Preparation and rheology characterization of branched polypropylene during reactive extrusion process

The aim of this study was to compare the rheological behavior of branched polypropylene and linear PP by reactive extrusion process. Samples were modified in the presence of a peroxide initiator, i.e., 2,5-dimethyl-2,5(tert-butyl peroxy) hexane which was dispersed at 45 wt% in CaCo3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{CaCo}}_{3}$$\end{document} (DHBP45), multi-functional monomer trimethylol propane triacrylate (TMPTA) as a graft monomer, and co-agent tetraethyl thiuram disulfide (TETDS) as a co-reactant, in an internal mixer. Rheological measurements and thermal analysis were used to characterize the structure of the modified PP samples. Using PP powder instead of PP granule, it was concluded that the elastic response of branched PP at low frequency was enhanced in comparison with linear PP. Rheological properties, such as increasing the G′ at low frequency, plateau in tanδ–ω plot, deviating from linear PP in Han plot and upturning at high viscosity in Cole–Cole plot, promoted the branching in PP backbone. Moreover, the results showed that by decreasing the amount of initiator, the chain scission can be controlled. TETDS could efficiently control side reactions, decrease the concentration of active free radicals simultaneously in system and improve the branching. When the quantity of TETDS decreased from moderate quantity, the functionality remained unchanged and failed to improve the branching.