Chemical modification of polypropylene with peroxide/pentaerythritol triacrylate by reactive extrusion

Abstract

SYNOPSISTo explore the possibility of producing branched polypropylene (PP) by a reactive extrusion (REX) process, isotactic PP was reacted with a polyfunctional monomer, pentaerythritol triacrylate (PETA), in the presence of 2,5-dimethyl-2,5(t-butylperoxy) hexane peroxide (Lupersol 101). Experiments were carried out in an intermeshing, corotating twin-screw extruder at 200°C using three concentrations of peroxide (200, 600, and 1000 ppm) and four concentrations of PETA (0.64, 1.8, 2.8, and 5.0%, by weight). Shear viscosity and MFI of the whole polymers was found to increase with PETA concentration and decrease with increasing the peroxide concentration at a given PETA concentration. The macrogel amount in the materials produced was determined in refluxing xylene using Soxhlet extraction and at PETA concentrations higher than 1.8 wt % the macrogel content increased with increasing peroxide concentration. No macrogel was detected at low PETA concentrations (~0 . 6 4 % ) a t all three peroxide levels, suggesting that low concentrations of PETA and peroxide should be used in order to minimize the formation of macrogels. The xylene soluble portions (sols) of the modified materials were characterized by FTIR and DSC. Generally, the relative intensities A1740/A841 in the FTIR spectra increased with increasing PETA incorporated into PP. Two melting peaks ( T m l and Tm2) were observed in the DSC traces of some of the sols, and the crystallization temperatures (T,) were higher than those of the virgin and degraded polypropylenes. The DSC behavior of the sols suggests that the modified PPs contain branched and/or lightly crosslinked chain structures. 0

Analytical Rheology of Polymer Melts: State of the Art

“…Adding LCB fixes the melt strength. LCB may be introduced synthetically, by postreactor chemical modification [47][48][49], or by electron beam irradiation [50][51][52].…”

Novel synthesis of branched polypropylene via solid-state shear pulverization

“…However, due to high extrusion temperatures, synthesis of branched PP by this approach is accompanied by undesirable b-scission, which leads to MW degradation and hinders formation of well-defined, uniform chain structures [22,24]. There is also a concern regarding homopolymerization of the functional monomer during the grafting process [25,26]. In order to suppress b-scission and/or homopolymerization of functional monomer, additives such as iniferter compounds [22,27] and heteroaromatic ring derivatives [25] have been used.…”

Comparison of rheological behavior of branched polypropylene prepared by chemical modification and electron beam irradiation under air and N2

“…Special rheological behaviour of branched polymers makes them suitable for thermo-forming processes. Some researchers have tried to introduce long-chain branches to polypropylene backbone for improving its melt strength (Wang et al, 1996;Graebling, 2002;Frounchi et al, 2007;Krause et al, 2004;Weng et al, 2003;Ye and Zhu, 2003;Graebling et al, 1997;Lagendijk et al, 2001;Lugao et al, 2000Lugao et al, , 2002Lugao et al, , 2003. Because of extreme sensitivity of low-frequency rheological response to molecular structure (Wong and Baker 1997;Dealy and Wissbrun, 1990), the rheological behaviour was used to characterize the branched polypropylene prepared via different methods (Graebling, 2002;Krause et al, 2004;Lagendijk et al, 2001;Tsenoglou and Gotsis, 2001;Romani et al, 2002;Auhl et al, 2004).…”