Waterproof membrane is a widely used building waterproof material in various construction projects. Among them, Styrene-Butadiene-Styrene (SBS) modified asphalt waterproof membrane is one of the most extensively researched building waterproof materials. It adopts high-strength non-woven fabric as the base layer and SBS thermoplastic elastomer modified asphalt as the impregnating and coating material. The prepared waterproof membrane exhibits excellent water impermeability, high and low temperature resistance, high ductility, strong tensile performance and convenient construction, maintaining reliable waterproof performance even in complex service environments.

For waterproof membranes, the bonding performance on concrete substrates under humid conditions is a critical performance indicator that urgently needs improvement. During the forming process of asphalt-based polymer waterproof membranes, plasticizers, residual monomers and degradation products are usually added, which tend to reduce surface polarity. This leads to low surface wettability and weak polarity, resulting in poor bonding capability.

Plasma treatment is a rapidly developing material surface modification technology in recent years. Plasma, known as the fourth state of matter, consists of electrons, ions and neutral particles with equal positive and negative charges. High-energy electric fields generate energetic particles such as charged particles, excited-state particles and free radicals, which bombard the material surface and alter its physical and chemical properties without changing the internal structure of the material. This technology is commonly used to modify surface functional groups and specific surface area, so as to improve surface adhesion, hydrophilicity and other properties, and expand the application scope of materials.

Taking reactive adhesive waterproof membrane as the research object, this paper systematically investigates the modification of chemical functional groups on the membrane surface under different plasma atmospheres and treatment durations by plasma treatment technology. XPS, Fourier transform infrared spectroscopy and contact angle measurement are used to characterize the changes in surface polarity, hydrophilicity and hydrophobicity, as well as functional group composition.

Plasma Modification Treatment

Plasma treatment was applied to the waterproof membrane surface under three atmospheres: nitrogen, oxygen and air, with treatment durations ranging from 10 s to 90 s. Surface characterization and peel strength tests were carried out on the treated samples.

SEM Characterization (Figure 1)

As shown in Figure 1, the membrane surface shows no obvious change after 90 s treatment with air plasma and oxygen plasma. In contrast, obvious folds appear on the membrane surface after 90 s nitrogen plasma treatment due to its strong bombardment effect.

Figure 1 Microscopic morphology of waterproof membrane surface after 90 s treatment under different plasma atmospheres

X-ray Photoelectron Spectroscopy (XPS) (Figure 2)

As shown in Figure 2, waterproof membranes treated with different plasma atmospheres present distinct surface characteristics.
After nitrogen plasma treatment, characteristic peaks appear at 399 eV and 401 eV, confirming the formation of N—H and N—O bonds.
After oxygen plasma treatment, the carbonyl oxygen characteristic peak at 531 eV and hydroxyl characteristic peak at 532.5 eV verify the generation of oxygen-containing polar functional groups such as —OH and —COOH, which are beneficial to the improvement of surface hydrophilicity and bonding performance.
Characteristic peaks of amino groups, carbonyl groups and hydroxyl groups simultaneously appear after air plasma treatment, proving the comprehensive modification effect of air plasma.
New functional chemical groups generated on the membrane surface after plasma treatment lay a foundation for the subsequent improvement of bonding performance with concrete.

Figure 2 XPS spectra of waterproof membrane surface treated with different plasma atmospheres

Fourier Transform Infrared Spectroscopy (FTIR) (Figure 3)

As shown in Figure 3, the absorption peak near 3400 cm⁻¹ of nitrogen plasma treated membrane is significantly enhanced, indicating an increase in —NH₂ functional groups, which is consistent with XPS results.
For oxygen plasma treated samples, the intensity of infrared absorption peaks at 1090 cm⁻¹, 1050 cm⁻¹, 881 cm⁻¹ and 1760 cm⁻¹ increases, corresponding to the stretching vibration and bending vibration of —C—O—, as well as the stretching vibration of C=O. This confirms the growth of polar groups such as hydroxyl and carboxyl groups.
Air plasma treatment enhances the characteristic absorption intensity of —OH, —COOH, —NH₂ and other groups on the membrane surface. The results further verify that new chemical groups are formed on the membrane surface after plasma atmosphere treatment.

Figure 3 FTIR spectra of waterproof membrane surface under different plasma atmospheres and treatment durations

Contact Angle Test (Figure 4)

As shown in Figure 4, the surface hydrophilicity of the waterproof membrane is improved after treatment under all three atmospheres, and the hydrophilicity increases with the extension of treatment time.
Air plasma presents the most obvious contact angle change: after 90 s treatment, the surface contact angle drops from 95° to 15°, changing the surface from slightly hydrophobic to highly hydrophilic.
After 90 s oxygen plasma treatment, the contact angle is about 50°, showing moderately improved hydrophilicity.
After 90 s nitrogen plasma treatment, the contact angle is 72°, with only a slight increase in hydrophilicity.

Oxygen and air plasma introduce abundant —OH and —COOH groups, resulting in remarkable improvement of surface hydrophilicity. Nitrogen plasma mainly relies on physical bombardment and introduces a small amount of —NH₂ groups, leading to limited enhancement of hydrophilicity.

Figure 4 Surface contact angle of waterproof membrane under different plasma atmospheres and treatment durations

Changes in Peel Performance after Plasma Surface Treatment

As shown in Table 1, compared with untreated samples, the peel strength between waterproof membrane and concrete is improved after plasma treatment under all three atmospheres.Air plasma treatment achieves the most significant improvement: the maximum peel strength increases from 142 N (untreated) to 184 N.Nitrogen plasma treatment raises the maximum peel strength to 168 N.Oxygen plasma treatment shows a limited improvement, with the maximum peel strength only reaching 153 N.

The reactive bonded waterproof membrane was treated with plasma under various atmospheres and durations. Combined with SEM, XPS, FTIR and contact angle tests, the formation of new chemical groups on the membrane surface was verified from macroscopic, microscopic and molecular levels. Peel tests confirm that plasma treatment effectively enhances the interfacial adhesion between waterproof membrane and concrete. It is concluded that plasma treatment endows the low-polarity and functional-group-deficient membrane surface with

The reactive bonded waterproof membrane was treated with plasma under various atmospheres and durations. Combined with SEM, XPS, FTIR and contact angle tests, the formation of new chemical groups on the membrane surface was verified from macroscopic, microscopic and molecular levels. Peel tests confirm that plasma treatment effectively enhances the interfacial adhesion between waterproof membrane and concrete. It is concluded that plasma treatment endows the low-polarity and functional-group-deficient membrane surface with high polarity, high hydrophilicity and abundant surface functional groups, which is the key to improving the bonding performance of waterproof membranes.