PEEK is a special engineering plastic with excellent performance, which can be used for a long time at 250 ℃. It can maintain high bending strength and compression strength at high temperatures, has high rigidity, good dimensional stability, and a small coefficient of linear expansion.
Can withstand almost any chemical except concentrated sulfuric acid; And it can maintain good chemical stability even at higher temperatures, while also possessing flame retardancy.
PEEK film source: Dafu New Materials
PEEK film has high heat resistance, good electrical and mechanical properties, with continuous use temperature up to 240 ℃ and dielectric loss as low as 0.001-0.003; The transmittance reached 85.9%. Especially its chemical resistance, hydrolysis resistance, radiation resistance and other properties are quite outstanding even in high-performance films. 1、 The preparation methods of PEEK film in industry mainly include extrusion casting method and extrusion blow molding method. (1) PEEK film is prepared by extrusion casting using a T-shaped die, with a die temperature of 400 ℃ or above. The extruder screw can use a PA or PP film screw structure. In order to give PEEK film excellent properties such as high tensile strength, it can be subjected to uniaxial or biaxial stretching.
Li et al. prepared high-strength PEEK film by extrusion stretching, and the tensile strength after stretching reached 333 MPa, almost four times that of unstretched, mainly due to the synergistic effect of stretching orientation and crystallization. Among the three process parameters of stretching rate, stretching temperature, and stretching ratio, the stretching ratio has the most significant effect on the tensile strength of the film (see Figure 1).
Figure 1 Effect of stretching ratio on the tensile strength of PEEK film
Na et al. prepared PEEK/polyethersulfone coated multi walled carbon nanotube (MWCNT) composites by melt blending using a twin-screw extruder, and thin films were prepared by extrusion casting method. When used for broadband electromagnetic interference shielding, the film exhibits high thermal stability (decomposition temperature T5% at 5% mass loss is 586 ℃) and good mechanical properties (tensile strength of 101MPa when PEEK/polyethersulfone coated MWCNTs mass ratio is 91:9), which is superior to other electromagnetic shielding films previously reported (Table 1). Table 1 shows the electromagnetic shielding effectiveness, tensile strength, and T5% of different composite materials
A series of PEEK films were prepared using extrusion casting method, and it was found that their tensile strength increased from 129 MPa to 155 MPa with the increase of casting roll speed; The biaxial stretching after casting can significantly improve the mechanical properties of the film, and the longitudinal tensile strength can reach 203MPa
PEEK film was prepared by blending PEEK/MWCNT composite materials using a twin-screw extruder, and the film was prepared by extrusion casting method. When the MWCNT content is 0.68% (volume fraction), the dielectric constant of the film reaches 367.2 × 103Hz, which is about 100 times that of pure PEEK film; The tensile strength reaches 103.4 MPa, making it suitable for high dielectric constant materials with high requirements for mechanical properties.
(2) The extrusion blow molding method can also be used to prepare PEEK film, which can obtain thin films, but it is difficult to obtain wide films. The main component of PET/PEEK/PI (150/200/180, by mass) composite film was prepared by twin-screw three-layer co extrusion blow molding method.
When extruding, the main screw speed is 100-200r/min, the traction speed is 5-10m/min, the die diameter is 400mm, and the inflation ratio is 3-5. Composite films have low water vapor transmission, high peel strength, and high heat sealing strength. Zhu Guannan and others prepared PEEK films with a thickness of less than 0.5mm by extrusion blow molding method. The films are isotropic and have good wear resistance. 2、 Modification of PEEK film (1) Blending and filling modification: Song Wensheng et al. prepared a series of sulfonated polyether ether ketone (SPEEK) and PSF blend films with different compositions by blending method. It was found that with the increase of PSF content, the phase separation behavior of SPEEK/PSF films intensified, and the alcohol resistance at room temperature was improved; When the PSF content is 50%, the methanol permeability coefficient is only 1.3 × 10-7cm2/s, a decrease of 88.3%.
Phosphotungstic acid
Xue Song et al. dissolved SPEEK in dimethylacetamide and added phosphotungstic acid (PWA). After stirring evenly, a film was formed on a glass plate by diffusion flow. After drying and dehydration, a composite proton exchange membrane was prepared. The conductivity of SPEEK composite film with a sulfonation degree of 0.73 is higher than 10-2S/cm at PWA doping levels of 0.45% and 0.6% (mass ratio to SPEEK), and reaches 2.95 × 10-2S/cm and 3.88 × 10-2S/cm at around 80 ℃, respectively, which is significantly higher than Na fi on ® The conductivity of the 117 membrane. (2) Plasma modified INAGAKI and others used oxygen plasma to modify PEEK films, introducing C-O groups on the surface to enhance their hydrophilicity. Compared with untreated films (93 °), the surface contact angle of films treated with direct plasma and remote oxygen plasma is significantly reduced (56 °~78 °). Du Peng et al. used ion implantation to modify PEEK film, resulting in the formation of graphite phase with extremely incomplete structure on the surface, which reduces the polarity of the film, increases the contact angle with water, and significantly improves its surface hardness and modulus. (3) Chen et al. graft modified ultra-thin PEEK films by thermal grafting of divinylbenzene and radiation grafting of ethyl styrene sulfonate. The modified films exhibited higher hydrolytic stability in hot water, such as being very stable in water at 95 ℃, and the mass did not decrease after 5000 hours; And the methanol permeability is even lower, at 0.35 × 10-6cm2/s, less than Nafion ® One seventh of it can be used as an electrolyte membrane for direct methanol fuel cells.
Li et al. modified PEEK films by radiation-induced crosslinking and grafting, and prepared aromatic hydrocarbon electrolyte membranes with lower methanol permeability (Figure 2) and higher mechanical properties; Has durability in direct methanol fuel cells at high temperatures; The maximum power density reaches 106mW/cm2 at 95 ℃.
Figure 2 Relationship between methanol permeability and ion exchange capacity of cPEEK and cPEEK g-DVB electrolyte membranes
3、 The main application areas of PEEK film are seawater desalination, electronic product diaphragms, flexible printed circuits, and film potentiometers. Kiepfer et al. measured the anti fouling curves of pure PEEK film, talc filled PEEK film, and stainless steel film with artificial seawater, and found that among the three films, the adhesion between pure PEEK film and the measured substance was the weakest, which was attributed to its low polarity, low roughness, and uniform morphology. Therefore, PEEK film is suitable for in-situ cleaning in the process of hot seawater desalination. Hamada et al. prepared PEEK films containing nano-SiO2 through radiation-induced graft polymerization. The films showed the highest tensile strength (16.4MPa) when the nano-SiO2 content was 3% (mass fraction), which was higher than the films without SiO2 and Nafion, respectively ® 1.27 times and 1.64 times of 212; The ion exchange capacity of the membrane electrode module reached 3.30 mmol/g, and the maximum power density was 612 mW/cm2 at a relative humidity of 30%, an increase of 7%. Therefore, the graft electrolyte membrane of PEEK/nano-SiO2 hybrid membrane can be used in the field of fuel cells.
