A polytetrafluoroethylene nanofiber-based heat-shrinkable material and a manufacturing process thereof

Abstract

The present application relates to a kind of polytetrafluoroethylene nanofiber-based heat shrinkable material and its manufacturing process.The process includes the following steps: 1) after the pre-mixing of thermoplastic polymer, polytetrafluoroethylene, processing aid, etc., melt blending is carried out using blending extrusion equipment.2) after the extrusion of the melt state blending product, processing is carried out to obtain a blend film, pipe material, etc., and cooling is performed to set.3) a porous structure is manufactured by solvent etching or high-temperature ablation process.The process has good universality and can produce a variety of thermoplastic polymer materials with heat shrinkage properties.The produced heat shrinkable material can be recycled and reused.The heat shrinkable material with a porous structure can be manufactured to improve air permeability.The manufacturing process is simple, the equipment is flexible, the production efficiency is high, and the cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a polytetrafluoroethylene nanofiber-based heat-shrinkable material and a manufacturing process thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application, and is not necessarily regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] At present, most of the heat-shrinkable materials are obtained by cross-linking linear polymer materials into network polymer structures through chemical cross-linking and other methods, and after expansion and cooling setting, the obtained materials can shrink and recover under heating. However, the cross-linked heat-shrinkable material has a series of shortcomings. First, the polymer material after cross-linking has the characteristics of "insoluble and infusible", which is difficult to recycle and reprocess, and is also difficult to decompose in nature, thereby causing serious environmental damage; second, the heat-shrinkable material generally requires good flame retardant effect in application, so most cross-linked heat-shrinkable materials need to add a large amount of flame retardant, which also causes certain environmental pollution; third, most cross-linked heat-shrinkable materials are difficult to breathe, and water vapor aggregation easily leads to product corruption in fresh food preservation. SUMMARY

[0004] In order to overcome the deficiencies of the prior art, the present application provides a polytetrafluoroethylene nanofiber-based heat-shrinkable material and a manufacturing process thereof. Due to its unique crystal structure and surface properties, polytetrafluoroethylene is prone to fiberization under certain temperature and external force, forming nanoscale long fibers, and can be cooled and shaped at room temperature. The nanofiber network formed at high temperature can maintain its fiber structure at room temperature, but when heated to high temperature again, it tends to shrink to the initial state of aggregation. This process uses a blending extrusion device to introduce polytetrafluoroethylene into a thermoplastic polymer matrix, and by applying strong shear force to the polytetrafluoroethylene crystals during blending, it promotes strong fiberization of the crystals, thereby forming a physically entangled polytetrafluoroethylene nanofiber network during the blending process. Therefore, by utilizing the fiberization and shrinkage properties of polytetrafluoroethylene, the heat shrinkage of the polymer matrix driven by the shrinkage of polytetrafluoroethylene fibers at high temperature can be achieved by adjusting the matrix material and processing technology during the blending process. This process has its unique advantages in many aspects: first, through different material design, the heat shrinkage of different thermoplastic polymers can be achieved, with high versatility; second, through different extrusion processing technology, different macro shapes of heat shrinkable products such as heat shrinkable film and heat shrinkable tube can be directly produced. Third, the heat shrinkable material manufactured by this process can be recycled and reused, which is beneficial to resource and environmental protection. Fourth, according to actual needs, porous heat shrinkable materials with air permeability can be manufactured through certain post-processing processes such as etching and ablation. Fifth, this process flow is simple, the processing process is green and environmentally friendly, the equipment investment is low, and large-scale industrial production can be easily realized.

[0005] To achieve the above purpose, the application uses the following technical solutions:

[0006] The application provides a manufacturing process of a polytetrafluoroethylene nanofiber-based heat-shrinkable material, comprising the following steps:

[0007] 1) Dry the raw materials including thermoplastic polymer and polytetrafluoroethylene, and then melt blend them through a blending device;

[0008] 2) After the melt-blended composite material is processed into tubular or film-shaped material, it is cooled and shaped.

[0009] As a preferred, the thermoplastic polymer in step 1) can be a polymer and its solution having fluidity and certain strength under certain temperature, concentration, pressure, etc., such as thermoplastic polyurethane, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polyamide, polyvinyl alcohol, polyethylene glycol, polystyrene, polybutylene adipate terephthalate, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, etc.

[0010] As a preferred, in the step 1), the polytetrafluoroethylene raw material is in the form of powder, block or emulsion, with a molecular weight higher than 10 7 g / mol, a crystallinity of 60-95%, and a strong fiberization ability under external force. The raw material can be crushed or sieved to select the appropriate size, or the polytetrafluoroethylene can be modified to improve its compatibility with the thermoplastic polymer.

[0011] As a preferred, the raw material in the step 1) includes a processing aid. Different processing aids can be selected according to product requirements, such as pore-forming agents, antibacterial agents, foaming agents, antistatic agents, flame retardants, plasticizers, thermal stabilizers, antioxidants, light stabilizers, mildew-proof agents, coloring agents, whitening agents, fillers, coupling agents, lubricants, release agents, etc. Functionalized fillers such as thermal conductive fillers, conductive fillers, fiber fillers, and wear-resistant fillers can also be selected. The amount of processing aid can be added according to specific needs, and the amount can range from 0-30% based on the total mass of the raw material.

[0012] As a preferred, the drying conditions in the step 1) are flexibly selected according to different materials, with a temperature range of 30-200℃ and a time of 1-12 hours. Natural drying, vacuum drying or air drying can be used.

[0013] As a preferred, in the step 1), the mass fraction of the thermoplastic polymer in all raw materials fed into the blending equipment is 50-95%, and the mass fraction of the polytetrafluoroethylene is 5-50%.

[0014] As a preferred, the blending and extrusion equipment in the step 1) is a single-screw extruder, a twin-screw extruder, a triple-screw extruder, an open mill, a masticator, etc. The processing temperature of the raw material in the blending equipment is higher than the melting temperature of the thermoplastic polymer by 5-80℃, the rotation speed is 10-100rpm, and the blending duration is 3-180 minutes.

[0015] As a preferred, in the step 2), the blend can be directly extruded into pipe material, film material, sheet material, etc. through appropriate die design, or the blend can be extruded and then processed into pipe material or film material through stretching, calendering, and expansion, etc.

[0016] As a preferred, in the step 2), the cooling and shaping method can be liquid cooling, air cooling or air cooling.

[0017] As a preferred, the appropriate means such as solution etching, high temperature ablation, phase separation, etc. can be selected according to the properties of the polymer matrix, processing aids to build a porous structure. When the pores are formed by solvent dissolution, a solvent with certain solubility to the material should be selected, such as dichloromethane, chloroform, water, dimethylbenzene, methanol, ethanol, acetone, etc. When the pores are formed by ablation, according to the decomposition temperature or volatilization temperature of the polymer or processing aid, the ablation temperature is generally higher than the decomposition temperature of the polymer matrix by more than 50℃, and the processing time is greater than 30 minutes.

[0018] More preferably, when the thermoplastic polymer is polylactic acid, the film can be immersed in dichloromethane at room temperature for dissolution, the soaking time is 100-150 minutes, then the film is taken out and dried, and then repeated washing and dissolution for 8 hours to obtain a material with a porous structure.

[0019] The application also provides a polytetrafluoroethylene nanofiber-based heat-shrinkable material prepared by the above preparation process.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] 1) The preparation process of the application has strong universality and can give good heat-shrinkable properties to a variety of different thermoplastic polymers.

[0022] 2) The product obtained by the application is easy to process and can be directly used to produce different macroscopic shapes of heat-shrinkable products, such as heat-shrinkable films, heat-shrinkable tubes, etc.

[0023] 3) The heat-shrinkable material prepared by the application is a thermoplastic material, which can be recycled and reused.

[0024] 4) The application can manufacture heat-shrinkable materials with a porous structure, thereby realizing heat-shrinkable materials with air permeability.

[0025] 5) The application is convenient for adding various processing aids or modifiers to manufacture functionalized heat-shrinkable materials.

[0026] 6) The manufacturing process of the application is simple, the equipment requirement is low, the production efficiency is high, and the industrial production cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings accompanying the specification of the application form a part of the application and serve to provide further understanding of the application, the exemplary embodiments of the application and their descriptions serve to explain the application, and do not constitute an improper limitation on the application.

[0028] Figure 1 The application provides a high-thermal-conductivity polytetrafluoroethylene porous composite material manufacturing process flow chart.

[0029] Figure 2Figure 2 is a microstructure diagram of the internal nanofiber of the polylactic acid / polytetrafluoroethylene composite heat-shrinkable film prepared in Example 1 using the process scheme of the present application.

[0030] Figure 3 Figure 3 is a photograph of the sample before and after shrinking of the polylactic acid / polytetrafluoroethylene composite heat-shrinkable film prepared in Example 1 using the process scheme of the present application.

[0031] Figure 4 Figure 4 is a microstructure diagram of the internal nanofiber of the porous polytetrafluoroethylene heat-shrinkable film prepared in Example 2 using the process scheme of the present application.

[0032] Figure 5 Figure 5 is a photograph of the sample before and after shrinking of the porous polytetrafluoroethylene heat-shrinkable film prepared in Example 2 using the process scheme of the present application.

[0033] Figure 6 is a microstructure diagram of the heat-shrinkable polytetrafluoroethylene composite material prepared in Example 3 using the process scheme of the present application. Figure 6 Figure 7 is a photograph of the appearance and size of the film before and after heat-shrinking of the heat-shrinkable polytetrafluoroethylene composite material prepared in Example 3 using the process scheme of the present application.

[0034] Figure 7 Figure 8 is a photograph of the appearance and size of the film before and after heat-shrinking of the heat-shrinkable polytetrafluoroethylene composite material prepared in Example 3 using the process scheme of the present application. DETAILED DESCRIPTION

[0035] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0036] As introduced in the technical background, the heat-shrinkable materials manufactured by the traditional cross-linking method are difficult to recycle, cannot produce heat-shrinkable materials with porous structure and air permeability, and the product process is relatively complex. The traditional thermoplastic polymers are mostly linear molecular chains, and the heat-shrinking performance is poor. The present application proposes a process for creating a nanopolytetrafluoroethylene fiber network structure in a thermoplastic polymer matrix by melt blending, which gives the material physical cross-linking and thus good heat-shrinking ability. The process mainly includes the following operation steps (as shown in Figure 1

[0037] 1) Dry a certain proportion of thermoplastic polymer, polytetrafluoroethylene, processing aid, etc.

[0038] 2) Put the dried thermoplastic polymer, polytetrafluoroethylene, processing aid, etc. into a blending device through a feeding port for melt blending.

[0039] 3) Extrude the melt-blended product and process it to obtain a blend film, pipe, etc., and then cool and shape it.

[0040] ​​4) According to the actual needs, select the appropriate way such as solution etching, high temperature ablation, phase separation, etc. to create a porous structure in the product.

[0041] Example 1

[0042] The thermoshrinkable polylactic acid / polytetrafluoroethylene composite film was prepared by using the double screw extrusion process, taking polylactic acid (PLA) as the polymer matrix and polytetrafluoroethylene as the second phase. The raw materials were polylactic acid produced by Natureworks Company and polytetrafluoroethylene powder produced by Mitsubishi Chemical Company. The blending equipment used in the experiment was a micro double screw extruder.

[0043] Firstly, all the raw materials were placed in a vacuum drying oven and dried at 80°C for 6 hours.

[0044] Secondly, the polylactic acid raw material particles with a mass ratio of 95% and 5% polytetrafluoroethylene powder were put into the double screw extruder feeding port for blending. The temperature of the double screw extruder was set to 160°C, 180°C and 180°C, the screw speed was 50 rpm, the cavity pressure was controlled at about 7 MPa, and the cycle time was 10 minutes.

[0045] Thirdly, after the blending product was extruded, it was transferred to a hot press, the temperature of which was set to 200°C. The blend was pressed into a film with a thickness of 0.05 mm, which was immediately taken out and cooled to room temperature in cold water.

[0046] Fourthly, the film was cut into a square film with a side length of 5.5 cm and heated to 200°C again to allow it to shrink freely.

[0047] In this example, the microstructure of the obtained thermoshrinkable polylactic acid / polytetrafluoroethylene composite material is shown in Figure 2 The appearance and size of the film before and after thermal shrinkage are shown in Figure 3 After testing, the tensile strength of the film was about 60 MPa, the elongation at break was about 20%, and the radial thermal shrinkage rate was about 67%.

[0048] Example 2

[0049] The thermoshrinkable polytetrafluoroethylene porous film was prepared by using the double screw extrusion process and solvent dissolution etching process, taking polylactic acid as the thermoplastic polymer and dichloromethane as the etching solvent. The raw materials were polylactic acid produced by Natureworks Company and polytetrafluoroethylene powder produced by Mitsubishi Chemical Company. The blending equipment used in the experiment was a micro double screw extruder.

[0050] Firstly, all the raw materials were placed in a vacuum drying oven and dried at 80°C for 6 hours.

[0051] Second step, 70% of the mass ratio of polylactic acid raw material particles and 30% of the polytetrafluoroethylene powder into the twin screw extruder feeding port for blending, twin screw extruder temperature setting is 160℃, 180℃, 180℃, screw speed is 50 rpm, torque control in the pressure control in about 13 MPa, the cycle time is 10 minutes.

[0052] Third step, after extruding the blending product, transfer to the hot press, the hot press temperature is set to 200℃, the blend is pressed into a circular film with a thickness of 0.05mm and a diameter of about 7cm, and then taken out and cooled to room temperature in cold water.

[0053] Fourth step, immerse the film in analytical pure dichloromethane for dissolution. The solvent temperature is room temperature, and the soaking time is 120 minutes. Then the film is taken out and dried, and then washed and dissolved again for 8 hours by Soxhlet extractor using dichloromethane.

[0054] Fifth step, the film material is taken out and dried, and then heated to 200℃ again to make it shrink freely.

[0055] In this example, the microstructure of the heat-shrinkable polytetrafluoroethylene porous film obtained is shown in Figure 4 , and the nanoscale polytetrafluoroethylene fibers are entangled and stacked to form a network structure. The appearance and size of the film before and after heat shrinkage are shown in Figure 5 . The test shows that the tensile strength of the porous film is about 23MPa, the elongation at break is about 106%, and the radial heat shrinkage rate is about 50%.

[0056] Example 3

[0057] The thermoplastic polymer is polyvinyl alcohol (PVA), and the heat-shrinkable polytetrafluoroethylene porous film is prepared by using a double screw extrusion process and a high temperature ablation process. The raw material is polyvinyl alcohol produced by Changchun Chemical Industry Co., Ltd. and polytetrafluoroethylene powder produced by Mitsubishi Chemical Corporation. The blending equipment used in the experiment is a micro double screw extruder.

[0058] First step, all raw materials are placed in a vacuum drying oven and dried at 70℃ for 4 hours.

[0059] Second step, 70% of the mass ratio of PVA raw material particles and 30% of the polytetrafluoroethylene powder into the twin screw extruder feeding port for blending, twin screw extruder temperature setting is 170℃, 190℃, 190℃, screw speed is 50 rpm, torque control in the pressure control in about 15 MPa, the cycle time is 10 minutes.

[0060] Third step, after extruding the blending product, transfer to the hot press, the hot press temperature is set to 240℃, the blend is pressed into a film with a thickness of 0.2mm, and then heated for 60 minutes to make the polyvinyl alcohol decompose.

[0061] Fourthly, the hot-pressed film was taken out and cooled, and then cleaned with ethanol and water three times respectively and dried.

[0062] Fourthly, the film was cut into square films with a side length of 4.5 cm, and heated to 240℃ again to make it shrink freely.

[0063] In this example, the microstructure of the obtained heat-shrinkable polytetrafluoroethylene composite material is shown in FIG. 1, and after high-temperature ablation and washing, the polytetrafluoroethylene fibers form a network structure. The appearance and size of the film before and after heat shrinkage are shown in FIGS. 2 and 3, respectively. After testing, the tensile strength of the film is about 23 MPa, the elongation at break is about 108%, and the radial heat shrinkage rate is about 62%. Figure 6 Figure 7

[0064] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.​​

Claims

1. A manufacturing process of a polytetrafluoroethylene nanofiber-based heat-shrinkable material, characterized by, The process comprises the following steps: 1) drying raw materials including thermoplastic polymer, polytetrafluoroethylene, and then melt blending through a blending device; 2) after the melt blended material is processed into the required shape of tubular, film or sheet material, cooling and setting; The thermoplastic polymer in step 1) is selected from one of polylactic acid, polyvinyl alcohol; In the step 1), the polytetrafluoroethylene is in a powder, block, or emulsion form, with a molecular weight higher than 10 7 g / mol, and a crystallinity of 60-95%. When the thermoplastic polymer is polyvinyl alcohol, when ablation porosification is performed, according to the decomposition temperature or volatilization temperature of the polymer or processing aid, the selected ablation temperature is higher than the decomposition temperature of the polymer matrix by 50℃ or more, and the processing time is greater than 30 minutes; the radial heat shrinkage rate of the obtained heat shrinkable material is 62%; When the thermoplastic polymer is polylactic acid, the film is immersed in dichloromethane at room temperature for dissolution, the immersion time is 100-150 minutes, then the film is taken out and dried, and then repeated washing and dissolution is performed for 8 hours to obtain a material with a porous structure, and the radial heat shrinkage rate is 50% or 67%.

2. The manufacturing process of claim 1, wherein, The raw materials in step 1) include processing aids, which include one or more of porosification agents, antibacterial agents, foaming agents, antistatic agents, flame retardants, plasticizers, thermal stabilizers, antioxidants, light stabilizers, mildewproof agents, coloring agents, whitening agents, fillers, coupling agents, lubricants, release agents, or one or more of thermally conductive fillers, electrically conductive fillers, fibrous fillers, and wear-resistant fillers; the mass fraction is in the range of 0-30% based on the total mass of the raw materials.

3. The manufacturing process of claim 1, wherein, The drying temperature in step 1) is in the range of 30-200℃, and the time is 1-12 hours, and the drying is natural drying, vacuum drying or air blowing drying.

4. The manufacturing process of claim 1, wherein, In step 1), the mass proportion of the thermoplastic polymer in all raw materials fed into the blending device is 50-95%, and the mass proportion of polytetrafluoroethylene is 5-50%.

5. The manufacturing process of claim 1, wherein, The blending device is a single-screw extruder, a twin-screw extruder, a triple-screw extruder, an open mill or an internal mixer; the processing temperature of the raw materials in the blending device is higher than the melting temperature of the thermoplastic polymer by 5-80℃, the rotation speed is 10-100 rpm, and the blending duration is 3-180 minutes.

6. The manufacturing process of claim 1, wherein, In step 2), the blend is directly extruded into a pipe, a film or a sheet through appropriate die design, or the blend is extruded and then processed into a pipe or a film through stretching, calendering or expansion.

7. The manufacturing process of claim 1, wherein, In step 2), the cooling and setting method is liquid cooling, air cooling or air cooling.

8. A polytetrafluoroethylene nanofiber-based heat shrinkable material prepared by the process according to any one of claims 1-7.

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