A biodegradable polyester based on PET-oligopolysaccharide and its preparation method and application

Abstract

The present invention relates to the field of biodegradable polyesters, and discloses a biodegradable polyester based on PET-oligopolysaccharides, and a preparation method and application thereof. The biodegradable polyester of the present invention is a block copolymer composed of oligoethylene terephthalate segments and oligopolysaccharide segments alternately connected, which can improve the biodegradability of the polyester and also make the polyester have good processability. The preparation method of the present invention comprises the following steps: after ethylene glycol and terephthalic acid are polycondensed to form carboxyl-terminated oligomeric PET, the oligomeric PET solution is dissolved, the carboxyl groups in the oligomeric PET are acylated, an acylated oligomeric PET solution is obtained, and then mixed with an oligomeric polysaccharide solution, and a polymerization reaction is carried out at 60-80°C. The preparation method can introduce a biodegradable polysaccharide structure into a PET molecular chain in the form of a short chain, realize the synthesis of a block copolymer, and can also avoid the oxidative degradation of the oligomeric polysaccharide during the preparation process.

Description

Technical Field

[0001] The invention relates to the field of biodegradable polyesters, and in particular to a biodegradable polyester based on PET-oligopolysaccharide and a preparation method and application thereof. Background Art

[0002] As the ecological safety issues brought by non-degradable polymer materials become increasingly prominent, the development of biodegradable polymers has become a major trend in the development of materials. Polyethylene terephthalate (PET) is an aromatic polyester with excellent comprehensive performance. It is obtained by polymerization of terephthalic acid and ethylene glycol. It is often used as polyester fiber, plastic bottle flakes, non-woven fabrics, etc., and is widely used in textiles, packaging, civil engineering and other fields. However, PET polyester is difficult to degrade in the natural environment. If it is discarded at will, it will easily cause environmental hazards such as soil ecological imbalance, teratogenicity and death to wild animals. In addition, the daily use of PET will produce a large amount of microplastics, which will invade water, air and even the human body, threatening human health. As one of the non-degradable petroleum-based products used in large quantities, the green development of PET materials has aroused widespread concern. Developing degradable polyester based on PET raw materials, realizing the transformation and upgrading of the PET industry towards green and sustainable direction, conforming to my country's sustainable development strategy, and transforming and utilizing abundant PET production industrial resources are good strategies.

[0003] Polysaccharide natural polymers have excellent biodegradability and can be completely biodegraded in various natural environments (including soil, various natural water bodies, sludge, etc.). At the same time, there are a large number of alcohol hydroxyl groups in their structure, which can be introduced into PET instead of polyols, and are one of the options for PET degradable modification. However, due to the strong hydrogen bond network formed by a large number of hydroxyl groups in the structure of polysaccharide natural polymers, it is difficult to dissolve in the system of preparing PET by solvent method, and it is also difficult to melt in the system of preparing PET by melting method; and the natural polymers of polysaccharides have a high degree of polymerization, and the reaction accessibility introduced into the polyester chain by copolymerization is low, and the technical difficulty is relatively large; in addition, polysaccharides are easily oxidized and degraded at high temperatures, which increases the difficulty of introducing polysaccharide chain segments into PET. Therefore, most of the existing utilization methods are to physically blend natural polysaccharides with high polymerization degrees with polymer materials to prepare functional materials or degradable materials.

[0004] When polysaccharide natural polymers are blended with non-degradable polymers such as PET, completely biodegradable materials cannot be obtained, and the non-degradable PET component will still exist. For example, patent CN113882027A discloses a method for preparing a chitosan-based product, a product and a structure, wherein chitosan is blended and granulated with polymer materials such as polypropylene PP, polyethylene terephthalate PET, polyamide PA, polyvinyl chloride TPE, etc., and melt-processed to obtain materials such as melt-blown non-woven fabrics, but the product is not completely biodegradable. Summary of the invention

[0005] In order to solve the technical problem that a completely biodegradable material cannot be obtained by physically blending polysaccharide natural polymers with PET, the present invention provides a biodegradable polyester based on PET-oligopolysaccharide. The biodegradable polyester adopts the form of a block copolymer in which oligoethylene terephthalate segments and oligopolysaccharide segments are alternately connected, which can improve the biodegradability of the polyester and also make the polyester have better processability.

[0006] In order to solve the technical problem that it is difficult to introduce polysaccharide natural polymer blocks into PET molecular chains through reactions, the present invention provides a method for preparing biodegradable polyester based on PET-oligopolysaccharides. The preparation method can introduce biodegradable polysaccharide structures into PET molecular chains in the form of short chains to achieve the synthesis of block copolymers, while also avoiding oxidative degradation of oligopolysaccharides during the preparation process.

[0007] The specific technical scheme of the present invention is:

[0008] In a first aspect, the present invention provides a biodegradable polyester based on PET-oligopolysaccharide, wherein the biodegradable polyester is a block copolymer composed of oligoethylene terephthalate segments and oligopolysaccharide segments alternately connected.

[0009] The present invention introduces oligosaccharide segments into polyethylene terephthalate (PET) molecular chains in the form of block copolymers, and can utilize the excellent biodegradability of oligosaccharides in natural environments to make the block copolymers easily biodegraded into oligomeric PET segments; at the same time, the oligomeric polysaccharide segments can be used to introduce more hydrophilic hydroxyl groups into the block copolymers, thereby improving the degradability of the entire block copolymers; and the oligomeric polysaccharide segments and the monosaccharides generated by their degradation can be used as carbon sources to promote the growth and reproduction of soil microorganisms, thereby promoting the biodegradation of the oligomeric PET segments. In the above manner, the block copolymers can have good biodegradability and can be more thoroughly degraded under the action of microorganisms.

[0010] In addition, the present invention adopts the form of block copolymers, which can also avoid the poor compatibility between polysaccharide natural polymers and PET, the phase separation and the resulting decrease in melt strength, so that the biodegradable polyester has excellent processability, and can be obtained by solution or melt processing methods. Fibers, films and sheets, the product application forms are diverse and the application range is wide.

[0011] Preferably, the degree of polymerization of the oligosaccharide chain segment is 10-100.

[0012] The present invention team has noticed that when the degree of polymerization of the oligosaccharide chain segment is too high, the reaction difficulty of the oligosaccharide and the acylated oligomeric PET increases, and it is not easy to form an effective link to obtain a block copolymer under relatively mild conditions, while increasing the reaction temperature will cause oxidative degradation of the oligosaccharide, affecting the processability of the biodegradable polyester; when the degree of polymerization of the oligosaccharide chain segment is too low, it is not easy to form a macromolecular chain after reacting with the oligomeric PET, which will also affect the processability of the polyester. Based on this, the present invention controls the degree of polymerization of the oligosaccharide chain segment to 10-100, which can give the biodegradable polyester better processability.

[0013] Preferably, the degree of polymerization of the oligoethylene terephthalate chain segment is not higher than 25.

[0014] During the research process, the team of the present invention found that it is difficult for polyethylene terephthalate with a high degree of polymerization to react with oligomeric polysaccharides, and it is not easy to form effective links under relatively mild conditions. However, by controlling the degree of polymerization of oligomeric PET to below 25, the acylated oligomeric PET can undergo polymerization reaction with oligomeric polysaccharides at 60-80°C, and the oligomeric polysaccharides will not be oxidized and degraded due to excessively high reaction temperature.

[0015] Furthermore, the degree of polymerization of the polyethylene terephthalate chain segment is 2-25.

[0016] Preferably, the content of the oligosaccharide segments in the biodegradable polyester is 20-45 wt%.

[0017] In biodegradable polyester, as the content of oligosaccharide segments increases, the biodegradability of the polyester increases. However, when the content of oligosaccharide segments is too high, strong hydrogen bonds still exist between the polysaccharide segments in the polyester, making the polyester difficult to dissolve and melt, thereby reducing the processability of the polyester. Based on this, the present invention controls the content of oligosaccharide segments in the polyester to 20-45wt%, which can better balance the biodegradability and processability of the polyester.

[0018] Preferably, the structural formula of the oligoethylene terephthalate segment is as follows:

[0019]

[0020] Preferably, the structural formula of the oligosaccharide segment is as follows:

[0021]

[0022] Preferably, the polyethylene terephthalate chain segment and the oligosaccharide chain segment are connected via an ester bond or a peptide bond.

[0023] Preferably, the oligosaccharide chain segments are derived from depolymerization products of natural polysaccharides.

[0024] Furthermore, the natural polysaccharide includes one or more of cellulose, chitosan, alginic acid and starch.

[0025] In a second aspect, the present invention provides a method for preparing the biodegradable polyester, comprising the following steps:

[0026] (1) dissolving an oligopolysaccharide in solvent A to obtain an oligopolysaccharide solution;

[0027] (2) polycondensing ethylene glycol and terephthalic acid to prepare carboxyl-terminated oligomeric PET;

[0028] (3) dissolving the carboxyl-terminated oligomeric PET in solvent B to obtain an oligomeric PET solution;

[0029] (4) adding an acylation agent to the oligomeric PET solution to perform an acylation reaction of the carboxyl group to obtain an acylated oligomeric PET solution;

[0030] (5) mixing the oligosaccharide solution with the acylated oligomeric PET solution, performing a polymerization reaction at 60-80° C., and separating the product after the reaction to obtain a biodegradable polyester.

[0031] In the above preparation process, by reducing the degree of polymerization of the high molecular weight polysaccharide (using oligomeric polysaccharides), and using solvent A and solvent B to dissolve the oligomeric polysaccharides and oligomeric PET respectively, the polymerization reaction between the oligomeric polysaccharides and the oligomeric PET is carried out in a homogeneous solution, which can improve the reaction accessibility of the polysaccharide and the uniformity of the polymerization reaction, thereby successfully introducing the biodegradable polysaccharide structure into the PET molecular chain in the form of a short chain, so that the obtained biodegradable polyester can achieve more thorough biodegradation and has better processability.

[0032] The invention can improve the reaction activity of the oligomeric PET by acylation of the carboxyl groups in the oligomeric PET before the polymerization reaction of the oligomeric polysaccharide and the oligomeric PET. The polymerization temperature can be effectively reduced by cooperating with the homogeneous solution reaction system, so that the acylated oligomeric PET can be chemically bonded with the hydroxyl group and the amino group in the oligomeric polysaccharide at 60-80 DEG C to form a block copolymer, thereby avoiding oxidative decomposition of the oligomeric polysaccharide at a higher polymerization reaction temperature.

[0033] Preferably, in step (1), the solvent A comprises an ionic liquid A and an organic solvent A in a mass ratio of 100-50:0-50; the ionic liquid A is a molten salt formed by a cation containing an imidazole group or a pyridine group and an anion and having a melting point below 100°C.

[0034] Adding the ionic liquid A to the solvent A facilitates the dissolution of the oligosaccharide.

[0035] Preferably, in step (3), the solvent B comprises an ionic liquid B and an organic solvent B in a mass ratio of 0-50:100-50; the ionic liquid B is a molten salt formed by a cation containing an imidazole group or a pyridine group and an anion and having a melting point below 100°C.

[0036] Furthermore, the ionic liquid A or the ionic liquid B is a 1-butyl-3-methylimidazolium chloride ionic liquid.

[0037] Furthermore, the organic solvent A or organic solvent B is one or more of an amide solvent, a pyrrolidone solvent and an aromatic hydrocarbon solvent.

[0038] Furthermore, the organic solvent A or the organic solvent B is one or more of N,N′-dimethylacetamide, N-methylpyrrolidone and aniline.

[0039] Preferably, in step (4), the acylating agent is thionyl chloride and / or oxalyl chloride; the molar ratio of the acylating agent to the carboxyl group in the oligomeric PET is 1-3:1; and the conditions of the acylation reaction are as follows: temperature 40-80°C, time 5-8h.

[0040] Preferably, in step (2), the conditions of the polycondensation reaction are as follows: inert gas atmosphere, temperature 200-230° C., pressure 140-160 kPa, and time 1-8 h.

[0041] Preferably, in step (5), the polymerization reaction time is 8-24 hours.

[0042] Preferably, in step (2), the molar ratio of ethylene glycol to terephthalic acid is 1:2-4.

[0043] Preferably, in step (1), the mass fraction of the oligopolysaccharide solution is 5-10 wt %.

[0044] Preferably, in step (3), the mass fraction of the oligomeric PET solution is 30-50 wt %.

[0045] Preferably, in step (5), the process of separating the product comprises the following steps: mixing the reaction system with a precipitant to terminate the reaction and wash away the solvent in the system.

[0046] Furthermore, the precipitant is one or more of methanol, ethanol and water.

[0047] In a third aspect, the present invention provides use of the biodegradable polyester in a biodegradable material, wherein the biodegradable material is a fiber, a film or a sheet.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] (1) The biodegradable polyester of the present invention is in the form of a block copolymer, in which oligoethylene terephthalate segments and oligopolysaccharide segments are alternately connected, which can improve the biodegradability of the polyester and solve the problem that PET is difficult to completely degrade in the prior art of physical blending of polysaccharide natural polymers with PET. At the same time, the polyester can also have better processability, enriching the application form and application range of the product;

[0050] (2) In the biodegradable polyester of the present invention, by controlling the degree of polymerization of the oligoethylene terephthalate segment and the oligosaccharide segment, as well as the content of the oligosaccharide segment, the polyester can have good biodegradability and processability, and can achieve relatively thorough biodegradation while being able to obtain various forms of products through solution or melt processing methods;

[0051] (3) In the preparation process of biodegradable polyester, the polymerization reaction of oligosaccharides and oligomeric PET is carried out in a homogeneous solution, and the carboxyl groups in the oligomeric PET are acylated before the polymerization reaction, thereby improving the reaction accessibility of the polysaccharide and the uniformity of the polymerization reaction, thereby realizing the synthesis of block copolymers, and at the same time reducing the temperature of the polymerization reaction, thereby avoiding oxidative degradation of the oligosaccharide. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is the infrared spectrum of PET-oligocellulose polyester in Example 1;

[0053] Figure 2 This is an optical microscope photograph of the melt flow process of the refined PET-oligocellulose polyester in Example 2. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with examples. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies realized based on the above content of the present invention are encompassed within the scope that the present invention is intended to protect.

[0055] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods in the art; the reagents, materials, equipment, etc. used in the following examples are all commercially available unless otherwise specified.

[0056] Overall embodiment

[0057] The invention discloses a biodegradable polyester based on PET-oligopolysaccharide. The biodegradable polyester is a block copolymer composed of polyethylene terephthalate segments and oligopolysaccharide segments connected alternately.

[0058] As a specific implementation, the degree of polymerization of the oligosaccharide chain segment is 10-100, and the degree of polymerization of the polyethylene terephthalate chain segment is 2-25.

[0059] As a specific implementation, the content of the oligosaccharide segments in the biodegradable polyester is 20-45 wt%.

[0060] As a specific implementation, the structural formula of the oligoethylene terephthalate chain segment is as follows:

[0061]

[0062] The structural formula of the oligosaccharide segment is as follows:

[0063]

[0064] As a specific implementation, the polyethylene terephthalate chain segment and the oligosaccharide chain segment are connected via an ester bond or a peptide bond.

[0065] As a specific embodiment, the oligosaccharide chain segments are derived from the depolymerization products of natural polysaccharides. The natural polysaccharides can be selected from one or more of cellulose, chitosan, alginic acid and starch.

[0066] A method for preparing the above-mentioned biodegradable polyester comprises the following steps:

[0067] (1) dissolving an oligopolysaccharide in solvent A to obtain an oligopolysaccharide solution;

[0068] (2) polycondensing ethylene glycol and terephthalic acid to prepare carboxyl-terminated oligomeric PET;

[0069] (3) dissolving the carboxyl-terminated oligomeric PET in solvent B to obtain an oligomeric PET solution;

[0070] (4) adding an acylation agent to the oligomeric PET solution to perform an acylation reaction of the carboxyl group to obtain an acylated oligomeric PET solution;

[0071] (5) mixing the oligosaccharide solution with the acylated oligomeric PET solution, performing a polymerization reaction at 60-80° C., and separating the product after the reaction to obtain a biodegradable polyester.

[0072] As a specific embodiment, in step (1), the solvent A comprises an ionic liquid A and an organic solvent A in a mass ratio of 100-50:0-50; in step (3), the solvent B comprises an ionic liquid B and an organic solvent B in a mass ratio of 0-50:100-50; the ionic liquid A and the ionic liquid B are molten salts formed by cations and anions containing imidazole groups or pyridine groups and having a melting point below 100°C. The ionic liquid A or the ionic liquid B may be a 1-butyl-3-methylimidazolium chloride ionic liquid, and the organic solvent A or the organic solvent B may be selected from one or more of an amide solvent, a pyrrolidone solvent and an aromatic hydrocarbon solvent.

[0073] As a specific implementation, in step (1), the mass fraction of the oligosaccharide solution is 5-10wt%; in step (3), the mass fraction of the oligomeric PET solution is 30-50wt%.

[0074] As a specific implementation, in step (2), the molar ratio of ethylene glycol to terephthalic acid is 1:2-4; the conditions of the polycondensation reaction are as follows: inert gas atmosphere, temperature 200-230°C, pressure 140-160 kPa, time 1-8 h.

[0075] As a specific implementation, in step (4), the acylating agent is thionyl chloride and / or oxalyl chloride; the molar ratio of the acylating agent to the carboxyl group in the oligomeric PET is 1-3:1; the conditions of the acylation reaction are as follows: temperature 40-80°C, time 5-8h.

[0076] As a specific implementation, in step (5), the polymerization reaction time is 8-24h.

[0077] As a specific embodiment, in step (5), the process of separating the product includes the following steps: mixing the reaction system with a precipitant to terminate the reaction and wash away the solvent in the system. The precipitant can be selected from one or more of methanol, ethanol and water.

[0078] The application of the above biodegradable polyester in biodegradable materials, wherein the biodegradable materials are fibers, films or sheets.

[0079] Example 1

[0080] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligocellulose polyester) is prepared by the following steps:

[0081] (1) Weighing 5.4 g of oligocellulose with an average degree of polymerization of 10, adding it to 48.6 g of 1-butyl-3-methylimidazolium chloride ionic liquid (BmimCl), mechanically stirring for 0.5 h at 60° C. to dissolve, to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0082] (2) Weighing 1.2 g of ethylene glycol and 6.4 g of terephthalic acid, reacting at 200° C. and 150 kPa nitrogen pressure for 1 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 2-5;

[0083] (3) adding the obtained carboxyl-terminated oligomeric PET to 20.0 g of aniline, stirring and dissolving at 120° C. to obtain an oligomeric PET solution having a mass fraction of about 30 wt %;

[0084] (4) adding 1.8 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 5 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0085] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 60° C. for 8 h, added into hot ethanol, and stirred thoroughly, washed, and filtered to obtain a precipitate, which is the product PET-oligomeric cellulose polyester.

[0086] When the product is washed and filtered in step (5), the filtrate is collected, and the content of unreacted excess terephthalic acid is detected by ultraviolet spectrophotometry through the ultraviolet absorption peak of terephthalic acid at a wavelength of 240 nm, thereby obtaining the mass content of oligocellulose in the polyester, and the calculation formula is as follows:

[0087] M%=M 低聚纤维素 / (M 总投料 -M 未反应单体 )

[0088] According to calculation, the mass content of the oligocellulose segment in the PET-oligocellulose polyester prepared in this example is 45 wt %.

[0089] The obtained product PET-oligocellulose polyester was purified to remove residual BmimCl by the following method: the product was dissolved in DMSO and then stirred and precipitated in methanol; the precipitate was filtered and dried, then redissolved in DMSO and precipitated in water; this process was repeated twice to completely remove the residual solvent.

[0090] The infrared spectrum of the refined product is as follows: Figure 1 As shown in Figure 2, the absorption peak (3470 cm-1) belonging to the cellulose hydroxyl group can be observed simultaneously. -1 ), the absorption peak of the ester group formed by esterification (1714 cm -1) and the fingerprint region belongs to the absorption peak of the benzene ring of terephthalic acid (763cm -1 ), indicating that the product contains cellulose segments and PET segments.

[0091] The composting conditions were set according to GB / T 19277.2-2013, and the composting degradation rate of the refined product was tested. It was found that the degradation rate reached 90% in 28 days.

[0092] Example 2

[0093] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligocellulose polyester) is prepared by the following steps:

[0094] (1) Weigh 25.0 g of oligocellulose with an average degree of polymerization of 20, add it to 225.0 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0095] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0096] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0097] (4) adding 10.4 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 8 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0098] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 80° C. for 12 h, added into hot ethanol, and stirred thoroughly, washed, and filtered to obtain a precipitate, which is the product PET-oligomeric cellulose polyester.

[0099] The product refining, oligocellulose mass content determination and composting degradation rate determination were carried out according to the method in Example 1. It was measured that the mass content of oligocellulose segments in the PET-oligocellulose polyester prepared in this example was 20wt%, and the 56-day composting degradation rate reached 90%.

[0100] The melt flow temperature of the refined product was 210°C ( Figure 2 The product is melted at 210°C and drawn to obtain a fiber product.

[0101] Example 3

[0102] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligocellulose polyester) is prepared by the following steps:

[0103] (1) 32.0 g of oligocellulose with an average degree of polymerization of 100 was weighed and added to 76.0 g of BmimCl, and mechanically stirred at 60° C. for 0.5 h to dissolve, and then 76.0 g of N,N′-dimethylacetamide was added dropwise thereto under stirring to obtain an oligosaccharide solution with a mass fraction of 17.4 wt %;

[0104] (2) Weighing 9.8 g of ethylene glycol and 52.5 g of terephthalic acid, reacting at 230° C. and 150 kPa nitrogen pressure for 8 h to obtain a carboxyl-terminated oligomeric PET with a degree of polymerization of 25;

[0105] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 55.0 g of N,N′-dimethylacetamide and BmimCl in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0106] (4) adding 1.9 mL of thionyl chloride to the oligomeric PET solution, stirring and reacting at 80° C. for 8 h, and then performing a reduced pressure distillation treatment to obtain an acylated oligomeric PET solution;

[0107] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 80° C. for 24 h, added into hot ethanol, and stirred thoroughly, washed, and filtered to obtain a precipitate, which is the product PET-oligomeric cellulose polyester.

[0108] The product purification and oligocellulose mass content determination were carried out according to the method described in Example 1. It was determined that the mass content of the oligocellulose chain segment in the PET-oligocellulose polyester prepared in this example was 37 wt %.

[0109] In order to visualize the biodegradation of polyester, a biodegradable polyester film was prepared for composting experiment. The specific operation is as follows: the refined biodegradable polyester is dissolved in N,N-dimethylformamide, and the film is prepared by solvent evaporation method. The film is placed on a polypropylene (PP) grid with a pore size of 2mm, buried in the compost soil in a sealed can, and placed in a 56℃ constant temperature box. The sealed can is opened every 24 hours to supply oxygen, and water is added to keep the soil moisture at 50%. Take it out for observation and record at regular intervals. After 42 days of composting, its mass loss can reach 90%, showing good biodegradability.

[0110] Example 4

[0111] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligochitosan polyester) is prepared by the following steps:

[0112] (1) Weigh 5.4 g of oligosaccharide with an average degree of polymerization of 10, add it to 48.6 g of BmimCl, and dissolve it under mechanical stirring at 80° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0113] (2) Weighing 1.2 g of ethylene glycol and 6.4 g of terephthalic acid, reacting at 200° C. and 150 kPa nitrogen pressure for 1 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 2-5;

[0114] (3) adding the obtained carboxyl-terminated oligomeric PET to 20.0 g of N-methylpyrrolidone, stirring and dissolving at 120° C. to obtain an oligomeric PET solution having a mass fraction of about 30 wt %;

[0115] (4) adding 1.8 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 5 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0116] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 60° C. for 12 h, and then added to hot ethanol. After sufficient stirring, washing, and filtering, a precipitate is obtained, which is the product PET-oligomeric chitosan polyester.

[0117] The product purification, determination of the mass content of oligomolecular chitosan and determination of the composting degradation rate were carried out according to the method in Example 1. It was found that the mass content of the oligomolecular chitosan segment in the PET-oligomolecular chitosan polyester prepared in this example was 35wt%, and the composting degradation rate reached 90% in 42 days.

[0118] The melt flow temperature of the refined product was measured by hot stage heating and observation to be 230°C.

[0119] Example 5

[0120] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligomeric starch polyester) is prepared by the following steps:

[0121] (1) Weigh 50.0 g of oligomeric potato starch with an average degree of polymerization of 10, add it to 450.0 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0122] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0123] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0124] (4) adding 10.4 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 8 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0125] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 80° C. for 12 h, and then added to hot ethanol. After sufficient stirring, washing, and filtering, a precipitate is obtained, which is the product PET-oligomeric starch polyester.

[0126] Product refining, oligomeric starch mass content determination and composting degradation rate determination were carried out according to the method in Example 1. It was found that the mass content of oligomeric starch chain segments in the PET-oligomeric starch polyester prepared in this example was 40wt%, and the 28-day composting degradation rate reached 90%.

[0127] The melt flow temperature of the refined product was measured by heating on a hot plate and observed to be 195°C. The product was hot-pressed at 195°C to obtain a plastic sheet.

[0128] Comparative Example 1

[0129] The polyester is prepared by the following steps:

[0130] (1) Weigh 5.4 g of microcrystalline cellulose (average degree of polymerization: 220), add it to 48.6 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain a solution with a mass fraction of 10 wt %;

[0131] (2) Weighing 1.2 g of ethylene glycol and 6.4 g of terephthalic acid, reacting at 200° C. and 150 kPa nitrogen pressure for 1 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 2-5;

[0132] (3) adding the obtained carboxyl-terminated oligomeric PET to 20.0 g of aniline, stirring and dissolving at 120° C. to obtain an oligomeric PET solution having a mass fraction of about 30 wt %;

[0133] (4) adding 1.8 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 5 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0134] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution were mixed, reacted at 60° C. for 8 h, added into hot ethanol, and the product precipitate was obtained by thorough stirring, washing, and filtering.

[0135] After the precipitate was dried, its solubility in DMSO was tested and found to be insoluble. Then, the solubility of the insoluble matter was tested using hexafluoroisopropanol and found to be partially dissolved. The washed insoluble matter was detected by infrared spectroscopy to be unreacted cellulose.

[0136] Data analysis and conclusion: Compared with the use of polysaccharides with a high degree of polymerization (Comparative Example 1), the use of low-degree of polymerization polysaccharides with a degree of polymerization of 10 (Example 1) can effectively improve the accessibility of the reaction, so that the polysaccharide can be linked to the oligomeric PET chain segments, and the polysaccharide hydroxyl groups can undergo a derivatization reaction, thereby destroying the hydrogen bond network formed by the hydroxyl groups between the polysaccharide chains, thereby making the product soluble in DMSO; while the reaction of high-degree of polymerization polysaccharides with oligomeric PET chains (Comparative Example 1) is more difficult, and no effective link is formed at the reaction temperature. Therefore, the properties of the product are manifested as two independent parts that are insoluble in DMSO, namely, oligomeric PET that is soluble in hexafluoroisopropanol and unreacted cellulose polysaccharide that is insoluble in hexafluoroisopropanol.

[0137] Comparative Example 2

[0138] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligocellulose polyester) is prepared by the following steps:

[0139] (1) Weigh 25.0 g of oligocellulose with an average degree of polymerization of 5, add it to 225.0 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0140] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0141] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0142] (4) adding 10.4 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 8 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0143] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 80°C for 12 hours, and then added to hot ethanol. After sufficient stirring, washing, and filtering, a precipitate is obtained, which is the product PET-oligomeric cellulose polyester. After drying, the precipitate is viscous at room temperature.

[0144] Data analysis and conclusion: Compared with the use of polysaccharides with a low degree of polymerization (Comparative Example 2), the use of polysaccharides with an appropriate degree of polymerization (Example 2) can effectively form macromolecular chains, and the formed polymer is solid at room temperature, with a melt flow temperature of 210°C, and fiber products can be obtained by melt drawing; while the polysaccharide used has a low degree of polymerization (Comparative Example 2), and macromolecular chains cannot be formed after the reaction, and the polymer shows a viscous state of a oligomer at room temperature, which is difficult to process and use.

[0145] Comparative Example 3

[0146] The polyester is prepared by the following steps:

[0147] (1) 32.0 g of oligocellulose with an average degree of polymerization of 100 was weighed and added to 76.0 g of BmimCl, and mechanically stirred at 60° C. for 0.5 h to dissolve, and then 76.0 g of N,N′-dimethylacetamide was added dropwise thereto under stirring to obtain an oligosaccharide solution with a mass fraction of 17.4 wt %;

[0148] (2) Weighing 9.8 g of ethylene glycol and 52.5 g of terephthalic acid, reacting them at 230° C. and 150 kPa nitrogen pressure for 12 h to obtain a carboxyl-terminated oligomeric PET with a degree of polymerization of 60-65;

[0149] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 55.0 g of N,N′-dimethylacetamide and BmimCl in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0150] (4) adding 1.9 mL of thionyl chloride to the oligomeric PET solution, stirring and reacting at 80° C. for 8 h, and then performing a reduced pressure distillation treatment to obtain an acylated oligomeric PET solution;

[0151] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution were mixed, reacted at 80° C. for 24 h, added into hot ethanol, and the product precipitate was obtained by thorough stirring, washing, and filtering.

[0152] After the precipitate was dried, its solubility in DMSO was tested and found to be insoluble. Then, the solubility of the insoluble matter was tested using hexafluoroisopropanol and found to be partially dissolved. The washed insoluble matter was detected by infrared spectroscopy to be unreacted cellulose.

[0153] Data analysis and conclusion: Compared with the use of oligomeric PET with a higher degree of polymerization as a prepolymer (Comparative Example 3), the use of oligomeric PET with a lower degree of polymerization as a prepolymer (Example 3) allows the acylated oligomeric PET to effectively react with the oligomeric polysaccharide to form a polyester soluble in an organic solvent and prepare a film product; when the polymerization degree of the oligomeric PET is too high (Comparative Example 3), the acylated oligomeric PET is difficult to react with the oligomeric polysaccharide, and no effective link is formed at the reaction temperature. Therefore, the product properties are manifested as two independent parts that are insoluble in DMSO, namely, the oligomeric PET soluble in hexafluoroisopropanol and the unreacted cellulose polysaccharide that is insoluble in hexafluoroisopropanol.

[0154] Comparative Example 4

[0155] The polyester is prepared by the following steps:

[0156] (1) Weigh 25.0 g of oligocellulose with an average degree of polymerization of 20, add it to 225.0 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0157] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0158] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0159] (4) adding 10.4 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 8 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0160] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution were mixed, reacted at 120°C for 12 hours, and then added to hot ethanol. After sufficient stirring, washing, and filtering, a product precipitate was obtained. After drying, the precipitate was black and viscous at room temperature.

[0161] Data analysis and conclusion: Compared with the high temperature for the oligosaccharide and acylated oligomeric PET linking reaction (Comparative Example 4), the lower temperature (Example 2) can avoid the oxidative degradation of the oligosaccharide during the reaction and obtain a polymer with processability. However, the product obtained at a higher temperature (Comparative Example 4) is black and viscous after drying, indicating that the oligosaccharide is severely oxidatively degraded during the reaction and the product is difficult to process and use.

[0162] Comparative Example 5

[0163] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligocellulose polyester) is prepared by the following steps:

[0164] (1) Weigh 10.0 g of oligocellulose with an average degree of polymerization of 20, add it to 90.0 g of BmimCl, and dissolve it by mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0165] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0166] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0167] (4) adding 10.4 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 8 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0168] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 80° C. for 12 h, added into hot ethanol, and stirred thoroughly, washed, and filtered to obtain a precipitate, which is the product PET-oligomeric cellulose polyester.

[0169] The product refining, oligocellulose mass content determination and composting degradation rate determination were carried out according to the method in Example 1. It was measured that the mass content of the oligocellulose segment in the PET-oligocellulose polyester prepared in this comparative example was 7wt%, and the 180-day composting degradation rate was 5%.

[0170] Data analysis and conclusion: Compared with PET-oligocellulose polyester with a lower oligosaccharide mass content (Comparative Example 5), PET-oligocellulose polyester with a higher oligosaccharide mass content (Example 2) has good biodegradability, and the composting degradation rate in 56 days reaches 90%; while when the mass content of oligocellulose is 7wt% (Comparative Example 5), the composting degradation rate in 180 days is only 5%, and it is difficult to form biodegradable polyester at this content.

[0171] Comparative Example 6

[0172] A biodegradable polyester based on PET-oligopolysaccharide (PET-oligochitosan polyester) is prepared by the following steps:

[0173] (1) Weigh 9.5 g of oligosaccharide with an average degree of polymerization of 10, add it to 85.5 g of BmimCl, and dissolve it by mechanical stirring at 80° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0174] (2) Weighing 1.2 g of ethylene glycol and 6.4 g of terephthalic acid, reacting at 200° C. and 150 kPa nitrogen pressure for 1 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 2-5;

[0175] (3) adding the obtained carboxyl-terminated oligomeric PET to 20.0 g of N-methylpyrrolidone, stirring and dissolving at 120° C. to obtain an oligomeric PET solution having a mass fraction of about 30 wt %;

[0176] (4) adding 1.8 mL of oxalyl chloride to the oligomeric PET solution, adding 5 drops of N,N′-dimethylformamide (DMF) as a catalyst, stirring and reacting at 40° C. for 5 h, and then performing reduced pressure distillation to obtain an acylated oligomeric PET solution;

[0177] (5) The acylated oligomeric PET solution and the oligomeric polysaccharide solution are mixed, reacted at 60° C. for 12 h, and then added to hot ethanol. After sufficient stirring, washing, and filtering, a precipitate is obtained, which is the product PET-oligomeric chitosan polyester.

[0178] The mass content of oligomeric chitosan in the PET-oligomeric chitosan polyester prepared in this comparative example was calculated according to the method of Example 1. After the precipitate was dried, its solubility in DMSO and hexafluoroisopropanol was tested and found to be insoluble. The hot stage observation of the melt flow found that it was difficult to melt.

[0179] Data analysis and conclusion: Compared with PET-oligomeric chitosan polyester with too high oligomeric polysaccharide mass content (Comparative Example 6), PET-oligomeric chitosan polyester with appropriate oligomeric polysaccharide mass content (Example 4) can melt flow. When the oligomeric polysaccharide mass content is too high (Comparative Example 6), there is still a strong hydrogen bond between the polysaccharides, so the product is difficult to dissolve and melt, and has no processability.

[0180] Comparative Example 7

[0181] The polyester is prepared by the following steps:

[0182] (1) Weigh 50.0 g of oligomeric potato starch with an average degree of polymerization of 10, add it to 450.0 g of BmimCl, and dissolve it under mechanical stirring at 60° C. for 0.5 h to obtain an oligosaccharide solution with a mass fraction of 10 wt%;

[0183] (2) Weighing 19.5 g of ethylene glycol and 98.0 g of terephthalic acid, reacting them at 220° C. and 150 kPa nitrogen pressure for 4 h to obtain carboxyl-terminated oligomeric PET with a degree of polymerization of 8-10;

[0184] (3) adding the obtained carboxyl-terminated oligomeric PET to a solution of 240.0 g of aniline and BmimCl mixed in a mass ratio of 50:50, stirring and dissolving at 120° C. to obtain an oligomeric PET solution with a mass fraction of about 50 wt %;

[0185] (4) The oligomeric PET solution and the oligomeric polysaccharide solution were mixed, reacted at 80° C. for 12 h, added into hot ethanol, and the product precipitate was obtained by thorough stirring, washing, and filtering.

[0186] After the precipitate was dried, its solubility in DMSO was tested and it was found that it was insoluble; hexafluoroisopropanol was then used to test the solubility of the insoluble matter and it was found that it was partially soluble; the insoluble matter was washed and detected by infrared spectroscopy as unreacted starch.

[0187] Data analysis and conclusion: Compared with the PET oligomer that has not been modified by acylation (Comparative Example 7), the acylated PET oligomer (Example 5) can effectively react with the oligomeric polysaccharide to form a melt-flowable polyester and prepare a plastic sheet; while the PET oligomer that has not been modified by acylation cannot react with the oligomeric polysaccharide at 80°C, so the product properties are manifested as two independent parts that are insoluble in DMSO, namely, the oligomeric PET that is soluble in hexafluoroisopropanol and the unreacted starch polysaccharide that is insoluble in hexafluoroisopropanol.

[0188] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing biodegradable polyester based on PET-oligopolysaccharide, characterized in that: The following steps are involved: (1) dissolving an oligosaccharide having a degree of polymerization of 10-100 in solvent A to obtain an oligosaccharide solution; (2) subjecting ethylene glycol and terephthalic acid to a condensation reaction to prepare a carboxyl-terminated oligomeric PET having a degree of polymerization of not more than 25, and dissolving the oligomeric PET in solvent B to obtain an oligomeric PET solution; (3) adding an acylation agent to the oligomeric PET solution to carry out an acylation reaction of the carboxyl group to obtain an acylated oligomeric PET solution; (4) The oligosaccharide solution is mixed with the acylated oligomeric PET solution, and a polymerization reaction is carried out at 60-80° C. After the reaction is completed, the product is separated to obtain a biodegradable polyester having an oligosaccharide chain segment content of 20-45 wt %.

2. The preparation method according to claim 1, characterized in that In step (1), the solvent A comprises an ionic liquid A and an organic solvent A in a mass ratio of 100-50:0-50; the ionic liquid A is a molten salt formed by a cation containing an imidazole group or a pyridine group and an anion and having a melting point below 100°C.

3. The preparation method according to claim 1, characterized in that: In step (2), the solvent B comprises an ionic liquid B and an organic solvent B in a mass ratio of 0-50:100-50; the ionic liquid B is a molten salt formed by a cation containing an imidazole group or a pyridine group and an anion and having a melting point below 100°C.

4. The preparation method according to claim 1, characterized in that: In step (3), the acylating agent is thionyl chloride and / or oxalyl chloride.

5. The preparation method according to claim 1 or 4, characterized in that: In step (3), the molar ratio of the acylating agent to the carboxyl group in the oligomeric PET is 1-3:

1.

6. The preparation method according to claim 1, characterized in that In step (3), the conditions of the acylation reaction are as follows: temperature 40-80°C, time 5-8 h.

7. The preparation method according to claim 1, characterized in that In step (2), the conditions of the polycondensation reaction are as follows: inert gas atmosphere, temperature 200-230° C., pressure 140-160 kPa, and time 1-8 h.

8. A biodegradable polyester based on PET-oligopolysaccharide prepared by the preparation method according to any one of claims 1 to 7.

9. The use of the biodegradable polyester in biodegradable materials according to claim 8, characterized in that: The biodegradable material is fiber, film or sheet.

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