Process for the production of a low water absorption nylon 66

Abstract

The application relates to a preparation method of low water absorption rate nylon 66, which comprises the following steps: uniformly mixing 1-3 wt% cerium methacrylate, 1 wt% antioxidant and 96-98 wt% dried nylon 66 in a high-speed mixer; extruding and granulating through a double-screw extruder and a granulator, injection molding, and preparing the nylon 66 after electron beam irradiation with a dose of 50-100 kGy. In the application, cerium methacrylate is used as an irradiation crosslinking agent, the coordination of cerium enhances the crosslinking effect of the nylon 66, the saturated water absorption rate of the nylon 66 is significantly reduced, and the mechanical properties of the material are enhanced; the saturated water absorption rate of the nylon 66 in boiling water can be reduced to below 3.5% (the water absorption rate before modification is 7.2%), and the tensile strength of the material after water absorption is maintained above 70%; the irradiation dose is easy to control in the electron beam irradiation modification process, the irradiation time is short, the production efficiency is high, there is no pollution, and large-scale production can be realized.

Description

Technical Field

[0001] This invention relates to the field of nylon material modification technology, specifically to a method for preparing low water absorption nylon 66. Background Technology

[0002] Nylon has excellent overall properties. It is easy to mold and has low density. It has good heat insulation and electrical insulation properties. Moreover, nylon materials are not easily deformed at room temperature, can withstand high temperatures, and are resistant to friction and wear, making them widely used in the automotive, electronics and electrical fields.

[0003] Nylon readily absorbs moisture, exhibiting a high water absorption rate; its saturated water content at room temperature can exceed 3% (and its saturated water absorption rate in boiling water is greater than 7%). Even trace amounts of moisture can severely impact molding quality, affecting dimensional stability and electrical properties to some extent, particularly affecting the thickness of thin-walled parts. Water absorption also significantly reduces the mechanical properties of nylon, primarily manifested as a decrease in hardness, modulus, and tensile strength, a lower yield point, and poorer creep resistance. For example, the tensile strength of nylon 66 drops by more than 50% after saturating in boiling water. These drawbacks make it unsuitable for use under humid and high-load conditions, thus limiting its application range.

[0004] To reduce the water absorption rate of nylon, effective modification methods currently include surface modification, additive modification, copolymerization modification, and nanocomposite modification. Surface modification reduces water absorption by coating the nylon surface with a waterproof coating or adding surface treatment agents. Its advantages are simplicity and ease of implementation, and it can be applied to finished nylon products. However, its disadvantages include that modification is limited to the surface, and the coating may wear off or peel. Additive modification involves adding waterproof additives, such as silicone oil or waterproofing agents, to the nylon. These additives reduce the porosity of the nylon material, thus lowering the water absorption rate. Its advantages are relative economy and ease of implementation, but its disadvantages include affecting other properties of nylon, and the effectiveness of the additives may gradually diminish over time. Copolymerization modification involves copolymerizing nylon with other low-water-absorption copolymers to form copolymerized nylon. The presence of copolymers can reduce the water absorption of nylon, with the advantages of long-lasting and relatively stable modification effects. However, the selection of copolymers and reaction conditions are complex, and the reaction may disrupt hydrogen bonds in nylon, reducing the material's mechanical properties and thermal stability. Nanocomposite modification involves introducing nanomaterials into the nylon matrix to form nanocomposites. These nanomaterials can fill the micropores in nylon, reducing water absorption. This method has the advantages of significant modification effects with minimal impact on other nylon properties. However, the disadvantage is that the preparation of nanocomposites requires sophisticated processes, making industrial-scale application difficult. Summary of the Invention

[0005] In view of the defects and shortcomings of the existing technology, the purpose of this application is to provide a method for preparing low water absorption nylon 66 with a simple preparation process that can be industrialized and promoted.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing low water absorption nylon 66 includes the following steps:

[0008] 1) Preparation of crosslinking agent cerium methacrylate: Water and cerium carbonate were added sequentially to a three-necked flask and stirred to disperse. Then methacrylic acid was added, and the mixture was heated to 60-80℃ and stirred in a water bath for 2±0.5h. The mixture was filtered while hot, and the filtrate was distilled under reduced pressure to remove water. Anhydrous ethanol was added to dissolve the filtrate, and the mixture was distilled under reduced pressure and dried to obtain a white powder: cerium methacrylate.

[0009] 2) Pre-processing treatment: Mix 1-3 wt% cerium methacrylate, 1 wt% antioxidant, and 96-98 wt% dried nylon 66 evenly in a high-speed mixer for later use;

[0010] 3) Injection molding: The mixed materials are melted and extruded through a twin-screw extruder, granulated by a pelletizer, and then injection molded by an injection molding machine;

[0011] 4) Electron beam irradiation: The injection-molded product is irradiated with an electron beam to obtain nylon 66 with low water absorption.

[0012] The electron beam irradiation dose is 50-100 kGy.

[0013] Furthermore, in step 1, the molar ratio of methacrylic acid to cerium carbonate is 8-11:1.

[0014] Furthermore, the antioxidant is a mixture of type 168 antioxidant and type 1098 antioxidant in equal mass.

[0015] Furthermore, the processing screw temperature of the twin-screw extruder is 180-260℃.

[0016] This invention employs electron beam irradiation to modify nylon 66. The principle of irradiation crosslinking is as follows: high-energy rays irradiate the nylon surface, generating a large amount of ionization and excitation, thereby inducing the breakage of CH bonds in the molecular chain and generating free radicals. The free radicals between molecular chains react and bond to form crosslinking points. Adding an appropriate amount of cerium methacrylate (Ce(MAA)3) to the nylon 66 system as a crosslinking agent can promote the formation of crosslinking points during irradiation. As the number of crosslinking points increases, a dense crosslinked network structure is eventually formed, thereby reducing the water absorption rate of the material and improving its physical properties and chemical stability. Ce(MAA)3 contains three unsaturated C=C active groups. Through irradiation, C=C can undergo free radical polymerization to generate crosslinking points. At the same time, Ce has multiple coordination sites that can coordinate with the end groups of nylon 66, thereby improving its crosslinking effect and achieving efficient crosslinking of nylon 66 under low irradiation doses.

[0017] Compared with existing technologies, the innovation of this invention is that it uses cerium methacrylate (Ce(MAA)3) as an irradiation crosslinking agent. The coordination effect of Ce element enhances the crosslinking effect of nylon 66, significantly reducing the saturated water absorption rate of nylon 66 and also enhancing the mechanical properties of the material. The saturated water absorption rate of nylon 66 in boiling water can be reduced to below 3.5% (the water absorption rate before modification was 7.2%), while the tensile strength of the material after water absorption remains above 70%. The electron beam irradiation modification process allows for easy control of the irradiation dose, short irradiation time, high production efficiency, and no pollution, enabling large-scale production. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Example: A method for preparing a low-water-absorption nylon 66 material, comprising the following steps:

[0020] 1) Preparation of crosslinking agent cerium methacrylate: Water (H2O) and cerium carbonate (Ce2(CO3)3) were added sequentially to a three-necked flask and stirred to disperse. Then methacrylic acid (MAA) (the molar ratio of methacrylic acid to cerium carbonate was 8-11:1) was added. The mixture was heated to 60-80℃ and stirred in a water bath for 2±0.5h. The mixture was filtered while hot, and the filtrate was distilled under reduced pressure to remove water. Anhydrous ethanol was added to dissolve the filtrate, and the mixture was distilled under reduced pressure and dried to obtain a white powder: cerium methacrylate (Ce(MAA)3).

[0021] 2) Pre-processing treatment: 1-3 wt% cerium methacrylate, 1 wt% antioxidant (5‰ type 168 antioxidant + 5‰ type 1098 antioxidant), and 96-98 wt% dried nylon 66 are mixed evenly in a high-speed mixer and set aside.

[0022] 3) Twin-screw extrusion and pelletizing: The mixed material is melt-extruded through a twin-screw extruder and then granulated through a pelletizer. The processing screw temperature of the twin-screw extruder is 180-260℃.

[0023] 4) Injection molding: The prepared modified nylon 66 particles are dried and then injection molded using an injection molding machine;

[0024] 5) Electron beam irradiation: The product from step 4) is subjected to electron beam irradiation to obtain low water absorption nylon 66. The electron beam irradiation dose is 50-100 kGy.

[0025] Example 1

[0026] 1) Weigh out water (200.00 g), methacrylic acid (149.64 g), and cerium carbonate (100.00 g) using an electronic balance. Add water and cerium carbonate to a three-necked flask in sequence and stir to disperse. Then add methacrylic acid and stir in a water bath at 70°C for 2 ± 0.5 h. Filter while hot, remove water by vacuum distillation, dissolve in anhydrous ethanol, and continue vacuum distillation and drying to obtain a white powder: Ce(MAA)3.

[0027] 2) Weigh 500.00g of Nylon 66 particles using an electronic balance and dry them in a vacuum drying oven at 130±2℃ for 4h±15min. Then place them in a desiccator to cool to room temperature.

[0028] 3) Weigh out 1 wt% antioxidant (2.50 g of type 168 antioxidant and 2.50 g of type 1098 antioxidant), 1 wt% cerium methacrylate (5.00 g), and 98 wt% nylon 66 (490.00 g) using an electronic balance and mix them evenly in a high-speed mixer.

[0029] 4) The mixed material is melt-extruded through a twin-screw extruder and then granulated by a pelletizer. The twin-screw extruder processing screw temperatures are: Zone 1 185℃, Zone 2 240℃, Zone 3 255℃, Zone 4 255℃, and Zone 5 255℃.

[0030] 5) The prepared modified nylon 66 particles were dried and then injection molded into sample strips using an injection molding machine. The injection molding parameters were: barrel temperature 280℃, mold temperature 100℃, and holding pressure 0.5MPa.

[0031] 6) Irradiate the injection-molded sample with an electron beam dose of 50 kGy to obtain electron beam modified nylon 66.

[0032] The irradiated modified nylon 66 sample was dried in an oven at 50.0℃±2.0℃ for 24h±1h, then cooled to room temperature in a desiccator and weighed (mass m1). The sample was then completely immersed in a container of boiling distilled water. After immersion for 30min±2min, the sample was removed from the boiling water and cooled in room temperature distilled water for 15min±1min. After removal, the water on the sample surface was wiped off with filter paper, and the sample was weighed again (mass m2). This process of immersion and weighing was repeated every 30min±2min until the sample was saturated with water. (From formula:) Calculate the water absorption rate of the sample.

[0033] Example 2

[0034] The experiment was conducted according to the specific implementation steps of Example 1, wherein the irradiation dose was changed to 75 kGy.

[0035] Example 3

[0036] The experiment was conducted according to the specific implementation steps of Example 1, wherein the irradiation dose was changed to 100 kGy.

[0037] Example 4

[0038] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formulation in step 3 was changed to: 1wt% antioxidant (2.50g of type 168 antioxidant and 2.50g of type 1098 antioxidant), 2wt% cerium methacrylate (15.00g), and 97wt% nylon 66 (485.00g).

[0039] Example 5

[0040] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formulation in step 3 was changed to: 1wt% antioxidant (2.50g type 168 antioxidant and 2.50g type 1098 antioxidant), 3wt% cerium methacrylate (15.00g), and 96wt% nylon 66 (480.00g).

[0041] Example 6

[0042] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formula in step 1 was changed to: methacrylic acid (187.05g) and cerium carbonate (100.00g).

[0043] Example 7

[0044] The experiment was carried out according to the specific implementation steps of Example 1, wherein the water bath reaction temperature in step 1 was changed to 60°C.

[0045] Example 8

[0046] The experiment was carried out according to the specific implementation steps of Example 1, wherein the water bath reaction temperature in step 1 was changed to 80°C.

[0047] Example 9

[0048] The experiment was conducted according to the specific implementation steps of Example 1, wherein the screw temperature of the twin-screw extruder in step 4 was changed to 180°C in zone 1, 240°C in zone 2, 260°C in zone 3, 260°C in zone 4, and 255°C in zone 5.

[0049] Example 10

[0050] The experiment was conducted according to the specific implementation steps of Example 1, wherein the screw temperature of the twin-screw extruder in step 4 was changed to 190°C in zone 1, 240°C in zone 2, 260°C in zone 3, 255°C in zone 4, and 255°C in zone 5.

[0051] Comparative Example 1

[0052] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formulation in step 3 was changed to: 1wt% antioxidant (2.50g of type 168 antioxidant and 2.50g of type 1098 antioxidant), 99wt% nylon 66 (495.00g), and the irradiation dose was changed to: 0.

[0053] Comparative Example 2

[0054] The experiment was conducted according to the specific implementation steps of Example 3, wherein the irradiation dose was changed to 125 kGy.

[0055] Comparative Example 3

[0056] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formulation in step 3 was changed to: 1wt% antioxidant (2.50g of type 168 antioxidant and 2.50g of type 1098 antioxidant), 0.5wt% cerium methacrylate (2.50g), and 98.5wt% nylon 66 (492.50g).

[0057] Comparative Example 4

[0058] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formula in step 1 was changed to: methacrylic acid (130.93g) and cerium carbonate (100.00g).

[0059] Comparative Example 5

[0060] The experiment was conducted according to the specific implementation steps of Example 1, wherein the material formula in step 1 was changed to: methacrylic acid (224.46g) and cerium carbonate (100.00g).

[0061] Comparative Example 6

[0062] The experiment was carried out according to the specific implementation steps of Example 1, wherein the water bath reaction temperature in step 1 was changed to 55°C.

[0063] Comparative Example 7

[0064] The experiment was carried out according to the specific implementation steps of Example 1, wherein the water bath reaction temperature in step 1 was changed to 85°C.

[0065] The mechanical properties and saturated water absorption of modified nylon 66 under different irradiation doses are shown in Table 1:

[0066] Table 1

[0067]

[0068] As shown in Table 1, in Examples 1-3, when the cerium methacrylate content was 1 wt%, the tensile strength of the modified nylon 66 continuously increased with increasing irradiation dose, while the saturated water absorption rate decreased. In Example 3, under an irradiation dose of 100 kGy, the tensile strength of the modified nylon 66 before water absorption increased from 80 MPa (unirradiated, Comparative Example 1) to 89 MPa, an increase of 11.3%; the tensile strength after water absorption increased from 38 MPa to 69 MPa, an increase of 81.5%; and the saturated water absorption rate decreased from 7.16% to 2.95%, a decrease of 58.7%. Electron beam irradiation caused the free radicals between the nylon 66 molecular chains to react and crosslink, ultimately forming a dense crosslinked network structure, thereby improving the mechanical properties of the material and reducing the water absorption rate. In Comparative Example 2, the irradiation dose was increased again to 125 kGy, and the saturated water absorption rate of nylon 66 decreased again, from 2.95% to 2.87%. However, the tensile strength of nylon 66 before and after water absorption also showed a downward trend. This is because the excessively high irradiation dose led to an increase in the degree of decomposition of the nylon 66 molecular chain. At this time, the decomposition of the nylon molecular chain was greater than the cross-linking, and the mechanical properties decreased.

[0069] Table 2 shows the mechanical properties and water absorption of modified nylon 66 under different cerium methacrylate crosslinking agent contents and different processing parameters at 50 kGy:

[0070] Table 2

[0071]

[0072] As shown in Table 2, with the increase of the crosslinking agent cerium methacrylate, the saturated water absorption rate of nylon 66 continuously decreases, while the tensile strength before and after water absorption shows a trend of first increasing and then decreasing. The Ce in cerium methacrylate... 3+It can form coordination bonds with nylon 66 molecules, thereby preventing water molecules from entering the nylon molecules; at the same time, a small amount of crosslinking agent can fill the gaps between nylon molecular chains, making the molecules more compact, thereby improving the mechanical properties of the material and reducing the water absorption rate.

[0073] The yields of cerium methacrylate prepared at different feed amounts and reaction temperatures, and the mechanical properties of the modified nylon 66, are shown in Table 3.

[0074] Table 3

[0075]

[0076]

[0077] Table 3 shows that, under the same reaction temperature, changes in the amount of reactants affect the yield of cerium methacrylate and the mechanical properties of the modified nylon 66. In Comparative Example 4, the molar ratio of methacrylic acid to cerium carbonate was 7:1. At this point, the amount of methacrylic acid was too low, and cerium carbonate did not fully participate in the reaction, resulting in a very low yield of cerium methacrylate, only 53.3%. In Comparative Example 5, the amount of methacrylic acid was too high, making it difficult to remove completely during subsequent purification, ultimately resulting in a yield of only 46.5% for cerium methacrylate. Under the same material ratio, the yield of cerium methacrylate showed a trend of first increasing and then decreasing with increasing reaction temperature. At 60-80℃, the yield of cerium methacrylate remained above 75%. The effect of different reaction temperatures on the mechanical properties of the modified nylon 66 for cerium methacrylate was minimal.

[0078] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing low-absorption nylon 66, characterized in that, Includes the following steps: 1) Preparation of crosslinking agent cerium methacrylate: Water and cerium carbonate were added sequentially to a three-necked flask and stirred to disperse. Then methacrylic acid was added, and the mixture was heated to 60-80℃ and stirred in a water bath for 2±0.5h. The mixture was filtered while hot, and the filtrate was distilled under reduced pressure to remove water. Anhydrous ethanol was added to dissolve the filtrate, and the mixture was distilled under reduced pressure and dried to obtain a white powder: cerium methacrylate. 2) Pre-processing: Mix 1-3 wt% cerium methacrylate, 1 wt% antioxidant, and 96-98 wt% dried nylon 66 evenly in a high-speed mixer for later use; 3) Injection molding: The mixed materials are melted and extruded through a twin-screw extruder, granulated by a pelletizer, and then injection molded by an injection molding machine; 4) Electron beam irradiation: The injection-molded product is irradiated with an electron beam to obtain nylon 66 with low water absorption. The electron beam irradiation dose is 50-100 kGy; In step 1), the molar ratio of methacrylic acid to cerium carbonate is 8-11:

1.

2. The method for preparing low-absorption nylon 66 as described in claim 1, characterized in that, The antioxidant is a mixture of type 168 antioxidant and type 1098 antioxidant in equal mass.

3. The method for preparing low-absorption nylon 66 as described in claim 1, characterized in that, The screw temperature of the twin-screw extruder is 180-260℃.

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