Branched polylactic acid polymer and preparation method thereof

Abstract

The invention relates to a branched polylactic acid polymer with improved rheological properties, and a preparation method thereof. The present invention provides a branched polylactic acid polymer containing derived units from a polylactic acid polymer, having an average number of long chain branches per molecule of 3 to 10, and having a mass flow rate of 1 g / 10 minutes to 20 g / 10 minutes measured according to ASTM D1238 conditions at 190 DEG C and a load of 2.16 kg, and a method for preparing the same.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0001715, filed on January 5, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a branched polylactic acid polymer with improved rheological properties and a preparation method thereof. Background Art

[0004] Polylactic acid polymer (hereinafter referred to as "PLA") is a biodegradable and environmentally friendly material, and many studies have been conducted recently to develop its uses. Unless modified, PLA is a generally linear molecule that behaves like a thermoplastic polymer and can be used as a material for various films, fibers, and other molded products.

[0005] However, PLA is brittle and has low rheological properties (including melt strength), is not suitable for applications due to low crystallinity, high thermal and mechanical properties, and has great limitations in blow molding processes and injection molding processes due to low rheological properties.

[0006] In order to solve this problem, the technology of blending or copolymerizing the biodegradable resins polybutylene succinate and polybutylene adipate terephthalate similar to PLA with resins with higher heat resistance such as PP and PE has been tried. However, there are compatibility problems between these resins, and the effect achieved by blending or copolymerization is not obvious.

[0007] As another embodiment, the thermoplastic polymer needs to have a lower shear viscosity to form a melt that is easy to process, and at the same time, the melt needs to have sufficient strength and / or dimensional stability to maintain the desired shape after forming. Generally, the melt strength can be increased by increasing the molecular weight of the polymer, but the increase in molecular weight will also increase the shear viscosity, making processing difficult. Therefore, in order to improve the melt strength and processability of PLA at the same time, people try to use chain extenders or branching agents to introduce long chain branches (LCB) into PLA to change the linear structure of PLA, thereby changing its performance. Chain extenders and branching agents include isocyanate compounds, such as diphenylmethane diisocyanate and hexamethylene diisocyanate; epoxy compounds, such as multifunctional epoxy styrene-acrylic oligomers; and anhydride compounds, such as pyromellitic dianhydride.

[0008] In addition, KR10-2007-0049140A (2007.05.10) discloses a polylactic acid resin containing long chain branches obtained by reacting a polylactic acid resin with an acrylate polymer or copolymer containing epoxy groups, and a preparation method thereof. However, the problem is that the viscosity of the polylactic acid resin prepared by reacting the acrylate polymer or copolymer increases significantly, making it difficult to control in the molding process, and reducing the industrial application field of the polylactic acid resin to a very limited extent.

[0009] Therefore, there is a need to develop PLA having improved melt strength, maintaining high reactivity of epoxy groups, and improving rheological properties by appropriately increasing viscosity, and a preparation method thereof.

[0010] [Prior art literature]

[0011] [Patent Document] (Patent Document 1) 10-2017-0049140A (2007.05.10.) Summary of the invention

[0012] Technical issues

[0013] The present invention aims to solve the problems existing in the prior art and aims to provide a branched polylactic acid polymer with excellent melt strength and rheological properties.

[0014] In addition, another object of the present invention is to provide a method for preparing the branched polylactic acid polymer.

[0015] Technical Solution

[0016] To solve the above problems, the present invention provides a branched polylactic acid polymer and a method for preparing the branched polylactic acid polymer.

[0017] (1) The present invention provides a branched polylactic acid polymer, which contains derivative units from a polylactic acid polymer, wherein the average number of long chain branches per molecule is 3 to 10, and the mass flow rate measured at 190°C and 2.16 kg load according to ASTM D1238 conditions is 1 g / 10 min to 20 g / 10 min.

[0018] (2) The present invention provides a branched polylactic acid polymer as described in (1), which further comprises a unit derived from an epoxy group-containing acrylic ester copolymer, wherein the epoxy group-containing acrylic ester copolymer contains 30 wt % to 50 wt % of repeating units derived from a first alkyl (meth)acrylate monomer, 30 wt % to 60 wt % of repeating units derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of repeating units derived from a second alkyl (meth)acrylate monomer, wherein the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0019] (3) The present invention provides a branched polylactic acid polymer as described in (2), wherein the content of the derived units derived from the epoxy group-containing acrylate copolymer is 0.5 to 1.0 parts by weight based on 100 parts by weight of the derived units derived from the polylactic acid polymer.

[0020] (4) The present invention provides a branched polylactic acid polymer as described in (2) or (3), wherein the number of epoxy groups per molecule of the epoxy group-containing acrylate copolymer is 30 to 80.

[0021] (5) The present invention provides a branched polylactic acid polymer according to any one of (2) to (4), wherein the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are each independently at least one or more selected from methyl (meth)acrylate, butyl acrylate and 2-ethylhexyl acrylate, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0022] (6) The present invention provides the branched polylactic acid polymer according to any one of (1) to (5), wherein the weight average molecular weight of the polylactic acid polymer measured by gel permeation chromatography using a polystyrene standard is 30,000 g / mol to 250,000 g / mol.

[0023] (7) The present invention provides a branched polylactic acid polymer as described in any one of (1) to (6), wherein when measured by multi-angle light scattering-gel permeation chromatography, its absolute weight average molecular weight is 100,000 g / mol to 1,500,000 g / mol and its polydispersity index is 2.0 to 3.5.

[0024] (8) The present invention provides a branched polylactic acid polymer according to any one of (1) to (7), wherein the branched polylactic acid polymer has two peaks on a differential molecular weight distribution diagram obtained by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight, and the first peak (Pt 1) is 0.8 to 1.2, the first peak (Pt 2 ) is 0.1 to 0.6.

[0025] (9) The present invention provides a branched polylactic acid polymer according to any one of (1) to (8), wherein the branched polylactic acid polymer has two peaks on a differential molecular weight distribution diagram measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight, and the first peak (Pt 1 ) exists at 4.5≤log(M)≤5.8, the second peak (Pt 2 ) exists in 5.8 <log(M)≤6.5。

[0026] (10) The present invention provides a branched polylactic acid polymer as described in any one of (1) to (9), wherein at 180°C, the slope of a graph of complex viscosity (Pa.s) relative to angular frequency (rad / s) is -0.1 to -0.6.

[0027] (11) The present invention provides a method for preparing a branched polylactic acid polymer, which comprises the steps of mixing a polylactic acid polymer with an epoxy group-containing acrylic ester copolymer and simultaneously heating the mixture within a temperature range of 180°C to 200°C, wherein the epoxy group-containing acrylic ester copolymer is prepared by polymerizing, in a solvent and in the presence of an emulsifier, 30% to 50% by weight of repeating units derived from a first alkyl (meth)acrylate monomer, 30% to 60% by weight of repeating units derived from a glycidyl (meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0028] (12) The present invention provides a method for preparing a branched polylactic acid polymer as described in (11) or (12), wherein the amount of the epoxy group-containing acrylate copolymer is 0.5 to 1.0 parts by weight based on 100 parts by weight of the polylactic acid polymer.

[0029] (13) The present invention provides the method for preparing a branched polylactic acid polymer as described in (11), wherein the number of epoxy groups per molecule of the epoxy group-containing acrylate copolymer is 30 to 80.

[0030] Beneficial Effects

[0031] The branched polylactic acid polymer of the present invention has a modified linear structure and has excellent melt strength and elasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a differential molecular weight distribution diagram of each branched or unbranched polylactic acid polymer in the embodiments and comparative examples of the present invention.

[0033] Figure 2a to Figure 2d is a multi-angle light scattering-gel permeation chromatography analysis diagram of the branched polylactic acid polymer of Example 1 of the present invention, wherein Figure 2a is the curve of refractive index changing with retention volume, Figure 2b is the curve of MALS signal (MALS intensity, 90° scattering angle) changing with retention volume, Figure 2c is a plot of long chain branching (branching, branching index) versus retention volume, and Figure 2d It is a curve showing the change of weight average molecular weight with retention volume.

[0034] Figure 3a to Figure 3d is a multi-angle light scattering-gel permeation chromatography analysis diagram of the branched polylactic acid polymer of Example 2 of the present invention, wherein Figure 3a The refractive index is plotted against the retention volume, Figure 3b is the curve of MALS signal (MALS intensity, 90° scattering angle) changing with retention volume, Figure 3c is a plot of long chain branching (branching, branching index) versus retention volume, and Figure 3d It is a curve showing the change of weight average molecular weight with retention volume.

[0035] Figures 4a to 4d is a multi-angle light scattering-gel permeation chromatography analysis diagram of the unbranched polylactic acid polymer of Comparative Example 1 of the present application, wherein Figure 4a is the curve of refractive index changing with retention volume, Figure 4b is the curve of MALS signal (MALS intensity, 90° scattering angle) changing with retention volume, Figure 4c is a plot of long chain branching (branching, branching index) versus retention volume, and Figure 4d It is a curve showing the change of weight average molecular weight with retention volume.

[0036] Figure 5a to Figure 5d is a multi-angle light scattering-gel permeation chromatography analysis diagram of the branched polylactic acid polymer of Comparative Example 2 of the present application, wherein Figure 5a is the curve of refractive index changing with retention volume, Figure 5b is the curve of MALS signal (MALS intensity, 90° scattering angle) changing with retention volume, Figure 5c is a plot of long chain branching (branching, branching index) versus retention volume, and Figure 5d It is a curve showing the change of weight average molecular weight with retention volume.

[0037] Figure 63 is a graph showing the relationship between the complex viscosity (Pa.S) and the angular frequency (rad / s) of each branched or unbranched polylactic acid polymer at 180°C in the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0038] Hereinafter, the present invention will be described in more detail to help understanding of the present invention.

[0039] It should be understood that the words or terms used in the specification and claims of the present invention should not be interpreted as the meanings defined in common dictionaries. It should be further understood that, based on the principle that the inventor can appropriately define the meanings of words or terms to preferably interpret the present invention, these words or terms should be interpreted as having meanings consistent with the meanings of the technical concept of the present invention.

[0040] Definition of terms

[0041] In the present specification, the term "long chain branch (LCB)" refers to a long chain in which the number of carbon atoms in the branch chain is similar to that of the backbone chain so that it cannot be distinguished from the backbone chain.

[0042] In the present specification, the terms "derived unit and derived repeating unit" may refer to a component, unit or structure derived from a certain material, and may also refer to the material itself.

[0043] In this specification, the term "peak top" refers to the maximum dw / dlog(M) value on a differential molecular weight distribution graph measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the concentration fraction W differentiated by the logarithmic molecular weight. In addition, in the differential molecular weight distribution graph, if the graph is a unimodal graph, there is one peak top, and if the graph is a multimodal graph, there are multiple peak tops.

[0044] In the present specification, the term "polydispersity index (PDI)" refers to weight average molecular weight (Mw) / number average molecular weight (Mn), and the weight average molecular weight and number average molecular weight can be measured by gel permeation chromatography (GPC) equipped with a differential refractive index detector (RI).

[0045] Measurement method

[0046] In this specification, long chain branching was analyzed by multi-angle light scattering-gel permeation chromatography (MALS-GPC) under the following conditions using a Viscotek VE2001 GPC / SEC system equipped with a Viscotek TDA 305 triple detector array module (light scattering, viscometer and refractive index detector), and all result data were calculated using OmniSEC version 4.7 software.

[0047] Column: Two Plgel mixed-B columns (Agilent)

[0048] Solvent: Tetrahydrofuran (THF)

[0049] Flow rate: 1.0ml / min

[0050] Column temperature: 40°C

[0051] Sample: 3.0mg / 1.0ml THF

[0052] Standard material: Polystyrene

[0053] In the present specification, the relative weight average molecular weight and the differential molecular weight distribution pattern are measured by gel permeation chromatography (GPC) equipped with a differential refractive index detector (RI), and the gel permeation chromatography is measured under the following conditions.

[0054] Column: Two PLgel Olexis columns (Polymer Laboratories)

[0055] Solvent: Tetrahydrofuran (THF)

[0056] Flow rate: 0.3ml / min

[0057] Column temperature: 40°C

[0058] Sample: 1.5mg / 1.0ml THF

[0059] Standard material: Polystyrene

[0060] In this specification, the complex viscosity diagram for each frequency was measured using an advanced rheological expansion system (ARES, TA instruments). Using a parallel plate with a diameter of 25.0 mm and a gap of 1.0 mm and an angular frequency sweep mode, the sample was measured at 180 ° C, with a strain of 5% and a frequency of 0.1 rad / s to 500 rad / s. The van Gurp-Plamen diagram (vGP) was plotted using the values ​​determined by the frequency sweep mode measurement. In addition, the slope of the above figure was calculated by replacing the individual complex viscosity values ​​under the entire set frequency with logarithms and calculating the average of all X and Y values.

[0061] Branched polylactic acid polymer

[0062] The invention provides a branched polylactic acid polymer with improved melt strength and rheological properties by modifying the linear structure.

[0063] The branched polylactic acid polymer according to one embodiment of the present invention is characterized in that it contains derivative units from a polylactic acid polymer, and the average number of long-chain branches per molecule is 3 to 10, and the mass flow rate measured at 190°C and 2.16 kg load according to ASTM D1238 conditions is 1 g / 10 min to 20 g / 10 min.

[0064] Here, "per molecule" refers to each polymer chain constituting the branched polylactic acid polymer (ie, each chain).

[0065] Polylactic acid polymer is biodegradable, environmentally friendly material, can be used as the material of various films, fiber and other molded products, but has linear structure and is brittle, rheological characteristics (comprising melt strength) is lower, has remarkable restriction in blow molding process and injection molding process.In addition, because degree of crystallinity is lower, is not suitable for the purposes that thermal property and mechanical property are required higher.In order to address these problems, attempt polybutylene succinate (biodegradable resin of similar PLA) and thermotolerance higher resin (such as PP and PE) blend or copolymerization, or attempt to utilize chain extender or branching agent to introduce long chain side chain (LCB) to change linear structure and the property thereof of polylactic acid polymer in PLA, but there is the problem that compatibility is lower between resin, and effect is not obvious.

[0066] In addition, a polylactic acid resin having long chain branches introduced by reacting a polylactic acid polymer with an acrylate polymer or copolymer containing an epoxy group has been proposed, but there is a problem that the viscosity of the polylactic acid resin prepared by reacting with the acrylate polymer or copolymer increases significantly, making it difficult to control in the molding process, which greatly reduces the industrial application field of the polylactic acid resin. However, by using an acrylate copolymer containing an epoxy group prepared by polymerizing a first (meth) alkyl acrylate monomer, a glycidyl (meth) acrylate monomer, and a second (meth) alkyl acrylate monomer different from the first (meth) alkyl acrylate monomer as a branching agent, a long chain molecule is introduced into the polylactic acid polymer, and the branched polylactic acid polymer of the present invention is prepared, which can improve linearity without the problem of rapid viscosity increase, and due to the high reactivity of the epoxy group in the branching agent and the excellent miscibility with the polylactic acid resin, the melt strength and rheological properties are improved, so it can be used for a very wide range of purposes.

[0067] Hereinafter, the branched polylactic acid polymer of the present invention will be described in more detail by being divided into various components contained therein.

[0068] Derivative units from polylactic acid polymers

[0069] In the present invention, the derived unit from the polylactic acid polymer is derived from the polylactic acid polymer (and the polylactic acid polymer is the starting material constituting the branched polylactic acid polymer skeleton), for example, it can refer to the unit derived from the polylactic acid polymer in the branched polylactic acid polymer formed by reacting the polylactic acid polymer with the epoxy group-containing acrylate copolymer by the preparation method described later.

[0070] Polylactic acid polymers are thermoplastic polyesters obtained by polymerizing lactide or lactic acid, including 3 )]-structured repeating units of the polymer.

[0071] In addition, the polylactic acid polymer may also have repeating units derived from alkylene oxide, or repeating units derived from other monomers copolymerizable with lactide, in which case the repeating units derived from alkylene oxide and the repeating units derived from other monomers copolymerizable with lactide may be present in the form of blocks and / or random arrangement. In addition, if the polylactic acid polymer contains repeating units derived from alkylene oxide or repeating units derived from other monomers copolymerizable with lactide, the content may be 10% by weight or less, particularly 5% by weight or less.

[0072] In addition, the polylactic acid polymer may have a relative weight average molecular weight of 30,000 to 250,000 g / mol and a molecular weight distribution of 1.5 to 2.0 when measured by gel permeation chromatography using a polystyrene standard.

[0073] In another embodiment, the polylactic acid polymer can be selected and used according to the needs of the desired effect and purpose, and has a polymer with a suitable relative weight average molecular weight within the above range. For example, a polylactic acid polymer with a relatively low molecular weight can be selected and used, and its relative weight average molecular weight is 30000g / mol to 120000g / mol, and a polylactic acid polymer with a relatively high molecular weight can also be selected and used, and its relative weight average molecular weight is 120000g / mol to 250000g / mol.

[0074] Units derived from acrylate copolymers containing epoxy groups

[0075] The branched polylactic acid polymer of the present invention is characterized in that it further comprises a unit derived from an epoxy group-containing acrylic acid ester copolymer, wherein the epoxy group-containing acrylic acid ester copolymer contains 30 wt % to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0076] The derived unit from the epoxy group-containing acrylate copolymer in one embodiment of the present invention is derived from the epoxy group-containing acrylate copolymer, for example, may refer to the unit derived from the epoxy group-containing acrylate copolymer in the branched polylactic acid polymer formed by reacting the epoxy group-containing acrylate copolymer with a polylactic acid polymer by the preparation method described below.

[0077] The epoxy group-containing acrylic copolymer includes repeating units derived from a first alkyl (meth)acrylate monomer, repeating units derived from a glycidyl (meth)acrylate monomer, and repeating units derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer may be different from each other.

[0078] In particular, the epoxy group-containing acrylate copolymer may include 30 to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0079] In the above, the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer may independently be at least one selected from methyl (meth)acrylate, butyl (meth)acrylate and 2-ethylhexyl acrylate, in particular, the first alkyl (meth)acrylate monomer may be methyl methacrylate, and the second alkyl (meth)acrylate monomer may be butyl methacrylate.

[0080] In addition, the glycidyl (meth)acrylate monomer may be a glycidyl methacrylate monomer or a glycidyl acrylate monomer.

[0081] Branched polylactic acid polymer

[0082] The branched polylactic acid polymer of one embodiment of the present invention may contain 0.5 to 1.0 parts by weight of a derivative unit from an epoxy group-containing acrylate copolymer based on 100 parts by weight of the derivative unit from the polylactic acid polymer. In this case, the branched polylactic acid polymer containing the same may have uniform branching characteristics and will not cause the problem of gel formation due to branching.

[0083] In another embodiment, the branched polylactic acid polymer may have an average number of long chain branches per molecule of 3 to 10, and a mass flow rate of 1 to 20 g / 10 min measured under ASTM D1238 conditions at 190° C. and 2.16 kg load.

[0084] In another embodiment, the average number of long chain branches per molecule of the branched polylactic acid polymer may be 5 to 10, or 7 to 10, and the mass flow rate measured at 190° C. and 2.16 kg load according to ASTM D1238 conditions is 1 g / 10 min to 20 g / 10 min, 1 g / 10 min to 7 g / 10 min, or 7 g / 10 min to 20 g / 10 min.

[0085] In another embodiment, the branched polylactic acid polymer can satisfy the average number and mass flow rate of long chain branches within a certain range according to the molecular weight characteristics of the polylactic acid polymer constituting the polylactic acid polymer derived unit, but can show different mass flow rate characteristics. For example, in the case of a polylactic acid polymer derived unit containing a low molecular weight polylactic acid polymer, the mass flow rate can be 7g / 10 minutes to 20g / 10 minutes, and in the case of a polylactic acid polymer derived unit containing a high molecular weight polylactic acid polymer, the mass flow rate can be 1g / 10 minutes to 7g / 10 minutes.

[0086] In addition, the branched polylactic acid polymer may have an absolute weight average molecular weight of 100,000 to 1,500,000 g / mol and a polydispersity index of 2.0 to 3.5 when measured by multi-angle light scattering-gel permeation chromatography.

[0087] In another embodiment, the absolute weight average molecular weight characteristics measured by multi-angle light scattering-gel permeation chromatography can be different according to the molecular weight characteristics of the polylactic acid polymer constituting the derived units from the polylactic acid polymer. For example, in the case of the derived units from the polylactic acid polymer containing the polylactic acid polymer derived from low molecular weight, the absolute weight average molecular weight can be 100000g / mol to 500000g / mol, and the polydispersity index can be 2.0 to 3.5, and in the case of the derived units from the polylactic acid polymer containing the polylactic acid polymer derived from high molecular weight, the absolute weight average molecular weight can be 500000g / mol to 1500000g / mol, and the polydispersity index can be 2.0 to 3.5.

[0088] In another embodiment, the branched polylactic acid polymer may have two peaks on a differential molecular weight distribution graph measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight, the first peak (Pt 1 ) can be 0.8 to 1.2, the second peak (Pt 2 ) can be from 0.1 to 0.6.

[0089] In another embodiment, the first peak top (Pt 1 ) can be 1.0 to 1.2, the second peak (Pt 2 ) can be from 0.2 to 0.6.

[0090] In addition, the branched polylactic acid polymer can have two peaks on the differential molecular weight distribution diagram measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight. The first peak (Pt 1 ) can exist at 4.5≤log(M)≤5.8, the second peak (Pt 2 ) can exist in 5.8 <log(M)≤6.5。

[0091] In another embodiment, the slope of the complex viscosity (Pa.s) of the branched polylactic acid polymer at 180°C versus angular frequency (rad / s) may be -0.1 to -0.6 or -0.3 to -0.6. Here, the slope is calculated as the average of all X and Y values ​​by replacing each complex viscosity across the frequency with a logarithm.

[0092] Method for preparing branched polylactic acid polymer

[0093] The present invention provides a method for preparing a branched polylactic acid polymer.

[0094] The method for preparing a branched polylactic acid polymer according to an embodiment of the present invention is characterized in that it includes the step of mixing a polylactic acid polymer with an epoxy group-containing acrylic ester copolymer and heating at a temperature range of 180° C. to 200° C., wherein the epoxy group-containing acrylic ester copolymer is prepared by copolymerizing 30% to 50% by weight of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30% to 60% by weight of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10% to 20% by weight of a repeating unit derived from a second alkyl (meth)acrylate monomer in a solvent in the presence of an emulsifier, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0095] The specific description about the polylactic acid polymer starting material is the same as described above.

[0096] In addition, the polylactic acid polymer can be purchased and used according to methods generally known in the art, or it can be prepared and used. If it is prepared and used, the polylactic acid polymer can be prepared by a common polymerization method in the art using lactide or lactic acid as a monomer.

[0097] In addition, the epoxy group-containing acrylic acid ester copolymer can be prepared by polymerizing a first alkyl (meth)acrylate monomer, a glycidyl (meth)acrylate monomer, and a second alkyl (meth)acrylate monomer different from the first alkyl (meth)acrylate monomer in the presence of an emulsifier in a solvent, wherein the specific materials of the first alkyl (meth)acrylate monomer, the glycidyl (meth)acrylate monomer, and the second alkyl (meth)acrylate monomer are the same as described above.

[0098] Specifically, the epoxy group-containing acrylic acid ester copolymer can be prepared by polymerizing 30 to 50 wt % of a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a second alkyl (meth)acrylate monomer different from the first alkyl (meth)acrylate monomer in a solvent in the presence of an emulsifier, and in this case, the polymerization can be performed at 70 to 80° C. for 3 to 10 hours.

[0099] Furthermore, the polymerization may be carried out in an aqueous solvent, in which case the solvent is distilled water.

[0100] The emulsifier may be one or more selected from the group consisting of anionic emulsifiers, cationic emulsifiers and nonionic emulsifiers, for example, one or more selected from the group consisting of alkyl aryl sulfonates, alkali methyl alkyl sulfates, fatty acid soaps, oleic acid alkali salts, rosin acid alkali salts, lauric acid alkali salts, diethylhexyl sodium phosphate, phosphonated polyoxyethylene alcohols and phosphonated polyoxyethylene phenols. In addition, the emulsifier may be used in an amount of 5 parts by weight or less, particularly 3.0 parts by weight or less, or 0.5 to 2.5 parts by weight, based on 100 parts by weight of the total monomers.

[0101] In addition, the polymerization can be further carried out using a polymerization initiator. In this case, the initiator can use an inorganic peroxide or an organic peroxide, for example, a water-soluble polymerization initiator such as potassium persulfate, sodium persulfate and ammonium persulfate, and an oil-soluble polymerization initiator such as hydroxyisopropylbenzene peroxide and benzoyl peroxide.

[0102] In addition, an activator may be further used together with the polymerization initiator to promote the initiation of the peroxide reaction. Such an activator may be one or more selected from sodium formaldehyde sulfoxylate, sodium ethylenediaminetetraacetate, ferrous sulfate and glucose.

[0103] In addition, the polymerization initiator may be used in an amount of 0.1 to 10 parts by weight, for example, 0.1 to 5 parts by weight, based on 100 parts by weight of the total monomers.

[0104] In another embodiment, a chain transfer agent can be further used to improve the efficiency of the polymerization reaction. As the chain transfer agent, a straight or branched alkylthiol compound having 5 to 20 carbon atoms can be used. For example, one or more selected from hexylthiol, cyclohexylthiol, adamantanethiol, heptylthiol, octylthiol, nonylthiol, decanethiol, undecanethiol, dodecanethiol, hexadecylthiol and octadecylthiol can be used.

[0105] In addition, the chain transfer agent may be used in an amount of 0.1 parts by weight to 10 parts by weight, or 0.1 parts by weight to 5 parts by weight, based on 100 parts by weight of the monomer.

[0106] In addition, the epoxy group-containing acrylate copolymer can be prepared by further performing one or more steps selected from washing, dehydration and drying after polymerization. In this case, washing, dehydration and drying can be performed by methods generally known in the art.

[0107] Example

[0108] The present invention will be explained in more detail below with reference to Examples. However, the following Examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0109] Preparation Example

[0110] 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzene sulfonate (SDBS) were injected into the reactor and stirred, while the temperature was raised to 70°C. 0.2 parts by weight of potassium persulfate (KPS) was added thereto, stirred for 20 minutes, and a mixture of 45 parts by weight of methyl methacrylate, 40 parts by weight of glycidyl methacrylate, 15 parts by weight of butyl methacrylate and 0.7 parts by weight of 1-octanethiol was continuously added to the reactor within 4 hours. After the addition was completed, the temperature was lowered to 25°C and stirred for 30 minutes to prepare an emulsion polymerization latex. The prepared emulsion polymerization latex was coagulated with an aqueous potassium acetate solution, the temperature was raised to 90°C, dehydrated, and dried at 60°C for 16 hours to prepare an acrylate copolymer containing epoxy groups.

[0111] Comparative Preparation Example

[0112] 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzene sulfonate (SDBS) were injected into the reactor and stirred, while the temperature was raised to 70°C. 0.2 parts by weight of potassium persulfate (KPS) was added thereto, stirred for 20 minutes, and a mixture of 65 parts by weight of methyl methacrylate, 20 parts by weight of glycidyl methacrylate, 15 parts by weight of butyl methacrylate and 0.7 parts by weight of 1-octanethiol was continuously added to the reactor within 4 hours. After the addition was completed, the temperature was lowered to 25°C and stirred for 30 minutes to prepare an emulsion polymerization latex. The prepared emulsion polymerization latex was coagulated with an aqueous potassium acetate solution, the temperature was raised to 90°C, dehydrated, and dried at 60°C for 16 hours to prepare an acrylate copolymer containing epoxy groups.

[0113] Example 1

[0114] A polylactic acid polymer (4032D, Mw=214900 g / mol, Natureworks) was prepared by drying at 80° C. for 24 hours.

[0115] 100 parts by weight of the polylactic acid polymer thus prepared was mixed with 0.5 parts by weight of the copolymer prepared in Preparation Example to prepare a mixture, and then blended at 180° C. at 60 rpm for 10 minutes using a mixer (Lab batch mixer) to prepare a branched polylactic acid polymer.

[0116] Example 2

[0117] A branched polylactic acid polymer was prepared in the same manner as in Example 1, except that 1.0 part by weight of the copolymer prepared in Preparation Example was used in Example 1.

[0118] Example 3

[0119] A branched polylactic acid polymer was prepared in the same manner as in Example 1, except that 0.75 parts by weight of the copolymer prepared in Preparation Example was used in Example 1.

[0120] Comparative Example 1

[0121] The polylactic acid polymer (4032D, Natureworks) was dried at 80° C. for 24 hours and used as comparative data for the non-branched polylactic acid polymer.

[0122] Comparative Example 2

[0123] In Example 1, a branched polylactic acid polymer was prepared in the same manner as in Example 1, except that 4368 (Mn=2000 g / mol, 7 epoxy groups per molecule on average), rather than the copolymer prepared in Preparation Example.

[0124] Comparative Example 3

[0125] In Example 1, a branched polylactic acid polymer was prepared in the same manner as in Example 1, except that the copolymer prepared in Comparative Preparation Example was used in Example 1 instead of the copolymer prepared in Preparation Example.

[0126] Experimental Example 1

[0127] The molecular weight characteristics and rheological properties of various branched or unbranched polylactic acid polymers prepared in the examples and comparative examples were compared and analyzed. The results are shown in Tables 1 and Figures 1 to 6 shown.

[0128] (1) Molecular weight characteristics

[0129] The relative molecular weight characteristics of gel permeation chromatography (GPC) analysis using polystyrene as standard material were compared with those of multi-angle light scattering-gel permeation chromatography (MALS-GPC) analysis.

[0130] 1) Relative molecular weight characteristics

[0131] Regarding the relative molecular weight characteristics, the weight average molecular weight, the number average molecular weight and the molecular weight distribution were determined by measuring a molecular distribution chart obtained by using gel permeation chromatography (GPC) equipped with a differential refractive index detector (RI) under the following conditions.

[0132] In addition, the differential molecular weight distribution diagram (see Figure 1 ) to confirm the peak top characteristics. The figure is the differential of the concentration fraction w and the logarithmic molecular weight, where the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M).

[0133] Column: Two PLgel Olexis columns (Polymer Laboratories)

[0134] Solvent: Tetrahydrofuran (THF)

[0135] Flow rate: 0.3ml / min

[0136] Column temperature: 40°C

[0137] Sample: 1.5mg / 1.0ml THF

[0138] Standard material: Polystyrene

[0139] 2) Multi-angle light scattering-gel permeation chromatography

[0140] The analysis was performed using a Viscotek VE2001 GPC / SEC system equipped with a Viscotek TDA305 triple detector array module (light scattering, viscometer and refractive index detector) under the following conditions, and all the result data were calculated using OmniSEC version 4.7 software.

[0141] Column: Two Plgel mixed-B columns (Agilent)

[0142] Solvent: Tetrahydrofuran (THF)

[0143] Flow rate: 1.0ml / min

[0144] Column temperature: 40°C

[0145] Sample: 3.0mg / 1.0ml THF

[0146] Standard material: Polystyrene

[0147] (2) Rheological properties

[0148] The rheological properties were compared by measuring complex viscosity, storage modulus and vGP plots (van Gurp-Palmen) using a viscometer.

[0149] In particular, the measurement was performed using an Advanced Rheological Dilatation System (ARES, TA instruments). The sample was measured at 180°C using parallel plates with a diameter of 25.0 mm, so that the gap was 1.0 mm, and the measurement was performed in angular frequency sweep mode with a strain of 5% and a frequency of 0.1 rad / s to 500 rad / s. The values ​​determined by the frequency sweep mode measurement were plotted as vGP (van Gurp-Plamen diagram) (see Figure 6 ). In addition, the slope of the complex viscosity plot is calculated as the average of all X and Y values ​​by replacing the individual complex viscosities across a set frequency with their logarithms.

[0150] (3) Mass flow rate (MFR)

[0151] The measurement was carried out according to ASTM D1238 conditions at 190°C and a load of 2.16 kg using MI-4 (Gottfer Company).

[0152] [Table 1]

[0153]

[0154] In Table 1 above, Bn represents the average number of long-chain branches per molecule, and the slope represents the Mark-Houwink slope, with smaller values ​​indicating a higher degree of branching.

[0155] It can be confirmed from Table 1 that the branched polylactic acid polymers of Examples 1 to 3 meet the requirements of the present invention that the average number of long chain fractions per molecule is 3 to 10, and the MFR is 1 g / 10 min to 20 g / 10 min. In addition, it can be confirmed that Examples 1 to 3 are prepared using polylactic acid polymers having a relatively high molecular weight, and the average number of long chain branches per molecule is 3 to 10, and the MFR is 1 g / 10 min to 7 g / 10 min.

[0156] In contrast, the unbranched or branched polylactic acid polymers in Comparative Examples 1 to 3 cannot satisfy the average number of long chain branches per molecule of 3 to 10, or cannot satisfy the MFR requirement of 1 to 20 g / 10 min.

[0157] Experimental Example 2

[0158] Blown films were manufactured using the branched or unbranched polylactic acid polymers prepared in Examples and Comparative Examples to confirm the properties of the blown films. The results are shown in Table 2 below.

[0159] The blown film was made by molding the above-mentioned various polymers into a thickness of 0.08 mm using a single screw extruder (Collin Lab & Pilot Solutions, Blown Film Line E Entranc, Blown Film M / C, 19 pi, L / D = 25) at an extrusion temperature of 210° C. to 220° C. In this case, the blow ratio of the film was about 1.8.

[0160] The processability of blown films is compared by the pressure (bar) value measured at the exit from the die. The higher the viscosity of the extruded pellets after processing or the lower the degree of branching, the higher the pressure value. This means that the lower the pressure value, the better the processability.

[0161] [Table 2]

[0162]

[0163] It can be confirmed from Table 2 that the branched polylactic acid polymers of Examples 1 to 3 have an average number of long chain branches per molecule of 3 to 10 and an MFR of 1 g / 10 min to 20 g / 10 min, and have better blown film processability than Comparative Examples 1 to 3.

[0164] In particular, it can be confirmed that, in the case of Comparative Example 1, both the average number of long-chain branches per molecule and the MFR did not meet the requirements, and the blown film processability was significantly reduced to about 81% to 90% compared with Examples 1 to 3; in the case of Comparative Example 2, although the above-mentioned condition of the average number of long-chain branches per molecule was met, the MFR was low, and the blown film processability was significantly deteriorated to about 63% to 70% compared with Examples 1 to 3, and in Comparative Example 3, although the MFR requirement was met, the above-mentioned condition of the average number of long-chain branches per molecule was not met, and the blown film processability was reduced to about 85% to 95% compared with Examples 1 to 3.

Claims

1. A branched polylactic acid polymer comprising a derivative unit from a polylactic acid polymer, wherein: The average number of long chain branches per molecule is from 3 to 10, and The mass flow rate measured according to ASTM D1238 conditions at 190° C. and a load of 2.16 kg is 1 g / 10 minutes to 20 g / 10 minutes.

2. The branched polylactic acid polymer according to claim 1, wherein Also comprises units derived from an acrylate copolymer containing epoxy groups, and The epoxy group-containing acrylic copolymer comprises 30 to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, wherein the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

3. The branched polylactic acid polymer according to claim 2, wherein The unit derived from the epoxy group-containing acrylate copolymer may be included in an amount of 0.5 to 1.0 parts by weight based on 100 parts by weight of the unit derived from the polylactic acid polymer.

4. The branched polylactic acid polymer according to claim 2, wherein The epoxy group-containing acrylate copolymer has 30 to 80 epoxy groups per molecule.

5. The branched polylactic acid polymer according to claim 2, wherein The first (meth)acrylic acid alkyl ester monomer and the second (meth)acrylic acid alkyl ester monomer are each independently at least one or more selected from the group consisting of methyl (meth)acrylate, butyl acrylate and 2-ethylhexyl acrylate, and The first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

6. The branched polylactic acid polymer according to claim 1, wherein The polylactic acid polymer has a weight average molecular weight of 30,000 to 250,000 g / mol as measured by gel permeation chromatography using polystyrene standards.

7. The branched polylactic acid polymer according to claim 1, wherein When measured by multi-angle light scattering-gel permeation chromatography, the branched polylactic acid polymer has an absolute weight average molecular weight of 100,000 g / mol to 1,500,000 g / mol, and a polydispersity index of 2.0 to 3.

5.

8. The branched polylactic acid polymer according to claim 1, wherein The branched polylactic acid polymer has two peaks on the differential molecular weight distribution diagram measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight. The first peak (Pt1) is 0.8 to 1.2, and The second peak top (Pt2) is 0.1 to 0.

6.

9. The branched polylactic acid polymer according to claim 1, wherein The branched polylactic acid polymer has two peaks on the differential molecular weight distribution diagram measured by gel permeation chromatography using a polystyrene standard, wherein the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), i.e., the differential of the concentration fraction w and the logarithmic molecular weight. The first peak (Pt1) exists at 4.5≤log(M)≤5.8, and The second peak (Pt2) exists at 5.8 <log(M)≤6.5。 10. The branched polylactic acid polymer according to claim 1, wherein At 180°C, the slope of the complex viscosity (Pa.s) versus angular frequency (rad / s) is -0.1 to -0.

6.

11. A method for preparing a branched polylactic acid polymer, the method comprising: a step of mixing a polylactic acid polymer with an acrylate copolymer containing an epoxy group and heating the mixture at a temperature ranging from 180° C. to 200° C., The epoxy group-containing acrylic acid ester copolymer is prepared by polymerizing 30 wt % to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer in a solvent in the presence of an emulsifier, and The first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

12. The method for preparing a branched polylactic acid polymer according to claim 11, wherein: The epoxy group-containing acrylate copolymer is used in an amount of 0.5 to 1.0 parts by weight based on 100 parts by weight of the polylactic acid polymer.

13. The method for preparing a branched polylactic acid polymer according to claim 11, wherein: The epoxy group-containing acrylate copolymer has 30 to 80 epoxy groups per molecule.

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