High-toughness low-melting-point flame-retardant copolyamide composite material and preparation method thereof

Abstract

The invention provides a high-toughness low-melting-point flame-retardant copolyamide composite material and a preparation method thereof.The preparation method comprises the steps that a copolymerization modification method is adopted, PA612, PA610 and PA510 serve as copolymerization components and are added into nylon 66 salt, PA612 / 66, PA610 / 66 and PA510 / 66 copolymers are synthesized through a melt polycondensation method, the sequence state structure of copolymerization products is disturbed through multi-component copolymerization, and therefore the copolyamide composite material with the high toughness, the low melting point and the flame retardance is obtained. And finally, the melting point of the polymer is reduced, so that the polymer is easy to form and process, and flame-retardant modification is facilitated. In one embodiment of the invention, the elongation at break of the PA510 / 66 reaches up to 37.2% and is far higher than 12.0% of the PA66, and the elongation at break of the PA510 / 66 is improved by 314.0% compared with the PA66. Compared with pure PA66, the IZOD notch impact strength of the PA510 / 66 is improved by 21.3%, and it is proved that the PA510 / 66 has the good toughness characteristic. In addition, the lowest vicat softening point of the PA510 / 66 is 235.4 DEG C, and the lowest melting point of the PA510 / 66 is 244.48 DEG C. And the PA510 / 66 is indicated to have excellent molding processing performance.

Description

Technical Field

[0001] This invention relates to the field of polyamide technology, specifically to a high-toughness, low-melting-point flame-retardant copolyamide composite material and its preparation method. Background Technology

[0002] Polyamide 66, chemically known as polyhexamethylene adipamide (PA66), is a thermoplastic resin formed by the condensation polymerization of adipic acid and hexamethylenediamine. It has amide bonds in its molecular backbone structure. Since DuPont began industrial production in 1939, it has been widely used in synthetic fibers, the automotive industry, electronics, and rail transportation due to its heat resistance, wear resistance, chemical resistance, and self-lubricating properties.

[0003] With the continuous expansion of its application fields, the importance of its mechanical and flame-retardant properties has gradually gained attention. Industrially, blending modification is commonly used to introduce fillers and flame retardants to enhance its mechanical properties and achieve flame-retardant modification. However, the addition of fillers and flame retardants usually significantly increases the viscosity of nylon and reduces its flowability, thereby decreasing its molding and processing performance. Therefore, without changing the existing matrix and filler system, how to improve the flowability of polyamide 66 resin to make it more conducive to reinforcement and flame-retardant modification has become an important research direction. A key challenge is how to introduce other monomers for copolymerization to lower the melting point of polyamide 66 resin, improve its flowability, and ensure its overall physical properties and chemical stability. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a high-toughness, low-melting-point flame-retardant copolyamide composite material and its preparation method.

[0005] The technical solution adopted by this invention is as follows: The first aspect of this invention provides a method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material, comprising the following steps: S1. Adipic acid and hexamethylenediamine are mixed in a molar ratio of 1:(0.5-1.5) and added to a solvent. The mixture is stirred at 70-90°C to neutralize and generate PA66 salt. 5-15 wt.% of a copolymer salt is added to obtain a copolymer nylon salt solution. The copolymer salt is at least one of PA612 salt, PA610 salt, and PA510 salt. S2. Concentrate the copolymer nylon salt solution; S3. The concentrated copolymer nylon salt solution is transferred to a polymerization reactor, and after heating and pressurizing, holding pressure, depressurizing, and vacuuming, the following is obtained; S4. The copolymer nylon melt is extruded from the polymerization reactor, cooled and pelletized to obtain the copolymer amide composite material.

[0006] Preferably, the copolymer salt is PA510 salt.

[0007] Preferably, in step S1, 10 wt.% of the copolymer component salt is added.

[0008] Preferably, in step S2, the concentration of the copolymer nylon salt solution is concentrated to 60-80%.

[0009] Preferably, in step S3, the temperature for heating and pressurizing is 200-240℃, and the pressure is 1.75-1.85 MPa.

[0010] Preferably, in step S3, the pressure holding time is 30-90 min and the pressure holding temperature is 250-280℃.

[0011] Preferably, in step S3, the pressure relief temperature is 255-285℃ and the pressure relief time is 30-90min.

[0012] Preferably, in step S3, the temperature for vacuuming is 260-290℃.

[0013] A second aspect of the present invention provides a high-toughness, low-melting-point flame-retardant copolyamide composite material prepared by the preparation method described above.

[0014] The beneficial effects of this invention are as follows: This invention employs a copolymerization modification method, adding PA612, PA610, and PA510 as copolymer components to nylon 66 salt, and synthesizing PA612 / 66, PA610 / 66, and PA510 / 66 copolymers respectively through melt polycondensation. By using multi-component copolymerization, the ordered structure of the copolymer products is disrupted, reducing the probability of intermolecular hydrogen bond formation and thus reducing the crystallinity of the polymer. Ultimately, this lowers the melting point of the polymer, making it easier to mold and process, and facilitating flame retardant modification.

[0015] In one embodiment of the present invention, PA510 / 66 exhibits an elongation at break of 37.2%, significantly higher than PA66's 12.0%, representing a 314.0% increase compared to PA66. PA510 / 66 also demonstrates a 21.3% increase in IZOD notched impact strength compared to pure PA66, confirming its superior toughness. Furthermore, PA510 / 66 has the lowest Vicat softening point of 235.4°C and the lowest melting point of 244.48°C, indicating excellent molding and processing properties. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0017] Figure 1 The tensile properties of different copolyamide composites prepared in Examples 1-3 and Comparative Example 1 and pure PA66 are shown in the following graphs: (a) tensile strength and tensile modulus, (b) elongation at break, (c) flexural strength and flexural modulus, and (d) IZOD notched impact strength. Figure 2 Tensile cross-sectional morphology of different copolyamide composites prepared in Examples 1-3 and Comparative Example 1 and pure PA66: (a) PA66, (b) PA612 / 66, (c) PA610 / 66, (d) PA510 / 66, (e) PA56 / 66; Figure 3 The DSC curves are for the different copolyamide composites prepared in Examples 1-3, Comparative Example 1, and pure PA66. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] Example 1 This embodiment provides a high-toughness, low-melting-point flame-retardant copolyamide composite material PA612 / 66 and its preparation method, which includes the following steps: S1. Salt formation: Adipic acid and hexamethylenediamine are mixed in a 1:1 molar ratio and added to demineralized water. The mixture is stirred and mixed at 70-90℃ to neutralize and generate PA66 salt. 10wt.% of the copolymer component PA612 salt is added to obtain a copolymer nylon salt solution. S2. Concentration: The concentration of the copolynylon salt solution is concentrated to 70% by evaporating away excess water to reduce the solvent content and increase the concentration of reactants, thereby improving the efficiency of the polycondensation reaction. S3. Heating and pressurizing: Transfer the copolymer nylon salt solution to the polymerization reactor, and gradually increase the temperature to 220°C at a rate of 5°C / min, with a pressure of 1.75-1.85 MPa; S4. Holding pressure: Maintain the reaction for 1 hour to exothermic, remove moisture and low molecular weight byproducts, and increase the temperature to 265℃ at the end of the reaction. S5. Depressurization: Maintain the temperature at 270℃ and gradually reduce the pressure inside the reactor. Depressurize for 1 hour to further remove residual moisture and low molecular weight byproducts. S6. Vacuuming: Control the temperature to 275℃, turn on the vacuum pump to draw a vacuum, further remove the water between molecules, and make the polymer molecular weight rise sharply to obtain the copolymer nylon melt. S7. Pelletizing: Nitrogen gas is introduced into the polymerization reactor to extrude the copolymer nylon melt from the bottom of the reactor. After cooling to room temperature in a water bath, it is then cut into pellets of a certain size using a pelletizer.

[0020] Example 2 This embodiment provides a high-toughness, low-melting-point flame-retardant copolyamide composite material PA610 / 66 and its preparation method. In the preparation method and step S1, the added copolymer component is PA610 salt.

[0021] Example 3 This embodiment provides a high-toughness, low-melting-point flame-retardant copolyamide composite material PA510 / 66 and its preparation method. In the preparation method and step S1, the added copolymer component is PA510 salt.

[0022] Comparative Example 1 This embodiment provides a high-toughness, low-melting-point flame-retardant copolyamide composite material PA56 / 66 and its preparation method. In the preparation method and step S1, the added copolymer component is PA56 salt.

[0023] Performance Characterization The copolyamide composite materials obtained in Examples 1-3 and Comparative Example 1, along with pure P66, were injection molded into standard specimens for tensile, flexural, and IZOD notched impact tests using an injection molding machine (MA900III / 280, Haitian Plastics Machinery Group Co., Ltd.). The injection temperatures from the sprue to the injection port were 280°C, 285°C, 286°C, 287°C, and 288°C, respectively; the injection pressure was 50-75 bar; the cooling time was 8 seconds; the injection cycle was 45 seconds; and the back pressure was 3 bar. The notches on the standard specimens for the IZOD notched impact test were prepared using a notching machine (CEAST, Instron (Shanghai) Test Equipment Trading Co., Ltd.).

[0024] The tensile strength and modulus of elasticity of the specimens were tested using a universal testing machine according to GB / T 1447-2005, at a test rate of 30 mm / min. The flexural strength and modulus of flexural strength of the specimens were tested using a universal testing machine according to GB / T 1449-2005, at a bending rate of 10 mm / min and a span of 64 mm. The IZOD notched impact strength of the specimens was tested using a cantilever beam impact tester according to GB / T 1843-2008, with a remaining notch width of 8 mm, a pendulum energy of 2.75 J, and an angle of 150°.

[0025] from Figure 1 (a) It can be seen that for pure PA66, its tensile strength and tensile modulus are 79.3 MPa and 5833.65 MPa, respectively. Adding different copolymer components for copolymerization modification has little effect on the tensile strength of PA66; for example, the tensile strength of PA610 / 66 is only 4.2% higher than that of PA66. However, the addition of different copolymer components all reduce the tensile modulus of PA66. For example, the tensile modulus of PA510 / 66 is 35.6% lower than that of PA66. This is because PA612, PA610, PA510, and PA56 themselves have relatively low tensile moduli.

[0026] from Figure 1 (b) It can be seen that the elongation at break of PA66, PA612 / 66, PA610 / 66, and PA56 / 66 is in the range of 9%-13%, while the elongation at break of PA510 / 66 is as high as 37.2%, which is much higher than the 12.0% of PA66, and the elongation at break is increased by 314.0% compared with PA66. It can be seen that PA510 / 66 has high toughness.

[0027] from Figure 1 (c) It can be seen that, except for PA610 / 66, whose flexural strength and flexural modulus are close to those of PA66, the tensile properties of the other three composite materials are lower than those of PA66. This is because PA612, PA510 and PA56 have relatively low flexural strength and flexural modulus.

[0028] from Figure 1 (d) It can be seen that the addition of salt components of PA612, PA510, and PA56 significantly improved the IZOD notched impact strength of PA66 composite materials, especially PA510 / 66, whose IZOD notched impact strength increased by 21.3% compared with pure PA66, confirming that PA510 / 66 has good toughness characteristics. This is consistent with... Figure 1(b) This aligns with the conclusion that PA510 / 66 exhibits the highest elongation at break and toughness. In summary, the addition of PA610 salt has little impact on the tensile and flexural properties of PA66, maintaining its original tensile and flexural properties while significantly improving its IZOD notched impact strength and toughness. Conversely, the addition of PA510 salt, while sacrificing the tensile modulus and flexural properties of PA66, significantly enhances its IZOD notched impact strength and toughness.

[0029] Polyamide PA66 is a semi-crystalline thermoplastic polymer with excellent mechanical properties. However, PA66 has a regular and symmetrical structure, low steric hindrance, and a high melting point. Its high melt processing temperature places high demands on equipment materials and energy consumption. Therefore, reducing the melting point and molding processing temperature of PA66 to achieve energy efficiency is of great significance. Introducing PA612, PA610, PA510, and PA56 salts as raw materials and disrupting the ordered structure of the copolymer through multi-component copolymerization can reduce the probability of intermolecular hydrogen bond formation to a certain extent, thereby reducing the crystallinity of the polymer and ultimately lowering its melting point, making it easier to mold and process. To investigate the effects of the copolymer components PA612, PA610, PA510, and PA56 salts on the molding processing temperature of PA66, the Vicat softening point and melting point of different polyamide copolymers were tested. The Vicat softening point mainly refers to the temperature at which an amorphous polymer begins to soften. This experiment used a heat distortion Vicat softening point tester according to GB / T1633-2000 standard. The test sample was subjected to a 1kg load, and the temperature was lowered by 1mm. 2 The temperature at which the indenter needle is pressed to a depth of 1 mm was determined at a heating rate of 120℃ / h, and the results are shown in Table 1. Table 1 shows that PA510 / 66 has the lowest Vicat softening point at 235.4℃, while the Vicat softening points of PA612 / 66, PA610 / 66, and PA56 / 66 are all higher than 235.4℃, and could not be obtained because they exceed the equipment's heating limit. However, the depth of the indenter penetration at 235.4℃ can qualitatively determine the Vicat softening point of the sample. For example, the indenter penetration depths of PA612 / 66, PA610 / 66, and PA56 / 66 at 235.4℃ are 0.527mm, 0.511mm, and 0.542mm, respectively, all significantly lower than the 3.146mm of PA510 / 66. This indicates that they have a higher Vicat softening point temperature and are more difficult to mold. Therefore, the addition of PA510 salt can further reduce the Vicat softening point of PA66, indicating an improvement in the molding and processing performance of PA66.

[0030] Table 1. Vicat softening point test of different isopolyamide copolymers Melting point is the critical temperature at which nylon changes from a solid to a liquid state after being heated to a certain temperature. To investigate the effect of the copolymer components PA612, PA610, PA510, and PA56 salts on the melting point of PA66, this experiment used DSC equipment to test the melting points of different polyamide copolymers. The results are as follows: Figure 3 As shown, PA510 / 66 has a minimum melting point of 244.48℃, indicating that PA510 / 66 possesses excellent molding and processing properties.

[0031] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material, characterized in that, Includes the following steps: S1. Adipic acid and hexamethylenediamine are mixed in a molar ratio of 1:(0.5-1.5) and added to a solvent. The mixture is stirred at 70-90°C to neutralize and generate PA66 salt. 5-15 wt.% of a copolymer salt is added to obtain a copolymer nylon salt solution. The copolymer salt is at least one of PA612 salt, PA610 salt, and PA510 salt. S2. Concentrate the copolymer nylon salt solution; S3. The concentrated copolymer nylon salt solution is transferred to a polymerization reactor, and after heating and pressurizing, holding pressure, depressurizing, and vacuuming, the following is obtained; S4. The copolymer nylon melt is extruded from the polymerization reactor, cooled and pelletized to obtain the copolymer amide composite material.

2. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: The copolymer component salt is PA510 salt.

3. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S1, 10 wt.% of the copolymer component salt is added.

4. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S2, the concentration of the copolymer nylon salt solution is concentrated to 60-80%.

5. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S3, the temperature for heating and pressurizing is 200-240℃, and the pressure is 1.75-1.85 MPa.

6. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S3, the pressure holding time is 30-90 minutes and the pressure holding temperature is 250-280℃.

7. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S3, the pressure relief temperature is 255-285℃, and the pressure relief time is 30-90 minutes.

8. The method for preparing a high-toughness, low-melting-point flame-retardant copolyamide composite material according to claim 1, characterized in that: In step S3, the vacuum temperature is 260-290℃.

9. The high-toughness, low-melting-point flame-retardant copolyamide composite material prepared by the preparation method according to any one of claims 1-8.

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