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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2011

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Effects of deformation rates on mechanical properties of PP/SEBS blends

Balkan O., Demirer H., Kayali E. S.

Journal of Achievements in Materials and Manufacturing Engineering

2011

Vol. 47, nr 1

26--33

Purpose: The goal of this study is to examine effects of tensile deformation rates ( e) on tensile properties of polypropylene/poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer (PP/SEBS) blends and to determine suitable S for accurate and reliable evaluation of mechanical properties of the blends in accordance with the results of Izod impact tests. Design/methodology/approach: PP/SEBS blends containing ϕ_e= 0, 2.5, 5 and 10 volume % of SEBS thermoplastic elastomer were compounded using a twin-screw extruder, and then moulded with an injection moulding machine. Morphology of PP/SEBS blends were analysed by scanning electron microscopy (SEM). Mechanical properties of the blends were investigated tensile and Izod impact tests. Tensile deformation rates έ=1.67 ms^-1 and έ₂=16.67 ms^-1 were used to determine ultimate tensile properties. Findings: Morphological analyses revealed that SEBS elastomer particles were well-dispersed throughout PP matrix in irregular forms with a narrow size distribution and evidenced a two-phase system formation. At low deformation rate(έ), PP and PP/SEBS blends did not fail during tensile tests despite maximum tensile deformation, ε_max = 600%; therefore, tensile toughness (U_T), stress and strain values at break point (σ_b and ε_b) of the blends were not determined. However, at high deformation rate ( έ₂), all specimens tested in this study failed; a slight decrease in ob of the blends with SEBS elastomer was associated with a significant increase in ε_b and U_T. Strain-rate-sensitivity of PP/SEBS blends was promoted with SEBS elastomer. Research limitations/implications: Mechanical properties determined through high-velocity tests are beyond the scope of this study. Practical implications: έ of tensile testing machines is readily adjustable, while ε_max of tensile testing machines is limited. Consequently, in order to evaluate reliably mechanical properties of ductile materials like PP/SEBS blends, e must be so high that ductile materials can fail during tensile tests. Originality/value: Tensile testing at high strain rate έ₂ was concluded to be more suitable for evaluation of mechanical properties of PP/SEBS blends than that of at low strain rate έ₁.