Elastic properties of polypropylene/ethylene–octene copolymer blends

• Published in: Polymer testing 2010-09, Vol.29 (6), p.742-748
• Main Authors: Svoboda, Petr, Theravalappil, Rajesh, Svobodova, Dagmar, Mokrejs, Pavel, Kolomaznik, Karel, Mori, Keisuke, Ougizawa, Toshiaki, Inoue, Takashi
• Format: Article
• Language: English
• Subjects: Applied sciences; Blends; Breaking; DSC; Elastic properties; Elongation; Ethylene–octene copolymer; Exact sciences and technology; Mechanical properties; Organic polymers; Physicochemistry of polymers; Polymer blends; Polypropylene; Polypropylenes; Properties and characterization; Residual strain; Strain; Stress concentration; Stresses; TEM
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/j.polymertesting.2010.05.014

Blends of polypropylene (PP) and ethylene–octene copolymer (EOC) across the whole composition range (10, 20, …, 80, 90 wt.%) were investigated with focus on mechanical properties. Samples (0–50% of PP) were stretched in a tensile machine to given elongations (100, 200 and 300%) and then the crosshead returned to the initial position. The residual strain values were obtained from the hysteresis curves. These residual strain values were plotted as a function of applied strain and PP content. Stress at given elongation (M100 and M300) was also plotted as a function of PP content. At low PP content (0–20%), residual strain and stress at given elongation are close to those of pure EOC. A steeper increase in these values was observed for concentrations 20–50% of PP. Another set of experiments involved tensile testing to break (full range of concentrations). From these experiments, tensile modulus and stress at break were evaluated and plotted as a function of PP content. Modulus values were close to that of pure EOC in the range of 0–25% of PP. Then, the values start to increase almost linearly with increasing PP content. The mechanical properties of the blends were correlated with the structure observed by transmission electron microscopy (TEM). At 20% PP, there are PP particles with round shape uniformly dispersed in the EOC matrix. When the PP content increased to 30%, the shape of the PP particles changed to elongated. In the case of 40% of PP, the structure resembles a co-continuous one. Differential scanning calorimetry (DSC) revealed the nature of the excellent elastic behavior of EOC. EOC crystals at 7 wt% act as tie points for amorphous chains (physical cross-linking).