Impact modified isotatic polypropylene with controlled rubber intrinsic viscosities: Some new aspects about morphology and fracture

Abstract

ABSTRACT:The influence of the molecular weight of the dispersed phase of ethylene-propylene rubber modified isotactic polypropylene (iPP/EPR) reactor blends was studied in a systematic way by varying their intrinsic viscosity (IV) from 1.7 to 6 dg/L while keeping the matrix melt flow rate (MFR) constant. Standard Charpy measurements were completed by a continuous analysis of the impact properties over a wide range of temperatures at fixed test speed. As expected, the higher the IV, the tougher the iPP/EPR blends. However, ductile-brittle transitions as key mechanical descriptors did not correlate linearly with M w , suggesting the macroscopic behavior of the blend to be controlled primarily by the morphology of the EPR particles. Moreover, strong correlations were found between impact mechanical properties, amount of stress-whitening, and strength of the molecular relaxations estimated from dynamical mechanical analysis.

On the influence of nucleation on the toughness of iPP/EPR blends with different rubber molecular architectures

“…Hence, for the non-nucleated systems no significant difference is observed between the ductile-brittle transitions of PP-1.9 and PP-4.2. Remembering that in an earlier study for iPP/EPR blends with 20 wt% of rubber the grade with the highest IV(XCS) outperformed by far its counterpart [28], one might conclude that the fracture behaviour of PP-4.2 is controlled primarily by the size of its particles while PP-1.9 is dominated by inter-particle factors. In other world, the initiation of the damage mechanisms (e.g.…”

Polypropylene/ethylene-propylene rubber (PP/EPR) blends for the automotive industry: Basic correlations between EPR-design and shrinkage

“…As both matrix viscosity and the composition of the EPR is similar for all samples the phase viscosity ratio between matrix and rubber can be assumed to be the driving force for this development [17][18][19][20][21][22]. For heterophasic polymer systems like the investigated ethylene-propylene copolymers (also termed rTPOs for 'reactor thermoplastic polyolefins') the viscosity ratio " between dispersed phase and matrix phase is known to control the final morphology.…”

Mechanical and optical effects of elastomer interaction in polypropylene modification: Ethylene-propylene rubber, poly-(ethylene-co-octene) and styrene-butadiene elastomers

“…The seemingly high difference in flowability resp. molecular weight between the two base polymers results from the wish to have a comparable matrix viscosity, as the PP-I matrix component (PP homopolymer) has a comparable viscosity to the PP-R [10,11]. As external elastomers, three different types selected from two of the aforementioned classes were selected:…”

“…in density when talking about PP and PE mix). The particle size is, however, directly related to compatibility and viscosity ratio, both in extruder blend systems [5][6][7][8][9] and in reactor-made multiphase copolymers [8][9][10][11][12][13]. Especially for materials with good flowability elastomer components of very low viscosity are required which necessarily only deliver a very limited contribution to the impact strength [10].…”

“…910 kg/m 3 and -62°C for a styrene content of 30 wt% -and the good compatibility between the elastomer blocks and iPP allow unique blend properties, especially when targeting soft compositions [26]. In most of the papers cited so far single examples of external elastomer types have been studied in combination with a homogeneous iPP matrix or, in some cases, as compatibilizers between iPP and high density polyethylene (HDPE) [10,27,28]. When modifying reactor-based high-impact EP copolymers, the effect of interactions with the internal EPR and PE phases needs to be considered as well.…”