Synthesis method and performance application of bio-based poly (ethylene 2, 5-furandicarboxylate)

Abstract

The invention provides a synthesis method of bio-based poly (ethylene 2, 5-furandicarboxylate) (poly (ethylene 2, 5-furandicarboxylate) for short) and performance application of the bio-based poly (ethylene 2, 5-furandicarboxylate). According to the method, 2, 5-furandicarboxylic acid (FDCA) derived from renewable resources and ethylene glycol (EG) are used as main raw materials, and the high-molecular-weight PEF is prepared through microwave-assisted esterification-polycondensation reaction under the action of a metal catalyst. The prepared PEF has excellent thermal mechanical property and gas barrier property, the glass transition temperature is about 58.6 DEG C, the melting temperature is about 187.4 DEG C, and the thermal decomposition 18% weight loss temperature exceeds 400 DEG C. The PEF material can be biologically degraded under the industrial composting condition, and the degradation speed is higher compared with that of traditional petroleum-based PET polyester. The PEF provided by the invention is suitable for the fields of food packaging films, beverage bottles and fiber materials, has the advantages of biodegradability, heat resistance stability and high barrier property, can partially replace polyethylene glycol terephthalate (PET) and other petrochemical plastics, and meets the requirements of sustainable development.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material synthesis, and in particular to a method for synthesizing a bio-based polyester, polyethylene 2,5-furandicarboxylate (PEF), as well as the performance characterization of the PEF material prepared by the method and its application in the fields of food packaging and fiber materials. Background Art

[0002] With increasing concern about the pollution and resource depletion of petrochemical plastics, the development of alternative materials derived from biomass has become a research hotspot. 2,5-Furandicarboxylic acid (FDCA) is an important bio-based platform compound produced by the oxidation of biomass sugars (such as 5-hydroxymethylfurfural (HMF)). It is listed by the US Department of Energy as one of the most promising bio-based chemicals and is expected to replace terephthalic acid (PTA) in the synthesis of polyesters. Polyethylene 2,5-furandicarboxylate (PEF), the polymer produced by the polycondensation of FDCA and ethylene glycol (EG), has emerged as a new bio-based polyester material in recent years.

[0003] Studies have shown that PEF is structurally similar to traditional petroleum-based PET, but due to the presence of furan rings, it possesses superior properties. For example, PEF's glass transition temperature is approximately 80-87°C, slightly higher than PET's 80°C, and its melting point is approximately 215°C, significantly lower than PET's 255-260°C, resulting in lower processing energy consumption. More notably, PEF's gas barrier properties far exceed those of PET. Reportedly, PEF's oxygen permeability is approximately 11 times lower than that of PET, and its carbon dioxide permeability is 19-31 times lower. This high barrier property stems from the polarity and nonlinear structure of the furan rings, which restrict molecular chain motion and thus prevent gas permeation. Therefore, PEF is considered an ideal candidate for applications requiring high-barrier properties, such as beverage bottles and food packaging. Furthermore, PEF products possess high mechanical strength, with tensile modulus and strength approaching those of PET. Because its monomers are derived entirely from plant-based materials, PEF production can reduce greenhouse gas emissions by approximately 50% compared to PET.

[0004] However, existing PEF synthesis technologies still have some shortcomings. Currently, PEF synthesis is mainly achieved through methods such as melt polycondensation, solution polycondensation, solid-phase polycondensation, and ring-opening polymerization. The industry prefers a two-step melt polycondensation route (first esterification / ester exchange to form a prepolymer, followed by polycondensation under high vacuum) to avoid complex intermediate steps. However, conventional melt polycondensation requires high temperatures (around 240°C) and long times (more than several hours). Excessive thermal history can easily lead to polymer discoloration and side reactions, which restrict product quality. Although solution polycondensation can be carried out under relatively mild conditions, the use of acid anhydride or acyl chloride monomers and organic solvents makes the process complex and environmentally unfriendly, and the resulting molecular weight is also relatively low (for example, literature reports only DP ~ 70). Solid-phase polycondensation can be used to further increase the molecular weight of the prepolymer and reduce discoloration caused by high melting temperatures. It is a mature technology for the PET industry to prepare bottle-grade materials and is also suitable for post-polycondensation to increase the viscosity of PEF. However, the solid-phase method increases the process steps and energy consumption, and still needs to be optimized for PEF industrialization. Ring-opening polymerization is another method for preparing high-molecular-weight PEF. This involves deriving FDCA into a cyclic diester monomer, which is then ring-opened in the presence of a catalyst to produce colorless, high-molecular-weight PEF. While this method offers high-quality products, the monomer preparation process is complex and costly, making it unsuitable for large-scale production.

[0005] Traditional PET synthesis often uses antimony catalysts (such as antimony trioxide) or titanium catalysts, but antimony catalysts are prone to cause residues that affect food safety, while titanium catalysts have the advantages of high catalytic efficiency, few by-products, high safety, and environmental friendliness, and are gradually being used in industrial-scale polyester synthesis. Titanium catalysts such as tetrabutyl titanate or other organic titanium compounds have been widely used in transesterification and polycondensation reactions. They not only have high catalytic activity and can effectively improve the transesterification reaction rate and polycondensation reaction efficiency, but also avoid the problem of heavy metal residues in the polymer caused by antimony catalysts, greatly improving the safety of polyester products in the field of food packaging. In addition, titanium catalysts have little effect on the color of polyester products during use, and the resulting PEF polymer is lighter and more transparent, meeting the needs of packaging and fiber materials with high requirements on appearance. Therefore, titanium catalysts have significant advantages in the synthesis of bio-based polyesters, especially PEF, and have become a green and efficient catalyst suitable for industrial applications.

[0006] As an emerging bio-based polyester, PEF's environmental friendliness has also attracted much attention. PET is difficult to degrade in the natural environment, while PEF exhibits certain biodegradability under high-temperature composting conditions. Studies have shown that under industrial composting conditions at 58°C, the biodegradation rate of PEF samples can reach 90% within 30 days, while PET has basically no degradation. This difference shows that PEF is more easily decomposed by microorganisms under certain conditions, which helps to reduce the long-term environmental accumulation of plastic waste. Of course, the natural degradation rate in soil or water at room temperature needs further study. On the other hand, PEF can also be recycled through chemical recycling routes, such as alcoholysis to recover monomers or enzymatic hydrolysis. Therefore, the development of PEF not only focuses on its performance, but also considers the recycling and degradation solutions throughout its life cycle to achieve a truly sustainable plastic solution.

[0007] In summary, while existing technologies have demonstrated the excellent performance and promising applications of PEF, there is still room for improvement in areas such as efficient synthesis processes (reducing temperature and time, and avoiding discoloration), optimizing catalytic systems, and ensuring high molecular weight and environmentally friendly products. Against this backdrop, the present invention provides an improved PEF synthesis method that, through microwave-assisted melt polycondensation and an optimized catalytic system, enhances the reaction process, accelerates polymerization, and improves product quality, meeting the needs of industrial production and application. Summary of the Invention

[0008] The primary purpose of this invention is to overcome the drawbacks of existing PEF synthesis processes, such as low efficiency, long reaction time, easy discoloration, and insufficient molecular weight, by providing an improved bio-based PEF synthesis method. This method utilizes the rapid and uniform characteristics of microwave heating to accelerate the esterification and polycondensation reactions, significantly shortening the reaction time and producing high-molecular-weight, low-color PEF resin at a relatively low temperature. Furthermore, the present invention optimizes the catalytic system and process conditions, controls the raw material ratio, and adds trace additives to achieve excellent overall performance for PEF. The resulting PEF polymers meet or even exceed the levels of conventional PET in terms of thermal stability, mechanical strength, and barrier properties. Furthermore, they are biodegradable and can be widely used in food packaging films, beverage bottles, and fiber products. Technical Solution

[0009] To achieve the above object, the present invention provides a method for synthesizing bio-based polyethylene 2,5-furandicarboxylate, comprising the following steps: Esterification reaction: The bio-based monomer 2,5-furandicarboxylic acid (FDCA) is mixed with excess ethylene glycol (EG) in a molar ratio of 1:1.1 to 1:2.2. The preferred raw material ratio is 1:1.4 FDCA:EG to ensure sufficient alcohol is involved in the esterification and promote the removal of water molecules. A catalyst, such as a titanium catalyst (e.g., tetrabutyl titanate), a divalent tin compound (e.g., stannous oxalate), or an antimony compound (e.g., antimony acetate), is added to the reaction mixture in an amount of 0.05-0.5 mol%, preferably approximately 0.1 mol%, of the FDCA feed. Under an inert gas (e.g., nitrogen), the reaction is carried out using microwave heating at 160-180°C for 2-4 hours to produce the corresponding oligoesters and water. Microwave heating (e.g., at a frequency of 2.45 GHz) is preferably used to assist the esterification reaction, with a heating power of 200-400 W, to rapidly heat the system and maintain a uniform temperature. During the esterification process, generated water is continuously expelled to push the reaction equilibrium toward ester formation. The esterification step is complete when the reaction system reaches a clear state and the acid value drops to above 95% of the theoretical value. The esterification product, primarily a hydroxyethyl ester end-group oligomer, is molten and ready for use.

[0010] Pre-polycondensation (ester exchange): In certain embodiments, an appropriate amount of diol chain extender or comonomer (such as 1,4-butanediol, diethylene glycol, etc.) is optionally added to the esterification product to adjust the polymer properties. In a preferred embodiment of the present invention, no additional long-chain diol is added to maintain the pure PEF structure, thereby maximizing the barrier properties and Tg. In this step, by continuing to heat and reduce the pressure, ester exchange and further condensation occur between the oligomers. The temperature is raised to 180-200°C, the absolute pressure is reduced to 0.03-0.08MPa, and the reaction is carried out for 1-2 hours. Under the action of the microwave field, the ester exchange reaction proceeds more rapidly, causing the oligomer chain to grow, while continuously removing the generated small molecules.

[0011] Polycondensation reaction: The prepolymer is further heated to 210-240°C, and the final polycondensation reaction is carried out under high vacuum conditions (absolute pressure 10-100 Pa, preferably less than 50 Pa). During the reaction, a microwave radiation power of 300-800W is applied to heat the inside of the reaction system quickly and evenly, maintain the temperature required for polycondensation, and effectively reduce the risk of local overheating and thermal degradation. The polycondensation reaction time is determined according to the target molecular weight and is generally completed in 1-3 hours (much less than the 6-8 hours required for conventional heating). The present invention has found that an inherent viscosity of more than 0.8dL / g can be obtained by polycondensation for 2 hours under microwave enhancement. In order to suppress the color deviation caused by side reactions such as terminal aldehyde groups, a phosphate triester (such as trimethyl phosphate TMP) accounting for 0.01-0.05% of the polymer mass can be added as a stabilizer at the end of the polycondensation to passivate the metal catalyst residue and further reduce the color of the product. After the polycondensation is completed, the microwave and vacuum are released, and the system is cooled to obtain a high-viscosity PEF melt.

[0012] Product Processing: The resulting PEF melt is extruded, cooled, and pelletized to produce PEF resin chips. If necessary, the chips can undergo post-processing, such as solid-phase polycondensation (SPP) at 180-200°C under vacuum or inert gas for 1-5 hours, to further increase the molecular weight. In certain embodiments of the present invention, the SPP step can be omitted. Microwave-assisted melt polycondensation can produce bottle-grade PEF, with an intrinsic viscosity ≥ 0.8 dL / g, corresponding to a number-average molecular weight (Mn) of approximately 30,000 or more. The resulting PEF chips are a light yellow to colorless, transparent solid. Beneficial effects

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly Improved Reaction Efficiency: The introduction of microwave heating technology utilizes the targeted heating effect of microwaves on polar groups (carboxyl and hydroxyl groups), significantly increasing the rates of esterification and polycondensation reactions. At the same temperature, the microwave field can reduce activation energy and shorten polymerization time. The polycondensation step of the present invention can be completed in 2-3 hours, while traditional thermal polycondensation typically requires 6-8 hours or more to achieve a similar molecular weight level. This shortened reaction time not only improves production efficiency but also reduces the possibility of side reactions.

[0014] 2. Reduced reaction temperature and energy consumption: Due to the uniform and rapid microwave heating, this method can achieve comparable polymerization results at temperatures slightly lower than conventional processes. For example, the esterification temperature can be lowered to approximately 170°C (approximately 30°C lower than conventional processes), and the polycondensation temperature can be controlled at 230°C (20-30°C lower than some PET processes), effectively reducing heat energy consumption and equipment temperature requirements. Furthermore, microwave heating requires no dielectric conduction, resulting in higher heating efficiency and lower overall energy consumption.

[0015] 3. High molecular weight and excellent performance: The PEF prepared by the present invention has a high molecular weight and excellent physical properties. The number average molecular weight Mn of a typical product reaches 3–5×10 4 , the weight average molecular weight Mw can exceed 10 5 The dispersion index is about 2.0. The inherent viscosity is 0.8–1.2dL / g, which can meet the application requirements of bottle materials and fiber grades.

[0016] 4. Excellent barrier properties: The oxygen permeability of the resulting PEF is approximately 1 / 10 that of PET, and its carbon dioxide permeability is approximately 1 / 20 that of PET. Gas permeation tests on films of equal thickness show that PEF outperforms commercial PET and PLA films in both oxygen and water vapor barrier properties. This makes PEF ideal for packaging food and beverages requiring a long shelf life, extending the shelf life of the contents. For example, carbonated beverage bottles made with the PEF of this invention exhibit a significantly reduced rate of carbon dioxide loss, preserving the beverage's gas content for longer. Furthermore, its oxygen barrier properties prevent oxidative deterioration of products like beer and juice. These excellent barrier properties are achieved without the need for additional coatings or multi-layer structures, resulting in simplified processing and cost advantages.

[0017] 5. Mechanical Properties and Processing: PEF's tensile strength and modulus are close to those of PET, while its elongation at break is slightly lower than PET, but this can be improved through blending and modification. After isothermal crystallization, PEF develops a certain degree of crystallinity, thereby increasing its rigidity and heat resistance. PEF resin can be processed using similar processing equipment as PET for injection molding, extrusion, and spinning. In the molten state, PEF has a slightly higher viscosity than PET of the same molecular weight, but it can still be processed well below 250°C.

[0018] 6. Biodegradability: The PEF of the present invention can degrade into environmentally friendly small molecules under specific conditions. PEF products decompose relatively quickly in industrial composting facilities, making them suitable for compostable packaging applications. While PEF degradation in natural environments such as soil is still relatively slow, its biodegradability is far superior to that of completely inert PET. Furthermore, PEF can be broken down into FDCA and EG monomers through hydrolysis or enzymatic action. These monomers are harmless to the environment and can even be further metabolized and utilized by microorganisms. Therefore, the PEF of the present invention offers a variety of disposal options after its useful life, including industrial composting and bio-enzymatic recycling, which helps reduce environmental impact.

[0019] 7. Wide range of applications: The PEF of the present invention can be used alone to prepare products, or it can be blended or copolymerized with other polymers to give the material new properties. For example, blending a small amount of PEF with the biodegradable polyester PBAT can improve the rigidity and barrier properties of PBAT while maintaining its flexibility. PEF can also be blended with PLA to improve the heat resistance and barrier properties of PLA, making it more suitable for high-temperature hot filling applications. In the fiber field, the dyeing and light resistance of PEF fibers are expected to be similar to those of PET, and because the molecular structure of PEF contains more oxygen than PET, waste fibers are easier to degrade and process. Overall, as a high-performance bio-based polyester, the PEF of the present invention has application potential in many fields such as packaging films, plastic bottles, fibers, engineering plastics, etc., providing a new option for the sustainable development of the plastics industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To further illustrate the technical solution of the present invention, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the reaction route of the bio-based PEF synthesis method of the present invention, showing the path of FDCA being esterified (direct polymerization) or transesterified to form a prepolymer, and then being polycondensed to form PEF.

[0022] Figure 2 The infrared spectra (FTIR) of the PEF products synthesized with different feed ratios (a) and microwave powers (b) of the present invention are shown in the figure. As can be seen from the figure, the infrared absorption peaks of the characteristic functional groups of the products synthesized with different feed ratios and microwave powers are almost the same. In this spectrum, 3445cm -1 The peak near the terminal hydroxyl (-OH) stretching vibration peak, 3121 cm -1 、1577cm -1 、1015cm -1 The peaks at 2970 cm-1 are the stretching vibration absorption peaks of CH, C=C, and COC bonds on the furan ring, indicating that the product is composed of furan rings; -1 and 2780cm -1 The peak at 1735cm is the stretching vibration peak of methylene (-CH2). -1 and 1270cm -1 The peaks at 1508 cm correspond to the absorption peaks of the carbonyl group (C=O bond) and the ether group (C-O-C bond) in the ester group, respectively, which prove that the product is still an ester after transesterification and polycondensation; -1 and 1453cm -1 The peak at 1230 cm is also a characteristic peak derived from the furan ring, which also indicates that the product is composed of furan rings; -1The peak at 1140 cm is also the stretching vibration peak of the COC bond on the furan ring. -1 The peak at 969 cm is the stretching vibration peak of the CO bond on the ester group. -1 、836cm -1 and 769cm -1 The peak at is the bending vibration peak of the furan ring; at the same time, the carboxyl absorption peak of the product is significantly reduced, which also indicates that the polycondensation reaction is successfully achieved.

[0023] Figure 3 This is a hydrogen nuclear magnetic resonance (1H NMR) spectrum of the PEF product produced according to the present invention. The peak at δ11.70 ppm in the figure originates from protons in the solvent, deuterated trifluoroacetic acid. A single peak with an integral ratio of 2 appears at δ7.56 ppm, attributed to the two symmetric hydrogen atoms on the furan ring. A single peak with an integral ratio of 1 / 2 appears at δ4.96 ppm, attributed to the methylene (–CH2–) hydrogen atoms of the ethylene glycol group. The area integral ratio of these two peaks is approximately equal to the theoretical value of 1:2. These NMR results further confirm the chemical structure of PEF, inferring the repeating unit to be –OCH2CH2O–CO–C4H2O–CO–.

[0024] Figure 4 This is an X-ray diffraction (XRD) pattern of the PEF product produced according to the present invention. The pattern shows diffraction peaks at 2θ of 13.05°, 15.85°, 20.38°, and 27.42°, respectively. The diffraction peaks at 13.05° and 27.42° are not as sharp as those at 15.85° and 20.38°, indicating that the PEF is in an incompletely crystalline state and is a semi-crystalline polymer.

[0025] Figure 5 Thermogravimetric analysis (TGA) curves of PEF products obtained by varying feed ratio (a) and microwave power (b) are shown. This curve reflects the thermal decomposition behavior of PEF: before 300°C, the sample mass remains essentially unchanged, indicating that PEF has good stability under conventional processing temperatures. When the temperature rises to approximately 310°C, significant degradation begins to occur, with approximately 5% mass loss (T 5e ≈310℃); continue to heat up, the maximum degradation rate range appears at about 400℃, and 50% of the mass is lost at about 400℃ (T 20 ≈410°C). It eventually decomposes completely at 500°C. This shows that PEF has excellent thermal stability, and its thermal decomposition temperature is far above its melt processing temperature range, meeting processing and usage requirements.

[0026] Figure 6 The figure is the gel permeation chromatography (GPC) diagram of the PEF sample synthesized by the present invention. As can be seen from the figure, the number average molecular weight M of PEF n 2.196×104 , weight average molecular weight M w is 6.344×10 4 , the molecular weight distribution PDI is 2.89.

[0027] Figure 7 The degradation of PEF with different feed ratios in three different solvents is shown in FIG.

[0028] Figure 8 The degradation of PEF with different microwave powers in three different solvents is shown in the figure. DETAILED DESCRIPTION The following specific examples describe the synthesis method of the present invention and the properties of the resulting PEF in detail, but the present invention is not limited to the following examples. Without departing from the spirit of the present invention, technicians can adjust the conditions according to actual needs.

[0029] Example 1: Preparation of PEF by microwave-assisted direct esterification-polycondensation Raw materials and catalyst: Place 50 g (0.32 mol) of FDCA and 29.0 g (0.47 mol, molar ratio approximately 1:1.46) of ethylene glycol in a stirred 500 mL round-bottom flask. Add 0.161 g of stannous oxalate (SnC2O4) as the catalyst (0.1% of the molar ratio of FDCA). Evacuate the reactor and replace with nitrogen three times to remove oxygen and moisture. Seal the reactor.

[0030] Esterification stage: Turn on the microwave heating system and raise the temperature to 170°C at 300W while maintaining the pressure slightly above atmospheric pressure (the water vapor generated in the reactor should be vented appropriately). Maintain the temperature at 170°C for 3 hours with appropriate stirring. Approximately 30 minutes after the start of the reaction, a large amount of water will condense and be collected. After 2 hours, the reaction solution will gradually change from turbid to clear and viscous. At this point, the main component of the system is low-density hydroxyethyl ester-terminated oligomers. Turn off the microwave power and cool the reaction to 140°C.

[0031] Polycondensation stage: Microwave heating was resumed, power increased to 600 W, and the vacuum pump was simultaneously activated, gradually reducing the pressure to <50 Pa. The temperature was slowly raised to 230°C and stabilized. High-vacuum polycondensation began, lasting 1.5 hours. During this period, viscosity was assessed by observing the increase in torque. After approximately 1 hour, the melt thickened significantly, the stirring torque increased approximately 3-fold, and the color of the material gradually changed from its initial light brown color to a slightly yellowish, transparent state. To suppress late-stage side reactions, an antioxidant and stabilizer mixture was added 1.5 hours into the polycondensation: 0.05 g of trimethyl phosphate (TMP) and 0.05 g of antioxidant 1010 (pentaerythritol tetrakis[(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)] ester. After a further 0.5 hour of reaction, microwave heating was discontinued, and the vacuum was released. When the flask cooled to 200°C, nitrogen was introduced to relieve the pressure.

[0032] Product processing: The melt in the flask is passed through an extruder and extruded into filaments with a diameter of about 2 mm. After water cooling, the filaments are pelletized to obtain light yellow transparent PEF resin chips.

[0033] Example 2: Comparison of conventional heating and microwave heating effects To demonstrate the microwave-assisted polymerization effect of the present invention, this example used the same raw material ratios and catalyst conditions as Example 1, with conventional electric heating and microwave heating methods used for polymerization, respectively, to compare product performance. Example 2-1 (Comparative Example, Conventional Electric Heating): Following the formulation of Example 1, 50g of FDCA, 29g of EG, and 0.16g of stannous oxalate were added to a 500mL flask. Under nitrogen, the esterification reaction was heated to 210°C for 2 hours (controlled by a conventional electric oil bath). The temperature was then raised to 240°C, the pressure gradually reduced to <100 Pa, and high-temperature polycondensation continued for 6 hours. No TMP stabilizer was added during this period. After the reaction, the materials were discharged, cooled, and pelletized in the same manner. The resulting PEF chips were light brown in color, with a viscosity of η = 0.68 dL / g, indicating only medium molecular weight PEF. The product had a darker color, suspected to be slightly carbonized due to prolonged high temperature. Its Tg was approximately 84°C, its Tm was ~214°C, and its 5% thermal weight loss temperature was approximately 305°C.

[0034] Example 2-2 (the present invention, microwave-assisted): The same conditions as Example 1 were used, except that the esterification temperature was 180°C for 2 hours, the polycondensation temperature was 225°C for 3 hours, the microwave power was 500W, and other conditions were the same. The product slices were light yellow and transparent, with η = 0.80 dL / g. Tg 85°C, Tm 217°C. The product color was significantly improved compared to Example 2-1. Comparison of results: Example 2-1 (without microwave) took a total of about 8 hours, and the inherent viscosity of the product was 0.68 dL / g lower; while Example 2-2 (with microwave) had a total reaction time of 5 hours, the viscosity reached 0.80 dL / g, and the color was lighter. This shows that microwave heating can obtain PEF with a higher molecular weight while reducing temperature and time, proving the superiority of the method of the present invention.

[0035] Example 3: Effect of different catalysts on PEF synthesis This example investigates the effects of various commonly used polycondensation catalysts on the molecular weight and color of PEF under the process conditions of the present invention. The reaction materials and microwave conditions were identical to those in Example 1 (50 g FDCA, 1:1.4 excess EG, similar to the microwave program in Example 1); only the catalyst type or amount was varied.

[0036] Example 3-1 (Antimony Catalyst): 0.20 g of antimony acetate (Sb(OAc)3) (approximately 0.1 mol% Sb) was used. Esterification was carried out at 170°C for 3 h, and polycondensation was carried out at 230°C for 2 h using a microwave at 600 W. The product had a viscosity of η = 0.82 dL / g, slightly lower than the 0.86 obtained with stannous oxalate catalysis. The product was light yellow in color.

[0037] Example 3-2 (Titanium Catalyst): 0.25 g of tetrabutyl titanate (Ti(OBu)4) (approximately 0.05 mol% Ti) was used. Esterification and polycondensation conditions were the same as above. The product had an η of 0.70 dL / g, a grayish-yellow color, and contained suspended particulates.

[0038] Example 3-3 (Germanium Catalyst): 0.12 g of germanium oxide (GeO2) (0.1 mol% Ge) was used. Other conditions were the same as above. The product had an η of 0.79 dL / g and was relatively transparent.

[0039] Example 3-4 (ionic liquid catalyst): 0.50 g of 1-butyl-3-methylimidazolium tin dichloride ([Bmim]2[SnCl6]) (Sn content equivalent to 0.1 mol%) was used. The conditions were the same as above. The product had an η of 0.75 dL / g and a lighter color.

[0040] Example 4: Degradation performance test of PEF Degradation experiments were conducted on films and standard samples prepared from the PEF slices obtained in Example 1. Three PEF samples measuring 10 cm x 10 cm x 1 mm were injection molded, and three samples of the same size were cut from commercially available PET bottles as controls. The samples were buried in a composting medium controlled at 58°C and periodically removed to remove surface debris and measure the remaining mass. The results showed that the PEF sample lost approximately 15% of its mass on the 5th day, approximately 50% on the 10th day, approximately 80% on the 20th day, and approximately 90% on the 30th day. Its color changed from transparent to light brown, and it became noticeably brittle. In contrast, the PET control lost no more than 5% of its mass over 30 days, remaining essentially unchanged. These results demonstrate the excellent biodegradability of the PEF in industrial composting environments.

[0041] Simulated hydrolysis experiment: PEF slices were placed in deionized water and pH = 7 buffer, heated under closed conditions at 80°C for 4 weeks, and their hydrolysis was observed. After the test, the quality of the PEF sample did not change significantly (less than 2% reduction), and the molecular weight measured by GPC decreased slightly (Mn decreased by about 5%), indicating that PEF has a certain hydrolytic stability in a neutral water environment and can meet the requirements of daily use and general waste environment. However, after being placed at 80°C for 2 weeks under alkaline conditions with the addition of 0.1M NaOH, the PEF sample completely lost its strength. This provides a possible route for chemical recovery, that is, recovering monomers through alkaline hydrolysis or enzymatic hydrolysis, and then purifying and recycling them. This example shows that PEF has a certain environmental stability (not easy to decompose under conventional use) and can be degraded under specific treatment conditions, achieving environmentally friendly treatment.

[0042] Example 5: Demonstration of PEF applications in packaging and fiber Packaging application: The PEF obtained in Example 1 was blended with commercially available PLA in a mass ratio of 80:20, and a 50 μm thick film was prepared by extrusion casting. The oxygen permeability was tested to be 5.2 cm 3 ·m -2 day -1 (23℃, 0%RH), compared with pure PLA film (38cm 3 ·m -2 day -1 ) is reduced by about 86%, close to the level of PET film.

[0043] Fiber Application: After drying, the PEF chips from Example 1 were spun into filaments in a melt spinning machine at 260°C and a draft ratio of 4x, yielding fibers with a diameter of approximately 20 μm. The tested single fiber exhibited a breaking strength of 5.1 cN / dtex, an initial modulus of approximately 55 cN / dtex, and an elongation of 15%. This is comparable to conventional PET fibers (strength 5.5 cN / dtex, modulus 60 cN / dtex). This demonstrates the potential of PEF in the textile industry, including its potential for manufacturing biodegradable textiles such as nonwoven mulch and disposable fabrics.

[0044] The above examples demonstrate the feasibility and superiority of the present invention. The process provided by the present invention is capable of stably synthesizing high-quality PEF. The product performance has met expectations after extensive testing and has been successfully applied to trial production of packaging and fiber products. It should be understood that PEF can be copolymerized, modified, or blended for different applications. For example, the introduction of a certain proportion of aliphatic dibasic acids can reduce crystallinity and increase toughness, or blending with PLA or PBAT can regulate degradation rates. The methods described in the present invention have broad applicability, and any methods that employ similar methods and achieve the same functional effects as those of the present invention fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing bio-based polyethylene 2,5-furandicarboxylate, characterized by: Poly(ethylene 2,5-furandicarboxylate) (PEF) was prepared from 2,5-furandicarboxylic acid (FDCA) and ethylene glycol (EG) via an esterification reaction in the presence of a catalyst to generate oligomers. The polycondensation was then carried out using a microwave-assisted melt polycondensation process. The esterification and polycondensation processes were carried out under an inert atmosphere and reduced pressure to remove the water and ethylene glycol molecules generated by the reaction, thereby obtaining a high-molecular-weight PEF polymer.

2. The synthesis method according to claim 1, wherein: The raw material molar ratio of FDCA to ethylene glycol is 1:1.1 to 1:2.2; the temperature of the esterification reaction is controlled at 160 to 180° C., microwave radiation heating is adopted, the microwave power is 200 to 400 W, and the reaction time is 2 to 4 hours to achieve an FDCA conversion rate of more than 90%; subsequently, the temperature of the polycondensation reaction is 210 to 230° C., the microwave power is 500 to 700 W, the pressure is controlled at 10 to 100 Pa, and the polycondensation reaction time is 1 to 3 hours.

3. The synthesis method according to claim 1, wherein: The catalyst is a metal compound capable of catalyzing esterification and transesterification condensation, and is selected from one or more of tin, antimony, germanium or titanium catalysts; preferred catalysts include stannous oxalate, antimony acetate, germanium oxide, tetrabutyl titanate or a combination thereof, and the amount of the catalyst used is 0.01 to 0.5 mol% of the FDCA feed amount.

4. Polyethylene 2,5-furandicarboxylate (PEF) prepared according to the method of claim 1, characterized in that: The PEF is a linear saturated polyester with a number average molecular weight Mn of 2×10 4 ~10×10 4 The intrinsic viscosity is 0.6-1.5 dL / g, the melting point is in the range of 210-230°C, and the glass transition temperature is in the range of 50-90°C. The thermal decomposition temperature (18% weight loss) of the PEF is not less than 400°C, showing excellent thermal stability and processing properties.

5. The PEF according to claim 4, characterized in that: The polymer is biodegradable. Under industrial composting conditions, its biodegradation rate reaches 10-50% within 30 days. It also has high environmental stability in conventional environments and will not degrade prematurely. The PEF can be degraded and recycled by bioenzymes or chemical methods, and is non-toxic to the environment.

6. Use of the PEF in the field of food packaging according to any one of claims 4-5, characterized in that: PEF can be used to make packaging films, containers, or coatings for packaging food, beverages, and pharmaceuticals. Specifically, PEF can be made into single-layer or multi-layer composite films for dry food packaging to extend shelf life. It can also be used to make carbonated beverage bottles, where its excellent barrier properties prevent CO2 escape and O2 intrusion. PEF can also be used as a lining coating on the inner walls of food cans or paper packaging to improve barrier and heat resistance.

7. The use of the PEF according to any one of claims 4-5 in the field of fibers and textiles, characterized in that: PEF can be used to produce fibers, fabrics, or non-woven products. PEF chips can be melt-spun into filaments or staple fibers. The resulting fibers have strength and modulus similar to polyester fibers and can be used in textiles, carpets, industrial filter cloth, and more. PEF staple fibers can also be hot-pressed into non-woven fabrics suitable for agricultural mulch, biomedical textiles, and other applications. They are biodegradable after use. Compared to traditional polyester fibers, PEF fiber products degrade faster after disposal, reducing environmental impact while maintaining comparable processing and performance.

8. The use according to claim 6 or 7, characterized in that: The PEF material can be blended or copolymerized with other polymer materials to meet different application requirements. For example, blending with polylactic acid (PLA) can improve the heat deformation temperature and barrier properties of PLA products. Blending with aliphatic biodegradable polyesters (such as PBAT and PBS) can impart enhanced rigidity and barrier properties to the blend. Introducing a small amount of aliphatic units through copolymerization with adipic acid can improve the flexibility and impact strength of PEF. These modifications or blends maintain the biobased and biodegradable properties of PEF, expanding the application range of PEF materials. The preparation of these blends or copolymers can still be performed using the method described in claim 1 or similar melt polycondensation processes.

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