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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.

Morphological and mechanical properties of hot gas welded PE, PP and PVC sheets

Balkan O., Demirer H., Yildirim H.

Journal of Achievements in Materials and Manufacturing Engineering

2008

Vol. 31, nr 1

60-70

Purpose: The goal of the paper is to investigate morphological and mechanical properties of hot gas butt-welds on polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) sheets for four different procedures, which are single and double V-welds with and without a welding shoe. Design/methodology/approach: Welding energy (Ew), which is transferred onto weld surfaces, was calculated to evaluate weld quality. Morphology of welds was analyzed by polarized light, stereo, and scanning electron microscopy. Findings: Polarized light microscopy studies indicated that the heat-affected zone (HAZ) consists of welding rod core, molten zone, and deformed spherulitic zone. The results of tensile, bending, and impact tests indicated that the weld strengths of PVC sheets are lower than those of PE and PP sheets. When the welding shoe was used, weld strength increased significantly for each material due to the presence of sufficient welding pressure and the effective heating on surfaces. Practical implications: The best results were attained for the double V-welds with the welding shoe. Originality/value: Morphological and mechanical properties of hot gas welded PE, PP and PVC sheet were evaluated.