A semi-aromatic high-temperature resistant nylon and its preparation method

Abstract

The present invention belongs to the field of polymer materials, and discloses a semi-aromatic high-temperature resistant nylon and a preparation method thereof. The preparation raw materials include nylon salt and additives. Among them, the nylon salt includes: semi-aromatic salt, with a molar fraction of 60% - 100%; PA66 salt, with a molar fraction of 0% - 40%; the additives include a branching agent, a catalyst and demineralized water. The branching agent is a polyamide acid, and the addition amount is 0.1 - 1% of the total mass of the nylon salt. In the present invention, the polyamide acid is added as a high-temperature resistant branching additive to the prepolymerization system and introduced into the main chain of the nylon molecular chain. After prepolymerization and solid-phase viscosity increase, the prepared semi-aromatic high-temperature resistant nylon has a relatively high relative viscosity. While having excellent mechanical properties, it also has better toughness and melt fluidity, and better processing performance. In addition, the preparation method is simple, easy to mass-produce and promote, and has a wide application field.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and specifically relates to a semi-aromatic high-temperature resistant nylon and a preparation method thereof. Background Art

[0002] Semi-aromatic polyamides are a class of high-performance polyamide materials containing both aliphatic and aromatic units in the main chain, combining the flexibility of aliphatic polyamides and the heat resistance and mechanical strength of aromatic polyamides. Among them, the aliphatic units provide flexibility and processability; the aromatic units enhance heat resistance, mechanical strength, and chemical stability.

[0003] Semi-aromatic polyamides have excellent heat resistance, with a glass transition temperature (Tg) above 100 °C; small deformability, shrinkage, and creep, and relatively stable dimensions; mechanical properties are superior to those of general aliphatic polyamides; have a low water absorption rate, and have little effect on the product size and mechanical properties after water absorption; excellent electrical insulation performance, and outstanding arc resistance and tracking resistance; have good solvent and corrosion resistance; small linear expansion coefficient, low warpage, and good processability. Semi-aromatic polyamides can be widely used in fields such as automobiles, electronic and electrical, and industrial materials, and future research will further improve their performance and environmental friendliness.

[0004] Although semi-aromatic high-temperature resistant polyamides have excellent properties, there are still certain problems in terms of processability, cost, performance, and environmental protection. For example, the melting point of semi-aromatic polyamides is usually higher than 300 °C, and high-temperature equipment is required during processing, increasing energy consumption and equipment costs; the melt viscosity of semi-aromatic high-temperature resistant polyamides is high, and the fluidity is poor, making it difficult to fill the mold during injection or extrusion molding; although its strength and rigidity are high, the toughness is relatively poor, and brittle fracture is likely to occur; semi-aromatic polyamides are difficult to biodegrade and may cause environmental pollution after being discarded.

[0005] Chinese Patent with Publication No. CN109575273A discloses a high-temperature resistant semi-aromatic copolyamide and a preparation method thereof. The polyamide includes the following components in parts by weight: 80 - 100 parts of terephthalic acid, 40 - 50 parts of isophthalic acid, 10 - 15 parts of adipic acid, 90 - 120 parts of hexamethylenediamine, 0.1 - 0.3 part of catalyst, 0.05 - 0.2 part of nucleating agent, 0.5 - 2.5 parts of end-capping agent, 0.25 - 0.6 part of anti-yellowing agent, and 80 - 120 parts of deionized water. The synthesized semi-aromatic copolyamide has a melting point of about 300 ± 20 °C, and its melting point is lower than the thermal decomposition temperature, and it can be directly subjected to melt extrusion molding.

[0006] Chinese Patent No. CN102477219A discloses a semi-aromatic high-temperature resistant nylon and its preparation method. 75-95 parts of nylon salt, 0.2-0.8 part of end-capping agent, 0.1-0.6 part of catalyst, 0.5-1 part of antioxidant, 0.1-0.5 part of lubricant, and 30-50 parts of deionized water are added to a stirring high-pressure polymerization kettle. A high-temperature resistant nylon prepolymer is synthesized in the high-pressure stirring reaction kettle. This prepolymer is melt-extruded twice through a twin-screw extruder, which improves the devolatilization efficiency, shortens the viscosity increasing time, and enables the smooth discharge of the high-viscosity polymer in the reaction kettle. Different extrusion temperatures are used successively to prevent the high-temperature degradation of the prepolymer.

[0007] Chinese Patent No. CN118325071A discloses a preparation method of bio-based semi-aromatic high-temperature resistant nylon PA5T / 56. Using terephthalic acid (PTA) and 1,5-pentanediamine as raw materials, copolymerizing with adipic acid, adding antioxidant and brightening agent, and finally obtaining bio-based semi-aromatic high-temperature resistant nylon PA5T / 56 through salt formation, prepolymerization, and solid-phase viscosity increasing. Some raw materials of this technology come from biomass, reducing the dependence on petroleum resources and being degradable.

[0008] Therefore, for the current preparation methods of semi-aromatic high-temperature resistant nylon, while ensuring excellent mechanical properties, the properties such as toughness and melt fluidity need to be further improved.

[0009] In view of this, the present invention is specifically proposed. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to at least overcome one of the deficiencies of the prior art, and provide a semi-aromatic high-temperature resistant nylon and its preparation method. The relative viscosity of the semi-aromatic high-temperature resistant nylon prepared by the present invention is relatively high, with excellent mechanical properties, good toughness, good fluidity, and better processing performance. In addition, the preparation method has simple steps, is suitable for large-scale production and popularization, and has a wide application field.

[0011] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0012] The present invention provides a semi-aromatic high-temperature resistant nylon, and the preparation raw materials include nylon salt and additives. Among them,

[0013] The nylon salt includes:

[0014] Semi-aromatic salt, with a molar fraction of 60%-100%;

[0015] PA66 salt, with a molar fraction of 0%-40%;

[0016] The additives include:

[0017] The branching agent is a polybasic acid amide, and the addition amount is 0.1-1% of the total mass of the nylon salt;

[0018] The catalyst, the addition amount is 0.01-0.5% of the total mass of the nylon salt;

[0019] Demineralized water, the addition amount is 50-120% of the total mass of the nylon salt.

[0020] In the raw materials of the semi-aromatic high-temperature resistant nylon of the present invention, a polybasic acid amide is added as a branching agent. The polybasic acid amide is a reaction product of a polybasic acid ester and a diamine. Among them, the polybasic acid ester provides an ester group (-COOR), which reacts with the amino group (-NH2) of the diamine in the polycondensation reaction to form an amide bond (-CONH-). The polybasic acid amide contains a terminal amino group, which can further undergo an amidation reaction with the terminal carboxyl group of the nylon salt in the prepolymerization reaction. On the one hand, the polybasic acid amide can be introduced into the main chain of the nylon molecular chain to improve the flexibility of the molecular chain, thereby improving the toughness of the semi-aromatic high-temperature resistant nylon; on the other hand, it can make the spacing of the high-temperature resistant nylon molecular chain larger, making the high-temperature resistant nylon easier to untangle during processing, and its melt fluidity is also improved, improving its processability.

[0021] The nylon salt described in the present invention can all be semi-aromatic salts and does not contain PA66 salt; it can also be a mixture of semi-aromatic salts and PA66 salts, which can be selected according to specific requirements. The ratio of the semi-aromatic salt and the PA66 salt determines the performance of the final polymer, and the performance changes with the change of the ratio of the two. The ratio of the semi-aromatic salt and the PA66 salt can be optimized and adjusted according to the requirements of the melting point, mechanical properties, and fluidity of the product. Further, the polybasic acid amide is a reaction product of a polybasic acid ester and a diamine.

[0022] Further, the molar ratio of the polybasic acid ester and the diamine is 1:(3-3.01).

[0023] In the present invention, the polybasic acid amide uses a polybasic acid ester and a diamine as reaction raw materials. The polybasic acid ester can undergo an ester-amide exchange reaction with a short-chain diamine. The polybasic acid ester provides an ester group (-COOR), which reacts with the amino group (-NH2) of the diamine in the polycondensation reaction to form an amide bond (-CONH-). The reaction conditions of this reaction are simple and the yield is high.

[0024] Further, the polybasic acid ester is selected from one or more of trimethyl citrate, triethyl citrate, tributyl citrate, triethyl phosphate, and tributyl phosphate;

[0025] Further, the diamine is selected from one or more of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine.

[0026] As an alternative embodiment, the method for preparing the polyamide includes: adding diamine into a reaction vessel, starting stirring and heating, and after the temperature reaches 60-90 °C, slowly adding the polyacid ester into the diamine solution, refluxing and heating for reaction for 4-12 h, and after the mixed reactants are cooled, performing extraction, separation, and drying to obtain the polyamide.

[0027] It has been found through experiments that when the addition amount of the branching agent is increased within a certain range, it is also helpful to further improve the toughness of the heat-resistant nylon, and at the same time its melt index also increases. Further, the semi-aromatic salt is selected from one or more of PA6T salt, PA6I salt, and PA6F salt.

[0028] Further, the catalyst is selected from one or more of phosphoric acid, sodium hypophosphite, triphenyl phosphate, trioctyl phosphite, and sodium pyrophosphate.

[0029] Further, the notched impact strength of the semi-aromatic heat-resistant nylon is 5.8-7.1 kJ / m 2 ; the tensile strength is 88-109 MPa; the flexural strength is 135-148 MPa; the melt index is 68-88 g / 10 min.

[0030] The present invention also provides a method for preparing a semi-aromatic heat-resistant nylon, including the following steps:

[0031] (1) Adding a catalyst, nylon salt, branching agent, and demineralized water into a polymerization kettle, filling with an inert gas to displace the air in the polymerization kettle, inflating and pressurizing, heating and stirring to perform a prepolymerization reaction to obtain a prepolymer;

[0032] (2) Separating the prepolymer into solid and liquid, and drying and pulverizing the prepolymer;

[0033] (3) Performing solid-phase polycondensation reaction on the pulverized prepolymer to obtain a semi-aromatic heat-resistant nylon.

[0034] Further, in step (1), the conditions of the prepolymerization reaction include:

[0035] First, heating to 170 °C - 200 °C, reacting for 0.5 h - 2 h, draining water and maintaining the pressure stable at 0.5 - 1.0 MPa;

[0036] Continuing to heat to 200 °C - 240 °C, the pressure is 1.8 - 3.0 MPa, and reacting for 1 h - 4 h;

[0037] Continuing to heat to 250 °C - 280 °C, reacting for 1 - 3 h, slowly reducing the pressure and reducing it to atmospheric pressure to obtain a semi-aromatic heat-resistant nylon prepolymer.

[0038] In the preparation method of the present invention, the conditions of the prepolymerization reaction adopt a method of programmed stage temperature rise. In this way, the molecular weight of the prepolymer can be controlled, and the prepared high-temperature resistant nylon resin has good fluidity while maintaining excellent mechanical properties, solving the problem that semi-aromatic nylon has poor fluidity and is not conducive to subsequent processing. If a direct temperature rise method is used, it will cause the molecular weight distribution of the polymerization to become wider and the mechanical properties to decline.

[0039] In a further embodiment, in step (2), the prepolymer is transported to a solid-liquid separator, and solid-liquid separation is carried out in the solid-liquid separator.

[0040] In a further embodiment, in step (3), the conditions of the solid-phase polycondensation reaction include: under nitrogen protection, the reaction temperature is 230-280 °C, and the reaction time is 5h-10h;

[0041] Preferably, the solid-phase polycondensation reaction is carried out in a solid-phase viscosity-increasing reaction bed or a vacuum drum.

[0042] In a further embodiment, the relative viscosity of the obtained semi-aromatic high-temperature resistant nylon is 1.85-3.2.

[0043] After adopting the above technical solutions, the present invention has the following beneficial effects compared with the prior art.

[0044] 1. In the semi-aromatic high-temperature resistant nylon prepared by the present invention, a polyamide polyacid is added as a branching agent to the raw materials. The polyamide polyacid is the reaction product of a polyacid ester and a diamine. The preparation method of this branching agent is simple and has a high yield. It can be effectively introduced into the main chain of the high-temperature resistant nylon molecular chain by copolymerization, improving the flexibility of the molecular chain and the toughness of the semi-aromatic high-temperature resistant nylon; on the other hand, after introduction, it can also increase the distance between the high-temperature resistant nylon molecular chains, making the high-temperature resistant nylon easier to disentangle during processing, improving its melt fluidity, and enhancing its processability.

[0045] In addition, it has been found through experiments that increasing the addition amount of the branching agent within a certain range helps to further improve its toughness; at the same time, the melt index increases, which is beneficial to subsequent processing.

[0046] 2. In the preparation method of the semi-aromatic high-temperature resistant nylon of the present invention, a method of programmed stage temperature rise is adopted in the prepolymerization reaction. In this way, the molecular weight of the prepolymer can be controlled, and the prepared high-temperature resistant nylon resin has good fluidity while maintaining excellent mechanical properties, solving the problem that semi-aromatic nylon has poor fluidity and is not conducive to subsequent processing.

[0047] 3. The preparation method of the semi-aromatic high-temperature resistant nylon provided by the present invention has simple operation steps and easy-to-control conditions, which is conducive to large-scale production and market promotion and application, and has broad prospects and application fields. Specific Embodiments

[0048] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will, in combination with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments. The following embodiments are used to illustrate the present invention but not to limit the scope of the present invention.

[0049] In the embodiments of the present invention, the test methods for relative viscosity, melting point, and mechanical properties are as follows:

[0050] 1. Relative viscosity test conditions: The relative viscosity of the solution after dissolving heat-resistant nylon with concentrated sulfuric acid with a concentration of 98% is tested at a temperature of 25°C, a concentration of 0.01 g / ml, and tested in accordance with ISO307 standard.

[0051] 2. Melting point test: Using the DSC method, weigh 5 - 8 mg of the sample. Under a nitrogen atmosphere, heat from room temperature to 400°C at a rate of 20°C / min, hold for 5 min, then cool to room temperature at a rate of 20°C / min, and then heat to 400°C at a rate of 10°C / min. The endothermic peak temperature at this time is the polymer melting point.

[0052] 3. Mechanical property test: The prepared heat-resistant nylon injection-molded test specimens are used to test the tensile strength according to the GB / T1040.2 standard, the flexural strength and flexural modulus according to the GB / T9341-2008 standard, and the notched izod impact strength according to the GB / T1043.1 standard.

[0053] 4. Melt index: Tested according to ISO1133, the test temperature is 330°C, and the weight of the weight is 5 kg.

[0054] The experimental materials used in the following embodiments, unless otherwise specified, can be purchased from conventional biochemical reagent companies. The preparation method of the polyamide in the following embodiments includes: adding diamine to the reaction vessel, starting stirring and heating. After the temperature reaches 60 - 90°C, slowly add the polyacid ester to the diamine solution, reflux and heat for 4 - 12 h. After the mixed reactants are cooled, they are extracted, separated, and dried to obtain the polyamide.

[0055] Example 1

[0056] This example prepares heat-resistant nylon by the following steps:

[0057] This example prepares heat-resistant nylon by the following steps:

[0058] (1) In the polymerization kettle, after adding 17 kg (60 mol) of PA6T salt, 10.5 kg (40 mol) of PA66 salt, 70 g of sodium hypophosphite, 80 g of trimethyl citrate - ethylenediamine reactant (molar ratio of trimethyl citrate to ethylenediamine is 1:3), and 30 kg of deionized water, inert gas N2 is filled to displace the air in the polymerization kettle. It is pressurized to 0.8 MPa, heated and stirred, and the temperature is raised to 180 °C for reaction for 1.5 h, and the water is drained to keep the pressure stable; the temperature is continuously raised to 225 °C, the pressure is maintained at 2.2 MPa, and the reaction is carried out for 3 h; the temperature is continuously raised to 275 °C, the reaction is carried out for 2 h, and the pressure is slowly reduced and reduced to atmospheric pressure to obtain a PA6T / 66 prepolymer;

[0059] (2) The prepolymer obtained in step (1) is transported to a solid - liquid separator for solid - liquid separation to obtain a solid product. Then the prepolymer is dried and pulverized;

[0060] (3) The prepolymer powder obtained in step (2) is fed into a vacuum rotary drum for solid - phase polymerization reaction at a temperature of 260 °C and a residence time of 3 h to obtain heat - resistant nylon PA6T / 66.

[0061] Example 2

[0062] The formulation process is the same as that of Example 1, except that the trimethyl citrate - ethylenediamine reactant (molar ratio of trimethyl citrate to ethylenediamine is 1:3) is 240 g.

[0063] Example 3

[0064] The formulation process is the same as that of Example 1, except that the tributyl citrate - ethylenediamine reactant (molar ratio of tributyl citrate to ethylenediamine is 1:3) is 80 g.

[0065] Example 4

[0066] This example prepares heat - resistant nylon by the following steps:

[0067] (1) In the polymerization kettle, after adding 20 kg (70 mol) of PA6T salt, 7.9 kg (30 mol) of PA66 salt, 70 g of sodium hypophosphite, 80 g of triethyl citrate - ethylenediamine reactant (molar ratio of triethyl citrate to ethylenediamine is 1:3), and 20 kg of deionized water, inert gas N2 is filled to displace the air in the polymerization kettle. It is pressurized to 0.8 MPa, heated and stirred, and the temperature is raised to 184 °C for reaction for 1.5 h, and the water is drained to keep the pressure stable; the temperature is continuously raised to 230 °C, the pressure is maintained at 2.2 MPa, and the reaction is carried out for 3 h; the temperature is continuously raised to 280 °C, the reaction is carried out for 2 h, and the pressure is slowly reduced and reduced to atmospheric pressure to obtain a PA6T / 66 prepolymer;

[0068] (2) The prepolymer obtained in step (1) is transported to a solid - liquid separator for solid - liquid separation to obtain a solid product. Then the prepolymer is dried and pulverized;

[0069] (3) Feed the prepolymer powder obtained in step (2) into a vacuum rotary drum for solid-phase polymerization reaction at a temperature of 260 °C and a residence time of 3 h to obtain heat-resistant nylon PA6T / 66.

[0070] Example 5

[0071] The following steps are adopted in this example to prepare heat-resistant nylon:

[0072] (1) In a polymerization kettle, add 14.7 kg (52 mol) of PA6T salt, 13.5 kg (48 mol) of PA6I salt, 100 g of sodium pyrophosphate, 85 g of the reaction product of triethyl citrate-1,3-propanediamine (molar ratio of triethyl citrate to propanediamine is 1:3), and 15 kg of demineralized water. Then, fill inert gas N2 to displace the air in the polymerization kettle, pressurize it to 0.8 MPa, heat and stir, raise the temperature to 182 °C and react for 1.5 h, drain the water to keep the pressure stable; continue to raise the temperature to 232 °C, keep the pressure at 2.2 MPa and react for 3 h; continue to raise the temperature to 272 °C and react for 1.5 h, then slowly reduce the pressure and drop it to atmospheric pressure to obtain PA6T / 6I prepolymer;

[0073] (2) Transport the prepolymer obtained in step (1) to a solid-liquid separator for solid-liquid separation to obtain a solid product. Then, dry and crush the prepolymer;

[0074] (3) Feed the prepolymer powder obtained in step (2) into a vacuum rotary drum for solid-phase polymerization reaction at a temperature of 272 °C and a residence time of 0.5 h to obtain heat-resistant nylon PA6T / 6I.

[0075] Example 6

[0076] The following steps are adopted in this example to prepare heat-resistant nylon:

[0077] (1) In a polymerization kettle, add 17 kg (60 mol) of PA6T salt, 5.6 kg (20 mol) of PA6I salt, 5.2 kg (20 mol) of PA66 salt, 110 g of triphenyl phosphite, 200 g of the reaction product of triethyl phosphate-ethylenediamine (molar ratio of triethyl phosphate to ethylenediamine is 1:3), and 33 kg of demineralized water. Then, fill inert gas N2 to displace the air in the polymerization kettle, pressurize it to 0.8 MPa, heat and stir, raise the temperature to 180 °C and react for 1.5 h, drain the water to keep the pressure stable; continue to raise the temperature to 231 °C, keep the pressure at 2.2 MPa and react for 3 h; continue to raise the temperature to 263 °C and react for 2.2 h, then slowly reduce the pressure and drop it to atmospheric pressure to obtain PA6T / 6I / 66 prepolymer;

[0078] (2) Transport the prepolymer obtained in step (1) to a solid-liquid separator for solid-liquid separation to obtain a solid product. Then, dry and crush the prepolymer;

[0079] (3) Feed the prepolymer powder obtained in step (2) into a vacuum rotary drum for solid-phase polymerization reaction at a temperature of 255 °C for a residence time of 4 h to obtain heat-resistant nylon PA6T / 6I / 66.

[0080] Example 7

[0081] The following steps are used to prepare heat-resistant nylon in this example:

[0082] (1) In a polymerization kettle, add 16.3 kg (60 mol) of PA6F salt, 10.5 kg (40 mol) of PA66 salt, 140 g of trioctyl phosphite, 240 g of triethyl phosphate-1,4-butanediamine reactant (molar ratio of triethyl phosphate: 1,4-butanediamine is 1:3), and 13.5 kg of deionized water. Then fill with inert gas N2 to displace the air in the polymerization kettle, pressurize with gas to 0.8 MPa, heat and stir, raise the temperature to 180 °C and react for 1.5 h, drain the water and keep the pressure stable; continue to raise the temperature to 231 °C, keep the pressure at 2.2 MPa and react for 3 h; continue to raise the temperature to 263 °C and react for 2 h, then slowly reduce the pressure and drop to atmospheric pressure to obtain PA6F / 66 prepolymer;

[0083] (2) Transfer the prepolymer from step (1) to a solid-liquid separator for solid-liquid separation to obtain a solid product. Then dry and crush the prepolymer;

[0084] (3) Feed the prepolymer powder obtained in step (2) into a vacuum rotary drum for solid-phase polymerization reaction at a temperature of 280 °C for a residence time of 2.2 h to obtain heat-resistant nylon PA6F / 66.

[0085] Example 8

[0086] The following steps are used to prepare heat-resistant nylon in this example:

[0087] (1) In a polymerization kettle, add 15.8 kg (58 mol) of PA6F salt, 11.8 (42 mol) of PA6I salt, 40 g of phosphoric acid, 200 g of tributyl phosphate-ethylenediamine reactant (molar ratio of tributyl phosphate: ethylenediamine is 1:3), and 22 kg of deionized water. Then fill with inert gas N2 to displace the air in the polymerization kettle, pressurize with gas to 0.8 MPa, heat and stir, raise the temperature to 180 °C and react for 1.5 h, drain the water and keep the pressure stable; continue to raise the temperature to 231 °C, keep the pressure at 2.2 MPa and react for 3 h; continue to raise the temperature to 263 °C and react for 2.5 h, then slowly reduce the pressure and drop to atmospheric pressure to obtain PA6F / 6I prepolymer;

[0088] (2) Transfer the prepolymer from step (1) to a solid-liquid separator for solid-liquid separation to obtain a solid product. Then dry and crush the prepolymer;

[0089] (3) Feed the prepolymer powder obtained in step (2) into a vacuum rotary drum for solid-phase polymerization reaction at a temperature of 256 °C and a residence time of 3 h to obtain heat-resistant nylon PA6F / 6I.

[0090] Comparative Example 1

[0091] The formulation process is the same as that in Example 1, except that: trimethyl citrate-ethylenediamine reactant is not added.

[0092] Comparative Example 2

[0093] The formulation process is the same as that in Example 1, except that: the trimethyl citrate-ethylenediamine reactant is replaced by trimesic acid,

[0094] with the same dosage.

[0095] Comparative Example 3

[0096] The formulation process is the same as that in Example 1, except that: the amount of trimethyl citrate-ethylenediamine reactant is 280 g.

[0097] Comparative Example 4

[0098] The formulation is the same as that in Example 1, except that in step (1), the stepwise temperature increase method is not adopted, and the heat-resistant nylon is prepared by the following steps:

[0099] (1) In a polymerization kettle, add 17 kg (60 mol) of PA6T salt, 10.5 kg (40 mol) of PA66 salt, 70 g of sodium hypophosphite, 80 g of trimethyl citrate-ethylenediamine copolymer and 30 kg of deionized water, then fill the inert gas N2 to displace the air in the polymerization kettle, pressurize to 0.8 MPa, heat and stir, raise the temperature to 275 °C, and react for 5 h to obtain PA6T / 66 prepolymer.

[0100] Steps (2) and (3) are the same as those in Example 1.

[0101] Table 1 Test results of heat-resistant nylon prepared in examples and comparative examples

[0102]

[0103] Result analysis:

[0104] It can be seen from Table 1 that the polyacid amide prepared in the present invention is introduced into the main chain of the heat-resistant nylon molecular chain, improving the flexibility of the molecular chain, increasing the notch impact strength, and increasing its content helps to further improve its toughness; at the same time, the melt index increases, which is beneficial to subsequent processing.

[0105] Compared with Example 1, in Example 2, the addition amount of the branching agent (trimethyl citrate-ethylenediamine copolymer) is more, and both the notched impact strength and the melt index are improved.

[0106] When comparing Example 1 and Example 3, in Example 3, tributyl citrate-ethylenediamine is used as the branching agent. It can be seen that the notched impact strength and the melt index have little difference, indicating that both trimethyl citrate-ethylenediamine and tributyl citrate-ethylenediamine can play a role in improving toughness and have similar effects.

[0107] In Example 4, when the content of nylon 6T is increased, the melting point of the copolymer increases, which is due to the increase in the melting point; the tensile strength and bending properties are improved, which is due to the increase in the content of rigid groups in the molecular chain, and its impact strength decreases significantly.

[0108] Compared with Example 1, in Comparative Example 1, no polyacid amide is added. The tensile strength and bending strength of the copolymer change little, but the notched impact strength and the melt index decrease. This is because the addition of the branching agent introduces flexible chain segments into the PA6T / 66 chain segments, improving the impact resistance of the polymer. At the same time, the special structure of the branching agent makes the molecular chain spacing of the high-temperature nylon larger, and it is easier to disentangle during processing, and its fluidity is improved.

[0109] In Comparative Example 2, when the same content of trimellitic acid is added, both the notched impact strength and the melt index of the polymer decrease. This is because the side chain of trimellitic acid is shorter. After adding, the melt index can be slightly increased compared with Comparative Example 1, but its impact on the impact strength is not significant.

[0110] In Comparative Example 3, when an excessive amount of branching agent is added, its terminal amino group will react with the terminal carboxyl group of the high-temperature nylon chain, acting as a capping agent, making its molecular weight unable to continue to increase, having a relatively low viscosity, and poor mechanical properties.

[0111] In Comparative Example 4, instead of using stepwise temperature increase, it directly raises the temperature to 275°C for high-temperature and high-pressure reaction to form a prepolymer. Its mechanical properties decrease significantly. This is because the stepwise temperature increase polymerization process is adopted, and by controlling the temperature and pressure at different polymerization stages, the prepolymerization reaction of nylon salt is effectively controlled, the salt decomposition is inhibited, and the controllable polymerization reaction of polyamide salt solution is realized, ensuring the stable and controllable growth of the polymer viscosity. While using the direct temperature increase process, it will lead to a wider molecular weight distribution of the polymerization and a decrease in mechanical properties.

[0112] The above are only the preferred embodiments of the present invention, and there is no limitation to the present invention in any form. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of the present invention can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content prompted above within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the present invention's solution.

Claims

1. A semi-aromatic high-temperature resistant nylon, characterized in that, The raw materials for preparation include nylon salt and additives. Among them, the nylon salt includes: semi-aromatic salt, with a molar fraction of 60% - 100%; PA66 salt, with a molar fraction of 0% - 40%; the additives include: a branching agent, which is a polyamide of polybasic acid, and the addition amount is 0.1 - 1% of the total mass of the nylon salt; a catalyst, and the addition amount is 0.01 - 0.5% of the total mass of the nylon salt; demineralized water, and the addition amount is 50 - 120% of the total mass of the nylon salt.

2. The semi-aromatic high-temperature resistant nylon according to claim 1, wherein The polyamide of polybasic acid is the reaction product of polybasic acid ester and diamine.

3. The semi-aromatic high-temperature resistant nylon according to claim 2, characterized in that, The polybasic acid ester is selected from one or more of trimethyl citrate, triethyl citrate, tributyl citrate, triethyl phosphate, and tributyl phosphate; the diamine is selected from one or more of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine.

4. The semi-aromatic high-temperature resistant nylon according to any one of claims 1-3, characterized in that, The semi-aromatic salt is selected from one or several of PA6T salt, PA6I salt, and PA6F salt.

5. The semi-aromatic high-temperature resistant nylon according to any one of claims 1 to 3, characterized in that, The catalyst is selected from one or more of phosphoric acid, sodium hypophosphite, triphenyl phosphate, trioctyl phosphite, and sodium pyrophosphate.

6. The semi-aromatic high-temperature resistant nylon according to any one of claims 1-3, characterized in that, The notched impact strength of the semi-aromatic high-temperature resistant nylon is 5.8 - 7.1 kJ / m 2 ; the tensile strength is 88 - 109 MPa; the flexural strength is 135 - 148 MPa; the melt index is 68 - 88 g / 10 min.

7. A method for preparing a semi-aromatic high-temperature resistant nylon according to any one of claims 1-6, characterized in that, It includes the following steps: (1) Add the catalyst, nylon salt, branching agent, and demineralized water into the polymerization kettle, fill with inert gas to displace the air in the polymerization kettle, inflate and pressurize, heat and stir to carry out a prepolymerization reaction to obtain a prepolymer; (2) Carry out solid-liquid separation on the prepolymer, and dry and crush the prepolymer; (3) Carry out a solid-phase polycondensation reaction on the crushed prepolymer to obtain semi-aromatic high-temperature resistant nylon.

8. The preparation method according to claim 7, characterized in that, In step (1), the conditions of the prepolymerization reaction include: First, raise the temperature to 170°C - 200°C, react for 0.5 h - 2 h, drain water and keep the pressure stable at 0.5 - 1.0 MPa; Continue to raise the temperature to 200°C - 240°C, the pressure is 1.8 - 3.0 MPa, and react for 1 h - 4 h; Continue to raise the temperature to 250°C - 280°C, react for 1 - 3 h, slowly reduce the pressure and reduce it to atmospheric pressure to obtain a semi-aromatic high-temperature resistant nylon prepolymer.

9. The preparation method according to claim 7, characterized in that, In step (3), the conditions of the solid-phase polycondensation reaction include: under nitrogen protection, the reaction temperature is 230 - 280°C, and the reaction time is 5 h - 10 h.

10. The preparation method according to claim 7, wherein The solid-phase polycondensation reaction is carried out in a solid-phase viscosity-increasing reaction bed or a vacuum drum.

11. The preparation method according to any one of claims 7-10, characterized in that, The relative viscosity of the obtained semi-aromatic high-temperature resistant nylon is 1.85 - 3.2.

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