Beta nucleating agent for polypropylene pipe and preparation method of beta nucleating agent

Abstract

The invention provides a beta nucleating agent for a polypropylene pipe and a preparation method of the beta nucleating agent, and relates to the technical field of nucleating agents. The preparation method of the beta nucleating agent for the polypropylene pipe comprises the following steps: dissolving lanthanum nitrate hexahydrate and 2, 6-pyridinedicarboxylic acid in a mixed solvent of ethanol and water, and carrying out reflux reaction to generate a light yellow complex precipitate La (PDA) 3; the preparation method comprises the following steps: dispersing La (PDA) 3 in an ethanol solution of cetyltrimethylammonium bromide, adding tetraethoxysilane, adding ammonia water to catalyze hydrolysis, carrying out centrifugal collection after reaction, and calcining to remove cetyltrimethylammonium bromide so as to obtain a La-PDA coated SiO2 primary nucleating agent; dispersing the La-PDA coated SiO2 in absolute ethyl alcohol, adding a silane coupling agent, carrying out reflux reaction for grafting, filtering and drying to obtain the beta nucleating agent. According to the beta nucleating agent provided by the invention, the nucleating efficiency of the beta nucleating agent in polypropylene is improved.

Description

Technical Field

[0001] The invention relates to the technical field of nucleating agents, and in particular to a beta nucleating agent for polypropylene pipes and a preparation method thereof. Background Art

[0002] Polypropylene exists in five crystal structures: α, β, γ, δ, and pseudo-hexagonal. The α crystal is the most common thermodynamically stable crystal, while the β crystal is a metastable crystal that generally gradually transforms into a stable α crystal over a period of approximately seven days. β-crystal polypropylene has unique properties. Compared to α-crystal polypropylene, β-crystal polypropylene exhibits significant advantages in impact toughness, heat deformation temperature, and crack resistance. Introducing β-crystals into polypropylene pipes can significantly improve the pipe's impact resistance, especially in low-temperature environments. It effectively prevents the pipe from rupturing due to external impact, thereby extending the pipe's service life and improving its safety and reliability.

[0003] At present, the nucleation efficiency of some β-nucleating agents on the market is low. On the one hand, they cannot induce the formation of a sufficient amount of β-crystal in polypropylene. On the other hand, the existing β-nucleating agents on the market will also transform into α-crystal over time, causing the pipe to gradually form α-crystal after a period of time, resulting in a decrease in impact resistance and low-temperature impact resistance. This results in the performance improvement effect of polypropylene pipes not being obvious, and it is difficult to meet some application scenarios with high requirements for pipe performance. In some building water supply and drainage systems in cold areas, pipes need to have good low-temperature impact resistance, and β-nucleating agents with low nucleation efficiency cannot enable polypropylene pipes to maintain sufficient toughness at low temperatures, increasing the risk of pipes breaking in low-temperature environments. Based on this, the present invention provides a β-nucleating agent for polypropylene pipes and a preparation method thereof, which can obtain stable β-crystals and can prolong the time for β-crystals to transform into α-crystals. Summary of the Invention

[0004] The purpose of the present invention is to provide a β-nucleating agent for polypropylene pipes and a preparation method thereof, thereby improving the nucleation efficiency of the β-nucleating agent in polypropylene and improving the impact resistance, heat deformation temperature, and crack resistance of polypropylene pipes in low-temperature environments.

[0005] In one aspect, the present invention provides a method for preparing a β-nucleating agent for polypropylene pipes, comprising the steps of: (1) Lanthanum nitrate hexahydrate and 2,6-pyridinedicarboxylic acid are dissolved in a mixed solvent of ethanol and water, and refluxed to form a light yellow complex precipitate La(PDA)3; (2) La(PDA)3 was dispersed in an ethanol solution of hexadecyltrimethylammonium bromide, ethyl orthosilicate was added, and ammonia was added to catalyze the hydrolysis. After the reaction, the mixture was centrifuged and calcined to remove the hexadecyltrimethylammonium bromide to obtain the La-PDA@SiO2 primary nucleating agent. (3) La-PDA@SiO2 is dispersed in anhydrous ethanol, a silane coupling agent is added, and the grafting is carried out by reflux reaction. After filtering and drying, the β-nucleating agent is obtained.

[0006] Furthermore, in step (1), the reflux reaction temperature is 75-85° C. and the reaction time is 3.5-4.5 h.

[0007] Furthermore, in step (1), the molar ratio of lanthanum nitrate hexahydrate to 2,6-pyridinedicarboxylic acid is 1:2.5-3.5.

[0008] Furthermore, in step (2), the reaction temperature is 45-55° C., and the reaction time is 5-7 h; in step (2), the calcination temperature is 500-600° C., and the calcination time is 3.5-4.5 h.

[0009] Furthermore, in step (2), the usage ratio of La(PDA)3, hexadecyltrimethylammonium bromide, ethanol and ethyl orthosilicate is 1 g: (0.7-0.9) g: (70-80) mL: (0.8-1.2) g.

[0010] Furthermore, in step (2), the ethyl orthosilicate is an ethanol solution of ethyl orthosilicate with a mass fraction of 15-25%.

[0011] Furthermore, in step (2), ammonia water is added to adjust the pH to 10±0.2.

[0012] Furthermore, in step (3), the reflux reaction temperature is 75-85° C. and the reaction time is 100-140 min.

[0013] Furthermore, the silane coupling agent in step (3) is silane coupling agent KH-550, wherein the usage ratio of the La-PDA@SiO2, anhydrous ethanol and silane coupling agent is 1: (20-30) mL: (0.04-0.06) g.

[0014] On the other hand, the present invention also provides a β-nucleating agent for polypropylene pipes, which is prepared using the above-mentioned preparation method.

[0015] The beneficial effects of the present invention are: The present invention provides a method for preparing a beta-nucleating agent for polypropylene pipes. The beta-nucleating agent is prepared by a multi-step reaction. First, a light yellow complex La(PDA)3 is synthesized to precipitate, which is then dispersed in a specific solution. TES and ammonia are added to catalyze hydrolysis to prepare a La-PDA@SiO2 primary nucleating agent. Finally, a silane coupling agent is used for grafting to obtain the final beta-nucleating agent.

[0016] The present invention dissolves lanthanum nitrate hexahydrate and 2,6-pyridinedicarboxylic acid in a mixed solvent of ethanol and water, and refluxes the reaction to generate a light yellow complex precipitate La(PDA)3. This process is based on the principle of coordination chemistry. The lanthanum ions in lanthanum nitrate hexahydrate have empty orbitals, while the carboxyl oxygen atoms and pyridine nitrogen atoms in 2,6-pyridinedicarboxylic acid have lone pairs of electrons, which can form a stable complex La(PDA)3 through coordination bonds. This La(PDA)3 with a stable structure and high purity lays a good foundation for the subsequent compounding with SiO2 to form a La-PDA@SiO2 primary nucleating agent, which makes the primary nucleating agent have a uniform chemical composition and structure, thereby being able to better play a nucleating role in the polypropylene matrix and improve the nucleation efficiency of β crystals.

[0017] The present invention disperses La(PDA)3 in an ethanol solution of hexadecyltrimethylammonium bromide, adds tetraethyl orthosilicate, and performs a hydrolysis reaction under the catalysis of ammonia water. Tetraethyl orthosilicate undergoes hydrolysis and polycondensation under alkaline conditions to generate SiO2. Hexadecyltrimethylammonium bromide, as a surfactant, acts as a template during the reaction. It can be adsorbed on the surface of La(PDA)3, guiding SiO2 to grow around La(PDA)3, forming a La-PDA@SiO2 composite structure. The composite structure of La(PDA)3 and SiO2 exerts a synergistic effect. La(PDA)3 has specific chemical properties and structures, and can interact with polypropylene molecular chains to a certain extent, guiding the polypropylene molecular chains to nucleate at specific locations. SiO2 can improve the dispersibility of La(PDA)3 in the polypropylene matrix, prevent its agglomeration, enable the nucleating agent to be more evenly distributed in the polypropylene, and increase the number of nucleation sites. At the same time, it provides a suitable surface structure for subsequent grafting reactions, further enhancing the nucleating ability of the nucleating agent in polypropylene.

[0018] The present invention disperses La-PDA@SiO2 in anhydrous ethanol and adds a silane coupling agent KH-550 for reflux reaction grafting. Two different functional groups in the silane coupling agent molecule, one of which reacts with the hydroxyl group on the SiO2 surface, and the other produces a bridging effect with the polypropylene matrix, forming a chemical bond between the nucleating agent and the polypropylene matrix, which can stabilize the nucleation site of the β crystal and effectively inhibit the conversion of the β crystal to the α crystal. This chemical bond enhances the interfacial bonding force between the nucleating agent and the polypropylene matrix, allowing the nucleating agent to be more firmly fixed in the polypropylene matrix. During the polypropylene crystallization process, the nucleating agent can more effectively guide the polypropylene molecular chains to arrange in an orderly manner on the surface of the nucleating agent, forming more β crystals. Moreover, the β crystal nucleating agent of the present application can delay the efficiency of the conversion to α crystal, allowing the β crystal to exist stably in the polypropylene for a longer period of time. The β-crystal form has a tighter molecular arrangement and higher stability. Its existence can not only improve the toughness of polypropylene and enhance the impact resistance of polypropylene pipes in low-temperature environments, but also improve the crystal structure of polypropylene, increase its heat deformation temperature and crack resistance. Because the β-crystal form has a tighter molecular arrangement and higher stability, it can resist external deformation and cracking stress. DETAILED DESCRIPTION

[0019] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0020] Example 1 This embodiment provides a method for preparing a β-nucleating agent for polypropylene pipes, comprising the following steps: (1) Dissolve 10 mmol of lanthanum nitrate hexahydrate and 30 mmol of 2,6-pyridinedicarboxylic acid in a mixed solvent of 100 mL of ethanol and 50 mL of water. Reflux at 80°C for 4 h to generate a light yellow complex precipitate La(PDA)3. Centrifuge, wash with ethanol three times, and vacuum dry at 60°C for 12 h. (2) Disperse 1 g of dried La(PDA)3 and 0.8 g of hexadecyltrimethylammonium bromide in 75 mL of ethanol solution, add 20% ethanol solution containing 1 g of ethyl orthosilicate dropwise, add ammonia water to adjust the pH to 10 for catalytic hydrolysis, react at 50 ° C for 6 h, collect by centrifugation, and calcine at 550 ° C for 4 h to remove hexadecyltrimethylammonium bromide to obtain La-PDA@SiO2 primary nucleating agent; (3) Disperse 1 g of La-PDA@SiO2 in 25 mL of anhydrous ethanol, add 0.05 g of silane coupling agent KH-550, reflux at 80 °C for 120 min for grafting, filter, and vacuum dry at 60 °C for 12 h to obtain the β-nucleating agent.

[0021] Example 2 This embodiment provides a method for preparing a β-nucleating agent for polypropylene pipes, comprising the following steps: (1) Dissolve 10 mmol of lanthanum nitrate hexahydrate and 25 mmol of 2,6-pyridinedicarboxylic acid in a mixed solvent of 100 mL of ethanol and 50 mL of water. Reflux at 75°C for 3.5 h to generate a light yellow complex precipitate La(PDA)3. Centrifuge, wash with ethanol three times, and dry in a vacuum at 60°C for 12 h. (2) Disperse 1 g of dried La(PDA)3 and 0.7 g of hexadecyltrimethylammonium bromide in 70 mL of ethanol solution, add dropwise 15% ethanol solution containing 0.8 g of ethyl orthosilicate, add aqueous ammonia to adjust the pH to 10 for catalytic hydrolysis, react at 45 °C for 5 h, collect by centrifugation, and calcine at 500 °C for 3.5 h to remove hexadecyltrimethylammonium bromide to obtain La-PDA@SiO2 primary nucleating agent; (3) Disperse 1 g of La-PDA@SiO2 in 20 mL of anhydrous ethanol, add 0.04 g of silane coupling agent KH-550, reflux at 75 °C for 100 min for grafting, filter, and vacuum dry at 60 °C for 12 h to obtain the β-nucleating agent.

[0022] Example 3 This embodiment provides a method for preparing a β-nucleating agent for polypropylene pipes, comprising the following steps: (1) Dissolve 10 mmol of lanthanum nitrate hexahydrate and 35 mmol of 2,6-pyridinedicarboxylic acid in a mixed solvent of 100 mL of ethanol and 50 mL of water. Reflux at 85°C for 4.5 h to generate a light yellow complex precipitate La(PDA)3. Centrifuge, wash with ethanol three times, and vacuum dry at 60°C for 12 h. (2) Disperse 1 g of dried La(PDA)3 and 0.9 g of hexadecyltrimethylammonium bromide in 80 mL of ethanol solution, add 25% ethanol solution containing 1.2 g of ethyl orthosilicate dropwise, add ammonia water to adjust the pH to 10 for catalytic hydrolysis, react at 55 °C for 7 h, collect by centrifugation, and calcine at 600 °C for 4.5 h to remove hexadecyltrimethylammonium bromide to obtain La-PDA@SiO2 primary nucleating agent; (3) Disperse 1 g of La-PDA@SiO2 in 30 mL of anhydrous ethanol, add 0.06 g of silane coupling agent KH-550, reflux at 85 °C for 140 min for grafting, filter, and vacuum dry at 60 °C for 12 h to obtain the β-nucleating agent.

[0023] Example 4 This embodiment provides a method for preparing a β-nucleating agent for polypropylene pipes, comprising the following steps: (1) Dissolve 10 mmol of lanthanum nitrate hexahydrate and 25 mmol of 2,6-pyridinedicarboxylic acid in a mixed solvent of 100 mL of ethanol and 50 mL of water. Reflux at 85°C for 3.5 h to generate a light yellow complex precipitate La(PDA)3. Centrifuge, wash with ethanol three times, and vacuum dry at 60°C for 12 h. (2) Disperse 1 g of dried La(PDA)3 and 0.9 g of hexadecyltrimethylammonium bromide in 70 mL of ethanol solution, add dropwise 15% ethanol solution containing 1.2 g of ethyl orthosilicate, add aqueous ammonia to adjust the pH to 10 for catalytic hydrolysis, react at 45 °C for 7 h, collect by centrifugation, and calcine at 500 °C for 4.5 h to remove hexadecyltrimethylammonium bromide to obtain La-PDA@SiO2 primary nucleating agent; (3) Disperse 1 g of La-PDA@SiO2 in 20 mL of anhydrous ethanol, add 0.06 g of silane coupling agent KH-550, reflux at 75 °C for 140 min for grafting, filter, and vacuum dry at 60 °C for 12 h to obtain the β-nucleating agent.

[0024] Comparative Example 1 In Comparative Example 1, the amount of 2,6-pyridinedicarboxylic acid was changed to 15 mmol, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0025] Comparative Example 2 In Comparative Example 2, cetyltrimethylammonium bromide (CTAB) was not added, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0026] Comparative Example 3 In Comparative Example 3, the amount of ethyl orthosilicate was changed to 2 g (20% ethanol solution), and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0027] Comparative Example 4 In Comparative Example 4, no ethyl orthosilicate was added, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0028] Comparative Example 5 In Comparative Example 5, the amount of silane coupling agent KH-550 was changed to 0.2 g, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1. Comparative Example 6 In Comparative Example 6, no silane coupling agent KH-550 was added, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0029] Comparative Example 7 In Comparative Example 7, 10 mmol of cerium nitrate hexahydrate was used instead of lanthanum nitrate hexahydrate, and the rest of the reaction was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0030] Comparative Example 8 In Comparative Example 8, 30 mmol of oxalic acid was used instead of 2,6-pyridinedicarboxylic acid, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0031] Test Example 1: The β-nucleating agents prepared in Examples 1-4 and Comparative Examples 1-8 were tested as follows: Accurately weigh 0.03 parts by weight of a β-nucleating agent, 0.05 parts of antioxidant 330, 0.1 parts of antioxidant 168, 0.08 parts of calcium stearate, and 100 parts of polypropylene (brand PPR-P00, melt flow rate 0.25g / 10min). Mix and disperse them in a high-speed mixer for 30 minutes, then granulate them through an SJ20 twin-screw extruder. Test bars are then extruded through an injection molding machine and conditioned in a constant temperature and humidity chamber (23°C, 50% humidity) for at least 48 hours before testing. After the bars were left at room temperature for 24 hours, mechanical properties were tested. The test performance is as follows: Simple supported beam notched impact strength (23℃ / -20℃): GB / T1043.1-2008; Flexural modulus: GB / T9341-2008; Tensile yield stress: GB / T1040.1-2018; related results are shown in Table 1.

[0032] Pure polypropylene PPR-P00 was injected into test specimens according to the same processing procedure and used as a reference for the above mechanical property tests.

[0033] The test results are shown in Table 1 below: Table 1 Note: NB means none of the splines were broken, P means partial failure.

[0034] Combined with the above, it can be seen that the β-nucleating agents prepared in Examples 1-4 significantly improved the overall performance of polypropylene. The Charpy impact strength at both 23°C and -20°C was significantly higher than that of pure polypropylene PPR-P00, and remained stable over time, with no fracture. The low-temperature impact strength at -20°C increased by 86% to 95% compared to pure polypropylene PPR-P00, indicating that β-crystals effectively alleviated low-temperature brittleness. The flexural modulus increased by 18% to 21%, and the tensile yield stress increased by 8% to 9%, demonstrating that β-crystals enhance toughness while maintaining material rigidity.

[0035] In Comparative Example 1, the amount of 2,6-pyridinedicarboxylic acid is insufficient, and the coordination unsaturation leads to a decrease in the ability to induce β crystals, and the impact strength decays over time. In Comparative Example 2, the CTAB surfactant is missing, the SiO2 coating layer has structural defects, the bending modulus is significantly reduced, and the impact strength improvement is limited. In Comparative Example 3, there is an excess of ethyl orthosilicate. The excess ethyl orthosilicate cannot completely grow around La(PDA)3, forming free silicon groups, which promote the formation of α crystals, resulting in a sudden drop in impact strength and spline fracture. In Comparative Example 4, there is a lack of ethyl orthosilicate, and La(PDA)3 is directly exposed, causing the β crystal to lose stability, and the impact strength is close to the level of pure polypropylene PPR-P00. In Comparative Example 5, there is an excess of KH-550, and the excess coupling agent destroys the surface properties, and the impact strength and modulus decrease simultaneously. In Comparative Example 6, there is a lack of KH-550, and the poor interface compatibility leads to uneven dispersion of β crystals, and the impact strength improvement is weak. In Comparative Example 7, cerium (Ce) replaced lanthanum (La). The change in rare earth elements reduced β-crystal selectivity and significantly decreased impact strength. In Comparative Example 8, oxalic acid replaced 2,6-pyridinedicarboxylic acid. The ligand lacked a rigid aromatic ring structure and lost its β-crystal inducing ability.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a β-nucleating agent for polypropylene pipes, characterized in that the steps include: (1) Lanthanum nitrate hexahydrate and 2,6-pyridinedicarboxylic acid are dissolved in a mixed solvent of ethanol and water, and refluxed to form a light yellow complex precipitate La(PDA)3; (2) La(PDA)3 was dispersed in an ethanol solution of hexadecyltrimethylammonium bromide, ethyl orthosilicate was added, and ammonia was added to catalyze the hydrolysis. After the reaction, the mixture was centrifuged and calcined to remove the hexadecyltrimethylammonium bromide to obtain the La-PDA@SiO2 primary nucleating agent. (3) La-PDA@SiO2 is dispersed in anhydrous ethanol, a silane coupling agent is added, and the grafting is carried out by reflux reaction. After filtering and drying, the β-nucleating agent is obtained.

2. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: The reflux reaction temperature in step (1) is 75-85° C. and the reaction time is 3.5-4.5 h.

3. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: In the step (1), the molar ratio of lanthanum nitrate hexahydrate to 2,6-pyridinedicarboxylic acid is 1:2.5-3.

5.

4. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: The reaction temperature in step (2) is 45-55° C., and the reaction time is 5-7 h; the calcination temperature in step (2) is 500-600° C., and the calcination time is 3.5-4.5 h.

5. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: In the step (2), the usage ratio of La(PDA)3, hexadecyltrimethylammonium bromide, ethanol and ethyl orthosilicate is 1 g: (0.7-0.9) g: (70-80) mL: (0.8-1.2) g.

6. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 5, characterized in that: In the step (2), the ethyl orthosilicate is an ethanol solution of ethyl orthosilicate with a mass fraction of 15-25%.

7. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: In step (2), ammonia water is added to adjust the pH to 10±0.

2.

8. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: The reflux reaction temperature in step (3) is 75-85° C. and the reaction time is 100-140 min.

9. The method for preparing a β-nucleating agent for polypropylene pipes according to claim 1, characterized in that: The silane coupling agent in step (3) is silane coupling agent KH-550, wherein the usage ratio of La-PDA@SiO2, anhydrous ethanol and silane coupling agent is 1g: (20-30)mL: (0.04-0.06)g.

10. A β-nucleating agent for polypropylene pipes, characterized in that: The method is prepared by any one of claims 1 to 9.

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