Dorina Chipara

On orientation memory in high density polyethylene - Carbon nanofibers composites

Abstract An orientation memory effect in high density polyethylene (HDPE) filled with vapor grown carbon nanofibers (VGCNF) is reported. Two-dimensional X-ray (2DXR) confirmed the reorientation of HDPE crystallites upon the uniaxial stretching of HDPE and HDPE filled by VGCNFs. This anisotropy of 2DXR spectra was decreased by heating all stretched samples (loaded or not loaded by VGCNFs) from room to the melting temperature of HDPE. Upon cooling these samples to room temperature, it was noticed that only the nanocomposite retained a weak partial (uniaxial) order, while HDPE showed a completely isotropic 2DXR spectrum. It was concluded that during the stretching of nanocomposites the crystallites and VGCNFs were aligned along the uniaxial stress. Upon heating, the crystalline phase was melted, while the orientation of the VGCNFs was not significantly disturbed. The recrystallization of the polymer started preferentially from the VGCNF – polymer interphase, resulting into an anisotropic crystalline structure.