Лако-красочные материалы — производство

The adhesion of polyethylene or polypropylene can be demonstrated in a simple experiment. Both materials can be carefully melted without considerably exceeding the melting point, such that the surface is prevented from oxidizing. A well-cleaned aluminum surface is then coated with the molten polyethylene. As might be expected, if the surface is well wetted the polyethylene can easily be stripped from the aluminum sheet, such that no polyethylene residues can seen macroscopically to remain on the sheet. Measurement of the surface tension of the sheet surface will be approximately 30 mN m-1 inside the wetted area, but 72 mN m-1 outside the wetted area (i. e. there is more absorbed water). Hence, it is concluded that although the polyethylene could be stripped off with ease, its residues remained on the aluminum surface, and that cohesive failure had taken place within the polyethyl­ene near the interface between the two materials. This situation cannot be explained by either of the adhesion theories described in Section 3.2, thus confirming an observation made earlier [20, 21], namely that adhesion failure is rare and the properties of the bond are controlled by the surface influencing the condition of the polymer near the interface.

3.3.3