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Plasma surface treatment of polymer Plasma polymer modification method

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10 Mar,2021

Plasma surface treatment of polymer Plasma polymer modification method:
In the use of plastic film, rubber, fiber fabric and other solid polymer materials, the properties of the material is not only related to its volume performance, the surface performance of the material also accounts for a considerable proportion. For example, it involves adhesion, friction, surface hardness and so on. Therefore, in order to meet the requirements of modern society for multi-functional materials, the surface modification of materials is often carried out. A new dry modification method, plasma-polymer modification, is introduced.

CRF plasma surface treatment
Plasma is excited by the high energy received by some gaseous material. It is composed of electrons, ions, atoms, molecules, free radicals and photons. It is generally electrically neutral. Plasma is the state in which all kinds of matter exist, at the same level as solids, liquids, and gases. Some people call plasma the fourth state of matter.
So how does plasma-polymer modification interact with the surface of polymer materials?


The experiment was carried out with surface hydrophobic polyester film and treated with argon plasma for 5 minutes. The contact Angle of water was 100° after removal and 70° after standing for one day. Why is the film becoming more hydrophilic? This is because the surface of general polymer materials after NH4, O2, H2, N2, Ar will be excited to produce a variety of free radicals. After treatment, free radicals will quickly react with oxygen in the air to generate polar groups such as carboxyl group, hydroxyl group and amino group. Thereby increasing the hydrophilicity of its surface.


Among these gases, inert gases such as hydrogen, nitrogen, and argon are non-reactive plasmas, while ammonia and oxygen plasmas are reactive plasmas. The so-called non-reactive type refers to the free radicals and ions in the plasma do not react with the surface of the material, but only play the role of excitation free energy. The material needs to contact with the air, thus causing changes in the surface chemical structure. Reactivity refers to the free radicals or ions in the plasma directly interact with the surface of the material and connect into new functional groups.


The adhesion of polymer materials can be improved by the hydrophilic modification of plasma. For example, the surface tension of polyurethane composite adhesive is high, and the surface polarity of PP, PE and other plastic films is low, so the surface polarity of polyurethane adhesive can be improved by surface treatment modification of plastic film, and it can be well spread on the surface of plastic film, thus greatly improving the adhesion.


In addition, it is not difficult for us to think that if fluorine gas is used to stimulate plasma surface treatment of materials, will the surface polarity of materials be reduced? Yes, for example, some hydrophilic fiber fabrics, after gasification of carbon tetrafluorocarbon (CF4) and difluoromethane (CH2F2) treatment, hydrophobic obvious. But research has found that this is true, meaning that hydrophobicity disappears after a while.


According to the analysis, this is the result of the deposition of fluorine-containing groups on the surface. Fluorine gas is excited into plasma, and then partially adsorbed on the fabric surface, resulting in hydrophobic effect. The longer the treatment time is, the more gas is introduced and the more hydrophobic the surface is. But after a period of use, the modification effect wears off because the fluorine-containing components are not chemically bonded to the surface of the fabric, which is usually the result of physical adsorption.


In addition to the hydrophilic and hydrophobic surface modification of plasma surface treatment, there is another basic and obvious function of plasma -- etching. Photoresist is a common example and has been used in practical production. The typical application of etching in polymer materials is to increase the printability of the fabric.


Some inert gases, such as argon, helium and high molecular weight gases, are excited into plasmas and bombarded the surface of the fibers, which greatly increases the surface roughness, destroys the crystalline phase, loosens the surface structure, and increases the micro-clearance, thus increasing the accessible area of the dyes. Of course, another convenience is to introduce polar groups on the fiber surface at the same time, which increases the adsorption force with the dye molecules. These plasma-polymer modifications are sufficient to greatly improve the dyeability of the fabric.

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