5 hours. After removing the product from the reactor, the product was devolitilized at 140°C under reduced pressure of 1 to 5 torr for about 3 hours to remove the monomer, and finally poly(lactic acid-b-3-hydroxypropionic acid) block copolymer was produced.

[0034] Examples 2 to 7: Preparation of poly(lactic acid-b-3-hydroxypropionic acid) block copolymers The same procedure as in Example 1 was followed, but the starting materials were changed as shown in Table 1 below to prepare poly(lactic acid-b-3-hydroxypropionic acid) block copolymers. [Table 1]

[0035] Comparative Example: Production of Polylactic Acid Lactide (25g), 1-octanol (0.027g), tin(II) ethylhexanoate (0.014g) as a catalyst, and toluene (100uL) were added to the reactor and dried for about 30 minutes to 1 hour. The reactor was then placed in an oil bath pre-heated to 180°C and polymerization was carried out for 1.5 hours. After removing the product from the reactor, the product was devolitilized at 140°C under reduced pressure of 1 to 5 torr for about 3 hours to remove the monomer, and finally polylactic acid homopolymer was produced.

[0036] Experimental Example The properties of the copolymers prepared in the above Examples and Comparative Examples were evaluated as follows.

[0037] Weight average molecular weight: Measured by GPC using Agilent 1200 series and PC standard. -Elongation, tensile strength and tensile modulus: According to ASTM D638, ASTM D536 V Type test pieces were prepared using a hot-press machine (Limotem QM900S), and then measured using a UTM machine (Universal Testing Machine) at 10mm / s and 60kg / f load. - 3-hydroxypropionic acid content (wt%) in block copolymer: Measured by NMR analysis of the block copolymer. The measurement results are shown in Table 2 below. [Table 2]

Claims

1. In the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer represented by the following chemical formula 1, The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has a tensile strength of 32 MPa or more. Poly(lactic acid-b-3-hydroxypropionic acid) block copolymer: [Chemical formula 1] 【Chemical 1】 In the above Chemical Formula 1, m is an integer from 100 to 1000, n is an integer from 500 to 4000, The m / n is 0.21 to 0.

60.

2. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to claim 1, wherein m is 250 to 650.

3. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to claim 1 or 2, wherein n is 600 to 1,400.

4. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to claim 1, wherein m / n is 0.25 to 0.

30.

5. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to any one of claims 1 to 4, wherein the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has a tensile strength of 60 MPa or less.

6. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to any one of claims 1 to 5, wherein the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has an elongation of 30% to 250%.

7. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to any one of claims 1 to 6, wherein the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has a tensile modulus of 1.0 to 2.0 GPa.

8. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to any one of claims 1 to 7, wherein the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer has a weight average molecular weight of 50,000 to 350,000.

9. The poly(lactic acid-b-3-hydroxypropionic acid) block copolymer according to claim 8, wherein the weight average molecular weight of the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer is 130,000 to 170,000.

10. An article comprising the poly(lactic acid-b-3-hydroxypropionic acid) block copolymer of any one of claims 1 to 9.

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