CN113307957B - Degradable copolyester and preparation method and application thereof - Google Patents

Abstract

The invention discloses 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-500000g/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

A degradable copolyester and its preparation method and application

Technical Field

The present invention relates to the field of degradable polymer materials, and more specifically to a degradable copolyester and a preparation method and application thereof.

Background Art

The increasingly severe marine plastic pollution and its harm to marine ecology and human life have attracted widespread attention. In the long run, the development and use of degradable plastic products in seawater to replace general non-degradable plastic products is a fundamental and effective way to prevent the continued development of this problem. Among all polymer materials, polyester is particularly susceptible to biodegradation by water and microorganisms in the environment due to the presence of ester bonds in the chain segments, generating environmentally friendly carbon dioxide and water. This process usually goes through three steps: 1) The material is broken under the combined action of light, oxygen, water, and organisms; 2) The polyester chain segments are hydrolyzed through enzymatic hydrolysis and (or) non-enzymatic hydrolysis processes, and the polymer chain segments are continuously degraded into oligomers or monomers; 3) These oligomers and monomers enter the microbial cells and form biomass under the action of intracellular depolymerases of microorganisms, or are mineralized into carbon dioxide and water. The second step of the hydrolysis process, that is, the hydrolysis of polymer segments to low molecules, is the rate-determining step of the biodegradation process, while the third step of microbial assimilation and the generation of carbon dioxide products is the most direct evidence of whether the biodegradation process has occurred. On the one hand, the degradation rate and degree of polyester are closely related to the intrinsic properties of the polymer chain segment structure, molecular weight, crystallinity, etc. For example, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) as engineering plastics have high crystallinity due to the presence of benzene rings in the chain segments, are not sensitive to water and microorganisms, and are extremely difficult to degrade in room temperature soil. They only show certain hydrolysis properties in high temperature and high humidity environments, and it is difficult to generate small molecular compounds such as carbon dioxide by hydrolysis. Biodegradable polyester polylactic acid (PLA) degrades slowly in soil and water, sometimes even taking decades, and can only be rapidly degraded in compost (58-65°C, 6-9 months for complete degradation).

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

In order to accelerate the degradation rate of biodegradable polyester in water, the prior art has adopted a method of blending starch with biodegradable polyester. However, since the degradation rate of starch itself is limited in water, especially seawater, and starch filling greatly reduces the mechanical properties of the blend, the application of the material is limited. (Journal of Applied Polymer Science 2019, 136 (2).) In addition, although the overall weight loss of the material is significantly increased by blending the easily water-soluble polyvinyl alcohol (PVA) with the biodegradable polyester, the compatibility of PVA with the resin matrix is poor, and the degradation performance of PVA itself and the biosafety of the final degradation product of the blend are questionable; (Polymer Degradation and Stability 2019, 163, 195-205) The prior art also includes blending the easily hydrolyzed polyglycolic acid (or polyglycolide, PGA), polylactic acid-glycolic acid copolyester (PLGA), polyethylene oxalate and other polyesters that can be rapidly hydrolyzed in water with the biodegradable resin matrix PLA. On the one hand, the easily hydrolyzed part can be rapidly degraded in water, and the overall weight loss is obvious. On the other hand, the intermediate products with carboxyl groups formed by degradation can further catalyze the biodegradation process of the difficultly hydrolyzed PLA. (CN103210043A, CN10332580A) However, the system is complex when blending is used, and the compatibility leads to limited mechanical properties. It is necessary to add corresponding additives, which affects biological safety.

By synthetically modifying existing biodegradable polyester materials, the hydrophilicity and crystallinity of plastics can be improved, and the probability of plastics interacting with water and microorganisms can be increased, thereby improving their degradation performance in water bodies. For example, in the prior art, butanediol and a certain proportion of terephthalic acid and adipic acid are copolymerized, and a certain proportion of PBA polyester units (terephthalic acid/succinic acid molar ratio is less than 5.5/4.5) are introduced into the difficult-to-degrade PBT segment to form a semi-aromatic copolyester polybutylene terephthalate adipate (PBAT), which has a lower crystallinity, increased molecular chain flexibility, and water molecules are more likely to enter the amorphous region for hydrolysis. Therefore, it has good degradation performance in compost and soil, but degradation in water bodies is still slow. (PolymerDegradation and Stability 2010, 95 (12), 2641-2647; Journal of Applied PolymerScience 2019, 136 (2).)

In the prior art, there is a method of synthesizing and modifying polyfurandicarboxylic acid butylene glycol homopolymer by lactic acid or by a two-step method, respectively, by polycondensation and then copolymerization, to obtain a polyfurandicarboxylic acid butylene glycol copolymer having certain hydrolysis performance. The high cost of furandicarboxylic acid has relatively limited application of this type of polyester. (Industrial & Engineering Chemistry Research 2018, 57 (32), 11020-11030.) The prior art also includes the formation of easily hydrolyzable copolyesters with glycolic acid, lactic acid-glycolic acid as easily hydrolyzed fragments, polybutylene succinate, polybutylene terephthalate and other aliphatic polyesters and copolyesters as difficult hydrolyzed fragments. The easily hydrolyzable fragments in the disclosed copolyesters are made of glycolic acid, which is relatively expensive relative to lactic acid, and is not conducive to industrialization and application. Moreover, the copolyesters show certain hydrolysis performance in pure water and natural seawater through molecular weight and weight loss tests, but the biodegradability of the copolyesters in natural environments, especially in seawater environments, is not disclosed. (CN 109762143A) The prior art also discloses a triblock polymer containing PLA and aliphatic/aromatic polyester segments with lactic acid as the end-capping group. It uses lactide, dibasic acid and diol as raw materials, and is obtained by multi-step prepolymerization and chain extension. The synthesis is complex and the product contains a chain extender. In addition, since the polylactic acid segment is formed by ring-opening polymerization of lactide, the cost is high. (CN102443145A, CN103788599A) The prior art also uses butanediol, succinic acid and lactic acid as raw materials and single tetrabutyl titanate as catalyst to synthesize PBS-LA block copolymers and random copolymers by one-step and two-step prepolymerization-polycondensation methods, respectively. However, the disclosed copolyester has a number average molecular weight of only 13600-16700 g/mol, has no mechanical strength, and cannot be used alone as a plastic. (Journal of Polymers and the Environment 2018, 26(7), 3060-3068) The prior art includes a PBT-LA copolymer synthesized by a two-step prepolymerization-polycondensation method using butanediol, terephthalic acid, and lactic acid as raw materials and a single tetrabutyl titanate as a catalyst. However, the disclosed copolyester has a number average molecular weight of only 13100-26100 g/mol and a tensile strength of less than 6.4 MPa, making it difficult to use as a plastic alone. (Synthesis and modification of degradable PLA-PBT copolyester, [Dissertation] Wang Bingtao 2010-Zhejiang University: Polymer Chemistry and Physics)

In summary, although the existing technology provides a series of solutions, the prepared polyester still has problems such as high cost, low molecular weight, poor mechanical properties, and inability to be efficiently biodegraded in soil and natural water bodies, especially seawater.

Therefore, it is necessary to provide a new degradable copolymer and a preparation method thereof to solve the above-mentioned technical problems.

Summary of the invention

The first object of the present invention is to provide a degradable copolyester, which is a random copolyester or a diblock copolyester formed by combining a difficult hydrolyzable segment and an easily hydrolyzable segment by copolymerization, has a high molecular weight, does not contain an environmentally unfriendly chain extender, has good mechanical strength and toughness, is heat-resistant, has good processing properties, and can be used alone as a plastic. In various natural environments such as water bodies, soil, and compost, the polyester segments are attacked by water molecules and quickly disconnected from the easily hydrolyzable segments or sites to form low-molecular-weight difficult-to-hydrolyze fragments, thereby promoting the overall biodegradation process, so that the material can be completely degraded in the natural environment to form environmentally non-polluting carbon dioxide and water.

The second object of the present invention is to provide a method for preparing a degradable copolyester.

The third object of the present invention is to provide an application of a degradable copolyester.

In order to achieve the above first object, the present invention adopts the following technical scheme:

A degradable copolyester, which is a random copolymer or a diblock copolymer composed of a hardly hydrolyzable polyester segment and an easily hydrolyzable segment or site, and has a number average molecular weight of 30000 g/mol-500000 g/mol; the easily hydrolyzable segment or site is selected from polylactic acid with different segment lengths.

Preferably, the hardly hydrolyzable polyester is selected from aliphatic polyesters obtained by polycondensation of aliphatic dibasic acids and diols or diol esters thereof.

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

Preferably, the diol is selected from ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,8-octanediol, sorbitol, polyethylene glycol.

Preferably, the aliphatic dibasic acid is selected from oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecyl acid, tetradecyl acid.

Preferably, the aliphatic polyester is selected from one or two of polybutylene succinate, polybutylene adipate, polyhexylene adipate, polyoctane succinate, polyhexylene succinate, polyhexylene sebacate, and polybutylene sebacate.

Preferably, the copolyester contains the structure shown in the following formula I:

Among them, m is selected from natural numbers of 0 to 12; n is selected from natural numbers of 2 to 8; x is selected from natural numbers of 1 to 500; and p is selected from natural numbers of 1 to 500.

Preferably, m=0, 2, 4 or 8, and n=2, 4 or 8.

Preferably, m=2 or 4, n=2 or 4.

Preferably, x=1-200, p=1-200.

More preferably, x=1-100, p=1-100.

More preferably, x=1-50, p=1-10.

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

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

Preferably, the molar ratio of the hardly hydrolyzable polyester segment to the easily hydrolyzable polyester segment is 1:4-99:1.

More preferably, the molar ratio of the hardly hydrolyzable polyester segment to the easily hydrolyzable polyester segment is 1:2 to 99:1.

More preferably, the molar ratio of the hardly hydrolyzable polyester segment to the easily hydrolyzable polyester segment is 1:1 to 20:1.

The consensus in the prior art is that easily hydrolyzable polyesters are polyesters that are easily degraded and broken in water, usually including polyglycolide (PGA). Polylactic acid-glycolic acid copolyester (PLGA) is listed as easily hydrolyzed polyesters because they have a very high ester bond density and can undergo rapid hydrolysis in room temperature water for 3-6 months, showing a sharp drop in molecular weight and mechanics, and obvious weight loss. The TOC measured by the prescribed method is higher than 5ppm, preferably above 10ppm. The commercial PLA in the existing consensus has a higher molecular weight (number average molecular weight of 50,000 g/mol or more) and is difficult to hydrolyze in room temperature water. The weight loss rate of PLA specimens with a size of 25.0mm×4.0mm×2.0mm in natural seawater and pure water for one year will not exceed 2%, and the molecular weight is also difficult to reduce, and its TOC value is below 5ppm. The present invention uses cheaper lactic acid as a raw material, and the PLA fragments in the copolyester obtained by controlling the reaction conditions (with a relatively low degree of polymerization of 1 to 500, preferably 1 to 200, more preferably 1 to 100, and a relatively low fragment length) unexpectedly have similar easy hydrolysis properties as PGA and PLGA, and can be used as easy hydrolyzable fragments to promote the overall hydrolysis and biodegradation process of the copolyester.

In order to achieve the above second purpose, the present invention adopts the following technical solutions:

A method for preparing a copolyester comprises the following steps:

The dibasic acid, diol and lactic acid monomer used to form the chain segment of the hardly hydrolyzable polyester are mixed, and the temperature is programmed to esterify and polycondense in the presence of a catalyst to obtain the copolyester;

or

The dibasic acid, diol or lactic acid monomer used to form the chain segment of the hardly hydrolyzable polyester is subjected to programmed temperature increase in the presence of a catalyst, and firstly esterification and polycondensation are performed to obtain a hardly hydrolyzable polyester or a low molecular weight polylactic acid segment of a low molecular weight segment;

Then, during the esterification and polycondensation process of polylactic acid or hardly hydrolyzable polyester, the hardly hydrolyzable polyester or low molecular weight polylactic acid with the low molecular weight fragment is added for copolymerization to form the copolyester;

or

The difficultly hydrolyzable polyester chain segments and the easily hydrolyzable polylactic acid chain segments are formed respectively;

The chain segments of the hardly hydrolyzable polyester and the polylactic acid chain segments are mixed and melt-chain extended to obtain the copolyester.

Preferably, the catalyst is a composite catalyst, which is a mixture of 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, tetra-n-butyl titanate tetrapolymer, tetra-tert-butyl titanate, acetyl triisopropyl titanate, titanium acetate, titanium oxalate, titanium tetrachloride, tetramethyl titanate, tetraethyl titanate, and tetraisopropyl titanate.

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

Preferably, the antioxidant is selected from one or more of phosphates, pyrophosphates, phosphonates, phosphinates, phosphites, phosphates, salts of phosphonates, and 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.

Preferably, the catalyst is a mixture of 40wt% of a main catalyst, 10wt% of a secondary catalyst and 50wt% of an antioxidant; and, during the polymerization process, the composite catalyst is added in an amount of 3‰-6‰ of the mass of all acids, wherein it is added in proportion before esterification (0.5‰-1.5‰), before polycondensation (2‰-3.5‰) and in the later stage of polycondensation (0.5‰-1‰).

In order to achieve the third objective, the present invention provides the use of the copolyester as described above in the preparation of biodegradable products, thereby improving the problem of water pollution caused by plastic products.

Specifically, the copolyester is processed by vacuum forming, injection molding, blow molding, blown film, extrusion, casting, spinning, etc. to form various products, and the shapes of the products include sheets, film materials, pipes, etc. Specifically, they include disposable plates, straws, cups, knives, forks, spoons, packaging bags, packaging barrels, bottles, garbage bags, express bags, etc.

The natural environment in which the degradable material is degraded is a water body, soil, compost and other natural environments. The water body mentioned in the present invention includes rivers, lakes, seas, experimental water bodies or various sewage and the like.

The beneficial effects of the present invention are as follows:

1. Although copolyesters with thermal, mechanical and biodegradable properties can be prepared in the prior art, from the perspective of practical application, the cost is too high to be applied. The easily hydrolyzed fragments in the copolyester prepared by the present invention use lactic acid as raw material. Compared with the polyglycolic acid fragment PGA formed by glycolic acid as raw material, the raw materials are derived from bio-based, which is greener and has lower cost; compared with the lactide intermediate, the synthesis steps are reduced, energy is saved, and the obtained copolyester has excellent thermal, mechanical and biodegradable properties at the same time, and has good application prospects!

2. The existing technology mainly solves the problem of poor hydrolysis of biodegradable polyester by using a blending method. However, this method has a complex system, limited mechanical properties due to compatibility, and requires the addition of corresponding additives, which affects biological safety. The present invention combines the difficultly hydrolyzed segments and the easily hydrolyzed segments by copolymerization to synthesize high molecular weight random copolymers or block copolymers. The method is simple, does not contain environmentally unfriendly chain extenders, and has high safety!

3. In the prior art, the synthesis process of copolyester is mainly carried out by a single catalyst and a single addition, and it is difficult to synthesize high molecular weight copolyester. The present invention optimizes the preparation process, especially the temperature, catalyst, and catalyst addition method during the polycondensation process. The obtained copolyester has a high molecular weight and excellent mechanical strength and toughness, processing performance and heat resistance. It can effectively replace existing ordinary plastics in various fields such as disposable packaging, disposable tableware, chemical fiber, mulch film, fishery, etc.

4. Plastic degradation is divided into pyrolysis, photodegradation, oxidative degradation, non-enzymatic hydrolysis and biodegradation according to the mechanism, all of which can lead to the breakage of polymer segments, the decrease of molecular weight and mechanical properties, and even the generation of body weight loss. However, only the biodegradation process is the most environmentally friendly and thorough degradation process, because the final products of degradation are carbon dioxide and water. Although there is no lack of copolyesters that take into account thermal, mechanical and biodegradable properties in the prior art. However, these copolyesters usually have good biodegradability only in compost or soil environments, and can be converted into environmentally friendly carbon dioxide and water. However, in natural water bodies, especially natural seawater, they do not degrade, or it is difficult to completely degrade to generate environmentally friendly carbon dioxide and water. The easily hydrolyzed segment involved in the present invention is PLA, which usually degrades slowly in natural soil and natural water environments, especially seawater. The copolymer prepared by copolymerizing PLA into the difficultly hydrolyzed segment in the present invention makes PLA show the effect of easy hydrolysis. The copolyester obtained by the present invention can degrade in various natural environments while having heat resistance, good mechanical strength and toughness. Especially in natural seawater, as time goes by, not only weight loss, molecular weight and mechanical properties decrease, but also the generation of the final degradation product carbon dioxide can be detected.

5. In the present invention, by adjusting the molar ratio of lactic acid to dibasic acid added during copolymerization, the mechanical strength and toughness, hydrolysis performance, and biodegradability of the copolyester can be adjusted, and copolyesters with different mechanical properties and different degradation rates and degradation cycles in the natural environment can be obtained. The method is simple and the effect is outstanding.

In summary, although there are many types of biodegradable polyesters in the prior art and the synthesis methods are different, there are certain problems. The present invention conducts a large number of experimental verifications through the selection of biopolyester matrix and easily hydrolyzed matrix and their synthetic raw materials, copolymerization method, raw material ratio in the copolymerization process, temperature, vacuum degree, reaction time, catalyst selection and dosage and other key factors, and prepares a copolymer that is cheap, easy to obtain, has a high molecular weight, high mechanical properties, and can be efficiently degraded in compost, soil and natural water bodies, especially seawater environment. It can effectively replace existing ordinary plastics in various fields such as disposable packaging, disposable tableware, chemical fiber, mulch film, fishery, etc., and has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

FIG1 shows the NMR spectra of the copolyesters PBSLA10, PBSLA20, PBSLA30, PBSLA40, PBSLA50, PBSLA60 and PBSLA70 prepared in Example 1.

DETAILED DESCRIPTION

In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

The present invention provides a degradable copolyester, which is a random copolymer or a diblock copolymer composed of a hardly hydrolyzable polyester segment and an easily hydrolyzable segment or site, and has a number average molecular weight of 30000 g/mol-500000 g/mol. The easily hydrolyzable segment or site specifically refers to polylactic acid with different segment lengths.

Preferably, the sparingly hydrolyzable polyester is selected from aliphatic polyesters obtained by polycondensation of aliphatic dibasic acids and diols or diol esters thereof.

The random copolymer in the present invention refers to a copolymer in which the R value obtained by calculating the randomness in formula II is close to 1.

The block copolymer in the present invention refers to a block copolymer in which the R value obtained by calculating the randomness in formula II is close to 0.

_LA and _LB represent the average sequence lengths of the two segments in the copolyester, respectively, which are calculated from NMR data.

In the present invention, the hardly hydrolyzable polyester means that the TOC (total organic carbon content) is 5 ppm or less when a water dispersion with a concentration of 100 mg/10 ml is prepared for the sample polyester, the water dispersion is hydrolyzed at 45°C and 100 rpm for 7 days, and then the water dispersion is diluted 10 times and measured. In addition, water-soluble polyesters are not included.

Preferably, the diol is selected from ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,8-octanediol, sorbitol, and polyethylene glycol; and the aliphatic dibasic acid is selected from oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanoic acid, and tetradecanoic acid.

Preferably, the aliphatic polyester is selected from one or two of polybutylene succinate, polybutylene adipate, polyhexylene adipate, polyhexylene succinate, polyhexylene sebacate and polybutylene sebacate.

Preferably, the copolyester has a structure as shown in the following formula I:

Among them, m is selected from natural numbers of 0 to 12; n is selected from natural numbers of 2 to 8; x is selected from natural numbers of 1 to 500; and p is selected from natural numbers of 1 to 500.

Preferably, m=0, 2, 4 or 8; n=2, 4 or 8; more preferably, m=2 or 4; n=2 or 4.

Preferably, x=1-200, p=1-200, preferably, x=1-100, p=1-100.

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

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

The molar ratio of the hardly hydrolyzable polyester segment to the easily hydrolyzable polyester segment is 1:4 to 99:1. Preferably, the molar ratio of the two is 1:2 to 99:1. More preferably, the molar ratio of the two is 1:1 to 20:1.

The present invention provides a method for preparing a copolyester, comprising the following steps:

The dibasic acid, diol and lactic acid monomer used to form the chain segment of the hardly hydrolyzable polyester are mixed, and the temperature is programmed to esterify and polycondense in the presence of a catalyst to obtain the copolyester;

or

The dibasic acid, diol or lactic acid monomer used to form the chain segment of the hardly hydrolyzable polyester is subjected to programmed temperature increase in the presence of a catalyst, and firstly esterification and polycondensation are performed to obtain a hardly hydrolyzable polyester or a low molecular weight polylactic acid segment of a low molecular weight segment;

During the esterification and polycondensation of polylactic acid or hardly hydrolyzable polyester, the hardly hydrolyzable polyester or low molecular weight polylactic acid with the low molecular weight fragment is added for copolymerization to form the copolyester;

or

The difficultly hydrolyzable polyester chain segments and the easily hydrolyzable polylactic acid chain segments are formed respectively; the difficultly hydrolyzable polyester chain segments and the polylactic acid chain segments are mixed, melt-chain extended, and the copolyester is obtained.

Furthermore, the catalyst is a composite catalyst, which is a mixture of a main catalyst, a sub-catalyst and an antioxidant.

Preferably, the titanium-containing catalyst is selected from tetra-n-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetrapolymer, tetra-tert-butyl titanate, acetyl triisopropyl titanate, titanium acetate, titanium oxalate, titanium tetrachloride, tetramethyl titanate, tetraethyl titanate, and tetraisopropyl titanate.

Preferably, the tin- or zinc-containing catalyst is selected from stannous chloride, stannous oxide, stannous 2-ethylhexanoate, and zinc acetate.

Preferably, the antioxidant is selected from phosphate, pyrophosphate, phosphonate, phosphinate, phosphite or salt of phosphate or phosphonate, or phosphorus derivative of hydroxy acid. Further preferably, the antioxidant is trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triethylpropyl phosphate, tributyl phosphate, triphenyl phosphate, triethyl phosphite, trimethyl phosphite.

Preferably, the catalyst is a mixture of 40wt% titanium-containing catalyst, 10wt% tin or zinc-containing catalyst and 50wt% antioxidant. The amount of catalyst added during the polymerization process is 3‰-6‰ of the mass of all acids, and is added in steps according to proportions before esterification (0.5‰-1.5‰), before polycondensation (2‰-3.5‰) and in the late polycondensation (0.5‰-1‰). The catalyst can be added during the esterification reaction, or during the polycondensation reaction, or in steps.

Preferably, it is added during polycondensation, depending on the catalyst activity.

Preferably, the catalyst is added in stages according to its activity.

In the preparation method, a fourth monomer such as glycerol, pentaerythritol and other polyols and polyacids can be added during the preparation process to further increase the molecular weight and mechanical strength.

In the preparation method, an organic or inorganic nucleating agent (inorganic nanoparticles, fibers, etc.) can be added during the preparation process to improve the crystallization, heat resistance and mechanical properties of the copolyester.

In one embodiment, the preparation method comprises forming a segment of a hardly hydrolyzable polyester and a segment of an easily hydrolyzable polyester respectively; mixing the segment of the hardly hydrolyzable polyester and the segment of the easily hydrolyzable polyester, and performing melt chain extension to obtain the copolyester. The copolymer at this time is a block copolymer.

In the preparation method, the exemplary chain extender is preferably an environmentally friendly epoxy chain extender such as ADR. By melt chain extension, no solvent introduction is required, the process is easy, and the application range is wider.

Further, in some specific embodiments, 1,4-succinic acid or adipic acid, 1,4-butanediol and lactic acid are mixed, and the temperature is programmed to 180-240 degrees in the presence of a catalyst, and the copolyester is obtained by esterification and high vacuum polycondensation; or

In the presence of a catalyst, lactic acid is directly melt-polycondensed to form oligomer A, 1,4-succinic acid or adipic acid and 1,4-butanediol monomers are esterified and polycondensed to form oligomer B, oligomer A and oligomer B are mixed and further polycondensed to obtain the copolyester.

Furthermore, the lactic acid is one of L-lactic acid, D-lactic acid, L,D-lactic acid, or a mixture of several thereof.

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

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

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

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

Furthermore, without considering the cost, the polylactic acid segment can also be synthesized by lactide instead of lactic acid. The present invention provides the use of the copolyester described above in the preparation of degradable products, thereby improving the problem of plastic products polluting water bodies.

Specifically, the copolyester is processed by vacuum forming, injection molding, blow molding, blown film, extrusion, casting, spinning, etc. to form various products, and the shapes of the products include sheets, film materials, pipes, etc. Specifically, they include disposable plates, straws, cups, knives, forks, spoons, packaging bags, packaging barrels, bottles, garbage bags, express bags, etc.

The above applications also include filling the copolyester and then using it to reduce costs or improve heat resistance or mechanical properties.

The above application also includes blending the copolyester as a degradation accelerator in water with other polymer materials to increase the overall degradation rate in water.

The natural environment for the degradation of the degradable material is a water body, soil, compost and other natural environments. The water bodies mentioned in the present invention include rivers, lakes, seas, experimental water bodies or various sewage, etc. Among them, there are differences in the types and quantities of microorganisms, water temperature, pH value, etc. in different water environments. The hydrolyzable copolyester in this embodiment can be degraded in the aforementioned water bodies, and the degradation rate is higher than the degradation rate of existing commercial polyester products such as PBS and PLA in natural water environments. That is, the copolyester in this embodiment and the corresponding commercial biodegradable polyester with the same or similar molecular weight, in the same water environment, the copolyester shows faster mechanical properties, molecular weight decline and weight loss than the commercial biodegradable polyester. Or in the same water environment, the copolyester in this application takes a shorter time for its mechanical properties to drop to 50% of the original or weight loss to 50% of the original, or the molecular weight to drop to 20% than the commercial biodegradable polyester.

The technical solution of the present invention is described below in conjunction with some specific embodiments:

The raw materials involved in this embodiment are all commercially available, and the test methods involved are as follows:

After the resin raw material is dried in a vacuum oven at 45-80°C for 48 hours, it is processed into a standard tensile specimen on an injection molding machine according to the national standard GB/T1040-92. The effective length G0=25±1mm, width b=6.0±0.4mm, thickness d=2.0±0.2mm are used for mechanical property testing. The specimen with the size of length l=80±2mm, width b=10.0±0.2mm, thickness h=4.0±0.2mm is used for heat deformation temperature testing.

The molecular weight change of the sample was analyzed by Waters 1515 gel permeation chromatograph GPC; the tensile strength and elongation at break of the sample were monitored by universal material testing machine INSTRON-5699. 1H NMR detection was performed by Bruker AMX-300The, and the average sequence length and x, p values were calculated by integration and ratio at characteristic chemical shift. DSC detected the melting point of the value.

The technical solution of the present invention is described below in conjunction with some specific embodiments:

Example 1

A degradable copolyester, the preparation method of which comprises the following steps:

1,4-butanediol 10mol, 1,4-butanediol (excess) 15mol, lactic acid 1-7mol, tetraisopropyl titanate, stannous chloride, triethyl phosphate composed of composite catalyst 0.85-1.2g, 150℃ start to raise the temperature by 10℃ every 10min until it reaches 180℃, esterification is terminated after no more water is produced, add 3.5-5g of composite catalyst, vacuumize, raise the temperature by 10℃ every 10min to 230℃, control the reaction temperature at 230℃ and continue to react for 1 hour, add 1.5-3g of catalyst, continue to react for 1.5h, and obtain random copolyesters PBSLA10, PBSLA20, PBSLA30, PBSLA40, PBSLA50, PBSLA60, PBSLA70. Relevant data are shown in Table 1:

The copolyester prepared in Example 1 has the following molecular formula, and its basic properties are shown in Table 1. The molecular weight is relatively high, all greater than 75,000, and the mechanical properties are good, with a tensile strength greater than 30 MPa and an elongation at break exceeding 400%. The heat deformation temperature is high and the heat resistance is good.

Table 1

Figure 1: NMR spectra of copolyesters PBSLA10, PBSLA20, PBSLA30, PBSLA40, PBSLA50, PBSLA60, and PBSLA70.

Example 2

A degradable copolyester, the preparation method of which comprises the following steps:

1,4-Butanediol (15 mol, 1,4-butanediol (excess amount) and lactic acid (0.5 mol) were added to 160-180°C for esterification for 2 h, and then 5.5 g of tetraisopropyl titanate and 0.3 g of stannous 2-ethylhexanoate were added as catalysts. The mixture was subjected to high vacuum polycondensation at 200-230°C for 4.5 h to obtain a random copolyester PBSLA5, the structural formula of which is the same as that of Example 1.

Wherein x=120, p=60; the random copolyester has _Mn =46200 g/mol, a tensile strength of 42 MPa, an elongation at break of 430%, and a melting point of 105°C.

Example 3

A degradable copolyester, the preparation method of which comprises the following steps:

1,4-butanediol 10mol, 1,4-butanediol (excess) 15mol, esterification at 160-180℃ for 2h, add 7.0g of tetrabutyl titanate catalyst, program temperature rise at 200-230℃ and high vacuum polycondensation for 2h to obtain PBS oligomer. Lactic acid 20mol, stannous chloride 3g, esterification at 160℃ for 1h, high vacuum polycondensation at 170-180℃ for 0.5h to obtain PLA oligomer. After the above PBS oligomer and PLA oligomer are mixed, ADR epoxy chain extender is added, and chain extension is carried out at 120-180℃ in the upper screw extruder to obtain PBSLA2000 block copolyester, whose structure is the same as that in Example 1.

After measurement, where x=450, p=480; (whether it is p) its Mn=459600g/moL, tensile strength 41MPa, elongation at break 80%, melting point 102°C.

Example 4

A degradable copolyester, the preparation method of which comprises the following steps:

3 mol of lactic acid and 0.3 g of stannous chloride are esterified at 160°C for 1 h and polycondensed at 170-180°C for 0.5 h to obtain a PLA oligomer; 10 mol of 1,4-butanediol and 15 mol of 1,4-butanediol (excess) are mixed and esterified at 160-180°C for 2 h, and then 7.0 g of tetrabutyl titanate catalyst and the above-mentioned PLA oligomer are added, and the PBSLA30-x copolyester is obtained by high vacuum polycondensation at 200-230°C for 4 h, and the structural formula thereof is the same as that in Example 1.

After measurement, in the formula, x=126, p=200; its _Mn =108900g/mol, tensile strength 51MPa, elongation at break 480%, melting point 109°C.

Example 5

A degradable copolyester, the preparation method of which comprises the following steps:

10 mol of 1,4-butanediol and 15 mol of 1,4-butanediol (excess) were mixed, esterified at 160-180°C for 2 h, 7.0 g of tetrabutyl titanate catalyst was added, and high vacuum polycondensation was performed at 200-230°C for 1 h. Then 5 mol of lactic acid was added, and the mixture was reacted at 190°C for 1 h under low vacuum, and high vacuum polycondensation was performed at 200-230°C for 4 h to obtain PBSLA50-x, whose structural formula is the same as that of Example 1.

According to the measurement, in the formula, x=116, p=140; its _Mn =89200g/mol, tensile strength is 37MPa, elongation at break is 280%, and melting point is 93°C.

Example 6

A degradable copolyester, the preparation method of which comprises the following steps:

10 mol of 1,4-hexanedioic acid and 15 mol of 1,4-butanediol (excess) were mixed, esterified at 160-180°C for 2 h, 7.0 g of tetrabutyl titanate catalyst was added, and high vacuum polycondensation was performed at 200-230°C for 1 h. Then 5 mol of lactic acid was added, and the reaction was carried out at 190°C for 1 h under low vacuum, and high vacuum polycondensation was performed at 200-230°C for 4 h to obtain PBALA50.

After measurement, in the formula, x=60, p=120; its _Mn =99200g/mol, tensile strength 41MPa, elongation at break 280%, melting point 93°C.

Example 7

A degradable copolyester, the preparation method of which comprises the following steps:

1,4-hexanedioic acid 10mol, 1,8-octanediol (excess) 15mol were mixed, esterified at 160-180℃ for 2h, 7.0g of tetrabutyl titanate catalyst was added, and high vacuum polycondensation was performed at 200-230℃ for 1h, then 5mol of lactic acid was added, low vacuum reaction was performed at 190℃ for 1h, and high vacuum polycondensation was performed at 200-230℃ for 4h to obtain POALA50-y.

After measurement, in the formula, x=270, p=20; its _Mn =153200g/mol, tensile strength 39MPa, elongation at break 280%, melting point 103°C.

Example 8

A degradable copolyester, the preparation method of which comprises the following steps:

5 mol of sebacic acid and 10 mol of 1,4-butanediol (excess) were mixed, esterified at 160-180℃ for 2h, 7.0 g of tetrabutyl titanate catalyst was added, and high vacuum polycondensation was performed at 200-230℃ for 1h. Then 20 mol of lactic acid was added, and low vacuum reaction was performed at 190℃ for 1h, and high vacuum polycondensation was performed at 200-230℃ for 4h to obtain PBDLA50.

After measurement, in the formula, x=50, p=20; its _Mn =106700g/mol, tensile strength 39MPa, elongation at break 280%, melting point 104°C.

Example 9

The performance comparison data of some polyesters in Examples 1-8 and commercially available products were selected.

Comparative Example 1

Commercially available polybutylene succinate, sourced from Tunhe, Xinjiang, has a number average molecular weight of 52,000 and a mechanical strength of 45 MPa. It is injection molded into specimens for degradation performance testing.

Comparative Example 2

Commercially available polylactic acid, sourced from Natural Works in the United States, has a number average molecular weight of 168070 and a mechanical strength of 65 MPa. It was injection molded into specimens for degradation performance testing.

The test method is as follows:

Degradation experiment in pure water: The copolyester was processed into standard tensile specimens on an injection molding machine according to the national standard GB/T 1040-92. The effective length of the specimen G0 = 25 ± 1mm, the width b = 6.0 ± 0.4mm, and the thickness d = 2.0 ± 0.2mm; each specimen was numbered, weighed, and placed in 40 degrees Celsius distilled water in the laboratory. Samples were taken out from the seawater regularly, rinsed with distilled water, and then dried in a vacuum oven at 50°C for 48 hours to study the degradation weight loss rate.

Natural seawater degradation experiment: The copolyester was processed into standard tensile specimens on an injection molding machine according to the national standard GB/T 1040-92. The effective length of the specimen G0 = 25 ± 1mm, the width b = 6.0 ± 0.4mm, and the thickness d = 2.0 ± 0.2mm; each specimen was numbered and weighed, and every 3 specimens were packaged with a sleeve containing a mesh, and all the sleeves were strung with nylon knots and placed in Tianjin natural seawater. Three samples were taken out of the seawater regularly, cleaned with ultrasonic cleaning technology to remove the biofilm, rinsed with distilled water, and then dried in a vacuum oven at 50°C for 48h to study the degradation weight loss rate.

With reference to the national standard GB-T19277.2-2013 and ASTM standard D 6691-09, the final aerobic biodegradability of copolyester materials under controlled composting conditions and in controlled seawater was determined with cellulose as the reference. The biodegradability of the material in seawater was verified by directly or indirectly detecting the release of carbon dioxide, the terminal degradation product.

The test results are shown in Table 2 below.

Table 2

The formation of carbon dioxide degradation products can be detected in the copolyesters shown in compost and natural seawater, indicating that the copolyesters have undergone biodegradation rather than ordinary hydrolysis.

Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims (10)

1. A degradable copolyester is a random copolymer consisting of a difficult-to-hydrolyze polyester segment and an easy-to-hydrolyze segment, wherein the difficult-to-hydrolyze polyester segment is polybutylene succinate, the easy-to-hydrolyze segment is polylactic acid, and the copolyester is prepared from lactic acid, 1,4-succinic acid and 1,4-butanediol through esterification and polycondensation reactions, wherein the random copolymer comprises the following components:

wherein, x =400, p =2; or

x =260, p =5; or

x =190, p =10; or

x =150, p =30; or

x =90, p =50; or

x =54,p =70; or

x＝10，p＝100。

2. The copolyester of claim 1, wherein the copolyester is prepared under the condition that the molar ratio of the lactic acid and the 1,4-succinic acid is 1: 10,2: 10,3: 10,4: 10,5: 10,6: 10 or 7: 10.

3. A copolyester according to claim 1 or 2, characterized in that the number average molecular weight of the copolyester is 50000g/moL to 100000g/moL.

4. The copolyester of claim 1 or 2, wherein the copolyester has a number average molecular weight of 89681g/mol,88145g/mol,85816g/mol,84747g/mol,80924g/mol,76502g/mol, or 75203g/mol, respectively.

5. Process for the preparation of the copolyester according to any one of claims 1 to 4, characterized in that it comprises the following steps:

mixing 1,4-butanedioic acid, 1,4-butanediol and lactic acid, carrying out esterification reaction by temperature programming in the presence of a catalyst, continuously carrying out polycondensation under a vacuum condition after the esterification reaction is finished to obtain the copolyester,

wherein:

the molar ratio of lactic acid to 1,4-succinic acid is 1: 10,2: 10,3: 10,4: 10,5: 10,6: 10 or 7: 10,

the temperature programming comprises the steps of starting to heat up to 10 ℃ every 10min at 150 ℃ until the temperature is raised to 180 ℃,

the polycondensation is carried out by raising the temperature by 10 ℃ to 230 ℃ every 10min and controlling the reaction temperature at 230 ℃ for 1 hour,

adding a catalyst to the reaction mixture before continuing the polycondensation under the vacuum condition,

after the controlled reaction temperature was maintained at 230 ℃ for 1 hour, additional catalyst was added to the reaction mixture.

6. The method of claim 5, wherein the catalyst is present in an amount of 0.5 to 1.5% o by mass of the total mass of lactic acid and 1,4-succinic acid when mixing 1,4-succinic acid, 1,4-butanediol, lactic acid.

7. The process of claim 5 wherein a catalyst is added to the reaction mixture in an amount of 2 to 3.5 parts per thousand of the total mass of lactic acid and 1,4-succinic acid before continuing the polycondensation under vacuum conditions.

8. The method as claimed in claim 5, wherein the catalyst is further added to the reaction mixture in an amount of 0.5 to 1% by mass of the total mass of the lactic acid and the succinic acid after the controlled reaction temperature is maintained at 230 ℃ for 2 hours.

9. The method according to any one of claims 5 to 8, wherein the catalyst is a composite catalyst 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 and tetra-isopropyl titanate;

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

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

10. Use of the degradable copolyester of any one of claims 1 to 4 for the preparation of a biodegradable article.

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