Transparent degradable copolyester as well as preparation method and application thereof

Abstract

The invention discloses transparent degradable copolyester as well as a preparation method and application thereof. The copolyester is prepared from terephthalic acid or dimethyl terephthalate, 1, 4-cyclohexanedimethanol, 1, 4-butanediol and glycolic acid as raw materials through melt polymerization, the structure of the copolyester contains a fragment as shown in a formula I, the unit sequence length x is selected from 1-20, the unit sequence length y is selected from 1-20, and the unit sequence length z is selected from 4-6. A polyglycolic acid segment is introduced into a terephthalic acid-butanediol polyester chain segment to adjust the biodegradability of the copolyester, and on the basis, a 1, 4-cyclohexanedimethanol rigid dihydric alcohol structure is utilized to adjust the crystallization behavior of the degradable copolyester, so that the material is endowed with good transparency and biodegradability. The copolyester provided by the invention is transparent, has good mechanical properties and heat resistance, and is degradable in a full natural domain. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the field of transparent degradable copolyester materials, and more specifically to a transparent degradable copolyester and a preparation method and application thereof. Background Art

[0002] With the gradual expansion of the application fields and markets of degradable plastics, as an environmentally friendly alternative to general plastics, degradable plastics need to develop diversified performance to meet the needs of various application fields and scenarios, and transparency is one of the most important needs. Transparent degradable film materials can be used in many fields such as electrical packaging and daily chemical product packaging. The demand is strong, but there are very few resin products that can meet the demand. The existing biodegradable plastic PLA is highly transparent and biodegradable, but its toughness after film formation is poor, and it can only be degraded by composting, and it degrades slowly in seawater and soil. Other existing degradable resins such as polybutylene succinate (PBS), polyglycolic acid (PGA) and polyglycolic acid (PG) can meet good degradation performance, but they are not transparent materials. Polybutylene terephthalate-1,4-cyclohexane dimethanol (PBCT, also known as PBTG) is a copolyester formed by the polymerization of terephthalic acid, 1,4-butanediol and 1,4-cyclohexane dimethanol. It has high mechanical strength, heat resistance, good transparency and high gloss, but it is difficult to degrade under natural conditions. Therefore, how to modify PBCT and retain its performance while improving its degradability is an urgent problem to be solved in this field. Therefore, how to give polymer materials good degradation performance, film-forming performance, and transparency through molecular design is a difficulty in this field. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention provides a transparent degradable copolyester and its preparation method and application. A polyglycolic acid segment is introduced into the terephthalate-butylene glycol polyester segment to adjust the biodegradability of the copolyester. On this basis, the 1,4-cyclohexanedimethanol rigid diol structure is used to adjust the crystallization behavior of the degradable copolyester, thereby giving the material good transparency. The copolyester provided in the present invention is transparent, has good mechanical properties and heat resistance, and the copolyester is degradable in the entire natural domain.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In one aspect, the present invention provides a degradable copolyester, wherein the copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, and the copolyester structure contains a fragment shown in Formula I:

[0006]

[0007] Wherein, the unit sequence length x is selected from 1-20, y is selected from 1-20, and z is selected from 4-6.

[0008] Furthermore, x is selected from 1-10, y is selected from 1-10, and z is selected from 4-6.

[0009] Furthermore, x is selected from 1-5, y is selected from 1-5, and z is selected from 4-6.

[0010] That is, in the present invention, the glycolic acid unit always exists in the form of a single site or two sites in the main chain of the copolyester, and no obvious self-polymerization occurs.

[0011] The copolyester is prepared by introducing a polyglycolic acid segment into a terephthalate-butylene glycol polyester segment to adjust the biodegradability of the copolyester, and on this basis, the 1,4-cyclohexanedimethanol rigid diol structure is used to adjust the crystallization behavior of the degradable copolyester, thereby giving the material good transparency.

[0012] The copolyester has excellent biodegradability, with a significant decrease in molecular weight in compost, soil, and seawater environments, with a molecular weight decrease rate of more than 30% in 6 months; and good transparency, with a transparency of more than 50%, more preferably, greater than 80%.

[0013] Furthermore, the molar number of the 1,4-cyclohexanedimethanol is 1%-99% of the sum of the molar numbers of 1,4-cyclohexanedimethanol and 1,4-butanediol.

[0014] Furthermore, the molar number of the 1,4-cyclohexanedimethanol is 20%-80% of the sum of the molar numbers of 1,4-cyclohexanedimethanol and 1,4-butanediol.

[0015] Furthermore, the molar number of the 1,4-cyclohexanedimethanol is 40%-60% of the sum of the molar numbers of 1,4-cyclohexanedimethanol and 1,4-butanediol.

[0016] Furthermore, the mole number of the glycolic acid is 1%-200% of the mole number of terephthalic acid or dimethyl terephthalate.

[0017] Furthermore, the mole number of the glycolic acid is 10-140% of the mole number of terephthalic acid or dimethyl terephthalate.

[0018] Furthermore, the mole number of the glycolic acid is 20-120% of the mole number of terephthalic acid or dimethyl terephthalate.

[0019] Furthermore, the copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, wherein x is selected from 1-10, y is selected from 1-10, and z is selected from 4-6.

[0020] Furthermore, the mole number of the 1,4-cyclohexanedimethanol is 20%-80% of the sum of the moles of 1,4-cyclohexanedimethanol and 1,4-butanediol; the mole number of hydroxyacetic acid is 10%-140% of the mole number of terephthalic acid or dimethyl terephthalate.

[0021] Furthermore, the copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, wherein x is selected from 1-5, y is selected from 1-5, and z is selected from 4-6.

[0022] Furthermore, the mole number of the 1,4-cyclohexanedimethanol is 40%-60% of the sum of the moles of 1,4-cyclohexanedimethanol and 1,4-butanediol; the mole number of the hydroxyacetic acid is 20%-120% of the mole number of terephthalic acid or dimethyl terephthalate.

[0023] Furthermore, the number average molecular weight of the copolyester is 0.3×10 4 g / mol-7.0×10 4 g / mol, or a weight average molecular weight of 2.0×10 4 g / mol-10×10 4 g / mol.

[0024] Furthermore, the number average molecular weight of the copolyester is 3.0×10 4 g / mol-6.0×10 4 g / mol, or a weight average molecular weight of 6.0×10 4 g / mol-10×10 4 g / mol.

[0025] Furthermore, the copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, wherein the sum of the molar numbers of the raw materials 1,4-cyclohexanedimethanol and 1,4-butanediol is 1-2.5 times the molar number of terephthalic acid, that is, the diol reacts in excess to compensate for the loss of the alcohol monomer in the esterification and polycondensation reaction.

[0026] In another aspect, the present invention provides a method for preparing the transparent degradable copolyester as described above, the preparation method comprising the following steps:

[0027] Using terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, an esterification / ester exchange reaction is carried out in a molten state at a temperature of 160-240°C for 3-4 hours, and a condensation reaction is carried out under vacuum conditions at a temperature of 240-270°C for 1-3 hours.

[0028] In another aspect, the present invention provides a method for preparing the transparent degradable copolyester as described above, the preparation method comprising the following steps:

[0029] Using terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol and 1,4-butanediol as raw materials, a first esterification / ester exchange reaction is carried out in a molten state;

[0030] The temperature is lowered, and then glycolic acid is added, and the reaction time is controlled to carry out a second esterification reaction;

[0031] Then the temperature is raised and polycondensation reaction is carried out under vacuum conditions to obtain the copolyester.

[0032] Furthermore, when the raw materials for the first esterification reaction are terephthalic acid, 1,4-cyclohexanedimethanol and 1,4-butanediol,

[0033] The temperature of the first esterification reaction is 220-240°C, and the time is 3-4h. The temperature of the second esterification reaction is 160-220°C, and the time is 0.4h. The temperature of the polycondensation reaction is 240-270°C, and the time is 1-3h.

[0034] Furthermore, when the raw materials for the first esterification reaction are dimethyl terephthalate, 1,4-cyclohexanedimethanol and 1,4-butanediol,

[0035] The temperature of the first transesterification reaction is 200-220°C, and the time is 3-4h. The temperature of the second esterification reaction is 160-220°C, and the time is 0.4h. The temperature of the polycondensation reaction is 240-270°C, and the time is 1-3h.

[0036] Furthermore, the reaction is carried out in the presence of a catalyst.

[0037] Furthermore, the esterification reaction and the polycondensation reaction are both carried out in the presence of a catalyst. A portion of the catalyst can be added during the esterification reaction, and another portion of the catalyst can be added during the polycondensation reaction. By adding in this step-by-step manner, the hydrolysis efficiency of the catalyst during the esterification process can be effectively avoided, thereby ensuring efficient synthesis.

[0038] Furthermore, the catalyst is selected from titanium catalysts, tin catalysts, lanthanum catalysts, and other commonly used polycondensation catalysts, and can also be a composite catalyst composed of multiple catalysts and antioxidants. Exemplary catalysts include but are not limited to tetrabutyl titanate, titanium nanocomposite sol, and the like.

[0039] Furthermore, the polycondensation reaction sequentially includes a low vacuum reaction stage and a high vacuum reaction stage.

[0040] Furthermore, the pressure of the low vacuum reaction stage is 300-8000Pa, and the time is 0.5-1h; the pressure of the high vacuum reaction stage is <200Pa, and the time is 1-3h.

[0041] In another aspect, the present invention provides use of the transparent degradable copolyester described above in the preparation of a fully natural domain degradable material.

[0042] Furthermore, the "entire natural domain" in the present invention refers to the natural environment including composting environment, natural soil, lakes, and natural seawater environment.

[0043] The beneficial effects of the present invention are as follows:

[0044] The copolyester provided by the present invention is a transparent degradable material. In its structure, polybutylene terephthalate is a resin matrix and a skeleton structure, and the degradable unit hydroxyacetic acid that can be degraded by various microorganisms is introduced into the polyester main chain as a flexible and easily hydrolyzed fragment, which significantly improves the degradation performance of the copolyester; cyclohexanedimethanol is introduced into the polyester main chain as a rigid monomer to effectively adjust the crystallization performance of the material, give the material good transparency, and compensate for a part of the decrease in mechanical and heat resistance caused by the introduction of hydroxyacetic acid. Therefore, the material as a whole has high transparency, high mechanical strength and heat resistance, and significantly improved degradation performance. It is an ideal alternative product in the field of disposable packaging.

[0045] In addition, in the preparation method of the copolyester of the present invention, by step-by-step esterification, the esterification temperature, the feeding sequence, the degree of vacuum and other polymerization processes are controlled, so that glycolic acid is inserted into the main chain of the polyester matrix in the form of a specific short segment (polymerization degree 4-6), and the original main chain structure of the matrix is ​​maintained to the maximum extent, so that the material can be given significantly improved degradation performance while maintaining the mechanical properties or thermal properties of the matrix as much as possible. In addition, by adjusting the content of glycolic acid and cyclohexanedimethanol, the unit sequence structure and density on the molecular chain can be regulated, and the material can be given an adjustable degradation cycle and transparency, so that the structure and performance can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0047] Figure 1The PBCTG copolyester in the embodiment of the present invention is shown 1 H NMR spectrum and characteristic peak distribution positions.

[0048] Figure 2 The transparency of PBCT and PBCTG copolyester strips is shown.

[0049] Figure 3 The XRD spectrum of the copolyester prepared in the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0050] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0051] Example:

[0052] Preparation of glycolic acid (GA) modified polybutylene terephthalate-1,4-cyclohexane dimethanol ester (PBCTG):

[0053] In this embodiment, terephthalic acid (PTA), 1,4-cyclohexanedimethanol (CHDM), 1,4-butanediol (BDO) and glycolic acid (GA) are used as raw materials, and commonly used synthetic polyester catalysts such as titanium, tin, antimony, lanthanum, and composite catalysts are used to prepare PBCTG copolyester by step-by-step esterification-re-polycondensation. The raw material ratio is shown in Table 1. During the reaction, 1,4-butanediol (BDO) is excessive, and the total amount of 1,4-cyclohexanedimethanol (CHDM) and 1,4-butanediol (BDO) added is 1.2-2.5 times the total molar amount of terephthalic acid. The same ratio of feed can also be used to control the reaction time, catalyst and other experimental conditions to obtain copolyesters with different molecular weights. This embodiment uses some ratios for experiments, corresponding to different feed ratios of glycolic acid (GA) and 1,4-cyclohexanedimethanol (CHDM) for experiments, thereby obtaining copolyester PBC 50 T. PBC 50 TG5, PBC 50 TG30, PBC 50 TG50, PBC 50 TG80, PBC 50 TG100, PBC 50 TG140, PBC 50 TG200, PBC 10 TG50, PBC 10 TG100, PBC 90 TG50, PBC90 TG100.

[0054] The PBC listed in Table 1 50 Taking the synthesis of TG30 as an example, the one-step synthesis process of direct esterification is as follows:

[0055] PTA (1 mol, 166.13 g), CHDM (0.5 mol, 72.11 g) and excess BDO (1 mol, 90.12 g) were mixed and added to a 500 mL three-necked flask, and then tetrabutyl titanate (in terms of titanium content) accounting for 0.27 ‰ of the total mass of the acid was added. The reaction was carried out on a device equipped with an overhead stirrer. The system temperature was gradually raised from 220±5°C to 240±5°C at a rate of 10°C / h, and maintained at 240±5°C for 2h for esterification. After the mixture in the three-necked flask changed from milky white to clear and the distillation of the distillate slowed down significantly, the system temperature was lowered to 160±5°C, GA (0.3 mol, 22.82 g) was added, and the catalyst tetrabutyl titanate (accounting for 0.09wt‰ of the total mass of the acid, in terms of titanium content) was added, and the reaction was continued for 0.4h to complete the second esterification. After the esterification is completed, the system is set to a low vacuum of 300-8000Pa, and the system is quickly heated to 250±5℃ for polycondensation reaction. After 1 hour, the vacuum is controlled to less than 300Pa and the polycondensation is continued for about 3 hours. The reaction end point is considered when the system torque exceeds 60Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0056] In other embodiments, terephthalic acid can be replaced by dimethyl terephthalate, and the molar ratio of feed, feeding method, and heating and cooling method remain unchanged. When it is an ester exchange reaction, the reaction temperature is lower than the esterification temperature. 50 Taking the synthesis of TG30 as an example, the synthesis process is as follows:

[0057] Dimethyl terephthalate DMT (1 mol, 194.18 g), CHDM (0.5 mol, 72.11 g) and excess BDO (1 mol, 90.12 g) were added to a 500 mL three-necked flask, and then tetrabutyl titanate (in terms of titanium content) accounting for 0.27 ‰ of the total mass of the acid was added. The reaction was carried out in a device equipped with an overhead stirrer. The system temperature was gradually increased from 200° C. to 220° C. at a rate of 10° C. / h, and maintained at 220±5° C. for 2 h for esterification. After the mixture in the three-necked flask changed from milky white to clear and the distillation of the distillate slowed down significantly, the system temperature was lowered to 160±5° C., GA (0.3 mol, 22.82 g) was added, and the catalyst tetrabutyl titanate (accounting for 0.09 wt‰ of the total mass of the acid, in terms of titanium content) was added, and the reaction was carried out for 0.4 h to complete the second esterification. After the esterification is completed, the system is set to a low vacuum of 300-8000Pa, and the system is quickly heated to 250±5℃ for polycondensation reaction. After 1 hour, the vacuum is controlled to less than 300Pa and the polycondensation is continued for about 3 hours. The reaction end point is considered when the system torque exceeds 60Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0058] In this process, the catalyst tetrabutyl titanate is added in two steps, thereby effectively avoiding the reduction of hydrolysis efficiency during the catalyst esterification process and ensuring efficient synthesis. In this process, the esterification is carried out in two stages, first heating up, then cooling down and adding glycolic acid for the second step of esterification, and the second step of esterification time is controlled at 0.4h to ensure that the length of the polylactic acid segment in the main chain is controlled in the range of 4-6.

[0059] The present invention provides comparative examples 1 and 2. When GA is not contained in the system, the copolyester is synthesized by a one-pot method of adding materials simultaneously and gradually heating up to complete esterification-polycondensation.

[0060] The synthesis process is as follows:

[0061] Comparative Example 1

[0062] Preparation of polybutylene terephthalate (PBT):

[0063] PTA (1 mol, 166.13 g) and excess BDO (2 mol, 180.24 g) were mixed and added to a 500 mL three-necked flask, and then tetrabutyl titanate (in terms of titanium content) accounting for 0.27‰ of the total mass of the acid was added. The reaction was carried out on a device equipped with an overhead stirrer. The system temperature was gradually raised from 220±5℃ to 240±5℃ at a rate of 10℃ / h, and maintained at 240±5℃ for 2h for esterification. The esterification was completed after the mixture in the three-necked flask changed from milky white to clear and the distillation of the fraction was significantly slowed down. The catalyst tetrabutyl titanate (accounting for 0.09wt‰ of the total mass of the acid, in terms of titanium content) was added, the system was set to a low vacuum of 300-8000Pa, the temperature was raised to a reaction temperature of 240±5℃ at a rate of 10℃ / h, and the high vacuum was set to less than 300Pa for polycondensation for about 3h, and the system torque exceeding 60Ncm was regarded as the end of the reaction. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0064] Comparative Example 2

[0065] Preparation of polybutylene terephthalate-1,4-cyclohexane dimethanol ester (PBCT):

[0066] PTA (1 mol, 166.13 g), CHDM (0.5 mol, 72.11 g) and excess BDO (1 mol, 90.12 g) were mixed evenly and added to a 500 mL three-necked flask, and then 0.27‰ of tetrabutyl titanate (in terms of titanium content) was added to the total mass of the acid. The reaction was carried out in a device equipped with an overhead stirrer. The system temperature was gradually raised from 200±5°C to 240±5°C at a rate of 10°C / h, and maintained at 240±5°C for 2h for esterification. The esterification was completed when the mixture in the three-necked flask changed from milky white to clear and the distillation of the fraction was significantly slowed down. Add the catalyst tetrabutyl titanate (0.09wt‰ of the total acid mass, calculated as titanium content), set the system to low vacuum 300-8000Pa, heat up to the reaction temperature of 240±5℃ at a rate of 10℃ / h, set the high vacuum to less than 300Pa for polycondensation for about 3h, and regard the system torque exceeding 60Ncm as the reaction end point. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0067] The present invention provides comparative example 3, which uses a one-pot method to simultaneously add materials to synthesize copolyester PBC 50 In the synthesis process of TG100-x, GA is added together with dibasic acid and diol, and the temperature is raised for esterification-polycondensation, rather than cooling down and adding GA for step-by-step esterification. The synthesis process is as follows:

[0068] Comparative Example 3

[0069] PBC 50 TG30-x Synthesis:

[0070] PTA (1 mol, 166.13 g), CHDM (0.5 mol, 72.11 g), GA (0.3 mol, 22.82 g) and excess BDO (1 mol, 90.12 g) were mixed and added to a 500 mL three-necked flask, and then 0.27 ‰ of tetrabutyl titanate (in terms of titanium content) accounting for the total mass of the acid was added, and the reaction was carried out on a device equipped with an overhead stirrer. The system temperature was gradually raised from 160±5°C to 240±5°C at a rate of 10°C / h for esterification. After the mixture in the three-necked flask changed from milky white to clear and the distillation of the fraction was significantly slowed down, the catalyst tetrabutyl titanate (accounting for 0.09 wt‰ of the total mass of the acid, in terms of titanium content) was added, and the system was set to a low vacuum of 300-8000 Pa for polycondensation for 1 hour, and then set to a high vacuum of less than 300 Pa for polycondensation for about 3 hours, and the system torque exceeding 60Ncm was regarded as the end of the reaction. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0071] The present invention provides a comparative example 4, using the same method as in Example 2, first heating, then cooling, adding lactic acid for stepwise esterification and polycondensation to synthesize PBC 50 TG30-y, the difference is that the second step esterification time is controlled at 1.0h.

[0072] The synthesis process is as follows:

[0073] Comparative Example 4

[0074] PBC 50 TG30-y Synthesis:

[0075] Dimethyl terephthalate DMT (1 mol, 194.18 g), CHDM (0.5 mol, 72.11 g) and excess BDO (1 mol, 90.12 g) were added to a 500 mL three-necked flask, and then tetrabutyl titanate (in terms of titanium content) accounting for 0.27 ‰ of the total mass of the acid was added. The reaction was carried out in a device equipped with an overhead stirrer. The system temperature was gradually increased from 200° C. to 220° C. at a rate of 10° C. / h, and maintained at 220±5° C. for 2 h for esterification. After the mixture in the three-necked flask changed from milky white to clear and the distillation of the distillate slowed down significantly, the system temperature was lowered to 160±5° C., GA (0.3 mol, 22.82 g) was added, and the catalyst tetrabutyl titanate (accounting for 0.09 wt‰ of the total mass of the acid, in terms of titanium content) was added, and the reaction was carried out for 1.0 h to complete the second esterification. After the esterification is completed, the system is set to a low vacuum of 300-8000Pa, and the system is quickly heated to 250±5℃ for polycondensation reaction. After 1 hour, the vacuum is controlled to less than 300Pa and the polycondensation is continued for about 3 hours. The reaction end point is considered when the system torque exceeds 60Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0076] Table 1. Ratio of reaction raw materials and actual amount of introduction in the synthesis of PBCTG copolyester in various examples and comparative examples

[0077]

[0078]

[0079] Note: a: The percentage of cyclohexanedimethanol (CHDM) in the total molar amount of alcohol, n CHDM =CHDM / (CHDM+BDO)×100%;

[0080] b: The percentage of glycolic acid (GA) in the total molar amount of acid, nGA = GA / PTA × 100%.

[0081] The molecular weight, structure and properties of the PBCTG copolyester synthesized in the above examples are analyzed below:

[0082] 1. Gel permeation chromatography (GPC) test of molecular weight of PBCT and PBCTG copolyesters

[0083] Gel Permeation Chromatography (GPC): Measure the molecular weight (M) of PBCT and PBCTG copolyesters. n , M w ) and molecular weight distribution. Chloroform was used as the mobile phase, the flow rate was 1 mL / min, the column temperature was 35°C, the injection volume was 40 μL, and polystyrene (PS) was used as the standard. The results are shown in Table 2 below.

[0084] Table 2. Structural characterization and transparency of PBCTG copolyesters in various examples and comparative examples

[0085]

[0086]

[0087] in:

[0088]

[0089] The above X is a cyclohexanedimethanol fragment, Y is a 1,4-butanediol fragment, and Z is a glycolic acid fragment.

[0090] Taking the calculation of X as an example, CT, CTB, CTG, and CG represent the NMR integration results represented by the corresponding segment structures, namely Figure 1 In f1+f2, f3+f4, the integration results of the NMR spectrum are used to characterize the contents of different fragments and to calculate the average segment length.

[0091] In the calculation of Y above, BT, CTB, BTG, and BG respectively represent the NMR integration results represented by the corresponding segment structures.

[0092] In the above calculation of Z, GG, CG, BG, CTG, and BTG respectively represent the NMR integration results represented by the corresponding segment structures.

[0093] Among them, the segment structure of PBCTG copolyester is shown in the following formula:

[0094]

[0095] 2. Nuclear magnetic resonance hydrogen spectrum test ( 1 H NMR characterization of the structures of PBCT and PBCTG copolyesters

[0096] Using deuterated chloroform (CDCl3) as solvent and TMS as internal standard, the structure and composition of PBCT and PBCTG copolyesters were analyzed by Avance-400 NMR spectrometer produced by Bruker, Germany. 50 TG100 Polyester 1 HNMR results and characteristic peak distribution positions are shown in Figure 1 shown.

[0097] from Figure 1 It can be seen that the chemical shift at δ=8.10(a) is the proton peak of the hydrogen atom on the benzene ring, and δ=4.70-5.05ppm(g) is the proton peak of the methylene group near the carbonyl group of hydroxyacetic acid. δ=4.43ppm(a) and δ=1.97ppm(c) are the proton peaks of the methylene group in the middle and near the carboxyl group of 1,4-butanediol, respectively. δ=4.30ppm(f1) and δ=4.20ppm(f2) are the characteristic peaks of the methylene group connected to cyclohexane, and δ=1.5-1.8ppm, δ=1.9ppm and δ=2.0ppm are the characteristic peaks of H on cyclohexane (d, e). The introduction of hydroxyacetic acid makes it difficult to analyze the peaks related to the methylene group. The actual amount of hydroxyacetic acid introduced can only be determined by comparing the peak of hydroxyacetic acid at δ=2.35ppm(g) with the characteristic peak of terephthalic acid at δ=8.10(a) on the benzene ring.

[0098] As shown in Table 2 above, in all examples, glycolic acid was introduced into the copolyester segment in the form of 4-6 fragment lengths, and in Comparative Example 3 using a one-step esterification method, the glycolic acid unit sequence length was 1.42. In Comparative Example 4 using a stepwise esterification method and extending the second step esterification time to 1.0 h, the ε-caprolactone unit sequence length was 9.55.

[0099] 3. Characterization of Thermodynamic Stability of PBCT and PBCTG Copolyesters

[0100] Differential Scanning Calorimeter Test (DSC): Under nitrogen atmosphere, the heating and cooling curves of the copolyesters were obtained in the range of -30-240 °C at a heating rate of 10 °C / min and a cooling rate of -10 °C / min.

[0101] Thermogravimetric analysis (TGA): used to analyze the thermal stability of the sample. The test was performed from room temperature to 600°C at a constant heating rate of 10°C / min in a nitrogen atmosphere.

[0102] The thermal properties of PBCT and PBCTG copolyesters were characterized by DSC and TGA, and the results are shown in Table 3. The crystallinity of the copolyesters was characterized by XRD, and the results are shown in Table 3. Figure 3 Except for PBCTG5, PBCTG has no crystallization peak and melting peak, and is an amorphous polymer. No crystallization and melting behavior occurred in the DSC test. This may be because the introduction of glycolic acid destroys the regularity of the molecular chain and inhibits the crystallization of PBCT. The XRD spectrum (such as Figure 3 This is also reflected in the fact that different processing techniques can cause PBCT to appear in two states: transparent and opaque. In the opaque state, it has a crystallization peak (PBC 50 T-2). The glass transition temperature of PBCTG is lower than that of PBCT, and it decreases with the increase of glycolic acid content, indicating that the flexibility of the molecular chain is improved.

[0103] Moreover, during the hot-pressing injection molding process, PBCTG has better thermal oxidation resistance than PBCT. PBCT is easily oxidized to yellow and black during heating, while the thermal oxidation resistance is significantly improved after modification with glycolic acid. It can also be seen from Table 3 that the T d,5％ All above 385℃, T d,max All are greater than 427°C, indicating that the copolyester has good thermal stability.

[0104] Table 3 Thermal properties of PBCT and PBCTG copolyesters

[0105]

[0106]

[0107] 4. Mechanical properties characterization of PBCT and PBCTG copolyesters

[0108] PBCT and PBCTG copolyesters were prepared into standard dumbbell-shaped tensile specimens using an injection molding machine, and their effective dimensions were (25±1)×(4.0±0.4)×(2.0±0.2) mm. 3The mass is 1.5-2.0g. The injection temperature of PBCT and PBCTG copolyesters is set to 220-240℃, the mold temperature is 70-80℃, the injection time is 10s, the injection pressure is 500-800Pa, and the holding time is 15s.

[0109] Mechanical properties test (the sample is a standard tensile specimen stored at room temperature for seven days): 1) The test environment temperature is 25°C, the tensile rate is 10 mm / min, and to ensure the accuracy of the results, the average value ± standard deviation of three groups of parallel samples is used as the measurement result.

[0110] The tensile strength and elongation at break of the PBCT and PBCTG copolyesters obtained through testing are shown in Table 4. It can be seen from the table that the tensile strength of PBCT is 42.4MPa, and the elongation at break is 215%. The tensile strength of PBCTG is in the range of 41.2-25.8MPa, and the elongation at break is 414-1080%, with excellent comprehensive mechanical properties. After the introduction of glycolic acid, the toughness of the copolyester is improved compared to PBCT, and when the glycolic acid content reaches a certain value, PBCTG has good elastic recovery. 50 TG30-x,PBC 50 TG30-y is more 50 TG 30 The tensile strength and elongation at break are poor.

[0111] Table 4. Mechanical properties of PBCT and PBCTG copolyesters in the embodiments of the present invention

[0112] Serial number Sample name Tensile strength(MPa) Elongation at break (%) Comparative Example 1 PBT 59.7±0.3 107±17 Comparative Example 2 <![CDATA[PBC 50 T]]> 42.4±0.4 215±21 Comparative Example 3 <![CDATA[PBC 50 TG30-x]]> 44.7±1.8 228±14 Comparative Example 4 <![CDATA[PBC 50 TG30-y]]> 45.2±1.8 216±12 Example 1 <h2 style=";text-align:left;direction:ltr"><![CDATA[PBC <h2 style=";text-align:left;direction:ltr"> 50 <h2 style=";text-align:left;direction:ltr"> TG5]]><h2 style=";text-align:left;direction:ltr"> 42.6±0.8 210±11 Example 2 <![CDATA[PBC 50 TG30]]> 49.1±1.5 253±12 Example 3 <![CDATA[PBC 50 TG50]]> 48.2±0.6 142±41 Example 4 <![CDATA[PBC 50 TG80]]> 48.9±0.9 257±13 Example 5 <![CDATA[PBC 50 TG100]]> 49.3±0.8 262±18 Example 6 <![CDATA[PBC 50 TG140]]> 50.5±0.8 280±19 Example 7 <![CDATA[PBC 50 TG200]]> 49.5±0.5 246±15 Example 8 <![CDATA[PBC 10 TG50]]> 48.6±0.9 165±13 Example 9 <![CDATA[PBC 10 TG100]]> 46.9±1.1 239±15 Example 10 <![CDATA[PBC 90 TG50]]> 49.8±0.5 134±11 Embodiment 11 <![CDATA[PBC 90 TG100]]> 50.4±0.7 215±10

[0113] 5. Transparency of PBCT and PBCTG

[0114] The transmittance of visible light was tested using a UV spectrophotometer, and the samples were made by film blowing.

[0115] like Figure 2 As shown, from left to right are PBC 50 T. PBC 50 TG30, PBC 50 TG50, and PBC 50 The appearance of TG10 shows that these samples have excellent transparency. 50 TG30-x and PBC 50 TG30-y has lower transparency than PBC50TG30.

[0116] 6. Composting performance test of PBCTG

[0117] PBC was evaluated in a standard compost at 58±1°C according to ISO 14855-1:2005. 50 Compostability of TG100 copolyester. The biodegradability of copolyester was studied using powdered samples and microcrystalline cellulose as a reference. Degradation experiments are in progress.

[0118] The experimental results showed that PBC 50 T is non-biodegradable, and the degradation performance increases with the increase of G content. 50 T and PBC 50 The mineralization rate of TG after 6 months of degradation is shown in Table 5. The introduction of G makes the polyester biodegradable. With the increase of G content, the degradation performance increases. 50 TG5 has poor degradability, PBC 50 TG30-x and PBC 50 TG30-y has poorer degradability than PBC50TG30.

[0119] Table 5. Mineralization rate and degradation weight loss of PBCT and PBCTG copolyesters in the present invention after 6 months of degradation

[0120]

[0121] The changes in number average molecular weight of PBCT and PBCTG copolyesters after 6 months of degradation were tested, and the results are shown in Table 6 below.

[0122] Table 6. Molecular weight changes of PBCT and PBCTG copolyesters in the present invention after degradation for 6 months

[0123]

[0124]

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A transparent biodegradable copolyester, It is characterized in that The copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, and the copolyester structure contains a fragment shown in Formula I: Wherein, the unit sequence length x is selected from 1-20, y is selected from 1-20, and z is selected from 4-6.

2. The degradable copolyester according to claim 1, It is characterized in that The mole number of the 1,4-cyclohexanedimethanol is 1%-99% of the sum of the moles of 1,4-cyclohexanedimethanol and 1,4-butanediol, and the mole number of the hydroxyacetic acid is 1%-200% of the mole number of terephthalic acid or dimethyl terephthalate.

3. The degradable copolyester according to claim 1, It is characterized in that The copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, wherein x is selected from 1-10, y is selected from 1-10, and z is selected from 4-6; Preferably, the molar number of the 1,4-cyclohexanedimethanol is 20%-80% of the sum of the molar numbers of 1,4-cyclohexanedimethanol and 1,4-butanediol; the molar number of the hydroxyacetic acid is 10%-140% of the molar number of terephthalic acid or dimethyl terephthalate.

4. The degradable copolyester according to claim 1, It is characterized in that The copolyester is prepared by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, wherein x is selected from 1-5, y is selected from 1-5, and z is selected from 4-6; Preferably, the molar number of the 1,4-cyclohexanedimethanol is 40%-60% of the sum of the molar numbers of 1,4-cyclohexanedimethanol and 1,4-butanediol; the molar number of hydroxyacetic acid is 20%-120% of the molar number of terephthalic acid or dimethyl terephthalate.

5. The degradable copolyester according to any one of claims 1 to 4, It is characterized in that The number average molecular weight of the copolyester is 0.3×10 4 g / mol-7.0×10 4 g / mol, or a weight average molecular weight of 2.0×10 4 g / mol-10×10 4 g / mol.

6. A method for preparing a degradable copolyester according to any one of claims 1 to 5, It is characterized in that The steps include: Using terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol, 1,4-butanediol and glycolic acid as raw materials, an esterification / ester exchange reaction is carried out in a molten state at a temperature of 160-240°C for 3-4 hours; a polycondensation reaction is carried out under vacuum conditions at a temperature of 240-270°C for 1-3 hours.

7. A method for preparing a degradable copolyester according to any one of claims 1 to 5, It is characterized in that The steps include: Using terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanedimethanol and 1,4-butanediol as raw materials, a first esterification / ester exchange reaction is carried out in a molten state; The temperature is lowered, and then glycolic acid is added, and the reaction time is controlled to carry out a second esterification reaction; Then the temperature is raised and polycondensation reaction is carried out under vacuum conditions to obtain the copolyester.

8. The preparation method according to claim 7, It is characterized in that When the raw materials for the first esterification reaction are terephthalic acid, 1,4-cyclohexanedimethanol and 1,4-butanediol, The temperature of the first esterification reaction is 220-240°C and the time is 3-4h; The temperature of the second esterification reaction is 160-220°C and the time is 0.4h; The polycondensation reaction temperature is 240-270°C and the time is 1-3h; and / or When the raw materials for the first esterification reaction are dimethyl terephthalate, 1,4-cyclohexanedimethanol and 1,4-butanediol, The temperature of the first transesterification reaction is 200-220°C and the time is 3-4h; The temperature of the second esterification reaction is 160-220°C and the time is 0.4h; The temperature of the polycondensation reaction is 240-270° C., and the time is 1-3 hours.

9. The preparation method according to any one of claims 6 to 8, It is characterized in that The polycondensation reaction sequentially comprises a low vacuum reaction stage and a high vacuum reaction stage; Preferably, the pressure of the low vacuum reaction stage is 300-8000Pa, and the time is 0.5-1h; the pressure of the high vacuum reaction stage is <200Pa, and the time is 1-3h.

10. Use of the degradable copolyester according to any one of claims 1 to 5 as a fully natural degradable material.

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