TREATMENT OF POLYETHYLENE AND POLYPROPYLENE WITH CHLOROSULFONIC ACID TO STUDY THE SURFACE-MORPHOLOGY

Samples of low- and high-density polyethylene (PE) and polypropylene (PP) have been treated with chlorosulphonic acid at room temperature for various periods of time. Optical microscopy showed that the chlorosulphonic acid penetration rate was constant with time in bulk low-density PE. The treated polymers became black, and the chlorosulphonic acid penetration depth was also determined on the basis of a colour (blackness) scale. The blackness scale allowed the determination of chlorosulphonic acid penetration depth values smaller than 14-mu-m. Mild surface oxidation of low-density PE caused a significant increase in the initial chlorosulphonic acid penetration rate. A method for estimating the thickness of the oxidized surface layer is presented in this paper. The chlorosulphonic acid penetration rate was also found to decrease markedly with increasing crystallinity of PE. Chlorosulphonic acid treatment of PP led to digestion of the polymer without any appreciable formation of a black surface layer.