CN113045739A - Preparation method of melt direct-extrusion PET (polyethylene terephthalate) foam material - Google Patents
Preparation method of melt direct-extrusion PET (polyethylene terephthalate) foam material Download PDFInfo
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
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Abstract
The invention discloses a preparation method of a melt direct-extrusion PET (polyethylene terephthalate) foam material, which comprises the following steps: (1) mixing terephthalic acid, ethylene glycol and a catalyst, and carrying out a first esterification reaction; (2) carrying out a second esterification reaction; (3) preparing a branching agent solution from a mixed branching agent of alpha-triglycidyl isocyanurate and beta-triglycidyl isocyanurate; (4) after the second esterification reaction is finished, adding a branching agent solution, and stirring for reaction; (5) pre-polycondensation reaction; (6) final polycondensation reaction to obtain melt; (7) and conveying the melt into an extruder, injecting a foaming agent, and extruding, foaming and molding. The invention mixes the alpha-type and beta-type triglycidyl isocyanurate as the branching agent, can ensure that the branching agent partially reacts to obtain low-viscosity polyester with good conveying performance during final polycondensation, and the low-viscosity polyester continuously reacts with the remaining branching agent after being conveyed into an extruder to finally obtain high-viscosity high-melt-strength polyester, thereby realizing the integrated process of polymerization and extrusion foaming.
Description
Technical Field
The invention relates to the field of polyester preparation, in particular to a preparation method of a melt direct-extrusion PET (polyethylene terephthalate) foam material.
Background
Polyethylene terephthalate (PET) is a thermoplastic polyester and has the characteristics of high crystallinity, high melting point, corrosion resistance, hydrophobicity, good thermal stability and the like. In 2019, the global PET yield is about 7000 ten thousand tons, and China has about 5000 ten thousand tons of capacity and is the first place in the world. Currently, polyester is mainly used for preparing fibers, films and plastic bottles, and with the expansion of productivity and the reduction of petroleum price, the cost of polyester is lower and lower, and the productivity is excessive. The polyester foam material has the excellent performances of light weight, high specific strength, high rigidity, good electrical insulation, sound and heat insulation and the like, and can be used in the industries of food packaging, building materials, wire insulation, microwave containers, refrigerator inner plates, sports equipment, automobiles, aerospace industry and the like.
After PET foaming molding, the method mainly has the following advantages: (1) the coating has excellent surface barrier property and good barrier property to oxygen, carbon dioxide and water vapor; (2) higher closed cell rate and foaming ratio (up to 40 times); (3) the thermal stability is good, the maximum working temperature is about 200 ℃, and is higher than the working temperature of PS, PU, PVC and PP foams; (4) higher compressive strength, compressive modulus, shear strength and shear modulus; (5) low water absorption and good heat insulation, and is an ideal heat insulation material.
The conventional PET has low molecular weight, narrow molecular weight distribution and linear molecular chain structure, so that the melt strength is low, the increase of cells cannot be effectively supported in the foaming process, and the collapse, the breakage and the opening structure of the cells are easily caused. In the currently disclosed patents, PET with high molecular weight, wide molecular weight distribution, high degree of long chain branching and higher melt strength is obtained mainly by a branching modification method. The in situ polymerization process can produce high melt strength polyesters as desired for direct use in continuous extrusion foaming, such as chinese patent application No.: 201110270665.0, adopting polyatomic alcohol, polyatomic acid or polyatomic anhydride as branching agent to directly melt and polymerize, then preparing long-chain branched polyester slices with high melt strength through solid-phase tackification, and finally preparing the polyester foam board through extrusion, wherein the long-chain branched polyester slices have high melt index and high shear viscosity. Chinese patent application No.: 201711025316.6, in order to reduce the cost, the polyol is used as the chain extender to directly melt and polymerize the high-viscosity long-chain branched polyester chip, and then the polyester chip is extruded and foamed to prepare the polyester foam board.
However, the high melt strength polyester chip prepared by using polyol, polybasic acid or polybasic acid anhydride as branching agent has high viscosity, and is difficult to be directly conveyed into a twin-screw extruder through a melt pump after final polycondensation, so that an integrated polymerization and extrusion foaming process is urgently needed to be found, the energy consumption is saved, and the cost is reduced.
Disclosure of Invention
The invention aims to overcome the problems that high-melt-strength polyester chips prepared by using polyol, polybasic acid or polybasic acid anhydride as a branching agent in the prior art have high viscosity and are difficult to be directly conveyed into a double-screw extruder through a melt pump after final polycondensation, and provides a preparation method of a melt direct-extrusion PET (polyethylene terephthalate) foaming material.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing a melt direct-extrusion PET foaming material comprises the following steps:
(1) mixing terephthalic acid, ethylene glycol and a catalyst, uniformly stirring to prepare mixed slurry, and adding the mixed slurry into a reaction kettle to perform a first esterification reaction;
(2) when the mass of the esterification byproducts of the first esterification reaction reaches 85-95% of the theoretical value, carrying out a second esterification reaction;
(3) heating a mixed branching agent of alpha-triglycidyl isocyanurate and beta-triglycidyl isocyanurate and dihydric alcohol to 80-110 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the second esterification reaction is finished, adding a branching agent solution into the reaction kettle for stirring reaction;
(5) further vacuumizing for pre-polycondensation reaction, and vacuumizing to discharge glycol;
(6) after the pre-shrinking coalescence is finished, carrying out final polycondensation reaction, and carrying out high-vacuum polycondensation to obtain a melt;
(7) and conveying the melt into an extruder, injecting a foaming agent, extruding, foaming and molding to obtain the PET foaming material.
In order to solve the problems that high-viscosity polyester is difficult to convey through a melt booster pump and the polymerization and extrusion foaming integrated process cannot be realized, the molecular structure of the polyfunctional epoxy branching agent is researched, and finally, the mixture of alpha-triglycidyl isocyanurate and beta-triglycidyl isocyanurate is selected as the branching agent. Triglycidyl isocyanurate is a trifunctional monomer containing an epoxy group, has three chiral carbon atoms in a molecular structure, and has four symmetrical points in a chiral carbon atom configuration, namely RRR, SSS, RRS and SSR, so that the triglycidyl isocyanurate has two corresponding racemates:
triglycidyl isocyanurate of alpha (RRS and SSR) type and beta (RRR and SSS) type, and has a structural formula as follows:
α -triglycidyl isocyanurate:
beta-type triglycidyl isocyanurate:
the inventor researches and discovers that because the steric hindrance of the alpha-triglycidyl isocyanurate is smaller than that of the beta-triglycidyl isocyanurate, an epoxy group is easily attacked by carboxyl and hydroxyl, so that the reactivity is higher when the alpha-triglycidyl isocyanurate is used as a branching agent; when beta-triglycidyl isocyanurate is used as the branching agent, the reactivity is low due to the large steric hindrance.
Therefore, the invention adopts the mixture of the alpha-triglycidyl isocyanurate and the beta-triglycidyl isocyanurate as the branching agent, and utilizes the different reactivities of the alpha-triglycidyl isocyanurate branching agent and the beta-triglycidyl isocyanurate branching agent to ensure that only part of the branching agent with higher activity reacts firstly during final polycondensation to obtain low-viscosity polyester with better conveying property; after the low-viscosity polyester is effectively conveyed to an extruder, the low-viscosity polyester continues to react with the remaining branching agent with lower reactivity under the action of high temperature and screw shearing force, finally the high-viscosity high-melt-strength polyester is obtained, and the polyester foaming material is obtained after the foaming agent is injected for extrusion, so that the integrated process of polymerization and extrusion foaming is effectively realized.
Preferably, in the step (3), the molar ratio of the alpha-triglycidyl isocyanurate to the beta-triglycidyl isocyanurate in the mixing branching agent is 1: 1-1: 5; the mass ratio of the mixed branching agent to the dihydric alcohol is 1: 5-1: 8. By adopting the proportion of the alpha-type triglycidyl isocyanurate and the beta-type triglycidyl isocyanurate, the melt after the final polycondensation reaction has good conveying performance, and meanwhile, the finally obtained polyester has higher strength, and the foaming requirement is met.
Preferably, the diol in step (3) is one of ethylene glycol, propylene glycol or butylene glycol.
Preferably, the temperature in the step (4) is reduced to 200-230 ℃, a branching agent solution is added, the adding amount of the branching agent is 0.2-0.5% of the mass of the terephthalic acid, and the stirring reaction time is 15-60 minutes.
Preferably, the conveying speed of the melt in the step (7) is 5-10 kg/h; the foaming agent is supercritical carbon dioxide, nitrogen or pentane, and the amount of the foaming agent is 2-5% of the weight of the melt.
Preferably, the reaction pressure is controlled to be 6-20 MPa after the foaming agent is introduced in the step (7); the rotating speed of the extrusion screw is 60-150 r/min, and the extrusion temperature is 250-290 ℃.
Preferably, the molar ratio of the ethylene glycol to the terephthalic acid in the step (1) is 1.2-1.6: 1; the catalyst is one of antimony acetate, ethylene glycol antimony, tetrabutyl titanate and tetraisopropyl titanate, the dosage of the catalyst is 200-500 ppm, and the base number is the mass of the terephthalic acid; the temperature of the first esterification reaction is 220-250 ℃, the esterification pressure is 0.1-0.3 MPa, and the esterification reaction time is 1-3 h.
Preferably, the second esterification reaction in the step (2) is carried out at 240-260 ℃ under normal pressure for 0.5-1 h.
Preferably, the pre-polycondensation reaction in the step (5) is carried out at 260-280 ℃ for 0.5-1 hour, and the vacuum degree is less than 1000 Pa.
Preferably, the final polycondensation reaction in the step (6) is carried out at a temperature of 270-280 ℃, for 1-2 hours and under a vacuum degree of less than 100 Pa.
Therefore, the invention has the following beneficial effects:
(1) polymerization and reaction extrusion foaming are integrated, modification in a reactor and post-reactor modification are coupled, and the preparation of polyester chips is not needed independently, so that the process is simple, efficient, energy-saving and cost-reducing, and is suitable for large-scale production;
(2) the reaction activity of alpha-triglycidyl isocyanurate and beta-triglycidyl isocyanurate is different, so that only part of branching agent is reacted during final polycondensation, and low-viscosity polyester with good conveying performance is obtained; after the low-viscosity polyester enters the extruder, the low-viscosity polyester continues to react with the remaining branching agent under the action of high temperature and screw shearing force, and the high-viscosity high-melt-strength polyester is obtained.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is an SEM photograph of the foamed PET sheet obtained in example 3;
fig. 3 is an SEM image of the foamed PET sheet obtained in comparative example 1.
Detailed Description
The invention is further described with reference to the following detailed description and accompanying drawings.
In the present invention, all the equipment and materials are commercially available or commonly used in the art, and the methods in the following examples are conventional in the art unless otherwise specified.
Example 1:
(1) mixing a mixture of 1: 1.2 Putting Terephthalic Acid (PTA), ethylene glycol and 300ppm (relative to PTA) of catalyst ethylene glycol antimony into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 220 ℃, the esterification pressure is 0.3MPa, and the esterification reaction time is 3 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 240 ℃ under the normal pressure condition, and the esterification time is 1 h;
(3) mixing the components in a mass ratio of 1:5 (the molar ratio of alpha to beta is 1: 1) heating a mixed triglycidyl isocyanurate branching agent and glycol to 80 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after esterification, cooling circulating water is started to reduce the temperature of the kettle to 200 ℃, 0.3 percent mixed (alpha: beta molar ratio is 1: 1) triglycidyl isocyanurate (relative to PTA mass) glycol solution is added into the reaction kettle, and stirring reaction is carried out for 60 minutes;
(5) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 260 ℃, the reaction time is 1 hour, and the vacuum degree is 800 Pa;
(6) after the pre-condensation polymerization, carrying out final polycondensation reaction at 270 ℃ for 2 hours and under the vacuum degree of 50 Pa;
(7) after finishing polycondensation, conveying the melt into an SHJ-50 twin-screw extruder (the diameter of a screw is 50mm, the length-diameter ratio L/D is 30) at the speed of 5kg/h through a melt pump, injecting a supercritical carbon dioxide foaming agent at the speed of 7mL/min, extruding, foaming and molding to obtain a PET foaming material; the extrusion foaming parameters were as follows: the main machine rotating speed (150rpm), the feeding rotating speed (7rpm), the main machine current (7.74A), the main machine power (87.42%), the extrusion section T1(255 ℃), T2(265 ℃), T3(265 ℃), T4(265 ℃), T5(270 ℃), T6(260 ℃), T7(260 ℃), and the machine head pressure (15MPa) at 1T8(280 ℃).
Example 2:
(1) mixing a mixture of 1: 1.4 Putting Terephthalic Acid (PTA), ethylene glycol and a catalyst of ethylene glycol antimony 500ppm (relative to PTA) into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 250 ℃, the esterification pressure is 0.1MPa, and the esterification reaction time is 1 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 260 ℃ and under the condition of normal pressure, and the esterification time is 0.5 h;
(3) mixing the components in a mass ratio of 1:5 (the molar ratio of alpha to beta is 1: 3), heating the triglycidyl isocyanurate branching agent and glycol to 110 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after esterification, cooling circulating water is started to reduce the temperature of the kettle to 230 ℃, 0.5 percent mixed (alpha: beta molar ratio is 1: 5) triglycidyl isocyanurate (relative PTA) glycol solution is added into the reaction kettle, and stirring reaction is carried out for 30 minutes;
(5) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 280 ℃, the reaction time is 0.5 hour, and the vacuum degree is 800 Pa;
(6) after the pre-condensation polymerization, carrying out final polycondensation reaction at the temperature of 280 ℃ for 1 hour and under the vacuum degree of 50 Pa;
(7) after finishing polycondensation, the melt is conveyed into an SHJ-50 twin-screw extruder (the diameter of a screw is 50mm, the length-diameter ratio L/D is 30) at the speed of 10kg/h through a melt pump, and a supercritical carbon dioxide foaming agent is injected at the speed of 9mL/min and is extruded and foamed to form, so that the PET foaming material is obtained. The extrusion foaming parameters were as follows: the main machine rotating speed (150rpm), the feeding rotating speed (7rpm), the main machine current (7.74A), the main machine power (87.42%), the extrusion section T1(255 ℃), T2(265 ℃), T3(265 ℃), T4(265 ℃), T5(270 ℃), T6(260 ℃), T7(260 ℃), and the machine head pressure (15MPa) at 1T8(280 ℃).
Example 3:
(1) mixing a mixture of 1: 1.6 Putting Terephthalic Acid (PTA), ethylene glycol and a catalyst of ethylene glycol antimony (200 ppm (relative to PTA)) into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 230 ℃, the esterification pressure is 0.3MPa, and the esterification reaction time is 3 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 250 ℃ and under the condition of normal pressure, and the esterification time is 1 h;
(3) mixing the components in a mass ratio of 1:5 (the molar ratio of alpha to beta is 1: 5), heating the triglycidyl isocyanurate branching agent and glycol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after esterification, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, 0.2 percent mixed (alpha: beta molar ratio is 1: 5) triglycidyl isocyanurate (relative PTA) glycol solution is added into the reaction kettle, and stirring reaction is carried out for 30 minutes;
(5) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 270 ℃, the reaction time is 1 hour, and the vacuum degree is 800 Pa;
(6) after the pre-condensation polymerization, carrying out final polycondensation reaction at the temperature of 280 ℃ for 2 hours and under the vacuum degree of 50 Pa;
(7) after finishing polycondensation, the melt is conveyed into an SHJ-50 twin-screw extruder (the diameter of a screw is 50mm, the length-diameter ratio L/D is 30) at the speed of 8kg/h through a melt pump, and a supercritical carbon dioxide foaming agent is injected at the speed of 9mL/min and is extruded and foamed to form, so that the PET foaming material is obtained. The extrusion foaming parameters were as follows: the main machine rotating speed (150rpm), the feeding rotating speed (7rpm), the main machine current (7.74A), the main machine power (87.42%), the extrusion section T1(255 ℃), T2(265 ℃), T3(265 ℃), T4(265 ℃), T5(270 ℃), T6(260 ℃), T7(260 ℃), and the machine head pressure (15MPa) at 1T8(280 ℃).
FIG. 2 is a scanning electron microscope image of the PET foam material prepared by the process of this embodiment, which shows that the PET foam material has a uniform cell size, a small cell size of about 200 μm and a large foaming ratio, and the process realizes an integrated process of PET polymerization and extrusion foaming.
Comparative example 1 (without branching agent):
(1) mixing a mixture of 1: 1.6 Putting Terephthalic Acid (PTA), ethylene glycol and a catalyst of ethylene glycol antimony (200 ppm (relative to PTA)) into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 230 ℃, the esterification pressure is 0.3MPa, and the esterification reaction time is 3 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 250 ℃ and under the condition of normal pressure, and the esterification time is 1 h;
(3) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 270 ℃, the reaction time is 1 hour, and the vacuum degree is 800 Pa;
(4) after the pre-condensation polymerization, carrying out final polycondensation reaction at the temperature of 280 ℃ for 2 hours and under the vacuum degree of 50 Pa;
(5) after finishing polycondensation, the melt is conveyed into an SHJ-50 twin-screw extruder (the diameter of a screw is 50mm, the length-diameter ratio L/D is 30) at the speed of 8kg/h through a melt pump, and a supercritical carbon dioxide foaming agent is injected at the speed of 9mL/min and is extruded and foamed to form, so that the PET foaming material is obtained. The extrusion foaming parameters were as follows: the main machine rotating speed (150rpm), the feeding rotating speed (7rpm), the main machine current (7.74A), the main machine power (87.42%), the extrusion section T1(255 ℃), T2(265 ℃), T3(265 ℃), T4(265 ℃), T5(270 ℃), T6(260 ℃), T7(260 ℃), and the machine head pressure (15MPa) at 1T8(280 ℃).
FIG. 3 is a scanning electron microscope photograph of the PET foam prepared by the process of the present comparative example, from which it can be seen that the pore size is very non-uniform, the pore size is larger by about 500 μm, and the foaming ratio becomes smaller, indicating that the addition of the branching agent contributes to the improvement of the melt strength of the polyester and the improvement of the foaming effect.
Comparative example 2 (using only α -triglycidyl isocyanurate as catalyst):
(1) mixing a mixture of 1: 1.6 Putting Terephthalic Acid (PTA), ethylene glycol and a catalyst of ethylene glycol antimony (200 ppm (relative to PTA)) into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 230 ℃, the esterification pressure is 0.3MPa, and the esterification reaction time is 3 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 250 ℃ and under the condition of normal pressure, and the esterification time is 1 h;
(3) mixing the components in a mass ratio of 1: heating the alpha-triglycidyl isocyanurate branching agent of 5 and glycol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after esterification, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, 0.2 percent of glycol solution of alpha-type triglycidyl isocyanurate (relative to the mass of PTA) is added into the reaction kettle, and stirring reaction is carried out for 30 minutes;
(5) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 270 ℃, the reaction time is 1 hour, and the vacuum degree is 800 Pa;
(6) after the pre-condensation polymerization, carrying out final polycondensation reaction at the temperature of 280 ℃ for 2 hours and under the vacuum degree of 50 Pa;
(7) after the end of the polycondensation, the melt viscosity was too high to be conveyed by the melt pump into the SHJ-50 twin-screw extruder.
Comparative example 3 (using only beta-type triglycidyl isocyanurate as catalyst):
(1) mixing a mixture of 1: 1.6 Putting Terephthalic Acid (PTA), ethylene glycol and a catalyst of ethylene glycol antimony (200 ppm (relative to PTA)) into a slurry preparation tank for slurry preparation, and putting the prepared slurry into an esterification reactor for a first esterification reaction; the temperature of the first esterification reaction is 230 ℃, the esterification pressure is 0.3MPa, and the esterification reaction time is 3 h; the esterification byproduct is water, in the first esterification reaction process, the water is separated out by a fractionating tower and collected, the water yield is tested by a measuring cylinder, the theoretical water yield is calculated according to a monomer reaction equation, and the esterification completion amount is calculated according to the water yield;
(2) when the collection amount of the esterification byproducts reaches 90 percent of the theoretical value, carrying out a second esterification reaction; the second esterification reaction is carried out at the temperature of 250 ℃ and under the condition of normal pressure, and the esterification time is 1 h;
(3) mixing the components in a mass ratio of 1: heating the beta-triglycidyl isocyanurate branching agent of 5 and glycol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after esterification, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, 0.2 percent of glycol solution of beta-type triglycidyl isocyanurate (relative PTA) is added into the reaction kettle, and stirring reaction is carried out for 30 minutes;
(5) further vacuumizing for pre-polycondensation reaction, vacuumizing to discharge glycol, wherein the temperature is 270 ℃, the reaction time is 1 hour, and the vacuum degree is 800 Pa;
(6) after the pre-condensation polymerization, carrying out final polycondensation reaction at the temperature of 280 ℃ for 2 hours and under the vacuum degree of 50 Pa;
(7) after finishing polycondensation, the melt is conveyed into an SHJ-50 twin-screw extruder (the diameter of a screw is 50mm, the length-diameter ratio L/D is 30) at the speed of 8kg/h through a melt pump, and a supercritical carbon dioxide foaming agent is injected at the speed of 9mL/min and is extruded and foamed to form, so that the PET foaming material is obtained. The extrusion foaming parameters were as follows: the main machine rotating speed (150rpm), the feeding rotating speed (7rpm), the main machine current (7.74A), the main machine power (87.42%), the extrusion section T1(255 ℃), T2(265 ℃), T3(265 ℃), T4(265 ℃), T5(270 ℃), T6(260 ℃), T7(260 ℃), and the machine head pressure (15MPa) at 1T8(280 ℃).
The PET foams prepared in the above examples and comparative examples were tested for their properties, and the results are shown in table 1.
Table 1: and (5) testing the performance of the PET foaming material.
As can be seen from table 1, the PET foam materials obtained by the method of the present invention in examples 1 to 3 have a high expansion ratio and excellent mechanical properties, and preferably have an α: the beta molar ratio is 1: 3 as branching agent. Compared with the PET foaming material without the branching agent in the comparative example 1, the PET foaming material has the advantages of higher density, lower multiplying power and poorer foaming effect, and can not meet the use requirement; in comparative example 2, only alpha-triglycidyl isocyanurate is used as a branching agent, so that the reactivity is too high, the melt viscosity is too high after final polycondensation, the melt is difficult to convey, and the melt can not be directly extruded and foamed; in comparative example 3, only beta-triglycidyl isocyanurate is used as the branching agent, so that the reactivity is too low, the melt strength is low, the foaming effect is not ideal, and the use requirement is not met. In summary, the invention realizes the integration of polymerization and extrusion foaming by selecting proper branching agent types, configurations and proportions and utilizing different reactivity, and the prepared PET foaming material has the advantages of high foaming multiplying power, uniform pore size distribution and excellent mechanical property, simple process, high production efficiency, cost saving, low energy consumption and suitability for large-scale industrial production.
Claims (10)
1. A method for preparing a melt direct-extrusion PET foaming material is characterized by comprising the following steps:
(1) mixing terephthalic acid, ethylene glycol and a catalyst, uniformly stirring to prepare mixed slurry, and adding the mixed slurry into a reaction kettle to perform a first esterification reaction;
(2) when the mass of the esterification byproducts of the first esterification reaction reaches 85-95% of the theoretical value, carrying out a second esterification reaction;
(3) heating a mixed branching agent of alpha-triglycidyl isocyanurate and beta-triglycidyl isocyanurate and dihydric alcohol to 80-110 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the second esterification reaction is finished, adding a branching agent solution into the reaction kettle for stirring reaction;
(5) further vacuumizing for pre-polycondensation reaction, and vacuumizing to discharge glycol;
(6) after the pre-shrinking coalescence is finished, carrying out final polycondensation reaction, and carrying out high-vacuum polycondensation to obtain a melt;
(7) and conveying the melt into an extruder, injecting a foaming agent, extruding, foaming and molding to obtain the PET foaming material.
2. The method for preparing the melt direct extrusion PET foam material according to claim 1, wherein the molar ratio of the alpha-type triglycidyl isocyanurate to the beta-type triglycidyl isocyanurate in the mixing branching agent in the step (3) is 1: 1-1: 5; the mass ratio of the mixed branching agent to the dihydric alcohol is 1: 5-1: 8.
3. The method for preparing a melt direct extrusion PET foaming material according to claim 1 or 2, wherein the diol in the step (3) is one of ethylene glycol, propylene glycol or butylene glycol.
4. The method for preparing the PET foam material by direct extrusion of melt according to claim 1, wherein the temperature in the step (4) is reduced to 200-230 ℃, a branching agent solution is added, the adding amount of the branching agent is 0.2-0.5% of the mass of the terephthalic acid, and the stirring reaction time is 15-60 minutes.
5. The method for preparing the melt direct extrusion PET foaming material according to claim 1, wherein the conveying speed of the melt in the step (7) is 5-10 kg/h; the foaming agent is supercritical carbon dioxide, nitrogen or pentane, and the amount of the foaming agent is 2-5% of the weight of the melt.
6. The method for preparing the PET foaming material by directly extruding the melt according to the claim 1 or 5, wherein the reaction pressure is controlled to be 6-20 MPa after the foaming agent is introduced in the step (7); the rotating speed of the extrusion screw is 60-150 r/min, and the extrusion temperature is 250-290 ℃.
7. The method for preparing the melt direct extrusion PET foaming material according to claim 1, wherein the molar ratio of the ethylene glycol to the terephthalic acid in the step (1) is 1.2-1.6: 1; the catalyst is one of antimony acetate, ethylene glycol antimony, tetrabutyl titanate and tetraisopropyl titanate, the dosage of the catalyst is 200-500 ppm, and the base number is the mass of the terephthalic acid; the temperature of the first esterification reaction is 220-250 ℃, the esterification pressure is 0.1-0.3 MPa, and the esterification reaction time is 1-3 h.
8. The method for preparing the melt direct extrusion PET foaming material according to claim 1, wherein the second esterification reaction in the step (2) is carried out at 240-260 ℃ under normal pressure for 0.5-1 h.
9. The method for preparing the melt direct extrusion PET foaming material according to claim 1, wherein the pre-polycondensation reaction temperature in the step (5) is 260-280 ℃, the reaction time is 0.5-1 hour, and the vacuum degree is less than 1000 Pa.
10. The method for preparing the melt direct extrusion PET foaming material according to claim 1, wherein the final polycondensation reaction temperature in the step (6) is 270-280 ℃, the reaction time is 1-2 hours, and the vacuum degree is less than 100 Pa.
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