CN115651174A

CN115651174A - Method for synthesizing biodegradable PBAT-PLA copolyester by organic guanidine catalysis

Info

Publication number: CN115651174A
Application number: CN202211416915.1A
Authority: CN
Inventors: 黄森彪; 王敏; 廖广明; 岳林; 李兆远; 李建兵
Original assignee: Fuhai Dongying New Material Technology Co ltd
Current assignee: Fuhai Dongying New Material Technology Co ltd
Priority date: 2022-11-14
Filing date: 2022-11-14
Publication date: 2023-01-31
Anticipated expiration: 2042-11-14
Also published as: CN115651174B

Abstract

The invention discloses a method for synthesizing biodegradable PBAT-PLA copolyester by catalyzing with organic guanidine, belonging to the technical field of biodegradable materials. According to the invention, the organic guanidine catalyst is adopted, the acid value (hydroxyl value) and the molecular weight of each chain segment in the polymerization process are controlled, the commonly used 1,4-Butanediol (BDO) initiated lactide is replaced by polyether polyol with hydroxyl being more than or equal to 3 and the molecular weight of 600-3500g/mol, and the biodegradable PBAT-PLA copolyester with good chain segment compatibility, melt strength and flexibility is synthesized, so that the application range of the biodegradable PBAT-PLA copolyester in the fields of food, medicine, agriculture and the like is widened, and the downstream application requirements of film blowing, injection molding, foaming, double-stretching films and the like are better met.

Description

Method for synthesizing biodegradable PBAT-PLA copolyester by organic guanidine catalysis

Technical Field

The invention relates to the technical field of biodegradable materials, in particular to a method for synthesizing biodegradable PBAT-PLA copolyester by organic guanidine catalysis.

Background

With the increasing white pollution, biodegradable polyester becomes one of the most effective solutions to the plastic pollution problem, and can be degraded into carbon dioxide and water which are harmless to the environment under the composting condition or the natural condition. Among biodegradable polyesters, polybutylene terephthalate adipate (PBAT) and polylactic acid (PLA) are two major varieties with the largest yield and the widest application in the market at present. The PBAT is a copolymer of butylene terephthalate (PBT) and butylene adipate (PBA), has a rigid and flexible chain segment in the structure, and has high ductility and elongation at break, but the PBAT has low strength and rigidity, so that the PBAT is easy to bond in a film blowing process, a film product is soft, and the PBAT is easy to break in a using process. PLA has the advantages of high strength, high hardness, good transparency and processability, etc., however, PLA has the defects of low elongation at break, poor impact strength, poor toughness, etc., and is difficult to meet certain practical use requirements, thereby limiting the application of the PLA. In practice, direct blend processing of PBAT with PLA is typically employed to form PBAT-PLA blends with complementary properties. But the compatibility of PBAT and PLA is poor, and the performance of the blended product is unstable. Aiming at the problem of blending, the problem of poor blending compatibility is solved by carrying out chain extension reaction by using an isocyanate chain extender at present, but the problem of chain extender toxicity or wide molecular weight distribution of a product after chain extension exists in the chain extension reaction, and the product is adversely affected. Therefore, the development of a PBAT-PLA copolymer and a preparation method thereof are still a new problem to be solved urgently.

At present, some patents have been explored in this direction, for example, CN 107141458a uses prepolymer PBAT and prepolymer PLA, and puts them into a high vacuum reaction kettle, and controls the vacuum degree, so as to finally obtain PBAT-PLA copolyester with weight average molecular weight of 100000-250000.

Patent CN107163232A discloses a ring-opening polymerization method of PBAT-PLA block copolymer, aliphatic diol is put into a reaction kettle with prepolymer PBAT to prepare PBAT with hydroxyl at two ends; and (3) putting the PBAT with the hydroxyl at the two ends and the lactide into a reaction kettle, and adding a catalyst to react after materials in the kettle are completely melted to obtain the PBAT-PLA block copolymer.

Patent CN 113968961A discloses a poly (terephthalic acid) -co-butylene succinate-polylactic acid copolymer and a preparation method thereof, wherein the poly (terephthalic acid) -co-butylene succinate-polylactic acid copolymer is prepared by ring-opening polycondensation of L-lactide and poly (terephthalic acid) -co-butylene succinate under the action of a tin chloride catalyst.

The PBAT-PLA copolymer with rigidity and softness combined by adopting the copolymerization mode of PBAT and PLA and fully combining the flexibility of the PBAT chain segment and the rigidity of the PLA chain segment can better meet the downstream application requirements of film blowing, injection molding and the like. In the above patents, heavy metal catalysts such as tetrabutyl titanate and hydrated tin dichloride are used in the polymerization of PBAT and PLA, which may contaminate the product and affect the use of the product in the fields of food, medicine, etc. Secondly, there is no mention in the above patent of how to solve the problem of severe phase separation due to poor compatibility of PBAT segments and PLA segments. Finally, the melt strength and flexibility of conventional PBAT-PLA copolyesters are still inadequate in certain downstream applications such as foamed, biaxially stretched films.

Disclosure of Invention

The invention aims to solve the problems that the product is polluted by a heavy metal catalyst, the chain segments are seriously separated, the melt strength and the flexibility are insufficient and the like in the PBAT-PLA copolyester. By adopting the organic guanidine catalyst, controlling the acid value (hydroxyl value) and molecular weight of each chain segment in the polymerization process, and adopting polyether polyol with hydroxyl being more than or equal to 3 and molecular weight being 600-3500g/mol to replace 1,4-Butanediol (BDO) to initiate lactide, the biodegradable PBAT-PLA copolyester with good chain segment compatibility, melt strength and flexibility is synthesized, the application range of the copolyester in the fields of food, medicine, agriculture and the like is widened, and the downstream application requirements of film blowing, injection molding, foaming, double-stretching films and the like are better met.

Aiming at the problem of residual heavy metal titanium catalysts and tin catalysts, the invention adopts a good solution scheme that the thermal stability is good, the catalytic efficiency is high (the addition amount is only one to five parts per million of the added raw material monomers), and the nontoxic organic guanidine catalyst (the introduction of the heavy metal catalyst is avoided) is adopted in the preparation process of the PBAT-PLA copolyester. The invention adopts the organic guanidine catalyst to synthesize the biodegradable PBAT-PLA copolyester with good chain segment compatibility, melt strength and flexibility. Firstly, the organic guanidine catalyst has the characteristics of high heat resistance, large bulk volume, high delocalization of positive charge, high electrophilic induction capability and the like, and forms an activated esterified compound intermediate together with strong positive and negative charge coordination capability between the PBAT polymerization raw material terephthalic acid (PTA) and Adipic Acid (AA) and the PLA polymerization raw material lactide. Then 1,4-Butanediol (BDO) and the active esterified substance intermediate are subjected to ester exchange reaction, the polymerization reaction is rapidly promoted, the active polymer with controlled molecular weight is obtained, and the degradable block polyester high polymer material is further prepared.

Aiming at the problem of serious phase separation caused by poor compatibility of PBAT chain segments and PLA chain segments, the reactivity of BHBT, BHBA and PLA chain segments is improved by controlling the acid value (hydroxyl value) and molecular weight of each chain segment in the polymerization process, and better reaction fusion among different chain segments is realized. Aiming at the problem that the melt strength and flexibility of the common PBAT-PLA copolyester are still insufficient, polyether polyol with the hydroxyl group being more than or equal to 3 and the molecular weight being 600-3500g/mol is adopted to replace the lactide initiated by 1,4-Butanediol (BDO) which is usually used for preparing PLA polyol with a branched ether chain structure, so that the melt strength of the PBAT-PLA copolyester is improved, the flexibility is also improved, and the defects of the PBAT-PLA copolyester in the downstream application fields of foaming, double-stretching films and the like are overcome.

The specific technical scheme of the invention is as follows:

the method for synthesizing biodegradable PBAT-PLA copolyester under the catalysis of organic guanidine comprises the following steps:

s1, esterification-pre-polycondensation:

s11, esterification: adding terephthalic acid (PTA), 1,4-Butanediol (BDO) and an organic guanidine catalyst into a first esterification kettle to perform esterification reaction until the water yield of the reaction reaches a theoretical value; adding 1,6-Adipic Acid (AA), 1,4-Butanediol (BDO) and an organic guanidine catalyst into a second esterification kettle to perform esterification reaction until the water yield of the reaction reaches a theoretical value;

s12, pre-polycondensation: after the esterification reaction of the esterification kettle I and the esterification kettle II is finished, further improving the vacuum degree, carrying out pre-polycondensation, reducing the temperature in the kettle to below 180 ℃ after the acid value and the molecular weight of the chain segment of the oligomer BHBA of the terephthalic acid and 1,4-butanediol of the esterification kettle I and the oligomer BHBT of the oligomer 1,6-adipic acid and 1,4-butanediol of the esterification kettle II reach target values respectively, further distilling out redundant 1,4-Butanediol (BDO), and then transferring to a polymerization kettle III;

s2, synthesis of PLA polyol with branched ether structure: adding lactide, an organic guanidine catalyst and an initiator polyether polyol into a third polymerization kettle, heating to a target temperature, vacuumizing to perform ring-opening polymerization reaction until the molecular weight and the hydroxyl value of the PLA polyol with the branched ether structure reach target values;

s3, copolycondensation: transferring the reacted BHBA and BHBT into a third polymerization kettle, heating to a specified temperature, starting vacuum, and carrying out copolycondensation with the PLA polyhydric alcohol with the branched ether structure;

s4, final polycondensation: adding a heat stabilizer and an antioxidant into the third polymerization kettle, vacuumizing, performing polycondensation reaction, and then further improving the vacuum degree for final polycondensation to obtain biodegradable PBAT-PLA copolyester;

in step S1, the structural formula of the organoguanidine catalyst is:

wherein R is ₁ -R ₆ Is C1-C6 straight-chain alkylene, and X is glycollic acid or lactate anion.

Preferably, in step S1, the molar ratio of terephthalic acid to 1,6-adipic acid is 1.0 to 2.3; in the first esterification kettle, the molar ratio of terephthalic acid to 1,4-butanediol is 1.0-3.0; in the second esterification kettle, the molar ratio of 1,6-adipic acid to 1,4-butanediol is 1.0-3.0; the ratio of the total molar amount of terephthalic acid and 1,6-adipic acid and the molar amount of 1,4-butanediol was 1.0 to 3.0.

Further preferably, the organic guanidine catalyst is one or more of glycolic acid hexamethylguanidine, lactic acid hexamethylguanidine, glycolic acid hexaethylguanidine and lactic acid hexaethylguanidine. The concrete structure is as follows:

。

the preparation process of the hexamethylguanidine glycolate and hexamethylguanidine lactate is shown as follows:

。

hexamethyl guanidine chloride is taken as a raw material and reacts with sodium glycolate and sodium lactate respectively under the reflux condition to generate glycolic acid hexamethylguanidine and lactic acid hexamethylguanidine, and a seven-membered ring active esterified compound with a stable structure can be further formed. The same preparation method was used to prepare hexaethylguanidinium glycolate and hexaethylguanidinium lactate.

The guanidinium cation is a positively charged delocalized system with high stability and high electrophilic induction. Guanidinium cations readily associate with the carbonyl oxygen to increase the electrophilic capacity of the carbonyl carbon. The PBAT esterification reaction and the PLA ring-opening polymerization are carried out by using an organic guanidine catalyst, mainly comprising the steps of firstly forming a positive and negative ion pair compound by using an organic guanidine onium salt and a carboxylic acid compound line, obtaining a corresponding active esterified compound intermediate through intramolecular transfer, then carrying out ester exchange reaction on 1,4-Butanediol (BDO) and the active esterified compound intermediate, and rapidly promoting the polymerization reaction to prepare the PBAT resin. The reaction mechanism of hexamethyl guanidine chloride as a catalyst is shown as follows:

。

the reaction mechanism of the PLA polyol with a branched ether structure is shown as follows:

。

preferably, in step S12, at the end of the pre-polycondensation reaction, the acid values of the segments of the oligoester BHBT and the oligoester BHBA are 60-100mol/t, the weight-average molecular weight of the BHBT is 2000-8000 g/mol, and the weight-average molecular weight of the BHBA is 2000-8000 g/mol.

Preferably, in step S11, the amount of the organoguanidine catalyst in the first esterification reactor is 0.01 to 0.05 percent of the mole number of the terephthalic acid; in the second esterification kettle, the dosage of the organic guanidine catalyst is 0.01 to 0.05 percent of 1,6-adipic acid mole number; in the step S2, the dosage of the organic guanidine catalyst is 0.01 to 0.05 percent of the mole number of the lactide during the ring-opening polymerization.

Preferably, in the step S11, the esterification reaction temperature of the first esterification kettle is 140-250 ℃, the reaction time is 1-3h, and the reaction pressure is 70-100kPa; the esterification reaction temperature of the esterification kettle II is 130-240 ℃, the reaction time is 1-3h, and the reaction pressure is 70-100kPa; in the step S12, the temperature of the pre-polycondensation reaction is 200-260 ℃, the reaction pressure is 10-70kPa, and the reaction is carried out for 0.1-1.5h; in the step S2, the ring-opening polymerization reaction temperature of the lactide is 130-180 ℃, the reaction pressure is 3-10KPa, and the reaction time is 2-5h.

Preferably, in step S1, after terephthalic acid (PTA), 1,6-Adipic Acid (AA), 1,4-Butanediol (BDO) and the organoguanidine catalyst are added to the first esterification reactor and the second esterification reactor, respectively, high purity nitrogen is introduced and vacuum is applied to replace 1-2 times before esterification reaction.

Preferably, in step S2, the polyether polyol has hydroxyl group ≥ 3 and molecular weight 600-3500 g/mol.

Further preferably, in step S2, the polyether polyol is a glycerol (Gly) -based polyether, a Trimethylolpropane (TMP) -based polyether, or a Pentaerythritol (PER) -based polyether.

Preferably, in step S2, the molar ratio of the polyether polyol to the lactide is 1; the molar ratio of the molar amount of lactide to the total molar amount of terephthalic acid and 1,6-adipic acid is 1; the molecular weight of PLA polyol with a branched ether structure is controlled to be 20000-50000g/mol, and the hydroxyl value is controlled to be 30-100mgKOH/g.

Preferably, in the step S2, before the lactide is added, the polymerization kettle is communicated with high-purity nitrogen and vacuumized, and the replacement is carried out for 1 to 2 times.

Preferably, in step S3, the polycondensation reaction temperature is 180-250 ℃, the reaction pressure is 100-10000Pa, and the reaction time is 0.5-3.0h; and in the step S4, further increasing the vacuum degree to be below 100Pa for final polycondensation, reacting for 0.5-3.0h, and finishing the reaction to obtain the biodegradable PBAT-PLA copolyester.

Preferably, in step S3, before the melt which is prepolycondensation in step S1 is added, the polymerization kettle three is first introduced with high-purity nitrogen and vacuumized, and replaced 1-2 times.

Preferably, in step S4, the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, pentaerythrityl tetrakis [ β - (3,5-di-tert-butyl-4-hydroxyphenyl) propionate ], tris [ 2.4-di-tert-butylphenyl ] phosphite, and n-octadecyl β - (3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

Preferably, in step S4, the heat stabilizer is one or more of trimethyl phosphate, triethyl phosphate and triphenyl phosphate; the dosage of the heat stabilizer is 0.01-0.2% of the total weight of the raw materials, and the dosage of the antioxidant is 0.01-0.2% of the total weight of the raw materials.

Preferably, in step S4, before the melt, the heat stabilizer and the antioxidant which are copolycondensed in step S3 are added, the polymerization kettle three is first introduced with high-purity nitrogen and vacuumized, and replaced for 1-2 times.

Compared with the prior art, the invention has the following beneficial effects:

1. the organic guanidine used in the invention is a biological nontoxic organic catalyst, thereby avoiding the pollution problem of heavy metal residue caused by using traditional titanium series and tin series heavy metal catalysts in the polymerization process of PBAT and PLA. Meanwhile, the organic guanidine catalyst has the characteristics of good heat resistance, high catalytic efficiency and the like, and the addition amount is only one to five ten-thousandth of the added raw materials, so that the problem of catalyst residue is greatly reduced, and the application of the PBAT-PLA copolymer in the aspects of food and medical materials is expanded.

2. The PBAT-PLA prepared by the invention is block copolyester, the reactivity of the segments of BHBT, BHBA and PLA is improved by controlling the acid value (hydroxyl value) and the molecular weight of each segment, better reaction fusion among different segments is realized, the serious phase separation problem caused by poor compatibility among the segments is avoided, and the prepared PBAT-PLA copolyester has good rigidity and toughness balance property and comprehensive performance.

3. Polyether polyol with hydroxyl groups being more than or equal to 3 and molecular weight being 600-3500g/mol is used as an initiator, PLA polyol with a branched ether structure is prepared through ring-opening polymerization, PBAT-PLA copolyester with a branched ether structure is further prepared, the melt strength and flexibility are obviously improved, and downstream application requirements of film blowing, injection molding, foaming, double-stretching films and the like are better met.

Detailed Description

In order to facilitate understanding of the present invention, the present invention will be described below by way of examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The tests involved in the present invention are as follows:

1. melt index test

The measurement was carried out according to the method specified in GB/T3682-2000, where the test temperature was 190 ℃ and the load was 2.16kg. PBAT-PLA copolyesters have a lower Melt Index (MI) indicating greater melt strength at equivalent molecular weight sizes and distributions.

2. In the embodiment of the invention, the relative molecular mass of BHBT and BHBA is detected by Agilent 1260 gel chromatography, and a detector: 1260 MCN, column: agilent PL gel 5 μm MIXED-C (made in GB) and chloroform as mobile phase.

3. The acid value of the product is determined according to the regulations of GB/T32366-2015 biodegradable polybutylene terephthalate-adipate (PBAT) and the regulation of carboxyl end group test method A in GB/T14190-2008 test method for fiber-grade polyester chips (PET). The standard titration solution is potassium hydroxide-benzyl alcohol with the concentration of 0.01mol/L, and bromophenol blue is used as an indicator. Sample preparation: 0.5g of the sample was dissolved in a phenol-chloroform mixed solvent (2:3 by volume) and assayed according to a standard acid-base titration procedure.

4. Hydroxyl value test of branched ether structure polyol:

the hydroxyl value was measured by the phthaloylation method.

Preparing an acylating agent: 42g of phthalic anhydride was weighed out and dissolved in 300mL of dried pyridine, and after complete dissolution, the solution was stored in a brown bottle and placed in a desiccator for further use.

6g of imidazole are weighed out and added to the prepared acylating agent.

And (3) analysis program: accurately weighing a certain amount of sample on an analytical balance, placing the sample in an acylation bottle with a ground and a reflux condenser, accurately adding 25mL of acylating agent by a pipette, dissolving the sample, placing the dissolved sample in a constant-temperature water bath, and carrying out acylation reaction for 20-25min; after leaving the water bath, it was cooled to room temperature and then added finely to a condenser tube at its upper end along port wall at a ratio of 20mL 1:1, hydrolyzing residual anhydride, shaking uniformly, adding 3-5 drops of phenolphthalein indicator, titrating to pink by using 0.8mol/L or 1mol/L KOH standard solution, and performing a blank test by using the same method when 15s does not change. The hydroxyl value is calculated as follows, and the allowable error is less than 0.5 mg KOH/g;

5. and (3) testing the color of the product: adopting Alice X-Rite Ci7600 model, testing conditions are as follows: measuring in a reflection mode with an aperture of 25 mm; the color plate specification was 80 × 50 × 3mm.

6. Testing the thermal stability of the product: the cut PBAT particles were dried under vacuum at 85 ℃ for 6h, and PBAT thermogravimetric analysis was performed using Discovery TGA 55. And (3) testing conditions are as follows: weighing 8-10mg of sample in air atmosphere at 50-600 deg.C and heating rate of 10 deg.C/min. Using the temperature (T) at which weight loss is 5% by mass _5% ) To characterize the thermal stability properties of the PBAT resin.

7. Compatibility testing of the product: vacuum drying the cut PBAT particles at 85 ℃ for 6h, and performing glass transition temperature (T) of PBAT-PLA copolyester by using Discovery DSC250 _g ) And (6) analyzing. And (3) testing conditions are as follows: weighing 8-10mg of sample in nitrogen atmosphere at 50-200 deg.C and heating rate of 10 deg.C/min. With different glass transition temperatures (T) _g ) To characterize the compatibility of the PBAT-PLA copolyester.

8. Tensile strength test, specimen preparation: injection molding samples were carried out as specified in GB/T17037.1-1997, and type IA samples according to GB/T1040.2-2006 were prepared using the type A die of GB/T17037.1-1997. Suitable holding pressures were used during injection molding to obtain test specimens free of defects.

Particle material pretreatment: before forming the sample, the pellets are preheated and dried in an air-blast drying oven, the thickness of the pellets in a tray is less than 4cm, and the pellets are continuously dried for 5 hours at 80 ℃. The dried pellets were used immediately to prevent moisture absorption.

Sample preparation conditions: adopting FANUC ROBOSHOT alpha-S100 iA Japan Sonaceae full-electric injection molding machine, screw injection machine process:

conditioning of the samples and standard environment of the test: the conditioning of the samples was carried out as specified in GB/T2918-1998 under conditions of 23 ℃ C. + -. 2 ℃ C and conditioning time 40h. The test was carried out in a standard environment as specified in GB/T2918-1998 at a temperature of 23 ℃ C. + -. 2 ℃ and a relative humidity of 50%. + -. 10%.

And (3) testing conditions are as follows: the test is carried out according to the GB/T1040.2-2006 specification, and the test speed is 50mm/min.

Example 1

The feed rates of the materials in example 1 are shown in table 1:

table 1 example 1 feed meter

S1, esterification-pre-polycondensation:

adding weighed 1661.7g terephthalic acid (w/% > 99.90%), 994.3g 1, 4-butanediol (w/% > 99.70%) and 0.55g glycollic hexamethylguanidine into a 10L esterification kettle I, starting heating, stirring uniformly, gradually raising the temperature to 240 ℃, carrying out esterification dehydration reaction under the reaction pressure of 70KPa for 2h, and distilling off anhydrous when the water yield of the reaction reaches 360.0g of theoretical value. Then, the reaction pressure is gradually reduced to 10KPa, pre-polycondensation is carried out, the reaction is carried out for 1h, and samples are taken for molecular weight and acid value detection. After the molecular weight and the acid value reach the target, reducing the temperature to 180 ℃ to evaporate redundant 1,4-butanediol, and transferring the BHBT oligomer to a third polymerization kettle.

Adding 1789.4g 1, 6-adipic acid (w/% > 99.80%), 1213.0g 1, 4-butanediol (w/% > 99.70%) and 0.67g glycolylhexamethylguanidine into a 10L esterification kettle II, starting heating, stirring uniformly, gradually heating to 200 ℃, reacting at 70KPa for esterification dehydration reaction for 2h, and distilling off no water when the water yield of the reaction reaches 439.9 g. Then the reaction pressure is gradually reduced to 10KPa, pre-polycondensation is carried out, the reaction is carried out for 0.5h, and samples are taken for molecular weight and acid value detection. After the molecular weight and acid value reach the target, the temperature is reduced to 180 ℃, redundant 1,4-butanediol is evaporated, and BHBA oligomer is transferred to a third polymerization kettle.

S2, preparing PLA trihydric alcohol with a branched ether structure: adding weighed 802.16g of lactide (w/% > or more than 99.90%), 79.43g of glycerol polyoxypropylene triol (average molecular weight of 3000g/mol and hydroxyl value of 56 mgKOH/g) and 0.30g of glycolic acid hexamethylguanidine into a 20L polymerization kettle III, vacuumizing, replacing with nitrogen for 3 times, starting heating, uniformly stirring, carrying out ring-opening polymerization, gradually heating to 180 ℃, reacting for 3 hours under 5000Pa, and sampling for detecting the molecular weight and the hydroxyl value.

S3, copolycondensation: adding the reacted BHBT and BHBA into a 20L polymerization kettle III, copolymerizing with the branched ether structured PLA trihydric alcohol, gradually heating the reaction to 240 ℃, and reacting for 2 hours under the reaction pressure of 5000 Pa.

S4, final polycondensation: and (3) adding 0.63g of triphenyl phosphate and 0.63g of 2, 6-di-tert-butyl-4-methylphenol into the third polymerization kettle, reacting at 240 ℃, gradually reducing the reaction pressure to 80Pa, and reacting for 1.5h to finish the reaction.

Examples 2 to 4

The amounts of the materials used in examples 2-4 are shown in tables 2-4, and examples 2-4 were carried out using different organoguanidine catalysts, the reaction procedure being identical to that of example 1.

Table 2 example 2 feed table

Table 3 example 3 feed table

Table 4 example 4 feed table

Examples 5 to 8

The charge amounts of the respective materials of examples 5 to 8 are shown in tables 5 to 8, and the reaction procedure was in accordance with example 1, wherein trimethylolpropane polyoxypropylene triol having an average molecular weight of 3000g/mol and a hydroxyl value of 58 mgKOH/g; the average molecular weight of pentaerythritol polyoxypropylene tetraol is 600 g/mol, and the hydroxyl value is 374 mgKOH/g; examples 6 and 8 used lactic acid hexamethylguanidine catalyst.

Table 5 example 5 feed table

Table 6 example 6 feed table

Table 7 example 7 feed table

Table 8 example 8 feed meter

Example 9

The amounts of the respective materials charged in examples 9 and 10 are shown in tables 9 and 10, but the reaction procedure in examples 9 and 10 was carried out using a glycolic acid hexamethylguanidine organic catalyst, and the same procedure as in example 1 was followed, wherein the charge amount ratios of PTA, AA, BDO and lactide were different from those in examples 1 to 8, and the charge amount ratios of the catalyst, the heat stabilizer and the antioxidant were adjusted accordingly. In addition, the reaction conditions in the polycondensation stage were also changed.

Table 9 example 9 feed table

S1, esterification-pre-polycondensation:

adding weighed 1663.0g terephthalic acid (w/% > 99.90%), 1807.8g 1, 4-butanediol (w/% > 99.70%) and 0.22g glycollic hexamethylguanidine into a 10L esterification kettle I, starting heating, stirring uniformly, gradually raising the temperature to 140 ℃, carrying out esterification dehydration reaction under the reaction pressure of 80KPa for 1h, and distilling off anhydrous when the water yield of the reaction reaches the theoretical value of 360.0 g. Then, the reaction pressure was gradually reduced to 40KPa, pre-polycondensation was conducted, the reaction was conducted for 0.1 hour, and samples were taken for molecular weight and acid value measurement. After the molecular weight and the acid value reach the target, reducing the temperature to 180 ℃ to evaporate redundant 1,4-butanediol, and transferring the BHBT oligomer to a third polymerization kettle.

Adding 1464.3g of 1, 6-adipic acid (w/% > 99.80%), 1807.8g of 1, 4-butanediol (w/% > 99.70%) and 0.22g of glycolic acid hexamethylguanidine into a 10L esterification kettle II, starting heating, uniformly stirring, gradually heating to 130 ℃, reacting at a pressure of 80KPa, carrying out esterification dehydration reaction for 1h, and distilling off anhydrous when the water yield of the reaction reaches a theoretical value of 360.0 g. Then the reaction pressure is gradually reduced to 40KPa, pre-polycondensation is carried out, the reaction is carried out for 0.1h, and samples are taken for molecular weight and acid value detection. After the molecular weight and the acid value reach the target, the temperature is reduced to 180 ℃, redundant 1,4-butanediol is distilled out, and the BHBA oligomer is transferred to a third polymerization kettle.

S2, preparing PLA trihydric alcohol with a branched ether structure: adding weighed 720.7g lactide (w/% > 99.90%), 500g glycerol polyoxypropylene triol (average molecular weight is 3000g/mol, hydroxyl value is 56 mgKOH/g) and 0.11g glycollic hexamethylguanidine into a 20L polymeric kettle III, vacuumizing, replacing with nitrogen for 3 times, starting heating, uniformly stirring, carrying out ring-opening polymerization, gradually heating to 130 ℃, reacting for 2 hours under 3000Pa, and sampling for detecting molecular weight and hydroxyl value.

S3, copolycondensation: adding the reacted BHBT and BHBA into a 20L polymerization kettle III, copolymerizing with the branched ether structured PLA trihydric alcohol, gradually heating the reaction to 180 ℃, and reacting at the reaction pressure of 100Pa for 0.5h.

S4, final polycondensation: and (3) adding 0.75g of triphenyl phosphate and 0.75g of 2, 6-di-tert-butyl-4-methylphenol into the third polymerization kettle, reacting at 240 ℃, gradually reducing the reaction pressure to 80Pa, and reacting for 0.5h to finish the reaction.

Example 10

Table 10 example 10 feed table

S1, esterification-pre-polycondensation:

adding weighed 1663.0g terephthalic acid (w/% > 99.90%), 2711.7g 1, 4-butanediol (w/% > 99.70%) and 1.10g glycollic hexamethylguanidine into a 10L esterification kettle I, starting heating, stirring uniformly, gradually raising the temperature to 250 ℃, carrying out esterification dehydration reaction under the reaction pressure of 100KPa for 3h, and distilling off anhydrous when the water yield of the reaction reaches 360.0g of theoretical value. Then, the reaction pressure was gradually reduced to 70KPa, pre-polycondensation was conducted, the reaction was carried out for 1.5 hours, and samples were taken for molecular weight and acid value measurement. After the molecular weight and the acid value reach the target, the temperature is reduced to 180 ℃, redundant 1,4-butanediol is evaporated, and the BHBT oligomer is transferred to a third polymerization kettle.

Adding weighed 3367.9g of 1, 6-adipic acid (w/% > 99.80%), 6236.9g of 1, 4-butanediol (w/% > 99.70%) and 2.53g of glycolylhexamethylguanidine into a 10L esterification kettle II, starting heating, uniformly stirring, gradually raising the temperature to 240 ℃, carrying out esterification dehydration reaction under the reaction pressure of 100KPa, reacting for 3h, and distilling off no water when the water yield of the reaction reaches 828.0 g. Then the reaction pressure is gradually reduced to 70KPa, pre-polycondensation is carried out, the reaction is carried out for 1.5h, and samples are taken for molecular weight and acid value detection. After the molecular weight and the acid value reach the target, the temperature is reduced to 180 ℃, redundant 1,4-butanediol is distilled out, and the BHBA oligomer is transferred to a third polymerization kettle.

S2, preparing PLA trihydric alcohol with a branched ether structure: adding 1189.16g weighed lactide (w/% > 99.90%), 82.5g glycerol polyoxypropylene triol (average molecular weight of 3000g/mol, hydroxyl value of 56 mgKOH/g) and 0.91g glycolic acid hexamethylguanidine into a 20L polymeric kettle III, vacuumizing, replacing with nitrogen for 3 times, starting heating, stirring uniformly, performing ring-opening polymerization, gradually heating to 150 ℃, reacting for 5 hours under 3000Pa, and sampling for detecting the molecular weight and the hydroxyl value.

S3, copolycondensation: adding the reacted BHBT and BHBA into a 20L polymerization kettle III, copolymerizing with the branched ether structured PLA trihydric alcohol, gradually heating the reaction to 250 ℃, and reacting at 10000Pa for 3 hours.

S4, final polycondensation: and (3) adding 3.06g of triphenyl phosphate and 3.06g of 2, 6-di-tert-butyl-4-methylphenol into the third polymerization kettle, reacting at 240 ℃, gradually reducing the reaction pressure to 80Pa, and reacting for 3 hours to finish the reaction.

Comparative example 1

The feeding amount of each material in comparative example 1 is shown in table 11, tetrabutyl titanate and stannous octoate are used as catalysts, and the reaction steps are consistent with those of example 1:

table 11 comparative example 1 feed table

Comparative example 2

The feed rates of the materials in comparative example 2 are shown in Table 12. In the reaction process, the acid value of BHBT and BHBA chain segments is controlled to be more than or equal to 120 mol/t, and the hydroxyl value of PLA trihydric alcohol with a branched ether structure is controlled to be more than or equal to 50 mgKOH/g.

Table 12 comparative example 2 feed table

Comparative example 3

The feed rates of the materials in comparative example 3 are shown in Table 13. In the reaction process, the acid value of BHBT and BHBA chain segments is controlled to be less than 60 mol/t, and the hydroxyl value of PLA trihydric alcohol with a branched ether structure is not less than 50 mgKOH/g.

Table 13 comparative example 3 feed table

Comparative example 4

The feed rates of the materials in comparative example 4 are shown in Table 14. Polytetramethylene ether glycol (PTMEG) (molecular weight is 3000g/mol, hydroxyl value is 37 mgKOH/g) is used as an initiator to prepare PLA dihydric alcohol with a linear chain ether structure; in the reaction process, the acid values of the chain segments of BHBT and BHBA are controlled to be between 60 and 100mol/t, and the hydroxyl value of the PLA trihydric alcohol with the branched ether structure is controlled to be between 30 and 50 mgKOH/g.

Table 14 comparative example 4 feed table

Comparative example 5

The feed rates of the materials of comparative example 5 are shown in Table 18. Preparing PLA triol with a branched ether chain structure by using glycerol polyoxypropylene triol (the molecular weight is 500g/mol, and the hydroxyl value is 380 mgKOH/g) as an initiator; in the reaction process, the acid values of the chain segments of BHBT and BHBA are controlled to be between 60 and 100mol/t, and the hydroxyl value of the PLA trihydric alcohol with the branched ether structure is controlled to be between 30 and 100mgKOH/g.

Table 18 comparative example 5 feed table

Comparative example 6

The feed rates of the materials in comparative example 6 are shown in Table 16. Preparing PLA triol with a branched ether chain structure by using glycerol polyoxypropylene triol (the molecular weight is 5000g/mol, and the hydroxyl value is 32 mgKOH/g) as an initiator; in the reaction process, the acid values of the chain segments of BHBT and BHBA are controlled to be between 60 and 100mol/t, and the hydroxyl value of the PLA trihydric alcohol with the branched ether structure is controlled to be between 30 and 50 mgKOH/g.

TABLE 16 comparative example 6 feeding table

The acid value, tensile strength, elongation at break, appearance color and thermal stability of examples 1 to 10 and comparative examples 1 to 6 were measured as follows, and the results of the measurements are shown in tables 17 and 18:

TABLE 17 segmented molecular weights, acid values, etc. of the products of examples 1 to 10 and comparative examples 1 to 6

TABLE 18 melt index, acid number, color, mechanical properties, etc. of the products of examples 1 to 10 and comparative examples 1 to 6

From the test data of the PBAT-PLA copolyester in tables 17 and 18, it can be seen that the catalytic effect of each catalyst in examples 1-4 is that glycolic acid hexamethylguanidine > lactic acid hexamethylguanidine > > glycolic acid hexaethylguanidine > hexaethylguanidine under the same process conditions, the same catalyst addition amount and the condition of using glycerol polyoxypropylene triol as the lactide ring-opening polymerization initiator, and the PBAT-PLA copolyester prepared by using glycolic acid hexamethylguanidine and lactic acid hexamethylguanidine in examples 1-2 as the catalyst has better acid value, appearance color, tensile strength and thermal stability. This is because the steric hindrance of the ethyl group in hexaethylguanidine is significantly greater than that of the methyl group, and the combination of the chain segment and hexaethylguanidine catalyst is more difficult and the catalytic effect is relatively poor when esterification and polycondensation occur, so that the performance of the PBAT-PLA copolyester is significantly poor.

In the following examples 5-8, trimethylolpropane (TMP) and Pentaerythritol (PER) -based polyether polyols were used as lactide ring-opening polymerization initiators to prepare PLA triols and tetraols having branched ether structures, respectively, in the same catalytic amounts of hexamethylguanidine glycolate and hexamethylguanidine lactate as catalysts, and the influence of the Trimethylolpropane (TMP) and the Pentaerythritol (PER) -based polyether polyols on the properties of PBAT-PLA copolyester was examined. Under the condition of small molecular weight difference, the melt strength of pentaerythritol (hydroxyl is 4) branched structure (the melt index of example 7 is 1.2, the melt index of example 8 is 2.2) is obviously higher than that of glycerin and trimethylolpropane (hydroxyl is 3) (the melt index of example 5 is 3.9, the melt index of example 6 is 4.3), and the PBAT-PLA copolyester is more beneficial to the application in the fields of foaming and biaxial stretching films. Meanwhile, the elongation at break of the PBAT-PLA copolyester is reduced under the same condition due to the small molecular weight and high branching degree (4 branched chains) of the Pentaerythritol (PER) based polyoxypropylene tetraol.

In the comparative example 1, a titanate catalyst and stannous octoate are used as reaction catalysts, and the titanium catalyst is easy to hydrolyze in the esterification stage and cannot fully exert the catalytic effect, so that the esterification reaction is incomplete (the water yield does not reach the theoretical value), and the acid value, the color and the mechanical property of the PBAT-PLA copolyester are poor; meanwhile, the heavy metal titanium catalyst and the heavy metal tin catalyst are added, so that the problem of heavy metal residue is caused.

As can be seen in the comparison of examples 1-10, comparative example 2 and comparative example 3, by controlling the molecular weight and acid value (60-100 mol/t) of the BHBT and BHBA segments, the PBAT-PLA copolyester has excellent acid value, color, melt strength and mechanical properties while maintaining good compatibility of the BHBT, BHBA and the branched ether structure PLA polyol segments. When the molecular weight of the chain segment is smaller or the acid value is too large (more than or equal to 120 mol/t), as in comparative example 2, the acid value of the product is increased and the mechanical property is greatly reduced; when the molecular weight of the segment is large or the acid value is too small (60 mol/t or less), as in comparative example 3, the phase separation phenomenon (having two Tg's) occurs in the product due to poor compatibility between the molecular segments, so that the mechanical properties are also remarkably reduced.

In comparative example 4, in which polytetramethylene ether glycol (PTMEG, molecular weight 3000g/mol, hydroxyl value 37 mgKOH/g) was used to prepare PLA diol having a linear ether structure, it can be seen that the melt strength (melt index of 9.8) was significantly lower than that of example 1 (melt index of 4.2) due to the absence of a branched structure in the molecular chain at the same molecular weight; other aspects such as color and mechanical property are not very different, and the acid value is higher.

In example 1, comparative example 5 and comparative example 6, when glycerol propylene oxide triol (3000, 500 and 5000 g/mol) with different molecular weights is used as an initiator to prepare PLA triol with a branched ether structure, the elongation at break of the prepared PBAT-PLA copolyester shows obvious difference, the larger the molecular weight of the polyether triol is, the better the elongation at break (flexibility) is, however, the smaller or the larger the molecular weight of the polyether triol is, the mechanical property of the PBAT-PLA copolyester is obviously reduced.

Claims

1. The method for synthesizing biodegradable PBAT-PLA copolyester under the catalysis of organic guanidine is characterized by comprising the following steps:

s1, esterification-pre-polycondensation:

s11, esterification: adding terephthalic acid, 1,4-butanediol and an organic guanidine catalyst into a first esterification kettle to perform esterification reaction until the water yield of the reaction reaches a theoretical value; adding 1,6-adipic acid, 1,4-butanediol and an organic guanidine catalyst into a second esterification kettle to perform esterification reaction until the water yield of the reaction reaches a theoretical value;

s12, pre-polycondensation: after the esterification reaction of the esterification kettle I and the esterification kettle II is finished, further improving the vacuum degree, carrying out pre-polycondensation, reducing the temperature in the kettle to below 180 ℃ after the chain segment acid value and the molecular weight of the oligomer BHBT of the esterification kettle I and the oligomer BHBA of the esterification kettle II respectively reach target values, further steaming out redundant 1,4-butanediol, and then transferring to a polymerization kettle III;

s3, copolycondensation: transferring the reacted BHBA and BHBT into a third polymerization kettle, heating to a specified temperature, starting vacuum, and performing copolycondensation with the branched ether structure PLA polyhydric alcohol;

in step S1, the structural formula of the organoguanidine catalyst is:

wherein R is ₁ -R ₆ Is a C1-C6 linear alkylene group, and X is glycollic acid or lactate anion.

2. The method for catalytic synthesis of biodegradable PBAT-PLA copolyester by organic guanidine according to claim 1, characterized in that in step S1, the molar ratio of terephthalic acid to 1,6-adipic acid is 1.0-2.3; in the first esterification kettle, the molar ratio of terephthalic acid to 1,4-butanediol is 1.0-3.0; in the second esterification kettle, the molar ratio of 1,6-adipic acid to 1,4-butanediol is 1.0-3.0; the total molar amount of terephthalic acid and 1,6-adipic acid and the molar amount of 1,4-butanediol ratio is 1.0 to 3.0.

3. The method for synthesizing biodegradable PBAT-PLA copolyester under the catalysis of organic guanidine as claimed in claim 1, wherein in step S12, at the end of the pre-polycondensation reaction, the acid value of the chain segment of the oligomeric esterified compound BHBT and the oligomeric esterified compound BHBA is 60-100mol/t, the weight average molecular weight of BHBT is 2000-8000 g/mol, and the weight average molecular weight of BHBA is 2000-8000 g/mol.

4. The method for synthesizing biodegradable PBAT-PLA copolyester by using organic guanidine as catalyst in claim 1, wherein in step S11, the amount of the organic guanidine catalyst in the first esterification reactor is 0.01-0.05% of the mole number of terephthalic acid; in the second esterification kettle, the dosage of the organic guanidine catalyst is 0.01 to 0.05 percent of 1,6-adipic acid mole number; in the step S2, the dosage of the organic guanidine catalyst is 0.01 to 0.05 percent of the mole number of the lactide during the ring-opening polymerization.

5. The method for synthesizing biodegradable PBAT-PLA copolyester under the catalysis of organic guanidine according to claim 1, wherein in the step S11, the esterification reaction temperature of the first esterification kettle is 140-250 ℃, the reaction time is 1-3h, and the reaction pressure is 70-100kPa; the esterification reaction temperature of the esterification kettle II is 130-240 ℃, the reaction time is 1-3h, and the reaction pressure is 70-100kPa; in the step S12, the temperature of the pre-polycondensation reaction is 200-260 ℃, the reaction pressure is 10-70kPa, and the reaction is carried out for 0.1-1.5h; in the step S2, the ring-opening polymerization reaction temperature of the lactide is 130-180 ℃, the reaction pressure is 3-10KPa, and the reaction time is 2-5h.

6. The method for catalytic synthesis of biodegradable PBAT-PLA copolyester by organic guanidine according to claim 1, wherein in step S2, the hydroxyl group of polyether polyol is not less than 3, and the molecular weight is 600-3500 g/mol.

7. The method for the catalytic synthesis of biodegradable PBAT-PLA copolyester with organic guanidine according to claim 1, wherein in step S2, the molar ratio of polyether polyol to lactide is 1; the molar ratio of the molar amount of lactide to the total molar amount of terephthalic acid and 1,6-adipic acid is 1; the molecular weight of PLA polyol with a branched ether structure is controlled to be 20000-50000g/mol, and the hydroxyl value is controlled to be 30-100mgKOH/g.

8. The method for synthesizing biodegradable PBAT-PLA copolyester catalyzed by organic guanidine according to claim 1, wherein in the step S3, the polycondensation reaction temperature is 180-250 ℃, the reaction pressure is 100-10000Pa, and the reaction time is 0.5-3.0h; in step S4, further reducing the reaction pressure to be less than 100Pa to improve the vacuum degree for final polycondensation, reacting for 0.5-3.0h, and finishing the reaction to obtain the biodegradable PBAT-PLA copolyester.

9. The method of organoguanidine-catalyzed synthesis of biodegradable PBAT-PLA copolyester of claim 1, wherein in step S4 the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, pentaerythrityl tetrakis [ β - (3,5-di-tert-butyl-4-hydroxyphenyl) propionate ], tris [ 2.4-di-tert-butylphenyl ] phosphite, and n-octadecyl β - (3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

10. The method for organoguanidine-catalyzed synthesis of biodegradable PBAT-PLA copolyester of claim 1, wherein in step S4, the thermal stabilizer is one or more of trimethyl phosphate, triethyl phosphate, and triphenyl phosphate; the dosage of the heat stabilizer is 0.01-0.2% of the total raw material weight, and the dosage of the antioxidant is 0.01-0.2% of the total raw material weight.