A reprocessable bio-based cross-linked polyamide and preparation method thereof

Abstract

The present invention provides a reprocessable bio-based cross-linked polyamide and a preparation method thereof, belonging to the technical field of high molecular polymers. The present invention can obtain an amino-terminated prepolymer by first prepolymerizing a linear diamine and phthalaldehyde, and then polymerizing it with trimethyl citrate, which is conducive to the full completion of the reaction, so that the imine bond is introduced into the polymer, so that the cross-linked polyamide has reprocessability, self-healing and degradability; the method provided by the present invention is simple to operate, and does not require the addition of organic solvents and highly toxic catalysts, and the process cost is low and more environmentally friendly. The results of the examples show that the polyamide prepared by the present invention has a tensile strength of >18MPa; elongation at break >10%; melting temperature >98.6°C; 20°C < glass transition temperature <60°C; thermal decomposition 5% temperature >260°C; and mechanical property retention rate of repeated processing >85%.

Description

Technical Field

[0001] The invention relates to the technical field of high molecular polymers, and in particular to a reprocessable bio-based cross-linked polyamide and a preparation method thereof. Background Art

[0002] Polyamide elastomers, due to their unique three-dimensional network structure, exhibit excellent wear resistance, chemical resistance and good impact resistance, and are widely used in electronic appliances, new energy vehicles, LED optics and other fields. However, traditional cross-linked polyamide elastomer polymer materials can only be formed once, and due to the stability and irreversibility of the cross-linked structure, their reprocessing and reuse are limited. In today's sustainable development environment, how to prepare reprocessable cross-linked polymer materials is a technical problem that urgently needs to be solved in this field.

[0003] In addition, traditional polyamide elastomers are usually synthesized from petrochemical resource monomers. As petrochemical resources are gradually depleted, exploring the development of bio-based, high-efficiency and sustainable polyamide materials has become a hot topic in industry research. As a renewable resource, biomass has unique advantages, such as extremely short life cycle, low carbon emissions and relatively low cost. Existing renewable and degradable cross-linked polymers are mainly concentrated in materials such as polyurethane and polyimide. For example, Chinese patent CN202211581234.0 discloses a bio-based polyamide imide Vitrimer material and preparation method based on anhydrous ethanol as a base solvent. However, this method has a low proportion of bio-based raw materials on the one hand, and requires the addition of organic solvents on the other hand, and the process is complicated. For example, Chinese patent CN202210546302.3 discloses a preparation method and application of a high-biomass-based polyimide self-healing polymer. The preparation process of this patent is complicated, and p-toluenesulfonic acid needs to be added as a catalyst, which is highly toxic.

[0004] Therefore, there is an urgent need to provide a method for preparing a bio-based cross-linked polyamide material that does not require the addition of an organic solvent or a highly toxic catalyst and can be processed repeatedly. Summary of the invention

[0005] The object of the present invention is to provide a bio-based cross-linked polyamide material which does not require the addition of an organic solvent or a highly toxic catalyst and can be repeatedly processed, and a preparation method thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0008] (1) mixing a linear diamine and phthalaldehyde, and performing a prepolymerization reaction under an inert atmosphere to obtain an amino-terminated prepolymer;

[0009] (2) mixing the amino-terminated prepolymer obtained in step (1) with trimethyl citrate to carry out a polymerization reaction to obtain a reproducible bio-based cross-linked polyamide;

[0010] In the step (2), the molar ratio of -COOCH3 of trimethyl citrate and -NH2 of the amino-terminated prepolymer is (0.9-1.1):1.

[0011] Preferably, the linear diamine in step (1) comprises one or more of butanediamine, pentamethylenediamine, and decanediamine.

[0012] Preferably, in step (1), the molar ratio of the linear diamine to phthalaldehyde is (3-6):(2-5).

[0013] Preferably, the temperature of the prepolymerization reaction in step (1) is 100 to 150° C.; and the time of the prepolymerization reaction is 10 to 200 min.

[0014] Preferably, the polymerization reaction in step (2) comprises a first polymerization reaction, a second polymerization reaction and a aging reaction which are carried out in sequence, and the temperature of the second polymerization reaction is higher than the temperature of the first polymerization reaction.

[0015] Preferably, the temperature of the first polymerization reaction is 130-180° C.; the time of the first polymerization reaction is 10-200 min.

[0016] Preferably, the temperature of the second polymerization reaction is 140-200° C.; and the time of the second polymerization reaction is 10-200 min.

[0017] Preferably, the aging reaction temperature is 150-200° C. and the aging reaction time is 1-20 h.

[0018] Preferably, the aging reaction is carried out under negative pressure, and the pressure of the negative pressure is 10-300Pa.

[0019] The present invention also provides a bio-based cross-linked polyamide that can be repeatedly processed and is prepared by the preparation method described in the above technical solution.

[0020] The invention provides a method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps: mixing a linear diamine and phthalaldehyde, and performing a prepolymerization reaction under an inert atmosphere to obtain an amino-terminated prepolymer; mixing the amino-terminated prepolymer and trimethyl citrate, and performing a polymerization reaction to obtain a reproducible bio-based cross-linked polyamide; the molar ratio of -COOCH3 of the trimethyl citrate to -NH2 of the amino-terminated prepolymer is (0.9-1.1):1. The linear diamine used in the present invention is derived from biomass raw materials, and trimethyl citrate is used as a bio-based cross-linking agent, which can reduce the application of petrochemical resources; the present invention can obtain an amino-terminated prepolymer by first prepolymerizing the linear diamine and phthalaldehyde, and then polymerizing with trimethyl citrate, which is conducive to the full completion of the reaction, so that the imine bond is introduced into the polymer, so that the cross-linked polyamide has reprocessability, self-healing and degradability; the method provided by the present invention is simple to operate, and does not require the addition of organic solvents and highly toxic catalysts, and the process cost is low and more environmentally friendly. The results of the embodiment show that the polyamide prepared by the present invention; can be repeatedly processed and degraded, and the tensile strength is>18MPa; the elongation at break is>10%; the melting temperature is>98.6℃; 20℃<glass transition temperature<60℃; the thermal decomposition 5% temperature is>260℃; the mechanical property retention rate of repeated processing is>85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the infrared spectrum of the amino-terminated prepolymer prepared in step (1) of Examples 1 to 4 of the present invention;

[0022] Figure 2 The infrared spectra of the reprocessable bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention;

[0023] Figure 3 The hydrogen spectrum of the amino-terminated prepolymer prepared in step (1) of Examples 1 to 4 of the present invention;

[0024] Figure 4 The carbon spectrum of the amino-terminated prepolymer prepared in step (1) of Examples 1 to 4 of the present invention;

[0025] Figure 5 DSC test curves of the reproducible bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention;

[0026] Figure 6 The fragments of the re-processable bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention and the pictures of the samples obtained after re-pressing;

[0027] Figure 7 Thermogravimetric curves of the reproducible bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention;

[0028] Figure 8 This is a photograph of the re-processable bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention standing in a hydrochloric acid solution for 0 hours;

[0029] Fig. 9 This is a photograph of the reprocessable bio-based cross-linked polyamide prepared in Examples 1 to 4 of the present invention standing in a hydrochloric acid solution for 24 hours;

[0030] Fig.10 This is a photo of the product prepared in Comparative Example 1 of the present invention;

[0031] Fig.11 This is a photo of the product prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0033] (1) mixing a linear diamine and phthalaldehyde, and performing a prepolymerization reaction under an inert atmosphere to obtain an amino-terminated prepolymer;

[0034] (2) mixing the amino-terminated prepolymer obtained in step (1) with trimethyl citrate to carry out a polymerization reaction to obtain a reproducible bio-based cross-linked polyamide;

[0035] In the step (2), the molar ratio of -COOCH3 of trimethyl citrate and -NH2 of the amino-terminated prepolymer is (0.9-1.1):1.

[0036] In the present invention, unless otherwise specified, the chemical reagents used in the present invention are all conventional commercial products in the art.

[0037] The invention mixes linear diamine and phthalaldehyde, and performs prepolymerization reaction under an inert atmosphere to obtain an amino-terminated prepolymer.

[0038] In the present invention, the linear diamine preferably includes one or more of butanediamine, pentamethylenediamine, and decanediamine, and more preferably decanediamine. When the present invention uses the above linear diamine, the terminal groups on both sides are amino groups, which is more conducive to the formation of a prepolymer containing an imine bond; and decanediamine is derived from bio-based castor oil, and pentamethylenediamine and butanediamine can be prepared by a biological fermentation method, which are bio-based raw materials and can reduce the application of petrochemical resources.

[0039] In the present invention, the phthalaldehyde preferably includes isophthalaldehyde or terephthalaldehyde, and more preferably terephthalaldehyde. The present invention uses phthalaldehyde as a monomer, which can react with a linear diamine to form a prepolymer containing an imine bond.

[0040] In the present invention, the molar ratio of the linear diamine to phthalaldehyde is preferably (3-6):(2-5), more preferably (4-6):(3-5). The present invention controls the usage of the two within the above range, so that the linear diamine is excessive to form an amino-terminated prepolymer.

[0041] The present invention has no special limitation on the method for mixing the linear diamine and phthalaldehyde. A conventional mixing method can be used as long as the two can be mixed evenly.

[0042] In the present invention, the inert atmosphere is preferably nitrogen. In the present invention, the reaction is carried out under an inert atmosphere to prevent the occurrence of side reactions.

[0043] In the present invention, the temperature of the prepolymerization reaction is preferably 100-150°C, more preferably 120-140°C; the time of the prepolymerization reaction is preferably 10-200 min, more preferably 30-180 min. The present invention controls the temperature and time of the prepolymerization reaction within the above ranges, so that the prepolymerization reaction can be fully carried out.

[0044] The present invention has no special limitation on the device for the prepolymerization reaction, and any conventional polymerization reaction device can be used. In the present invention, the device for the prepolymerization reaction is preferably a reactor.

[0045] In the present invention, during the prepolymerization reaction, the pressure in the reactor is preferably controlled to be 300-1000 Pa, more preferably 300-500 Pa. By controlling the pressure to be within the above range, the present invention can promote the discharge of product water and prevent the imine bond from decomposing when exposed to water.

[0046] After obtaining the amino-terminated prepolymer, the present invention mixes the amino-terminated prepolymer with trimethyl citrate to carry out polymerization reaction to obtain a bio-based cross-linked polyamide that can be repeatedly processed.

[0047] In the present invention, the trimethyl citrate is used as a bio-based cross-linking agent, which can reduce the application of petrochemical resources.

[0048] In the present invention, the molar ratio of -COOCH3 of the trimethyl citrate and -NH2 of the amino-terminated prepolymer is (0.9-1.1):1, preferably (0.95-1.05):1. In the present invention, the molar ratio of -COOCH3 of the trimethyl citrate and -NH2 of the amino-terminated prepolymer is referred to as the molar ratio of -COOCH3 / -NH2. When the molar ratio of -COOCH3 / -NH2 is within the above range, the system can be fully crosslinked.

[0049] The present invention has no special limitation on the method of mixing the amino-terminated prepolymer and trimethyl citrate. Conventional mixing methods can be used to uniformly mix the two.

[0050] In the present invention, the polymerization reaction preferably includes a first polymerization reaction, a second polymerization reaction and a aging reaction which are performed in sequence, and the temperature of the second polymerization reaction is higher than the temperature of the first polymerization reaction.

[0051] In the present invention, the temperature of the first polymerization reaction is preferably 130-180°C, more preferably 140-160°C; the time of the first polymerization reaction is preferably 10-200min, more preferably 30-180min. In the present invention, the temperature of the second polymerization reaction is preferably 140-200°C, more preferably 150-180°C; the time of the second polymerization reaction is preferably 10-200min, more preferably 30-180min. The present invention can make the polymerization reaction dynamic by carrying out the first polymerization reaction and the second polymerization reaction in sequence and carrying out the polymerization reaction in two stages. This is because as the degree of crosslinking and the molecular weight increase, the energy required for the reaction becomes higher and higher, and dynamic temperature increase helps to gradually react and ensure a uniform increase in molecular weight.

[0052] In the present invention, the first polymerization reaction and the second polymerization reaction are preferably carried out under reduced pressure distillation. The present invention can discharge by-products through reduced pressure distillation.

[0053] In the present invention, the temperature of the aging reaction is preferably 150-200°C, more preferably 155-180°C; the time of the aging reaction is preferably 1-20h, more preferably 5-10h. In the present invention, the aging reaction is preferably carried out under negative pressure, and the pressure of the negative pressure is preferably 10-300Pa, more preferably 10-100Pa. The present invention does not specifically limit the device for the aging reaction, and a conventional heating device can be used. In the present invention, the product obtained after the second polymerization reaction is a pre-cured product, and the viscosity is relatively high, which is not conducive to discharging and later industrial production. The present invention is more conducive to subsequent discharging and industrial production by taking out the pre-cured product obtained by the second polymerization reaction for aging.

[0054] The linear diamine used in the present invention is derived from biomass raw materials, which can reduce the application of petrochemical resources; the scheme provided by the present invention can introduce imine bonds into polymers, so that cross-linked polyamides have reprocessability, self-repairability and degradability; the method provided by the present invention is simple to operate, does not require the addition of organic solvents and toxic catalysts, has low process costs and is more environmentally friendly.

[0055] The present invention also provides a bio-based cross-linked polyamide that can be repeatedly processed and is prepared by the preparation method described in the above technical solution.

[0056] The invention introduces imine bonds into the polymer, so that the cross-linked polyamide has reprocessability, self-repairability and degradability; and adopts bio-based raw materials, reducing the application amount of petrochemical resources.

[0057] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] Example 1

[0059] A method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0060] (1) adding decanediamine and terephthalaldehyde into a reaction kettle at a molar ratio of 3:2, introducing nitrogen to raise the temperature to 130° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 600 Pa, and continuing the reaction for 100 minutes to complete the prepolymerization reaction and obtain an amino-terminated prepolymer;

[0061] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate is added to the reactor of the amino-terminated prepolymer obtained in the step (1) to mix the two, and a polymerization reaction is carried out. While distilling under reduced pressure, the temperature is continuously raised to 140°C and reacted for 100 min to carry out a first polymerization reaction, and then the temperature is further raised to 150°C and reacted for 100 min to carry out a second polymerization reaction. The obtained precured product is taken out and placed in a vacuum oven at 155°C for heating for 5 hours for maturation to obtain a reproducible bio-based cross-linked polyamide.

[0062] The structural formula of the bio-based cross-linked polyamide prepared in this embodiment that can be repeatedly processed is as follows:

[0063]

[0064] Example 2

[0065] A method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0066] (1) adding decanediamine and terephthalaldehyde into a reaction kettle at a molar ratio of 4:3, introducing nitrogen to raise the temperature to 140° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 500 Pa, and continuing the reaction for 110 minutes to complete the prepolymerization reaction, thereby obtaining an amino-terminated prepolymer;

[0067] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate is added to the reactor of the amino-terminated prepolymer obtained in the step (1) to mix the two, and a polymerization reaction is carried out. While distilling under reduced pressure, the temperature is continuously raised to 150°C and reacted for 110 min to carry out a first polymerization reaction, and then the temperature is further raised to 160°C and reacted for 110 min to carry out a second polymerization reaction. The obtained precured product is taken out and placed in a vacuum oven at 165°C for heating for 5 hours for maturation to obtain a reproducible bio-based cross-linked polyamide.

[0068] Example 3

[0069] A method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0070] (1) adding decanediamine and terephthalaldehyde into a reaction kettle at a molar ratio of 5:4, introducing nitrogen to raise the temperature to 150° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 400 Pa, and continuing the reaction for 120 minutes to complete the prepolymerization reaction and obtain an amino-terminated prepolymer;

[0071] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate is added to the reactor of the amino-terminated prepolymer obtained in the step (1) to mix the two, and a polymerization reaction is carried out. While distilling under reduced pressure, the temperature is continuously raised to 160°C and reacted for 120 min to carry out a first polymerization reaction, and then the temperature is further raised to 170°C and reacted for 120 min to carry out a second polymerization reaction. The obtained precured product is taken out and placed in a vacuum oven at 175°C for heating for 5 hours for maturation to obtain a reproducible bio-based cross-linked polyamide.

[0072] Example 4

[0073] A method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps:

[0074] (1) adding decanediamine and terephthalaldehyde into a reaction kettle at a molar ratio of 6:5, introducing nitrogen to raise the temperature to 150° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 300 Pa, and continuing the reaction for 130 minutes to complete the prepolymerization reaction and obtain an amino-terminated prepolymer;

[0075] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate is added to the reactor of the amino-terminated prepolymer obtained in the step (1) to mix the two, and a polymerization reaction is carried out. While distilling under reduced pressure, the temperature is continuously raised to 160°C and reacted for 130 min to carry out a first polymerization reaction, and then the temperature is further raised to 170°C and reacted for 130 min to carry out a second polymerization reaction. The obtained precured product is taken out and placed in a vacuum oven at 185°C for heating for 5 h for maturation to obtain a reproducible bio-based cross-linked polyamide.

[0076] Comparative Example 1

[0077] A method for preparing polyamide:

[0078] (1) adding decanediamine and terephthalaldehyde into a reaction kettle at a molar ratio of 6:5, introducing nitrogen to raise the temperature to 150° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 300 Pa, and continuing the reaction for 130 minutes to complete the prepolymerization reaction and obtain an amino-terminated prepolymer;

[0079] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate was added to the reactor of the amino-terminated prepolymer obtained in step (1) to mix the two, and a polymerization reaction was carried out. The temperature was raised to 160°C and reacted for 130 minutes to carry out a first polymerization reaction, and then the temperature was raised to 170°C and reacted for 130 minutes to carry out a second polymerization reaction to obtain a precured product. No further aging was carried out, and the obtained product was directly pressed and formed. Fig.10 As shown. Fig.10 It can be seen that the polymer obtained by the comparative method cannot be pressed into a smooth sample sheet. This is because the comparative method cannot make the polymer fully react and cross-link, so the obtained polyamide material has poor performance and cannot be repeatedly processed.

[0080] Comparative Example 2

[0081] A method for preparing polyamide, comprising the following steps:

[0082] (1) adding decanediamine and sebacic acid into a reaction kettle at a molar ratio of 6:5, introducing nitrogen to raise the temperature to 170° C., reacting at this temperature for 30 minutes, maintaining the nitrogen atmosphere unchanged, reducing the pressure to 300 Pa, and continuing the reaction for 130 minutes to complete the prepolymerization reaction and obtain an amino-terminated prepolymer;

[0083] (2) According to the molar ratio of -COOCH3 / -NH2 being 1:1, trimethyl citrate is added to the reactor of the amino-terminated prepolymer obtained in the step (1) to mix the two, and a polymerization reaction is carried out. While distilling under reduced pressure, the temperature is continuously raised to 180°C and reacted for 130 min to carry out a first polymerization reaction, and then the temperature is further raised to 185°C and reacted for 130 min to carry out a second polymerization reaction. The obtained precured product is taken out and placed in a vacuum oven at 185°C for heating for 5 h to mature, thereby obtaining a bio-based cross-linked polyamide.

[0084] Repeatedly processed samples Fig.11 As shown, from Fig.11 It can be seen that the product prepared in this comparative example has cracks and cannot be fused together. Since it does not contain imine bonds, it cannot be processed repeatedly.

[0085] Test Case

[0086] (1) The infrared spectrum of the amino-terminated prepolymer prepared in step (1) of Examples 1 to 4 is as follows: Figure 1 As shown. Figure 1 In the figure, Y3:2, Y4:3, Y5:4 and Y6:5 are infrared spectra of the amino-terminated prepolymers prepared in step (1) of Examples 1 to 4, respectively.

[0087] The infrared spectra of the reprocessable bio-based cross-linked polyamide prepared in Examples 1 to 4 are as follows: Figure 2 As shown. Figure 2 In the figure, J3 to 2, J4 to 3, J5 to 4 and J6 to 5 are infrared spectra of the reprocessable bio-based cross-linked polyamides prepared in Examples 1 to 4, respectively.

[0088] exist Figure 1 Medium, 3300cm -1 The characteristic peak of the capped amino group; 1640 cm -1 It is the characteristic peak of imine bond. Figure 2 Medium, 3400cm -1 NH stretching vibration peak in amide bond; 1738cm -1 The carbonyl (C=O) stretching vibration peak of trimethyl citrate did not appear, proving that trimethyl citrate participated in the reaction and the formation of cross-linked products. Figure 1 and Figure 2 It can be seen that the present invention introduces imine bonds into the bio-based cross-linked polyamide.

[0089] (2) The hydrogen spectrum of the amino-terminated prepolymer prepared in step (1) of Examples 1 to 4 is as follows: Figure 3 As shown; the carbon spectrum is as Figure 4 As shown. Figure 3 and Figure 4The structure of the amino terminated prepolymer can be derived and includes an imine bond in the structure.

[0090] (3) The DSC test curves of the reproducible bio-based cross-linked polyamide prepared in Examples 1 to 4 are as follows: Figure 5 As shown. Figure 5 It can be seen that the glass transition temperature and melting temperature of bio-based cross-linked polyamide gradually increase with the increase of prepolymer molecular weight.

[0091] (4) The fragments of the reprocessable bio-based cross-linked polyamide prepared in Examples 1 to 4 and the samples obtained after re-pressing are shown in the figure. Figure 6 As shown. Figure 6 In the same column, the fragments of bio-based cross-linked polyamide prepared in the same embodiment and the pictures of the sample pressed by the fragments are shown. The temperature for pressing the fragments is 150°C, 10MPa, and the pressing time is 15min. Figure 6 It can be seen that the bio-based cross-linked polyamide prepared by the present invention can be reshaped by hot pressing after being crushed, and has the property of being repeatable.

[0092] (5) The tensile strength and elongation at break of the reprocessable bio-based cross-linked polyamide prepared in Examples 1 to 4 were tested.

[0093] The calculation formula of tensile strength retention is shown in the following formula (1):

[0094] Tensile strength retention rate = A1 / B1×100% Formula (1)

[0095] In formula (1), B1 is the tensile strength test result of bio-based cross-linked polyamide, and A1 is the result of pressing the fragments of bio-based cross-linked polyamide after crushing and performing a tensile strength test, the pressing temperature is 150°C, 10MPa, and the pressing time is 15min. The international standard implemented for the tensile strength test is GB-T 1040.1-2006.

[0096] The calculation formula of the elongation at break retention rate is shown in the following formula (2):

[0097] Elongation at break retention = A2 / B2×100% Formula (2)

[0098] In formula (2), B2 is the elongation at break test result of bio-based cross-linked polyamide, A2 is the result of breaking the bio-based cross-linked polyamide and pressing the fragments, and then testing the elongation at break, the pressing temperature is 150°C, 10MPa, and the pressing time is 15min. The international standard for the elongation at break test is GB-T 1040.1-2006.

[0099] The tensile strength and elongation at break of the reprocessable bio-based cross-linked polyamide (before reprocessing) prepared in Examples 1 to 4 are shown in Table 1:

[0100] Table 1 Tensile strength and elongation at break of reprocessable bio-based cross-linked polyamide

[0101] Tensile strength / MPa Elongation at break / % Example 1 18.1 10.3 Example 2 23.5 12.5 Example 3 24.2 15.7 Example 4 25.4 22.0

[0102] It can be seen from Table 1 that the tensile strength of the products prepared in Examples 1 to 4 is greater than 18 MPa, and the elongation at break is greater than 10%.

[0103] The thermogravimetric curves of the reproducible bio-based cross-linked polyamide prepared in Examples 1 to 4 are as follows: Figure 7 As shown. Figure 7 It can be seen that the 5% thermal decomposition temperature of the reproducible bio-based cross-linked polyamide prepared in the embodiment of the present invention is greater than 260°C.

[0104] The reprocessing performance retention rates of the reprocessable bio-based cross-linked polyamides prepared in Examples 1 to 4 are shown in Table 2:

[0105] Table 2 Re-processing performance retention rate of re-processable bio-based cross-linked polyamide

[0106] Example Example 1 Example 2 Example 3 Example 4 Tensile strength retention rate / % 93 99 98 99 Retention rate of elongation at break / % 89 94 97 94

[0107] It can be seen from the results in Table 2 that the bio-based cross-linked polyamide prepared in the present invention can be re-pressed into sheets after being crushed, has the property of being reprocessable, and the re-pressed samples have excellent mechanical retention.

[0108] (6) The reprocessable bio-based cross-linked polyamides prepared in Examples 1 to 4 were respectively placed in a hydrochloric acid solution with a concentration of 0.5 mol / L and allowed to stand at room temperature for 24 h. Figure 8 For photos taken after 0 hours of rest, Fig. 9 This is a photo taken after 24 hours. Figure 8 and 9 It can be seen that the bio-based cross-linked polyamide prepared by the present invention can not only be processed repeatedly, but also has good degradation performance.

[0109] It can be seen from the results of the above examples that the present invention introduces an imine bond when preparing polyamide, so that the bio-based cross-linked polyamide prepared by the present invention has the property of being reproducible and has excellent mechanical retention and degradability.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a reproducible bio-based cross-linked polyamide, comprising the following steps: (1) mixing a linear diamine and phthalaldehyde, and performing a prepolymerization reaction under an inert atmosphere to obtain an amino-terminated prepolymer; (2) mixing the amino-terminated prepolymer obtained in step (1) with trimethyl citrate to carry out a polymerization reaction to obtain a reproducible bio-based cross-linked polyamide; The linear diamine in step (1) includes one or more of butanediamine, pentamethylenediamine, and decanediamine; In the step (2), the molar ratio of -COOCH3 of trimethyl citrate and -NH2 of amino-terminated prepolymer is (0.9-1.1):1; The polymerization reaction in step (2) comprises a first polymerization reaction, a second polymerization reaction and a aging reaction which are carried out in sequence, and the temperature of the second polymerization reaction is higher than the temperature of the first polymerization reaction.

2. The preparation method according to claim 1, characterized in that: In the step (1), the molar ratio of the linear diamine to phthalaldehyde is (3-6):(2-5).

3. The preparation method according to claim 1, characterized in that: The temperature of the prepolymerization reaction in the step (1) is 100-150° C.; the time of the prepolymerization reaction is 10-200 min.

4. The preparation method according to claim 1, characterized in that: The temperature of the first polymerization reaction is 130-180° C.; the time of the first polymerization reaction is 10-200 min.

5. The preparation method according to claim 1, characterized in that: The temperature of the second polymerization reaction is 140-200° C.; the time of the second polymerization reaction is 10-200 min.

6. The preparation method according to claim 1, characterized in that: The temperature of the aging reaction is 150-200° C.; the time of the aging reaction is 1-20 hours.

7. The preparation method according to claim 1 or 6, characterized in that: The aging reaction is carried out under negative pressure, and the pressure of the negative pressure is 10-300Pa.

8. The reprocessable bio-based cross-linked polyamide prepared by the preparation method according to any one of claims 1 to 7.

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