Optimizing the balance between impact strength and stiffness in polypropylene/elastomer blends by incorporation of a nucleating agent

Abstract

Isotactic polypropylene (iPP) blends were prepared with two different thermoplastic elastomers, a triblock copolymer styrene–ethylene butylene–styrene (SEBS) and a metallocenic ethylene‐octene copolymer (EO). The mechanical properties and morphology of blends with 0–50 wt% elastomer were studied to determine the influence of the presence of the elastomer on the improvement of toughness. The addition of a nucleating agent as a third component exerted a significant effect on the overall properties. Dynamic mechanical properties, flexural modulus, and impact strength as well as morphology were studied for nucleated and nonnucleated iPP/SEBS and iPP/EO blends. The improvement of impact properties found in binary blends was accompanied by a decrease in stiffness. However, the addition of the nucleating agent provided a good balance between impact strength and stiffness. From the results, SEBS was determined to be a better impact modifier for iPP than EO. The nucleated iPP/SEBS blends demonstrated improved mechanical properties compared with both the nucleated iPP/EO blends and the nonnucleated blends. POLYM. ENG. SCI., 48:80–87, 2008. © 2007 Society of Plastics Engineers

Thermal & morphological evaluation of linear and radial SEBS- polypropylene blends

“…In the other hand, it can observe that SEBS presence causes a slight decrease in melting temperature when SEBS amount increase in blends, being more significant for linear than radial SEBS, indicative that PP crystalline phase is changing due the presence of processing oil added. There are reports that SBS and SEBS have a nucleating effect in blends with isotactic PP and nylon 6, which it is not observed in present work [7] . …”

“…The addition of a nucleant agent has been studied to improve the mechanical properties in a PP/SEBS proportion close to 50% [7] . An important issue in SEBS-PP blends is the processing conditions (temperature profile, screw and feeding speed), due to mechanical properties on phase dispersion can vary according to the conditions.…”

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

“…The respective influence of nucleating agents (α or β) on the mechanical performances of heterophasic systems composed of an iPP matrix and an ethylene-propylene rubber (EPR) is still controversial, consequence of a lack of published experimental data. Whereas several studies have reported positive effects of nucleation on the fracture resistance of iPP/EPR blends [6][7][8][9][10][11][12], other contributions showed limited (for β-nucleation) [4,[13][14][15][16] or even negative (for α-nucleating agents) ones [4,17,18]. The goal of the present investigation was to identify potential coupling effect between the matrix crystalline structure induced by nucleation and the morphology of the rubbery phase in order to clarify this apparent contradiction.…”

Improvement of the impact strength of ethylene‐propylene random copolymers by nucleation

“…In both cases, however, polymer structure plays a decisive role for the actual effects. Toughness increase by α-nucleation has been demonstrated for high-flow PP homopolymers 10 , for blends with external elastomers 24 and for heterophasic ethylenepropylene copolymers with specific elastomer design 25 . No such data, which reports the enhancement of impact resistance by specific nucleation, have been shown for random copolymers so far.…”