A biodegradable poly (adipate / butylene terephthalate)-isosorbide copolyester and its preparation method and application

Abstract

The present invention belongs to the field of degradable polyesters and specifically discloses a biodegradable poly (adipate / butylene terephthalate-isosorbide) copolyester and its preparation method and application. The method comprises the following steps: 1) mixing terephthalic acid or dimethyl terephthalate, adipic acid, butylene glycol, and isosorbide to obtain a monomer mixture; heating the mixture under an inert atmosphere until the monomer mixture is melted, adding a catalyst, and continuing to heat the mixture to 160-205°C for reaction to obtain a prepolymer; 2) polycondensation reaction: continuing to heat the prepolymer to 240°C, gradually reducing the reaction system pressure to 0.01-0.2 kPa, and then heating to 250°C for reaction for 5-7 hours. After the reaction is completed, the product is obtained. The present invention obtains a PBIAT copolyester with higher toughness and strength by improving the synthesis process of PBAT. Compared with pure PBAT copolyester, the tensile strength of PBIAT copolyester can be increased to 27.1 MPa, the elongation at break is increased to 784-2574%, and the melting point is higher than 100°C. It has excellent processing performance and can be widely used in the field of bio-based degradable film packaging.

Description

Technical Field

[0001] The invention belongs to the field of degradable polyester synthesis, and particularly relates to a biodegradable polyadipate / butylene terephthalate-isosorbide copolyester and a preparation method and application thereof. Background Art

[0002] Plastics have become a staple of our current economy due to their versatility, durability, high strength-to-weight ratio, and excellent economic efficiency, primarily used in disposable products such as packaging. However, after a brief initial use, approximately 90% of plastics are not recycled but instead end up in landfills, incinerated, or even released into the natural environment. Recycled plastics are only used in low-value products, significantly lower than the recycling rates of two other major materials: paper (58%) and steel (85%). Therefore, there is widespread consensus on the use of biodegradable and compostable new plastics for single-use plastic packaging products, and biodegradable plastics are currently undergoing intensive research, development, and industrialization. Seven representative categories of biodegradable plastics are: polylactic acid (PLA), poly (3-hydroxyalkanoate) (PHA), poly (ε-caprolactone) (PCL), polyesters (PBS / PBSA), aliphatic aromatic copolyesters (PBAT), polyvinyl alcohol (PVA), and carbon dioxide copolymers (PPC).

[0003] Polybutylene adipate / terephthalate (PBAT) has the most comprehensive properties similar to those of the general-purpose plastic polyethylene and has become one of the three biodegradable materials being developed globally. Although PBAT holds the largest market share in replacing traditional disposable packaging and film materials, these biodegradable materials all have certain drawbacks compared to traditional plastics, such as higher production costs, lower strength, and lower thermal physical properties. Furthermore, PBAT is a fossil-based biodegradable plastic that still contributes to carbon dioxide emissions. Therefore, research into biodegradable plastics derived from novel bio-based rigid monomers derived from renewable energy sources is of great significance.

[0004] Currently, the main bio-based rigid monomers on the market are furandicarboxylic acid (FDCA) and isosorbide (IS). The former is one of the 12 bio-based platform compounds identified by the U.S. Department of Energy for priority development and utilization. However, the production technology of FDCA is not yet mature and the price remains high. Its price is difficult to accept as a monomer for the production of plastic packaging products for the consumer market. The latter is currently the only bio-based rigid monomer that is commercially produced on a large scale and can be fully introduced into the consumer market.

[0005] The structure of isosorbide contains two cis-fused tetrahydrofuran (THF) rings with a ring angle of 120°. The overall molecule presents a "V"-shaped structure. The two hydroxyl groups it carries extend one outside the "V"-shaped ring structure (exo) and one inside the "V"-shaped ring structure (endo). The difference in the reactivity of the two hydroxyl groups causes polymers containing isosorbide to have problems such as low molecular weight. Patent CN113861399A discloses a biodegradable polyester PBIAT and a preparation method thereof. Adipic acid, terephthalic acid, isosorbide and butanediol are mixed uniformly and added to a reactor to first undergo an esterification reaction. Then, a catalyst is added and the temperature is increased to carry out a condensation reaction to obtain a PBIAT copolyester. This patent has the following problems: (1) a common problem in the field that a large amount of prepolymer is extracted during vacuuming in the condensation stage; (2) due to the complex monomer composition, the use of a single temperature in the preparation process will result in insufficient reaction; (3) due to the low reactivity of isosorbide, a low temperature is not conducive to the polymerization reaction. The above problems will lead to low molecular weight and poor performance of the product, so it is difficult to obtain PBIAT copolyester with high molecular weight and excellent performance according to this patent. Summary of the Invention

[0006] In view of the problems and shortcomings in the prior art, the present invention aims to provide a biodegradable poly (butylene adipate / terephthalate)-isosorbide (PBIAT) copolyester and its preparation method and application.

[0007] To achieve the purpose of the invention, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of the present invention provides a method for preparing a biodegradable PBIAT copolyester, comprising the following steps:

[0009] (1) mixing terephthalic acid or methyl terephthalate with adipic acid, butanediol, and isosorbide to obtain a monomer mixture; heating the mixture under an inert atmosphere until the monomer mixture is melted, adding a catalyst, and continuing to heat the mixture to 180-205° C. for reaction to obtain a prepolymer;

[0010] (2) The prepolymer is further heated to 235-245° C., the pressure of the reaction system is reduced to 0.01-0.2 kPa, and then the temperature is raised to 250-255° C. for reaction for 5-7 hours. After the reaction is completed, the biodegradable PBIAT copolyester is obtained.

[0011] In the present invention, in step (1), terephthalic acid or methyl terephthalate, adipic acid, butanediol, and isosorbide are stirred and mixed under an inert atmosphere, heated and melted, and then a catalyst is added to carry out an esterification or transesterification reaction. If 1,4-butanediol is selected, an oligomer containing the following four structural units is obtained:

[0012]

[0013] Among them, IA represents a polyadipic acid / isosorbide polyester structural unit, BT represents a polyadipic acid / 1,4-butanediol polyester structural unit, IT represents a polyterephthalic acid / isosorbide polyester structural unit, and BA represents a polyadipic acid / 1,4-butanediol polyester structural unit.

[0014] According to the preparation method, preferably, the specific operation of adding the catalyst in step (1) and continuing to heat the reaction to 180-205°C is as follows: adding the esterification catalyst, sealing the reaction system and heating it to 160-170°C, and keeping the temperature to react for 1-2 hours; then starting the condensation reflux, and then heating it to 180-205°C to react. The closed system reaction for 1-2 hours allows the water and methanol generated during the reaction to exist in the reaction system in a gaseous state, making the system pressure slightly higher than atmospheric pressure, so that the raw materials react under a slightly positive pressure state, thereby improving the reaction efficiency.

[0015] According to the preparation method, preferably, the step (1) of continuing to heat the reaction to 180-205°C is performed by first heating the reaction to 180-185°C for 1-1.5 hours, and then heating the reaction to 200-205°C for at least 1 hour. The present invention adopts a gradient temperature increase strategy to allow the reaction system to reach the optimal reaction temperature of adipic acid, isosorbide, and dimethyl terephthalate in sequence, so that each raw material can fully react and improve the reaction efficiency.

[0016] According to the preparation method, preferably, the step (2) of reducing the pressure of the reaction system to 0.01-0.2 kPa comprises: first reducing the pressure of the reaction system to 1.5-2.0 kPa, maintaining the pressure for 30-40 minutes, and then continuing to reduce the pressure by 0.01-0.2 kPa.

[0017] According to the preparation method, preferably, the speed of reducing the pressure of the reaction system to 1.5-2.0 kPa is to reduce the system pressure by half every 15 minutes.

[0018] The present invention adopts the method of gradually and slowly reducing the system pressure during the vacuum melt polycondensation stage, particularly maintaining the pressure at 1.5-2.0 kPa for 30-40 minutes, and finally performing melt polycondensation under high vacuum conditions at 250°C. This can effectively improve the polycondensation reaction efficiency and prevent the large-scale extraction of prepolymer, thereby increasing the molecular weight of the copolyester.

[0019] According to the preparation method, preferably, based on the total molar mass of isosorbide and butanediol as 100 mol%, the molar mass percentage of isosorbide in step (1) is 5-40 mol%, and the molar mass percentage of butanediol is 60-95 mol%.

[0020] The present invention introduces isosorbide into PBAT and utilizes the rigid ring structure of isosorbide to strengthen the copolyester molecular chain, which can significantly improve the mechanical properties of the copolyester PBAT. At the same time, the unique V-shaped structure of isosorbide is used to destroy the crystallinity of the copolyester and improve the elongation at break of PBAT. However, when the molar mass percentage of isosorbide is too high, the polymerization reaction becomes more difficult, which in turn leads to a simultaneous decrease in the molecular weight and crystallinity of the copolyester and a decrease in mechanical properties. Therefore, the molar mass percentage of isosorbide in the present invention is controlled to 5-40 mol%, preferably 5-20 mol%.

[0021] According to the preparation method, preferably, the sum of the molar masses of butanediol and isosorbide is denoted as n1, and the sum of the molar masses of terephthalic acid or methyl terephthalate and adipic acid is denoted as n2, with n1:n2 being 1.1-1.3:1. If n1:n2 ≤ 1.1, especially when n1:n2 ≤ 0.9, the polymerization rate decreases significantly, making it difficult to obtain a copolyester with a higher molecular weight. Therefore, the present invention controls n1:n2 to be 1.1-1.3:1, preferably n1:n2 = 1.1:1.

[0022] According to the preparation method, preferably, the amount of the catalyst used is 0.02 wt% to 0.06 wt% of the total mass of terephthalic acid or dimethyl terephthalate, adipic acid, butanediol, and isosorbide.

[0023] According to the preparation method, preferably, the catalyst is at least one of tetrabutyl titanate, isopropyl titanate, antimony trioxide and titanium-magnesium bimetallic catalyst.

[0024] According to the preparation method, preferably, the butanediol is one or more of 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, and 2,3-butanediol.

[0025] The second aspect of the present invention provides a biodegradable PBIAT copolyester product prepared using the preparation method described in the first aspect.

[0026] The third aspect of the present invention provides an application of the biodegradable PBIAT copolyester product described in the second aspect in the field of plastic packaging.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention successfully introduces the bio-based rigid monomer isosorbide with a bicyclic structure into the molecular chain of PBAT through a "one-pot synthesis method" to prepare a bio-based degradable PBIAT copolyester. The process route is simple and can be synthesized using existing copolyester production equipment. It is easy to industrialize and continuously produce and has high economic benefits.

[0029] (2) In the esterification stage, the present invention first allows the raw materials to react for a certain period of time under a slightly positive pressure state, and then gradually raises the temperature to different temperatures for a certain period of time. The temperature strategy of gradient heating is adopted to enable the reaction system to reach the optimal reaction temperature of adipic acid, isosorbide and dimethyl terephthalate in turn, so that each raw material can fully react and improve the reaction efficiency.

[0030] (3) The present invention adopts the method of gradually and slowly reducing the system pressure during the polycondensation stage, especially maintaining the pressure at 1.5-2.0 kPa for a certain period of time, and then raising the temperature to carry out high vacuum melt polycondensation, which effectively improves the polycondensation reaction efficiency and prevents the large-scale extraction of prepolymer, thereby improving the molecular weight and mechanical properties of PBIAT copolyester.

[0031] (4) The present invention improves the synthesis process of PBAT to obtain PBIAT copolyester with higher toughness and strength. Compared with pure PBAT copolyester, the PBIAT copolyester prepared by the present invention can increase the tensile strength to 27.1MPa and the elongation at break to 784-2574%. It has a melting point above 100°C and has excellent processing properties. It can be widely used in the field of bio-based degradable film packaging.

[0032] (5) The bio-based rigid monomer isosorbide introduced into the molecular weight of PBAT by the present invention is derived from the chemical intermediates of starch and sorbitol. It is a completely renewable bio-based monomer that can not only significantly improve the mechanical properties of PBAT, but also reduce the use of fossil resources, which is beneficial to energy conservation and environmental protection, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The synthetic route of the biodegradable poly (adipate / butylene terephthalate)-isosorbide copolyester of the present invention is shown in FIG.

[0034] Figure 2 The copolyester obtained in Example 1, Example 4 and Comparative Example 1 1 H-NMR spectrum;

[0035] Figure 3 The infrared spectra of the copolyesters obtained in Examples 1-5 and Comparative Example 1 are shown;

[0036] Figure 4 1-2 are stress-strain curves of the copolyesters obtained in Examples 1-5 and Comparative Examples 1-2;

[0037] Figure 5 The ultimate tensile strength and elongation at break of the copolyesters obtained in Examples 1-5 and Comparative Examples 1-2 are shown;

[0038] Figure 6The DSC curves of the copolyesters obtained in Examples 1-4 and Comparative Example 1 are shown, where (a) is a secondary heating curve and (b) is a cooling curve.

[0039] Figure 7 These are compression-molded sheets of the copolyester obtained in Example 5 and Comparative Example 1. The brown transparent sheet on the left corresponds to Example 5, and the white sheet on the right corresponds to Comparative Example 1. DETAILED DESCRIPTION

[0040] The following examples are intended only to further illustrate the present invention. It should be noted that all technical and scientific terms used herein have the same meanings as in the art to which the present invention pertains, unless otherwise specified. Experimental methods in the following examples, where specific conditions are not specified, were based on conventional techniques in the art or the conditions recommended by the manufacturer. Reagents and instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0041] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0042] The following examples and comparative examples provide a method for preparing a biodegradable poly(adipate / butylene terephthalate)-isosorbide (PBIAT) copolyester. The chemical structure of the PBIAT is shown in Formula I:

[0043]

[0044] The raw materials in the following examples and comparative examples can all be obtained commercially. The monomer names and their corresponding abbreviations are shown in Table 1.

[0045] Table 1 Monomer names and abbreviations used in the examples

[0046] Monomer name Monomer abbreviation Monomer residue abbreviation Terephthalic acid PTA T Dimethyl terephthalate DMT T Adipic acid AA A 1,4-Butanediol BDO B Isosorbide IS I

[0047] In the following specific implementation manner, the test and analysis methods used are described as follows:

[0048] Thermal analysis: The DSC curve of the sample was determined by using a Shimadzu DSC-60Plus from Japan. A thermal cycle program of one heating-cooling-two heating procedures was adopted. The test temperature range was -40 to 180 °C, the heating and cooling rate was 10 °C / min, and the holding time was 3 min.

[0049] Mechanical properties: Type 5B specimens specified in ISO 572-2 were pressed using a vacuum laminator, and the tensile strength and elongation at break of the copolyesters PBAT and PBIAT were measured using a UTM-2502 electronic universal testing machine produced by Xinsansi Metrology Technology Co., Ltd. at a tensile rate of 100 mm / min.

[0050] Chemical structure characterization: The chemical structure of the copolyester film samples was determined using a Thermo Fisher Nicolet iS10 Fourier transform infrared spectrometer in ATR mode. Further characterization was performed using a Bruker AVANCE III HD600 MHz nuclear magnetic resonance spectrometer, using deuterated chloroform as the solvent and tetramethylsilane as the internal standard.

[0051] Example 1

[0052] Preparation of PB 95 I5AT copolyester, wherein the total molar mass of BDO and IS is 100 mol%, B 95 and I5 represent 95 mol% of BDO and 5 mol% of IS, respectively. The specific preparation method includes the following steps. The synthesis route can be found in Figure 1 :

[0053] (1) Preparation of PB by esterification reaction 95 I5AT copolyester prepolymer

[0054] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 18.81g (0.209mol) of 1,4-butanediol, and 1.606g (0.011mol) of isosorbide into a three-necked flask, then place the three-necked flask in an electric furnace, set up a condensing device and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% catalyst of the total weight of the monomers. Tetrabutyl titanate (0.01 g) was added. The reaction system was sealed and the valve to the condenser was closed. The temperature was raised to 160°C. The system was first subjected to an esterification reaction for 1.5 hours under a slightly positive pressure generated by the vaporization of by-products water and methanol. The valve to the condenser was then opened to continue the esterification reaction. The temperature was raised to 180°C for 1.5 hours and then to 200°C for at least 1 hour. The reaction was terminated until the volume of the collected by-products (water and methanol) reached approximately 85% of the theoretical value. A transparent liquid, namely PB, was obtained. 95 I5AT copolyester prepolymer.

[0055] (2) Preparation of PB by polycondensation reaction 95 I5AT copolyester

[0056] Replace the above condensation collection device with a vacuum device and collect the obtained PB 95The prepolymer of I5AT copolyester is further heated to 240℃ and gradually and slowly vacuumed. The system pressure is reduced by half every 15 minutes until the system pressure drops to about 1.5kPa. It is maintained for 30 minutes. The vacuum is continued to maintain the pressure at 0.01-0.2kPa. The reaction temperature is then raised to 250℃ and the reaction is carried out for 5-7 hours. When the product viscosity is relatively high, the vacuum is stopped and the final product PB is collected. 95 I5AT copolyester.

[0057] Example 2

[0058] Preparation of PB 90 I 10 AT copolyester, wherein the total molar mass of BDO and IS is 100 mol%, B 90 and I 10 Respectively represent 90 mol% BDO and 10 mol% IS. The specific preparation method includes the following steps. The synthesis route can be found in Figure 1 :

[0059] (1) Preparation of PB by esterification reaction 90 I 10 AT copolyester prepolymer

[0060] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 17.82g (0.198mol) of 1,4-butanediol, and 3.212g (0.022mol) of isosorbide into a three-necked flask, then place the three-necked flask into an electric furnace, set up a condenser and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% of the total weight of the monomers as a catalyst. The reaction system was sealed and the valve to the condenser was closed. The temperature was raised to 170°C. The system was first subjected to an esterification reaction for 2 hours under a slightly positive pressure generated by the vaporization of by-products water and methanol. The valve to the condenser was then opened to continue the esterification reaction. The temperature was raised to 185°C for 1.5 hours and then to 205°C for at least 1 hour. The reaction was terminated until the volume of the collected by-products (water and methanol) reached about 85% of the theoretical value. A transparent liquid, namely PB, was obtained. 90 I 10 AT copolyester prepolymer.

[0061] (2) Preparation of PB by polycondensation reaction 90 I 10 AT copolyester

[0062] Replace the above condensation collection device with a vacuum device and collect the obtained PB 90 I 10The AT copolyester prepolymer is further heated to 235 ° C and vacuum is started. The pressure is reduced by half every 15 minutes until the system pressure drops to about 1.5 kPa. It is maintained for 30 minutes. The vacuum is continued to maintain the pressure at 0.01-0.2 kPa. The reaction temperature is then raised to 250 ° C and the reaction is carried out for 5-7 hours. When the product viscosity is relatively large, the vacuum is stopped and the final product PB is collected. 90 I 10 AT copolyester.

[0063] Example 3

[0064] Preparation of PB 85 I 15 AT copolyester, wherein the total molar mass of BDO and IS is 100 mol%, B 85 and I 15 Respectively represent 85 mol% BDO and 15 mol% IS. The specific preparation method includes the following steps. The synthesis route can be found in Figure 1 :

[0065] (1) Preparation of PB by esterification reaction 85 I 15 AT copolyester prepolymer

[0066] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 16.83g (0.187mol) of 1,4-butanediol, and 4.818g (0.033mol) of isosorbide into a three-necked flask, then place the three-necked flask into an electric furnace, set up a condensing device and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% of the total weight of the monomers as a catalyst. The reaction system was sealed and the valve to the condenser was closed. The temperature was raised to 165°C. The system was first subjected to an esterification reaction for 2 hours under a slightly positive pressure generated by the vaporization of by-products water and methanol. The valve to the condenser was then opened to continue the esterification reaction. The temperature was raised to 185°C for 1.5 hours and then to 200°C for at least 1 hour. The reaction was terminated until the volume of the collected by-products (water and methanol) reached about 85% of the theoretical value. A transparent liquid, namely PB, was obtained. 85 I 15 AT copolyester prepolymer.

[0067] (2) Preparation of PB by polycondensation reaction 85 I 15 AT copolyester

[0068] Replace the above condensation collection device with a vacuum device and collect the obtained PB 85 I 15The AT copolyester prepolymer is further heated to 240 ° C and vacuum is started. The pressure is reduced by half every 15 minutes until the system pressure drops to about 1.5 kPa. It is maintained for 30 minutes. The vacuum is continued to maintain the pressure at 0.01-0.2 kPa. The reaction temperature is then raised to 250 ° C and the reaction is carried out for 5-7 hours. When the product viscosity is large, the vacuum is stopped and the final product PB is collected. 85 I 15 AT copolyester.

[0069] Example 4

[0070] Preparation of PB 80 I 20 AT copolyester, wherein the total molar mass of BDO and IS is 100 mol%, B 80 and I 20 Respectively represent 80 mol% BDO and 20 mol% IS. The specific preparation method includes the following steps. The synthesis route can be found in Figure 1 :

[0071] (1) Preparation of PB by esterification reaction 80 I 20 AT copolyester prepolymer

[0072] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 15.84g (0.176mol) of 1,4-butanediol, and 6.424g (0.044mol) of isosorbide into a three-necked flask, then place the three-necked flask in an electric furnace, set up a condensing device and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% catalyst of the total weight of the monomers. Tetrabutyl titanate (0.01 g) was added. The reaction system was sealed and the valve to the condenser was closed. The temperature was raised to 165°C. The system was first subjected to an esterification reaction for 1.5 hours under a slightly positive pressure generated by the vaporization of by-products water and methanol. The valve to the condenser was then opened to continue the esterification reaction. The temperature was raised to 180°C for 1.5 hours and then to 200°C for at least 1 hour. The reaction was terminated until the volume of the collected by-products (water and methanol) reached approximately 85% of the theoretical value. A transparent liquid, namely PB, was obtained. 80 I 20 AT copolyester prepolymer.

[0073] (2) Preparation of PB by polycondensation reaction 80 I 20 AT copolyester

[0074] Replace the above condensation collection device with a vacuum device and collect the obtained PB 80 I 20The AT copolyester prepolymer is further heated to 245 ° C and vacuum is started. The pressure is reduced by half every 15 minutes until the system pressure drops to about 1.5 kPa. It is maintained for 30 minutes. The vacuum is continued to maintain the pressure at 0.01-0.2 kPa. The reaction temperature is then raised to 255 ° C and the reaction is carried out for 5-7 hours. When the product viscosity is large, the vacuum is stopped and the final product PB is collected. 80 I 20 AT copolyester.

[0075] Example 5

[0076] Preparation of PB 60 I 40 AT copolyester, wherein the total molar mass of BDO and IS is 100 mol%, B 60 and I 40 Respectively represent 60 mol% of BDO and 40 mol% of IS, and the specific preparation method includes the following steps:

[0077] (1) Preparation of PB by esterification reaction 60 I 40 AT copolyester prepolymer

[0078] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 11.88g (0.132mol) of 1,4-butanediol, and 12.848g (0.088mol) of isosorbide into a three-necked flask, then place the three-necked flask into an electric furnace, set up a condensing device and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% of the total weight of the monomers as a catalyst. The reaction system was sealed and the valve to the condenser was closed. The temperature was raised to 165°C. The system was first subjected to an esterification reaction for 2 hours under a slightly positive pressure generated by the vaporization of by-products water and methanol. The valve to the condenser was then opened to continue the esterification reaction. The temperature was raised to 185°C for 1.5 hours and then to 205°C for at least 1 hour. The reaction was terminated until the volume of the collected by-products (water and methanol) reached about 85% of the theoretical value. A transparent liquid, namely PB, was obtained. 60 I 40 AT copolyester prepolymer.

[0079] (2) Preparation of PB by polycondensation reaction 60 I 40 AT copolyester

[0080] Replace the above condensation collection device with a vacuum device and collect the obtained PB 60 I 40The AT copolyester prepolymer is further heated to 245 ° C and vacuum is started. The pressure is reduced by half every 15 minutes until the system pressure drops to about 1.5 kPa. It is maintained for 30 minutes. The vacuum is continued to maintain the pressure at 0.01-0.2 kPa. The reaction temperature is then raised to 255 ° C and the reaction is carried out for 5-7 hours. When the product viscosity is large, the vacuum is stopped and the final product PB is collected. 60 I 40 AT copolyester.

[0081] Comparative Example 1

[0082] Preparation of PBAT, specifically comprising the following steps:

[0083] (1) Preparation of PBAT copolyester prepolymer by esterification reaction

[0084] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, and 19.8g (0.22mol) of 1,4-butanediol into a three-necked flask, then place the three-necked flask in an electric furnace to build a condenser and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% catalyst tetrabutyl titanate (0.01g) based on the total mass of the monomer, seal the reaction system and close the valve to the condenser, heat to 175°C, and allow the system to undergo esterification reaction for 2h under the slightly positive pressure generated by the gasification of by-products water and methanol. Then, open the valve to the condenser to continue the esterification reaction, heat to 180°C for 1.5h, and then 200°C for at least 1h, until the volume of the collected by-products (water and methanol) reaches about 85% of the theoretical value, terminate the reaction, and obtain a transparent liquid, i.e., a prepolymer of PBAT copolyester.

[0085] (2) Preparation of PBAT copolyester by polycondensation reaction

[0086] The condensation collection device was replaced with a vacuum device, and the obtained PBAT copolyester prepolymer was further heated to 240°C and vacuumed. The pressure was reduced by half every 15 minutes until the system pressure dropped to about 1.5 kPa, maintained for 30 minutes, and vacuumed. After the pressure was maintained at 0.01-0.2 kPa, the reaction temperature was raised to 250°C and reacted for 5-7 hours. When the product viscosity was large, vacuuming was stopped and the final product PBAT copolyester was collected.

[0087] Comparative Example 2

[0088] Preparation of PB 95 I5AT * The specific preparation method of copolyester comprises the following steps:

[0089] (1) Preparation of PB by esterification reaction 95I5AT * Copolyester prepolymer

[0090] Weigh 19.42g (0.1mol) of dimethyl terephthalate, 14.61g (0.1mol) of adipic acid, 18.81g (0.209mol) of 1,4-butanediol, and 1.606g (0.011mol) of isosorbide into a three-necked flask, then place the three-necked flask in an electric furnace to build a condenser and a stirring device, introduce N2 to continuously purge the reaction system and start heating. When the raw materials are completely liquid, add 0.02% of the total mass of the monomer as catalyst tetrabutyl titanate (0.01g), heat to 200°C and react for 4-5h until the volume of the collected by-products (water and methanol) reaches about 85% of the theoretical value, then terminate the reaction to obtain a transparent liquid, namely PB 95 I 50 AT * Copolyester prepolymer.

[0091] (2) Preparation of PB by polycondensation reaction 95 I5AT * Copolyester

[0092] Replace the above condensation collection device with a vacuum device and collect the obtained PB 95 I5AT * The copolyester prepolymer is further heated to 240 ° C and vacuum is started until the system pressure drops to 0.01-0.2 kPa. Then the reaction temperature is raised to 250 ° C and the reaction is carried out for 5-7 hours. When the product viscosity is large, the vacuum is stopped and the final product PB is collected. 95 I5AT * Copolyester.

[0093] For ease of comparison, some reaction conditions for preparing copolyesters in Examples 1-5 and Comparative Examples 1-2 are listed in Table 2 based on the raw material amounts. In Table 2, based on the total molar mass of 1,4-butanediol and isosorbide as 100 mol%, 1,4-butanediol accounts for 60 mol% to 95 mol% and isosorbide accounts for 5 mol% to 40 mol%. Based on the total molar mass of dimethyl terephthalate and adipic acid as 100 mol%, dimethyl terephthalate accounts for 50 mol% and adipic acid accounts for 50 mol%, as shown below:

[0094] Table 2 Raw material dosage and reaction process

[0095] project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Product Name <h2 style=";text-align:left;direction:ltr"><![CDATA[PB <h2 style=";text-align:left;direction:ltr"> 95 <h2 style=";text-align:left;direction:ltr"> I5AT]]><h2 style=";text-align:left;direction:ltr"> <![CDATA[PB 90 I 10 AT]]> <![CDATA[PB 85 I 15 AT]]> <![CDATA[PB 80 I 20 AT]]> <![CDATA[PB 60 I 40 AT]]> PBAT <h2 style=";text-align:left;direction:ltr"><![CDATA[PB <h2 style=";text-align:left;direction:ltr"> 95 <h2 style=";text-align:left;direction:ltr"> I5AT*]]><h2 style=";text-align:left;direction:ltr"> 1,4-Butanediol (mol%) 95 90 85 80 60 100 95 Isosorbide (mol%) 5 10 15 20 40 0 5 Dimethyl terephthalate (mol%) 50 50 50 50 50 50 50 Adipic acid (mol%) 50 50 50 50 50 50 50 Esterification stage / slightly positive pressure state have have have have have have none Polycondensation stage / staged depressurization have have have have have have none

[0096] Structural characterization and performance testing

[0097] 1. H NMR spectroscopy

[0098] Figure 2The nuclear magnetic resonance hydrogen spectra of the PBIAT copolyester obtained in Example 1 and Example 4 and the PBAT copolyester obtained in Comparative Example 1 are shown in FIG. Figure 2 of 1 The H-NMR spectrum was analyzed. The sharp and strong peak d at δ8.09ppm was attributed to the proton on the benzene ring. The two similar peaks at δ4.43, 4.37, 4.14, and 4.09ppm were respectively attributed to the methylene e and e' on the ester carbonyl adjacent to the aliphatic group or aromatic group on 1,4-butanediol. Among them, the chemical shift of the proton on the methylene adjacent to the ester carbonyl on 1,4-butanediol moved to the low field due to the formation of a larger conjugated structure by the ester carbonyl connected to the benzene ring; the sharp peak at δ2.32ppm was attributed to The peak at δ1.97ppm is attributed to the proton g on the methylene group adjacent to the ester carbonyl group on the adipic acid segment; the peak at δ1.97ppm is attributed to the proton f on the methylene group not adjacent to the ester carbonyl group in the 1,4-butanediol unit; the peak at δ1.65ppm is attributed to the proton h on the methylene group not adjacent to the ester carbonyl group in the adipic acid unit; among them, the characteristic peak of the isosorbide unit is very small and concentrated between δ5.5-3.5ppm. As shown in the figure, the characteristic peak increases significantly with the increase of the amount of isosorbide added, which proves that the isosorbide segment has successfully entered the copolyester.

[0099] 2. Infrared spectroscopy

[0100] Figure 3 IR spectra of the PBIAT copolyesters obtained in Examples 1-5 and the PBAT copolyesters obtained in the comparative example. Figure 3 Medium 1713cm -1 The strong and sharp absorption peak at 1238cm comes from C=O -1 The strong absorption peak at 1016 cm is derived from the asymmetric vibration of the ArC-OC bond in the polyester ester group. -1 The stretching vibration of the C—C bonds connected by multiple methylene groups is 874 cm -1 The weak peak at 723 cm represents the benzene ring. -1 The strong and sharp absorption peak is caused by the out-of-plane stretching vibration of CH on the benzene ring. Compared with Comparative Example 1, Examples 1-5 have a strong absorption peak at 972 cm -1 There is a very weak absorption peak at , which is the characteristic peak of the isosorbide unit in the polyester segment. It comes from the symmetrical vibration of the COC group in the isosorbide fused bicyclic ring, indicating that PBIAT is successfully prepared in this embodiment of the present invention.

[0101] 3. Mechanical properties

[0102] The copolyester samples prepared in the above examples 1-5 and comparative examples 1-2 were subjected to mechanical property tests. Figure 4 The stress-strain curves of the copolyesters obtained in Examples 1-5 and Comparative Examples 1-2 are shown. Figure 5The graph shows the ultimate tensile strength and elongation at break of the copolyesters obtained in Examples 1-5 and Comparative Examples 1-2. Specific data in the graph are shown in Table 3. The tensile strength and elongation at break were determined in accordance with the national standard GB / T 1040.3-2006.

[0103] Table 3 Mechanical properties data of Examples 1-4 and Comparative Examples 1-2:

[0104] serial number Sample name Tensile strength (MPa) Elongation at break (%) Example 1 <h2 style=";text-align:left;direction:ltr"><![CDATA[PB <h2 style=";text-align:left;direction:ltr"> 95 <h2 style=";text-align:left;direction:ltr"> I5AT]]><h2 style=";text-align:left;direction:ltr"> 27.1 1271.8 Example 2 <![CDATA[PB 90 I 10 AT]]> 17.6 1035.2 Example 3 <![CDATA[PB 85 I 15 AT]]> 14.2 1024.1 Example 4 <![CDATA[PB 80 I 20 AT]]> 9.1 784.3 Example 5 <![CDATA[PB 60 I 40 AT]]> 1.6 2574.5 Comparative Example 1 PBAT 12.2 778.3 Comparative Example 2 <h2 style=";text-align:left;direction:ltr"><![CDATA[PB <h2 style=";text-align:left;direction:ltr"> 95 <h2 style=";text-align:left;direction:ltr"> I5AT*]]><h2 style=";text-align:left;direction:ltr"> 14.9 800.7

[0105] from Figure 4 、 Figure 5 As can be seen from Table 3, compared to the PBAT (comparative example 1) not introducing isosorbide, the adding of isosorbide (embodiment 1) has significantly enhanced the mechanical property of copolyesters PBIAT, this is due to the introduction of rigid ring in the isosorbide structure having a certain reinforcing effect on polymer molecular chain, and the unique V-shaped structure of isosorbide destroys the crystallinity of multipolymer, thereby causing the tensile strength of PBIAT and the lifting of elongation at break.But along with the increase (embodiment 2-embodiment 4) of isosorbide consumption, there is a downward trend in mechanical property again, this is due to the low reactivity of-OH in isosorbide making polymerization reaction difficult, causing polymer molecular weight to reduce, and then affecting mechanical property.When isosorbide unit content further increases in molecular chain (embodiment 5), multipolymer presents amorphous state, and now copolymer strength is very low and has high elongation at break.

[0106] Compared to Comparative Example 2 in which the preparation process is not optimized (i.e., a slightly positive pressure state is not maintained in the esterification stage and there is no segmented temperature increase, and no segmented depressurization is performed in the polycondensation stage), the mechanical properties of the samples of Example 1-Example 4 are greatly improved. This is because the esterification stage maintains a slightly positive pressure state for a period of time to improve the reaction efficiency, and the gradient temperature increase strategy adopted in the esterification stage can make the reaction system reach the optimal reaction temperature of adipic acid, isosorbide and dimethyl terephthalate in sequence, thereby maximizing the reaction efficiency. In addition, the present invention adopts segmented depressurization in the vacuum melt polycondensation stage, especially maintaining a long time at about 1.5kpa, and finally polycondensing under vacuum conditions at 250°C, which can effectively prevent a large amount of extraction of prepolymer, significantly improve the molecular weight of copolyester, and thus affect the mechanical properties of the sample.

[0107] 4.DSC curve

[0108] Figure 6 The DSC curves of the PBIAT copolyester obtained in Examples 1-4 and the PBAT copolyester obtained in Comparative Example 1 are shown, where (a) is the DSC curve of the second heating, and (b) is the DSC curve of the cooling. The thermal transition performance data in the figure are listed in Table 4. c Indicates crystallization temperature, △H crepresents the crystallization enthalpy, T g represents the glass transition temperature, T cc Indicates cold crystallization temperature, △H cc represents the cold crystallization enthalpy, T m Indicates melting point, △H m It represents the melting enthalpy.

[0109] Table 4 Thermal transition properties

[0110]

[0111] from Figure 6 As can be seen from Table 4, with the increase of the content of isosorbide with a rigid structure in the polymer chain segment, the movement of the chain segment becomes increasingly difficult, which is reflected in the T g The above shows an upward trend. The difficulty of chain segment movement and the V-shaped structure of isosorbide jointly destroy the regularity of the molecular weight, resulting in a significant decrease in the crystallinity of the PBIAT copolyester with the increase of isosorbide units, which is specifically manifested in the simultaneous decrease in the melting point, crystallization temperature and crystallization enthalpy of the copolyester. Furthermore, when the proportion of isosorbide is greater than 15 mol% (Examples 3 and 4), a clear cold crystallization peak appears. Therefore, as the isosorbide content continues to increase (Example 5), we can predict that the copolyester will show transparency due to the decrease in crystallinity.

[0112] 5. Transparency

[0113] like Figure 7 Shown are compression molded sheets of the PBIAT copolyester obtained in Example 5 and the copolyester obtained in Comparative Example 1. The figures show that the PBIAT copolyester has a certain degree of transparency, which is consistent with the predicted results of the present invention.

[0114] In summary, the present invention optimizes the PBIAT copolyester preparation process to produce PBIAT copolyesters with enhanced toughness and strength. Compared to pure PBAT copolyester, the PBIAT copolyesters prepared in this invention have a tensile strength of up to 27.1 MPa, an elongation at break of 784-2574%, and a melting point above 100°C. These materials exhibit excellent processing properties and are widely applicable to biodegradable film packaging applications.

[0115] The above embodiments are specific implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any other combination, change, modification, substitution, and simplification that does not exceed the design concept of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a biodegradable PBIAT copolyester, characterized in that: The following steps are involved: (1) Terephthalic acid or dimethyl terephthalate is mixed with adipic acid, butanediol, and isosorbide to obtain a monomer mixture; the mixture is heated to 180-205°C under an inert atmosphere until the monomer mixture is melted, a catalyst is added, and the mixture is heated to 180-205°C for reaction to obtain a prepolymer; the specific operation of adding the catalyst and heating the mixture to 180-205°C for reaction is as follows: adding the catalyst, sealing the reaction system and heating the mixture to 160-170°C, and keeping the reaction system in a slightly positive pressure state for reaction for 1-2 hours; then opening a condensation collection device, heating the mixture to 180-185°C for reaction for 1-1.5 hours, and then heating the mixture to 200-205°C for reaction for at least 1 hour; (2) continuing to heat the prepolymer to 235-245°C, reducing the pressure of the reaction system to 0.01-0.2 kPa, and then heating to 250-255°C for reaction for 5-7 hours, to obtain the biodegradable PBIAT copolyester after the reaction is completed; reducing the pressure of the reaction system to 0.01-0.2 kPa comprises: first reducing the pressure of the reaction system to 1.5-2.0 kPa at a rate of reducing the pressure of the system by half every 15 minutes, maintaining the pressure for 30-40 minutes, and then continuing to reduce the pressure to 0.01-0.2 kPa; Based on the total molar mass of isosorbide and butanediol being 100 mol%, the molar mass percentage of isosorbide in step (1) is 5-15 mol%, and the molar mass percentage of butanediol is 85-95 mol%.

2. The preparation method according to claim 1, characterized in that The sum of the molar masses of butanediol and isosorbide is recorded as n1, and the sum of the molar masses of adipic acid and terephthalic acid or dimethyl terephthalate is recorded as n2, n1:n2 = 1.1-1.3:

1.

3. The preparation method according to claim 1, characterized in that The amount of the catalyst used is 0.02 wt%-0.06 wt% of the total mass of terephthalic acid or methyl terephthalate, adipic acid, butanediol and isosorbide.

4. A biodegradable PBIAT copolyester product prepared by the preparation method according to any one of claims 1 to 3.

5. Application of the biodegradable PBIAT copolyester product according to claim 4 in the field of plastic packaging.

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