Study of iPP crosslinking by means of dynamic and steady rheology measurements

The crosslinking of isotactic polypropylene (iPP) using crosslinking agents (CAs) based on a peroxide/sulfur/accelerator system is a very attractive new method that has been reported recently. The present work deals with the study of the dynamic rheological behavior of iPP during and after the crosslinking process. The influence of the CA concentration and the processing temperature T on the rheological behavior of the iPP was analyzed. The kinetics of the crosslinking reaction was established using the technique described by G. A. Harpell and D. H. Walrod. This reaction is found to be of order one. At T = 180 degrees C, the crosslinking reaction was faster. By varying the crosslinking agent content, different crosslinking degrees of iPP, expressed by the corresponding gel content, are achieved. On the other hand, the modified polypropylene exhibits an unexpected viscosity-shear rate pattern, which describes the reverse crosslinking reaction mainly occurring by the opening of the bridges of the new interpenetrating network (IPN) formed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012