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Melt blending is a promising and practical method to prepare electrical conductive polymer composites containing multiwalled carbon nanotubes (MWCNTs). The key is to achieve a good dispersion of MWCNTs in polymer matrix. In this study, olefin block copolymer (OBC)/MWCNTs composites were prepared using co-rotating twin-screw extruder with high rotation speed and the influence of screw rotation speed on the dispersion, shortening of MWCNTs and the macro-properties of composites was systematically investigated. It was found that the entangled agglomerates of MWCNTs could be easily destroyed by using high rotation speed and an improved dispersion of MWCNTs was observed as increasing of rotation speed from 50 to 500 rpm. However, with further increasing of rotation speed from 500 to 1000 rpm, no better dispersion was evidenced but a reduction of nanotubes length was detected. As a result, the best electrical conductivity and mechanical properties of OBC/MWCNTs composites were achieved via using the rotation speed of 500 rpm. And the electrical percolation threshold obtained was about 1.5 wt%. This study provides significant guidance for large-scale preparation of conductive composites materials by using co-rotating twin-screw extruder with high rotation speed. [ABSTRACT FROM AUTHOR]

In this study, the crystalline morphology and mechanical property of Olefin Block Copolymer (OBC) were tailored by adding a small amount (up to 10 wt%) of ultrahigh molecular weight polyethylene (UHMWPE). To do this, OBC and UHMWPE was solution blended first and then subjected to compression molding or injection molding, respectively. It was found that a small quantity of UHMWPE (0.5 wt%, 1 wt%) can be fully mixed with OBC, while phase separation occurs when UHMWPE content is higher than 2.5 wt%, as suggested by SEM and DSC results. For compression molded samples, an obvious increase of Young's modulus from 12 MPa to 22 MPa while maintaining the good elasticity of OBC was observed as the content of UHMWPE is less than 2.5 wt% (in the phase miscible range). With further increasing of UHMWPE content to 10 wt%, only slightly increased Young's modulus is seen. Thus the miscibility between OBC and UHMWPE plays an important role in determining the mechanical property for compression molded samples. However, a continuous increase of Young's modulus was observed with the increase of UHMWPE content for samples obtained via injection molding, with a slight increase (from 23 MPa to 40 MPa) as the content of UHMWPE is less than 2.5 wt%, while with a large increase (from 40 MPa to 156 MPa) as the content of UHMWPE increases from 2.5 wt% to 10 wt%, accompanied with a greatly decrease of elongation (from 1100% to 50%). Even elastomer-to-plastic transition takes place when the content of UHMWPE is large (5 wt%, 10 wt%). Structural analysis of injection-molded samples shows that shish-kebab-like structures can be successfully induced as addition of UHMWPE along with gradually increased crystal orientation. It was interesting to find that small-addition of UHMWPE favors increased tie-effect due to the miscibility between OBC and UHMWPE, which is helpful to the elasticity retaining as well as strength enhancement, while large-addition of UHMWPE gives rise to phase separation and mixed shish-kebabs (OBC/UHMWPE hybrid shish-kebabs and UHMWPE homo-shish-kebabs), leading to elastomer-to-plastic transition. [ABSTRACT FROM AUTHOR]