CN113004504B - Preparation method of special PET (polyethylene terephthalate) with high fluidity and high melt strength for foaming - Google Patents
Preparation method of special PET (polyethylene terephthalate) with high fluidity and high melt strength for foaming 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
- C08G63/68—Polyesters containing atoms other than carbon, hydrogen and oxygen
- C08G63/685—Polyesters containing atoms other than carbon, hydrogen and oxygen containing nitrogen
- C08G63/6854—Polyesters containing atoms other than carbon, hydrogen and oxygen containing nitrogen derived from polycarboxylic acids and polyhydroxy compounds
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- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
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- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
- C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
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- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/06—CO2, N2 or noble gases
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- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
Abstract
The invention discloses a preparation method of special PET for foaming with high fluidity and high melt strength, which comprises the following steps: (1) mixing terephthalic acid, ethylene glycol and a catalyst, and carrying out 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) preparing a branching agent solution from a beta-triglycidyl isocyanurate branching agent; (4) after the second esterification reaction is finished, adding a branching agent solution into the reaction kettle; (5) carrying out pre-polycondensation reaction; (6) and (4) final polycondensation. The invention adopts beta-triglycidyl isocyanurate as branching agent to carry out in-situ polymerization, and the branching agent is prepared into solution to be added after esterification reaction, the reaction is uniform and mild, the generation of local cross-linking and gel is avoided, and the special PET for foaming with high fluidity and high melt strength is prepared.
Description
Technical Field
The invention relates to the technical field of polyester preparation, in particular to a preparation method of special PET for foaming with high fluidity and high melt strength.
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, plastic bottles and the like, and with the expansion of productivity and the reduction of petroleum price, the cost of polyester is lower and the productivity is excessive. Therefore, the advantages of cost performance of PET are urgently needed to be fully utilized, the added value of PET is improved, and the application field of PET is further developed and expanded.
To solve this problem, it has been proposed in the industry to use PET foam as the core material instead of PVC foam. Firstly, from the attribute of the PET material, the PET material can be recycled as an environment-friendly thermoplastic material, and meanwhile, the material cost is greatly reduced. Secondly, the semi-crystalline polymer has higher heat-resistant temperature which can reach 200 ℃ in a short time, so that the curing process of the shell layer of the blade has wider adaptability. The foam can be used as a sandwich material and applied to various fields of wind power blades, rail transit, ships, industrial application and the like.
The conventional PET has lower molecular weight, narrow molecular weight distribution and linear molecular chains, so that the melt strength is low, the increase of cells cannot be effectively supported in the foaming process, and the cells are easy to collapse and break. In the currently disclosed patents, the PET with high molecular weight, wide molecular weight distribution and high long chain branching degree and higher melt strength is obtained mainly by a chain extension modification method. Most patents adopt polyhydric alcohol, polybasic acid or polybasic acid anhydride as a chain extender to carry out two methods of reactive extrusion and in-situ polymerization, but the reactive extrusion method is limited by the using amount of the chain extender, equipment and raw material PET, and has larger limitation. The in-situ polymerization method can prepare high melt strength PET as required, and is directly used for continuous extrusion foaming, thereby avoiding the defects of reaction extrusion, such as Chinese patent application numbers: 201110270665.0, adopting polyol, polybasic acid or polybasic acid anhydride as branching agent to directly melt and polymerize, then preparing long-chain branching PET with high melt strength through solid-phase tackification, and finally preparing the PET foam board through extrusion, wherein the long-chain branching PET has high melt index and high shear viscosity. Chinese patent application No.: 201711025316.6, in order to reduce the cost, the high-viscosity long-chain branched PET is prepared by direct melt polymerization by using the polyol as the chain extender, and the PET foam board is prepared by extrusion foaming.
The polyol, polybasic acid or polybasic acid anhydride as branching agent can only react with the terminal carboxyl or terminal hydroxyl of the polyester for branching to form short chain branched polyester with high melt strength, and has poor fluidity, high energy consumption in processing and high requirement on equipment. Thus, there is a need to produce a high flow, high melt strength PET suitable for processing and extrusion foaming.
Disclosure of Invention
The invention aims to overcome the problems that in the prior art, polyol, polybasic acid or polybasic acid anhydride is used as a branching agent and can only react with terminal carboxyl or terminal hydroxyl of polyester to carry out branching to form short chain branched polyester with high melt strength and the flowability is poor, and provides a preparation method of special PET for foaming with high flowability and high melt strength.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of special PET for foaming with high fluidity and high melt strength 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 beta-triglycidyl isocyanurate branching agent and dihydric alcohol to 80-110 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the second esterification reaction is finished, adding the branching agent solution into a reaction kettle, and stirring and reacting for 0.5-1 h at the temperature of 220-240 ℃ under normal pressure;
(5) further vacuumizing for pre-polycondensation reaction, and vacuumizing to discharge glycol;
(6) and after the preshrinking and coalescence, carrying out final polycondensation reaction, carrying out high-vacuum polycondensation to obtain a melt, and discharging, cooling and granulating the melt to obtain the special PET for foaming with high fluidity and high melt strength.
The invention adopts polyfunctional epoxy compounds as branching agents to carry out in-situ polymerization, and epoxy groups have high activity, so that the epoxy groups can react with terminal carboxyl and terminal hydroxyl of polyester, and the reactivity of the epoxy groups with carboxyl is higher than that of hydroxyl. However, the reactivity of a general polyfunctional epoxy branching agent is difficult to control, and the branched polyester is easy to crosslink to generate gel because of high reactivity, so that the fluidity of the polyester is reduced, and the foaming requirement is not met.
Therefore, in order to solve the problem that the polyfunctional epoxy branching agent is easy to form gel, the invention further researches the molecular structure of the polyfunctional epoxy branching agent, and finally selects the beta-triglycidyl isocyanurate 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 when the alpha-triglycidyl isocyanurate is used as a branching agent, the reactivity is high, the branched polyester is easy to crosslink to generate gel, and the fluidity of the polyester is reduced because the steric hindrance of the alpha-triglycidyl isocyanurate is smaller than that of the beta-triglycidyl isocyanurate and the epoxy group is easy to be attacked by carboxyl and hydroxyl. When the beta-triglycidyl isocyanurate is used as the polyfunctional epoxy branching agent, the reaction activity can be reduced by utilizing larger steric hindrance, the branching reaction is mild, and the generation of gel is avoided, so that long-chain branched polyester with high branching degree is formed, and the PET has high fluidity and high melt strength.
Meanwhile, the branching agent is heated and dissolved in the dihydric alcohol to prepare a branching agent solution, and the solution is added into a reaction kettle after esterification, so that the branching agent is favorably dispersed and uniformly reacted, the reduction of melt strength caused by local crosslinking is avoided, and finally the PET with high fluidity and high melt strength suitable for foaming is obtained.
Preferably, the catalyst in the step (1) is antimony acetate or ethylene glycol antimony, the dosage of the catalyst is 200-500 ppm, and the base number is the mass of the terephthalic acid; the molar ratio of the ethylene glycol to the terephthalic acid is 1.2-1.6: 1.
Preferably, in the step (1), 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 mass ratio of the beta-triglycidyl isocyanurate branching agent to the glycol in the step (3) is 1: 5-8. Within the range, the beta-triglycidyl isocyanurate branching agent can effectively form long-chain branched polyester with high branching degree, so that the PET has high fluidity and high melt strength, and the gelation phenomenon can be avoided.
Preferably, the amount of the branching agent added in the step (4) is 0.5 to 1% by mass based on the terephthalic acid.
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.
Preferably, the PET for foaming obtained in the step (6) has an intrinsic viscosity of 0.8 to 1.4dL/g, a melt index of 5 to 30g/min, and a melt viscosity of 250 to 400 Pa.S.
Therefore, the invention has the following beneficial effects:
(1) the beta-triglycidyl isocyanurate is used as a polyfunctional epoxy branching agent to carry out in-situ polymerization, has good thermal stability, is not sensitive to water, can react with carboxyl and hydroxyl, has low activity and mild reaction, avoids the generation of gel, can form polyester with high branching degree and long chain branching, shows high fluidity and high melt strength, and is suitable for foaming;
(2) the branching agent is heated and dissolved in the dihydric alcohol to prepare a branching agent solution, and the solution is added into a reaction kettle after esterification, so that the branching agent is favorably dispersed and uniformly reacted, and the reduction of melt strength caused by local crosslinking is avoided.
Drawings
FIG. 1 is an SEM photograph of the high-fluidity high-melt-strength PET exclusive for foaming obtained in 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) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) heating 4.34g of beta-triglycidyl isocyanurate branching agent and 30g of ethylene glycol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, and a branching agent solution is added into the reaction kettle and stirred for reaction 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-polycondensation reaction is finished, carrying out final polycondensation reaction at the temperature of 280 ℃, the reaction time of 2 hours and the vacuum degree of 50 Pa; and after finishing polycondensation, discharging the melt, cooling and granulating to obtain the special foaming PET slice with high fluidity and high melt strength.
Example 2:
(1) 1660g of terephthalic acid (PTA), 744g of ethylene glycol and 300ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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 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 240 ℃ under the normal pressure condition, and the esterification time is 1 h;
(3) heating 6.51g of beta-triglycidyl isocyanurate and 30g of propylene glycol to 80 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, starting cooling circulating water to reduce the temperature of the kettle to 230 ℃, adding the branching agent solution into the reaction kettle, and stirring and reacting for 40 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; and after finishing polycondensation, discharging the melt, cooling and granulating to obtain the special foaming PET slice with high fluidity and high melt strength.
Example 3:
(1) 1660g of terephthalic acid (PTA), 992g of glycol and 500ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) heating 8.68g of beta-triglycidyl isocyanurate and 30g of butanediol to 110 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, starting cooling circulating water to reduce the temperature of the kettle to 240 ℃, adding the branching agent solution into the reaction kettle, and stirring and reacting for 60 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-polycondensation reaction, final polycondensation reaction is carried out, wherein the temperature is 280 ℃, the reaction time is 2 hours, and the vacuum degree is 50 Pa. And after finishing polycondensation, discharging the melt, cooling and granulating to obtain the special foaming PET slice with high fluidity and high melt strength.
Comparative example 1 (branching agent not added via solution):
(1) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) after the esterification is finished, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, 6.51g of beta-type triglycidyl isocyanurate is added into the reaction kettle, and the stirring reaction is carried out for 30 minutes;
(4) 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;
(5) after the pre-polycondensation reaction, final polycondensation reaction is carried out, wherein the temperature is 280 ℃, the reaction time is 2 hours, and the vacuum degree is 50 Pa. And after finishing polycondensation, discharging the melt, cooling and dicing to obtain the PET slice special for foaming.
Comparative example 2 (use of triglycidyl isocyanurate type a as branching agent)
(1) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) heating 4.34g of alpha-triglycidyl isocyanurate and 30g of ethylene glycol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, and a branching agent solution is added into the reaction kettle and stirred for reaction 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-polycondensation reaction, final polycondensation reaction is carried out, wherein the temperature is 280 ℃, the reaction time is 2 hours, and the vacuum degree is 50 Pa. And after finishing polycondensation, discharging the melt, cooling and granulating to obtain the special foaming PET slice with high fluidity and high melt strength.
Comparative example 3 (no branching agent added):
(1) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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-polycondensation reaction, final polycondensation reaction is carried out, wherein the temperature is 280 ℃, the reaction time is 2 hours, and the vacuum degree is 50 Pa. And after finishing polycondensation, discharging the melt, cooling and dicing to obtain the PET slice special for foaming.
Comparative example 4 (too little branching agent added):
(1) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) heating 2.17g of beta-type triglycidyl isocyanurate and 30g of butanediol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, and a branching agent solution is added into the reaction kettle and stirred for reaction 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; and after finishing polycondensation, discharging the melt, cooling and dicing to obtain the PET slice special for foaming.
Comparative example 5 (branching agent added in excess):
(1) 1660g of terephthalic acid (PTA), 868g of glycol and 200ppm (relative to PTA) of ethylene glycol antimony as a catalyst are put into a preparation kettle, are uniformly stirred to prepare mixed slurry, and are added into a reaction kettle to carry out 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) heating 10.85g of beta-triglycidyl isocyanurate and 30g of butanediol to 100 ℃, stirring and dissolving to prepare a branching agent solution;
(4) after the esterification is finished, cooling circulating water is started to reduce the temperature of the kettle to 220 ℃, and a branching agent solution is added into the reaction kettle and stirred for reaction 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; and after finishing polycondensation, discharging the melt, cooling and dicing to obtain the PET slice special for foaming.
Foaming experiments were performed on the PET chips prepared in the above examples and comparative examples, and various properties of the foamed materials were tested, with the results shown in fig. 1 and table 1.
The foaming experiment method comprises the following steps: the melt foaming experiment was carried out in a supercritical autoclave, in which the PET chips were placed in an autoclave, which was then sealed and placed in an oil bath at the set temperature. First using low pressure CO2Purging the autoclave three times, then introducing a certain amount of CO into the autoclave2Melting and saturating the sample at the set temperature and pressure for the appropriate time to allow CO2The diffusion in the molten polyester reaches equilibrium. Then quickly opening a pressure relief valve to release CO in the high-pressure kettle2And (3) gas is used for initiating bubble nucleation, the kettle cover is opened, ice water is injected into the kettle, the foaming sample is cooled to be fixed and formed, and then the sample is taken out for analysis and characterization.
The performance evaluation method comprises the following steps:
intrinsic Viscosity (IV): testing by adopting a polyester national standard method: GB/T-14190-1993.
Melt index (MFI): testing was performed using the ASTM1238 standard.
Melt viscosity: the length-diameter ratio of the neck ring mold is 30:1 and the shearing rate is 5mm/s by adopting a capillary rheometer for detection.
Extrusion expansion ratio: DS ═ D/D0D is the maximum diameter of the extrudate, D0Is the diameter of the die hole.
Cell characterization: brittle-breaking the molten and foamed polyester sample strip in liquid nitrogen, spraying gold on the surface, and observing the surface appearance by using a JSM-6360LV type scanning electron microscope. Density of foamed sample (. rho.)f) Obtained by means of a balance provided with a density module and supplied by the company Mettler Toledo, the test standard being ASTM 792-00. The volume expansion ratio (Rv) of the foamed sample, defined as the density (. rho.) of the unfoamed samplep) With the density of the foamed sample (. rho.)f) The ratio of: rv ═ ρp/ρf。
Table 1: and (5) testing the physicochemical property of the PET slice.
As can be seen from fig. 1 and table 1, in examples 1 to 3, the PET chips prepared by using the beta-triglycidyl isocyanurate as the branching agent have good fluidity, higher melt strength, good foaming properties, and less collapse and rupture of cells.
In comparative example 1, the beta-triglycidyl isocyanurate branching agent was not prepared as a solution and was added directly after the esterification reaction, and the resulting chips had poor flowability and low melt strength, which may be due to uneven distribution of the triglycidyl isocyanurate branching agent in the esterification solution, resulting in local crosslinking; in comparative example 2, when α -triglycidyl isocyanurate was used as the branching agent, the reactivity was too high, gel formation was easy, and foaming was not facilitated; in comparative example 3, no branching agent was added, the melt strength was low, the blowing agent escaped easily, the cells broke easily, and it was not suitable for foaming because of low molecular weight, narrow distribution, no branching structure, and weak entanglement between molecular chains, resulting in low melt strength; too much or too little branching agent was added in comparative examples 4 and 5, which also did not contribute to the foaming, indicating that the amount of branching agent added had a significant effect on the foaming properties of the polyester. Generally, the PET slices prepared by using the beta-type triglycidyl isocyanurate with the optimal content as the branching agent have the advantages of equivalent fluidity and high melt strength, are suitable for processing and extrusion foaming, simplify the foaming process, improve the production efficiency and are beneficial to reducing the cost.
Claims (7)
1. A preparation method of special PET for foaming with high fluidity and high melt strength 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; the molar ratio of the ethylene glycol to the terephthalic acid is 1.2-1.6: 1;
(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 beta-triglycidyl isocyanurate branching agent and dihydric alcohol to 80-110 ℃, stirring and dissolving to prepare a branching agent solution; the mass ratio of the beta-triglycidyl isocyanurate branching agent to the dihydric alcohol is 1: 5-8;
(4) after the second esterification reaction is finished, adding the branching agent solution into a reaction kettle, and stirring and reacting for 0.5-1 h at the temperature of 220-240 ℃ under normal pressure; the mass ratio of the added branching agent to the terephthalic acid is 4.34:1660 or 6.51:1660 or 8.68: 1660;
(5) further vacuumizing for pre-polycondensation reaction, and vacuumizing to discharge glycol;
(6) and after the preshrinking and coalescence, carrying out final polycondensation reaction, carrying out high-vacuum polycondensation to obtain a melt, and discharging, cooling and granulating the melt to obtain the special PET for foaming with high fluidity and high melt strength.
2. The method for preparing the special PET for foaming with high fluidity and high melt strength as claimed in claim 1, wherein the catalyst in the step (1) is antimony acetate or ethylene glycol antimony, the amount of the catalyst is 200-500 ppm, and the base number is the mass of the terephthalic acid.
3. The method for preparing PET special for foaming with high fluidity and high melt strength as claimed in claim 1 or 2, wherein the first esterification reaction temperature in the step (1) is 220-250 ℃, the esterification pressure is 0.1-0.3 MPa, and the esterification reaction time is 1-3 h.
4. The method for preparing the PET special for foaming with high fluidity and high melt strength as claimed in 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.
5. The method for preparing PET special for foaming with high fluidity and high melt strength as claimed in 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.
6. The method for preparing PET special for foaming with high fluidity and high melt strength as claimed in claim 1, wherein the final polycondensation reaction temperature in the step (6) is 270 to 280 ℃, the reaction time is 1 to 2 hours, and the vacuum degree is less than 100 Pa.
7. The method for preparing the PET special for high fluidity and high melt strength foaming according to claim 1 or 6, wherein the PET special for high fluidity and high melt strength foaming obtained in the step (6) has an intrinsic viscosity of 0.8 to 1.4dL/g, a melt index of 5 to 30g/min and a melt viscosity of 250 to 400 Pa.S.
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| KR100441795B1 (en) * | 2004-01-10 | 2004-07-30 | 주식회사 현대페스 | The Preparation Method for Triglycidylisocyanurate |
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Address after: 311200 29 Chenghu Road, Yaqian Town, Xiaoshan District, Hangzhou City, Zhejiang Province Patentee after: Zhejiang Hengyi Petrochemical Research Institute Co.,Ltd. Patentee after: Zhejiang University Address before: 311200 29 Chenghu Road, Yaqian Town, Xiaoshan District, Hangzhou City, Zhejiang Province Patentee before: ZHEJIANG HENGLAN TECHNOLOGY Co.,Ltd. Patentee before: Zhejiang University |