Rheology and Thermal Properties of Polypropylene Modified by Reactive Extrusion with Dicumyl Peroxide and Trimethylol Propane Triacrylate

Trimethylol propane triacrylate (TMPTA) and dicumyl peroxide (DCP) were used to modify polypropylene (PP) by reactive extrusion in a twin-screw extruder. The effects of TMPTA concentration on oscillatory shear rheology, melt elongational rheology, and thermal properties were comparatively evaluated. Fourier transform infrared spectroscopy indicated that the grafting reaction took place and TMPTA had been grafted onto the PP backbone. Differential scanning calorimetric results showed that the crystallization temperatures of modified PPs were higher than those of the initial and degraded PPs. The rheological characteristics such as higher storage modulus (G') at low frequency, increased degree of shear thinning, a plateau in tan delta-omega plot, and upturning at high viscosity in the Cole-Cole plots proved that the long-chain branches have been added to the linear PP molecule. The melt elongational rheology showed that the modified PPs exhibit improved melt strength and increased elongational viscosity in the presence of TMPTA and DCP, which further confirmed the existence of long-chain branching (LCB) in their backbone. According to the analytical results from oscillatory shear rheology and elongational rheology, it can be inferred that the LCB level in modified samples increases with an increase in TMPTA concentration. (C) 2009 Wiley Periodicals, Inc. Adv Polym Techn 28: 16-25, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20146