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

Author(s): O. Balkan | H. Demirer | E. Sabri Kayalı

Journal: Journal of Achievements in Materials and Manufacturing Engineering
ISSN 1734-8412

Volume: 47;
Issue: 1;
Start page: 26;
Date: 2011;
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Keywords: Tensile deformation rate | Polypropylene blends | SEBS thermoplastic elastomer

Purpose: The goal of this study is to examine effects of tensile deformation rates ( ) on tensile properties of polypropylene/poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer (PP/SEBS) blends and to determine suitable 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 φe = 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 1= 1.67 ms–1 and 2 = 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 ( 1), PP and PP/SEBS blends did not fail during tensile tests despite maximum tensile deformation, εmax = 600%; therefore, tensile toughness (UT), stress and strain values at break point (σb and εb) of the blends were not determined. However, at high deformation rate ( 2), all specimens tested in this study failed; a slight decrease in σb of the blends with SEBS elastomer was associated with a significant increase in εb and UT. 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: of tensile testing machines is readily adjustable, while εmax of tensile testing machines is limited. Consequently, in order to evaluate reliably mechanical properties of ductile materials like PP/SEBS blends, must be so high that ductile materials can fail during tensile tests.Originality/value: Tensile testing at high strain rate 2 was concluded to be more suitable for evaluation of mechanical properties of PP/SEBS blends than that of at low strain rate.

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