CN115677986A - Preparation method of thermal aging-resistant degradable aliphatic polyester - Google Patents
Preparation method of thermal aging-resistant degradable aliphatic polyester Download PDFInfo
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Abstract
The invention discloses a preparation method of heat-aging-resistant degradable aliphatic polyester. The method comprises the following steps: (1) Prepolymerizing a molten material of a cyclic ester monomer in a static mixer to obtain a hydroxycarboxylic acid prepolymer; (2) Finally polymerizing the hydroxycarboxylic acid prepolymer through tackifying equipment, and granulating to obtain granular polyhydroxycarboxylic acid; and (3) heating the granular polyhydroxycarboxylic acid under negative pressure to obtain the heat aging resistant degradable aliphatic polyester.
Description
Technical Field
The invention relates to the field of polymer preparation, in particular to a preparation method of heat-aging-resistant degradable aliphatic polyester.
Background
Degradable aliphatic polyesters, such as polyglycolic acid, polylactic acid, and polyglycolic acid-lactic acid copolymers, are considered to be biodegradable polymer materials with little environmental impact, because they are degradable by microorganisms or enzymes present in nature, such as soil, rivers, and sea. The degradable aliphatic polyester can be synthesized by, for example, dehydration polycondensation of α -hydroxycarboxylic acid such as glycolic acid or lactic acid, but the molecular weight of the polymer obtained by direct dehydration polycondensation is low and the melt processing strength is poor, and in order to efficiently synthesize a polymer having a relatively high molecular weight, an intermolecular cyclic di-ester of α -hydroxycarboxylic acid may be synthesized first and then subjected to ring-opening polymerization, and for example, glycolide, which is an intermolecular cyclic di-ester of glycolic acid, may be subjected to ring-opening polymerization to prepare high-molecular-weight polyglycolic acid, or lactide, which is an intermolecular cyclic di-ester of lactic acid, may be subjected to ring-opening polymerization to prepare high-molecular-weight polylactic acid. However, during the ring-opening polymerization of cyclic esters, unreacted cyclic ester monomers inevitably remain in the finally produced polyester product, and these remaining monomers induce side reactions such as thermal degradation of the polymer under the influence of high temperature during the subsequent melt-molding process of the polyester, which seriously affect the properties (e.g., mechanical strength, aging resistance, etc.) of the final material. In addition, existing reactive extrusion equipment (e.g., reactive twin-screw extruders) for producing aliphatic polyesters such as polyglycolic acid generally require polymerization of glycolide at a relatively high reaction temperature (e.g., 220 to 240 ℃) in order to obtain products having a relatively high molecular weight in practical use. However, a higher reaction temperature not only means high energy consumption, but also easily causes great or severe thermal degradation of the produced polyglycolic acid, which is not beneficial to the improvement of the molecular weight of the final product, and also causes the broadening of the molecular weight distribution of the final product, which can cause adverse effects on the mechanical properties, aging resistance and the like of the material, thereby not only increasing the uncertainty of the service cycle of the material, but also greatly limiting the application range and the service life of the material.
Therefore, there is a strong need in the art to provide a method for preparing a degradable aliphatic polyester, which is effective in reducing the residue of cyclic ester monomers and can avoid high temperature polymerization.
Disclosure of Invention
The invention aims to provide a preparation method of degradable aliphatic polyester.
The invention provides a preparation method of heat aging resistant degradable aliphatic polyester, which comprises the following steps:
(1) Prepolymerizing a molten material of a cyclic ester monomer in a static mixer to obtain a hydroxycarboxylic acid prepolymer;
(2) Finally polymerizing the hydroxycarboxylic acid prepolymer through tackifying equipment, and granulating to obtain granular polyhydroxycarboxylic acid; and
(3) The granular polyhydroxycarboxylic acid is subjected to negative pressure heating treatment to obtain the heat-aging-resistant degradable aliphatic polyester.
In another embodiment, the molten mass of cyclic ester monomer in step (1) contains reaction aids including a catalyst, a polyol, and a dehydrating agent.
In another embodiment, the catalyst is used in an amount of 0.001 to 1wt% thereof, the polyol is used in an amount of 0.01 to 0.1wt% thereof, and the dehydrating agent is used in an amount of 0.1 to 2wt% thereof, based on the mass of the cyclic ester monomer.
In another embodiment, the catalyst is selected from at least one of tin-based compounds, antimony-based compounds, or zinc-based compounds; the dehydrating agent is selected from at least one of carbodiimide, polycarbodiimide or a carbodiimide-based compound.
In another embodiment, the polyol is selected from at least one of 1,4-butanediol, glycerol, pentaerythritol, xylitol, sorbitol, 1,6-hexanediol, triethylene glycol, and dipropylene glycol.
In another embodiment, the static mixer used in step (1) is a gradient mixer with at least 2 stages, the first stage being in the range of 120-180 ℃ and the last stage being in the range of 180-200 ℃.
In another embodiment, the second section of the static mixer is increased in temperature by between 10-80 ℃ over the first section; the temperature of the last section is increased by 0-20 ℃ compared with the temperature of the previous adjacent section.
In another embodiment, the tackifying equipment in step (2) is devolatilized at an absolute pressure of less than or equal to 500Pa and a temperature of 220 to 250 ℃.
In another embodiment, the particle size of the granulated polyhydroxycarboxylic acid obtained in step (2) is 10mm or less.
In another embodiment, the negative pressure heat treatment condition in the step (3) is that the absolute pressure is less than or equal to 1kPa, and the temperature is 100-220 ℃.
Accordingly, the invention provides a preparation method of degradable aliphatic polyester, which can effectively reduce the residue of cyclic ester monomer and avoid high-temperature polymerization.
Detailed Description
The inventors have made extensive and intensive studies to allow a polymerization reaction to be carried out in a static mixer, to minimize the influence of oxygen and moisture on the polymerization reaction, and to enable a molecular chain to be stably extended for a longer period of time in the polymerization reaction; the activation energy of the ring-opening polymerization reaction of the cyclic ester monomer is reduced by the reaction auxiliary agent formed by compounding the catalyst, the polyhydric alcohol and the dehydrating agent, so that the ring-opening polymerization reaction of the cyclic ester can be carried out in a reaction system at a lower temperature to generate the polyhydroxycarboxylic acid with high molecular weight and relatively narrow molecular weight distribution, and the content of the residual cyclic ester monomer in the polyhydroxycarboxylic acid product can be reduced; and finally, granulating the polyhydroxycarboxylic acid prepared by final polymerization of tackifying equipment, and then carrying out negative pressure heating treatment, and timely removing residual cyclic ester monomers from product particles under the action of negative pressure, so that the content of the residual cyclic ester monomers in the polyhydroxycarboxylic acid product can be further reduced. On the basis of this, the present invention has been completed.
Definition of
The tackifying equipment plays a role in devolatilizing, can promote the further polymerization of the hydroxycarboxylic acid prepolymer, and timely remove the generated micromolecules to further improve the molecular weight of the polymer and correspondingly further increase the viscosity of the polymer; the "tackifying means" in the present invention may be, for example, but not limited to, a twin-screw extruder provided with only a devolatilization section.
As used herein, "cyclic ester monomer" refers to a bimolecular cyclic ester or lactone of an alpha-hydroxycarboxylic acid, for example, but not limited to, one or a mixture of two or more of glycolide, which is a bimolecular cyclic ester of glycolic acid, lactide, which is a bimolecular cyclic ester of lactic acid, beta-butyrolactone, delta-valerolactone, epsilon-caprolactone, and the like.
As used herein, "hydroxycarboxylic acid" refers to alpha-hydroxycarboxylic acids such as, but not limited to, glycolic acid, lactic acid, alpha-hydroxybutyric acid, alpha-hydroxyvaleric acid, alpha-hydroxycaproic acid, and the like.
As used herein, "polyhydroxycarboxylic acid" refers to a polymer prepared by ring-opening polymerization of a cyclic ester and/or lactone monomer, and examples thereof include, but are not limited to, polyglycolic acid, polylactic acid, polyglycolic acid-lactic acid copolymers, polyepsilon-caprolactone, polyglycolic acid-epsilon-caprolactone copolymers, and the like.
Preparation method
The invention provides a preparation method of heat aging resistant degradable aliphatic polyester, which comprises the following steps:
firstly, adding a cyclic ester monomer into a melting and mixing kettle, adding a reaction auxiliary agent into the melting and mixing kettle after the cyclic ester monomer is completely melted, and uniformly mixing the melted cyclic ester monomer and the reaction auxiliary agent to obtain a melted material of the cyclic ester monomer;
secondly, introducing the molten material of the cyclic ester monomer into a static mixer for prepolymerization to obtain a hydroxycarboxylic acid prepolymer;
and thirdly, final polymerization is carried out on the hydroxycarboxylic acid prepolymer in tackifying equipment to generate polyhydroxycarboxylic acid, and the granulated polyhydroxycarboxylic acid obtained by granulation is subjected to negative pressure heating treatment to obtain the product, namely the heat-aging-resistant degradable aliphatic polyester.
In the first step, the purity of the used cyclic ester monomer is not less than 98 percent; preferably not less than 98.5%, and acidity not exceeding 20mmol/kg. In one embodiment of the present invention, glycolide is used in the first step.
The melting temperature is selected in the first step above according to the cyclic ester monomer, and in one embodiment of the invention, the glycolide is completely melted at 90-120 ℃.
The reaction auxiliary used in the above first step comprises a catalyst, a polyhydric alcohol and a dehydrating agent; in terms of the amount of the reaction assistant, the catalyst is used in an amount of about 0.001 to 1wt% based on the mass of the cyclic ester monomer, the polyol is used in an amount of about 0.01 to 0.1wt% based on the mass of the cyclic ester monomer, and the dehydrating agent is used in an amount of about 0.1 to 2wt% based on the mass of the cyclic ester monomer.
The catalyst may be selected from at least one of tin-based compounds, antimony-based compounds, or zinc-based compounds, such as, but not limited to, stannous octoate, stannous chloride, tin lactate, antimony trioxide, diethyl zinc, or zinc acetate dihydrate.
The polyalcohol can be one or more selected from 1,4-butanediol, glycerol, pentaerythritol, xylitol, sorbitol, 1,6-hexanediol, triethylene glycol and dipropylene glycol.
The dehydrating agent may be selected from a carbodiimide, a polycarbodiimide, or a carbodiimide-based compound (such as, but not limited to, N' -diisopropylcarbodiimide, dicyclohexylcarbodiimide, etc.).
To prevent local excess concentrations of the reaction aid in molten glycolide, in one embodiment of the invention, the reaction aid may be added drop-wise to the melt-mixing kettle by injection.
As an embodiment, the molten material of the cyclic ester monomer in the first step can be obtained by the following method: introducing the cyclic ester monomer into a melting and mixing kettle, heating to completely melt the cyclic ester monomer, and then adding a reaction auxiliary agent into the melting and mixing kettle while stirring to uniformly mix the melted cyclic ester monomer and the reaction auxiliary agent.
The static mixer in the second step adopts at least 2-section gradient heating mode, for example, 2-10 section gradient heating mode; preferably, 3 to 7 stages are employed.
In one embodiment of the invention, the first stage temperature of the static mixer ranges from 120 to 180 ℃, such as but not limited to 140-170 ℃, 150-180 ℃, and the like; the final temperature range is 180-200 deg.C, such as but not limited to 180-190 deg.C, 190-200 deg.C, etc.
In one embodiment of the invention, the second stage of the static mixer is increased in temperature by between 10-80 ℃ over the first stage, such as but not limited to 40-50 ℃, 20-70 ℃, 30-60 ℃, etc.; the last stage is raised from the temperature of the previous adjacent stage by 0-20 deg.C, such as but not limited to 0-15 deg.C, 5-10 deg.C, etc.
In one embodiment of the invention, the static mixer is provided with three sections, wherein the temperature of the first section is set to be 120-180 ℃, the temperature of the second section is set to be 180-190 ℃, and the temperature of the third section is set to be 190-200 ℃.
In one embodiment of the invention, the static mixer is provided with four sections, wherein the temperature of the first section is set to be 120-150 ℃, the temperature of the second section is set to be 150-180 ℃, the temperature of the third section is set to be 180-190 ℃, and the temperature of the fourth section is set to be 190-200 ℃.
In one embodiment of the invention, the static mixer is provided with five sections, wherein the temperature of the first section is set to be 120-150 ℃, the temperature of the second section is set to be 150-170 ℃, the temperature of the third section is set to be 170-180 ℃, the temperature of the fourth section is set to be 180-190 ℃, and the temperature of the fifth section is set to be 190-200 ℃.
In one embodiment of the invention, the total length of time the material is in the static mixer during operation is generally not more than 150 minutes, such as, but not limited to, 60-90 minutes.
The weight average molecular weight of the hydroxycarboxylic acid prepolymer obtained in the above second step is about 5 to 15 ten thousand.
In the above-mentioned third step, the viscosity increasing means may be, for example, a twin-screw extruder provided only with a devolatilization section, and the final polymerization is carried out under conditions of an absolute pressure of 500Pa or less and a temperature of 220 to 250 ℃ to devolatilize the residual cyclic ester monomer so that the content of the residual cyclic ester monomer is reduced to 0.3 to 1% by weight (calculated by dividing the mass of glycolide remaining in the polymer obtained by the final polymerization by the mass of the polymer obtained by the final polymerization).
It should be noted that, in the present invention, the tackifying device plays a role in devolatilizing, which can promote further polymerization of the hydroxycarboxylic acid prepolymer, and remove the generated small molecules in time, so as to further increase the molecular weight of the polymer.
The third step may be pelletized using methods conventional in the art, such as, but not limited to, conventional extrusion pelletization, underwater pelletizing, and the like.
In one embodiment of the present invention, the particle size of the granulated polyhydroxycarboxylic acid in the third step is 10mm or less.
In one embodiment of the present invention, the pelletized polyhydroxycarboxylic acid in the third step is subjected to a negative pressure heating treatment in an evacuable pressure vessel (for example, but not limited to, an evacuable pressure tank or the like) under conditions of: controlling the absolute pressure to be less than or equal to 1kPa and the temperature to be 100-220 ℃.
The molecular weight distribution index of the heat aging resistant degradable aliphatic polyester prepared by the method of the present invention is not more than about 1.6, such as, but not limited to, about 1.2 to 1.5.
The thermal aging resistant degradable aliphatic polyester product prepared by the method has the content of residual cyclic ester monomer not more than 0.1wt% based on the total mass of the product.
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
All features defined herein as numerical ranges or percentage ranges, such as values, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.
As used herein, the term "about" when used to modify a numerical value means within 5% of the error margin measured for that value.
The features mentioned above with reference to the invention, or the features mentioned with reference to the embodiments, can be combined arbitrarily. All features disclosed in this specification may be combined in any combination, provided that there is no conflict between such features and the combination, and all possible combinations are to be considered within the scope of the present specification. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, the features disclosed are merely generic examples of equivalent or similar features.
The main advantages of the invention are:
1. the method comprises the steps of coupling a melt mixing kettle with a static mixer, fully and uniformly mixing cyclic ester (such as glycolide) and a reaction auxiliary agent through the melt mixing kettle to obtain a premix, introducing the premix into the static mixer for prepolymerization, creatively utilizing high-efficiency mixing to play a role in low-shear high-dispersion on the premix, being beneficial to preventing and eliminating heat accumulation in local areas in materials, and effectively preventing the local areas from being overhigh in temperature and causing side reactions such as thermal degradation and the like due to uneven heating in the materials, so that the cyclic ester (such as glycolide) can be ensured to perform good prepolymerization reaction, obtain hydroxycarboxylic acid prepolymer (such as glycolic acid prepolymer) with certain molecular weight, introducing the hydroxycarboxylic acid prepolymer (such as glycolic acid prepolymer) into tackifying equipment (such as a double-screw extruder only provided with a devolatilization section) for final polymerization, effectively shortening the time of the high shearing action of the materials in the tackifying equipment, being beneficial to inhibiting the side reactions such as thermal degradation and the occurrence of ester exchange reaction, thereby reducing the content of low polymer and/or low-molecular weight of the prepared substances, and improving the molecular weight distribution of the polyhydroxylated acid molecules (such as polyglycolic acid) to be relatively small molecular weight.
2. The invention introduces the fluid premix of the molten cyclic ester (such as glycolide) into a static mixer, utilizes a cross flow mode to enhance the mixing effect between the cyclic ester (such as glycolide) and the reaction auxiliary agent, so that the reaction auxiliary agent can be more uniformly dispersed in the reaction system, simultaneously utilizes a gradient temperature rising mode to firstly mildly initiate the ring-opening polymerization reaction of the cyclic ester (such as glycolide) at a relatively low temperature and in a relatively short time, then appropriately raise the temperature and appropriately prolong the time so as to form a more stable and reactive hydroxycarboxylic acid molecular chain (such as glycolic acid molecular chain) in the reaction system, and then further promote the growth of the hydroxycarboxylic acid molecular chain (such as glycolic acid molecular chain) at a relatively high temperature and in a relatively long time so as to obtain the hydroxycarboxylic acid prepolymer (such as glycolic acid prepolymer) with a certain molecular weight.
3. In the aspect of reaction auxiliary agents, the catalyst is compounded with the polyhydric alcohol and the dehydrating agent, wherein the introduction of the polyhydric alcohol is beneficial to reducing the activation energy of the ring-opening polymerization reaction of the cyclic ester (such as glycolide), so that the ring-opening polymerization reaction of the cyclic ester (such as glycolide) can be carried out at a lower temperature (compared with the common case that the glycolide needs to carry out the ring-opening polymerization at 220-230 ℃) to generate the polyhydroxycarboxylic acid (such as polyglycolic acid) with high molecular weight and narrow molecular weight distribution, the monomer conversion rate is beneficial to being improved, the polymerization energy consumption can be effectively reduced, the carbonization generation is low, and the lower polymerization temperature is beneficial to reducing or inhibiting the thermal degradation degree of the polyhydroxycarboxylic acid (such as polyglycolic acid) generated in the polymerization process, so that the finally obtained polyhydroxycarboxylic acid (such as polyglycolic acid) has good mechanical strength and thermal aging resistance.
4. The main polymerization reaction of the invention is carried out in a static mixer, compared with a double-screw extruder in a dynamic mixing range, the static mixer has better air tightness and can reduce the influence of oxygen and moisture on the polymerization reaction to the maximum extent.
5. The method granulates the polyhydroxycarboxylic acid (such as polyglycolic acid) prepared by final polymerization of tackifying equipment (such as a twin-screw extruder only provided with a devolatilization section), and then carries out negative pressure heating treatment, so that residual monomers (such as residual glycolide) in product particles are heated and can be timely removed from the product particles under the action of negative pressure, thereby obtaining the granulated polyhydroxycarboxylic acid product with the residual monomers (such as residual glycolide) reduced as much as possible, and being beneficial to further improving the heat aging resistance of the material.
6. The device provided by the invention is suitable for industrial scale-up production, can be used for modifying a production line by using the existing production equipment, has good flexibility and applicability, can realize stable output of polyhydroxycarboxylic acid (such as polyglycolic acid) products, realizes low-carbonization production, and has good economic benefit.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers. All percentages, ratios, proportions, or parts are by weight unless otherwise specified. The weight volume percentage units in the present invention are well known to those skilled in the art and refer to, for example, the weight (g) of solute in 100ml of solution. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.
The cyclic ester reaction mass (e.g., glycolide) used in the examples below, wherein the glycolide content was determined using gas chromatography methods well known in the art, and the acidity was determined using potentiometric titration methods well known in the art (e.g., using an automated potentiometric titrator).
The content of residual monomer (i.e., glycolide) in the obtained polyglycolic acid was measured by the following method:
about 300mg of the sample was heated in about 6g of dimethyl sulfoxide (DMSO) at 150 ℃ for about 10min, dissolved, cooled to room temperature, and then filtered. To this filtrate was added a quantity of the internal standard 4-chlorobenzophenone and acetone. 2. Mu.l of this solution was measured and injected into a gas chromatograph to measure.
As used herein, "distribution index" is a parameter D representing the width of molecular weight distribution, D = M (w)/M (n), where M (w) is the weight average molecular weight, M (n) is the number average molecular weight, D =1 is a polymer of uniform molecular weight, and the value of D is broader in its molecular weight distribution and greater in the degree of polydispersity as the value of D is greater than 1. The measurement method generally includes measuring M (w) and M (n) of a sample by Gel Permeation Chromatography (GPC), and calculating the ratio of the two.
For the test of the molecular weight and the distribution of polyglycolic acid, gel Permeation Chromatography (GPC) method is used for the test, which is as follows:
a0.2 g sample of PGA was dissolved in 100mL of hexafluoroisopropanol solution having a sodium trifluoroacetate content of 5mmol/L, filtered through a polytetrafluoroethylene filter having a pore size of 0.4. Mu.m, and 20. Mu.L of the filtrate was introduced into an "LC-20AD GPC" sample injector manufactured by Shimadzu (Japan) under test conditions: the column temperature is 40 ℃; eluent: hexafluoroisopropanol with 5mmol/L of sodium trifluoroacetate dissolved therein; the flow rate is 1mL/min; a detector: an RI detector; and (3) correction: molecular weight correction was performed using five different standards of polymethyl methacrylate varying in molecular weight between 7000 and 200000.
The following examples 1-6 are given by way of example of the preparation of polyglycolic acid by the following method:
step 1): mixing glycolide (D) 90 Not more than 200 mu m, the purity not less than 98.5 percent and the acidity not more than 20 mmol/kg), heating at 90-120 ℃ to completely melt the mixture, adding a reaction auxiliary agent into the melt mixing kettle while stirring to uniformly mix the molten cyclic ester and the reaction auxiliary agent to obtain a molten material of glycolide, and introducing the molten material of glycolide into a static mixer for prepolymerization to obtain a glycolic acid prepolymer with a certain molecular weight;
step 2): carrying out final polymerization on the glycolic acid prepolymer prepared in the step 1) in tackifying equipment, carrying out conventional extrusion granulation on the generated polyglycolic acid to obtain granular polyglycolic acid with the particle size of less than or equal to 10mm, and carrying out negative pressure heating treatment.
In the step 1), in order to prevent the concentration of the molten glycolide local reaction auxiliary agent from being too high, the reaction auxiliary agent can be dropwise added into the melting and mixing kettle by adopting an injection mode.
The amounts of the reaction assistants added in examples 1 to 6 are shown in the following tables 1 to 1.
TABLE 1-1
The kinds of reaction assistants used in examples 1 to 6 were selected as shown in tables 1 to 2 below.
Tables 1 to 2
The heating temperatures of the melt mixing kettle in examples 1-6 are shown in tables 1-3 below.
Tables 1 to 3
| Item | Example 1 | Example 2 | Example 3 | Example 4 | Example 5 | Example 6 |
| Temperature (. Degree.C.) | About 90 | About 110 | About 120 | About 115 | About 118 | About 106 |
Note: the time from the time each batch of glycolide powder entered the melt-mixing kettle to the time the premix was obtained was about 20min.
The temperature parameters of the stages of the static mixer of examples 1-6 are shown in tables 2-1 below:
TABLE 2-1
| Item | Static mixer | First stage | Second section | Third stage | Fourth stage | Fifth stage |
| Example 1 | Three segments in total | About 120 deg.C | About 180 deg.C | About 190 deg.C | / | / |
| Example 2 | Three segments in total | About 178 deg.C | About 190 deg.C | About 200 deg.C | / | / |
| Example 3 | Four sections in total | About 120 deg.C | About 150 deg.C | About 180 deg.C | About 198 deg.C | / |
| Example 4 | Four sections in total | About 150 deg.C | About 160 deg.C | About 190 deg.C | About 200 deg.C | / |
| Example 5 | Five sections in total | About 125 deg.C | About 165 deg.C | About 175 deg.C | About 180 deg.C | About 195 deg.C |
| Example 6 | Five sections in total | About 152 deg.C | About 170 deg.C | About 180 deg.C | About 190 deg.C | About 200 deg.C |
The time required for the material to pass through the stages in the static mixer of examples 1-6 is shown in tables 2-2 below:
tables 2 to 2
| Item | Static mixer | First stage | Second section | Third stage | Fourth stage | Fifth stage |
| Example 1 | Three segments in total | About 5min | About 15min | About 70min | / | / |
| Example 2 | Three segments in total | About 5min | About 15min | About 70min | / | / |
| Example 3 | Four sections in total | About 5min | About 10min | About 15min | About 60min | / |
| Example 4 | Four sections in total | About 5min | About 10min | About 15min | About 60min | / |
| Example 5 | Five sections in total | About 5min | About 5min | About 10min | About 15min | About 55min |
| Example 6 | Total five sections | About 5min | About 5min | About 10min | About 15min | About 55min |
The tackifying apparatuses used in examples 1 to 6 were twin-screw extruders provided with only a devolatilization section, whose devolatilization section parameters were set as shown in the following table 3-1:
TABLE 3-1
| Item | Temperature (. Degree.C.) | Absolute pressure (Pa) | Length-diameter ratio of screw | Screw rotation speed (r/min) |
| Example 1 | About 220 | About 200 | 55 | 30 |
| Example 2 | About 228 | About 120 | 50 | 45 |
| Example 3 | About 230 | About 150 | 50 | 40 |
| Example 4 | About 236 | About 250 f | 55 | 35 |
| Example 5 | About 250 f | About 500 | 60 | 50 |
| Example 6 | About 240 | About 100 | 50 | 45 |
Note: the time for the materials to pass through the devolatilization section of the tackifying equipment is controlled to be about 15min
The residual glycolide monomer content of the polyglycolic acid produced by the final polymerization of the tackified devices in examples 1 to 6 is shown in the following table 3-2: (the content is based on the total mass of polyglycolic acid obtained by final polymerization)
TABLE 3-2
The process parameters for the negative pressure heat treatment in examples 1-6 are shown in Table 4 below:
TABLE 4
The weight average molecular weight of the glycolic acid prepolymer formed by the static mixer, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index and the residual glycolide content of the finally obtained polyglycolic acid in examples 1 to 6 are shown in table 5 below:
TABLE 5
Comparative example 1
This comparative example is substantially the same as example 6, except that the reaction aid used comprises only the catalyst (i.e., stannous octoate mixed with antimony trioxide at a mass ratio of 2:1) in the same amount as in example 6.
Comparative example 2
This comparative example is substantially the same as example 6 except that the reaction assistant used comprises only the catalyst (i.e., stannous octoate mixed with antimony trioxide in a mass ratio of 2:1) and the dehydrating agent (i.e., carbodiimide), and the amounts of the catalyst and the dehydrating agent are the same as in example 6.
Comparative example 3
This comparative example is substantially the same as example 6 except that the negative pressure heating treatment was not performed, and the remainder was the same as example 6.
Comparative example 4
This comparative example used glycolide powder (D) 90 No more than 200 μm, purity no less than 98.5%, acidity no more than 20 mmol/kg), polyglycolic acid was prepared by a conventional reaction type twin-screw extruder (without using a static mixer), the reaction assistant used and the amount thereof used were the same as in example 6, and polyglycolic acid pellets (particle size no more than 10 mm) prepared by the reaction type twin-screw extruder were treated at an absolute pressure of 100Pa at 218 ℃ for 3 hours.
In this comparative example, the specific process conditions of the reactive twin-screw extruder are shown in the following Table 6-1.
TABLE 6-1
Note: glycolide powder and reaction aid in comparative example 4All the agents are added at the beginning of the first section of the mixing section, and the absolute pressure of the devolatilization section is controlled to be 100P a
Comparative example 5
This comparative example used glycolide powder (D) 90 No more than 200 mu m, the purity no less than 98.5 percent and the acidity no more than 20 mmol/kg), and preparing polyglycolic acid by a conventional reaction type twin-screw extruder (without using a static mixer), wherein the used reaction auxiliary agent only comprises a catalyst (namely stannous octoate and antimony trioxide are mixed according to the mass ratio of 2:1), the using amount of the catalyst is the same as that of the example 6, and the polyglycolic acid granules (the grain diameter is no more than 10 mm) prepared by the reaction type twin-screw extruder are treated for 3 hours under the conditions of the absolute pressure of 100Pa and the temperature of 218 ℃.
In this comparative example, the specific process conditions of the reactive twin-screw extruder are shown in Table 6-2 below.
TABLE 6-2
Note: in comparative example 5, glycolide powder and the reaction assistant were added from the beginning of the first stage of the mixing section, and the absolute pressure of the devolatilization section was controlled to 100P a
In the above comparative examples 4 and 5, the screw length-diameter ratios and the screw rotation speeds of the respective stages in the conventional reaction type twin-screw extruder are shown in the following tables 6 to 3.
Tables 6 to 3
| Item | Screw length to diameter ratio of mixing section | Length-diameter ratio of screw in reaction section | Length-diameter ratio of screw of devolatilization section | Screw rotation speed ( r / m i n ) |
| Reaction type double-screw extruder | 35 | 70 | 54 | 45 |
The polyglycolic acid obtained by the above comparative examples 1 to 5 has a number average molecular weight, a weight average molecular weight, a molecular weight distribution index and a residual glycolide content, see the following Table 7.
TABLE 7
Performance testing
The tensile strength and elongation at break of the PGAs obtained in examples 1-6 and comparative examples 1-5 were measured according to GB/T1040.1-2006 test standards, and the specific test results are shown in Table 8 below:
TABLE 8 test results
Note: the tensile rate in the above tensile test was 50mm/min
Based on the test results of table 8 above, the data of comparative example 6 and comparative examples 1 to 5 are emphasized. As is clear from table 8, the polyglycolic acid material obtained in example 6 exhibited about 4.7% and 12.5% reductions in tensile strength and elongation at break, respectively, after the hot air aging test. The polyglycolic acid material obtained in the comparative example 3 which is most similar to the polyglycolic acid material obtained in the example 6 has the tensile strength and the elongation at break which are respectively reduced by about 11.3 percent and 19.0 percent after being subjected to the hot air aging test, and are obviously higher than the results of the example 6; this is probably because the negative pressure heating treatment of the granulated polyglycolic acid in example 6 can effectively remove the residual glycolide from the polyglycolic acid product, which can reduce the influence of the residual glycolide on the heat aging resistance of the PGA product as much as possible, and specifically can maintain the mechanical strength of the material well without causing a rapid deterioration in the mechanical strength of the material.
As for comparative examples 1 and 2, in comparison with example 6, the reaction assistant of comparative example 1 contains only a catalyst, the reaction assistant of comparative example 2 contains only a catalyst and a dehydrating agent, and the reaction assistant of both pairs contains no polyol, which may be disadvantageous in reducing the activation energy of the ring-opening polymerization of glycolide, so that the degree of reaction is reduced in comparison with example 6, and the increase in molecular weight of the product is disadvantageous, which also makes the PGA products obtained in comparative examples 1 and 2 lower in mechanical strength than in example 6; in addition to this effect, it may be disadvantageous to reduce the residual glycolide content in the final PGA product, which may result in a material having a greater degree of deterioration of mechanical strength under relatively high temperature and humidity conditions, as compared to the PGA products of comparative examples 1 and 2, as compared to example 6.
Comparing the results of the tests in table 8, it can be seen that the mechanical strength and thermal aging resistance of the PGA material produced by the conventional reaction type twin-screw extruder are significantly weaker than those of example 6, probably because the conventional reaction type twin-screw extruder has poor air tightness and heat transfer effect, and the high shear thereof easily causes the local temperature of the reaction system to rise too fast, so that side reactions such as thermal degradation and the like occur early, which is not beneficial to the increase of the molecular weight of the final product, and also causes the molecular weight distribution of the final product to widen, which results in a significant decrease in the mechanical strength and thermal aging resistance of the final PGA material, compared with example 6 in comparative examples 4 and 5, which employ the conventional reaction type twin-screw extruder to produce polyglycolic acid (without using a static mixer).
The materials obtained in example 6 and comparative examples 1 to 5 were subjected to a thermal weight loss test (purged atmosphere: 20ml/min of nitrogen gas; crucible: al2O3 without lid; heating rate: 5 ℃/min) using a thermal analyzer (model: NETZSCH STA 2500), and the temperatures corresponding to 3% mass loss of the materials were measured, respectively, and the test results are shown in Table 9 below.
TABLE 9 results of thermo-gravimetric test of materials
From the test results in Table 9, it can be seen that the polyglycolic acid product obtained according to example 6 of the process of the present invention has excellent heat aging resistance, and the temperature corresponding to 3% mass loss is about 283 ℃ as compared with the temperature corresponding to 3% mass loss of the polyglycolic acid material obtained according to comparative example 3, which is the closest to example 6, is about 271 ℃ and about 12 ℃ lower than example 6, and this is probably caused by the fact that example 6 employs a negative pressure heat treatment to remove residual monomers (i.e., residual glycolide) from the polyglycolic acid product as much as possible, which is advantageous in improving the heat aging resistance of the material.
In addition, the polyglycolic acid materials obtained in comparative examples 1 and 2 had a mass loss of 3% at temperatures of about 256 ℃ and 262 ℃ respectively, which were significantly lower than those of example 6. Compared with example 6, the reaction auxiliary agent used in comparative example 1 only comprises the catalyst, the reaction auxiliary agent used in comparative example 2 only comprises the catalyst and the dehydrating agent, and the residual monomer (namely residual glycolide) content in the polyglycolic acid products obtained in corresponding comparative examples 1 and 2 is 0.25% and 0.14%, respectively.
Compared with example 6, comparative example 4 adopts a conventional reaction type twin-screw extruder to prepare polyglycolic acid (without using a static mixer), and the high shearing action of the conventional reaction type twin-screw extruder easily causes the local temperature of the reaction system to rise too fast, so that side reactions such as serious thermal degradation and the like are caused, the reduction of the content of residual glycolide in the polyglycolic acid product is not facilitated, the molecular weight distribution of the polyglycolic acid product is widened, the thermal aging resistance of the product is greatly reduced, and the temperature corresponding to the mass loss of 3% of the polyglycolic acid material obtained in comparative example 4 is only about 244 ℃. While comparative example 5 uses a reaction aid comprising only the catalyst as compared to comparative example 4, the temperature corresponding to a 3% mass loss of the polyglycolic acid material obtained in comparative example 5 is lower, only about 232 ℃, which is probably due to an excessive residual glycolide content in the polyglycolic acid product obtained in comparative example 5.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the scope of the invention, which is defined by the claims appended hereto, and any other technical entity or method that is encompassed by the claims as broadly defined herein, or equivalent variations thereof, is contemplated as being encompassed by the claims.
Claims (10)
1. A preparation method of a thermal aging resistant degradable aliphatic polyester is characterized by comprising the following steps:
(1) Prepolymerizing a molten material of a cyclic ester monomer in a static mixer to obtain a hydroxycarboxylic acid prepolymer;
(2) Finally polymerizing the hydroxycarboxylic acid prepolymer through tackifying equipment, and granulating to obtain granular polyhydroxycarboxylic acid;
(3) The granular polyhydroxycarboxylic acid is subjected to negative pressure heating treatment to obtain the heat-aging-resistant degradable aliphatic polyester.
2. The method according to claim 1, wherein the molten material of the cyclic ester monomer in the step (1) contains a reaction auxiliary agent comprising a catalyst, a polyhydric alcohol and a dehydrating agent.
3. The process according to claim 2, wherein the catalyst is used in an amount of 0.001 to 1% by weight, the polyol is used in an amount of 0.01 to 0.1% by weight, and the dehydrating agent is used in an amount of 0.1 to 2% by weight, based on the mass of the cyclic ester monomer.
4. The production method according to claim 2, wherein the catalyst is at least one selected from the group consisting of tin-based compounds, antimony-based compounds, and zinc-based compounds; the dehydrating agent is selected from at least one of carbodiimide, polycarbodiimide, or carbodiimide-based compound.
5. The method of claim 2, wherein the polyol is at least one selected from the group consisting of 1,4 butanediol, glycerol, pentaerythritol, xylitol, sorbitol, 1,6 hexanediol, triethylene glycol, and dipropylene glycol.
6. The method of claim 1, wherein the static mixer used in step (1) is at least 2 stages of gradient temperature rise, the first stage being in the range of 120-180 ℃ and the last stage being in the range of 180-200 ℃.
7. The method of claim 6, wherein the temperature of the second section of the static mixer is increased by between 10-80 ℃ over the temperature of the first section; the temperature of the last section is increased by 0-20 ℃ compared with the temperature of the previous adjacent section.
8. The method according to claim 1, wherein the step (2) is a step of devolatilizing the tackified device at an absolute pressure of 500Pa or less and a temperature of 220 to 250 ℃.
9. The process according to claim 1, wherein the particle size of the granulated polyhydroxycarboxylic acid obtained in the step (2) is 10mm or less.
10. The production method according to claim 1, wherein the negative pressure heat treatment condition in the step (3) is an absolute pressure of 1kPa or less and a temperature of 100 to 220 ℃.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116284698A (en) * | 2023-02-21 | 2023-06-23 | 内蒙古久泰新材料科技股份有限公司 | Production process for simultaneously preparing various molecular weight gradient degradable materials |
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