High density polyethylene (HDPE) nanocomposite reinforced with 2 weight percent carbon nanotube (CNT) was fabricated using mechanical milling method. Microscopic evaluations revealed appropriate dispersion of CNTs in the matrix, and tensile tests demonstrated that the tensile strength was increased by 17%. Thermal and mechanical properties of the composite samples were investigated after equal channel angular pressing (ECAP) for up to 3 passes via route A at temperature of 80°C. Density and differential scanning calorimetry (DSC) results represented decrement in crystallinity after ECAP which was led to drop in hardness and tensile yield strength of the deformed samples. Micro Vickers and Shore D hardness results also revealed clear anisotropy in mechanical properties caused by ECAP. Dilatometry results and observation of the impact fractured surfaces of deformed samples demonstrated that oriented structures formed in amorphous and crystalline regions of the composite. This microstructure evolution also caused increase in impact strength of ECAP deformed specimens. Dynamic mechanical behavior of the processed samples was modified following ECAP. The α and γ relaxation temperatures were decreased due to the reduction of thickness of crystalline lamella obtained from DSC results, in 1 pass ECAP deformed sample. Dynamic storage and loss modulus of 3 passes ECAP deformed samples were significantly decreased due to the sharp drop in their crystallinity. KEYWORDS carbon nanotube, equal channel angular pressing, oriented structure, polyethylene 1 | INTRODUCTION Many solid state forming processes have been recently used to improve structure and properties of monolithic polymers and polymer matrix composite materials. Uniaxial 1 and biaxial 2 deformation, rolling, 3 and extrusion 4 are among the shaping techniques that alter the structural and mechanical properties of polymers and their composites by imposing large plastic deformations. These deformations are usually accompanied by significant reduction in the cross-sectional area of the initial sample. However, in severe plastic deformation (SPD) techniques, it is possible to impose large plastic deformation without any change in the initial dimensions of the billet. Among the various SPD techniques, equal channel angular pressing (ECAP) is widely usedto enhance structural and mechanical properties of metals and metal matrix composites. 5 The successful experience of applying ECAP to several metallic systems causes a motivation for some researchers to use this type of SPD technique to improve the properties of polymeric materials. As illustrated in Figure 1, the process consists of pressing a specimen through a die with 2 equal cross-section channels intersecting at an angle. (Here for simplicity, the angle of intersection of 2 channels is taken 90°.) By moving through the intersection of 2 channels, the sample experiences simple shear deformation. Because the cross section of the billet is maintained constant during ECAP, it is possible to press a sample repetitively by...
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