阅读说明：本技术 一种超临界二氧化碳诱导pbat结晶/固相缩聚联用制备高分子量pbat的方法 (Method for preparing high molecular weight PBAT by combining supercritical carbon dioxide induced PBAT crystallization/solid phase polycondensation ) 是由 徐小武 甄崇汀 于 2020-10-20 设计创作，主要内容包括：本发明公开了一种超临界二氧化碳诱导PBAT结晶-固相缩聚联用制备高分子量PBAT材料的方法。本发明中采用超临界二氧化碳诱导PBAT结晶-固相缩聚联用新工艺,制备高分子量PBAT材料。本发明的有益特点为,聚合物分子量高,并且产品PBAT的分子量可在1.75×10~5～2.30×10~5范围内根据实际需求受控合成；产品分子量分布指数窄(PDI 1.55～1.80)；PBAT材料机械力学性能佳、残留单体含量更低无异味、色泽佳(白色)、抗水解性能优异。(The invention discloses a method for preparing a high molecular weight PBAT material by combining supercritical carbon dioxide induced PBAT crystallization and solid phase polycondensation. The invention adopts a new technology of combining supercritical carbon dioxide induced PBAT crystallization and solid phase polycondensation to prepare the high molecular weight PBAT material. The invention has the advantages that the molecular weight of the polymer is high, and the molecular weight of the PBAT product can be 1.75 multiplied by 10 5 ～2.30×10 5 Controlled synthesis is carried out within the range according to actual requirements; the molecular weight distribution index of the product is narrow (PDI 1.55-1.80); the PBAT material has the advantages of good mechanical property, lower content of residual monomers, no peculiar smell, good color (white) and excellent hydrolysis resistance.)

1. A method for preparing high molecular weight PBAT by combining supercritical carbon dioxide induced crystallization/solid phase polycondensation of PBAT is characterized by comprising the following steps:

the method comprises the following steps: adding PBAT raw materials into a reaction kettle, and performing gas replacement by using carbon dioxide gas;

step two: inducing PBAT crystallization by supercritical carbon dioxide;

step three: releasing the pressure and discharging;

step four: recrystallizing the product obtained in the third step;

step five: solid phase polycondensation.

2. The method for preparing the high molecular weight PBAT by combining the supercritical carbon dioxide-induced crystallization of the PBAT and the solid phase polycondensation according to claim 1, wherein in the second step, the supercritical carbon dioxide-induced crystallization of the PBAT is realized by introducing sufficient carbon dioxide gas into a reaction kettle, stirring, heating to 70-80 ℃, boosting to 13-15MPa, and inducing the crystallization for 60-120 min.

3. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in the third step, the pressure relief is specifically carried out by keeping the pressure relief temperature at 70-100 ℃; the pressure relief rate is 1-1.2 MPa/min, and the pressure is relieved to the micro-positive pressure of 1.05-1.1 ATM.

4. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 3, wherein: the crystallinity of the PBAT obtained in the third step is 25 to 30 percent.

5. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in the fourth step, the recrystallization comprises grinding, crushing, screening and drying.

6. The method of claim 4 for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization of PBAT and solid phase polycondensation, wherein: in the fourth step, screening out 30-40 mesh particle screen, wherein the drying time is 1-2 hours, and the drying temperature is 80-90 ℃.

7. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in the fifth step, the solid phase polycondensation reaction temperature is 100-.

8. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1 or 7, wherein: in the fifth step, the solid phase polycondensation is carried out in a fluidized state.

9. The method of claim 8 for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization of PBAT and solid phase polycondensation, wherein: in the fifth step, the fluidizing gas used in the solid phase polycondensation is one or two of carbon dioxide gas and nitrogen gas.

10. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 9, wherein: in the fifth step, when the fluidizing gas adopted by the solid-phase polycondensation is carbon dioxide gas, the flow rate of the carbon dioxide gas is 3-50L/min.

11. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in step five, the weight average molecular weight Mw of the PBAT obtained by solid phase polycondensation is 1.75X 10⁵～2.30×10⁵The molecular weight PDI is 1.55-1.80, and the density is 1.23 +/-0.02 g/cm³。

12. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in the first step, the PBAT raw material added into the reaction kettle is in one or more of granular shape, sheet shape and strip shape.

13. The method for preparing high molecular weight PBAT by using the combination of supercritical carbon dioxide-induced crystallization/solid phase polycondensation of PBAT according to claim 1, wherein: in the second step, supercritical carbon dioxide is used as an inducer, the temperature is higher than 31.1 ℃, and the pressure is higher than 7.4 MPa.

Technical Field

The invention belongs to the technical field of full biodegradable materials in the polymer industry, and particularly relates to a method for preparing high molecular weight PBAT by combining supercritical carbon dioxide induced PBAT crystallization/solid phase polycondensation.

Background

With the increasing environmental awareness, biodegradable polyesters are receiving more and more attention. Biodegradable polyesters generally require higher molecular weights to have suitable mechanical properties, thus meeting different functional requirements and application ranges. Polybutylene terephthalate adipate (PBAT) belongs to the all biodegradable polyester. The PBAT material prepared by the traditional melt polycondensation process has low molecular weight and low mechanical properties such as tensile strength, bending modulus and the like, thereby limiting the use of PBAT. Therefore, a suitable and effective method is found to improve the molecular weight of PBAT, and the PBAT has excellent mechanical properties and has important significance for popularization and use of PBAT.

In order to solve the problems of low molecular weight, reduced mechanical properties and the like, the chain extender (also called chain extender) is a commonly used auxiliary agent in the modified plastic industry at present. The action mechanism is mainly as follows: the multifunctional compound with good thermal stability reacts with the terminal hydroxyl or terminal carboxyl of the polyester, so that the molecular chain is diffused and prolonged, and the relative molecular weight of the polymer is improved.

In the aspect of chain extenders, the invention patent CN 109401227A of China adopts PLA/PBAT blending modified biodegradable resin prepared by chain extenders and a preparation method thereof. The chain extender KL-E is dissolved in ethyl acetate solution, and can be uniformly distributed in mixed particles by a spraying method, short-chain molecules and terminal carboxyl molecules are changed into long-chain macromolecules under the action of double-screw shearing force at a certain temperature, and the mechanical property is enhanced. The invention discloses a PBS/PBAT blending modified biodegradable resin prepared by adopting a chain extender and a preparation method thereof in Chinese patent CN 109553934A. Dissolving the chain extender KL-E into an ethyl acetate solution, volatilizing the ethyl acetate by a spraying method, uniformly adsorbing the chain extender on the surface of the particles, and changing short-chain molecules and terminal carboxyl molecules into long-chain macromolecules under the action of double-screw shearing force at a certain temperature to enhance the mechanical property.

However, the above-mentioned method of increasing the molecular weight by adding a chain extender has problems that: the chain extension reaction speed is high, the requirement on temperature and pressure control is high, the implosion is easy, the biodegradability and the degradation speed of the product can be influenced by externally added substances, the application of PBAT in the aspects of food and medicine is limited, and the obtained product is difficult to realize and is completely environment-friendly.

Disclosure of Invention

The main object of the present invention is to provide a method for preparing high molecular weight PBAT by combining supercritical carbon dioxide induced crystallization of PBAT/solid phase polycondensation, which can at least partially solve the above technical problems.

In order to solve the technical problems, the technical scheme of the invention is to provide a method for preparing high molecular weight PBAT by combining supercritical carbon dioxide induced PBAT crystallization/solid phase polycondensation, which comprises the following steps:

the method comprises the following steps: adding PBAT raw materials into a reaction kettle, and performing gas replacement by using carbon dioxide gas;

step two: inducing PBAT crystallization by supercritical carbon dioxide;

step three: releasing the pressure and discharging;

step four: recrystallizing the product obtained in the third step;

step five: solid phase polycondensation.

Among the mechanisms by which supercritical carbon dioxide induces polymer crystallization is that supercritical carbon dioxide (SC-CO2) has a liquid-like density and a gas-like viscosity and molecular diffusion coefficient. Small changes in temperature and pressure near the critical point can cause large changes in density, thereby changing many of the physicochemical properties associated with density. Many polymers have high solubility in supercritical carbon dioxide at high pressures, e.g., BDO monomer has some solubility in supercritical carbon dioxide. The dissolution of carbon dioxide can reduce the glass transition temperature of the polymer, and the free volume of an amorphous area can be increased at a lower temperature, so that the movement capacity of a polymer chain is improved, and the regular arrangement of polymer chain segments is easy to realize to form crystals.

Further, in the step one, the shape of the PBAT raw material added into the reaction kettle is one or more than one of granular shape, sheet shape and strip shape.

Further, in the second step, the supercritical carbon dioxide is used as an inducer, the temperature is higher than 31.1 ℃, and the pressure is higher than 7.4 MPa.

Further, in the second step, the supercritical carbon dioxide-induced crystallization of PBAT is specifically that sufficient carbon dioxide gas is introduced into the reaction kettle, stirred, heated to 70-80 ℃, and pressurized to 13-15MPa, which is the supercritical state of carbon dioxide, and the induced crystallization time is 60-120 min.

Further, in the third step, pressure relief is specifically carried out, namely, the pressure relief temperature is kept at 70-100 ℃; the pressure relief rate is 1-1.2 MPa/min, and the pressure is relieved to the micro-positive pressure of 1.05-1.1 ATM.

Further, the crystallinity of the PBAT obtained in the third step is 25 to 30 percent.

Further, in the fourth step, the recrystallization comprises grinding, crushing, screening and drying,

further, in the fourth step, the screened material is 30-40 mesh particles, the drying time is 1-2 hours, and the drying temperature is 80-90 ℃.

Further, in the fifth step, the temperature of the solid phase polycondensation is 100-.

The solid-phase polycondensation (also referred to as solid-state polycondensation or abbreviated as SSP) is a process in which a monomer or a prepolymer having a relatively low molecular weight is heated to a temperature higher than the glass transition temperature and lower than the melting point to perform a polymerization reaction, and the polymer is not substantially thermally degraded in the solid-phase polycondensation.

Since the SSP reaction is an equilibrium reaction, the by-products (water; monomers such as ethylene glycol; by-products such as acetaldehyde; or oligomers) from the SSP reaction must be efficiently removed from the reaction vessel in order to achieve the desired high polyester molecular weight. The removal of the by-product is achieved by applying a vacuum or by means of a gas flowing through the reaction vessel, which carries the by-product out of the reaction vessel.

For this reason, in the present invention, further, in the fifth step, the solid-phase polycondensation reaction is carried out in a fluidized state.

Further, in the fifth step, the fluidizing gas used in the solid phase polycondensation reaction is one or two of carbon dioxide gas and nitrogen gas.

Further, in the fifth step, when the preferable fluidizing gas for the solid phase polycondensation is carbon dioxide gas, the flow rate of the carbon dioxide gas is 3 to 50L/min.

Further, in the fifth step, the weight average molecular weight Mw of PBAT obtained by solid phase polycondensation was 1.75X 10⁵～2.30×10⁵The molecular weight PDI is 1.55-1.80, and the density is 1.23 +/-0.02 g/cm³。

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

the invention uses supercritical carbon dioxide as a physical solvent to induce PBAT crystallization, can improve the crystallinity and is beneficial to normal solid phase polycondensation.

Meanwhile, the supercritical carbon dioxide has the functions of extraction and devolatilization, can absorb small molecular substances in the PBAT polycondensation stage, and can effectively reduce the content of PBAT residual monomers, so that the PBAT material has no peculiar smell and good color (white).

Compared with the PBAT material prepared by melt polycondensation in the prior art, the combined solid phase polycondensation process can greatly improve the weight average molecular weight and the mechanical property of the PBAT material.

In conclusion, the PBAT performance is improved, other impurities are not introduced, and the essential environment-friendly characteristic of the PBAT can be still reserved.

The synthesized PBAT product is a completely biodegradable green plastic with the molecular weight of Mw1.75 multiplied by 10⁵～2.30×10⁵The molecular weight PDI is 1.55-1.80, and the density is 1.23 +/-0.02 g/cm³The composite material has the advantages of high molecular weight, narrow molecular weight distribution and high density, so that the material has good mechanical property, lower residual monomer content, no peculiar smell, good color (white) and excellent hydrolysis resistance.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments below:

the raw materials used in the present invention are illustrated below: PBAT starting material was purchased from sexin rich pharmaceutical ltd, zhejiang with a molar content of Butylene Terephthalate (BT) units of 45%. Carbon dioxide gas was purchased from the national pharmaceutical group chemical agents limited.

The method for preparing the high molecular weight PBAT material by adopting the supercritical carbon dioxide induced PBAT crystallization/solid phase polycondensation combined technology comprises the following steps:

step one, adding 5g of PBAT raw material into a stainless steel pressure reaction kettle which is provided with a stirrer and connected with a supercritical carbon dioxide pipeline, introducing carbon dioxide gas to replace the original gas in the stainless steel pressure reaction kettle, and replacing for three times;

step two, introducing sufficient carbon dioxide gas into the stainless steel pressure reaction kettle, starting a stirrer for stirring, gradually raising the temperature to 70 ℃, boosting the pressure to 15MPa, and inducing crystallization for 60-120 min;

and step three, observing through a sight glass of the stainless steel pressure reaction kettle, opening a vent valve at the top of the kettle when the crystallinity of the PBAT is more than 25 percent or the amorphous state of the surface is eliminated, and slowly releasing the pressure to the micro-positive pressure. The pressure relief is specifically realized by keeping the temperature at 70 ℃; the pressure relief rate is 1MPa/min, and the pressure is relieved to micro positive pressure;

step four, grinding and crushing the crystal particles discharged from the bottom of the kettle, screening out 30-40 mesh particle screen, then placing the screen in an open culture dish, placing the screen in an oven, and drying for 1.5 hours at the drying temperature of 80 ℃;

and step five, carrying out solid phase polycondensation on the dried PBAT particles, maintaining the reaction temperature at 100-140 ℃, the reaction pressure at 40KPaG, and the reaction time at 2-18 h. And adopting carbon dioxide gas as fluidizing gas, controlling the flow rate of the carbon dioxide gas at 3-50L/min, stopping heating after the specified reaction degree is reached, and cooling to normal temperature.

Finally, the PBAT material with high molecular weight, narrow molecular weight distribution and high density is obtained, so that the PBAT material has the advantages of good mechanical property, very low content of residual monomers, no peculiar smell, good color (white) and excellent hydrolysis resistance.

In examples 1 to 9, the time for induced crystallization, the time for solid phase polycondensation reaction, the temperature for solid phase polycondensation reaction, the particle size for solid phase polycondensation, and the flow rate of carbon dioxide were changed in this order. In comparative example 1, PBAT feedstock particles were used. In comparative example 2, in order to add epoxy group chain extender ADR-4730S chain extender of BASF company of Germany, the addition amount of the chain extender is 0.7 wt% of the mass of PBAT particles, the preparation method is that PBAT raw material particles are added into a double-screw extruder from a main feeding port, and the chain extender is added into the double-screw extruder from an auxiliary feeding port by a peristaltic pump, thus preparing PBAT material.

In examples 1 to 9, the time for inducing crystallization, the SSP pellets, the SSP reaction time, the SSP reaction temperature, and the carbon dioxide flow rate are shown in Table 1.

Table 1: example parameter settings

The product polymer weight average molecular weight was measured by GPC method and PBAT density was measured according to the hydrometer bottle method of GB/T1033.1-2008, and the results are shown in Table 2 below.

Table 2: weight average molecular weights of examples 1 to 9 and comparative examples 1 to 2

Table 2 shows that increasing the SSP time significantly increases the weight average molecular weight and density. The weight average molecular weight and density of the PBAT material prepared by the method are superior to those of a comparative example.

Crystallization behavior and thermal performance testing: measured using a differential scanning calorimeter (DSC,214Polyma, NETZSCH, Germany), nitrogen atmosphere.

Weighing 5-10 mg of test sample, in a non-isothermal melting crystallization test, heating the sample to 170 ℃ at a speed of 50 ℃/min from room temperature, keeping the temperature for 3min to eliminate thermal history, then cooling to-70 ℃ at a speed of 10 ℃/min, keeping the temperature for 3min at-70 ℃, and then heating to 170 ℃ at a speed of 10 ℃/min. In the cooling process at 10 ℃/min, the peak temperature of the exothermic peak is the melting crystallization temperature (Tc), and the area of the exothermic peak is the crystallization enthalpy (Delta Hc). In the course of temperature rise at 10 ℃/min, the peak temperature of the endothermic peak is the melting temperature (Tm), and the area of the endothermic peak is the melting enthalpy (. DELTA.Hm).

In the isothermal melt crystallization test, the sample is heated from room temperature to 170 ℃ at 50 ℃/min, and after the heat history is eliminated by keeping for 3min, the sample is rapidly cooled to 70 or 80 ℃ at 100 ℃/min, and the sample is kept for enough time to completely crystallize the polymer. Based on the data of isothermal crystallization, the semicrystallization time (t1/2) was calculated from the Avrami equation, in a specific way according to the document ACS Applied Materials & Interfaces,2009,1, 402-. The crystallinity is calculated as follows:

middle X type_PBAT-degree of crystallinity of PBAT%

ΔH_mMelting enthalpy of PBAT, J/g

Standard enthalpy of fusion at melting (114J/g)

Table 3: thermal performance parameters for examples 1, 2, 9 and comparative examples 1, 2

The higher the Tc and the Δ Hc, the higher the crystallization rate of the sample, the higher the crystallinity, and the better the modification effect of the induced crystallization. From table 3 it is shown that the crystallization temperature of pure PBAT in comparative example 1 is 52.5 deg.c, and that the crystallinity is significantly improved after crystallization is induced using supercritical CO 2. As can be seen by comparing examples 1, 2 and 9, the higher the crystallinity is, the longer the induction time is.

On the other hand, in order to study the influence of solid condensation on the mechanical properties of the PBAT material, the samples prepared in example 1 and comparative examples 1 and 2 were melted at 160 ℃ for 2min and then hot-pressed to form a film by a flat vulcanizing machine, the film was crystallized in a constant temperature oven at 85 ℃ for a certain time, and then cut into standard dumbbell-shaped sample bars, the length of which was 50mm, the cross-sectional width was 4.0mm, and the thickness was about 0.5 mm. And (4) performing unidirectional tensile test by using a universal material testing machine, wherein the tensile rate is 20.0 mm/min. Each sample was tested in at least five replicates and then averaged.

As can be seen from tables 1 and 4, the young's modulus, yield strength, and elongation at break of the PBAT material both increased with increasing solid phase polycondensation time, and the tensile strength was also reduced as limited by the elongation at break. The PBAT material prepared by solid phase polycondensation is slightly superior to a sample added with a nucleating agent in the aspects of Young modulus, yield strength, elongation at break and tensile strength mechanical properties.

Table 4: mechanical Property parameters of example 1 and comparative examples 1 and 2

Measuring the colour values according to GB/T14190-2008 at 5.5.2 using the CIE1976L a b color series

Table 5: color values of examples 1 and 9 and comparative examples 1 and 2

The test results show that the transparency of the PBAT material is reduced and the color is whitish along with the increase of the induced crystallization time, and meanwhile, the supercritical CO2 has the extraction/devolatilization function, so that small molecular substances in the PBAT polycondensation stage can be effectively removed, the content of residual monomers in the PBAT material is low, and no peculiar smell is generated.

Finally, it should be noted that the above-mentioned list is only a specific embodiment of the present invention. It is obvious that the present invention is not limited to the above embodiments, but many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.