CN118667152A - Polyamide capable of being degraded controllably in acidic environment and preparation method thereof - Google Patents

Abstract

The present invention relates to the technical field of polyamide acid degradation, and in particular to a polyamide based on 3,6-dioxanoic acid (DODA) structural units and degradable in an acidic environment and a preparation method thereof. The degradable polyamide is prepared by synthesizing 3,6-dioxanoic acid hexamethylenediamine salt from DODA and 1,6-hexamethylenediamine at a molar ratio of 1:1, and then by solution polymerization and melt polymerization. The present invention provides a degradable polyamide material, which achieves green recycling while retaining the performance of high value-added materials in the polyamide material, reduces environmental pollution, and improves resource utilization. The method of the present invention has a wide source of raw materials, low price, simple process operation, and a product yield of more than 90%, which is conducive to industrial production.

Description

A kind of polyamide with controllable degradation in acidic environment and preparation method thereof

Technical Field

The present invention relates to the technical field of acidic degradation of polyamides, and in particular to a polyamide based on 3,6-dioxanoic acid (DODA) structural units and degradable in an acidic environment and a preparation method thereof.

Background Art

Nylon (Polyamide, PA) is the general name of polyamide resin. Polyamide fiber, also known as nylon, is the first synthetic fiber in the world. The main chain of polyamide molecules contains amide groups, which have the characteristics of high mechanical strength, high rigidity, wear resistance, strong reinforcement, and impact resistance. It is one of the five major engineering plastics and has brought many benefits to mankind in the fields of transportation, clothing, entertainment, health, etc. However, due to the high crystallinity of polyamide, while it brings excellent mechanical properties and good thermal stability, it also makes it difficult to degrade efficiently, which seriously hinders the recycling and reuse of polyamide and its composite materials.

At present, most of the recycling methods of polyamides revolve around mechanical recycling, chemical recycling and other methods. While the above methods are harmful to the environment, they will also cause serious damage to the performance of high-value-added materials in composite materials [Hirschberg, V.; Rodrigue, D. Recycling of polyamides: Processes and conditions. Journal of Polymer Science 2023, doi: 10.1002/pol.20230154.].

Summary of the invention

In view of the problems existing in the prior art, the purpose of the present invention is to provide a polyamide based on DODA structural units and degradable in an acidic environment and a preparation method thereof. By adopting a method of modifying the molecular structure of polyamide, a structural unit with ether oxygen is introduced to make the polyamide easier to degrade, retain the performance of high value-added materials in polyamide materials and achieve green recycling.

The design concept of the present invention is: adipic acid, one of the monomers of polyamide-66, is replaced by DODA. The introduction of ether oxygen group increases the positive charge of the carbonyl C of the amide bond and the polarity of the C-N bond, making it easier to heterolytically split, so as to obtain a modified PA-66 material with better degradation effect.

The structural formula of the polyamide degradable in the acidic environment is:

Where n is a natural number between 25 and 35.

To achieve the above object, the technical solution of the present invention is:

A polyamide which can be controlled to degrade in an acidic environment is prepared by reacting DODA with 1,6-hexanediamine to synthesize 3,6-dioxanediamine diamine salt, and then by solution polymerization and melt polymerization.

The preparation method of the polyamide (poly (3,6-dioxanoic acid hexamethylenediamine, hereinafter referred to as modified PA-66)) that is degradable in an acidic environment is carried out according to the following steps:

Step 1: Weigh 1,6-hexanediamine, add anhydrous ethanol, and stir to dissolve it; weigh DODA, add anhydrous ethanol, and stir to dissolve it; slowly drop the ethanol solution of hexanediamine into the ethanol solution of DODA, and control the reaction temperature not to exceed 75°C; as the reaction proceeds, the solution system gradually becomes turbid, and then the reaction solution is completely transparent; then recrystallization is carried out, and the specific operation is: control the temperature of the entire system to 50-60°C and place it in an ice water bath until salt precipitates, filter and collect the solid product, and repeat the recrystallization process three times; dry the white crystals finally obtained to obtain anhydrous 3,6-dioxanediamine hexanediamine salt.

Step 2: In an inert atmosphere, 3,6-dioxanediamine octanedioate is mixed with N-methylpyrrolidone (NMP), stirring is started and the temperature is programmed: it takes 30 min to raise the reaction system from room temperature (25°C, the same below) to 190°C, and keep it warm for 1 hour; raise the temperature to 210°C at 6°C/min, and keep it warm for 0.5 hour; raise the temperature to 230°C at 6°C/min, and keep it warm for 0.5 hour; raise the temperature to 250°C at 6°C/min, and keep it warm for 0.5 hour; raise the temperature to 260°C at 6°C/min, and keep it warm for 1 hour; raise the temperature to 280°C at 6°C/min, and then vacuum the reaction for 0.5 hour to end; dry the product to obtain modified PA-66.

Preferably, in step 1, the molar ratio of DODA to 1,6-hexanediamine is 1:1.

Preferably, the drying temperature in step 1 is 50-60°C.

Preferably, in step 2, the usage ratio of 3,6-dioxanediamine salt of hexanediamine and NMP is 1 g:4 ml.

Preferably, in step 2, the stirring rate is 150-250 r/min and the drying temperature is 60°C.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention provides a degradable polyamide material, which can achieve green recycling while retaining the high value-added material performance of the polyamide material, reduce environmental pollution and improve resource utilization.

2. The present invention first prepares high-purity 3,6-dioxanoic acid hexanediamine salt and then polymerizes it. Compared with the traditional method of directly polymerizing diacids and diamines, on the one hand, it can better remove impurities introduced in the raw materials to obtain a polymer with higher purity. On the other hand, it can keep the number of carboxyl groups and amino groups the same, increase the degree of polymerization, and thus improve the performance of the material.

3. The present invention adopts a unique temperature rising procedure during the polymerization process, so that a product with a high degree of polymerization can be obtained under normal pressure conditions.

4. The method of the present invention has a wide range of raw materials, low prices, simple process operation, and a product yield of more than 90%, which is conducive to industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the nuclear magnetic resonance hydrogen spectra of PA-66 obtained in comparative example 1 and modified PA-66 obtained in example 1. Both PA-66 and modified PA-66 contain six H under different chemical conditions, of which 10ppm is a water peak and 7.3ppm is a deuterated formic acid solvent peak. The other five peak areas of PA-66 and modified PA-66 are the same, so the proportions of these five H atoms are the same, which meets the characteristics of the target product. Hydrogen No. 1 of PA-66 and modified PA-66 is relatively active and easily forms hydrogen bonds with water or replaces deuterium atoms in deuterated reagents, so their signals are not detected. Compared with PA-66, H atom No. 5 of modified PA-66 is affected by the inductive effect of O atoms in the ether bond and the inductive effect of O atoms in the amide bond, so its electron cloud density is lower than that of H atom No. 6, and the shielding effect is weaker, so the δ value is higher. There is no obvious difference between H atoms No. 2, 3, and 4 on the hexamethylenediamine side.

Figure 2 is the carbon NMR spectrum of the modified PA-66 obtained in Example 1, and Figure 3 is the carbon NMR spectrum of the PA-66 obtained in Comparative Example 1. Both PA-66 and modified PA-66 contain six Cs under different chemical conditions, of which 163ppm is the deuterated formic acid solvent peak. Compared with PA-66, the C atom No. 5 of the modified PA-66 is affected by the inductive effect of the O atom in the ether bond and the inductive effect of the O atom in the amide bond, so its electron cloud density is lower than that of the C atom No. 6, and the shielding effect is weaker, so the δ value is higher. There is no obvious difference between the C atoms No. 1, 2, and 3 on the hexamethylenediamine side.

Figure 4 is a Fourier transform infrared absorption spectrum of PA-66 obtained in Comparative Example 1 and modified PA-66 obtained in Example 1. PA-66: 1638 cm ^-1 is C=O stretching vibration, 1370 cm ^-1 is CN stretching vibration. Modified PA-66: 1637 cm ^-1 is C=O stretching vibration, 1382 cm ^-1 is CN stretching vibration, 1179 cm ^-1 is ether oxygen bond stretching vibration.

Figure 5 is the nuclear magnetic resonance hydrogen spectrum of the degradation solution after acidic degradation of modified PA-66 in Test Example 2. There are a total of 7 H under different chemical conditions in the product structure. Hydrogens 1 and 5 of the modified PA-66 degradation product are relatively active and easily form hydrogen bonds with water or replace deuterium atoms in the deuterated reagent, so the signal of hydrogen 5 is not detected, and hydrogen 1 has a small peak at 7.8ppm. Except for the peaks at 7.8 and 4.8ppm, the peak areas of the other 5 are the same. The peak at 4.8ppm is the heavy water solvent peak. It can be determined that the degradation product is as shown in the structural formula of Figure 5.

Figure 6 is the nuclear magnetic resonance hydrogen spectrum of the degradation solution of PA-66 after acidic degradation in Test Example 2. The peak at 4.8ppm is the peak of heavy water solvent, and there are no other peaks. This shows that there are no small molecular degradation products in the PA-66 degradation solution.

Figure 7 is the carbon NMR spectrum of the degradation solution after acidic degradation of modified PA-66 in Test Example 2. The degradation solution also contains six Cs under different chemical conditions, but the peak positions of these six Cs are different from those of modified PA-66. Three of them are at the same peak position as the three Cs of 3,6-dioxaoctanedioic acid, and the other three are at the same peak position as the Cs of hexamethylenediamine ion under acidic conditions.

Figure 8 is the carbon NMR spectrum of the degradation solution after acidic degradation of PA-66 in Test Example 2. There are no peaks in the spectrum, so it can be inferred that the degradation solution does not contain small organic molecules.

FIG9 is the XRD spectra of the PA-66 obtained in Comparative Example 1 and the modified PA-66 obtained in Example 1. From the peak areas of the two, it can be concluded that the crystallinity of the two is not much different.

FIG. 10 is a graph showing the dielectric constant spectra of the PA-66 obtained in Comparative Example 1 and the modified PA-66 obtained in Example 1.

FIG. 11 is a graph showing the dielectric loss spectra of the PA-66 obtained in Comparative Example 1 and the modified PA-66 obtained in Example 1.

DETAILED DESCRIPTION

The applicant will now describe the synthesis method of the present invention in detail in conjunction with specific examples, but it should be understood that the following examples are only used to illustrate the present invention, and are not used to limit the scope of protection claimed in the claims of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial sources.

Example 1

A method for preparing a polyamide that can be controlled to degrade in an acidic environment comprises the following steps:

Step 1: Take 10g of 1,6-hexanediamine and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Take 15.34g of DODA and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Under stirring, slowly drop the ethanol solution of hexanediamine into the ethanol solution of DODA, and control the reaction temperature not to exceed 75°C. As the reaction proceeds, the solution system gradually becomes turbid, and the reaction is stopped when the stirring reaction is completely transparent. Then recrystallization is carried out, and the specific operation is as follows: control the temperature of the entire system to 60°C and place it in an ice water bath until the salt precipitates, and collect the solid product after filtering. Repeat the recrystallization process three times. The white crystals finally obtained are placed in a vacuum drying oven and dried, and the drying temperature is maintained at 60°C to obtain anhydrous 3,6-dioxaoctanedioic acid hexanediamine salt with a yield of 86%.

Step 2 Take 5g of 3,6-dioxaoctanedioic acid hexanediamine salt and 20ml of N-methylpyrrolidone (NMP), put them into a three-necked flask, introduce high-purity nitrogen, set the stirring rate to 200r/min, and perform a temperature program: from room temperature (25°C, the same below) to 190°C in half an hour, keep warm for 1h; heat to 210°C at 6°C/min, keep warm for 0.5h; heat to 230°C at 6°C/min, keep warm for 0.5h; heat to 250°C at 6°C/min, keep warm for 0.5h; heat to 260°C at 6°C/min, keep warm for 1h; heat to 280°C at 6°C/min and then vacuum the reaction for 0.5h to end. The product was dried in a vacuum drying oven at 60°C for 24h to obtain modified PA-66 with a yield of 93%.

Comparative Example 1

A method for preparing polyamide-66 (PA-66) comprises the following steps:

Step 1: Take 10g of 1,6-hexanediamine and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Take 12.56g of adipic acid and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Under stirring, slowly drop the ethanol solution of hexanediamine into the ethanol solution of adipic acid, and control the reaction temperature not to exceed 75°C. As the reaction proceeds, the solution system gradually becomes turbid, and the reaction is stopped when the stirring continues until the reaction solution is completely transparent. Then recrystallize, and the specific operation is: control the temperature of the entire system to 60°C and place it in an ice water bath until the salt precipitates, and collect the solid product after filtering. Repeat the recrystallization process three times. The white crystals finally obtained are placed in a vacuum drying oven and dried, and the drying temperature is maintained at about 60°C to obtain anhydrous hexanediamine adipic acid salt.

Step 2: Take 5g of hexamethylenediamine adipate and 20ml of NMP, put them into a three-necked flask, introduce high-purity nitrogen, set the stirring rate to 200r/min, and perform a temperature program: heat from room temperature to 190°C in half an hour, keep warm for 1h; heat to 210°C at 6°C/min, keep warm for 0.5h; heat to 230°C at 6°C/min, keep warm for 0.5h; heat to 250°C at 6°C/min, keep warm for 0.5h; heat to 260°C at 6°C/min, keep warm for 1h; heat to 280°C at 6°C/min, and then vacuumize and react for 0.5h to end. Put the product into a vacuum drying oven and dry it, keep the drying temperature at 60°C, and dry it for 24h to obtain PA-66.

Table 1: ¹ H-NMR data of the products obtained in Example 1 and Comparative Example 1 (400 MHZ, deuterated formic acid)

Table 2: ¹³ C-NMR data of the products obtained in Example 1 and Comparative Example 1 (400 MHZ, deuterated formic acid)

Comparative Example 2:

A method for preparing polyamide-66 (PA-66) comprises the following steps:

Step 1: Take 10g of 1,6-hexanediamine and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Take 12.56g of adipic acid and add it to a beaker, then add anhydrous ethanol and stir quickly to dissolve. Under stirring, slowly drop the ethanol solution of hexanediamine into the ethanol solution of adipic acid, and control the reaction temperature not to exceed 75°C. As the reaction proceeds, the solution system gradually becomes turbid, and the reaction is stopped when the stirring continues until the reaction solution is completely transparent. Then recrystallize, and the specific operation is: control the temperature of the entire system to 60°C and place it in an ice water bath until the salt precipitates, and collect the solid product after filtering. Repeat the recrystallization process three times. The white crystals finally obtained are placed in a vacuum drying oven and dried, and the drying temperature is maintained at about 60°C to obtain anhydrous hexanediamine adipic acid salt.

Step 2: Take 5g of hexamethylenediamine adipate and 20ml of NMP, put them into a three-necked flask, introduce high-purity nitrogen, and set the stirring rate to 200r/min. Heat from room temperature to 190°C in half an hour, keep warm for 1h; heat to 280°C at 6°C/min, keep warm for 3h, and vacuum the reaction for 0.5h to end. Put the product into a vacuum drying oven and dry it at 60°C for 24h to obtain PA-66.

Test Example 1: Viscosity Test

The viscosity-average polymerization degree of PA-66 synthesized in Comparative Example 1 was measured by an Ubbelohde viscometer to be 36, while the viscosity-average polymerization degree of PA-66 synthesized in Comparative Example 2 was 20. The temperature increase program used in the polymerization process of the present invention can significantly increase the polymerization degree under normal pressure conditions.

From the data in Tables 3 and 4, it can be seen that the intrinsic viscosity of PA-66 synthesized in Comparative Example 1 is 44, while the intrinsic viscosity of modified PA-66 synthesized in Example 1 is 38. There is no significant difference between the two, and the polymerization degrees are similar.

Table 3: Ubbelohde viscometer test results of PA-66 obtained in Comparative Example 1 (solvent is 90wt% formic acid)

Table 4: Ubbelohde viscometer test results of modified PA-66 obtained in Example 1 (solvent is 90wt% formic acid)

Test Example 2: Degradation Performance Test

Step 1: Dry the modified PA-66 sample obtained in Example 1 in a vacuum drying oven at 60° C. for 24 h.

Step 2: Weigh an appropriate amount of modified PA-66 and record the weight m1, then react for one hour at 60° C., a stirring speed of 200 r/min, and 10 ml of 10 wt % sulfuric acid.

Step 3: After the reaction is completed, take out the product and filter it with filter paper to retain the solid and liquid products. The solid product is vacuum dried at 60°C to constant weight, weighed and recorded the weight m2, and the weight loss rate (%) is calculated as (m1-m2)/m1*100%. The liquid product is tested by nuclear magnetic resonance spectroscopy.

The PA-66 sample obtained in Comparative Example 1 was subjected to a degradation experiment according to the above steps to test the weight loss rate and the nuclear magnetic resonance spectrum.

Table 5: Degradation test results of samples obtained in Example 1 and Comparative Example 1

sample Mass before reaction m1(g) Mass after reaction m2(g) Weight loss rate (%) PA-66 0.0156 0.0156 0 Modified PA-66 0.0130 0 100

Table 6: ¹ H-NMR data of modified PA-66 degradation solution (400 MHZ, D ₂ O)

Table 7: ¹³ C-NMR data of modified PA-66 degradation solution (400 MHZ, D ₂ O)

According to the weight loss rate before and after degradation of the two polyamides (Table 5) and the nuclear magnetic resonance spectra (Figures 5-8), it can be concluded that in a 10wt% sulfuric acid solution, the modified PA-66 is completely degraded, while PA-66 is not degradable. The polyamide synthesized based on the 3,6-dioxanoic acid structural monomer of the present invention can be degraded in an acidic environment.

Test Example 3: Electrical Performance Test

The dielectric constant is the ratio of the charge stored in the insulating material between two metal plates to the charge that can be stored when the insulating material is replaced by vacuum or air. In polar polymer PA, dipoles are generated due to the imbalance of electron distribution, and these dipoles tend to align in the presence of an electric field. Therefore, PA performs well as an insulator. Dielectric loss refers to the energy loss caused by the insulating material under the action of an electric field due to the hysteresis effect of dielectric conductivity and dielectric polarization. The dielectric will lose its dielectric properties and become a conductor under the action of a sufficiently strong electric field, which is called dielectric breakdown, and the corresponding voltage is called breakdown voltage. The electric field strength at the time of dielectric breakdown is called breakdown field strength. The breakdown field strength of the sample was tested using the HKZGF-II60kV2mA model of fully intelligent DC high voltage generator, and the dielectric constant and dielectric loss of the sample were tested using the Agilent4294A model of dielectric tester, with silver-plated electrodes and a test frequency of 40Hz-10MHz.

Figures 10 and 11 are the dielectric constant and dielectric loss data of PA-66 obtained in Comparative Example 1 and the modified PA-66 obtained in Example 1, respectively. Combined with the breakdown field strength data in Table 8, the dielectric constant, dielectric loss and breakdown field strength of the modified PA-66 do not change by an order of magnitude compared with PA-66, indicating that the electrical insulation of the modified PA-66 is not significantly worse than that of PA-66, and the modified PA-66 is suitable for insulating components in the electronic and electrical fields.

Table 8: Breakdown voltage and breakdown field strength of samples obtained in Example 1 and Comparative Example 1

sample Thickness(mm) Breakdown voltage(kV) Breakdown field strength (V/m) PA-66 1.267 8.0 6.31×10 ⁶ Modified PA-66 0.931 6.3 6.77×10 ⁶

Claims (7)

1. A polyamide degradable in an acidic environment having the structural formula:

Wherein n is a natural number of 25 to 35.

2. A process for producing a polyamide which is degradable in an acidic environment as claimed in claim 1, wherein the 3, 6-dioxasuberic acid is synthesized from 3, 6-dioxasuberic acid and 1, 6-hexamethylenediamine by the reaction, and the polyamide is produced by solution polymerization and melt polymerization.

3. The method of manufacturing according to claim 2, comprising the steps of:

Step 1: weighing 1, 6-hexamethylenediamine, adding absolute ethyl alcohol, and stirring to dissolve the 1, 6-hexamethylenediamine; weighing 3, 6-dioxasuberic acid, adding absolute ethyl alcohol, and stirring to dissolve the 3, 6-dioxasuberic acid; slowly dripping ethanol solution of hexamethylenediamine into ethanol solution of 3, 6-dioxasuberic acid, wherein the reaction temperature is controlled to be not more than 75 ℃; as the reaction proceeds, the solution system becomes turbid, and then the reaction solution is completely transparent; then, recrystallization is carried out, and the specific operation is as follows: the temperature of the whole system is controlled to be 50-60 ℃, then the whole system is placed in an ice-water bath until salting out and precipitation are carried out, solid products are collected after filtration, and the recrystallization process is repeatedly operated for three times; drying the obtained white crystal to obtain anhydrous 3, 6-dioxasuberate hexanediamine salt;

Step 2: mixing 3, 6-dioxasuberate hexanediamine salt with N-methyl pyrrolidone in inert atmosphere, stirring and heating in sequence: the reaction system is heated to 190 ℃ from room temperature for 30min, and the temperature is kept for 1h; heating to 210 ℃ at a speed of 6 ℃/min, and preserving heat for 0.5h; heating to 230 ℃ at a speed of 6 ℃/min, and preserving heat for 0.5h; heating to 250 ℃ at a speed of 6 ℃/min, and preserving heat for 0.5h; heating to 260 ℃ at a speed of 6 ℃/min, and preserving heat for 1h; heating to 280 ℃ at a speed of 6 ℃/min, and then vacuumizing to react for 0.5h; the product is dried to obtain polyamide degradable in acid environment.

4. The process according to claim 3, wherein in step 1, the molar ratio of 3, 6-dioxasuberic acid to 1, 6-hexamethylenediamine is 1:1.

5. A process according to claim 3, wherein the drying temperature in step 1 is 50-60 ℃.

6. A process according to claim 3, wherein in step 2, the ratio of the amount of 3, 6-dioxasuberate hexanediamine salt to the amount of N-methylpyrrolidone is 1g:4ml.

7. A process according to claim 3, wherein in step 2, the stirring rate is 150-250r/min and the drying temperature is 60 ℃.