Copolyesters, modified polylactic acid, and methods of making and using the same

Abstract

The application relates to the field of high polymer chemical industry and discloses a copolyester, modified polylactic acid and a preparation method and application thereof. The copolyester has a tensile strength increased by 5-50% and an elongation at break increased by 5-42% after being irradiated by a 500W ultraviolet lamp with a wavelength of 365nm at a temperature of 60 DEG C. The preparation method of the copolyester comprises the following steps: (1) mixing a dibasic acid monomer, a dibasic alcohol monomer, modified monomer I with a structure shown in formula (I), modified monomer II with a structure shown in formula (II) and a polymerization inhibitor under esterification reaction conditions to carry out a first-stage reaction to obtain a prepolymer; and (2) mixing the prepolymer with a catalyst under polycondensation reaction conditions to carry out a second-stage reaction. The copolyester has excellent mechanical properties and good biodegradability.

Description

Technical Field

[0001] This invention relates to the field of polymer chemistry, specifically to a copolyester, modified polylactic acid, its preparation method, and its application. Background Technology

[0002] Thermoplastic elastomers (TPEs) are polymeric materials that combine the thermoplasticity of plastics with the elasticity of rubber. Unlike traditional rubber, they do not require cross-linking and vulcanization; they exhibit rubber-like elasticity at room temperature and can be plasticized and molded at high temperatures. Thermoplastic elastomers possess superior mechanical properties, high flexibility at low temperatures, excellent weather resistance, and are very easy to process. They can be directly processed using injection molding machines or extruders, resulting in high production efficiency and facilitating cost control for factories. Therefore, thermoplastic elastomers are currently widely used in medical, food, footwear, and wire and cable industries.

[0003] Traditional thermoplastic elastomers are typically saturated olefins, polyurethanes, etc. These materials generally have properties that are difficult to alter by changing the polymer molecular chain structure, which is usually determined by the polymer molecular chain structure. Thermoplastic polyester elastomers (TPEEs) are a class of linear polymers containing polybutylene terephthalate (PBT). Polybutylene terephthalate-butylene adipate (PBAT) and polybutylene succinate-co-butylene terephthalate (PBST) are both copolymerized from PBT. Their advantage lies in the ability to adjust the mechanical properties of the polymer by regulating the PBT content, thereby giving the polymer good ductility, elongation at break, heat resistance, and impact resistance. Both copolyesters use PBT as a hard segment, and the crystallization of PBT improves the heat resistance and rigidity of the copolyester. However, PBT is a non-degradable polymer, which significantly reduces the biodegradability of the copolyester.

[0004] Therefore, there is an urgent need to provide a copolyester that can ensure the biodegradability of the copolyester while also improving its mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that improving the mechanical properties of copolyesters through modification in the prior art leads to a decrease in their biodegradability. This invention provides a copolyester, modified polylactic acid, its preparation method, and its application. This copolyester has excellent mechanical properties and good biodegradability.

[0006] To achieve the above objectives, the first aspect of the present invention provides a copolyester, wherein the tensile strength of the copolyester is increased by 5-50% and the elongation at break is increased by 5-42% after being irradiated with an ultraviolet lamp with a power of 500W and a wavelength of 365nm at a temperature of 60°C.

[0007] A second aspect of the present invention provides a method for preparing a copolyester, the method comprising the following steps:

[0008] (1) Under esterification reaction conditions, a diacid monomer, a diol monomer, a modified monomer I having the structure shown in formula (I), a modified monomer II having the structure shown in formula (II) and a polymerization inhibitor are mixed and subjected to a first-stage reaction to obtain a prepolymer.

[0009]

[0010] Among them, R I R II R III R IV R V and R VI Each is independently selected from hydrogen or C1-C4 alkyl groups, m, p and q are each independent integers from 0 to 3, and n is an integer from 10 to 200;

[0011] (2) Under polycondensation reaction conditions, the prepolymer is mixed with the catalyst to carry out the second stage reaction.

[0012] The third aspect of the present invention provides the application of the copolyester described in the first aspect and / or the copolyester obtained by the preparation method described in the second aspect in the preparation of modified polylactic acid.

[0013] A fourth aspect of the present invention provides a modified polylactic acid, the preparation method of which includes: mixing the copolyester described in the first aspect or the copolyester obtained by the preparation method described in the second aspect with polylactic acid.

[0014] The beneficial effects of the present invention through the above technical solution are as follows:

[0015] The copolyester provided by this invention possesses excellent mechanical properties as well as good biodegradability. Especially when applied to modified polylactic acid (PLA), it significantly improves the impact strength and elongation at break of PLA without affecting its degradation rate. The preparation method of the copolyester provided by this invention modifies the copolyester using a modifying monomer I having the structure shown in formula (I) and a modifying monomer II having the structure shown in formula (II), enabling the prepared copolyester to undergo vulcanization to form a cross-linked network structure, thereby improving the mechanical and biodegradability of the copolyester. Furthermore, the process route for this copolyester is simple and easily facilitates continuous industrial production.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0017] Figure 1This is a synthetic route diagram of the copolyester having the structure shown in formula (VII) in this invention;

[0018] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the copolyester obtained in Example 3 of the present invention;

[0019] Figure 3 This is the Fourier transform infrared spectrum of the copolyester obtained in Example 3 of the present invention;

[0020] Figure 4 This is the differential scanning calorimetry (DSC) curve of the copolyester obtained in Example 3 of the present invention. Detailed Implementation

[0021] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] During the research process, the inventors of this invention unexpectedly discovered that adding modified monomer I with the structure shown in formula (I) and modified monomer II with the structure shown in formula (II) during the preparation of copolyester can enable the copolyester to have excellent mechanical properties as well as good biodegradability. In particular, when applied to modified polylactic acid, it can significantly improve the impact strength and elongation at break of modified polylactic acid without affecting the degradation rate of modified polylactic acid.

[0024] The first aspect of the present invention provides a copolyester, wherein the tensile strength of the copolyester is increased by 5-50% and the elongation at break is increased by 5-42% after being irradiated with an ultraviolet lamp with a power of 500W and a wavelength of 365nm at a temperature of 60°C.

[0025] In this invention, the tensile strength and elongation at break of the copolyester are tested according to the "Standard Test Method for Tensile Properties of Plastics" (ASTM / D638-91).

[0026] In this invention, the specific process of irradiating the copolyester with ultraviolet light includes: placing the copolyester in a flat vulcanizing machine, pressing it at 150°C to form a dumbbell-shaped sample with a thickness of 0.5 mm, placing the sample on a hot table at 60°C, and irradiating it with an ultraviolet light of 500W with a wavelength of 365nm for 7 minutes to obtain a photocrosslinked sample.

[0027] The copolyester provided by this invention has strong tensile strength and large elongation at break while ensuring biodegradability. Its mechanical properties can be improved after exposure to ultraviolet light. This copolyester is a thermoplastic elastomer.

[0028] When the copolyester provided by this invention is applied to modified polylactic acid, mixing the copolyester with modified polylactic acid can not only significantly improve the impact strength and elongation at break of the modified polylactic acid, but also does not affect the degradation rate of the modified polylactic acid.

[0029] According to the present invention, preferably, the tensile strength of the copolyester is increased by 37-50% and the elongation at break is increased by 28-42% after being irradiated with an ultraviolet lamp with a power of 500W and a wavelength of 365nm at a temperature of 60°C.

[0030] According to the present invention, preferably, the copolyester has a tensile strength of 20-27 MPa and an elongation at break of 400-600%.

[0031] According to the present invention, preferably, the copolyester contains structural unit (A) of formula (I) and structural unit (B) of formula (II);

[0032]

[0033] Among them, R I R II R III R IV R V and R VI Each of the components is independently selected from hydrogen or C1-C4 alkyl groups, m, p, and q are each independently integers from 0 to 3, and n is an integer from 10 to 200. The inventors have discovered that, under this preferred embodiment, the copolyester having structural unit (A) and structural unit (B) has better flexibility and lower crystallinity, and also exhibits excellent mechanical properties.

[0034] In this invention, R I R II R III R IV R V and R VIEach of these can be independently hydrogen, hydroxyl, straight-chain alkyl, or cycloalkyl, specifically methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, tert-butyl, or other feasible C1-C4 alkyl groups. Preferably, R I R II R III R IV R V and R VI Both can be hydrogen.

[0035] According to the present invention, in the copolyester, the content of the structural unit (A) is 8-60% by weight, and the content of the structural unit (B) is 1-10% by weight.

[0036] In this invention, the content of structural unit (A) and structural unit (B) in the copolyester can be obtained by nuclear magnetic resonance spectroscopy.

[0037] According to the present invention, the copolyester comprises a polyester segment and a polyether segment. The polyether segment is obtained by self-polymerization of an epoxy compound containing 2-4 carbon atoms. The polyether segment contains the above-mentioned structural unit (A). For example, the polyether segment can be a segment formed from at least one of polyethylene glycol, poly1,2-propylene glycol, poly1,3-propylene glycol, and polytetrahydrofuran. The polyester segment is obtained by polymerization of C2-C6 aliphatic diols and diacids. For example, the C2-C6 aliphatic diol is 1,4-butanediol, and the diacid is succinic acid and fumaric acid.

[0038] In this invention, the melting and crystallization temperatures of the polyester and polyether segments of the copolyester are measured using a differential scanning calorimeter, with a heating / cooling rate of 10°C / min, and a single cooling curve and a double heating curve are selected.

[0039] A second aspect of the present invention provides a method for preparing a copolyester, the method comprising the following steps:

[0040] (1) Under esterification reaction conditions, a diacid monomer, a diol monomer, a modified monomer I having the structure shown in formula (I), a modified monomer II having the structure shown in formula (II) and a polymerization inhibitor are mixed and subjected to a first-stage reaction to obtain a prepolymer.

[0041]

[0042] Among them, R I R II R III R IV R V and R VI Each is independently selected from hydrogen or C1-C4 alkyl groups, m, p and q are each independent integers from 0 to 3, and n is an integer from 20 to 200;

[0043] (2) Under polycondensation reaction conditions, the prepolymer is mixed with the catalyst to carry out the second stage reaction.

[0044] According to the present invention, the preparation method of the copolyester is simple and suitable for industrial production.

[0045] According to the present invention, R I R II R III R IV R V and R VI Each of them can be hydrogen, hydroxyl, straight-chain alkyl or cycloalkyl, specifically methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, tert-butyl or other feasible C1-C4 alkyl.

[0046] According to the present invention, in the modified monomer I having the structure shown in formula (I), when R I and R II When both are hydrogen and m is 1, the modified monomer I is polyethylene glycol; when R I For hydrogen, R II When methyl is present and m is 1, the modified monomer I is poly1,2-propanediol; when R... I and R II When both are hydrogen and m is 2, the modified monomer I is poly1,3-propanediol; when R I and R II When all monomers are hydrogen and m is 3, the modified monomer I is polytetrahydrofuran. Preferably, the modified monomer I is polyethylene glycol.

[0047] According to the present invention, preferably, the modified monomer I is selected from at least one of PEG1000, PEG2000, PEG4000, PEG6000 and PEG10000, and more preferably PEG6000.

[0048] According to the present invention, modified monomer II is a compound represented by formula (III);

[0049]

[0050] Among them, R VII It is hydrogen or a C1-C4 alkyl group.

[0051] In this invention, in the compound represented by formula (III), when R VII When hydrogen, p, and q are all 0, the modified monomer II is fumaric acid; when R VII When methyl, p, and q are all 0, the modified monomer II is dimethyl fumarate; when R III R IV and R VIIWhen all atoms are hydrogen, p is 1, and q is 0, the modified monomer II is gluconic acid; when R... III R IV and R VII When all atoms are hydrogen, p is 2, and q is 0, the modified monomer II is 2-hexenedioic acid; when R III R IV R V R VI and R VII When both monomers are hydrogen, p is 2, and q is 2, the modified monomer II is (E)-oct-4-ene-1,8-diacid. Preferably, the modified monomer II is fumaric acid.

[0052] According to the present invention, the diacid monomer can be any diacid different from the modified monomer II, and the diol monomer can be any diol different from the modified monomer I. Preferably, the diacid monomer is a C2-C6 aliphatic diacid, such as oxalic acid, malonic acid, succinic acid, glutaric acid, or adipic acid; and the diol monomer is a C2-C6 aliphatic diol, such as ethylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, or 1,6-hexanediol.

[0053] According to the present invention, in order to further improve the mechanical properties of the copolyester, preferably, the ratio of the total molar amount of the dicarboxylic acid monomer and modified monomer II to the total molar amount of the diol monomer and modified monomer I is 1:1-1.2, more preferably 1:1.01-1.05.

[0054] According to the present invention, in order to further improve the mechanical properties of the copolyester, preferably, the weight ratio of the modified monomer I to the diol monomer is 0.2-2.8:1, more preferably 0.4-1.3:1.

[0055] According to the present invention, in order to further improve the mechanical properties of the copolyester, preferably, the weight ratio of the modified monomer II to the dicarboxylic acid monomer is 1:2-20, and more preferably 1:8-10.

[0056] According to the present invention, the addition of a polymerization inhibitor in the first stage of the reaction can prevent polymerization between monomers from occurring before the required degree of esterification is reached during the esterification reaction, thereby improving the efficiency of the esterification reaction and the yield of the product. Preferably, the polymerization inhibitor is selected from at least one of ether-based polymerization inhibitors, phenol-based polymerization inhibitors, quinone-based polymerization inhibitors, and aromatic amine-based polymerization inhibitors; more preferably, the polymerization inhibitor is an ether-based polymerization inhibitor. Specifically, the ether-based polymerization inhibitor is p-hydroxyanisole.

[0057] In this invention, the content of the polymerization inhibitor can be selected according to the performance requirements of the copolyester. Preferably, the amount of polymerization inhibitor added is 0.5-3g relative to the total weight of 100g of copolyester raw material, specifically 0.5g, 1.5g, 3g, or any value between the two aforementioned values.

[0058] According to the present invention, preferably, the catalyst is tetrabutyl titanate and / or stannous octoate, more preferably tetrabutyl titanate.

[0059] In this invention, the content of the catalyst can be selected according to the performance requirements of the copolyester. Preferably, the amount of catalyst added is 0.1-1g relative to the total weight of 100g of copolyester raw material, specifically 0.1g, 0.5g, 1.0g, or any value between the two aforementioned values.

[0060] In this invention, the above-mentioned dicarboxylic acid monomer, diol monomer, modified monomer I, modified monomer II, polymerization inhibitor and catalyst can all be obtained commercially or prepared by means of methods disclosed in the prior art.

[0061] According to the present invention, in order to further improve the reaction rate and product yield of the first-stage reaction, preferably, the conditions of the esterification reaction include at least: isolation from oxygen; a temperature of 185-195°C, specifically 185°C, 190°C, 195°C, or any value between the two aforementioned values; and a time of 2-6 hours, specifically 2 hours, 4 hours, 6 hours, or any value between the two aforementioned values. Isolation from oxygen can be achieved by introducing an inert gas such as nitrogen or helium into the reaction system; specifically, nitrogen is used as the inert gas.

[0062] In this invention, the first stage reaction is carried out under stirring conditions. There is no particular limitation on the stirring rate, which can be determined by the experimenter based on the actual situation.

[0063] In this invention, the experimenter can determine the conditions for the end of the first-stage reaction based on the actual situation, for example, based on the amount of water in the product. Preferably, the conditions for the end of the first-stage reaction process also include: the amount of water produced is 70-90% of the theoretical amount of water, specifically 70%, 80%, 90%, or any value between the two aforementioned values.

[0064] According to the present invention, preferably, the conditions for the polycondensation reaction include at least the following: a temperature of 200-230°C, specifically 200°C, 210°C, 220°C, 230°C, or any value between the two aforementioned values; a vacuum degree of 0-50 Pa, specifically 0 Pa, 10 Pa, 20 Pa, 30 Pa, 40 Pa, 50 Pa, or any value between the two aforementioned values; and a time of 2-4 h, specifically 2 h, 3 h, 4 h, or any value between the two aforementioned values.

[0065] In this invention, the experimenters can also determine the conditions for the termination of the second-stage reaction process based on actual conditions. Preferably, the conditions for the termination of the second-stage reaction process further include: the product exhibiting a climbing effect. The inventors have found that, under this preferred embodiment, the product of the esterification reaction has a better polycondensation effect, improving the structural and performance stability of the copolyester.

[0066] According to the present invention, by way of example, when the dicarboxylic acid monomer is succinic acid, the diol monomer is 1,4-butanediol, the modified monomer I is PEG6000, and the modified monomer II is fumaric acid, in step (1), under the conditions of esterification reaction, succinic acid, fumaric acid, 1,4-butanediol and PEG6000 undergo esterification reaction, and the resulting prepolymer contains structural unit (a) of formula (IV), structural unit (b) of formula (V) and structural unit (c) of formula (VI):

[0067]

[0068] In this invention, under polycondensation reaction conditions, the prepolymer containing structural units (a), (b), and (c) is mixed with a catalyst to carry out a second-stage reaction, which can yield copolyesters with various structures. For example, a copolyester with the structure shown in formula (VII) can be obtained:

[0069]

[0070] Where w is 5-30, x is 0.075-2.5, y is 70-95, and z is 1.75-7.125.

[0071] The inventors discovered that by introducing the highly flexible polyethylene glycol into the molecular chain of polybutylene succinate / fumarate (PBSF), with the PBSF segment as the hard segment and the PBS segment as the soft segment, a new copolyester with better overall performance can be obtained compared to PBS, exhibiting better flexibility and lower crystallinity; and compared to PEG, it has better mechanical strength. By adjusting the content of PBSF and PEG, a new copolyester with better overall performance can be obtained.

[0072] The synthetic route diagram of the copolyester with the structure shown in formula (VII) is as follows: Figure 1 As shown, in this copolyester, fumaric acid creates unsaturated double bonds on the molecular chain, providing conditions for chain extension. Fumaric acid can form cocrystals with PBS and its copolymers, and the resulting copolyester achieves strict co-constitution.

[0073] The third aspect of the present invention provides the application of the copolyester described in the first aspect and / or the copolyester obtained by the preparation method described in the second aspect in the preparation of modified polylactic acid.

[0074] In this invention, when the above-mentioned copolyester is used as a toughening agent in modified polylactic acid, the mechanical properties of the modified polylactic acid can be significantly improved without affecting its degradation performance.

[0075] A fourth aspect of the present invention provides a modified polylactic acid, the preparation method of which includes: mixing the copolyester described in the first aspect or the copolyester obtained by the preparation method described in the second aspect with polylactic acid.

[0076] The modified polylactic acid provided by this invention is achieved by mixing copolyester and polylactic acid. During the mixing process, the copolyester can self-vulcanize to form a cross-linked network structure, which reacts with polylactic acid to generate a grafted polymer, greatly improving the compatibility between the two. This, in turn, improves the impact strength and elongation at break of the modified polylactic acid, without affecting its degradation rate.

[0077] The present invention does not impose any particular limitation on the weight ratio of copolyester to polylactic acid. Specifically, the weight ratio of the copolyester to the polylactic acid is 1:4.

[0078] According to the present invention, the modified polylactic acid can be prepared by mixing a copolyester and polylactic acid in a conventional manner. Specifically, the mixing conditions include: a temperature of 180°C, a rotation speed of 50 rpm, and a mixing time of 5 min.

[0079] According to the present invention, preferably, the modified polylactic acid has an elongation at break of 250-350% and a notched impact strength of 40-60 kJ / m. 2 .

[0080] In this invention, the elongation at break of modified polylactic acid is tested according to ASTM / D638-91 Standard Test Method for Tensile Properties of Plastics; the notched impact strength of modified polylactic acid is tested according to ASTM D256 Standard Test Method for Determination of the Shock Resistance of Plastics.

[0081] According to a particularly preferred embodiment of the present invention, a method for preparing a copolyester is provided, the method comprising the following steps:

[0082] (1) After mixing succinic acid, 1,4-butanediol, polyethylene glycol, fumaric acid and p-hydroxyanisole, esterification reaction was carried out under nitrogen atmosphere and temperature of 185-195℃ for 2-6 hours.

[0083] (2) The product of the esterification reaction obtained in step (1) is mixed with tetrabutyl titanate and polycondensed at a temperature of 200-230℃ and a vacuum of 0-50Pa for 2-4 hours to obtain a copolyester.

[0084] The polyethylene glycol has a molecular weight of 6000; the ratio of the total molar amount of succinic acid and fumaric acid to the total molar amount of 1,4-butanediol and polyethylene glycol is 1:1.01-1.05; the weight ratio of polyethylene glycol to 1,4-butanediol is 0.4-1.3:1; and the weight ratio of fumaric acid to succinic acid is 1:8-10. Relative to the total weight of 100g of copolyester raw materials, the amount of p-hydroxyanisole is 0.5-3g, and the amount of tetrabutyl titanate is 0.1-1g.

[0085] In the preferred embodiments described above, the prepared copolyester has excellent mechanical properties. In particular, when the copolyester is applied to modified polylactic acid, it can significantly improve the impact strength and elongation at break of the modified polylactic acid, while not affecting its degradation rate. It has significant market prospects and environmental benefits.

[0086] The present invention will be described in detail below with reference to embodiments, but this does not limit the scope of the invention.

[0087] In the following examples and comparative examples, fumaric acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99.5%; polyethylene glycol (Mn=6000) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; polylactic acid was purchased from Nature Works, Inc., USA, model 4032D; and other raw materials were all commercially available.

[0088] The tensile strength and elongation at break were tested in accordance with the "Standard Test Method for Tensile Properties of Plastics" (ASTM / D638-91).

[0089] The melting temperature and crystallization temperature were tested using a differential scanning calorimeter.

[0090] The notched impact strength was tested according to ASTM D256, "Standard Test Method for Determining the Impact Resistance of Plastics".

[0091] Example 1

[0092] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 21.697 g of succinic acid, 2.370 g of fumaric acid, 18.925 g of 1,4-butanediol, 8.600 g of polyethylene glycol (Mn = 6000), and 0.516 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.258 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0093] Example 2

[0094] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 22.023 g of succinic acid, 2.405 g of fumaric acid, 18.925 g of 1,4-butanediol, 14.743 g of polyethylene glycol (Mn = 6000), and 0.581 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.290 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0095] Example 3

[0096] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 22.461 g of succinic acid, 2.453 g of fumaric acid, 18.925 g of 1,4-butanediol, 22.933 g of polyethylene glycol (Mn = 6000), and 0.668 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.334 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0097] The proton NMR spectrum of the copolyester prepared in Example 3 is shown below. Figure 2 As shown, the Fourier transform infrared spectrum is as follows: Figure 3 As shown, the differential scanning calorimetry curve is as follows: Figure 4 As shown.

[0098] Example 4

[0099] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 19.624 g of succinic acid, 2.453 g of fumaric acid, 17.601 g of 1,4-butanediol, 7.750 g of polyethylene glycol (Mn = 6000), and 0.468 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.334 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0100] Example 5

[0101] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 24.53 g of succinic acid, 2.453 g of fumaric acid, 20.852 g of 1,4-butanediol, 25.823 g of polyethylene glycol (Mn = 6000), and 0.468 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.334 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0102] Example 6

[0103] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 22.826 g of succinic acid, 1.204 g of fumaric acid, 18.925 g of 1,4-butanediol, 3.820 g of polyethylene glycol (Mn = 1000), and 0.468 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.234 g of tetrabutyl titanate catalyst was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0104] Example 7

[0105] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 23.067 g of succinic acid, 2.520 g of fumaric acid, 18.925 g of 1,4-butanediol, 34.400 g of polyethylene glycol (Mn = 6000), and 0.534 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.267 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0106] Example 8

[0107] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 23.980 g of succinic acid, 2.619 g of fumaric acid, 18.925 g of 1,4-butanediol, 51.600 g of polyethylene glycol (Mn = 6000), and 0.971 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.486 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0108] Example 9

[0109] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 23.672 g of succinic acid, 2.586 g of fumaric acid, 18.925 g of 1,4-butanediol, 22.933 g of polyethylene glycol (Mn = 2000), and 0.681 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.341 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0110] Example 10

[0111] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 22.461 g of succinic acid, 2.453 g of fumaric acid, 18.925 g of 1,4-butanediol, 22.933 g of polyethylene glycol (Mn = 4000), and 0.668 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.334 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0112] Example 11

[0113] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 22.461 g of succinic acid, 2.453 g of fumaric acid, 18.925 g of 1,4-butanediol, 22.933 g of polyethylene glycol (Mn = 10000), and 0.668 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.334 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0114] Example 12

[0115] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.231 g of succinic acid, 7.260 g of fumaric acid, 18.925 g of 1,4-butanediol, 51.600 g of polyethylene glycol (Mn = 10000), and 0.950 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.475 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0116] Example 13

[0117] Modified polylactic acid was prepared according to the method of Example 1, except that 1,4-butanediol was replaced with 1,3-propanediol and succinic acid was replaced with malonic acid.

[0118] Example 14

[0119] Modified polylactic acid was prepared according to the method in Example 2, except that polyethylene glycol was replaced with polytetrahydrofuran.

[0120] Example 15

[0121] Modified polylactic acid was prepared according to the method in Example 1, except that fumaric acid was replaced with gluconic acid.

[0122] Example 16

[0123] Modified polylactic acid was prepared according to the method of Example 1, except that fumaric acid was replaced with methyl fumarate.

[0124] Comparative Example 1

[0125] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 24.067 g of succinic acid, 18.925 g of 1,4-butanediol, 8.600 g of polyethylene glycol (Mn = 6000), and 0.516 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.258 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0126] Comparative Example 2

[0127] In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 23.618 g of succinic acid, 5.804 g of fumaric acid, 23.657 g of 1,4-butanediol, and 0.516 g of the polymerization inhibitor p-hydroxyanisole were added. After starting the stirrer and introducing nitrogen for protection, the temperature was raised to 190°C and maintained at 190°C for stirring for 4 hours. Then, 0.258 g of the catalyst tetrabutyl titanate was added, and the temperature was raised to 205°C. The reactor was then evacuated and the vacuum degree was maintained at 25 Pa. The reaction was carried out at this temperature for 3.5 hours. Finally, the product underwent a climbing effect, and a brown product, which is the copolyester, was obtained.

[0128] Test Example 1

[0129] (1) The tensile strength and elongation at break of the copolyester samples obtained in Examples 1-16 and Comparative Examples 1-2 were tested respectively.

[0130] (2) The copolyester samples obtained in Examples 1-16 and Comparative Examples 1-2 were placed in a flat vulcanizing machine and pressed at 150°C to form dumbbell-shaped strips with a thickness of 0.5 mm. Each strip was placed on a hot table at 60°C and irradiated with a UV lamp with a power of 500W and a UV wavelength of 365nm for 7 minutes to obtain photocrosslinked strips. The tensile strength and elongation at break of the photocrosslinked strips were tested. The results of tensile strength and elongation at break, percentage increase in tensile strength and percentage increase in elongation at break, and degradation performance of the copolyesters of Examples 1-16 and Comparative Examples 1-2 before and after photocrosslinking are shown in Table 1.

[0131] (3) The above Examples 1-16 and Comparative Examples 1-2 were made into rectangular slices with a length of 30 mm, a width of 10 mm and a thickness of 0.5 mm. The slices were placed in Tris-HCl (pH=8, 0.1M) buffer solution containing 6 U / mL lipase and the samples were placed in a constant temperature incubator at 37°C for 60 days to degrade. The degradation results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As shown in Table 1, compared with Comparative Examples 1 and 2, the copolyester obtained by the preparation method provided by the present invention has good tensile strength and elongation at break. After short-term ultraviolet light crosslinking, its tensile strength and elongation at break can be further increased. In addition, the copolyester provided by the embodiments of the present invention can be degraded under the action of lipase, exhibiting excellent biodegradability.

[0136] Test Example 2

[0137] The crystallization temperatures (T) of the polyester and polyether segments of the copolyesters obtained in Examples 1-16 and Comparative Examples 1-2 c ), melting temperature (T) m The tests were conducted using a differential scanning calorimeter. The sample was heated to 140℃ and held at that temperature for 5 min to eliminate thermal history. Then, the temperature was lowered to -60℃ at a cooling rate of 10℃ / min, and then raised back to 140℃ at a heating rate of 10℃ / min. The crystallization temperatures of the polyester and polyether segments were taken from the exothermic peak value of the cooling curve, and the melting temperatures were taken from the endothermic peak value of the heating curve. The results are shown in Table 2.

[0138] Table 2

[0139]

[0140]

[0141] As can be seen from the results in Table 2, in the copolyester prepared by the embodiments of the present invention, the changes in the content of modified monomer I and modified monomer II only have a slight effect on the crystallization temperature and melting temperature of the polyester segment and polyether segment of the copolyester, and do not affect its processing performance.

[0142] Test Example 3

[0143] The content of structural unit (A) and structural unit (B) of the copolyesters obtained in Examples 1-16 and Comparative Examples 1-2 was tested. The content of structural unit (A) and structural unit (B) was obtained by nuclear magnetic resonance spectroscopy. The results are shown in Table 3.

[0144] Table 3

[0145]

[0146] Test Example 4

[0147] The copolyesters from Examples 1-16 and Comparative Examples 1-2 were blended with polylactic acid (PLA) in a Banbury mixer to obtain modified polylactic acid. The Banbury mixer temperature was 180℃, the speed was 50 rpm, and the mixing time was 8 min. The amount of copolyester used was 14 g, and the amount of PLA used was 56 g. Under the same experimental conditions, 14 g of PBS (purchased from Xinjiang Lanshan Tunhe Technology Co., Ltd., model TH803s) and 56 g of PLA were blended in a Banbury mixer to obtain modified polylactic acid, which was set as control group 1. Under the same experimental conditions, 14 g of PBAT (purchased from BASF AG, model C1200) and 56 g of PLA were blended in a Banbury mixer to obtain modified polylactic acid, which was set as control group 2. Under the same experimental conditions, the polylactic acid sample obtained by putting PLA in a Banbury mixer was set as the reference group. The elongation at break and notched impact strength of each sample were tested, and the results are shown in Table 4.

[0148] The modified polylactic acid in Examples 1-16, Comparative Examples 1-2, and Control Groups 1-2, as well as the polylactic acid in the reference group, were prepared into rectangular slices with a length of 30 mm, a width of 10 mm, and a thickness of 0.5 mm. The slices were placed in Tris-HCl (pH = 8, 0.1 M) buffer solution containing 6 U / mL proteinase K. The samples were placed in a constant temperature incubator at 37°C for 14 days to degrade, and the remaining mass was weighed. The results are shown in Table 4.

[0149] Table 4

[0150]

[0151]

[0152] As shown in Table 4, compared with the modified polylactic acid in the commercially produced control groups 1 and 2, the copolyester and polylactic acid blend provided by this invention can not only significantly improve the elongation at break and notched impact strength of polylactic acid, but also maintain the excellent biodegradability of polylactic acid.

[0153] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A copolyester, characterized in that, The copolyester exhibits a 5-50% increase in tensile strength and a 5-42% increase in elongation at break after being irradiated with a 500W UV lamp with a wavelength of 365nm at a temperature of 60°C. The copolyester contains structural unit (A) as shown in formula (I) and structural unit (B) as shown in formula (II); Equation (I); Formula (II); Among them, R I R II R III R IV R V and R VI Each is independently selected from hydrogen or C1-C4 alkyl groups, m is 1, p and q are each independently integers from 0 to 3, and n is an integer from 20 to 200; in the copolyester, the content of the structural unit (A) is 8-60% by weight, and the content of the structural unit (B) is 1-10% by weight.

2. The copolyester according to claim 1, characterized in that, The copolyester exhibits a 37-50% increase in tensile strength and a 28-42% increase in elongation at break after being irradiated with a 500W UV lamp with a wavelength of 365nm at a temperature of 60°C.

3. The copolyester according to claim 1 or 2, characterized in that, The copolyester has a tensile strength of 20-27 MPa and an elongation at break of 400-600%.

4. A method for preparing a copolyester as described in any one of claims 1 to 3, characterized in that, The method includes the following steps: (1) Under esterification reaction conditions, a diacid monomer, a diol monomer, a modified monomer I having the structure shown in formula (I), a modified monomer II having the structure shown in formula (II) and a polymerization inhibitor are mixed and subjected to a first-stage reaction to obtain a prepolymer. Equation (I); Formula (II); Among them, R I R II R III R IV R V and R VI Each is independently selected from hydrogen or C1-C4 alkyl groups, m is 1, p and q are each independently integers from 0 to 3, and n is an integer from 20 to 200; (2) Under polycondensation reaction conditions, the prepolymer is mixed with a catalyst to carry out a second-stage reaction; The ratio of the total molar amount of the diacid monomer and modified monomer II to the total molar amount of the diol monomer and modified monomer I is 1:1-1.2, the weight ratio of modified monomer I to the diol monomer is 0.2-2.8:1, and the weight ratio of modified monomer II to the diacid monomer is 1:2-20.

5. The preparation method according to claim 4, characterized in that, The modified monomer I is selected from at least one of PEG1000, PEG2000, PEG4000, PEG6000 and PEG10000; The dicarboxylic acid monomer is a C2-C6 aliphatic dicarboxylic acid, and the diol monomer is a C2-C6 aliphatic diol.

6. The preparation method according to claim 5, characterized in that, The polymerization inhibitor is selected from at least one of ether-based polymerization inhibitors, phenol-based polymerization inhibitors, quinone-based polymerization inhibitors, and aromatic amine-based polymerization inhibitors; The catalyst is tetrabutyl titanate and / or stannous octoate.

7. The preparation method according to claim 6, characterized in that, The polymerization inhibitor is an ether-based polymerization inhibitor, and the catalyst is tetrabutyl titanate.

8. The preparation method according to any one of claims 4 to 7, characterized in that, In step (1), the conditions for the esterification reaction include at least: a temperature of 185-195℃ and a time of 2-6h; In step (2), the conditions for the polycondensation reaction include at least the following: temperature of 200-230℃, vacuum degree of 0-50Pa, and time of 2-4h.

9. The use of the copolyester according to any one of claims 1 to 3 and / or the copolyester obtained by the preparation method according to any one of claims 4 to 8 in the preparation of modified polylactic acid.

10. A modified polylactic acid, characterized in that, The method for preparing the modified polylactic acid includes: mixing the copolyester according to any one of claims 1 to 3 or the copolyester obtained by the preparation method according to any one of claims 4 to 8 with polylactic acid; The modified polylactic acid has an elongation at break of 250-350% and a notched impact strength of 40-60 kJ / m. 2 .

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