Tianjin Tiansu Binhai Fluoroplastic Film Rod Sheet

Date:2022/8/17 9:42:10 /Read: /Source:本站

Tianjin Tiansu Binhai Fluoroplastic Film Rod Sheet http://www.tjtsjt.net//

Introduction of Polytetrafluoroethylene (PTFE) Surface Modification

1. Structural analysis of PTFE properties:

      In PTFE, fluorine atoms replace hydrogen atoms in polyethylene. Since the radius of fluorine atoms (0.064nm) is larger than that of hydrogen atoms (0.028nm), the carbon-carbon chain is formed by the flat, fully stretched zigzag of polyethylene. The conformation gradually twists to the helical conformation of PTFE. The helical conformation just surrounds the carbon chain skeleton of PTFE that is susceptible to chemical attack, forming a tight and completely "fluorinated" protective layer, so that the main chain of PTFE is not attacked by any external reagents, making PTFE unmatched by other materials. high solvent resistance, chemical stability and low cohesive energy density; at the same time, the carbon-fluorine bond is extremely strong, and its bond energy reaches 460.2kJ/mol, which is far greater than that of carbon-hydrogen bonds (410 kJ/mol) and carbon-carbon bonds. (372 kJ/mol) high, which makes PTFE have better thermal stability and chemical inertness. In addition, the electronegativity of the fluorine atom is extremely large, and the tetrafluoroethylene monomer has perfect symmetry, so that the attraction between PTFE molecules and the surface energy are low, so that PTFE has a very low surface friction coefficient and better low temperature. ductility; at the same time, the creep resistance of PTFE is poor, and it is prone to cold flow. The unbranched symmetrical main chain structure of PTFE also makes it highly crystalline, so processing is difficult.

2. PTFE surface modification method:

2.1 Reducing agent method (sodium-naphthalene solution replacement method)

      Among the various modification methods known at present, the sodium-naphthalene solution replacement method is the most effective and widely used.

      The principle is: Na transfers the outermost electrons to the empty orbital of naphthalene, forming anion radicals; and then forms ion pairs with Na+, releasing a large amount of resonance energy, forming a mixed solution of dark green metal-organic compounds. These compounds have high reactivity. When in contact with PTFE, sodium can destroy the C-F bond, tear off part of the fluorine atoms on the surface of PTFE, and leave a carbonized layer and -CH, -CO, C=C, -COOH and other groups on the surface. Polar group; the depth of the carbonized layer is about 0.05~1μm, the surface tension of PTFE is 18.5×10-3N/m, and the surface has a high surface energy.

      In addition to sodium-naphthalenetetrahydrofuran etching solution, sodium-biphenyl dioxane, sodium-naphthalene glycol dimethyl ether and other treatment solutions also have good results.

2.2 High temperature melting method

      The advantage of this method is that the weather resistance and heat and humidity resistance are significantly better than other methods, and it is suitable for long-term outdoor use; the disadvantage is that PTFE will release a toxic substance during high temperature sintering, and the shape of the PTFE membrane is not easy to maintain.

2.3 Plasma treatment

      Badey J P et al. treated PTFE co-currently with microwave plasma for surface modification. When PTFE is treated with O2/N2 or O2, the surface is not modified; when treated with NN3 plasma, the polar components and hydrophilicity of the PTFE surface increase.

2.4 Laser radiation method

      It has many advantages in material processing, which are incomparable with other surface treatment technologies:

The energy transfer is convenient, and the surface of the workpiece to be treated can be selectively strengthened locally;

The energy action is concentrated, the processing time is short, the heat affected zone is small, and the workpiece deformation is small after laser treatment;

It can handle workpieces with complex surface shapes, and it is easy to realize automatic production;

The modification effect is more obvious: fast speed, high efficiency and low cost;

Usually only some sheet metal can be processed, and it is not suitable for processing thicker plates;

Because of the harm of laser to human eyes, it affects the safety of staff, so it is necessary to develop safety facilities.

The steps of this method are: placing the PTFE film in a polymerizable monomer such as styrene, fumaric acid, methacrylate, etc., and irradiating it with Co60 to make the monomer form a layer of easy-to-adhesion on the surface of the PTFE film. Grafted polymer. The grafted PTFE grows uniformly in the three-dimensional direction and maintains its shape, but loses its original luster and lubricity; the surface roughness increases with the increase of the grafting amount, but the surface does not change color, and the surface resistance also decreases in a humid environment. does not change.

2.5 Silicic acid activation method

      After the porous PTFE is treated with SiX4, it can be hydrolyzed to achieve the purpose of activating the PTFE surface, which is the "silicic acid modification method".

Advantages: The traditional modification method will change the chemical structure of PTFE, thus affecting the inherent structure of PTFE to varying degrees; this modification method will not change the chemical structure of PTFE, but also achieve the purpose of surface activation.

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