CN115651174B - Method for synthesizing biodegradable PBAT-PLA copolyester by organic guanidine catalysis - Google Patents

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, and 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, so that the biodegradable PBAT-PLA copolyester with good chain segment compatibility, melt strength and flexibility is synthesized, 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

Organic guanidine catalyzed method for synthesizing biodegradable PBAT-PLA copolyester

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 technique

With the increasing white pollution, biodegradable polyester has become one of the most effective solutions to the problem of plastic pollution, which can be degraded into environmentally harmless carbon dioxide and water under composting conditions or natural conditions. Among biodegradable polyesters, polybutylene terephthalate-adipate (PBAT) and polylactic acid (PLA) are currently the two most productive and widely used varieties on the market. PBAT is a copolymer of butylene terephthalate (PBT) and butylene adipate (PBA). It has both rigid and flexible segments in its structure, and has high ductility and elongation at break. However, The strength and stiffness of PBAT are low, which leads to easy bonding during film blowing, soft film products and easy rupture during use. PLA has the advantages of high strength, high hardness, transparency, and good processability. However, PLA has disadvantages such as low elongation at break, poor impact strength, and poor toughness, which make it difficult to meet some practical requirements and limit its application. In practical applications, PBAT and PLA are usually directly blended to form PBAT-PLA blends with complementary properties. However, the compatibility between PBAT and PLA is poor, and the performance of the blended product is unstable. Aiming at the problem of blending, isocyanate chain extenders are commonly used for chain extension reaction to solve the problem of poor blending compatibility, but the chain extension reaction has the problem of the toxicity of the chain extender or the wide molecular weight distribution of the product after chain extension, which has adverse effects on the product. Impact. Therefore, researching and developing a kind of PBAT-PLA copolymer and preparation method is the new subject urgently waiting to be solved always.

At present, some patents have been explored in this direction, such as patent CN 107141458A, which uses prepolymer PBAT and prepolymer PLA, puts them into a high-vacuum reactor, controls the vacuum degree, and finally obtains a compound with a weight average molecular weight of 100,000-250,000. PBAT-PLA copolyester.

Patent CN107163232A discloses a method for ring-opening polymerization of PBAT-PLA block copolymers. Aliphatic diols are put into a reactor with prepolymer PBAT to prepare PBAT with hydroxyl groups at both ends; the two PBAT and lactide with hydroxyl groups at the end are put into the reaction kettle, and after the materials in the kettle are completely melted, a catalyst is added to react to obtain a PBAT-PLA block copolymer.

Patent CN 113968961 A discloses a polyterephthalic acid-co-butylene succinate-polylactic acid copolymer and its preparation method, polyterephthalic acid-co-butylene succinate-polylactic acid The copolymer is prepared by ring-opening polycondensation of L-lactide and polybutylene terephthalate-co-succinate under the action of tin chloride catalyst.

The above-mentioned patent adopts the copolymerization method of PBAT and PLA, which fully combines the flexibility of the PBAT segment and the rigidity of the PLA segment to form a rigid and flexible PBAT-PLA copolymer, which can better meet the downstream application requirements such as blown film and injection molding. In the above patents, heavy metal catalysts such as tetrabutyl titanate and tin dichloride hydrate are used in the polymerization of PBAT and PLA, which will pollute the product and affect the use of the product in the fields of food and medicine. Secondly, the above patents do not mention how to solve the problem of serious phase separation caused by the poor compatibility between the PBAT chain segment and the PLA chain segment. Finally, the melt strength and flexibility of ordinary PBAT-PLA copolyesters are still insufficient in some downstream applications such as foaming and bi-stretched films.

Contents of the invention

The purpose of the invention is to solve the problems of heavy metal catalyst pollution products, serious phase separation between chain segments, insufficient melt strength and flexibility in PBAT-PLA copolyester. By using organic guanidine catalysts, controlling the acid value (hydroxyl value) and molecular weight of each segment during the polymerization process, and using polyether polyols with a hydroxyl group ≥ 3 and a molecular weight of 600-3500 g/mol to replace the commonly used 1,4-butane Diol (BDO) triggers lactide to synthesize biodegradable PBAT-PLA copolyester with good segment compatibility, melt strength and flexibility, which broadens its application range in food, medicine, agriculture and other fields, and more It can meet the needs of downstream applications such as blown film, injection molding, foaming, and double-stretched film.

The present invention aims at the residual problem of heavy metal titanium series and tin series catalysts. In the preparation process of PBAT-PLA copolyester, it adopts the method with good thermal stability and high catalytic efficiency (the addition amount is only one ten-thousandth to 1/10000 of the added raw material monomers). 5/10,000), non-toxic organic guanidine catalysts (avoiding the introduction of heavy metal catalysts) may well be a good solution. The invention adopts the organic guanidine catalyst to synthesize the biodegradable PBAT-PLA copolyester with good chain segment compatibility, melt strength and flexibility. First of all, organoguanidine catalysts have the characteristics of high heat resistance, large bulk volume, highly delocalized positive charge, and high electrophilic induction ability. ), and PLA's polymerization raw material - lactide has a strong positive and negative charge coordination ability, and the activated esterified intermediate is first formed. Then 1,4-butanediol (BDO) undergoes transesterification reaction with the active esterified intermediate to rapidly promote the polymerization reaction to obtain an active polymer with controlled molecular weight, and then obtain polymer materials such as degradable block polyester .

Aiming at the serious phase separation problem caused by the poor compatibility of PBAT chain segment and PLA chain segment, by controlling the acid value (hydroxyl value) and molecular weight of each chain segment during the polymerization process, the reactivity of BHBT, BHBA and PLA chain segments is improved, and different chains are realized. Better responsive fusion between segments. Aiming at the problem that the melt strength and flexibility of ordinary PBAT-PLA copolyester are still insufficient, polyether polyols with a hydroxyl group ≥ 3 and a molecular weight of 600-3500 g/mol are used instead of the commonly used 1,4-butanediol (BDO) triggers lactide to prepare PLA polyols with branched ether chain structure. While improving the melt strength of PBAT-PLA copolyester, it also improves flexibility and solves the problem of foaming of PBAT-PLA copolyester. , Double stretched film and other downstream applications.

Concrete technical scheme of the present invention is:

The method for organic guanidine catalyzed synthesis of biodegradable PBAT-PLA copolyester comprises the following steps:

S1 esterification-precondensation:

S11 Esterification: Add terephthalic acid (PTA), 1,4-butanediol (BDO) and organic guanidine catalyst into esterification kettle 1 to carry out esterification reaction until the water output of the reaction reaches the theoretical value; Add 1,6-adipic acid (AA), 1,4-butanediol (BDO) and an organic guanidine catalyst to the second tank for esterification until the water yield of the reaction reaches the theoretical value;

S12 Pre-condensation: After the esterification reaction of esterification kettle 1 and esterification kettle 2 is completed, the vacuum degree is further increased to carry out pre-condensation, and the oligomerization of terephthalic acid and 1,4-butanediol in esterification kettle 1 After the segment acid value and molecular weight of the esterification product BHBT and the oligoesterification product BHBA of 1,6-adipic acid and 1,4-butanediol in the second esterification tank reach the target values, reduce the temperature in the tank to 180°C Next, further distill off excess 1,4-butanediol (BDO), and then transfer to polymerization tank three;

S2 Synthesis of PLA polyol with branched ether structure: add lactide, organic guanidine catalyst and initiator polyether polyol into polymerization kettle three, heat up to the target temperature, vacuumize and carry out ring-opening polymerization until the branched ether The molecular weight and hydroxyl value of structural PLA polyol reach the target value;

S3 co-polycondensation: transfer the completed BHBA and BHBT into the polymerization tank 3, raise the temperature to the specified temperature, turn on the vacuum, and co-condense with PLA polyols with branched ether structure;

S4 final polycondensation: add heat stabilizer and antioxidant to polymerization kettle three, vacuumize, carry out polycondensation reaction, then further increase the vacuum degree to carry out final polycondensation, and obtain biodegradable PBAT-PLA copolyester;

In step S1, the structural formula of the organic guanidine catalyst is:

Wherein, R ₁ -R ₆ are linear C1-C6 alkylene groups, and X is glycolic acid or lactate anion.

Preferably, in step S1, the molar ratio of terephthalic acid to 1,6-adipic acid is 1:1.0-2.3; The molar ratio is 1:1.0-3.0; in the second esterification tank, the molar ratio of 1,6-hexanedioic acid to 1,4-butanediol is 1:1.0-3.0; terephthalic acid and 1,6-hexanediol The molar ratio of the total molar weight of diacid to 1,4-butanediol is 1:1.0-3.0.

Further preferably, the organic guanidine catalyst is one or more of hexamethylguanidine glycolate, hexamethylguanidine lactate, hexaethylguanidine glycolate, and hexaethylguanidine lactate. The specific structure is as follows:

。

.

Taking hexamethylguanidine glycolate and hexamethylguanidine lactate as examples, the preparation process is as follows:

。

.

Using hexamethylguanidine chloride as raw material, react with sodium glycolate and sodium lactate under reflux conditions to generate hexamethylguanidine glycolate and hexamethylguanidine lactate, which can further form a seven-membered ring active ester with a stable structure . Using the same preparation method, hexaethylguanidine glycolate and hexaethylguanidine lactate were prepared.

The guanidinium cation is a positively delocalized system with high stability and high electrophile-inducing ability. The guanidinium cation easily associates with the carbonyl oxygen to enhance the electrophilic ability of the carbonyl carbon. Using organic guanidine catalysts for PBAT esterification and PLA ring-opening polymerization, mainly organic guanidinium salts first form positive and negative ion pairs with carboxylic acid compound lines, and obtain corresponding active ester intermediates through intramolecular transfer, and then 1, 4-Butanediol (BDO) undergoes transesterification reaction with the active esterified intermediate to rapidly promote the polymerization reaction to prepare PBAT resin. With hexamethylguanidine chloride as catalyst, its reaction mechanism is as follows:

。

.

The reaction mechanism of PLA polyol with branched ether structure is as follows:

。

.

Preferably, in step S12, when the precondensation reaction ends, the segmental acid value of the oligoester compound BHBT and the oligoester compound BHBA is 60-100 mol/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. The average molecular weight is 2000-8000g/mol.

Preferably, in step S11, in the first esterification kettle, the amount of the organic guanidine catalyst is 0.01-0.05% of the moles of terephthalic acid; in the second esterification kettle, the amount of the organic guanidine catalyst is 1,6-adipic acid 0.01-0.05% of the number of moles; in step S2, during the ring-opening polymerization, the amount of the organic guanidine catalyst used is 0.01-0.05% of the number of moles of lactide.

Preferably, in step S11, the esterification reaction temperature of esterification kettle 1 is 140-250°C, the reaction time is 1-3h, and the reaction pressure is 70-100kPa; the esterification reaction temperature of esterification kettle 2 is 130-240°C , the reaction time is 1-3h, and the reaction pressure is 70-100kPa; in step S12, the precondensation reaction temperature is 200-260°C, the reaction pressure is 10-70kPa, and the reaction is 0.1-1.5h; in step S2, lactide ring-opening The polymerization reaction temperature is 130-180°C, the reaction pressure is 3-10KPa, and the reaction time is 2-5h.

Preferably, in step S1, terephthalic acid (PTA), 1,6-adipic acid (AA), 1,4-butanediol (BDO) and organic guanidine catalysts are added to esterification tank 1 and esterification After the second kettle, before carrying out the esterification reaction, pass high-purity nitrogen and vacuumize, and replace 1-2 times.

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

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

Preferably, in step S2, the molar ratio of polyether polyol to lactide is 1:30.0-300.0; the molar weight of lactide and the total molar weight of terephthalic acid and 1,6-adipic acid The molar ratio of the PLA polyol is 1:0.1-10.0; the molecular weight of the controlled branched ether structure PLA polyol is 20000-50000g/mol, and the hydroxyl value is 30-100mgKOH/g.

Preferably, in step S2, before the lactide is added, the polymerizer is three-passed with high-purity nitrogen and vacuumized, and replaced 1-2 times.

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

Preferably, in step S3, before the pre-condensed melt in step S1 is added, the polymerization tank three is first vented with high-purity nitrogen and vacuumized, and replaced 1-2 times.

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

Preferably, in step S4, the heat stabilizer is one or more of trimethyl phosphate, triethyl phosphate and triphenyl phosphate; the amount of heat stabilizer is 0.01-0.2% of the total raw material weight, anti The dosage of the oxidizing agent is 0.01-0.2% of the total raw material weight.

Preferably, in step S4, before adding the co-polycondensed melt, heat stabilizer and antioxidant in step S3, the polymerization tank three is first passed with high-purity nitrogen and vacuumized, and replaced 1-2 times.

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

1. The organic guanidine used in the present invention is a biological non-toxic organic catalyst, which avoids the use of traditional titanium-based and tin-based heavy metal catalysts in the polymerization process of PBAT and PLA, and does not have the pollution problem of heavy metal residues. At the same time, the organic guanidine catalyst has the characteristics of good heat resistance and high catalytic efficiency, and the addition amount is only 1/10,000 to 5/10,000 of the raw material added, which greatly reduces the problem of catalyst residue and expands the use of PBAT-PLA copolymer in Applications in food and medical materials.

2. The PBAT-PLA prepared by the present invention is a block copolyester. By controlling the acid value (hydroxyl value) and molecular weight of each segment, the reactivity of the BHBT, BHBA and PLA segments can be improved, and the interaction between different segments can be achieved. Better reaction fusion avoids the serious phase separation problem caused by poor compatibility between the segments, and the prepared PBAT-PLA copolyester has good rigidity-toughness balance and comprehensive performance.

3. Use polyether polyol with hydroxyl ≥3 and molecular weight of 600-3500g/mol as the initiator to obtain PLA polyol with branched ether structure by ring-opening polymerization, and further obtain PBAT-PLA copolymerization with branched ether structure Ester, which significantly improves melt strength and flexibility, and better meets downstream application requirements such as blown film, injection molding, foaming, and double-stretched film.

Detailed ways

In order to facilitate understanding of the present invention, the present invention enumerates the following examples. It should be clear to those skilled in the art that the embodiments are only for helping to understand the present invention, and should not be regarded as specific limitations on the present invention.

The tests involved in the present invention are as follows:

1. Melt index test

The measurement is carried out according to the method specified in GB/T 3682-2000, wherein the test temperature is 190°C and the load is 2.16kg. PBAT-PLA copolyester, in the case of the same molecular weight and distribution, the smaller the melt index (MI), the greater the melt strength.

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

3. The acid value of the product is in accordance with the provisions of GB/T 32366-2015 "Biodegradable Polybutylene Terephthalate-Adipate (PBAT)", and according to GB/T14190-2008 "Fiber Grade Polyester Chip (PET) Test Carboxy-terminal test method A stipulated in Method ". The standard titration solution is potassium hydroxide-benzyl alcohol with a concentration of 0.01mol/L, and bromophenol blue is the indicator. Sample configuration: 0.5g sample is dissolved in phenol-chloroform mixed solvent (volume ratio 2:3), and tested according to standard acid-base titration operation.

4. Hydroxyl value test of polyols with branched ether structure:

The hydroxyl value was tested by the phthalylation method.

Preparation of acylating agent: Weigh 42g of phthalic anhydride and dissolve it in 300mL of dried pyridine. After the dissolution is complete, store it in a brown bottle and place it in a desiccator for later use.

Weigh 6g of imidazole and add it to the prepared acylating agent.

Analysis procedure: Accurately weigh a certain amount of sample on an analytical balance, place it in an acylation bottle with a ground mouth and install a reflux condenser, add 25mL of acylating agent accurately with a pipette, and place the sample at a constant temperature after dissolution In the water bath, the acylation reaction takes 20-25min; after taking it out of the water bath, cool to room temperature, and add 20mL of 1:1 pyridine-distilled aqueous solution from the upper end of the condenser along the mouth wall to hydrolyze the remaining anhydride, shake well and then add 3- Titrate 5 drops of phenolphthalein indicator with 0.8 mol/L or 1 mol/L KOH standard solution until it turns pink, and if it does not change within 15 seconds, it is the end point. Do a blank test in the same way. The calculation of hydroxyl value is as follows, and the allowable error is less than 0.5 mg KOH/g;

5. Product color test: use X-Rite Ci7600 model, test conditions: use 25mm aperture, reflective mode for measurement; color plate specification is 80*50*3mm.

6. Product thermal stability test: The cut PBAT particles were vacuum-dried at 85°C for 6 hours, and PBAT thermogravimetric analysis was carried out using Discovery TGA55. Test conditions: weighing 8-10mg sample, air atmosphere, temperature range 50-600°C, heating rate 10°C/min. The thermal stability of PBAT resin was characterized by the temperature (T _5% ) at the time of weight loss of 5% mass.

7. Product compatibility test: The cut PBAT particles were vacuum-dried at 85°C for 6 hours, and the glass transition temperature (T _g ) of PBAT-PLA copolyester was analyzed using DiscoveryDSC250. Test conditions: weighing 8-10mg sample, nitrogen atmosphere, temperature range 50-200°C, heating rate 10°C/min. The compatibility of PBAT-PLA copolyesters was characterized by different glass transition temperatures (T _g ).

8. Tensile strength test, sample preparation: Injection molding samples shall be carried out according to the regulations of GB/T17037.1-1997, and the A-type mold in GB/T17037.1-1997 shall be used to prepare in accordance with the IA type in GB/T1040.2-2006 sample. Use proper packing pressure for injection molding to obtain defect-free test strips.

Pretreatment of pellets: Before forming the samples, the pellets are preheated and dried in a blast drying oven, the thickness of the tray is less than 4cm, and they are dried continuously at 80°C for 5h. Use the dried pellets immediately to prevent moisture absorption.

Sample preparation conditions: FANUC ROBOSHOT ɑ-S100iA Japanese FANUC all-electric injection molding machine, screw injection machine process:

The state adjustment of the sample and the standard environment of the test: the state adjustment of the sample is carried out in accordance with the provisions of GB/T2918-1998, the condition of the state adjustment is temperature 23 °C ± 2 °C, and the adjustment time is 40h. The test is carried out under the standard environment specified in GB/T2918-1998, the temperature of the environment is 23°C±2°C, and the relative humidity is 50%±10%.

Test conditions: According to the provisions of GB/T1040.2-2006, the test speed is 50mm/min.

Example 1

The charging capacity of each material in embodiment 1 is as shown in table 1:

Table 1 Example 1 Feeding table

S1 esterification-precondensation:

Add 1661.7g of terephthalic acid (w/%≥99.90%), 994.3g of 1,4-butanediol (w/%≥99.70%) and 0.55g of hexamethylguanidine glycolate into 10L of esterification In Kettle 1, turn on the heating, stir evenly, gradually raise the temperature to 240°C, and the reaction pressure is 70KPa, carry out the esterification and dehydration reaction, and react for 2 hours. When the water yield of the reaction reaches the theoretical value of 360.0g, no more water will be distilled out. Then gradually reduce the reaction pressure to 10KPa, carry out pre-condensation, react for 1 hour, and take samples for molecular weight and acid value detection. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBT oligomer to the third polymerization tank.

Add the weighed 1789.4g 1,6-adipic acid (w/%≥99.80%), 1213.0g 1,4-butanediol (w/%≥99.70%) and 0.67g hexamethylguanidine glycolate In the 10L esterification kettle two, turn on the heating, stir evenly, gradually raise the temperature to 200°C, and the reaction pressure is 70KPa, carry out the esterification and dehydration reaction, and react for 2 hours. When the water output of the reaction reaches the theoretical value of 439.9g, no more water will be distilled out. Subsequently, the reaction pressure was gradually reduced to 10KPa, pre-condensation was carried out, and the reaction was carried out for 0.5h. Samples were taken for detection of molecular weight and acid value. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBA oligomer to the third polymerization tank.

Preparation of S2 branched ether structure PLA triol: weighed 802.16g lactide (w/%≥99.90%), 79.43g glycerol polyoxypropylene triol (average molecular weight 3000g/mol, hydroxyl value 56mgKOH/g ) and 0.30g of hexamethylguanidine glycolate were added to the 20L polymerization kettle 3, vacuumed and replaced with nitrogen for 3 times, turned on the heating, stirred evenly, and carried out ring-opening polymerization, gradually raised the temperature to 180°C, reacted at 5000Pa for 3h, and took samples Molecular weight and hydroxyl value detection.

S3 Copolycondensation: Add the completed BHBT and BHBA into the 20L polymerization kettle three, and carry out copolymerization with PLA triols with branched ether structure. The reaction temperature is gradually raised to 240°C, the reaction pressure is 5000Pa, and the reaction time is 2h.

S4 final polycondensation: Add 0.63g of triphenyl phosphate and 0.63g of 2,6-di-tert-butyl-4-methylphenol into the polymerization kettle three, the reaction temperature is 240°C, the reaction pressure is gradually reduced to 80Pa, and the reaction time is 1.5h , to end the reaction.

Example 2-4

The feeding amount of each material in Example 2-4 is shown in Table 2-4. Different organic guanidine catalysts were used in Example 2-4, and the reaction steps were consistent with Example 1.

Table 2 Example 2 Feeding Table

Table 3 Example 3 Feeding Table

Table 4 Example 4 Feeding Table

Example 5-8

The feeding amount of each material in embodiment 5-8 is as shown in table 5-8, and reaction procedure is consistent with embodiment 1, wherein the average molecular weight of trimethylolpropane polyoxypropylene triol is 3000 g/mol, and the hydroxyl value is 58 mgKOH/g; the average molecular weight of pentaerythritol polyoxypropylene tetraol is 600 g/mol, and the hydroxyl value is 374 mgKOH/g; embodiment 6 and embodiment 8 use hexamethylguanidine lactate catalyst.

Table 5 Example 5 Feeding Table

Table 6 Example 6 Feeding Table

Table 7 Example 7 Feeding Table

Table 8 Example 8 Feeding Table

Example 9

The feeding amount of each material in embodiment 9,10 is as shown in table 9,10, and embodiment 9,10 all is to adopt hexamethylguanidine glycolate organic catalyst, and reaction step is consistent with embodiment 1, wherein PTA, AA, BDO And the input amount ratio of lactide is different from that of Examples 1-8, and the input amount ratio of catalyst, heat stabilizer and antioxidant has also been adjusted accordingly. In addition, the reaction conditions in the polycondensation stage were also changed.

Table 9 Example 9 Feeding Table

S1 esterification-precondensation:

Add 1663.0g of terephthalic acid (w/%≥99.90%), 1807.8g of 1,4-butanediol (w/%≥99.70%) and 0.22g of hexamethylguanidine glycolate into 10L of esterification In Kettle 1, turn on the heating, stir evenly, gradually raise the temperature to 140°C, and the reaction pressure is 80KPa, carry out the esterification and dehydration reaction, and react for 1 hour. When the water yield of the reaction reaches the theoretical value of 360.0g, no more water will be distilled out. Then gradually reduce the reaction pressure to 40KPa, carry out pre-condensation, react for 0.1h, and sample for molecular weight and acid value detection. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBT oligomer to the third polymerization tank.

Add weighed 1464.3g 1,6-adipic acid (w/%≥99.80%), 1807.8g 1,4-butanediol (w/%≥99.70%) and 0.22g hexamethylguanidine glycolate In the 10L esterification kettle two, turn on the heating, stir evenly, gradually raise the temperature to 130°C, and the reaction pressure is 80KPa, carry out the esterification and dehydration reaction, and react for 1 hour. When the water output of the reaction reaches the theoretical value of 360.0g, no more water will be distilled out. Then the reaction pressure was gradually reduced to 40KPa, and the pre-condensation was carried out, and the reaction was carried out for 0.1h, and samples were taken for molecular weight and acid value detection. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBA oligomer to the third polymerization tank.

Preparation of S2 branched ether structure PLA triol: weighed 720.7g lactide (w/%≥99.90%), 500g glycerol polyoxypropylene triol (average molecular weight 3000g/mol, hydroxyl value 56mgKOH/g) Add 0.11g of hexamethylguanidine glycolate into a 20L polymerization kettle 3, vacuumize and replace with nitrogen for 3 times, turn on the heating, stir evenly, carry out ring-opening polymerization, gradually raise the temperature to 130°C, react at 3000Pa for 2h, and take samples to determine the molecular weight and hydroxyl value detection.

S3 Copolycondensation: Add the completed BHBT and BHBA into the 20L polymerization kettle three, and carry out copolymerization with PLA triol with branched ether structure. The reaction temperature is gradually raised to 180°C, the reaction pressure is 100Pa, and the reaction time is 0.5h.

S4 Final polycondensation: Add 0.75g of triphenyl phosphate and 0.75g of 2,6-di-tert-butyl-4-methylphenol to the polymerization kettle three, the reaction temperature is 240°C, the reaction pressure is gradually reduced to 80Pa, and the reaction time is 0.5h , to end the reaction.

Example 10

Table 10 Example 10 Feeding Table

S1 esterification-precondensation:

Add 1663.0g of terephthalic acid (w/%≥99.90%), 2711.7g of 1,4-butanediol (w/%≥99.70%) and 1.10g of hexamethylguanidine glycolate into 10L of esterification In Kettle 1, turn on the heating, stir evenly, gradually raise the temperature to 250°C, and the reaction pressure is 100KPa, carry out the esterification and dehydration reaction, and react for 3 hours. When the water yield of the reaction reaches the theoretical value of 360.0g, no more water will be distilled out. Then gradually reduce the reaction pressure to 70KPa, carry out pre-condensation, react for 1.5h, and take samples for molecular weight and acid value detection. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBT oligomer to the third polymerization tank.

Add 3367.9g of 1,6-adipic acid (w/%≥99.80%), 6236.9g of 1,4-butanediol (w/%≥99.70%) and 2.53g of hexamethylguanidine glycolate In the 10L esterification kettle two, turn on the heating, stir evenly, gradually raise the temperature to 240°C, and the reaction pressure is 100KPa, carry out the esterification and dehydration reaction, and react for 3 hours. When the water output of the reaction reaches the theoretical value of 828.0g, no more water will be distilled out. Subsequently, the reaction pressure was gradually reduced to 70KPa, pre-condensation was carried out, and the reaction was carried out for 1.5 hours. Samples were taken for detection of molecular weight and acid value. After the molecular weight and acid value reach the target, lower the temperature to 180°C to evaporate excess 1,4-butanediol, and transfer the BHBA oligomer to the third polymerization tank.

Preparation of S2 branched ether structure PLA triol: weighed 1189.16g lactide (w/%≥99.90%), 82.5g glycerol polyoxypropylene triol (average molecular weight 3000g/mol, hydroxyl value 56mgKOH/g ) and 0.91g of hexamethylguanidine glycolate were added to the 20L polymerization kettle 3, vacuumed and replaced with nitrogen for 3 times, turned on the heating, stirred evenly, and carried out ring-opening polymerization, gradually raised the temperature to 150°C, reacted at 3000Pa for 5h, and took samples Molecular weight and hydroxyl value detection.

S3 Copolycondensation: Add the completed BHBT and BHBA into the 20L polymerization kettle three, and carry out copolymerization with PLA triol with branched ether structure. The reaction temperature is gradually raised to 250°C, the reaction pressure is 10000Pa, and the reaction time is 3h.

S4 Final polycondensation: Add 3.06g of triphenyl phosphate and 3.06g of 2,6-di-tert-butyl-4-methylphenol into the polymerization kettle three, the reaction temperature is 240°C, the reaction pressure is gradually reduced to 80Pa, and the reaction time is 3h. End the reaction.

Comparative example 1

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

Table 11 Feeding table of comparative example 1

Comparative example 2

The feeding amount of each material in Comparative Example 2 is shown in Table 12. During the reaction process, the acid value of the BHBT and BHBA segments was controlled to be ≥120 mol/t, and the hydroxyl value of the PLA triol with branched ether structure was ≥50 mgKOH/g.

Table 12 Feeding table of comparative example 2

Comparative example 3

The feeding amount of each material in Comparative Example 3 is shown in Table 13. During the reaction process, the acid value of the BHBT and BHBA segments is controlled to be <60 mol/t, and the hydroxyl value of the PLA triol with branched ether structure is ≥50 mgKOH/g.

Table 13 Feeding Table of Comparative Example 3

Comparative example 4

The feeding amount of each material in Comparative Example 4 is shown in Table 14. Polytetramethylene ether glycol (PTMEG) (molecular weight 3000g/mol, hydroxyl value 37 mgKOH/g) was used as an initiator to prepare linear ether structure PLA diols; during the reaction, the acidity of the BHBT and BHBA segments was controlled The value is between 60-100mol/t, and the hydroxyl value of PLA triol with branched ether structure is between 30-50mgKOH/g.

Table 14 Feeding Table of Comparative Example 4

Comparative example 5

The feeding amount of each material in Comparative Example 5 is shown in Table 18. Using glycerol polyoxypropylene triol (molecular weight 500 g/mol, hydroxyl value 380 mgKOH/g ) as an initiator to prepare branched ether chain structure PLA triol; during the reaction, control the acid value of BHBT and BHBA segments at 60- Between 100 mol/t, the hydroxyl value of PLA trihydric alcohol with branched ether structure is between 30-100mgKOH/g.

Table 18 Feeding Table of Comparative Example 5

Comparative example 6

The feeding amount of each material in Comparative Example 6 is shown in Table 16. Using glycerol polyoxypropylene triol (molecular weight 5000 g/mol, hydroxyl value 32 mgKOH/g ) as an initiator to prepare PLA triol with branched ether chain structure; during the reaction, the acid value of BHBT and BHBA segments was controlled at 60 Between -100mol/t, the hydroxyl value of PLA trihydric alcohol with branched ether structure is between 30-50mgKOH/g.

Table 16 Comparative Example 6 Feeding Table

The following acid value, tensile strength, elongation at break, appearance color and thermal stability of Examples 1-10 and Comparative Examples 1-6 are detected, and the test results are as shown in Table 17 and Table 18:

Segment molecular weight, acid value etc. of table 17 embodiment 1-10 and comparative example 1-6 product

Table 18 Melt index, acid value, color and mechanical properties of the products of Examples 1-10 and Comparative Examples 1-6

From the test data of PBAT-PLA copolyester in Table 17 and Table 18, embodiment 1-4 is lactide ring-opening polymerization initiator Under the condition, the catalytic effect of each catalyst is hexamethylguanidine glycolate>hexamethylguanidine lactate>>hexaethylguanidine glycolate>hexaethylguanidine lactate, the hexamethylguanidine glycolate in embodiment 1-2 The PBAT-PLA copolyester prepared with hexamethylguanidine lactate as a catalyst has good 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, it is more difficult for the chain segment to combine with the hexaethylguanidine catalyst when esterification and polycondensation occur, and the catalytic effect is relatively poor, which leads to the co-production of PBAT-PLA. The performance of polyester is significantly worse.

In subsequent examples 5-8, trimethylolpropane (TMP) and pentaerythritol (PER)-based polyether polyols were used as propane under the same catalytic amount of hexamethylguanidine glycolate and hexamethylguanidine lactate. Lactide ring-opening polymerization initiators were used to prepare branched ether PLA triols and tetraols, and their effects on the properties of PBAT-PLA copolyester were investigated. In the case of little difference in molecular weight, the melt strength of pentaerythritol (4 hydroxyl groups) branched chain structure (the melt index of Example 7 is 1.2, the melt index of Example 8 is 2.2), significantly higher than that of glycerin and trihydroxy The melt strength (melt index of embodiment 5 is 3.9, the melt index of embodiment 6 is 4.3) of methyl propane (hydroxyl is 3) branched chain structure is more conducive to PBAT-PLA copolyester in foaming, two-way drawing Applications in the field of film stretching. At the same time, the pentaerythritol (PER)-based polyoxypropylene tetraol has a small molecular weight and a high degree of branching (4 branches) of the polyether, which makes the elongation at break of the PBAT-PLA copolyester lower under the same conditions.

In Comparative Example 1, a titanate catalyst and stannous octoate were used as the reaction catalyst. Since the titanium-based catalyst was easily hydrolyzed during the esterification stage, the catalytic effect could not be fully exerted, resulting in an incomplete esterification reaction (the water yield did not reach the theoretical value). The acid value, color and mechanical properties of PBAT-PLA copolyester are poor; at the same time, due to the addition of heavy metal titanium and tin catalysts, the problem of heavy metal residues is brought.

From the comparison of Examples 1-10, Comparative Example 2 and Comparative Example 3, it can be seen that by controlling the molecular weight and acid value (60-100 mol/t) of the BHBT and BHBA segments, the BHBT, BHBA and branched While the PLA polyol segment with ether structure has good compatibility, PBAT-PLA copolyester has excellent acid value, color, melt strength and mechanical properties. When the molecular weight of the segment is small or the acid value is too large (≥120 mol/t), as in Comparative Example 2, the acid value of the product will increase and the mechanical properties will be greatly reduced; when the molecular weight of the segment is large or the acid value When it is too small (≤60 mol/t), as in Comparative Example 3, due to the poor compatibility between molecular segments, the product will appear phase separation (two Tg), resulting in a significant decline in mechanical properties.

In comparative example 4, polytetramethylene ether glycol (PTMEG, molecular weight 3000g/mol, hydroxyl value 37mgKOH/g) was used to prepare PLA diol with linear ether structure. It can be seen that in the case of the same molecular weight, because There is no branched structure in the molecular chain, and its melt strength (melt index is 9.8) is significantly lower than that of Example 1 (melt index is 4.2); other aspects such as color and mechanical properties are not much different, and the acid value is higher than that of Example 1. higher.

In Example 1, Comparative Example 5 and Comparative Example 6, glycerin oxide propylene triols (3000, 500 and 5000 g/mol) with different molecular weights were used as initiators to prepare PLA triols with branched ether structure, and PBAT-PLA was obtained The elongation at break of copolyesters shows obvious differences. The larger the molecular weight of polyether triol, the better its elongation at break (flexibility), but the molecular weight of polyether triol is too small or too large. Lead to a significant decline in the mechanical properties of PBAT-PLA copolyester.

Claims (8)

1. the method for organic guanidine catalyzed synthetic biodegradation PBAT-PLA copolyester, is characterized in that, comprises the following steps: S1 esterification-precondensation: S11 Esterification: Add terephthalic acid, 1,4-butanediol and an organic guanidine catalyst into the first esterification kettle to carry out the esterification reaction until the water output of the reaction reaches the theoretical value; in the second esterification kettle, add 1 , 6-adipic acid, 1,4-butanediol and organic guanidine catalyst, carry out esterification reaction, until the water yield of the reaction reaches the theoretical value; S12 Pre-condensation: after the esterification reaction of esterification kettle 1 and esterification kettle 2 is completed, the vacuum degree is further increased, and pre-condensation is carried out, and the oligoesterification product BHBT of esterification kettle 1 and the oligoesterification product of esterification kettle 2 are After the segmental acid value and molecular weight of BHBA reach the target values, reduce the temperature in the kettle to below 180°C, further distill off excess 1,4-butanediol, and then transfer to polymerization kettle three; S2 Synthesis of PLA polyol with branched ether structure: add lactide, organic guanidine catalyst and initiator polyether polyol into polymerization kettle three, heat up to the target temperature, vacuumize and carry out ring-opening polymerization until the branched ether The molecular weight and hydroxyl value of structural PLA polyol reach the target value; S3 co-polycondensation: transfer the completed BHBA and BHBT into the polymerization tank 3, raise the temperature to the specified temperature, turn on the vacuum, and co-condense with PLA polyols with branched ether structure; S4 final polycondensation: add heat stabilizer and antioxidant to polymerization kettle three, vacuumize, carry out polycondensation reaction, then further increase the vacuum degree to carry out final polycondensation, and obtain biodegradable PBAT-PLA copolyester; In step S1, the organic guanidine catalyst is one or more of hexamethylguanidine glycolate, hexamethylguanidine lactate, hexaethylguanidine glycolate, and hexaethylguanidine lactate; In step S12, when the precondensation reaction ends, the segmental acid value of the oligoester compound BHBT and the oligoester 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; In step S2, the hydroxyl group of the polyether polyol is ≥3, and the molecular weight is 600-3500 g/mol; The molecular weight of PLA polyol with controlled branched ether structure is 20000-50000g/mol, and the hydroxyl value is 30-100mgKOH/g. 2. the method for organoguanidine catalyzed synthetic biodegradation PBAT-PLA copolyester as claimed in claim 1, is characterized in that, in step S1, the mol ratio of described terephthalic acid and 1,6-adipic acid is 1:1.0-2.3; in esterification kettle one, the molar ratio of terephthalic acid to 1,4-butanediol is 1:1.0-3.0; in esterification kettle two, 1,6-hexanedioic acid and 1, The molar ratio of 4-butanediol is 1:1.0-3.0; the molar ratio of the total molar weight of terephthalic acid and 1,6-hexanedioic acid to 1,4-butanediol is 1:1.0-3.0. 3. the method for organic guanidine catalyzed synthetic biodegradable PBAT-PLA copolyester as claimed in claim 1, is characterized in that, in step S11, in the esterification still one, the consumption of organic guanidine catalyst is terephthalic acid mole number 0.01-0.05% of 0.01-0.05%; in esterification kettle two, the consumption of organic guanidine catalyst is 0.01-0.05% of the molar number of 1,6-adipic acid; in step S2, during ring-opening polymerization, the consumption of organic guanidine catalyst is lactate 0.01-0.05% of the ester moles. 4. the method for organoguanidine catalyzed synthetic biodegradation PBAT-PLA copolyester as claimed in claim 1, it is characterized in that, in step S11, the esterification reaction temperature of esterification kettle one is 140-250 ℃, and the reaction time is 1-3h, the reaction pressure is 70-100kPa; the esterification reaction temperature of the esterification kettle 2 is 130-240°C, the reaction time is 1-3h, the reaction pressure is 70-100kPa; in step S12, the precondensation reaction temperature is 200 -260°C, reaction pressure 10-70kPa, reaction 0.1-1.5h; in step S2, lactide ring-opening polymerization reaction temperature is 130-180°C, reaction pressure is 3-10KPa, reaction time is 2-5h. 5. the method for organoguanidine catalyzed synthetic biodegradation PBAT-PLA copolyester as claimed in claim 1, is characterized in that, in step S2, the mol ratio of described polyether polyol and lactide is 1:30.0- 300.0; the molar ratio of the molar amount of lactide to the total molar amount of terephthalic acid and 1,6-adipic acid is 1:0.1-10.0. 6. The method for organic guanidine catalyzed synthesis of biodegradable PBAT-PLA copolyester as claimed in claim 1, characterized in that, in step S3, the polycondensation reaction temperature is 180-250°C, the reaction pressure is 100-10000Pa, and the reaction time 0.5-3.0h; in step S4, then further reduce the reaction pressure to less than 100Pa to increase the vacuum degree for final polycondensation, react for 0.5-3.0h, and end the reaction to obtain biodegradable PBAT-PLA copolyester. 7. the method for organoguanidine catalyzed synthetic biodegradation PBAT-PLA copolyester as claimed in claim 1, is characterized in that, in step S4, described antioxidant is 2,6-di-tert-butyl-4-methyl Phenol, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol, tris[2.4-di-tert-butylphenyl]phosphite and β-(3,5- One or more of n-octadecyl di-tert-butyl-4-hydroxyphenyl) propionate. 8. the method for organoguanidine catalyzed synthetic biodegradable PBAT-PLA copolyester as claimed in claim 1, is characterized in that, in step S4, described thermal stabilizer is trimethyl phosphate, triethyl phosphate and trimethyl phosphate One or more of phenyl esters; the amount of heat stabilizer is 0.01-0.2% of the total raw material weight, and the amount of antioxidant is 0.01-0.2% of the total raw material weight.