Polyamide 56 composition with reduced hygroscopicity

Abstract

Polyamide 56 compositions with reduced hygroscopicity are disclosed. The polyamide 56 composition comprises polyamide 56 and a cross-linking agent. And the cross-linking agent is triallyl isocyanurate. The polyamide 56 composition may then be further subjected to radiation crosslinking.

Description

Technical Field

[0001] The present invention relates to a polyamide 56 composition with reduced hygroscopicity. Specifically, the present invention relates to a polyamide 56 composition comprising polyamide 56 and a crosslinking agent. The polyamide 56 composition is crosslinked using electron beam radiation. The resulting polyamide composition has reduced hygroscopicity compared to polyamide 56 without a crosslinking agent. Background Art

[0002] Polyamides are some of the most widely used thermoplastic materials due to their physical properties. Polyamides are semi-crystalline polymers produced by the condensation of diacids and diamines. They have good abrasion resistance and wear resistance, as well as high chemical resistance and corrosion resistance. In addition to ultraviolet resistance, polyamides also have flexibility and low density. Given these properties, polyamides play an important role in many automotive applications, electrical applications, and consumer product applications.

[0003] Despite these beneficial properties, many polyamides have the disadvantage of being hygroscopic. Hygroscopicity can cause loss of tensile strength and modulus due to the interaction of moisture with the polyamide polymer chains. Products made of polyamides can also have loss of electrical properties and dimensional stability due to hygroscopicity.

[0004] Pramanik et al. described in the article "Radiation Processing of Nylon 6 by e-beam for improved properties" (Radiation Physics and Chemistry 78 (2009) 199-205) the limitations in the use of nylon 6 (polyamide) due to undesirable water absorption and insufficient strength properties. Pramanik et al. described irradiating nylon 6 with an electron beam in the presence of triallyl isocyanurate. The article described improvements in the hardness, tensile strength, and flexural strength of nylon 6, while the water absorption decreased after exposure to electron beam radiation.

[0005] In a subsequent article published in 2011, Pramanik et al. described the conversion of nylon 66 into a material with improved hardness, tensile strength, and flexural modulus by treating the material under optimized doses of electron beam radiation in the presence of a crosslinking agent. See "Modification of Nylon 66 by Electron Beam Irradiation for Improved Properties and Superior Performances", Journal of Applied Polymer Science, Vol. 122, No. 1 (193 - 202). As a result of their study, Pramanik et al. concluded the following: Thermogravimetric analysis indicated an improvement in the thermal stability of the material by radiation. The researchers concluded that the improvement in the physical properties of the material and the reduction in water absorption were due to the crosslinking of polyamide molecules.

[0006] In the article "Development of an Advanced Engineering Polymer from the Modification of Nylon 66 by e-Beam Irradiation" (Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 281 - 289), Pramanik et al. described the irradiation of nylon 66 in the presence of a combination of an impact modifier polyurethane and triallyl isocyanurate as a crosslinking agent, which resulted in a significant improvement in hardness, tensile strength, flexural modulus, impact strength, and a reduction in the percentage of water absorption of nylon 66. The authors speculated that the increase in dimensional stability might be attributed to a reduction in the crystallinity of the nylon 66 polymer.

[0007] Pramanik et al. published another article in 2021: "E-beam Induced Crosslinking of Highly Crystalline Nylon 6: Optimization of Triallyl Isocyanuarate Concentration" (Radiation Physics and Chemistry, Volume 187, October 2021). In this article, Pramanik et al. reported that the optimization of triallyl isocyanurate concentration led to further improvement in the properties of nylon 6 subjected to electron beam irradiation. The authors drew the following conclusions: The introduction of triallyl isocyanurate and electron beam irradiation disrupted the crystallinity of the nylon 6 matrix, thus resulting in increased crosslinking. As a result, they observed a significant decrease in the water absorption of the polymer.

[0008] Ovsik et al. described in "Influence of Cross-Linking Agent Concentration / Beta Radiation Surface Modification on the Micro-Mechanical Properties of Polyamide 6" (Materials 2021, 14, 6407) their study on the influence of electron beam irradiation in the dose range of 66 to 132 kGy on the micro-mechanical properties of polyamide 6 containing 1 wt%, 3 wt%, and 5 wt% of the cross-linking agent triallyl isocyanurate. The authors drew the following conclusions: To obtain maximum crosslinking, minimum degradation, and the highest increase in indentation hardness and modulus, polyamide 6 must contain 3 wt% or 5 wt% of triallyl isocyanurate and be irradiated with 132 kGy.

[0009] Since many polyamides are made from fossil fuels that emit carbon dioxide and contribute to global warming, there have been increasing attempts to use bio-based polyamides. Examples of bio-based polyamides include, but are not limited to, polyamide 56 and polyamide 1010. However, compared to conventional polyamides such as polyamide 6 or polyamide 66, many of these bio-based polyamides have the problem of increased water absorption. The increased water absorption leads to loss of dimensional stability and possibly electrical properties of the products formed from bio-based polyamides.

[0010] Gan et al. copolymerized bio-based polyamide 56 with polyamide 512 by melt polymerization in "The Investigation of Copolymer Composition Sequence on Non-Isothermal Crystallization Kinetics of Bio-Based Polyamide 56 / 512" (Polymers 2023, 15, 2345). The authors used this method to observe whether the low toughness and high water absorbency of pure polyamide 56 could be improved. Through thermogravimetric analysis, the authors found that the thermal stability of polyamide 56 / polyamide 512 increased with the increase in the proportion of polyamide 512 added to the composite material.

[0011] He et al.'s "Achieving Anti-moisture Absorption and High Thermal Properties in Bio-based Polyamide 56 / F-based Heat-Resistant Agent Composites through Crystal Regulation" (Journal of Applied Polymer Science, Vol. 140, No. 34 (June 23, 2023)) described their research on polyamide 56. The anti-moisture absorption and thermal properties of polyamide 56 were improved by adding heat-resistant agents, thus expanding the application of polyamide 56 in the automotive field. In their research, the alternating copolymer of N-(4-F-phenylmaleimide) and styrene (P(N-(4-F-phenylmaleimide)-alt-styrene, PFS) and the alternating copolymer of N-(4-phenylmaleimide) and triallyl isocyanurate (p(N-(4-pheylmaleimide)-alt-triallyl isocyanurate) were used as heat-resistant agents. By using these reagents, the anti-moisture absorption increased by 14.6% and 15.5%. The authors attributed this improvement in anti-moisture absorption to the crystallization of polyamide 56 caused by the introduction of heat-resistant agents.

[0012] Therefore, there is a need for a bio-based polyamide composition containing polyamide 56, which has reduced water absorbency compared to pure polyamide 56 and still maintains its mechanical properties. Summary of the Invention

[0013] One embodiment relates to a polyamide 56 composition comprising a crosslinking agent.

[0014] Another embodiment relates to a polyamide 56 composition comprising polyamide 56 and a crosslinking agent, wherein the polyamide 56 composition is further subjected to radiation.

[0015] Other features and advantages of the present invention will be apparent from the following more detailed description of preferred embodiments in conjunction with the accompanying drawings, which illustrate the principles of the present invention by way of example. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings incorporated herein and forming a part of the specification schematically illustrate one or more illustrative embodiments of the present invention and, together with the general description given above and the detailed description given below, are used to explain the principles of the present invention, and in which:

[0017] Figure 1 is a graph showing the dynamic mechanical analysis (DMA) characterization of polyamide 56 and polyamide 56 polymer compositions comprising polyamide 56 and various crosslinking agents.

[0018] Figure 2 (a) is a graph showing a comparative analysis of the water absorption of polyamide 66, polyamide 56, and polyamide 56 polymer compositions comprising polyamide 56 and various crosslinking agents using ASTM D570.

[0019] Figure 2 (b) is a graph showing a comparative analysis of polyamide 66, polyamide 56, polyamide 56 subjected to electron beam radiation, and polyamide 56 polymer compositions comprising polyamide 56 and various amounts of crosslinking agent TAIC and subjected to electron beam radiation.

[0020] Figure 3 is a graph showing the water absorption of polyamide 66, polyamide 56, polyamide 56 subjected to electron beam radiation, and polyamide 56 polymer compositions comprising polyamide 56 and various amounts of crosslinking agent TAIC.

[0021] Figure 4 (a)-(c) show a comparison of the tensile properties of polyamide 66, polyamide 56, polyamide 56 subjected to electron beam radiation, and polyamide 56 polymer compositions comprising various amounts of crosslinking agent. DETAILED DESCRIPTION

[0022] The description of illustrative embodiments in accordance with the principles of the present invention is intended to be read in conjunction with the accompanying drawings, which are to be considered a part of the entire written description. In the description of the embodiments of the present invention disclosed herein, any reference to direction or orientation is for convenience of description only and is not intended to limit the scope of the present invention in any way. Relative terms such as "lower," "higher," "horizontal," "vertical," "above," "below," "upper," "lower," "top," and "bottom" and their derivatives (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description only and do not require the device to be constructed or operated in a particular orientation unless expressly so stated. Unless otherwise expressly described, terms such as "attached," "fixed," "connected," "coupled," "interconnected," etc. refer to a relationship in which structures are fastened or attached to each other directly or indirectly through intervening structures, and include both movable or rigid attachments or associations.

[0023] In addition, the features and advantages of the present invention are described with reference to preferred embodiments. Accordingly, the present invention should be clearly not limited to such embodiments that illustrate some possible non-limiting combinations of features that may exist alone or in combination with other features, and the scope of the present invention is defined by the appended claims.

[0024] The polyamide 56 composition of the present invention comprises a bio-based polyamide. The bio-based polyamide can be prepared by a polycondensation process of diacids with different chain lengths. The composition of the present invention comprises polyamide 56. Polyamide 56 is polymerized from bio-based 1,5-diaminopentane and fossil-based adipic acid. Different from other polyamides, polyamide 56 has higher moisture absorption due to the higher amide group density and asymmetric chemical structure of the polymer. An example of commercially available polyamide 56 is ECOBLEND N56F from Shanghai Kumho Sunny Plastics Co., Ltd.

[0025] In addition to polyamide 56, the polyamide 56 composition further comprises a crosslinking agent. An example of a crosslinking agent that can be used in the polyamide 56 composition is triallyl isocyanurate (CAS No. 1-25-15-6). Preferably, triallyl isocyanurate (TAIC) in the range of about 0.5 wt% to about 3.0 wt% is added to the polyamide 56 composition. Most preferably, TAIC accounts for 0.5 wt% of the polyamide 56 composition.

[0026] Another example of a crosslinking agent that can be used in the polyamide 56 composition is triallyl cyanurate (TAC) (CAS No. 101-37-1). Preferably, triallyl cyanurate in the range of about 0.5 wt% to about 3.0 wt% of the composition is added to the polyamide composition. Most preferably, the TAC accounts for 0.5 wt% of the polyamide 56 composition.

[0027] Another example of a crosslinking agent that can be used in the polyamide 56 composition is trimethylolpropane trimethacrylate (CAS No. 3290-92-4), which is a low volatility trifunctional monomer. This material is available as SR350 from Sartomer Americas. Preferably, the material in the range of about 1 to about 2 wt% is added to the polyamide 56. Most preferably, it accounts for 1 wt% of the polyamide 56 composition.

[0028] The polyamide 56 composition can be further crosslinked using radiation. Examples of suitable forms of radiation include, but are not limited to, ultraviolet radiation, X-ray radiation, gamma radiation, and electron beam radiation. The amount and type of radiation used depend on the specific end properties of the desired final product to achieve the desired crosslinking. Preferably, electron beam radiation is used. The product made from the polyamide 56 composition is exposed to electron beam radiation in the range of 50 kGy (5 MRad) to 300 kGy (30 MRad), preferably in the range of 75 kGy (7.5 MRad) to 200 kGy (20 MRad), and most preferably 100 kGy (10 MRad) to obtain the desired crosslinking.

[0029] Other conventional additives can be added to the polyamide 56 composition. Examples of conventional additives include: pigments, dyes, voiding agents, antistatic agents, foaming agents, plasticizers, radical scavengers, antiblocking agents, dustproofing agents, antifouling agents, surfactants, slip aids, optical brighteners, viscosity modifiers, gloss improvers, dispersion stabilizers, UV stabilizers, UV absorbers, antioxidants (such as phenolic antioxidants or amine antioxidants), lubricants, heat stabilizers, hydrolysis stabilizers, crosslinking activators, coupling agents, layered silicates, radiation opacifiers (such as, but not limited to, barium sulfate), tungsten metal, non-oxide bismuth salts, fillers, colorants, reinforcing agents, adhesion promoters (such as, but not limited to, 2-hydroxyethyl-methacrylate-phosphate), impact strength improvers, and any combination thereof. Such additives can be included in conventional amounts.

[0030] In one embodiment, the polyamide 56 is blended with the crosslinking agent and any other desired additives by extrusion. Then the composition is injection molded to produce the desired parts. Then the parts are irradiated by applying electron beam radiation.

[0031] The polyamide 56 composition of the present invention has a variety of uses. For example, the composition can be molded into seals, gaskets, connectors, wires, cables, printed circuit boards or EMI shields, and other electronic or computer components. The composition can be used to make electronic components such as smartphones, general automotive parts, electric motors, e-powertrains, batteries and battery housings, chargers for electric vehicles, and other components of electric vehicles. Additionally, the composition of the present invention can be used to make molded parts. Furthermore, the polyamide composition of the present invention can also be used to make medical devices, surgical equipment, medical encapsulations, or wearable medical devices.

[0032] Examples

[0033] Various samples were prepared using ECOBLEND N56F (a polyamide 56) and various amounts of crosslinking agents (triallyl isocyanurate and trimethylolpropane trimethacrylate (SR 350)). The polyamide and various amounts of crosslinking agents were blended by extrusion. Then the samples were injection molded into plates for moisture analysis or dog-bone shaped strips for tensile evaluation. Additionally, two other samples of only polyamide 56 were molded into plates. Then some of the plates made from the individual polyamide 56 polymer, and polyamide 56 polymer compositions containing polyamide 56 and various amounts of TAIC (1 wt% and 2 wt% of the total composition), and polyamide 56 polymer compositions containing polyamide 56 and various amounts of SR350 (1 wt% and 2 wt% of the total composition) were radiation crosslinked with an electron beam radiation dose of 100 kGy.

[0034] All these samples were characterized by DMA using ASTM D4065. Figure 1 The results of the DMA characterization are shown. The DMA characterization measures the storage modulus as a function of temperature. It is believed that the crosslinking agent shortens the distance between polymer chains in the amorphous phase, thereby changing the flexibility of the chains and preventing the absorption and entry of water molecules into the chains. Based on these DMA characterization results, the polyamide 56 composition containing TAIC as the crosslinking agent that was subjected to electron beam radiation showed excellent results compared to the other tested plates. The plate with TAIC showed a greater degree of crosslinking compared to the plate with SR350 or the polyamide 56 plate that was subjected to electron beam radiation or the untreated polyamide 56 plate. Additionally, the plate with 2 wt% of TAIC in the total composition showed a greater crosslinking compared to the plate with 1 wt% of TAIC in the total composition.

[0035] The compositions of the present invention were also subjected to a moisture test in accordance with ASTM D570 (October 12, 2022) and ISO 62:2008. Two different moisture test procedures were used. In the first method, pre-dried samples (98.9 °C, 8 hours) of various compositions with dimensions of 60×60×1 mm were immersed in water at room temperature (approximately 25 °C) for 24 hours. The weights of the samples were recorded before and after immersion. The percentage increase in weight of the samples was calculated. Figure 2 (a) presents a comparative analysis of the absorption of various compositions using the first method. The results clearly show that when polyamide 56 is compounded with a crosslinking agent, the moisture absorption of the polymer composition is reduced. When the polyamide 56 composition with a crosslinking agent is further subjected to electron beam radiation, the moisture absorption of the polymer composition is reduced by 15% to 55% compared to the untreated polyamide 56 sample; preferably, the moisture absorption of the polymer composition is reduced by approximately 35% to approximately 45% compared to untreated polyamide 56.

[0036] In the second moisture test method, pre-dried samples (98.9 °C, 8 hours) of various compositions with dimensions of 60×60×1 mm were exposed to 50% relative humidity at room temperature until the samples reached saturation, which was determined when the weight of the samples stopped increasing. The compositions used in this example were polyamide 66, polyamide 56, polyamide 56 subjected to electron beam radiation, and polyamide 56 compositions containing polyamide 56 and various amounts of TAIC (0.5 wt% to 3.0 wt% of the total composition). The weights of the samples were measured before and after the test, and the percentage increase in weight was calculated. As seen from Figure 2 (b), the sample made from the composition containing polyamide 56 and 0.5% of TAIC showed the lowest moisture absorption after 140 hours.

[0037] Figure 3 The water absorption measurements of the individual plates under supersaturated conditions are shown. The plates used in these examples were 60×60×1 mm. These plates were exposed to room temperature (about 25 °C) and about 50% relative humidity for a period of 24 hours. Initial measurements and measurements were made when the samples reached supersaturation. Both the absolute moisture absorption value and the moisture absorption rate were calculated. Figure 3 The absolute moisture absorption values in show that by including a crosslinking agent, the moisture absorption of polyamide 56 is alleviated and the moisture absorption rate is slowed down. Based on these conditions, the composition containing polyamide 56 and 0.5% of TAIC subjected to 100 kGy electron beam radiation performed the best.

[0038] The effect of crosslinking agents on the tensile properties of various compositions was also studied. Sheets of different compositions were prepared and tested according to ASTM D0638-22 (July 21, 2022) at a rate of 5 mm / min using an Instron machine equipped with a 30 kN load cell to determine the effect of using crosslinking agents. Strain measurements were made using an extensometer. Compositions containing polyamide 66, polyamide 56, and various polyamide 56 compositions with crosslinking agents were tested under this standard. The results showed that the addition of crosslinking agents made the polymer compositions more brittle, as seen by the decrease in the elongation at break of the polymer compositions containing crosslinking agents. Nevertheless, even in the case of using crosslinking agents in the compositions, the modulus and strength of the polymer compositions remained fairly consistent. The results of these various compositions can be seen in Figure 4 a-4c. These results showed that polymer compositions containing polyamide 56 and crosslinking agents maintained strengths and moduli similar to those of polyamide 56 alone and polyamide 66.

Claims

1. A polyamide 56 composition comprising polyamide 56 and a crosslinking agent, wherein the polyamide 56 composition is subjected to radiation crosslinking and the hygroscopicity of the polyamide 56 composition is reduced by about 15% to about 55% compared to a polyamide composition without the crosslinking agent.

2. The composition of claim 1, wherein the crosslinking agent is triallyl isocyanurate.

3. The composition of claim 2, wherein the triallyl isocyanurate is present in an amount of about 0.5% to about 3% by weight of the composition.

4. The composition of claim 1 further comprising an additional crosslinking agent.

5. The composition of claim 1, wherein the radiation cross-linking is provided at a dose ranging from about 50 kGy to about 300 kGy.

6. The composition of claim 1, wherein the radiation cross-linking is provided at a dose ranging from about 75 kGY to about 200 kGy.

7. The composition of claim 1, wherein the crosslinking agent is trimethylolpropane trimethacrylate.

8. The composition of claim 7, wherein the trimethylolpropane trimethacrylate is present in an amount of about 0.5% to about 3% by weight of the composition.

9. The composition of claim 7, further comprising an additional crosslinking agent.

10. The composition of claim 7, wherein the radiation cross-linking is provided at a dose of 100 kGy.

11. A polyamide 56 composition comprising polyamide 56 and a cross-linking agent, wherein the polyamide 56 composition has reduced water absorption compared to a polyamide composition without the cross-linking agent.

12. The polyamide 56 composition of claim 11, wherein the crosslinking agent is selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, and trimethylolpropane trimethacrylate.

13. The polyamide 56 composition of claim 11, wherein the polyamide composition is subjected to radiation crosslinking.

14. The polyamide 56 composition of claim 11, wherein the radiation cross-linking is provided at a dose of 100 kGy.

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