A kinetic study of the corrosion of polyamide in sulfuric acid solution

Corrosion behaviors of polymeric materials were classified into diffusion-c ontrolled systems and reaction-controlled systems. In the former, in which the diffusion coefficient is small, the polymer decomposed from its surface . In the latter, in which the reaction rate of decomposition is small, the polymer degraded after penetration of the ambient solution. In the corrosio n of polyamide (PA) by sulfuric acid, mechanism found to involve the simult aneous diffusion of sulfuric acid into PA and the hydrolysis of PA. A kinet ic equation representing the decrease in molecular weight of PA by hydrolys is was then proposed, and the change in sulfuric acid concentration distrib ution over time was calculated using the experimentally determined diffusio n coefficient of sulfuric acid into PA. Finally, the rate of PA corrosion w as estimated numerically by combining the change in sulfuric acid concentra tion and the kinetic equation of molecular weight decrease. The analytical results agreed well with the experimental ones. A generalized corrosion mod el could be established by adjusting the diffusion coefficient and the rate constant of the kinetic equation in the analytical expression.