Degradation of polypropylene random copolymer in aqueous solution of chlorine dioxide: Effect of crystalline structure and morphology

The influence of crystal polymorphism (α, β, γ phases) and spherulite diameter (D_s) on the degradation of polypropylene random copolymer (PP-R) in chlorine dioxide (ClO₂) was investigated. Three PP-R samples—one neat (P) and two with α (A) or β (B) nucleating agents, resulting in initial spherulite diameters of P > B > A—were aged in 20 ppm ClO₂ solution at 60 °C. Chemical degradation, monitored by Carbonyl Index (FTIR) and elongation at break (tensile tests), was most pronounced in sample A (smallest spherulites) and least in sample P (largest spherulites). After 1440 h, sample A exhibited the highest carbonyl content, and its elongation at break reached 50 % of its initial value earlier than sample B, while sample P showed minimal degradation. Rheological and DSC analyses further characterized the degradation. The findings conclude that spherulite size, rather than crystalline phase, predominantly controls PP-R's chemical stability in ClO₂, with smaller spherulites rendering the material more susceptible to degradation.