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 lactic 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 polylactic acid fragment is introduced into a terephthalic acid-butanediol polyester chain segment to adjust the biodegradability of the copolyester, and 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.

Description

Technical Field

[0001] This invention relates to the field of transparent biodegradable copolyester materials. More specifically, it relates to a transparent biodegradable copolyester, its preparation method, and its applications. Background Technology

[0002] As the application fields and market for biodegradable plastics gradually expand, as an environmentally friendly alternative to general-purpose plastics, biodegradable plastics need to develop diverse performance characteristics to meet the needs of various application fields and scenarios, with transparency being one of the most important requirements. Transparent biodegradable film materials can be applied in multiple fields such as electrical appliance packaging and daily chemical product packaging, with strong demand, but very few resin products can meet these needs. Existing biodegradable plastic PLA is highly transparent and biodegradable, but its toughness after film formation is poor, and it can only degrade in compost, while degrading slowly in seawater and soil. Other existing biodegradable resins, such as polybutylene succinate (PBS), polyglycolic acid (PGA), and polylactic acid (PL), can meet good degradation performance, but they are not transparent materials. Polybutylene terephthalate-1,4-cyclohexanediethanol ester (PBCT, also known as PBTG) is a copolyester polymerized from terephthalic acid, 1,4-butanediol, and 1,4-cyclohexanediethanol. 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 to improve its degradability while retaining its performance characteristics is a pressing issue in this field. Consequently, how to simultaneously endow polymer materials with good degradability, film-forming properties, and transparency through molecular design is a significant challenge in this area. Summary of the Invention

[0003] To address the aforementioned problems in existing technologies, this invention provides a transparent biodegradable copolyester, its preparation method, and its applications. Polylactic acid segments are introduced into the terephthalic acid (or dimethyl terephthalate)-butanediol polyester chain to regulate the biodegradability of the copolyester. Furthermore, the rigid diol structure of 1,4-cyclohexanediethanol is used to regulate the crystallization behavior of the biodegradable copolyester, thereby imparting good transparency to the material. The copolyester provided by this invention is transparent, possesses good mechanical properties and heat resistance, and is biodegradable throughout its natural range.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] On one hand, the present invention provides a biodegradable copolyester, wherein the copolyester is melt-polymerized from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanediol, 1,4-butanediol and lactic acid as raw materials, and the copolyester structure contains the segment shown in Formula I:

[0006]

[0007] Among them, 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] In other words, in this invention, the lactic acid unit always exists in the copolyester backbone in the form of a single or two sites, without obvious self-polymerization.

[0011] The copolyester is formulated by introducing polylactic acid segments into the terephthalic acid (or dimethyl terephthalate)-butanediol polyester chain to regulate the biodegradability of the copolyester. Based on this, the crystallization behavior of the degradable copolyester is regulated by the rigid diol structure of 1,4-cyclohexanediethanol, thereby giving the material good transparency.

[0012] The copolyester exhibits excellent biodegradability, showing significant molecular weight reduction in composting, soil, and seawater environments, with a molecular weight reduction rate exceeding 30% within 6 months. Furthermore, the polyester possesses good transparency, exceeding 50%. More preferably, the transparency exceeds 80%.

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

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

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

[0016] Further, the molar amount of lactic acid is 1%-200% of the molar amount of terephthalic acid or dimethyl terephthalate.

[0017] Furthermore, the molar amount of lactic acid is 10%-140% of the molar amount of terephthalic acid or dimethyl terephthalate.

[0018] Further, the molar amount of lactic acid is 20%-120% of the molar amount of terephthalic acid or dimethyl terephthalate.

[0019] Furthermore, the copolyester is formed by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanediol, 1,4-butanediol and lactic 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] Further, the molar amount of 1,4-cyclohexanediethanol is 20%-80% of the sum of the molar amounts of 1,4-cyclohexanediethanol and 1,4-butanediol; the molar amount of lactic acid is 10-140% of the molar amount of terephthalic acid or dimethyl terephthalate.

[0021] Furthermore, the copolyester is formed by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanediol, 1,4-butanediol and lactic 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] Further, the molar amount of 1,4-cyclohexanediethanol is 40%-60% of the sum of the molar amounts of 1,4-cyclohexanediethanol and 1,4-butanediol; the molar amount of lactic acid is 20%-120% of the molar amount of terephthalic acid or dimethyl terephthalate.

[0023] Furthermore, the number-average molecular weight of the copolyester is 0.3 × 10⁻⁶. 4 g / mol - 7.0 × 10 4 g / mol, or a weight-average molecular weight of 2.0 × 10⁻⁶ g / mol. 4 g / mol⁻¹⁰×10⁻¹⁰ 4 g / mol.

[0024] Furthermore, the number-average molecular weight of the copolyester is 3.0 × 10⁻⁶. 4 g / mol - 6.0 × 10 4 g / mol, or a weight-average molecular weight of 6.0 × 10⁻⁶ g / mol. 4 g / mol⁻¹⁰×10⁻¹⁰ 4 g / mol.

[0025] Furthermore, the copolyester is formed by melt polymerization of terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanediethanol, 1,4-butanediol and lactic acid as raw materials. The sum of the molar amounts of 1,4-cyclohexanediethanol and 1,4-butanediol is 1-2.5 times the molar amount of terephthalic acid, that is, the diol reacts in excess to compensate for the loss of alcohol monomers in the esterification polycondensation reaction.

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

[0027] Using terephthalic acid or dimethyl terephthalate, 1,4-cyclohexanediol, 1,4-butanediol and lactic acid as raw materials, esterification / exchange reaction is carried out in the molten state at a temperature of 160-240℃ for 3-4 hours, followed by polycondensation reaction under vacuum at a temperature of 240-270℃ for 1-3 hours.

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

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

[0030] Cool down, then add lactic acid, and control the reaction time to carry out the second esterification reaction;

[0031] The temperature was then rapidly increased, and a polycondensation reaction was carried out under vacuum conditions to obtain the copolyester.

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

[0033] The first esterification reaction is carried out at a temperature of 220-240℃ for 3-4 hours, the second esterification reaction is carried out at a temperature of 160-220℃ for 0.8 hours, and the polycondensation reaction is carried out at a temperature of 240-270℃ for 1-3 hours.

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

[0035] The first transesterification reaction is carried out at a temperature of 200-220℃ for 3-4 hours, the second esterification reaction is carried out at a temperature of 160-220℃ for 0.8 hours, and the polycondensation reaction is carried out at a temperature of 240-270℃ for 1-3 hours.

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

[0037] Furthermore, both the esterification and polycondensation reactions are carried out in the presence of a catalyst. A portion of the catalyst can be added during the esterification reaction, and another portion during the polycondensation reaction. This stepwise addition effectively avoids the reduction in catalyst hydrolysis efficiency during esterification, ensuring efficient synthesis.

[0038] Furthermore, the catalyst is selected from titanium-based catalysts, tin-based catalysts, lanthanide catalysts, and other commonly used polycondensation catalysts, or it can be a composite catalyst composed of multiple catalysts and antioxidants. Exemplary catalysts include, but are not limited to, tetrabutyl titanate and titanium-based nanocomposite sols.

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

[0041] In another aspect, the present invention provides the application of the transparent biodegradable copolyester described above in the preparation of all-natural biodegradable materials.

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

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

[0044] The copolyester provided by this invention is a transparent biodegradable material. In its structure, polybutylene terephthalate serves as the resin matrix and backbone. Lactic acid, a biodegradable unit that can be degraded by various microorganisms, is introduced into the polyester backbone as a flexible and easily hydrolyzed segment, significantly improving the degradation performance of the copolyester. Cyclohexanediol is introduced into the polyester backbone as a rigid monomer, effectively regulating the crystallinity of the material, giving it good transparency, and compensating for some of the decrease in mechanical and heat resistance caused by the introduction of lactic acid. Therefore, the material as a whole possesses high transparency, high mechanical strength, and heat resistance, as well as significantly improved degradation performance, making it an ideal alternative product in the field of disposable packaging.

[0045] Furthermore, in the preparation method of the copolyester of this invention, through stepwise esterification and control of polymerization processes such as esterification temperature, feeding sequence, and vacuum degree, lactic acid is inserted into the main chain of the polyester matrix in the form of specific short segments (degree of polymerization 4-6). The original main chain structure of the matrix is ​​preserved to the maximum extent. Therefore, while maintaining the mechanical or thermal properties of the matrix as much as possible, the material can be endowed with significantly improved degradation performance. In addition, by adjusting the content of lactic acid and cyclohexanediol, the unit sequence structure and density on the molecular chain can be controlled, giving the material an adjustable degradation cycle and transparency, thus achieving controllable structure and performance. Attached Figure Description

[0046] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0047] Figure 1The PBCTL copolyester shown in the embodiments of the present invention is 1 H NMR spectrum and the location of characteristic peaks.

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

[0049] Figure 3 The XRD patterns of the PBCT and PBCTL copolyesters are shown. Detailed Implementation

[0050] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0051] Example:

[0052] Preparation of lactic acid (LA) modified polybutylene terephthalate-1,4-cyclohexanediethanol ester (PBCTL):

[0053] In this embodiment, terephthalic acid (PTA), 1,4-cyclohexanediethanol (CHDM), 1,4-butanediol (BDO), and lactic acid (LA) were used as raw materials. Common synthetic polyester catalysts, such as titanium-based, tin-based, antimony-based, lanthanide-based, and their composite catalysts, were employed to prepare PBCTL copolyester via stepwise esterification-repolymerization. The raw material ratios are shown in Table 1. During the reaction, 1,4-butanediol (BDO) was in excess, and the total amount of 1,4-cyclohexanediethanol (CHDM) and 1,4-butanediol (BDO) added was 1.2-2.5 times the total molar amount of terephthalic acid. With the same feed ratio, copolyesters with different molecular weights could be obtained by controlling the reaction time, catalyst, and other experimental conditions. This embodiment used various ratios for experiments, corresponding to different feed proportions of lactic acid (LA) and 1,4-cyclohexanediethanol (CHDM), thereby obtaining the copolyester PBCTL. 50 T, PBC 50 TL5, PBC 50 TL30, PBC 50 TL50, PBC 50 TL80, PBC 50 TL100, PBC 50 TL140, PBC 50 TL200, PBC 10 TL50, PBC 10 TL100, PBC 90 TL50, PBC 90TL100.

[0054] The PBCs listed in Table 1 50 Taking the synthesis of TL30 as an example, the synthesis process 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 thoroughly and added to a 500 mL three-necked flask. Tetrabutyl titanate (based on titanium content), accounting for 0.27‰ of the total acid mass, was then added. The reaction was carried out on a device equipped with a top stirrer. The system temperature was gradually increased from 220±5 °C to 240±5 °C at a rate of 10 °C / h, and maintained at 240±5 °C for 2 h for esterification. After the mixture in the three-necked flask changed from milky white to clear and the distillation rate slowed significantly, the system temperature was lowered to 160±5 °C, LA (0.3 mol, 27.02 g) was added, and tetrabutyl titanate catalyst (0.09 wt‰ of the total acid mass, based on titanium content) was added. The reaction was continued for 0.8 h to complete the second esterification. After esterification, the system was set to a low vacuum of 300-8000 Pa, and the system was rapidly heated to 250±5℃ for polycondensation. After 1 hour, the vacuum was controlled to be less than 300 Pa, and polycondensation was continued for about 3 hours. The reaction endpoint was considered to be when the system torque exceeded 60 Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0056] In other embodiments, terephthalic acid can be replaced with dimethyl terephthalate, while the molar ratio, feeding method, and heating / cooling method remain unchanged. When it is a transesterification reaction, the reaction temperature is lower than the esterification temperature. Using the PBCs listed in Table 1... 50 Taking the synthesis of TL30 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. Tetrabutyl titanate (based on titanium content) at 0.27‰ of the total acid mass was then added. The reaction was carried out on a device equipped with a top 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 fractions slowed down significantly, the system temperature was lowered to 160 ± 5 °C, LA (0.3 mol, 27.02 g) was added, and tetrabutyl titanate (0.09 wt‰ of the total acid mass, based on titanium content) was added as a catalyst. The reaction was carried out for 0.8 h to complete the second esterification. After esterification, the system was set to a low vacuum of 300-8000 Pa, and the system was rapidly heated to 250±5℃ for polycondensation. After 1 hour, the vacuum was controlled to be less than 300 Pa, and polycondensation was continued for about 3 hours. The reaction endpoint was considered to be when the system torque exceeded 60 Ncm. 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, which effectively avoids the reduction of hydrolysis efficiency during catalyst esterification and ensures efficient synthesis.

[0059] In this process, esterification is carried out in two stages. First, the temperature is raised, then the temperature is lowered and glycolic acid is added to carry out the second esterification. The second esterification time is controlled at 0.8 hours to ensure that the length of the polylactic acid fragment in the main chain is controlled within the range of 4-6.

[0060] The present invention provides Comparative Example 1 and Comparative Example 2. When the system does not contain LA, the copolyester synthesis adopts a one-pot method to simultaneously add materials and gradually raise the temperature to complete esterification-polymerization.

[0061] Its synthesis process is as follows:

[0062] Comparative Example 1

[0063] Preparation of polybutylene terephthalate (PBT):

[0064] PTA (1 mol, 166.13 g) and excess BDO (2 mol, 180.24 g) were mixed thoroughly and added to a 500 mL three-necked flask. Tetrabutyl titanate (based on titanium content), accounting for 0.27‰ of the total acid mass, was then added. The reaction was carried out on a device equipped with a top stirrer. The system temperature was gradually increased from 220±5 °C to 240±5 °C at a rate of 10 °C / h, and maintained at 240±5 °C for 2 h for esterification. Esterification was completed when the mixture in the three-necked flask changed from milky white to clear and the distillation rate slowed significantly. Tetrabutyl titanate catalyst (0.09 wt‰ of the total acid mass, based on titanium content) was added. The system was set to a low vacuum of 300-8000 Pa, and the temperature was increased to 240±5 °C at a rate of 10 °C / h. Polycondensation was then carried out at a high vacuum of less than 300 Pa for approximately 3 h. The reaction endpoint was considered reached when the system torque exceeded 60 Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0065] Comparative Example 2

[0066] Preparation of polybutylene terephthalate-1,4-cyclohexanediethanol ester (PBCT):

[0067] PTA (1 mol, 166.13 g), CHDM (0.5 mol, 72.11 g), and excess BDO (1 mol, 90.12 g) were mixed thoroughly and added to a 500 mL three-necked flask. Tetrabutyl titanate (based on titanium content) at 0.27‰ of the total acid mass was then added. The reaction was carried out on a device equipped with a top stirrer. The system temperature was gradually increased from 200±5 °C to 240±5 °C at a rate of 10 °C / h, and maintained at 240±5 °C for 2 h for esterification. Esterification was completed when the mixture in the three-necked flask changed from milky white to clear and the distillation rate slowed significantly. Add tetrabutyl titanate as a catalyst (0.09 wt‰ of the total acid mass, based on titanium content), set the system to a low vacuum of 300-8000 Pa, and heat to a reaction temperature of 240±5℃ at a rate of 10℃ / h. Then, set the system to a high vacuum of less than 300 Pa for about 3 hours for polycondensation. The reaction endpoint is considered to be when the system torque exceeds 60 Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0068] This invention provides Comparative Example 3, which describes the synthesis of copolyester PBC using a one-pot method with simultaneous feeding. 50 TL30-x is synthesized by adding LA together with a diacid and a diol, followed by esterification and polycondensation at elevated temperature, rather than by adding LA at lower temperature for stepwise esterification. The synthesis process is as follows:

[0069] Comparative Example 3

[0070] PBC 50 TL30 Synthesis:

[0071] PTA (1 mol, 166.13 g), CHDM (0.5 mol, 72.11 g), LA (0.3 mol, 27.02 g), and excess BDO (1 mol, 90.12 g) were mixed thoroughly and added to a 500 mL three-necked flask. Tetrabutyl titanate (based on titanium content), accounting for 0.27‰ of the total acid mass, was then added. The reaction was carried out on a device equipped with a top stirrer. The system temperature was gradually increased 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 rate slowed significantly, tetrabutyl titanate (0.09 wt‰ of the total acid mass, based on titanium content) was added as catalyst. The system was then subjected to a low vacuum of 300-8000 Pa for condensation reaction for 1 h, followed by a high vacuum of less than 300 Pa for approximately 3 h. The reaction endpoint was considered to be when the system torque exceeded 60 Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0072] This invention provides Comparative Example 4, which uses the same method as Example 2, first heating, then cooling, adding lactic acid for stepwise esterification and condensation polymerization to form PBC. 50 The difference with TL30-y is that the second esterification time is controlled at 1.0 h.

[0073] Its synthesis process is as follows:

[0074] Comparative Example 4

[0075] PBC 50 TL30-y synthesis:

[0076] 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. Tetrabutyl titanate (based on titanium content) at 0.27‰ of the total acid mass was then added. The reaction was carried out on a device equipped with a top 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 fractions slowed down significantly, the system temperature was lowered to 160 ± 5 °C, LA (0.3 mol, 27.02 g) was added, and tetrabutyl titanate (0.09 wt‰ of the total acid mass, based on titanium content) was added as catalyst. The reaction was carried out for 1.0 h to complete the second esterification. After esterification, the system was set to a low vacuum of 300-8000 Pa, and the system was rapidly heated to 250±5℃ for polycondensation. After 1 hour, the vacuum was controlled to be less than 300 Pa, and polycondensation was continued for about 3 hours. The reaction endpoint was considered to be when the system torque exceeded 60 Ncm. The obtained copolyester can be directly used for subsequent structural characterization and performance evaluation.

[0077] Table 1. Reaction feed ratios and actual amounts introduced in the synthesis of PBCTL copolyester in each example and comparative example.

[0078]

[0079]

[0080] Note: a: percentage of cyclohexanediethanol (CHDM) in the total molar amount of alcohol, n CHDM =CHDM / (CHDM+BDO)×100%;

[0081] b: The percentage of lactic acid (LA) in the total molar amount of acid, nLA = LA / PTA × 100%.

[0082] The molecular weight, structure, and properties of the PBCTL copolyester synthesized in the above examples are analyzed below:

[0083] 1. Gel permeation chromatography (GPC) determination of the molecular weight of PBCT and PBCTL copolyesters

[0084] Gel permeation chromatography (GPC): Measurement of the molecular weight (M) of the PBCT and PBCTL copolyesters n M w The molecular weight distribution was determined. Chloroform was used as the mobile phase at a flow rate of 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.

[0085] Table 2. Structural characterization and transparency of PBCTL copolyesters in each example and comparative example.

[0086]

[0087] in:

[0088]

[0089]

[0090] X represents the cyclohexanediethanol fragment, Y represents the 1,4-butanediol fragment, and Z represents the lactic acid fragment.

[0091] Taking the calculation of X as an example, CT, CTB, CTL, and CL represent the NMR integral results represented by the corresponding chain segment structures, i.e. Figure 1 The content of different fragments, f1+f2 and f3+f4, is characterized by the integral results of the NMR spectrum, which are used to calculate the average chain length.

[0092] In the above calculation of Y, BT, CTB, BTL, and BL represent the NMR integral results represented by the corresponding chain segment structures.

[0093] In the above calculation of Z, LL, CL, BL, CTL, and BTL represent the NMR integral results represented by the corresponding chain segment structures.

[0094] The chain segment structure of the PBCTL copolyester is shown in the following formula:

[0095]

[0096] 2. Nuclear magnetic resonance hydrogen spectrum test ( 1 H NMR characterization of the copolyester structure of PBCT and PBCTL

[0097] Using deuterated chloroform (CDCl3) as solvent and TMS as internal standard, the structure and composition of the PBCT and PBCTL copolyesters were analyzed using a Bruker Avance-400 nuclear magnetic resonance spectrometer (Germany). Among these analyses, PBC... 50 TL100 polyester 1 HNMR results and characteristic peak distribution positions are as follows: Figure 1 As shown.

[0098] from Figure 1 As can be seen, the chemical shift at δ = 8.10(a) represents the proton peak of the hydrogen atom on the benzene ring, and at δ = 5.35 ppm(g) represents the proton peak of the methylene group near the carbonyl group in lactic acid. δ = 4.43 ppm(a) and δ = 1.97 ppm(c) represent the proton peaks of the methylene groups in 1,4-butanediol, near the carboxyl group, respectively. δ = 4.30 ppm(f1) and δ = 4.20 ppm(f2) are characteristic peaks of the methylene group attached to cyclohexane, and δ = 1.5–1.8 ppm, δ = 1.9 ppm, and δ = 2.0 ppm are characteristic peaks (d, e) of H atoms on cyclohexane. The introduction of lactic acid makes the peaks related to the methylene group difficult to analyze; the actual amount of lactic acid introduced can only be determined by comparing the lactic acid peak at δ = 2.35 ppm(g) with the characteristic peak at δ = 8.10(a) on the benzene ring of terephthalic acid.

[0099] As shown in Table 2 above, in all examples, lactic acid was introduced into the copolyester segments in the form of 4-6 segments. In Comparative Example 3, which used a one-step esterification method, the lactic acid unit sequence length was 1.46. In Comparative Example 4, which used stepwise esterification and extended the second esterification time to 1.0 h, the ε-caprolactone unit sequence length was 2.71.

[0100] 3. Thermodynamic stability characterization of PBCT and PBCTL copolyesters

[0101] Differential scanning calorimetry (DSC): Heating and cooling curves of copolyesters were obtained in the range of -30 to 240°C under nitrogen atmosphere with a heating rate of 10°C / min and a cooling rate of -10°C / min.

[0102] Thermogravimetric analysis (TGA): Used to analyze the thermal stability of samples. The test is conducted under a nitrogen atmosphere, with the temperature increased from room temperature to 600°C at a constant heating rate of 10°C / min.

[0103] The thermal properties of the PBCT and PBCTL copolyesters were characterized by DSC and TGA, and the results are shown in Table 3. The crystallinity properties of the copolyesters were characterized by XRD, and the results are shown in Table 3. Figure 3 As shown in the figure, during the second heating (DSC) scan, PBCTL showed no crystallization or melting peaks, indicating it is an amorphous polymer. Only PBCT exhibited melting and cold crystallization peaks. Other samples did not show crystallization or melting behavior during DSC testing. This may be because the introduction of lactic acid disrupted the regularity of the molecular chains, inhibiting the crystallization of PBCT. (XRD patterns are shown in the figure). Figure 3 This is also reflected in the fact that different processing techniques can cause PBCT to exhibit both transparent and opaque states. In the opaque state, it has crystalline peaks (PBC). 50 T-2). The glass transition temperature of PBCTL is lower than that of PBCT, and it decreases with increasing lactic acid content, indicating that the flexibility of the molecular chain is improved.

[0104] Furthermore, during hot-press injection molding, PBCTL exhibits better heat oxidation resistance compared to PBCT. PBCT is prone to oxidation and turns yellow and black during heating, while lactic acid modification significantly improves its heat oxidation resistance. Table 3 also shows that the To of the copolyesters PBCT and PBCTL... d,5％ All are greater than 383℃, T d,max All values ​​were above 427℃, indicating the good thermal stability of the copolyester.

[0105] Table 3 Thermal properties of PBCT and PBCTL copolyesters

[0106] Serial Number sample T g (°C) T cc (°C) T m (°C) T d,5％ (°C) <![CDATA[T d,max (℃)]]> Comparative Example 1 PBT 64.8 225.9 399.4 435.2 Comparative Example 2 <![CDATA[PBC 50 T]]> 63.1 119.6 200.3 397.9 428.0 Comparative Example 3 <![CDATA[PBC 50 TL30-x]]> 56.7 123.5 176.6 395.5 426.4 Comparative Example 4 <![CDATA[PBC 50 TCL30-y]]> 57.9 122.5 178.1 396.7 426.8 Example 1 <![CDATA[PBC 50 TL5]]> 62.6 125.4 195.7 396.7 427.2 Example 2 <![CDATA[PBC 50 TL30]]> 57.1 123.8 175.9 395.1 426.8 Example 3 <![CDATA[PBC 50 TL50]]> 56.0 - - 387.5 425.6 Example 4 <![CDATA[PBC 50 TL80]]> 55.3 - - 387.4 425.8 Example 5 <![CDATA[PBC 50 TL100]]> 54.9 - - 384.2 425.1 Example 6 <![CDATA[PBC 50 TL140]]> 54.0 - - 383.7 425.2 Example 7 <![CDATA[PBC 50 TL200]]> 50.3 - - 383.5 423.2 Example 8 <![CDATA[PBC 10 TL50]]> 55.4 - - 389.5 426.1 Example 9 <![CDATA[PBC 10 TL100]]> 53.9 - - 383.5 425.6 Example 10 <![CDATA[PBC 90 TL50]]> 57.2 - - 394.9 427.8 Example 11 <![CDATA[PBC 90 TL100]]> 55.1 - - 387.8 427.1

[0107] 4. Mechanical property characterization of PBCT and PBCTL copolyesters

[0108] Standard dumbbell-shaped tensile specimens were prepared from PBCT and PBCTL copolyester using an injection molding machine. The 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 PBCTL 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 property test (samples are standard tensile specimens stored at room temperature for seven days): 1) The ambient temperature of the test is 25℃ and the tensile rate is 10mm / min. To ensure the accuracy of the results, the average value ± standard deviation of three parallel samples is used as the test result.

[0110] The tensile strength and elongation at break of the PBCT and PBCTL copolyesters obtained through testing are shown in Table 4. As can be seen from the table, PBCT has a tensile strength of 42.4 MPa and an elongation at break of 215%, while PBCTL has a tensile strength ranging from 41.2 to 25.8 MPa and an elongation at break ranging from 414% to 1080%, exhibiting excellent comprehensive mechanical properties. After the introduction of lactic acid, the toughness of the copolyester is improved compared to PBCT, and PBCTL exhibits good elastic recovery when the lactic acid content reaches a certain value. PBC... 50 TL30-x and PBC 50 TL30-y compared to PBC 50 TL 30 It has poor tensile strength and elongation at break.

[0111] Table 4. Mechanical properties of the PBCT and PBCTL 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 TL30-x]]> 41.2±1.8 208±20 Comparative Example 4 <![CDATA[PBC 50 TCL30-y]]> 40.7±1.8 215±17 Example 1 <![CDATA[PBC 50 TL5]]> 42.0±0.8 218±18 Example 2 <![CDATA[PBC 50 TL30]]> 45.4±0.3 234±13 Example 3 <![CDATA[PBC 50 TL50]]> 47.1±0.8 260±12 Example 4 <![CDATA[PBC 50 TL80]]> 49.0±0.8 210±15 Example 5 <![CDATA[PBC 50 TL100]]> 50.4±1.8 229±18 Example 6 <![CDATA[PBC 50 TL140]]> 49.3±0.8 260±19 Example 7 <![CDATA[PBC 50 TL200]]> 46.9±0.5 246±25 Example 8 <![CDATA[PBC 10 TL50]]> 48.6±0.9 235±21 Example 9 <![CDATA[PBC 10 TL100]]> 49.1±1.1 239±13 Example 10 <![CDATA[PBC 90 TL50]]> 46.8±0.5 204±19 Example 11 <![CDATA[PBC 90 TL100]]> 49.4±0.7 265±20

[0113] 5. Transparency of PBCT and PBCTL

[0114] The transmittance of visible light was tested using an ultraviolet spectrophotometer, and the sample was made by blown film.

[0115] like Figure 2 As shown, from left to right, they are PBCs. 50 T, PBC 50 TL30, PBC 50 TL50 and PBC 50 The morphological image of TL100 shows that these samples all possess excellent transparency, while the comparative PBC... 50 TL30-x, PBC 50 TL30-y compared to PBC 50 TL30 has poor transparency.

[0116] 6. Composting Degradation Performance Test of PBCTL

[0117] PBC was evaluated in standard compost at 58±1℃ according to standard ISO 14855-1:2005. 50 Compostability of TL100 copolyester. The biodegradability of the copolyester was studied using powdered samples, with microcrystalline cellulose as a reference. Degradation experiments are in progress.

[0118] Experimental results show PBC 50 T is non-biodegradable, but its degradation performance improves with increasing L content. (PBC) 50 T and PBC 50 Table 5 shows the mineralization rate of TL after 6 months of degradation. The introduction of L imparts biodegradable properties to the polyester; the degradation performance increases with increasing L content. 50 TL30-x, PBC 50 TL30-y compared to PBC 50 TL30 has poor degradation properties.

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

[0120]

[0121]

[0122] The number-average molecular weight changes of PBCT and PBCTL copolyesters after 6 months of degradation were tested, and the results are shown in Table 6 below.

[0123] Table 6. Molecular weight changes of PBCT and PBCTL copolyesters after 6 months of degradation in the embodiments of the present invention.

[0124]

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A transparent degradable copolyester characterized in that, The copolyester is melt-polymerized from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexane dimethanol, 1,4-butanediol and lactic acid, and contains a segment shown in formula I in the structure of the copolyester: In the formula, x is selected from 1 to 20, y is selected from 1 to 20, and z is selected from 4 to 6.

2. The degradable copolyester of claim 1, wherein, The mole number of the 1,4-cyclohexane dimethanol is 1% to 99% of the sum of the mole numbers of the 1,4-cyclohexane dimethanol and the 1,4-butanediol, and the mole number of the lactic acid is 1% to 200% of the mole number of the terephthalic acid or dimethyl terephthalate.

3. The degradable copolyester of claim 1, wherein, The copolyester is melt-polymerized from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexane dimethanol, 1,4-butanediol and lactic acid, and contains a segment shown in formula I in the structure of the copolyester: Preferably, the mole number of the 1,4-cyclohexane dimethanol is 20% to 80% of the sum of the mole numbers of the 1,4-cyclohexane dimethanol and the 1,4-butanediol, and the mole number of the lactic acid is 10% to 140% of the mole number of the terephthalic acid or dimethyl terephthalate.

4. The degradable copolyester of claim 1, wherein, The copolyester is melt-polymerized from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexane dimethanol, 1,4-butanediol and lactic acid, and contains a segment shown in formula I in the structure of the copolyester: Preferably, the mole number of the 1,4-cyclohexane dimethanol is 40% to 60% of the sum of the mole numbers of the 1,4-cyclohexane dimethanol and the 1,4-butanediol, and the mole number of the lactic acid is 20% to 120% of the mole number of the terephthalic acid or dimethyl terephthalate.

5. The degradable copolyester according to any one of claims 1-4, wherein, The number average molecular weight of the copolyester is 0.3 x 10 4 g / mol - 7.0 x 10 4 g / mol, or the weight average molecular weight is 2.0 x 10 4 g / mol - 10 x 10 4 g / mol.

6. The method of making a degradable copolyester according to any one of claims 1-5, wherein, The method comprises the following steps: The esterification / ester exchange reaction is carried out in a molten state from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexane dimethanol, 1,4-butanediol and lactic acid as raw materials, at a temperature of 160 to 240°C for 3 to 4 hours; and the polycondensation reaction is carried out under vacuum at a temperature of 240 to 270°C for 1 to 3 hours.

7. The method of making a degradable copolyester according to any one of claims 1-5, wherein, The method comprises the following steps: The first esterification / ester exchange reaction is carried out in a molten state from terephthalic acid or dimethyl terephthalate, 1,4-cyclohexane dimethanol and 1,4-butanediol as raw materials; The temperature is lowered, and then lactic acid is added, and the second esterification reaction is carried out by controlling the reaction time; The temperature is then raised, and the polycondensation reaction is carried out under vacuum to obtain the copolyester.

8. The preparation method according to claim 7, characterized in that, When the raw materials of the first esterification reaction are terephthalic acid, 1,4-cyclohexane dimethanol and 1,4-butanediol, The temperature of the first esterification reaction is 220 to 240°C, and the time is 3 to 4 hours; The temperature of the second esterification reaction is 160 to 220°C, and the time is 0.8 hours; The temperature of the polycondensation reaction is 240 to 270°C, and the time is 1 to 3 hours; and / or When the raw materials of the first esterification reaction are dimethyl terephthalate, 1,4-cyclohexane dimethanol and 1,4-butanediol, The temperature of the first ester exchange reaction is 200 to 220°C, and the time is 3 to 4 hours; The temperature of the second esterification reaction is 160 to 220°C, and the time is 0.8 hours; The temperature of the polycondensation reaction is 240-270 DEG C, and the time is 1-3 hours.

9. The method of any one of claims 6-8, wherein, The polycondensation reaction comprises a low vacuum reaction stage and a high vacuum reaction stage in sequence. Preferably, the pressure of the low vacuum reaction stage is 300-8000 Pa, and the time is 0.5-1 hour; the pressure of the high vacuum reaction stage is < 200 Pa, and the time is 1-3 hours.

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

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