Use of polytrifluoroethylene, a porous polytetrafluoroethylene tubular membrane and a method for its production and use

Abstract

The application belongs to the technical field of polymers, and particularly relates to application of polytrifluoroethylene, a porous polytetrafluoroethylene tubular membrane and a preparation method and application thereof. The application provides application of polytrifluoroethylene in preparation of a porous polytetrafluoroethylene tubular membrane. The application applies polytrifluoroethylene to the preparation process of the porous polytetrafluoroethylene tubular membrane, can improve the radiation resistance of the porous polytetrafluoroethylene tubular membrane, does not affect the high-temperature resistance, hydrophobicity and pore formation of the porous polytetrafluoroethylene tubular membrane, and improves the purification performance of the porous polytetrafluoroethylene tubular membrane on radioactive wastewater.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to the application of polytrifluoroethylene, a porous polytetrafluoroethylene tubular membrane and its preparation method and application. Background Technology

[0002] Membrane distillation is a technology that uses hydrophobic microporous membranes to purify and reduce the volume of wastewater by allowing only volatile components such as water vapor to pass through the membrane pores. Therefore, the quality of the filter membrane has a significant impact on the purification effect of membrane distillation.

[0003] Traditional microporous membranes are mainly porous polytetrafluoroethylene (PTFE) tubular membranes. However, porous PTFE tubular membranes have poor radiation resistance. Therefore, when treating radioactive wastewater, the membranes are easily damaged, affecting the purification capacity of porous PTFE tubular membranes for radioactive wastewater.

[0004] In the prior art, Chinese patent CN111040346A discloses a radiation-resistant polytetrafluoroethylene (PTFE) composite material. The radiation resistance of PTFE is improved by adding nano-boron nitride and polyphenylene sulfide. However, the addition of nano-boron nitride affects the formation of pores in the porous PTFE tubular membrane during the preparation process, resulting in a decrease in porosity. At the same time, the addition of polyphenylene sulfide increases the hydrophilicity of the PTFE composite material, ultimately leading to a reduction in its ability to purify radioactive wastewater. Summary of the Invention

[0005] The purpose of this invention is to provide an application of polytrifluoroethylene (PTFE), a porous PTFE tubular membrane, its preparation method, and its application. This invention applies PTFE to the preparation of porous PTFE tubular membranes, which can improve the radiation resistance of the porous PTFE tubular membranes without affecting their hydrophobicity and pore formation, thereby improving the purification capacity for radioactive wastewater.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides the application of polytrifluoroethylene in the preparation of porous polytetrafluoroethylene tubular membranes.

[0008] The present invention also provides a porous polytetrafluoroethylene tubular membrane, wherein the raw materials for preparing the porous polytetrafluoroethylene tubular membrane include polytetrafluoroethylene, polytrifluoroethylene and a pore-forming agent.

[0009] Preferably, the polytetrafluoroethylene has a weight-average molecular weight > 10. 7 .

[0010] Preferably, the weight-average molecular weight of the polytrifluoroethylene is >10. 7 .

[0011] Preferably, the pore-forming aid comprises isoalkanes and / or aviation kerosene.

[0012] Preferably, the mass ratio of polytetrafluoroethylene to polytrifluoroethylene is 60:40 to 99:1.

[0013] Preferably, the mass ratio of the total mass of the polytetrafluoroethylene and polytrifluoroethylene to the mass of the pore-forming agent is 75:25 to 85:15.

[0014] The present invention also provides a method for preparing the porous polytetrafluoroethylene tubular membrane described above, comprising the following steps:

[0015] Polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTFE), and a pore-forming agent are mixed and then subjected to aging, preforming, paste extrusion, calendering, longitudinal stretching, degreasing, sintering and annealing in sequence to obtain the porous PTFE tubular membrane.

[0016] Preferably, the aging temperature is 30–40°C and the aging time is 10–30 hours;

[0017] The pressure of the preforming is 20-30 MPa;

[0018] The temperature of the paste extrusion is 30-40℃, and the extrusion speed is 0.5-2 mm / s;

[0019] The rolling temperature is 200–220°C;

[0020] The longitudinal stretching temperature is 200-220℃, the longitudinal stretching rate is 300-500 mm / min, and the longitudinal stretching ratio is 50-100%.

[0021] The degreasing temperature is 200–220°C;

[0022] The sintering and shaping temperature is 370-380℃, and the sintering and shaping time is 1-10 min;

[0023] The annealing temperature is 100–120°C, and the annealing time is 4–6 hours.

[0024] The present invention also provides the application of the porous polytetrafluoroethylene tubular membrane described in the above technical solution or the porous polytetrafluoroethylene tubular membrane prepared by the preparation method described in the above technical solution in wastewater treatment.

[0025] This invention provides an application of polytrifluoroethylene (PTFE) in the preparation of porous PTFE tubular membranes. By applying PTFE to the preparation process of porous PTFE tubular membranes, this invention improves the radiation resistance of the membranes without affecting their hydrophobicity and pore formation, thereby enhancing the wastewater purification performance of the membranes. Attached Figure Description

[0026] Figure 1 The images show the porous polytetrafluoroethylene tubular membrane obtained in Example 1 before and after irradiation.

[0027] Figure 2 The images are SEM images of the porous polytetrafluoroethylene tubular membrane obtained in Example 1 before and after irradiation, where a is before irradiation and b is after irradiation.

[0028] Figure 3 The results are the contact angle test results of the porous polytetrafluoroethylene tubular membranes obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0029] This invention provides the application of polytrifluoroethylene in the preparation of porous polytetrafluoroethylene tubular membranes.

[0030] The present invention also provides a porous polytetrafluoroethylene tubular membrane, wherein the raw materials for preparing the porous polytetrafluoroethylene tubular membrane include polytetrafluoroethylene, polytrifluoroethylene and a pore-forming agent.

[0031] In this invention, the weight-average molecular weight of the polytetrafluoroethylene is preferably >10. 7 In this invention, the weight-average molecular weight of the polytrifluoroethylene is preferably >10. 7 .

[0032] In this invention, the pore-forming aid preferably comprises isoalkanes and / or aviation kerosene. In this invention, the boiling point of the isoalkanes is preferably 167–176°C. In this invention, the isoalkanes are preferably Isopar G. In this invention, when the pore-forming aid is isoalkanes and aviation kerosene, there is no particular limitation on the ratio of the two; they can be mixed in any proportion.

[0033] In this invention, the mass ratio of polytetrafluoroethylene to polytrifluoroethylene is preferably 60:40 to 99:1, more preferably 65:35 to 95:5, and even more preferably 70:30 to 90:10.

[0034] In this invention, the mass ratio of the total mass of polytetrafluoroethylene and polytrifluoroethylene to the mass of the pore-forming agent is preferably 75:25 to 85:15, more preferably 76:24 to 84:16, and even more preferably 77:23 to 83:17.

[0035] The present invention also provides a method for preparing the porous polytetrafluoroethylene tubular membrane described above, comprising the following steps:

[0036] Polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTFE), and a pore-forming agent are mixed and then subjected to aging, preforming, paste extrusion, calendering, longitudinal stretching, degreasing, sintering and annealing in sequence to obtain the porous PTFE tubular membrane.

[0037] Before the mixing process, the present invention preferably includes a pre-cooling treatment of the polytetrafluoroethylene (PTFE). In the present invention, the temperature of the pre-cooling treatment is preferably the crystal transformation point of the PTFE. Preferably, the temperature of the pre-cooling treatment is 17–20°C, and the time is preferably 20–48 hours. In a specific embodiment of the present invention, the pre-cooling treatment process preferably involves storing the PTFE at the pre-cooling temperature. The present invention, by pre-cooling the PTFE, enables the PTFE to have a more regular crystal structure, which is more conducive to stretching and pore formation.

[0038] In this invention, the mixing is preferably carried out under stirring conditions. The present invention does not impose any particular limitation on the stirring parameters; any parameters well known to those skilled in the art can be used. In this invention, the stirring method is preferably mechanical stirring or ultrasonic vibration.

[0039] In this invention, the aging temperature is preferably 30-40°C, more preferably 32-38°C, and even more preferably 35-36°C; the aging time is preferably 10-30 hours, more preferably 12-28 hours, and even more preferably 15-25 hours.

[0040] In this invention, the preforming pressure is preferably 20-30 MPa, more preferably 22-28 MPa, and even more preferably 25-26 MPa. In this invention, the paste extrusion temperature is preferably 30-40°C, more preferably 32-38°C, and even more preferably 35-36°C; the extrusion speed is preferably 0.5-2 mm / s, more preferably 0.8-1.8 mm / s, and even more preferably 1.0-1.5 mm / s. In this invention, both preforming and paste extrusion are performed in a plunger extruder. This invention does not impose any special limitations on the specific processes of preforming and paste extrusion; processes well-known to those skilled in the art can be used.

[0041] In this invention, the rolling temperature is preferably 200-220°C.

[0042] In this invention, the longitudinal stretching temperature is preferably 200–220°C, more preferably 205–215°C, and even more preferably 210°C; the longitudinal stretching rate is preferably 300–500 mm / min, more preferably 350–450 mm / min, and even more preferably 380–400 mm / min; and the longitudinal stretching ratio is preferably 50–100%, more preferably 60–90%, and even more preferably 70–80%.

[0043] The present invention does not impose any particular limitation on the calendering and longitudinal stretching processes; any process well known to those skilled in the art can be used. In the present invention, calendering and longitudinal stretching enable the pore-forming agent to evaporate completely, resulting in a tube blank with a microporous structure.

[0044] In this invention, the degreasing temperature is preferably 200–220°C, more preferably 205–215°C, and even more preferably 210°C. This invention does not impose any particular limitation on the degreasing process; any process well-known to those skilled in the art can be used.

[0045] In this invention, the sintering temperature is preferably 370–380°C, more preferably 372–378°C, and even more preferably 373–375°C; the time is preferably 1–10 min, more preferably 2–9 min, and even more preferably 3–8 min. This invention does not impose any special limitations on the sintering process; any process well-known to those skilled in the art can be used.

[0046] In this invention, the annealing temperature is preferably 100–120°C, more preferably 105–115°C, and even more preferably 110°C; the annealing time is preferably 4–6 hours, and even more preferably 5 hours. This invention does not impose any special limitations on the annealing process; any process well-known to those skilled in the art can be used.

[0047] After the annealing is completed, the present invention preferably further includes winding the obtained product. The present invention does not have specific limitations on the winding process; any process well known to those skilled in the art can be used.

[0048] The present invention also provides the application of the porous polytetrafluoroethylene tubular membrane described in the above technical solution or the porous polytetrafluoroethylene tubular membrane prepared by the preparation method described in the above technical solution in wastewater treatment.

[0049] In this invention, the wastewater treatment is preferably radioactive wastewater treatment.

[0050] The present invention does not impose any special limitations on the specific implementation of the application, and can be carried out in a manner known to those skilled in the art.

[0051] To further illustrate the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, describes the application of polytrifluoroethylene provided by the present invention, a porous polytetrafluoroethylene tubular membrane and its preparation method and application, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] Take 1.0 kg of polytetrafluoroethylene (weight average molecular weight 1.2 × 10⁻⁶). 7 0.2 kg of polytrifluoroethylene (weight average molecular weight is 1.3 × 10⁻⁶) 7 ) and 0.25 kg of isoparaffin Isopar G;

[0054] Polytetrafluoroethylene (PTFE) was stored at 19°C for 24 hours. Then, PTFE, polytrifluoroethylene (PTFE), and isoparaffin Isopar G were mixed and subjected to aging, preforming, paste extrusion, calendering, longitudinal stretching, degreasing, sintering and shaping, annealing, and winding to obtain a porous PTFE tubular membrane. The conditions and parameters are shown in Table 1.

[0055] Table 1. Conditions for preparing porous polytetrafluoroethylene tubular membranes in this embodiment.

[0056] Aging temperature 30℃ Aging time 24h Preforming pressure 30MPa Extrusion speed 1mm / s Paste extrusion temperature 35℃ Rolling temperature 210℃ Longitudinal stretch rate 300mm / min Longitudinal stretch ratio 70％ Longitudinal stretching temperature 205℃ Degreasing temperature 205℃ Sintering and shaping temperature 370℃ Sintering time 4min Annealing temperature 100℃ Annealing time 4h

[0057] Comparative Example 1

[0058] Take 1.0 kg of polytetrafluoroethylene (weight average molecular weight 1.2 × 10⁻⁶). 7 ) and 0.25 kg of isoparaffin Isopar G;

[0059] Polytetrafluoroethylene (PTFE) was stored at 19°C for 24 hours. Then, PTFE and isoparaffin Isopar G were mixed and subjected to aging, preforming, paste extrusion, calendering, longitudinal stretching, degreasing, sintering and shaping, annealing and winding in sequence to obtain a porous PTFE tubular membrane. The condition parameters are shown in Table 2.

[0060] Table 2. Conditions for preparing porous polytetrafluoroethylene tubular membranes in this embodiment.

[0061] Aging temperature 30℃ Aging time 24h Preforming pressure 30MPa Extrusion speed 1mm / s Paste extrusion temperature 35℃ Rolling temperature 210℃ Longitudinal stretch rate 300mm / min Longitudinal stretch ratio 70％ Longitudinal stretching temperature 205℃ Degreasing temperature 205℃ Sintering and shaping temperature 370℃ Sintering time 4min Annealing temperature 100℃ Annealing time 4h

[0062] Performance testing

[0063] Test Example 1

[0064] The porosity change rate of the porous polytetrafluoroethylene tubular membrane obtained in Example 1 after aging at 90°C for 1008 hours is shown in Table 3.

[0065] Table 3. Aging test results of the porous polytetrafluoroethylene tubular membrane in Example 1 at 90°C

[0066]

[0067] As can be seen from Table 3, the porous polytetrafluoroethylene tubular membrane obtained in Example 1 underwent an aging test at 90°C, and the porosity change rate was only 0.1% within 1008 hours, indicating that the porous polytetrafluoroethylene tubular membrane obtained in Example 1 has excellent high-temperature resistance at 90°C.

[0068] Test Example 2

[0069] The radiation resistance of the porous polytetrafluoroethylene tubular membranes obtained in Example 1 and Comparative Example 1 was tested.

[0070] Place the porous polytetrafluoroethylene tubular membrane into 60 In a Co-γ irradiation field, the sample was irradiated statically. The total irradiation dose was accumulated to 3 × 10⁻⁶ by multiplying the fixed irradiation dose rate by the irradiation time. 5 Gy, intermediate irradiation dose is taken as 10 4 Gy and 10 5 Gy, respectively tested the porosity change rate under the above three irradiation doses;

[0071] The porous polytetrafluoroethylene tubular membrane obtained in Example 1 was used before irradiation and at an irradiation dose of 3×10⁻⁶. 5 The actual image after Gy irradiation is shown below. Figure 1 As shown, from Figure 1 It can be seen that the porous polytetrafluoroethylene tubular membrane obtained in Example 1 was irradiated with a dose of 3×10⁻⁶. 5 The appearance remained intact after Gy irradiation;

[0072] The porous polytetrafluoroethylene tubular membrane obtained in Example 1 was used before irradiation and at an irradiation dose of 3×10⁻⁶. 5 SEM images after Gy irradiation, such as Figure 2 As shown, where a represents before irradiation and b represents after irradiation, from... Figure 2 It can be seen that the porous polytetrafluoroethylene tubular membrane obtained in Example 1 was irradiated with a dose of 3×10⁻⁶. 5 No significant changes were observed in the microstructure after Gy irradiation;

[0073] The porous polytetrafluoroethylene tubular membranes obtained in Example 1 and Comparative Example 1 were subjected to an irradiation dose of 10... 5 Gy irradiation and irradiation dose of 3 × 10 5 After Gy irradiation, a pressure test was conducted. The test results showed that the porous polytetrafluoroethylene tubular membrane obtained in Comparative Example 1 had an irradiation dose of 10... 5 The sample irradiated with Gy developed cracks after being pressed.

[0074] The porous polytetrafluoroethylene tubular membrane obtained in Comparative Example 1 was irradiated with a dose of 10.5 The porosity change rate after Gy irradiation is shown in Table 4.

[0075] Table 4 shows the porous polytetrafluoroethylene tubular membrane of Comparative Example 1 after 10... 5 Porosity test results before and after Gy irradiation

[0076]

[0077] As can be seen from Table 4, the porous polytetrafluoroethylene tubular membrane obtained in Comparative Example 1 was irradiated with a dose of 10. 5 The porosity change rate after Gy irradiation was 5.2%, indicating that the porous polytetrafluoroethylene tubular membrane obtained in Comparative Example 1 can withstand 10... 5 Gy irradiation dose;

[0078] The porous polytetrafluoroethylene tubular membrane obtained in Example 1 was irradiated with a dose of 10. 5 The sample irradiated with Gy showed no cracks after being pressed, and the irradiation dose was 3×10⁻⁶. 5 The sample irradiated with Gy did not show any cracks when pressed;

[0079] The porous polytetrafluoroethylene tubular membrane obtained in Example 1 was irradiated with a dose of 3 × 10⁻⁶. 5 The porosity change rate after Gy irradiation is shown in Table 5.

[0080] Table 5 shows the porous polytetrafluoroethylene tubular membrane of Example 1, measured at 3×10⁻⁶ mm. 5 Porosity test results before and after Gy irradiation

[0081]

[0082] As can be seen from Table 5, the porous polytetrafluoroethylene tubular membrane obtained in Example 1 was irradiated with a dose of 3 × 10⁻⁶. 5 The porosity change rate after Gy irradiation was 8.3%, indicating that the porous polytetrafluoroethylene tubular membrane obtained in Example 1 can withstand 3×10⁻⁶ ppm. 5 Gy irradiation dose.

[0083] Test Example 3

[0084] Contact angle tests were conducted on the porous polytetrafluoroethylene tubular membranes obtained in Example 1 and Comparative Example 1, and the results are as follows: Figure 3 As shown, the left side is Comparative Example 1, and the right side is Example 1. Figure 3 It can be seen that the hydrophobicity of the porous polytetrafluoroethylene tubular membrane obtained by the present invention does not change significantly.

[0085] Test Example 4

[0086] The porous polytetrafluoroethylene tubular membrane obtained in Example 1 was used for membrane distillation to purify radioactive wastewater with a conductivity of 30 mS / cm. The conductivity of the purified water obtained was 0.1 μS / cm, which met the purity standard of Grade I water. This shows that the porous polytetrafluoroethylene tubular membrane obtained in this invention can be used for the purification of radioactive wastewater.

[0087] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A porous polytetrafluoroethylene tubular membrane, characterized in that, The raw materials for preparing the porous polytetrafluoroethylene tubular membrane are polytetrafluoroethylene, polytrifluoroethylene, and pore-forming aids. The pore-forming aid is an isoparaffin and / or aviation kerosene.

2. The porous polytetrafluoroethylene tubular membrane according to claim 1, characterized in that, The weight-average molecular weight of the polytetrafluoroethylene is >10. 7 .

3. The porous polytetrafluoroethylene tubular membrane according to claim 1, characterized in that, The weight-average molecular weight of the polytrifluoroethylene is >10. 7 .

4. The porous polytetrafluoroethylene tubular membrane according to any one of claims 1 to 3, characterized in that, The mass ratio of polytetrafluoroethylene to polytrifluoroethylene is 60:40 to 99:

1.

5. The porous polytetrafluoroethylene tubular membrane according to claim 4, characterized in that, The total mass ratio of polytetrafluoroethylene and polytrifluoroethylene to the pore-forming agent is 75:25 to 85:

15.

6. The method for preparing the porous polytetrafluoroethylene tubular membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: Polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTFE), and a pore-forming agent are mixed and then subjected to aging, preforming, paste extrusion, calendering, longitudinal stretching, degreasing, sintering and annealing in sequence to obtain the porous PTFE tubular membrane.

7. The preparation method according to claim 6, characterized in that, The aging temperature is 30–40°C, and the aging time is 10–30 hours. The pressure of the preforming is 20-30 MPa; The temperature of the paste extrusion is 30-40℃, and the extrusion speed is 0.5-2 mm / s; The rolling temperature is 200–220°C; The longitudinal stretching temperature is 200-220℃, the longitudinal stretching rate is 300-500 mm / min, and the longitudinal stretching ratio is 50-100%. The degreasing temperature is 200–220°C; The sintering and shaping temperature is 370-380℃, and the sintering and shaping time is 1-10 min; The annealing temperature is 100–120°C, and the annealing time is 4–6 hours.

8. The application of the porous polytetrafluoroethylene tubular membrane according to any one of claims 1 to 5 or the porous polytetrafluoroethylene tubular membrane prepared by the preparation method according to any one of claims 6 to 7 in wastewater treatment.

Images