Flame-retardant PET foamed polyester and method for preparing the same

Abstract

The application discloses a kind of flame-retardant PET foamed polyester and its preparation method, according to percentage by weight, its raw material composition includes: polyethylene terephthalate matrix 92%~95.2%, flame retardant 4%~7.5%, pentaerythritol 0.1%~0.3% and flow promoter 80T 0.1~0.5%, the foaming ratio of the polyester is 20.3~34.6;Its preparation method includes the following steps: terephthalic acid, ethylene glycol, catalyst, flame retardant, pentaerythritol and flow promoter 80T are mixed, esterification and polycondensation reaction is carried out, and flame-retardant PET chip is obtained, then solid-phase tackiness is carried out, and finally foaming obtains flame-retardant PET foamed polyester;By adding flow promoter 80T, the viscosity of PET polyester is reduced, and the foaming ratio is large.

Description

Technical Field

[0001] This invention relates to a polyester and its preparation method, and particularly to a flame-retardant PET foamed polyester and its preparation. Background Technology

[0002] Flame-retardant PET foam material is a PET polyester prepared by esterification and polycondensation processes using terephthalic acid (PTA), ethylene glycol, phosphorus-containing monomers, and additives under the action of a catalyst. When this polyester is placed in carbon dioxide gas under high temperature and pressure, and then rapidly depressurized or cooled, it forms a porous material. This material has advantages such as low density, high specific strength, low thermal conductivity, good sound insulation, and excellent cushioning performance, making it suitable for applications requiring flame retardancy.

[0003] Conventional flame-retardant polyesters have low foaming ratios, requiring modification of the polyester in terms of molecular weight, molecular weight distribution, and the degree of long-chain branching. The focus of modification is usually on increasing the number of branched structures in the polyester. However, using polyols, polyacids, or polyacid anhydrides as branching agents with polyesters of high intrinsic viscosity results in poor flowability, high energy consumption during processing, and demanding equipment requirements. Furthermore, poor flowability leads to longer residence time of the polyester in the screw, increased viscosity drop, and a reduction in the polyester's molecular weight, which is detrimental to foaming. Summary of the Invention

[0004] Purpose of the invention: The first purpose of this invention is to provide a flame-retardant PET foamed polyester with good flowability and high foaming ratio; the second purpose of this invention is to provide a method for preparing the polyester.

[0005] Technical solution: The flame-retardant PET foamed polyester of the present invention comprises, by weight percentage: 92% to 95.2% polyethylene terephthalate matrix, 4% to 7.5% flame retardant, 0.1% to 0.3% pentaerythritol, and 0.1% to 0.5% flow promoter 80T; the foaming ratio of the polyester is 20.3 to 34.6.

[0006] The limiting oxygen index of the polyester is 29.1 to 34.5.

[0007] The polyester has a melt index of 19.6–21.7 g / 10 min at 280°C and 2.16 kg.

[0008] The flow promoter is Tolsa's 80T product, which is organically modified sepiolite. The organic matter is bonded to the inorganic powder via silicon-oxygen bonds, and the organic matter accounts for 10% of the product. The inorganic powder has the chemical formula (Si12)(Mg8)O30(OH)4(OH2)4·8H2O, and the oxides account for 62% silicon oxide and 24% magnesium oxide. The basic characteristic of the organic matter in this product is that it contains phenyl or aliphatic chain groups with carboxyl groups, which are bonded to the silicon-oxygen bonds in the form of ester bonds. The basic principle is that 80T, through its similar compatibility with phenyl or carboxyl groups in PET polyester, affects the intermolecular forces in the chain segments. When its content is greater than 1 wt%, it has a thickening effect due to the attraction between silicon-oxygen bonds, reducing the fluidity of the melt. When the component content is less than 0.5 wt%, the thickening effect is reduced due to the weakening of the mutual attraction. The organic part dissolves in the chain segments, and the inorganic part weakens the secondary valence bonds between the chain segment molecules, increasing the mobility of the chain segment molecular bonds, reducing the crystallinity of the chain segment molecules, increasing the plasticity of the chain segment molecules, enhancing their flexibility, and promoting fluidity.

[0009] The polyethylene terephthalate (PET) matrix is ​​a foaming base material synthesized from terephthalic acid and ethylene glycol, with antimony glycolate as the catalyst. The mass of PET is the mass remaining after removing 2 moles of water molecules from 1 mole of terephthalic acid and 1 mole of ethylene glycol.

[0010] The flame retardant functions to prevent the polyester from continuing to burn during the combustion process. Preferably, the flame retardant is a phosphorus-based flame retardant, such as 2-carboxyethylphenyl hypophosphite, bis(4-carboxyphenyl)phenylphosphine oxide, or 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0011] The pentaerythritol is a branching agent. Its terminal hydroxyl groups react with the carboxyl groups of PTA in the polyester to form ester bonds. The four hydroxyl groups participate in the reaction together to form a network structure in the polyester, which increases the branching structure in the polyester chain and is beneficial to polyester foaming.

[0012] The method for preparing flame-retardant PET foamed polyester of the present invention includes the following steps: mixing terephthalic acid, ethylene glycol, catalyst, flame retardant, pentaerythritol and flow promoter 80T, carrying out esterification and polycondensation reactions to obtain flame-retardant PET chips, then carrying out solid-phase thickening, and finally carrying out foaming to obtain flame-retardant PET foamed polyester.

[0013] Preferably, the esterification reaction is carried out at a temperature of 180–240°C and a pressure of 0.15–0.50 MPa (gauge pressure). The pressure is released when the output water reaches 1000 grams, and the esterification reaction ends.

[0014] Preferably, the polycondensation reaction is carried out at a temperature of 260–290°C and an absolute pressure of 20–120 Pa, and the intrinsic viscosity of the polyester is controlled to 0.72 dL / g before the reaction is terminated to obtain flame-retardant PET chips.

[0015] Preferably, the solid-phase viscosity enhancement temperature is 190–210°C, the pressure is 20–100 Pa absolute pressure, and the process is stopped when the viscosity reaches approximately 1.2 dL / g.

[0016] Preferably, the foaming process employs supercritical carbon dioxide foaming.

[0017] Preferably, the supercritical carbon dioxide foaming pressure is 8-15 MPa (gauge pressure) and the foaming temperature is 220-280°C.

[0018] Mechanism of Invention: Sepiolite is a fibrous, hydrated magnesium silicate commonly used for fiber reinforcement. Its principle is to enhance the intermolecular forces by utilizing the attractive forces between silicon-oxygen bonds, thereby increasing fiber strength. However, the inventors discovered that sepiolite 80T, modified with organic compounds containing carboxyl groups or aliphatic chain groups, has organic compounds linked to silicon-oxygen bonds via ester bonds. Through the similarity and compatibility of these organic and carboxyl groups with the phenyl or carboxyl groups in PET polyester, it affects the intermolecular forces within the chain segments. When the content of 80T is greater than 1 wt%, the attractive forces between silicon-oxygen bonds result in a thickening effect, reducing melt flowability. When the component content is less than 1 wt%, especially less than 0.5 wt%, the thickening effect decreases due to the weakened intermolecular forces. The organic components partially dissolve within the chain segments, while the inorganic components weaken the secondary valence bonds between chain segment molecules, increasing the mobility of chain segment molecules, reducing the crystallinity of chain segment molecules, increasing their plasticity, enhancing their flexibility, and promoting flowability.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By adding flow promoter 80T, the viscosity of PET polyester is reduced, the fluidity is good, and the foaming ratio is large; (2) The preparation method is simple, the 80T powder does not affect the polyester preparation process, and the powder content used does not affect the polyester output. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the embodiments.

[0021] Example 1

[0022] The flame-retardant PET foamed polyester of this invention comprises, by weight percentage: 92% polyethylene terephthalate matrix, 7.4% flame retardant 2-carboxyethylphenyl hypophosphite, 0.1% pentaerythritol, and 0.5% flow promoter 80T. Its preparation method is as follows:

[0023] (1) Esterification and polycondensation reaction

[0024] In a 20-liter polymerization reactor, 4700g of terephthalic acid, 3200g of ethylene glycol (terephthalic acid and ethylene glycol converted to PET amounting to 5440g), 437.5g of flame retardant 2-carboxyethylphenyl hypophosphite, 5.9g of pentaerythritol, 1.8g of antimony glycolate catalyst, and 29.6g of flow promoter 80T were added. After purging three times with high-purity nitrogen, the initial pressure was adjusted to 0.10MPa (gauge pressure). The mixture was heated and stirred. Esterification was carried out at 0.15–0.50MPa pressure and 180–240℃. When the water output reached 1000g, the pressure was released to end the esterification reaction, and the temperature was increased while the pressure was reduced. Polycondensation was carried out at an absolute pressure of 20–120Pa and 260–290℃. When the intrinsic viscosity of the polyester reached 0.72dL / g, the polycondensation reaction was stopped, yielding flame-retardant PET chips.

[0025] (2) Solid-phase thickening

[0026] The flame-retardant chips were subjected to solid-phase thickening in a vacuum drum at a temperature of 190–210°C and an absolute pressure of 20–100 Pa until the viscosity reached approximately 1.2 dL / g.

[0027] (3) Foaming

[0028] The modified flame-retardant sample after solid-phase thickening was placed into a twin-screw continuous extrusion foaming equipment. The carbon dioxide pressure was set to 8 MPa (gauge pressure) to diffuse into the modified flame-retardant polyester melt at a temperature of 220–280°C. The screw speed was 20 Hz. Through rapid pressure reduction foaming, flame-retardant PET foam material was obtained.

[0029] Example 2

[0030] The flame-retardant PET foamed polyester of this invention comprises, by weight percentage: 95.2% polyethylene terephthalate matrix, 4.4% flame retardant 2-carboxyethylphenyl hypophosphite, 0.3% pentaerythritol, and 0.1% flow promoter 80T. Its preparation method is as follows:

[0031] (1) Esterification and polycondensation reaction

[0032] In a 20L polymerization reactor, 4700g of terephthalic acid, 3200g of ethylene glycol (terephthalic acid and ethylene glycol converted to PET amounting to 5440g), 251.4g of flame retardant 2-carboxyethylphenyl hypophosphite, 17.1g of pentaerythritol, 1.8g of antimony glycolate catalyst, and 5.71g of flow promoter 80T were added. After purging three times with high-purity nitrogen, the initial pressure was adjusted to 0.10MPa (gauge pressure). The mixture was heated and stirred. Esterification was carried out at 180–240℃ under a gauge pressure of 0.15–0.50MPa. When the water output reached 1000g, the pressure was released to end the esterification reaction, and the temperature was increased while the pressure was reduced. Polycondensation was carried out at 260–290℃ under an absolute pressure of 20–120Pa. When the intrinsic viscosity of the polyester was 0.72dL / g, flame-retardant PET chips were obtained.

[0033] (2) Solid-phase thickening

[0034] The flame-retardant chips were subjected to solid-phase thickening in a vacuum drum at a temperature of 190–210°C and an absolute pressure of 20–100 Pa until the viscosity reached approximately 1.2 dL / g.

[0035] (3) Foaming

[0036] The modified flame-retardant sample after solid-phase thickening was placed into a twin-screw continuous extrusion foaming equipment. The carbon dioxide pressure was set to 10 MPa (gauge pressure) to diffuse into the modified flame-retardant polyester melt at a temperature of 220–280°C. The screw speed was 20 Hz. Through rapid pressure reduction foaming, flame-retardant PET foam material was obtained.

[0037] Example 3

[0038] The flame-retardant PET foamed polyester of this invention comprises, by weight percentage: 92% polyethylene terephthalate matrix, 7.5% 2-carboxyethylphenyl hypophosphite, 0.2% pentaerythritol, and 0.3% flow promoter 80T. Its preparation method is as follows:

[0039] (1) Esterification and polycondensation reaction

[0040] In a 20L polymerization reactor, 4700g of terephthalic acid, 3200g of ethylene glycol (terephthalic acid and ethylene glycol converted to PET amounting to 5440g), 443.5g of flame retardant 2-carboxyethylphenyl hypophosphite, 11.8g of pentaerythritol, 1.8g of antimony glycolate catalyst, and 17.7g of flow promoter 80T were added. After purging three times with high-purity nitrogen, the initial pressure was adjusted to 0.10MPa (gauge pressure). The mixture was heated and stirred. Esterification was carried out at 180–240℃ under a gauge pressure of 0.15–0.50MPa. When the water output reached 1000g, the pressure was released to end the esterification reaction, and the temperature was increased while the pressure was reduced. Polycondensation was carried out at 260–290℃ under an absolute pressure of 20–120Pa. When the intrinsic viscosity of the polyester was 0.72dL / g, flame-retardant PET chips were obtained.

[0041] (2) Solid-phase thickening

[0042] The flame-retardant chips were subjected to solid-phase thickening in a vacuum drum at a temperature of 190–210°C and an absolute pressure of 20–100 Pa until the viscosity reached approximately 1.2 dL / g.

[0043] (3) Foaming

[0044] The modified flame-retardant sample after solid-phase thickening was placed into a twin-screw continuous extrusion foaming equipment. The carbon dioxide pressure was set to 15 MPa (gauge pressure) to diffuse into the modified flame-retardant polyester melt at a temperature of 220–280°C. The screw speed was 20 Hz. Through rapid pressure reduction foaming, flame-retardant PET foam material was obtained.

[0045] Example 4

[0046] The flame-retardant PET foamed polyester of this invention comprises, by weight percentage: 95.2% polyethylene terephthalate matrix, 4% flame retardant 2-carboxyethylphenyl hypophosphite, 0.3% pentaerythritol, and 0.5% flow promoter 80T. Its preparation method is as follows:

[0047] (1) Esterification and polycondensation reaction

[0048] In a 20L polymerization reactor, 4700g of terephthalic acid, 3200g of ethylene glycol (terephthalic acid and ethylene glycol converted to PET amounting to 5440g), 228.6g of flame retardant 2-carboxyethylphenyl hypophosphite, 17.1g of pentaerythritol, 1.8g of antimony glycolate catalyst, and 28.6g of flow promoter 80T were added. After purging three times with high-purity nitrogen, the initial pressure was adjusted to 0.10MPa (gauge pressure). The mixture was heated and stirred. Esterification was carried out at 180–240℃ under a gauge pressure of 0.15–0.50MPa. When the water output reached 1000g, the pressure was released to end the esterification reaction, and the temperature was increased while the pressure was reduced. Polycondensation was carried out at 260–290℃ under an absolute pressure of 20–120Pa. When the intrinsic viscosity of the polyester was 0.72dL / g, flame-retardant PET chips were obtained.

[0049] (2) Solid-phase thickening

[0050] The flame-retardant chips were subjected to solid-phase thickening in a vacuum drum at a temperature of 190–210°C and an absolute pressure of 20–100 Pa until the viscosity reached approximately 1.2 dL / g.

[0051] (3) Foaming

[0052] The modified flame-retardant sample after solid-phase thickening was placed into a twin-screw continuous extrusion foaming equipment. The carbon dioxide pressure was set to 10 MPa (gauge pressure) to diffuse into the modified flame-retardant polyester melt at a temperature of 220–280°C. The screw speed was 20 Hz. Through rapid pressure reduction foaming, flame-retardant PET foam material was obtained.

[0053] Comparative Example 1

[0054] Based on Example 2, without the addition of flow promoter 80T (blank control group).

[0055] Comparative Example 2

[0056] Based on Example 2, the mass of flow promoter 80T was increased to 55g (the content of 80T was 1%).

[0057] Performance testing

[0058] The performance of the samples prepared in Examples 1-4 and Comparative Examples 1-2 was tested using the following methods:

[0059] (1) Intrinsic viscosity (IV): Tested using the national standard method for polyester: GB / T-14190-1993;

[0060] (2) Melt Flow Index (MFI): Tested according to ASTM1238 standard, test conditions: 280℃, 2.16kg, 10min;

[0061] (3) Extrusion expansion rate: DS = D / D0, where D is the maximum diameter of the extrudate and D0 is the diameter of the die orifice;

[0062] (4) Cell characterization: The melt-foamed polyester strips were brittlely fractured in liquid nitrogen, and then gold was sprayed onto the surface. The surface morphology was observed using a JSM-6360LV scanning electron microscope. The density (ρf) of the foamed samples was obtained using a balance equipped with a density component provided by Mettler Toledo, and the test standard was ASTM 792-00. The volume expansion ratio (Rv) of the foamed samples was defined as the ratio of the density (ρp) of the unfoamed sample to the density (ρf) of the foamed sample: Rv = ρp / ρf;

[0063] The Cole-Cole plot is a graph of η" (η" = G' / ω) against η' (η' = G" / ω). For linear chains, the Cole-Cole plot is semi-circular; the larger the molecular weight, the larger the diameter of the semi-circle. Since the changes in rheological behavior in the low-frequency region are contributed by long relaxation times, when the Cole-Cole curve deviates from the semi-circular shape and gradually rises in the high-viscosity region (i.e., the low-frequency region), it indicates a longer relaxation time. This relaxation time is caused by the appearance of long branched structures, and the degree of upward rise increases with the increase of long branched structures. The Cole-Cole plot can reflect the changes in branched structure in the system as viscosity increases.

[0064] (5) Limiting oxygen index test: The performance index was analyzed according to the method of GB / T2406-2009;

[0065] The test results are shown in Table 1.

[0066] Table 1. Test results of samples from Examples 1 to 2 and Comparative Examples 1 to 2

[0067]

[0068] As can be seen from the data in Table 1, the polyesters prepared in Examples 1-4 have high foaming ratios and good foaming effects, with Example 4 showing the best foaming effect, reaching a foaming ratio of 34.6. Comparative Example 1, without the addition of flow promoter 80T, has a foaming ratio of only 12.5; Comparative Example 2, with the addition of a large amount of flow promoter 80T, suffers from difficult discharge, making it unfeasible for industrial production.

Claims

1. A flame-retardant PET foamed polyester, characterized in that, By weight percentage, the raw material composition includes: 92%~95.2% polyethylene terephthalate matrix, 4%~7.5% flame retardant, 0.1%~0.3% pentaerythritol, and 0.1%~0.5% flow promoter 80T; the foaming ratio of the polyester is 20.3~34.

6. The flow promoter 80T is a product of Tolsa Corporation under the brand name 80T. It is an organically modified sepiolite, with the organic matter linked to the inorganic powder through silicon-oxygen bonds. The organic matter accounts for 10% of the composition, while the inorganic powder has the chemical formula (Si... 12 (Mg8)O 30 (OH)4(OH2)4·8H2O, the proportion of each oxide is 62% silicon oxide and 24% magnesium oxide; the basic characteristic of the organic matter in this product is that it contains phenyl or aliphatic chain groups with carboxyl groups, which are linked to silicon-oxygen bonds in the form of ester bonds.

2. The polyester according to claim 1, characterized in that, The limiting oxygen index of the polyester is 29.1 to 34.

5.

3. The polyester according to claim 1, characterized in that, The polyester has a melt index of 19.6~21.7 g / 10 min at 280℃ and 2.16 kg.

4. The polyester according to claim 1, characterized in that, The flame retardant is a phosphorus-based flame retardant.

5. A method for preparing the polyester according to claim 1, characterized in that, The process includes the following steps: mixing terephthalic acid, ethylene glycol, catalyst, flame retardant, pentaerythritol and flow promoter 80T, carrying out esterification and polycondensation reactions to obtain flame-retardant PET chips, then performing solid-phase thickening, and finally foaming to obtain flame-retardant PET foamed polyester.

6. The method for preparing polyester according to claim 5, characterized in that, The esterification reaction is carried out at a temperature of 180~240℃ and a pressure of 0.15~0.50 MPa (gauge pressure).

7. The method for preparing polyester according to claim 5, characterized in that, The polycondensation reaction is carried out at a temperature of 260~290℃ and a pressure of 20~120Pa absolute pressure.

8. The method for preparing polyester according to claim 5, characterized in that, The solid-phase thickening temperature is 190~210℃, and the pressure is 20~100Pa absolute pressure.

9. The method for preparing polyester according to claim 5, characterized in that, The foaming process employs supercritical carbon dioxide foaming.

10. The method for preparing polyester according to claim 9, characterized in that, The pressure for supercritical carbon dioxide foaming is 8~15 MPa (gauge pressure), and the foaming temperature is 220~280℃.

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