Nanoporous polyethylene film is a material that introduces nanoscale pore structures into polyethylene (PE) matrix through physical or chemical methods. Its pore size is usually between 50-1000nm, with high porosity and high specific surface area. This type of film not only retains the excellent chemical stability and flexibility of polyolefin materials, but also exhibits new functional properties such as high breathability and selective adsorption ability due to its unique nanoporous structure. Nano porous polyolefin films have high transmittance for infrared light, and due to their pore size, they can scatter visible light, resulting in an overall opaque characteristic of visible light. These characteristics make them potentially valuable in the field of textile applications.

Nanoporous polyethylene film has important application potential in multiple fields due to its excellent physical and chemical properties and multifunctional advantages. However, due to its low surface energy and strong hydrophobicity, its application in specific scenarios is limited to some extent. Surface modification technology can expand the application potential of nanoporous polyethylene films in various fields.

Plasma processing technology

Low temperature plasma treatment technology uses an electric field to excite gas molecules to ionize and form plasma, which is then used for physical etching and chemical grafting to modify the material surface. By introducing functional groups on the surface of the material or changing its chemical composition, hydrophilic functional groups such as carboxyl, hydroxyl, or amino groups can be precisely introduced, significantly improving the hydrophilicity and chemical reactivity of the film. The hydrophilic treatment of nano porous polyolefin film using low-temperature air plasma treatment technology can improve the hydrophilicity of the film while preserving its porous structure, avoiding the loss of film structural characteristics.

To achieve hydrophilic treatment without damaging the nano porous structure of the film, low-temperature plasma technology is used to modify the film, as shown in Figure 1-1. It is an energy-saving, pollution-free, and dry surface modification process that can introduce a large number of hydrophilic oxygen-containing functional groups on the polymer surface while preserving the porous structure of the film.

Figure 1-1 Hydrophilic mechanism of nanoPE7 film surface treated by low-temperature plasma

In order to investigate the effect of low-temperature plasma (LTP) treatment technology on the surface hydrophilicity of nanoporous polyethylene films, different treatment times were set to explore the changes in contact angle. As shown in Figure 2-1, after 3 minutes of treatment, the contact angle of nanoPE significantly decreased, and its hydrophilicity was greatly enhanced. NanoPE is composed of linear or branched carbon hydrogen chains, which are relatively flexible and more prone to breakage or recombination during plasma treatment, resulting in the formation of more active sites and polar groups and significantly improving the surface hydrophilicity.

Figure 2-1 Changes in surface hydrophilicity of nanoporous polyethylene film before and after plasma treatment

Figure 3-1a shows the infrared spectra of nanoPE7 films before and after low-temperature plasma (LTP) treatment. The untreated nanoPE7 film exhibits asymmetric and symmetric stretching vibration peaks of C-H bonds at 2913cm-1 and 2850cm-1, respectively, reflecting its carbon hydrogen skeleton structure; The symmetric bending vibration peak at 1463cm-1 further confirms the existence of C-H bond, while the C-H rocking vibration peak at 720cm-1 is a characteristic peak of polyethylene long-chain structure. After LTP treatment, a new absorption peak appeared at 1714cm-1 in the spectrum, corresponding to the hydrophilic C=O group, indicating that LTP technology successfully introduced oxygen-containing functional groups into the surface of nanoPE7, endowing it with hydrophilicity. As shown in Figure 3-1b, the surface roughness of the LTP treated film increases, which is conducive to the improvement of hydrophilicity. At the same time, the original nanoporous structure is basically retained, which can effectively store moisture absorbing solutions and provide convenience for water molecules to evaporate and absorb according to temperature changes. The film treated with low-temperature plasma technology not only greatly improves its hydrophilicity, but also retains the nanoporous structure of nanoPE7 film, which is conducive to the evaporation and absorption of water molecules from the MAnanoPE porous structure according to temperature changes without any impact.

Figure 3-1 ATR-FTIR spectra of LTP nanoPE and nanoPE7, (b) Scanning electron microscopy images of LTP nanoPE and nanoPE7

As shown in Figure 4-1a, before low-temperature plasma treatment, the nanoPE7 film exhibits hydrophobicity with a water contact angle of 120.12 °; After treatment, the water contact angle decreased to 33.27 ° and the hydrophilicity was significantly improved. Immerse the nanoPE7 film and LTP nanoPE film in deionized water, as shown in Figure 4-1b. Untreated nanoPE7 is hydrophobic, preventing water molecules from entering the pores, while the hydrophilic treated LTP nanoPE film allows water molecules to enter the pores through capillary effect, resulting in a semi transparent state of the film.

Figure 4-1 Contact angles before and after LTP treatment, (b). Comparison of LTP nanoPE and nanoPE7 immersion in aqueous solution