A method of reducing crystallinity of a polyamide composite

Abstract

This invention belongs to the field of polymer composite materials technology, specifically relating to a method for reducing the crystallinity of polyamide composite materials. The method for reducing the crystallinity of polyamide composite materials includes the following steps: adding pure polyamide and glass fiber in a certain proportion to a twin-screw extruder for melting, extrusion, cooling, drying, and pelletizing, then pressing the pellets on a compression molding machine. After compression molding, the product undergoes a moisture conditioning treatment to reduce its crystallinity and improve the stability and durability of the product.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and specifically to a method for reducing the crystallinity of polyamide composite materials. Background Technology

[0002] Polyamide 66 resin (PA66) possesses high strength, high rigidity, excellent wear resistance and heat resistance, good oil and chemical resistance, stable electrical properties, and is a self-extinguishing material. It is widely used in applications requiring high load and heat resistance. Modified PA66 materials are mainly used in automotive engine compartments and surrounding components, such as radiator tanks, fan covers, intake manifolds, engine hoods, gears, and bearings; it is also used in power tool housings, sporting goods, industrial gears, structural components, and other engineering parts requiring high strength, heat resistance, and wear resistance.

[0003] PA66 is a highly crystalline plastic, and its significant crystallization tendency leads to improved product density, tensile strength, hardness, heat distortion temperature, chemical resistance, dimensional stability, and barrier properties. However, crystallization also reduces the material's elasticity, elongation at break, notched impact strength (especially at low temperatures or in dry conditions), and transparency. Due to the rapid crystallization rate and high crystallinity of PA66, uneven cooling rates and temperature distribution during molding can easily cause differences in internal crystallinity and morphology, resulting in significant uneven shrinkage and internal stress, ultimately manifesting as warping deformation. Temperature is the most sensitive factor in the crystallization process of polyamide 66 during molding. Greater supercooling leads to faster nucleation, shorter crystallization time, less perfect crystal structure, smaller grain size, lower crystallinity, smaller and more numerous spherulites, and a significantly lower temperature for reaching the maximum crystallization rate, resulting in a loose internal structure and decreased strength and heat resistance. Conversely, smaller supercooling allows for more efficient molecular chain movement, a more complete crystallization process, more perfect crystals, larger grain size, and higher crystallinity. High crystallinity and large-size spherulite structure improve the tensile strength, rigidity and heat resistance of the product, but the impact toughness (especially low temperature toughness) and elongation at break decrease, and the product tends to be brittle.

[0004] To improve the grain structure, increase the crystallization temperature, and enhance mechanical properties (toughness) and durability of polyamides and their composites, inorganic fillers are often added as heterogeneous nucleating agents during blending modification. This enhances the mechanical properties, crystallinity, crystallization temperature, and durability of polyamide 66. However, sometimes defects such as excessively high crystallinity and incomplete crystal formation still exist, resulting in limited enhancement of mechanical properties and decreased toughness. Because crystallization is heterogeneous nucleation, there is a contradiction between the fastest crystallization speed and the formation of crystal nuclei, leading to defects such as decreased impact strength in PA66.

[0005] Therefore, it is necessary to study processes that can reduce the crystallinity of polyamide composites. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for reducing the crystallinity of polyamide composite materials, which can improve the crystal structure and enhance the performance of the products.

[0007] The technical solution adopted by the present invention to solve the above problems is as follows:

[0008] A method for reducing the crystallinity of polyamide composites includes the following steps:

[0009] S1. Glass fiber is added to polyamide granules and mixed evenly, wherein the glass fiber accounts for 30-35% of the total mass of all materials and the polyamide accounts for 65-70% of the total mass of all materials;

[0010] S2. The mixture from step S1 is fed into a twin-screw extruder for melting, extrusion, cooling, drying, and pelletizing.

[0011] S3. Molding is performed using a vacuum molding machine;

[0012] S4. Moisten with hot water for 2-3 hours, then soak for 2-3 hours. The hot water temperature is 50-90℃.

[0013] As a further improvement of the present invention, the polyamide in step S1 is PA66.

[0014] As a further improvement of the present invention, the hot water temperature is 50±2℃.

[0015] As a further improvement of the present invention, the length of the glass fiber in step S1 is 0.2mm-6mm.

[0016] As a further improvement of the invention, the glass fiber accounts for 35% of the total mass of all materials.

[0017] As a further improvement of the present invention, the melt extrusion temperature of the twin screw in step S2 is 240~275℃.

[0018] As a further improvement of the present invention, the molding temperature of the vacuum molding machine in step S3 is 270~280℃.

[0019] As a further improvement of the present invention, the immersion temperature in step S4 is 23±2℃.

[0020] As a further improvement of the present invention, the glass fiber and polyamide need to be dried before mixing in step S1. The polyamide is vacuum dried at 100±2℃ for 5 hours, and the glass fiber is vacuum dried at 150±2℃ for 2 hours.

[0021] The beneficial effects of adopting the above technical solution are as follows:

[0022] The method provided by this invention improves the mechanical properties, thermal properties, dimensional stability, and rigidity of polyamide composites by adding glass fiber as a heterogeneous nucleating agent, extruding and pelletizing with a twin-screw extruder, and then molding. Furthermore, through the synergistic mechanism of heat-controlled humidification and constant-temperature immersion, the gentle thermal environment provided by 50-90℃ hot water allows water molecules to penetrate into the interior of the polyamide composite, interfering with the orderly stacking of molecular chains, inhibiting spherulite growth and crystallization, and suppressing the growth and maturation of spherulites at the filler-polyamide interface, thus achieving a directional reduction in crystallinity. Subsequent constant-temperature immersion at 23±2℃ fixes the low-crystallinity state, effectively reducing the crystalline structure and preventing crystallinity rebound. This solves the problem of blind crystallinity control in traditional processes, thereby significantly reducing the crystallinity of the material and improving the dimensional stability and durability of the product. Detailed Implementation

[0023] The research found that adding heterogeneous nucleating agents to polyamide improved the mechanical properties, thermal properties, dimensional stability, and rigidity of polyamide composites, but the toughness was not ideal. Through repeated investigations, it was accidentally discovered that hot water conditioning and constant-temperature immersion of the nucleated material improved its toughness and altered its crystallinity. Based on this discovery, extensive practical verification was conducted, leading to the technical solution of this invention. This invention enables the obtained polyamide composite material to maintain an ideal balance between rigidity and toughness, achieving better overall performance.

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the invention will be described clearly and completely below in conjunction with specific embodiments. Except for the content specifically mentioned below, all of which are common knowledge and general knowledge in the field.

[0025] In this embodiment, the PA66 used was purchased from Kyocera, item number A1247HM; the glass fiber GF was purchased from Taishan Glass Fiber Co., Ltd., item number ECS10-3.0-T435TM.

[0026] Example 1

[0027] A method for reducing the crystallinity of polyamide composites includes the following steps:

[0028] Pretreatment: Dry PA66 at 100℃ for 5 hours and glass fiber at 150℃ for 2 hours to remove moisture.

[0029] S1: Dried PA66 and GF were mixed uniformly at a ratio of 65 wt.% PA66 and 35 wt.% GF. PA66 / GF composite materials were prepared using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The screw length-to-diameter ratio was 42:1, and the rotation speed was 100 rpm. The obtained extrudate was cylindrical strips, which were cooled by air and then granulated using a granulator.

[0030] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a sheet.

[0031] S3: The thin sheets obtained in step S1 are subjected to conditioned conditions, specifically conditioned at 50℃ for 2, 3, and 4 hours; conditioned at 75℃ for 2, 3, and 4 hours; and conditioned at 90℃ for 2, 3, and 4 hours. After conditioned, each sheet is immediately immersed in pure water at room temperature (23℃) and removed after 2 hours. The resulting composite material is named according to the glass fiber mass ratio, conditioned temperature, and time. For example, conditioned at 50℃ for 2 hours, the material name is GF35-50-2.

[0032] Comparative Example 1

[0033] Pretreatment: Dry PA66 at 100℃ for 5 hours to remove moisture.

[0034] S1: Dried PA66 was processed into pure PA66 material using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The extruder screw speed was 100 rpm. The resulting extrudate was cylindrical strips, which were air-cooled and then granulated using a granulator. The screw length-to-diameter ratio was 42:1, and the speed was 100 rpm. The resulting extrudate was cylindrical strips, which were air-cooled and then granulated using a granulator.

[0035] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a sheet.

[0036] S3: The sheet obtained in step S1 is subjected to conditioned temperature treatment, specifically conditioned at 50℃ for 2 hours, 3 hours, and 4 hours; conditioned at 75℃ for 2 hours, 3 hours, and 4 hours; and conditioned at 90℃ for 2 hours, 3 hours, and 4 hours. After conditioned, each sheet is immediately immersed in pure water at room temperature (23℃) and removed after 2 hours. The resulting material is named Pure PA66-conditioned temperature-time. For example, conditioned at 50℃ for 2 hours, the material name is Pure PA66-50-2.

[0037] Comparative Example 2

[0038] Pretreatment: Dry pure PA66 at 100℃ for 5 hours to remove moisture.

[0039] S1: Dried PA66 was used to prepare pure PA66 material using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The extruder screw speed was 100 rpm. The obtained extrudate was a cylindrical strip, which was air-cooled and then granulated using a granulator. The screw length-to-diameter ratio was 42:1, and the speed was 100 rpm. The obtained extrudate was a cylindrical strip, which was air-cooled and then granulated using a granulator.

[0040] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a sheet. No moisture conditioning is performed. The material name is PurePA66.

[0041] Comparative Example 3

[0042] Pretreatment: Dry PA66 at 100℃ for 5 hours and glass fiber at 150℃ for 2 hours to remove moisture.

[0043] S1: Dried PA66 and GF were mixed uniformly at a ratio of 65 wt.% PA66 and 35 wt.% GF. PA66 / GF composite materials were prepared using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The screw length-to-diameter ratio was 42:1, and the rotation speed was 100 rpm. The obtained extrudate was cylindrical strips, which were cooled by air and then granulated using a granulator.

[0044] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a thin sheet. The resulting composite material is named GF35.

[0045] Comparative Example 4

[0046] Pretreatment: Dry PA66 at 100℃ for 5 hours and glass fiber at 150℃ for 2 hours to remove moisture.

[0047] S1: The dried PA66 and GF were mixed uniformly at a ratio of 80 wt.% PA66 and 20 wt.% GF. PA66 / GF composite materials were prepared using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The screw length-to-diameter ratio was 42:1, and the rotation speed was 100 rpm. The obtained extrudate was cylindrical strips, which were cooled by air and then granulated using a granulator.

[0048] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a thin sheet. The resulting composite material is named GF20.

[0049] Comparative Example 5

[0050] Pretreatment: Dry PA66 at 100℃ for 5 hours and glass fiber at 150℃ for 2 hours to remove moisture.

[0051] S1: The dried PA66 and GF were mixed uniformly at a ratio of 80 wt.% PA66 and 20 wt.% GF. PA66 / GF composite materials were prepared using a twin-screw extruder. The extruder consisted of six heating zones and a die head heating zone. The temperatures maintained in the extruder heating zones were 240℃ in zone 1, 245℃ in zone 2, 250℃ in zone 3, 265℃ in zone 4, 270℃ in zone 5, 275℃ in zone 6, and 270℃ at the die head. The screw length-to-diameter ratio was 42:1, and the rotation speed was 100 rpm. The obtained extrudate was cylindrical strips, which were cooled by air and then granulated using a granulator.

[0052] S2: The granulated particles are hot-pressed in a vacuum membrane press. The mold is 10cm×10cm×0.2cm, the hot-pressing temperature is 270℃, the pressure is 2500KN, and the hot-pressing time is 15 minutes to obtain a sheet.

[0053] S3: The thin sheets obtained in step S1 are subjected to conditioned conditions, specifically conditioned at 50℃ for 2, 3, and 4 hours; conditioned at 75℃ for 2, 3, and 4 hours; and conditioned at 90℃ for 2, 3, and 4 hours. After conditioned, each sheet is immediately immersed in pure water at room temperature (23℃) and removed after 2 hours. The resulting composite material is named according to the glass fiber mass ratio, conditioned temperature, and time. For example, conditioned at 50℃ for 2 hours, the material name is GF20-50-2.

[0054] Results Column 1 Performance Test

[0055] (1) The crystallinity of the materials obtained in Example 1 and Comparative Examples 1-5 was tested using a differential scanning calorimeter. The test standard was based on GB / T 19466.3-2004 "Plastics - Differential Scanning Calorimetry (DSC) - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpies". This standard is equivalent to ISO 11357-3:1999, which specifies the test methods for determining the melting and crystallization temperatures and enthalpies of crystalline and semi-crystalline polymers.

[0056] Instrument: Differential scanning calorimeter: DSC, Q2000, TA Instruments, USA.

[0057] Sample: 3mg-8mg is placed in a DSC (Differential Scanning Calorimeter).

[0058] Melting characteristics: Tested on a differential scanning calorimeter (DSC) with a sample size of 3-8 mg; starting from room temperature (20°C), heating to 280°C at 40°C / min, holding for 5 min to eliminate thermal history, then cooling to 20°C at 20°C / min, and finally heating to 280°C at 20°C / min).

[0059] Formula for calculating crystallinity:

[0060] X c (%) = ΔH m / ΔH * ×100%,

[0061] In the formula ΔH m It is the enthalpy of fusion of the sample; ΔH * It is the enthalpy of fusion of 100% crystalline PA66, which is approximately 190 J / g.

[0062] The test results are shown in Tables 1, 2 and 5.

[0063] (2) A microcomputer-controlled universal testing machine was used for tensile tests and three-point bending tests. The tensile test standard was based on GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics"; the three-point bending test standard was based on GB / T 9341-2024 "Determination of bending properties of plastics". The tensile property data included tensile strength and elongation at break, and the three-point bending property data included bending strength, bending strain and bending modulus. At least three parallel samples were tested for each condition, and the average value and standard deviation were taken. All samples were tested at 23±2℃ and 50±5%RH to ensure environmental consistency.

[0064] Instrument: 30kN microcomputer-controlled universal testing machine, model AI-7000MU1-GD, High-speed rail testing instruments (Dongguan) Co., Ltd.

[0065] Specimens: Tensile test specimens were prepared according to the standard, using type 1A dumbbell specimens, with a tensile test speed of 10 mm / min; Bending specimens were prepared according to the standard, with an 80×10×4 mm specimen, a span-to-thickness ratio of 16:1, and a speed of 2 mm / min.

[0066] The test results are shown in Tables 3 and 4.

[0067] Table 1. DSC data of PA66-GF35 wt.% composite material under different conditions.

[0068]

[0069] Table 2. DSC data of pure PA66 under different conditions

[0070]

[0071] Table 3. Tensile mechanical properties and three-point bending data of PA66-GF35 wt.% composite material

[0072]

[0073] Table 4. Tensile mechanical properties and three-point bending data of pure PA66

[0074]

[0075] Table 5. DSC data of PA66-GF20 wt.% composite material under different conditions.

[0076]

[0077] In summary, a comparison of the performance parameters in Tables 1 and 2 shows that pure PA66 without glass fiber, after direct humidification, generally exhibits increased crystallinity. The trend of crystallinity change is opposite to that after humidification with glass fiber. Compared to the composite material GF35, the crystallinity generally decreases after humidification, but the humidification time should be controlled to no more than 3 hours. Furthermore, a comparison of the performance parameters in Tables 1 and 5 shows that the crystallinity of 20wt.%GF after humidification does not fluctuate significantly, and the crystallinity is consistently higher than in the unhumidified state. This crystallization exhibits continuous plasticization, which is detrimental to the material's toughness and other mechanical stability. As can be seen from the tensile strength, elongation at break, and three-point bending data in Tables 3 and 4, the composite material PA66-GF35wt.% maintained high levels of tensile strength and elongation at break at conditioning temperatures of 50-90℃ for 2-3 hours, with significantly improved toughness and increased bending strain to 6.5%-7.0%, while maintaining a high strength of over 200 MPa, exhibiting strong load-bearing capacity and a moderate flexural modulus, achieving a good balance between stiffness and toughness. The mechanical properties of the polyamide composite material obtained under the conditioning and soaking process are superior to those obtained using the unconditioned material and the base material with low glass fiber content, improving the durability and dimensional stability of the product.

[0078] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the crystallinity of polyamide composite materials, characterized in that, Includes the following steps: S1. Glass fiber is added to polyamide granules and mixed evenly, wherein the glass fiber accounts for 30-35% of the total mass of all materials and the polyamide accounts for 65-70% of the total mass of all materials; S2. The mixture from step S1 is fed into a twin-screw extruder for melting, extrusion, cooling, drying, and pelletizing. S3. Molding is performed using a vacuum molding machine; S4. Moisten with hot water for 2-3 hours, then soak for 2-3 hours. The hot water temperature is 50-90℃.

2. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, The polyamide mentioned in step S1 is PA66.

3. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, The hot water temperature is 50±2℃.

4. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, The length of the glass fiber in step S1 is 0.2mm to 60mm.

5. The method for reducing the crystallinity of polyamide composite materials according to claim 4, characterized in that, The glass fiber accounts for 35% of the total mass of all materials.

6. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, The melt extrusion temperature of the twin-screw extruder in step S2 is 240~275℃.

7. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, In step S3, the molding temperature of the vacuum molding machine is 270~280℃.

8. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, The immersion temperature in step S3 is 23±2℃.

9. The method for reducing the crystallinity of polyamide composite materials according to claim 1, characterized in that, In step S1, the glass fiber and polyamide need to be dried before mixing. The polyamide is vacuum dried at 100±2℃ for 5 hours, and the glass fiber is vacuum dried at 150±2℃ for 2 hours.

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