Reticulation, mecanisme reactionnel du polypropylene isotactique et du polypropylene isotactique reticule

Abstract

The present work deals essentially with a new method to modify chemically the isotactic Polypropylene (iPP) by introducing and controlling the new structure thus obtained. Crosslinked iPP is prepared via reactive blending using active crosslinking agents based on dicumyl peroxide (DCP), sulfur (S) and tetramethyl thiuram disulfide (TMTDS). A Brabender plastograph is used to follow, in real time, and to evaluate the crosslinking reaction through the Monsanto method. The chemically modified materials are analyzed and characterized by different techniques; i.e. FTIR; RMN C13, DSC, DRX, DMTA as well as static and dynamic rheology. The results obtained revealed that the materials are crosslinked indeed (apparition of new covalent bonds C-S, C-N, S-S and C-C in the IR and NMR spectra) and bi- and tri-dimensional interpenetrating networks are obtained. During the crosslinking process, a new ethylenic chain is generated, inducing a change of the rheological behavior, and new crystalline forms β and γ as well as (α +β) and (α +γ) appear. This is followed by a new transition temperature Tg β at – 50°C and a decrease in the storage modulus and tanδ which favors ductility. From these results, a reactional mechanism has been proposed; such a mechanism is very close to that of the crosslinking reaction as well as to that of the reversible crosslinking. A rigourous combination (type and concentration) of the different crosslinking agents is a useful chemical tool to impose a given material structure and to control the structure thus obtained.