CN113307956A

CN113307956A - Degradable copolyester and preparation method and application thereof

Info

Publication number: CN113307956A
Application number: CN202010125653.8A
Authority: CN
Inventors: 王格侠; 季君晖; 能文博; 卢波; 甄志超
Original assignee: Technical Institute of Physics and Chemistry of CAS
Current assignee: Technical Institute of Physics and Chemistry of CAS
Priority date: 2020-02-27
Filing date: 2020-02-27
Publication date: 2021-08-27

Abstract

The invention discloses a degradable copolyester, which is a random copolymer or a diblock copolymer consisting of polyester segments which are difficult to hydrolyze and segments or sites which are easy to hydrolyze, and has the number average molecular weight of 30000g/mol-500000 g/mol; the easily hydrolyzed segments or sites are selected from polylactic acid with different chain segment lengths. The copolyester has high molecular weight, does not contain an environment-friendly chain extender, has good mechanical strength and toughness, is heat-resistant, has good processability, and can be independently used as plastic. In various natural environments such as water, soil, compost and the like, the biodegradable organic fertilizer can be completely degraded in the natural environment to form carbon dioxide and water without environmental pollution. The invention also discloses a preparation method and application of the degradable copolyester.

Description

Degradable copolyester and preparation method and application thereof

Technical Field

The invention relates to the field of degradable high polymer materials. More particularly, relates to degradable copolyester and a preparation method and application thereof.

Background

The increasing pollution of marine plastics and their harm to marine ecology and human life has attracted much attention. The development and use of seawater degradable plastic products to replace general purpose difficult degradable plastic products in the long run is a radical effective way to prevent the problem from continuing to develop. In all high molecular materials, polyester is particularly easy to degrade under the action of water and microorganisms in the environment due to the ester bond in the chain segment, and carbon dioxide and water which are pollution-free to the environment are generated. This process typically goes through three steps: 1) the material is broken under the combined action of light, oxygen, water and organisms; 2) the polyester chain segment is hydrolyzed through an enzymatic hydrolysis process and/or a non-enzymatic hydrolysis process, and is continuously degraded into an oligomer or a monomer from a high molecular chain segment; 3) these oligomers and monomers enter the microbial cells and form biomass under the action of microbial intracellular depolymerases, or mineralize to carbon dioxide and water. The second hydrolysis step of the three processes, i.e. hydrolysis of the high molecular chain segment to low molecular weight, is the rate-determining step of the biodegradation process. On one hand, the degradation speed and degradation degree of polyester are closely related to the intrinsic properties of a high molecular chain segment structure, molecular weight, crystallinity and the like, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) which are engineering plastics, because of the existence of benzene rings in the chain segment, the crystallinity is high, the polyester is insensitive to water and microorganisms, the polyester is extremely difficult to degrade in soil at room temperature, certain hydrolysis performance is shown only in a high-temperature high-humidity environment, and small molecular compounds are difficult to completely generate by hydrolysis. Biodegradable polyester polylactic acid (PLA) is slowly degraded in soil, sometimes even decades of time, and can be rapidly degraded only in compost (the degradation is complete in 6-9 months at 58-65 ℃).

On the other hand, the degradation rate and degradation degree of polyester are also closely related to external factors such as temperature, humidity, pH, microbial community, etc. in the environment. In most of water bodies including distilled water, natural river water and natural seawater, particularly in deep sea and ocean environments, the average temperature is low, the number of specific microorganisms is less than that in compost, the second hydrolysis process in the biodegradation process is slow, and the overall degradation rate of the material is greatly influenced. Therefore, the existing resin materials, including engineering plastics such as PBT and PET, and commercial biodegradable PLA, PBS, PBAT and the like, are slowly degraded in seawater and are difficult to degrade even for a long time.

In order to accelerate the degradation rate of biodegradable polyester in water, a method for blending starch and biodegradable polyester is adopted in the prior art, but the application of the material is limited because the degradation rate of the starch in the water, particularly seawater, is limited and the mechanical property of the blend is greatly reduced by starch filling. (Journal of Applied Polymer Science 2019,136 (2)) also by blending a water-soluble polyvinyl alcohol (PVA) with a biodegradable polyester, although the weight loss of the material as a whole is significantly increased, the compatibility of the PVA with a resin matrix is poor, and the degradation performance of the PVA itself and the biosafety of the degradation end product of the blend are questioned; (Polymer Degradation and Stability 2019,163, 195-. (CN103210043A, CN10332580A) however, blending is adopted, the system is complex, the compatibility causes the mechanical property to be limited, corresponding auxiliary agents need to be added, and the biological safety is influenced.

The hydrophilicity and crystallinity of the plastic can be improved by carrying out synthesis modification on the existing biodegradable polyester material, and the probability of the action of the plastic on water and microorganisms is increased, so that the degradation performance of the plastic in water is improved. For example, in the prior art, butanediol, terephthalic acid and adipic acid in a certain proportion are copolymerized, a certain proportion of PBA polyester units (the molar ratio of terephthalic acid to succinic acid is less than 5.5/4.5) are introduced into a PBT chain segment which is difficult to degrade to form semi-aromatic copolyester polybutylene terephthalate adipate (PBAT), the crystallinity is low, the flexibility of a molecular chain is increased, and water molecules can enter an amorphous region more easily to be hydrolyzed, so that the degradation performance is good in compost and soil, but the degradation in a water body is still slow. (Polymer Degradation and Stablity 2010,95(12), 2641-2647; Journal of Applied Polymer Science 2019,136 (2))

In the prior art, lactic acid or polybutylene furan dicarboxylate homopolymer is synthesized and modified, a two-step method is adopted, and polycondensation and copolymerization are respectively carried out to obtain the polybutylene furan dicarboxylate copolymer with certain hydrolysis performance, wherein the furan dicarboxylate has high cost, and the application of the polyester is relatively limited. (Industrial & Engineering Chemistry Research 2018,57(32), 11020. about. 11030.) the prior art also includes an easily hydrolysable copolyester formed by using glycolic acid, lactic acid-glycolic acid as easily hydrolysable segments and aliphatic polyesters such as polybutylene succinate and polybutylene terephthalate as hardly hydrolysable segments. The easily-hydrolyzed segment in the disclosed copolyester takes glycolic acid as a raw material, has higher cost relative to lactic acid, is not beneficial to industrialization and application, and shows a certain hydrolysis performance in pure water and natural seawater through a molecular weight and weight loss test, but the biodegradation performance of the copolyester in a natural environment, particularly a seawater environment, is not disclosed. (CN 109762143A) the prior art also discloses a triblock polymer which takes lactic acid as an end-capping group and contains PLA and aliphatic/aromatic polyester segments, the triblock polymer takes lactide, dibasic acid and dihydric alcohol as raw materials and is obtained by means of multi-step prepolymerization and chain extension, the synthesis is complex, a product contains a chain extender, and in addition, the polylactic acid segment is formed by lactide ring-opening polymerization, so the cost is high. (CN102443145A, CN103788599A) in the prior art, butanediol, succinic acid and lactic acid are used as raw materials, tetrabutyl titanate is used as a catalyst, and a PBS-LA block copolymer and a random copolymer are synthesized by a one-step method and a two-step prepolymerization-polycondensation method respectively, but the number average molecular weight of the disclosed copolyester is only 13600-16700g/mol, and the copolyester has no mechanical strength and cannot be used alone as plastic. (Journal of Polymers and the environmental 2018,26(7),3060-3068) the prior art comprises a two-step prepolymerization-polycondensation method for synthesizing a PBT-LA copolymer by using butanediol, terephthalic acid and lactic acid as raw materials and tetrabutyl titanate as a catalyst, but the number average molecular weight of the disclosed copolyester is only 13100-26100g/mol, the tensile strength is less than 6.4MPa, and the copolyester is difficult to be used as a plastic independently. (Synthesis and modification of degradable PLA-PBT copolyester, [ academic paper ] Wangzhongtao 2010-Zhejiang university: polymer chemistry and physics)

In conclusion, although the prior art provides a series of solutions, the prepared polyester still has the problems of high cost, low molecular weight, poor mechanical property, incapability of efficiently biodegrading in soil and natural water bodies, particularly seawater and the like.

Therefore, it is desirable to provide a novel degradable copolymer and a method for preparing the same to solve the above-mentioned problems.

Disclosure of Invention

The first purpose of the invention is to provide degradable copolyester, which is block copolyester obtained by combining a difficult-to-hydrolyze chain segment and an easy-to-hydrolyze chain segment by a copolymerization method, has high molecular weight, does not contain an environmentally-unfriendly chain extender, has good mechanical strength and toughness, is heat-resistant and has good processability, and can be independently used as plastic. In various natural environments such as water, soil, compost and the like, the polyester chain segment is attacked by water molecules and is quickly disconnected from the easily hydrolyzed chain segment or site to form a low-molecular-weight difficultly hydrolyzed segment, so that the whole biodegradation process is promoted, and the material can be completely degraded in the natural environment to form carbon dioxide and water without environmental pollution.

The second purpose of the invention is to provide a preparation method of degradable copolyester.

The third purpose of the invention is to provide the application of the degradable copolyester.

In order to achieve the first purpose, the invention adopts the following technical scheme:

a degradable copolyester is a random copolymer or a block copolymer consisting of difficult-to-hydrolyze polyester segments and easy-to-hydrolyze polyester segments, the number average molecular weight of the copolyester is 30000g/mol-500000g/mol, the easy-to-hydrolyze segments or sites refer to polylactic acids with different segment lengths, and the difficult-to-hydrolyze segments contain aromatic rings.

Preferably, the non-hydrolyzable polyester is selected from aliphatic-aromatic polyesters and/or copolyesters obtained by polycondensation of aromatic dibasic acids and aliphatic dihydric alcohols or their glycol esters.

Preferably, the polyester having a TOC (total organic carbon content) of 5ppm or less as measured by a predetermined method and being hardly hydrolyzed does not contain a water-soluble polyester.

Preferably, the diol is selected from the group consisting of ethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 2-propanediol, 1, 8-octanediol, sorbitol, polyethylene glycol; the aromatic dibasic acid is selected from terephthalic acid, isophthalic acid and phthalic acid.

Preferably, the aliphatic-aromatic polyester is preferably selected from one or both of polybutylene terephthalate and polyethylene terephthalate; the aliphatic-aromatic copolyester is preferably one or two of poly (terephthalic acid & adipic acid-butylene glycol), poly (terephthalic acid & ethylene glycol) s, poly (terephthalic acid & succinic acid-butylene glycol), poly (terephthalic acid & adipic acid-ethylene glycol), poly (terephthalic acid & ethylene glycol) s, poly (terephthalic acid & sebacic acid-butylene glycol) s, and poly (terephthalic acid & sebacic acid-ethylene glycol).

Preferably, the copolyester contains a structure as shown in any one of the following formulas 1 to 3:

wherein m is a natural number of 0-12; n is a natural number of 2-8; x is a natural number of 1-500; y is a natural number of 1-500; p is selected from natural numbers of 1-500.

Preferably, m is 0, 2, 4 or 8; n is 2, 4 or 8; further preferably, m is 2 or 4; n is 2 or 4.

Preferably, x is 1 to 200, y is 1 to 200, and p is 1 to 200, more preferably, x is 1 to 100, y is 1 to 100, and p is 1 to 100.

Preferably, the number average molecular weight of the copolyester is 40000g/moL to 200000 g/moL.

Preferably, the number average molecular weight of the copolyester is 50000g/moL to 100000 g/moL.

Preferably, the molar ratio of the chain segment of the difficult-to-hydrolyze polyester to the chain segment of the easy-to-hydrolyze polyester is 1:4 to 99: 1.

More preferably, the molar ratio of the chain segment of the difficult-to-hydrolyze polyester to the chain segment of the easy-to-hydrolyze polyester is 1:2 to 99: 1.

More preferably, the molar ratio of the chain segment of the difficult-to-hydrolyze polyester to the chain segment of the easy-to-hydrolyze polyester is 1:1 to 20: 1.

The easily hydrolysable polyester commonly known in the prior art is a polyester which is easy to degrade and break chains in water, and usually comprises Polyglycolide (PGA), and polylactic-co-glycolic acid (PLGA) is listed as an easily hydrolysable polyester, because the easily hydrolysable polyester has very high ester bond density, rapid hydrolysis can be carried out in water at room temperature for 3-6 months, and the phenomena of rapid reduction of molecular weight and mechanics, obvious weight loss and the like are presented. TOC measured by a prescribed method is higher than 5ppm, preferably 10ppm or more. The existing commercialized PLA has a high molecular weight (the number average molecular weight is more than 50000 g/mol), and is difficult to hydrolyze in water at room temperature. The weight loss rate of a PLA sample strip with the size of 25.0mm multiplied by 4.0mm multiplied by 2.0mm after being placed in natural seawater and pure water for one year does not exceed 2 percent, the molecular weight is difficult to reduce, and the TOC value is less than 5 ppm. According to the invention, cheaper lactic acid is used as a raw material, PLA segments (with a small polymerization degree of 1-500, preferably 1-200, more preferably 1-100 and a low segment length) in the copolyester obtained by controlling reaction conditions have an easy hydrolysis performance similar to that of PGA and PLGA unexpectedly, and can be used as an easy hydrolysis segment to promote the whole hydrolysis and biodegradation processes of the copolyester.

In order to achieve the second purpose, the invention adopts the following technical scheme:

a preparation method of copolyester comprises the following steps:

mixing dibasic acid, dihydric alcohol and lactic acid monomer which are used for forming chain segments of the difficult-to-hydrolyze polyester, carrying out temperature programming in the presence of a catalyst, and carrying out esterification and polycondensation to obtain the copolyester;

or

Heating the dibasic acid, the dihydric alcohol or the lactic acid monomer which is used for forming the chain segment of the difficult-to-hydrolyze polyester in the presence of a catalyst, and firstly carrying out esterification and polycondensation to obtain the low-molecular-weight-segment difficult-to-hydrolyze polyester or the low-molecular-weight polylactic acid segment;

adding the low molecular weight segment of the non-hydrolyzable polyester or the low molecular weight polylactic acid into the esterification and polycondensation process of the polylactic acid or the non-hydrolyzable polyester for copolymerization to form the copolyester;

or

Respectively forming a chain segment of the difficult-to-hydrolyze polyester and a segment of the easy-to-hydrolyze polylactic acid; and mixing the chain segment of the difficult-to-hydrolyze polyester with the polylactic acid chain segment, and carrying out melt chain extension to obtain the copolyester.

Preferably, the catalyst is a composite catalyst and is formed by mixing a main catalyst, a secondary catalyst and an antioxidant.

Preferably, the main catalyst is a titanium-containing catalyst selected from one or more of tetra-n-propyl titanate, tetra-n-butyl titanate tetramer, tetra-tert-butyl titanate, acetyl tri-isopropyl titanate, titanium acetate, titanium oxalate, titanium tetrachloride, tetramethyl titanate, tetraethyl titanate and tetra-isopropyl titanate.

Preferably, the secondary catalyst is a tin or zinc-containing catalyst selected from one or more of stannous chloride, stannous oxide, stannous 2-ethyl hexanoate and zinc acetate.

Preferably, the antioxidant is selected from one or more of phosphates, pyrophosphates, phosphonates, phosphinates, phosphites, salts of phosphates, phosphonates, phosphorus derivatives of hydroxy acids.

More preferably, the antioxidant is selected from trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triethylpropyl phosphate, tributyl phosphate, triphenyl phosphate, triethyl phosphite, trimethyl phosphite.

Furthermore, the catalyst is formed by mixing 40 wt% of a main catalyst, 10 wt% of a secondary catalyst and 50 wt% of an antioxidant, wherein the adding amount of the composite catalyst in the polymerization process is 3-6 per mill of the mass of all acids, and the composite catalyst is added in steps according to the proportion before esterification (0.5-1.5 per mill), before polycondensation (2-3.5 per mill) and after polycondensation (0.5-1 per mill).

In order to achieve the third object, the present invention provides the use of the copolyester as described above in the preparation of biodegradable articles, so as to improve the problem of water pollution of plastic articles.

Specifically, such copolyesters are processed by suction molding, injection molding, blow molding, blown film, extrusion, casting, spinning, etc. to form various articles, including sheets, film materials, tubes, etc. in shape. The novel disposable food tray specifically comprises a disposable food tray, a straw, a cup, a knife, a fork, a spoon, a packaging bag, a packaging barrel, a bottle, a garbage bag, an express bag and the like.

The natural environment for degrading the degradable material is water, soil, compost and other natural environments, and the water mentioned in the invention comprises rivers, lakes, seas, experimental water or various sewages and the like.

The invention has the following beneficial effects:

1. according to the invention, by introducing the lactic acid easily-hydrolyzed segment into the aliphatic-aromatic polyester and the copolyester, the integral degradation rate of the copolyester can be remarkably promoted. Particularly, when the difficult-to-hydrolyze polyester is butylene terephthalate and ethylene terephthalate, the difficult-to-hydrolyze polyester has excellent heat resistance and mechanical property as engineering plastics, but is difficult to degrade in soil, compost and other environments, and belongs to non-biodegradable plastics. By the introduction of polylactic acid segments, the disclosed copolyesters exhibit excellent biodegradability, not only in compost and soil, but also in seawater.

2. In the prior art, although the copolyester with thermal, mechanical and biodegradable properties can be prepared, the cost is too high to be applied from the perspective of practical application. The easily-hydrolyzed segment in the copolyester prepared by the invention takes lactic acid as a raw material, and compared with the polyglycolic acid segment PGA formed by taking glycolic acid as a raw material, the raw material is derived from a bio-base, so that the copolyester is more green and has lower cost; compared with lactide intermediate, the method reduces the synthesis steps, saves energy, simultaneously combines excellent thermal and mechanical properties and biodegradability, and has good application prospect!

3. In the prior art, the problem of poor hydrolysis of biodegradable polyester is mainly solved by adopting a blending method, however, the method is complex in system, the mechanical property is limited due to compatibility, and the biological safety is influenced by adding corresponding auxiliary agents. The invention synthesizes the high molecular weight random copolymer or block copolymer by combining the difficult-to-hydrolyze fragment and the easy-to-hydrolyze fragment through a copolymerization method, has simple method, does not contain an environmentally-unfriendly chain extender, and has high safety!

4. The invention optimizes the preparation process, especially the temperature, catalyst and catalyst adding mode in the polycondensation process, so that the obtained copolyester has high molecular weight, excellent mechanical strength, toughness, processability and heat resistance, and can effectively replace the existing common plastics in various fields such as disposable packaging, disposable tableware, chemical fiber, mulching film, fishery and the like.

5. The degradation of plastics is classified into pyrolysis, photodegradation, oxidative degradation, non-enzymatic hydrolysis, biodegradation and the like according to mechanisms, which all can lead to the breakage of polymer chain segments, the reduction of molecular weight and mechanical properties, and even the generation of bulk weight loss. But only biodegradation is one of the most environmentally friendly and thorough degradation processes because the end products of degradation are carbon dioxide and water. In the prior art, although the copolyester with thermal, mechanical and biodegradable properties is not always considered. However, these copolyesters generally have good biodegradability only in compost or soil environments and can be converted into environmentally non-polluting carbon dioxide and water. But does not degrade in natural water body, especially natural seawater, or is difficult to completely degrade to generate carbon dioxide and water without environmental pollution. The easily-hydrolyzed fragment related to the invention is PLA, which is generally slowly degraded in natural soil and natural water environment, especially seawater, the copolymer prepared by copolymerizing and embedding the PLA into the difficult-hydrolyzed fragment enables the PLA to show the effect of easy hydrolysis, and the copolyester obtained by the invention can be degraded in various natural environments while having heat resistance, good mechanical strength and toughness. Particularly, the method can not only show weight loss and reduce molecular weight and mechanical property in natural seawater along with the time, but also detect the generation of a degradation end product carbon dioxide.

6. According to the invention, the molar ratio of the added lactic acid to the dibasic acid is adjusted during copolymerization, so that the adjustment of the mechanical strength, toughness, hydrolysis performance and biodegradability of the copolyester can be realized, the copolyester with different mechanical properties and different degradation rates and degradation periods in natural environment can be obtained, the method is simple, and the effect is outstanding.

In conclusion, although the biodegradable polyester in the prior art has various varieties and different synthetic methods, a certain problem exists, the invention carries out a large number of experimental verifications through key factors such as selection of a biological polyester matrix and a hydrolysis-susceptible matrix and synthetic raw materials thereof, a copolymerization method, raw material proportion in a copolymerization process, temperature, vacuum degree, reaction time, catalyst selection and dosage and the like, prepares a copolymer which is cheap and easy to obtain, has high molecular weight and high mechanical property, can be efficiently degraded in compost, soil and natural water bodies, particularly in a seawater environment, can effectively replace the existing common plastic in various fields such as disposable packaging, disposable tableware, chemical fibers, mulching films, fishery and the like, and has wide application prospect.

Drawings

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

FIG. 1 shows the nuclear magnetic spectrum of PBTL series polymers.

Detailed Description

In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.

The invention provides a degradable copolyester, which is a random copolymer or a block copolymer consisting of a polyester segment difficult to hydrolyze and a polyester segment easy to hydrolyze at one end, wherein the number average molecular weight of the copolyester is 30000g/mol-500000g/mol, and the polyester segment easy to hydrolyze is polylactic acid.

The random copolymer in the present invention means that the R value obtained by calculation of the randomness in formula 4 approaches 1.

The block copolymer in the present invention means that the R value obtained by calculation of the randomness in formula 4 approaches 0.

L_A，L_BRespectively represent the average sequence length of two fragments in the copolyester, and are calculated by nuclear magnetic data.

In the present invention, the difficult-to-hydrolyze polyester means that a sample polyester is prepared as an aqueous dispersion at a concentration of 100mg/10ml, the aqueous dispersion is hydrolyzed at 45 ℃ and 100rpm for 7 days, and then the aqueous dispersion is diluted 10 times to measure the TOC (total organic carbon content) of 5ppm or less. In addition, water-soluble polyesters are not included.

Preferably, the polyester having a TOC (total organic carbon content) of 5ppm or less as measured by a predetermined method and being hardly hydrolyzed does not contain a water-soluble polyester. Selected from aliphatic polyester and/or aliphatic-aromatic copolyester obtained by polycondensation, excluding polylactic acid (PLA) and Polycaprolactone (PCL) aliphatic polyester generated by ring-opening polymerization.

The aliphatic-aromatic polyester is preferably one or two of polybutylene terephthalate and polyethylene terephthalate; the aliphatic-aromatic copolyester is preferably one or two of poly (terephthalic acid & adipic acid-butylene glycol), poly (terephthalic acid & ethylene glycol) butylene glycol, poly (terephthalic acid & succinic acid-butylene glycol), poly (terephthalic acid & adipic acid-ethylene glycol), poly (terephthalic acid & ethylene glycol) glycol, poly (terephthalic acid & sebacic acid-butylene glycol) and poly (terephthalic acid & sebacic acid-ethylene glycol).

Preferably, m is 0, 2, 4, 8; n is 2, 4, 8; further preferably, m is 2, 4; n is 2, 4.

More preferably, the number average molecular weight of the copolyester is 50000 g/moL-100000 g/moL.

The molar ratio of the chain segment of the difficult-to-hydrolyze polyester to the chain segment of the easy-to-hydrolyze polyester is 1:4-99: 1. Preferably, the molar ratio of the two is 1: 2-99: 1. More preferably, the molar ratio of the two is 1:1 to 20: 1.

The invention provides a preparation method of copolyester, which comprises the following steps:

or

Preferably, the antioxidant is selected from one or more of phosphates, pyrophosphates, phosphonates, phosphinates, phosphites, salts of phosphates, phosphonates, phosphorus derivatives of hydroxy acids. Further preferably, the antioxidant is trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, triethyl phosphite, trimethyl phosphite.

Preferably, the catalyst is formed by mixing 40 wt% of a main catalyst, 10 wt% of a secondary catalyst and 50 wt% of an antioxidant, the adding amount of the composite catalyst in the polymerization process is 3-6 per mill of the mass of all acids, and the composite catalyst is added in steps according to the proportion before esterification (0.5-1.5 per mill), before polycondensation (2-3.5 per mill) and after polycondensation (0.5-1 per mill).

The catalyst can be added during the esterification reaction, during the polycondensation reaction, or added in steps.

Preferably, it is added at the time of polycondensation, depending on the catalyst activity.

Preferably, the addition is carried out in stages, depending on the catalyst activity.

In the preparation method, fourth monomers such as glycerol, pentaerythritol and other polyols and polybasic acids can be added in the preparation process, so that the molecular weight and the mechanical strength are further improved.

In the preparation method, organic or inorganic nucleating agents (inorganic nano particles, fibers and the like) can be added in the preparation process, so that the crystallization, heat resistance and mechanical properties of the copolyester are improved.

In one embodiment, the preparation method comprises forming a segment of a difficult-to-hydrolyze polyester and a segment of a easy-to-hydrolyze polyester, respectively; and mixing the chain segments of the difficult-to-hydrolyze polyester and the chain segments of the easy-to-hydrolyze polyester, and carrying out melt chain extension to obtain the copolyester. The copolymer in this case is a block copolymer.

In the preparation method, the chain extender is preferably an epoxy chain extender such as ADR which is environment-friendly. Through the mode of melting chain extension, need not solvent introduction, easily processing, application scope is wider.

Further, in some specific embodiments, 1, 4-butanediol or adipic acid, 1, 4-butanediol and lactic acid are mixed, and subjected to 180-240 ℃ temperature programming in the presence of a catalyst, esterification and high vacuum polycondensation to obtain the copolyester; or

In the presence of a catalyst, directly carrying out melt polycondensation on lactic acid to form an oligomer A, carrying out esterification and polycondensation on 1, 4-butanediol or adipic acid and 1, 4-butanediol monomer to form an oligomer B, mixing the oligomer A and the oligomer B, and continuously carrying out polycondensation to obtain the copolyester.

Further, the lactic acid is one or a mixture of L-lactic acid, D-lactic acid and L, D-lactic acid.

Further, the molar ratio of the 1, 4-butanediol or adipic acid to the 1, 4-butanediol is 1: 1-1: 2.

Further, the molar ratio of the 1, 4-butanediol or adipic acid to the 1, 4-butanediol is 1: 1.2-1: 1.5.

Furthermore, the adding amount of the lactic acid is 1-400 wt% of the adding amount of the 1, 4-succinic acid or the adipic acid.

Furthermore, the adding amount of the lactic acid is 10-100 wt% of the adding amount of the 1, 4-succinic acid or the adipic acid.

Further, the polylactic acid segment can be synthesized from lactide instead of lactic acid without considering the cost.

The invention provides application of the copolyester in preparation of degradable products, so that the problem of pollution of plastic products to water bodies is solved.

The applications also include filling copolyesters for subsequent use to reduce cost or to improve heat or mechanical properties.

The application also comprises the step of blending the copolyester serving as a degradation promoter in the water body with other high polymer materials so as to improve the degradation rate of the whole copolyester in the water body.

The natural environment for degrading the degradable material is water, soil, compost and other natural environments, and the water mentioned in the invention comprises rivers, lakes, seas, experimental water or various sewages and the like. Wherein, the types and the quantity of microorganisms, water temperature, pH value and the like in different water environments are different. The hydrolysable copolyester in the embodiment can be degraded in the water body, and the degradation rate is higher than that of the existing commercial polyester products such as PBS and PLA in natural water environment. That is, the copolyester in the embodiment and the corresponding commercial biodegradable polyester with the same or similar molecular weight show faster mechanical property, molecular weight reduction and weight loss than the commercial biodegradable polyester in the same water environment. Or the time for the mechanical property of the copolyester in the application to be reduced to 50 percent or the weight loss of the copolyester to be 50 percent in the same water body environment is shorter than that of the commercialized biodegradable polyester when the molecular weight of the copolyester is reduced to 20 percent.

The technical solution of the present invention is described below with reference to some specific examples:

the raw materials involved in this example were all commercially available sources and the test methods involved were as follows:

drying the resin raw material in a vacuum oven at 45-80 ℃ for 48h, and processing the resin raw material into a standard tensile sample strip on an injection molding machine according to the national standard GB/T1040-92. The effective length G0 is 25 + -1 mm, the width b is 6.0 + -0.4 mm, and the thickness d is 2.0 + -0.2 mm, which is used for testing the mechanical property. The specimens with dimensions of length l 80. + -.2 mm, width b 10.0. + -. 0.2mm and thickness h 4.0. + -. 0.2mm were used for the heat distortion temperature measurement.

Analyzing the change of the molecular weight of the sample strip by using a Waters1515 gel permeation chromatograph GPC; the tensile strength and elongation at break of the specimens were monitored by means of an universal testing machine INSTRON-5699. 1H NMR detection is carried out by using Bruker AMX-300The, and average chain segment length x, y and p values are calculated through integration and proportion at characteristic chemical shift.

example 1

10mol of terephthalic acid, 15mol of 1, 4-butanediol (excessive), 2-10mol of lactic acid, 0.85-1.2g of composite catalyst consisting of tetrabutyl titanate, stannous chloride and triethyl phosphate, wherein the temperature is increased by 10min from 180 ℃ to 230 ℃, esterification is finished after water is not discharged, 3.5-5g of composite catalyst is supplemented, vacuum pumping is performed, the temperature is increased by 10 ℃ from 10min to 250 ℃, the reaction temperature is controlled to be 250 ℃, reaction is continued for 1 hour, 1.5-3g of catalyst is supplemented, reaction is continued for 1.5 hours, random copolyesters PBTLA20, PBTLA40, PBTLA60, PBTLA80 and PBTLA100 are obtained, the nuclear magnetic spectrum of the obtained PBTL series polymer is shown in figure 1, and related data are shown in Table 1:

TABLE 1

Example 2

10mol of terephthalic acid, 13mol of ethylene glycol (excessive), 2-8mol of lactic acid, 0.85-1.2g of composite catalyst consisting of tetrabutyl titanate, stannous chloride and triethyl phosphate, heating to 230 ℃ every 10min from 180 ℃, ending esterification after no water is discharged, adding 3.5-5g of composite catalyst, vacuumizing, heating to 10 ℃ every 10min, raising the temperature to 260 ℃, controlling the reaction temperature to 260 ℃ and continuing to react for 1 hour, adding 1.5-3g of catalyst, and continuing to react for 1.5 hours to obtain random copolyesters PETLA20, PETLA40, PETLA60, PETLA80 and PETLA 100. The relevant data are shown in table 2:

TABLE 2

Example 3

A degradable copolyester is prepared by the following steps:

4.5mol of terephthalic acid, 5.5mol of adipic acid, 15mol of 1, 4-butanediol (excess), 4-6mol of lactic acid, 1.0g of composite catalyst consisting of tetrabutyl titanate, stannous chloride and triethyl phosphate, heating to 210 ℃ every 10min at 180 ℃, ending esterification after water is not discharged, supplementing 4.0g of composite catalyst, vacuumizing, heating to 250 ℃ every 10min, raising the temperature to 250 ℃, controlling the reaction temperature to react for 1 hour at 250 ℃, supplementing 1.5g of catalyst, and continuing to react for 1.5 hours to obtain random copolyesters PBATL33, PBTLA40 and PBATL 60. The relevant data are shown in table 3:

TABLE 3

Example 4

A degradable copolyester is prepared by the following steps:

10mol of terephthalic acid, 18mol of 1, 4-butanediol (excessive), adding 7.0g of tetrabutyl titanate serving as a catalyst after esterification at 220 ℃ for 2h, and performing high-vacuum polycondensation at 250 ℃ for 1h to obtain the PBS oligomer at 230 ℃. 40mol of lactic acid, 0.3g of stannous chloride, esterification at 160 ℃ for 1h, and high vacuum polycondensation at 170 ℃ and 180 ℃ for 0.5h to obtain the PLA oligomer. And mixing the PBT oligomer and the PLA oligomer, adding an ADR epoxy chain extender, and carrying out chain extension at 230 ℃ in an upper screw extruder to obtain the PBTLA4000 block copolyester, wherein the structure of the PBTLA4000 block copolyester is the same as that in example 1.

Measured, x is 496, z is 420; its Mn is 459600, tensile strength is 68MPa, elongation at break is 345% and melting point is 212 deg.C.

Example 5

A degradable copolyester is prepared by the following steps:

3mol of lactic acid, 0.3g of stannous chloride, esterification at 160 ℃ for 1h, and temperature programmed polycondensation at 170-180 ℃ for 1h to obtain PLA oligomer; 10mol of isophthalic acid and 15mol of 1, 4-butanediol (excessive) are mixed, after esterification is carried out at the temperature of 180 ℃ for 2h, catalyst tetrabutyl titanate 7.0g and the PLA oligomer are added, and high vacuum polycondensation is carried out at the temperature of 250 ℃ for 4h at 210 ℃ to obtain PBTLA30-y copolyester. The structural formula is as follows:

the determination shows that x is 26 and z is 8; m thereof_n38900, tensile strength 31MPa, elongation at break 180%, melting point 99 ℃.

Example 6

A degradable copolyester is prepared by the following steps:

10mol of terephthalic acid and 20mol of 1, 4-butanediol (excessive) are mixed, after esterification is carried out at the temperature of 180 ℃ and 210 ℃ for 2h, 7.0g of tetrabutyl titanate serving as a catalyst is added, after high vacuum polycondensation is carried out at the temperature of 210 ℃ and 250 ℃ for 1h, 5mol of lactic acid is added, low vacuum reaction is carried out at the temperature of 190 ℃ for 1h, and temperature programming and high vacuum polycondensation are carried out at the temperature of 210 ℃ and 250 ℃ for 4h to obtain PBSLA50-x, wherein the structural formula of the PBTLA50 in the embodiment 1 is the same.

The determination shows that x is 16, z is 14; m thereof_n49200, tensile strength 37MPa, elongation at break 280%, melting point 93 ℃.

Example 7

A degradable copolyester is prepared by the following steps:

10mol of terephthalic acid, 15mol of 1, 6-hexanediol (excessive), esterification at the temperature of 180 ℃ for 2h, adding 7.0g of tetrabutyl titanate serving as a catalyst, programmed heating at the temperature of 210 ℃ for high-vacuum polycondensation for 1h, adding 5mol of lactic acid, low-vacuum reaction at the temperature of 210 ℃ for 1h, and high-vacuum polycondensation at the temperature of 210 ℃ for 4h to obtain PATLA50, wherein the structural formula is as follows:

the determination shows that x is 440, p is 14; m thereof_n56200, tensile strength 51MPa, elongation at break 380%, melting point 190 ℃.

Example 8

The comparison data of the properties of a portion of the polyesters of examples 1 to 7 with those of commercial products were selected.

Comparative example 1

The commercially available poly (butylene succinate) is from Xinjiang Tunhe, has the number average molecular weight of 52000 and the mechanical strength of 45MPa, and is processed into sample bars by injection molding for degradation performance test.

Comparative example 2

The polylactic acid is commercially available from national works of America, has the number average molecular weight of 168070 and the mechanical strength of 65MPa, and is processed into sample strips for degradation performance test.

The test method is as follows:

degradation experiments in pure water: the copolyesters were processed on an injection molding machine to standard tensile bars according to the national standard GB/T1040-92. The effective length G0 of the sample strip is 25 +/-1 mm, the width b is 6.0 +/-0.4 mm, and the thickness d is 2.0 +/-0.2 mm; each sample strip was numbered separately, weighed, and placed in 40 ℃ distilled water in a laboratory. Samples were periodically taken from seawater, rinsed with distilled water, and then dried in a vacuum oven at 50 ℃ for 48h to study the rate of weight loss upon degradation.

Natural seawater degradation experiment: the copolyesters were processed on an injection molding machine to standard tensile bars according to the national standard GB/T1040-92. The effective length G0 of the sample strip is 25 +/-1 mm, the width b is 6.0 +/-0.4 mm, and the thickness d is 2.0 +/-0.2 mm; numbering each sample strip, weighing, packaging each 3 sample strips with sleeves containing mesh holes, stringing all the sleeves with nylon knots, and placing in Tianjin natural seawater. Three samples were periodically taken from seawater, cleaned by ultrasonic cleaning technique to remove biofilm, rinsed with distilled water, and then dried in a vacuum oven at 50 ℃ for 48h to study the rate of weight loss on degradation.

The final aerobic biological decomposition capacity of the copolyester material under controlled composting conditions and in controlled seawater was determined with reference to national standard GB-T19277.2-2013 and ASTM standard D6691-09, respectively, and with reference to cellulose. The biodegradability of the material in seawater is verified by directly or indirectly detecting the release amount of carbon dioxide which is a degradation end product.

The test results are shown in table 4 below.

TABLE 4

The formation of carbon dioxide degradation products can be detected by the copolyester shown in compost and natural seawater, which indicates that the copolyester is subjected to a biodegradation process rather than ordinary hydrolysis.

It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.

Claims

1. A degradable copolyester is characterized in that the copolyester is a random copolymer or a diblock copolymer consisting of polyester segments difficult to hydrolyze and segments or sites easy to hydrolyze, and the number average molecular weight is 30000g/mol-500000 g/mol; the easy-to-hydrolyze segments or sites are selected from polylactic acids with different segment lengths, and the difficult-to-hydrolyze segments contain aromatic rings.

2. The copolyester of claim 1, wherein the non-hydrolyzable polyester is selected from aliphatic-aromatic polyesters or copolyesters obtained by polycondensation of aromatic dibasic acids and aliphatic diols or their esters;

preferably, the aliphatic diol is selected from the group consisting of ethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 2-propanediol, 1, 8-octanediol, sorbitol, polyethylene glycol; the aromatic dibasic acid is selected from terephthalic acid, isophthalic acid and phthalic acid.

3. The copolyester of claim 2, wherein the aliphatic-aromatic polyester is selected from one or both of polybutylene terephthalate and polyethylene terephthalate; the aliphatic-aromatic copolyester is selected from one or two of poly (terephthalic acid) & adipic acid-butylene glycol ester, poly (terephthalic acid) & ethanedioic acid-butylene glycol ester, poly (terephthalic acid) & adipic acid-ethylene glycol ester, poly (terephthalic acid) & ethanedioic acid-ethylene glycol ester, poly (terephthalic acid) & decanedioic acid-butylene glycol ester and poly (terephthalic acid) & decanedioic acid-ethylene glycol ester.

4. The copolyester of claim 2, wherein the copolyester has a structure represented by any one of the following formulas 1 to 3:

5. The copolyester of claim 4, wherein m is 0, 2, 4 or 8; n is 2, 4 or 8; preferably, m is 2 or 4; n is 2 or 4.

6. The copolyester of claim 5, wherein the molar ratio of the chain segments of the difficult-to-hydrolyze polyester to the chain segments of the easy-to-hydrolyze polyester is 1:4 to 99: 1.

7. A process for the preparation of a copolyester according to any one of claims 1-/6, comprising the steps of:

or

then adding the low molecular weight segment of the non-hydrolyzable polyester or the low molecular weight polylactic acid into the esterification and polycondensation process of the polylactic acid or the non-hydrolyzable polyester for copolymerization to form the copolyester;

or

Respectively forming a chain segment of the polyester which is difficult to hydrolyze and a chain segment of polylactic acid which is easy to hydrolyze;

and mixing the chain segment of the difficult-to-hydrolyze polyester with the polylactic acid chain segment, and carrying out melt chain extension to obtain the copolyester.

8. The preparation method according to claim 7, wherein the catalyst is a composite catalyst and is formed by mixing a main catalyst, a secondary catalyst and an antioxidant;

the main catalyst is a titanium-containing catalyst and is selected from one or more of tetra-n-propyl titanate, tetra-n-butyl titanate tetramer, tetra-tert-butyl titanate, acetyl triisopropyl titanate, titanium acetate, titanium oxalate, titanium tetrachloride, tetramethyl titanate, tetraethyl titanate, tetra-isopropyl titanate and the like;

the side catalyst is a catalyst containing tin or zinc, and is selected from one or more of stannic chloride, stannous oxide, stannous 2-ethyl hexanoate, zinc acetate and the like;

the antioxidant is selected from one or more of phosphate, pyrophosphate, phosphonate, phosphinate, phosphite, phosphate, salt of phosphonate, phosphorus derivative of hydroxy acid, etc.

9. The preparation method according to claim 8, wherein the catalyst is prepared by mixing 40 wt% of a main catalyst, 10 wt% of a sub-catalyst and 50 wt% of an antioxidant, and the composite catalyst is added in an amount of 3-6% by mass of all acids during the polymerization, wherein the catalyst is added in steps of (0.5-1.5%) before esterification, (2-3.5%) before polycondensation and (0.5-1%) after polycondensation.

10. Use of the degradable copolyester of any one of claims 1 to 6 for the preparation of a biodegradable article.