Kinetics in high-temperature free-radical reactive processing: Grafting maleic anhydride onto polypropylene in the presence of nanoclay-supported peroxide

Grafting maleic anhydride onto polypropylene in the presence of nanoclay-supported peroxide mechanism (Muñoz et al., 2021). [Display omitted] •Macroradical recombination at high temperatures leads an almost negligible chain-scission rate after 3 minutes of reaction.•During grafting, MA homopolymerization takes place and is enhanced by the presence of o-MMT through chemical adsorption.•The via-radical reaction can be suppressed by using free radicals, enabling the collection of data on the reaction kinetics.•The kinetic data demonstrated the need to account for the effects of MA homopolymerization and PP macroradical recombination. The kinetics of grafting and chain scission reactions during maleic anhydride (MA) grafting onto polypropylene (PP) using nanoclay-supported peroxide (o-MMT/DCP) in the molten state were evaluated through the development of a new methodology. A combination of characterization techniques and mathematical data manipulation was employed for this assessment. To inhibit radical propagation and recombination, tetramethylpiperidine-1-oxyl (TEMPO) was used as a free radical scavenger. Rheological stability tests demonstrated that TEMPO was more effective as a reaction inhibitor. The kinetics dataindicated that the use of o-MMT/DCP resulted in products with higher MA grafted levels and molecular weight (MW) compared to grafting performed in the absence of o-MMT. Additionally, some changes in molecular architecture were observed. The chain scission distribution function (CSDF) revealed that during the MA grafting process, the molecular weight of PP was reduced through chain scission, with a preference for longer chains. Furthermore, the presence of o-MMT was found to restrain the level of PP chain scission, likely due to recombination on the clay surface.