Aluminum foil glass fiber composite fabric is a thermal protection material made of glass fiber (referred to as "glass fiber" in this article) fabric as the base fabric and aluminum foil composite on the surface. It has excellent thermal protection performance and is widely used in equipment such as firefighting suits and forest fire shelters. On the one hand, the surface of aluminum foil is relatively smooth and lacks active functional groups, resulting in poor bonding strength with adhesives, which leads to weak peeling strength of aluminum foil fiberglass composite fabric. After repeated use, it is easy to peel off, greatly reducing the thermal protection performance of the composite fabric and endangering the safety of the wearer's life. On the other hand, the compactness of the composite of aluminum foil and binder is not good enough, which is not conducive to the improvement of thermal protection performance

Plasma is a commonly used surface modification technique for materials, which can improve material roughness, increase contact area, and enhance surface activity through etching. This article uses plasma treatment technology to modify the surface of aluminum foil, and studies the effects of plasma treatment time, treatment power, and two key factors on the surface contact angle and peel strength of aluminum foil. The surface morphology of aluminum foil before and after modification is compared.

The influence of plasma treatment process on contact angle and peel strength

Testing and characterization

Contact angle test: Use a contact angle measuring instrument to test the contact angle of plasma treated aluminum foil, using water-based silicone resin as the reagent.

Peel strength test: Referring to GB/T2792-2014 "Test Method for Peel Strength of Adhesive Tape", the peel performance of double-layer fiberglass/aluminum foil composite fabric was tested using an electronic fabric strength machine. Make a 20cm × 20cm double-layer fiberglass fabric with aluminum foil sample (i.e. 2 pieces of fiberglass fabric with 1 piece of aluminum foil in between, bonded with adhesive), dry and cure the made sample, and then cut it into a strip of cloth with a width of 25mm. The peel performance test sample of aluminum foil fiberglass fabric composite fabric is shown in Figure 1.

Figure 1 Peel strength test sample of aluminum foil fiberglass composite fabric

The influence of plasma treatment time on contact angle and peel strength

When the processing power is 300W and the nozzle height is 3mm, the effects of plasma treatment time of 0, 100, 200, 300, and 400s on the contact angle and peel strength of aluminum foil fiberglass composite fabric were analyzed. The results are shown in Figures 2 and 3, respectively. According to Figure 2, the contact angle of the untreated aluminum foil surface is 61.4 °. After plasma treatment, the contact angle shows a significant decrease with the extension of treatment time. When the treatment time increases from 100s to 400s, the contact angle gradually decreases from 40.5 ° to 19.8 °, indicating that plasma treatment can effectively improve the affinity between the aluminum foil surface and the adhesive. This may be because plasma treatment increases the roughness of the aluminum foil surface, leading to an increase in contact area and a decrease in contact angle.

Figure 2: The Effect of Plasma Treatment Time on the Contact Angle of Aluminum Foil Surface

Figure 3: The Effect of Plasma Treatment Time on Peel Strength

From Figure 3, it can be seen that the peel strength of the untreated sample is 7.2N. After 100-400s of treatment, its values increased to 9.5, 10.6, 11.7, and 11.9N, respectively, indicating that the affinity between the aluminum foil and the adhesive has improved, which is conducive to the improvement of the bonding strength between the two; After processing for more than 300 seconds, the increase in peel strength is relatively small, which may be due to excessive surface etching leading to microstructure homogenization.

The influence of plasma treatment power on contact angle and peel strength

The effects of plasma treatment power of 100, 200, 300, 400, and 500W on the contact angle and peel strength of aluminum foil fiberglass composite fabric were analyzed under processing time of 300s and nozzle height of 3mm. The results are shown in Figures 4 and 5, respectively. According to Figure 4, the contact angle of aluminum foil shows a trend of first decreasing and then increasing with the increase of plasma treatment power. When the processing power increases from 100W to 300W, the contact angle significantly decreases from 52.6 ° to 20.6 °; When the power continues to increase to 500W, the contact angle actually rises to 47.5 °. This may be because when the power is less than 300W, as the plasma treatment power gradually increases, etching is formed on the surface of the aluminum foil, resulting in an increase in roughness and a decrease in contact angle; When the processing power exceeds 300W, the surface of the aluminum film may melt at higher power, flattening the original etching marks and reducing roughness. At a processing power of 300W, the contact angle reaches a minimum value, exhibiting optimal hydrophilic properties.

Figure 4: The Effect of Plasma Processing Power on Contact Angle

Figure 5: The Effect of Plasma Treatment Power on Peel Strength

According to Figure 5, the peel strength of aluminum foil fiberglass composite fabric shows a trend of first increasing and then decreasing with the increase of plasma treatment power. When the processing power increases from 100W to 300W, the peeling strength significantly increases from 7.8N to 11.7N; however, when the power continues to increase to 500W, the peeling strength actually drops to 8.3N. This may be because when the plasma processing power is below 300W, as the power gradually increases, more grooves will be formed on the surface of the aluminum foil due to plasma etching, the surface roughness increases, the contact angle decreases, and the contact area with the adhesive increases, so the peeling strength also increases. However, when the power exceeds 300W, high-energy plasma will trigger the melting phenomenon of the surface material of the aluminum film, causing the previously formed etched structure to become smoother, ultimately leading to a decrease in surface roughness, a gradual reduction in contact area with the adhesive, and a decrease in peel strength.

Comparative analysis of surface morphology of aluminum foil

Figure 6 shows SEM images of aluminum foil before and after plasma treatment. The surface of aluminum foil without plasma treatment is relatively flat, which is also the main reason for the insufficient peeling strength of aluminum foil fiberglass composite fabric. In contrast, the surface of aluminum foil treated with plasma has formed numerous micrometer level grooves, which on the one hand increases the interface contact area between it and the resin, and on the other hand reduces the resin contact angle on the surface of the aluminum foil, thereby promoting a tighter bond between the aluminum foil and fiberglass fabric, improving the bonding strength, and enhancing the peeling strength of the aluminum foil fiberglass fabric.

Figure 6 SEM image of aluminum foil (× 5000)

After plasma treatment, the contact angle of water-based silicone resin on the surface of aluminum foil decreased to 19.3 °, and the peel strength of composite fabric increased to 12.1N. This process significantly enhanced the interfacial adhesion performance between aluminum foil and glass fiber.