High toughness nylon 6 material and method of making same

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a high-toughness nylon 6 material and a preparation method thereof. The high-toughness nylon 6 material is prepared by soaking nylon 6 raw materials in an aqueous solution of an ionic liquid. The ionic liquid can be [BMIM]BF4. The concentration of the aqueous solution of the ionic liquid is 2-10 wt.%. The application provides more choices for the modification of the high-toughness nylon 6, expands the application range of the high-toughness nylon 6, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a high-toughness nylon 6 material and a preparation method thereof. BACKGROUND

[0002] Polyamide 6 (PA6), commonly known as nylon 6, is a typical semi-crystalline thermoplastic engineering plastic, which is widely used due to its excellent mechanical strength, wear resistance and chemical resistance. However, the intermolecular hydrogen bond formed by the amide group (C=O…N-H) in the molecular chain repeat unit of nylon 6 exists, which promotes the crystallization behavior of PA6 molecules due to the ordered arrangement of PA6 molecules. Therefore, PA6 has the disadvantage of poor toughness in dry and low temperature states. Improving the toughness of nylon mainly starts from breaking the strong hydrogen bond between PA6 molecular chains and increasing the activity of macromolecular chains.

[0003] The existing methods for improving the toughness of nylon 6 mainly achieve it by adding modified components and copolymerizing with other materials. However, these modification methods will add more other components (such as modifiers, rubbers, etc.), which will have a great impact on the original mechanical properties, thermal stability or processing performance of nylon 6. Therefore, in order to meet the needs of more application scenarios, it is urgent to develop more methods for modifying the toughness of nylon 6 in the field.

[0004] As a new type of "green solvent", ionic liquids have been widely used in industrial processing due to their excellent properties such as extremely low vapor pressure, good electrical conductivity and good solubility for many substances. According to the classification of anion and cation, ionic liquids can be divided into cationic ionic liquids and anionic ionic liquids. Among them, the cationic ionic liquids mainly include pyridine, imidazole, quaternary phosphonium, quaternary ammonium, etc., and the anionic ionic liquids mainly include halide salts and new types of ionic liquids. At present, some studies have tried to combine ionic liquids with nylon 6 to form a composite material (for example: CN115558142A Preparation method of a plasticized nylon 6 material), however, this method mainly has a plasticizing effect on nylon 6 and has no effect on improving the toughness. Whether ionic liquids can be used to improve the toughness of nylon 6 has not been reported yet. SUMMARY

[0005] In view of the problems of the prior art, the present application provides a high-toughness nylon 6 material and a preparation method thereof, which aims to modify nylon 6 using a simple process and improve its toughness without affecting the processing performance.

[0006] A high-toughness nylon 6 material is prepared by soaking nylon 6 raw materials in an aqueous solution of ionic liquid.

[0007] Preferably, the ionic liquid is selected from imidazolium ionic liquids.

[0008] Preferably, the ionic liquid is at least one of 1-butyl-3-methylimidazolium salt, 1-vinyl-3-butylimidazolium salt or 1-ethyl-3-methylimidazolium salt; the 1-butyl-3-methylimidazolium salt is at least one of [BMIM]BF4, [BMIM]PF6 or [BMIM]Cl.

[0009] Preferably, the aqueous solution of the ionic liquid has a concentration of 2-10 wt.%.

[0010] Preferably, the aqueous solution of the ionic liquid has a concentration of 2 wt.%.

[0011] Preferably, the nylon 6 raw material is a film-shaped material, and the film thickness is 160-180 μm.

[0012] Preferably, the soaking condition is 15-40℃ for 24-72h.

[0013] The application further provides a preparation method of the high-toughness nylon 6 material, characterized by comprising the following steps: soaking a nylon 6 raw material in an aqueous solution of an ionic liquid.

[0014] Preferably, the ionic liquid is selected from imidazolium ionic liquids.

[0015] Preferably, the ionic liquid is at least one of 1-butyl-3-methylimidazolium salt, 1-vinyl-3-butylimidazolium salt or 1-ethyl-3-methylimidazolium salt; the 1-butyl-3-methylimidazolium salt is at least one of [BMIM]BF4, [BMIM]PF6 or [BMIM]Cl.

[0016] The application further provides a use of the high-toughness nylon 6 material in manufacturing high-performance double-pull nylon film, automobile electrical appliances, automobile connectors, automobile circuit breakers, railway sleeper pads, railway insulation sleeves, railway baffle seats or railway elastic strip rail blocks.

[0017] The application provides a simple process of soaking nylon 6 in an ionic liquid solution, which can effectively improve the toughness of the nylon 6. Meanwhile, it is found through experiments that the nylon 6 material still has good processing performance after being processed by the process of the application. The application provides more choices for the modification of high-toughness nylon 6, expands the application range of high-toughness nylon 6, and has good application prospect.

[0018] Obviously, according to the above content of the application, according to the ordinary technical knowledge and common means in the art, other various forms of modifications, replacements or changes can be made without departing from the above basic technical idea of the application.

[0019] The above description of the present application is further illustrated in detail by the following specific embodiments in the form of examples. However, it should not be understood that the above subject matter of the present application is limited to the following examples. Any technology realized based on the above description of the present application falls within the scope of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Stress-strain curve test results in Experimental Example 1;

[0021] Figure 2 Experimental results of the influence of the amount of [BMIM]BF4 on the mechanical properties of PA6 in Experimental Example 1;

[0022] Figure 3 Infrared absorption spectrum of [BMIM]BF4;

[0023] Figure 4 FTIR spectrum of [BMIM]BF4-PA6 in Experimental Example 1;

[0024] Figure 5 Crystallization curve and melting curve of [BMIM]BF4-PA6 in Experimental Example 1, wherein the left graph is the first cooling curve and the right graph is the second heating curve;

[0025] Figure 6 Crystallization morphology graph (x400) of [BMIM]BF4-PA6 system in Experimental Example 1;

[0026] Figure 7 XRD spectrum of [BMIM]BF4-PA6 system in Experimental Example 1;

[0027] Figure 8 Thermogravimetric curve of [BMIM]BF4-PA6 system in Experimental Example 1. DETAILED DESCRIPTION

[0028] In the following examples and experimental examples, the reagents and raw materials not specifically explained are commercially available.

[0029] Example 1 High-toughness PA6

[0030] This example provides a high-toughness PA6, and the preparation method is as follows:

[0031] 1. Raw materials

[0032] PA6 base film: Ube 1013B, Tonen CM1017, Haiyang HY2500I, Xinhui M2500I

[0033] Ionic liquid [BMIM]BF4: M08713, Shanghai Maier Chemical Reagent Co., Ltd.

[0034] 2. Procedure of the steps

[0035] The PA6-based film was immersed in the deionized aqueous solution of the ionic liquid [BMIM]BF4 with different mass fractions for 72 h, and was obtained. The immersion condition was room temperature (25°C).

[0036] Five samples (denoted as [BMIM]BF4-PA6 below) and one control sample were prepared in this example, and the specific conditions were as follows:

[0037] Table 1 Preparation method of the samples

[0038]

[0039] The application will be further described through experiments below.

[0040] Experimental Example 1 Performance of high-toughness PA6

[0041] The samples used in this experimental example were the five samples prepared in Example 1 and one control sample.

[0042] I. Experimental method

[0043] Tensile test: The test was performed at room temperature according to ISO527-2-2012, and the tensile rate was 50 mm / min.

[0044] Infrared spectrum analysis (FTIR): The test frequency was 4 cm -1 , the test times were 32, and the test range was 4000-400 cm -1 .

[0045] Polarized light microscope test: The sample was placed on a glass slide, the sample was melted at 250°C, and a cover glass was used to press into a thin sheet. After constant temperature for 5 min, the sample was naturally cooled to 180°C, and crystallized at this temperature for 10 min, and then naturally cooled to room temperature. The crystal morphology was observed by transmission and reflection polarized light microscope.

[0046] DSC test: In a nitrogen atmosphere, about 5 mg of the sample was heated from 30°C to 250°C at a rate of 20°C / min, and after constant temperature for 5 min to eliminate thermal history, the sample was cooled from 250°C to room temperature at a rate of 10°C / min, and finally the sample was heated to 250°C at a rate of 10°C / min. The nitrogen flow rate was 50 mL / min. X-ray diffractometer test (XRD): One-dimensional XRD test was performed on the PA6-based film. The copper target (Cu Ka) wavelength was 0.154 nm, the voltage was 45 kV, the current was 40 mA, the test range was 10°-30°, and the scanning rate was 4° / min.

[0047] Thermogravimetric analysis (TG): In a nitrogen atmosphere, approximately 5 mg of sample was heated from 30 °C to 700 °C at a heating rate of 20 °C / min, and the thermogravimetric curve was recorded.

[0048] II. Experimental Results

[0049] (1) Tensile property analysis

[0050] The mechanical properties of PA6 after immersion in [BMIM]BF4 are as follows: Figure 1 and Figure 2 As shown, the control sample WS exhibits typical high strength (31.0 MPa) and high modulus (505.97 MPa) tensile behavior. However, the sample soaked in 2 wt% [BMIM]BF4 significantly reduced the yield strength and modulus of the PA6 system. Its yield strength was 17.4 MPa, a 44% decrease compared to the control sample WS, and its modulus was reduced by 59%. This is mainly because the interaction between [BMIM]BF4 and the amide group weakens the hydrogen bonding between PA6 molecules, increasing the mobility of PA6 molecular chain segments and thus improving the flexibility of the PA6 system.

[0051] With further increases in the [BMIM]BF4 content in the aqueous solution, the yield strength and modulus of the system did not change significantly. Detailed data on tensile strength, elongation at break, yield strength, and Young's modulus are shown in Table 2.

[0052] Table 2 Mechanical property data of PA6-[BMIM]BF4 system

[0053]

[0054]

[0055] The above experimental results show that soaking PA6 in an ionic liquid solution effectively improves its toughness, while the concentration of the ionic liquid solution has little effect on the improvement effect.

[0056] (2) Infrared spectral analysis

[0057] Figure 3 This is the infrared absorption spectrum of [BMIM]BF4. 3168 cm⁻¹ and 3120 cm⁻¹ are the absorption peaks at 3168 cm⁻¹ and 3120 cm⁻¹, respectively, representing the absorption peaks of the imidazole ring of [BMIM]BF4 at C(4,5)-H and C(2)-H stretching vibrations. 2968 cm⁻¹ is the absorption peak. -1 2872cm -1 The peak at 1570 cm⁻¹ represents the stretching vibration absorption of the methyl (-CH₃) group of the butyl chain on the N(3) ring of the imidazole ring and the saturated CH group on the (-CH₂-) methylene group. -1 The absorption peaks of the nearby functional groups are absorption peaks of the stretching vibrations of the imidazole ring skeleton.

[0058] Figure 4 It can be observed that the PA6 system after being soaked in [BMIM]BF4 reaches a depth of 1167 cm⁻¹. -1 An absorption peak for the stretching vibration of the NH group on the imidazole ring appeared at 1570 cm⁻¹. -1 The absorption peak of the nearby functional group is the stretching vibration absorption peak of the imidazole ring skeleton, 1167 cm⁻¹. -1 The peak is near the stretching vibration of the imidazole ring, and it increases to 1167 cm⁻¹ with increasing concentration of [BMIM]BF₄ aqueous solution. -1 The peak value of the absorption peak at that location also increases accordingly, which indicates that the proportion of ionic liquid [BMIM]BF4 in the PA6 system increases stepwise with the increase of solution concentration.

[0059] Figure 4 The wavenumbers corresponding to the functional group stretching vibration absorption peaks of the PA6 system are consistent with the absorption peaks of various groups on the PA6 molecular chain as indicated in the literature. The [BMIM]BF4-PA6 base film at 3305 cm⁻¹... -1 3431cm -1 An absorption peak for the amino group (NH) stretching vibration of the amide II band appeared at 1636 cm⁻¹. -1 The functional group absorption peak at 1545 cm⁻¹ is the stretching vibration absorption peak of amide I with carbonyl (C=O) on the PA6 molecular chain. -1 It is a combination of NH bending vibration and CN stretching vibration of the amide II band.

[0060] Figure 4 [BMIM]BF4-PA6 at 3299cm -1 The absorption intensity of the amide II band (NH stretching vibration peak) decreases, and it is located at 1636 cm⁻¹. -1 The absorption peak of the amide I band (carbonyl C=O stretching vibration) at [BMIM]BF4 is weakened. These results indicate that the hydrogen on the imidazole ring in [BMIM]BF4 forms hydrogen bonds with the nitrogen (CN) and oxygen (C=O) on the amide group in the PA6 molecule, thus weakening the hydrogen bonding on the amide band of the PA6 molecular chain.

[0061] (3) DSC analysis

[0062] The DSC curves of PA6 after soaking in [BMIM]BF4 aqueous solutions of different concentrations are shown below. Figure 5The corresponding DSC parameters are shown in Table 3. It can be observed from the figure that with the increase of the content of [BMIM]BF4, the melting curve of PA6 system moves to low temperature direction, and the crystallization direction of PA6 system also moves to low temperature direction. As shown in Table 4, with the increase of the content of [BMIM]BF4 in the aqueous solution, the Tm and Tc of the system gradually decrease, the Tm decreases from 220.1°C to 213.8°C, the Tc of the pure PA6 system decreases from 182.8°C to 173.6°C, and the ΔT increases obviously, and the crystallinity of the system decreases by 12%. This is mainly because the interaction between [BMIM]BF4 and the amide group in PA6 forms new intermolecular forces, which destroys part of the hydrogen bond interaction between the molecular chains of PA6, resulting in the decrease of the crystallization ability of PA6, the order between the molecular chains becomes worse, and it is difficult to form regular spherulites. Figure 5 As can be seen from the right figure, the pure PA6 sample has obvious α crystal form melting peak (about 220°C) and γ crystal form melting peak (about 210°C), and with the increase of the content of [BMIM]BF4 in the soaking solution, the γ crystal form melting peak gradually becomes less obvious in the melting curve. When [BMIM]BF4 enters the molecular structure of nylon, the rotation of amide bond is hindered, and the formation of γ crystal form is affected.

[0063] Table 3 Melting peak, crystallization peak, melting enthalpy and crystallinity of [BMIM]BF4-PA6

[0064]

[0065] (4) Polarizing microscope (POM) analysis

[0066] The crystalline morphology of PA6 sample after [BMIM]BF4 immersion is shown in Figure 6 The PA6 base film shows larger and more obvious crystal grains, while the sample after [BMIM]BF4 immersion has obviously smaller crystal grains, which indicates that the crystallization of [BMIM]BF4-PA6 is more difficult than that of PA6, which corresponds to the decrease of melting point by DSC. Once the crystal nucleus of PA6 is generated, the growth rate of the crystal will be faster, so it is easy to generate larger spherulites. After the penetration of ionic liquid into PA6, the solvation degree of amide bond is higher, the interaction between polar segments is weaker, and the regular arrangement of molecular segments is difficult, so smaller crystal grains are formed. For macromolecules containing imperfect crystal regions, deformation is easy under the action of external force, and the material usually shows the improvement of toughness.

[0067] (5) XRD crystal structure analysis

[0068] PA6 can form several different crystal structures (such as α, γ and β) with the change of molecular chain conformation and hydrogen bond distribution, among which the most common are α and γ crystal forms. The α crystal form is monoclinic, and the hydrogen bond forms a fully extended zigzag chain conformation in the anti-parallel chain, which is the most stable thermodynamic form; while in the γ crystal form, the hydrogen bond forms a twisted conformation in the anti-parallel chain, which causes the chain axis to repeat to be short and form folded lamellae.

[0069] From Figure 7 The characteristic diffraction peak of γ crystal form at 2θ = 21.5° and the diffraction peaks of (020) and (200) of α crystal form at 2θ = 20.3° and 2θ = 23.5° can be identified from Table 4. The crystal form of PA6 system does not change due to the introduction of [BMIM]BF4. This means that even though the strong interaction between [BMIM]BF4 and PA6 affects the arrangement of hydrogen bonds between PA6 molecules, since the soaking process does not affect the crystallization process of PA6, this strong interaction only exists in the amorphous region of PA6 and has little effect on the crystallization and crystal form of PA6.

[0070] Table 4 Crystal structure data of [BMIM]BF4-PA6 based film system

[0071]

[0072] (6) TG thermal stability analysis

[0073] Figure 8 The thermal stability diagram of PA6 system after soaking in different concentrations of [BMIM]BF4 aqueous solution. From Figure 8 it can be observed that with the addition of [BMIM]BF4, the maximum thermal weight loss peak of PA6 is advanced, which indicates that the addition of [BMIM]BF4 will reduce the thermal stability of PA6; there is no physical adsorption dehydration weight loss phenomenon in the PA6 film curve, but it directly enters the thermal decomposition process. With the increase of the content of ionic liquid, the thermal weight loss curve of PA6 system soaked in different concentrations of ionic liquid moves gently to low temperature, and the moving direction of the whole thermal weight loss process is consistent with that of PA6 pure sample, and there is no weight loss phenomenon.

[0074] The cation in the [BMIM]BF4 molecule has a large steric hindrance imidazole ring, which increases the distance between part of the PA6 molecular chains, further destroys the hydrogen bond interaction between the PA6 macromolecular chains, and reduces the order and regularity of the arrangement of the molecular chains of the PA6 plasticized film, so the thermal stability of PA6 will decrease with the increase of the amount of ionic liquid added.

[0075] It can be observed in Table 5 that the temperature at Td5% of the [BMIM]BF4-PA6 system decreases with the increase of the content of the ionic liquid, but the thermal weight loss curve of the PA6 system with different concentrations of the ionic liquid does not change obviously, but as a whole, it has a certain change trend, wherein the [BMIM]BF4-PA6 obtained when the concentration of the ionic liquid is the lowest of 2wt.% has the best thermal stability.

[0076] Table 5 Td5%, Td50% and thermal decomposition temperature of the [BMIM]BF4-PA6 system

[0077]

[0078] In addition, although the thermal stability of the PA6 system after being soaked in the aqueous solution of [BMIM]BF4 with different concentrations decreases to a certain extent, the initial decomposition temperature is always greater than 300℃, which is higher than the forming and processing temperature of PA6, and thus has no influence on the forming and processing of PA6.

[0079] It can be seen from the above examples and experimental examples that the PA6 is modified by a simple process, the toughness of the PA6 can be effectively improved, the process has little influence on the thermal stability of the PA6, and has no influence on the forming and processing of the PA6. The present application provides more choices for the modification of high-toughness nylon 6, expands the application range of the high-toughness nylon 6, and has good application prospect.

Claims

1. A high-toughness nylon 6 material, characterized in that, It is made by soaking nylon 6 raw material in an aqueous solution of an ionic liquid; the ionic liquid is [BMIM]BF4, and the concentration of the aqueous solution of the ionic liquid is 2wt% or 6wt%.

2. The high-toughness nylon 6 material according to claim 1, characterized in that: The nylon 6 raw material is a film material with a film thickness of 160-180 μm; And / or, the soaking conditions are: soaking at 15-40℃ for 24-72 hours.

3. A method for preparing the high-toughness nylon 6 material according to any one of claims 1-2, characterized in that, include: The nylon 6 raw material is obtained by soaking it in an aqueous solution of an ionic liquid.

4. The preparation method according to claim 3, characterized in that: The ionic liquid is [BMIM]BF4.

5. Use of the high-toughness nylon 6 material according to any one of claims 1-2 in the manufacture of high-performance biaxially stretched nylon films, automotive electrical components, automotive connectors, automotive circuit breakers, railway sleeper pads, railway insulating sleeves, railway baffle seats, or railway elastic gauge blocks.

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