Processing and properties of melt processed high density polyethylene-carbon nanofiller composites

• Main Author: Xiang, Dong
• Published: Queen's University Belfast 2015
• Subjects: 620
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676504

The main aim of this work was to investigate the process-structure-property relationship of high density polyethylene (HOPE)/carbon nanofiller composites. A secondary aim was to develop thin thermoplastic films with enhanced electrical and mechanical properties for the potential use in aerospace applications. Three types of carbon nanofillers with different dimensions, multi-walled carbon nanotubes (MWCNTs), graphite nanoplatelets (GNPs) and carbon black (CB) respectively, were used to reinforce the polymer matrix. The melt-mixed HOPE/carbon nanofiller composites were processed by compression moulding, biaxial stretching and blown film extrusion, and the structure and properties of the resulting composites were characterised. The crystallinity and melting temperature of the material are barely influenced by the addition of carbon nanofillers, while the crystallization temperature is slightly increased due to a heterogeneous nucleation effect. The incorporation of carbon nanofillers has a positive effect on the modulus of the composites studied and a negative effect on the stress at break and strain at break. The relative effectiveness of generating rheological and conductive networks in the polymer is as follows: GNPs < CB < MWCNTs. The inclusion of carbon nanofillers led to significant strain hardening during the biaxial stretching of the material. The carbon nanofillers were further dispersed in the matrix by biaxial stretching. The mechanical properties of all the HOPE/carbon nanofiller composites were clearly improved after biaxial stretching. However, the volume resistivity of biaxially stretched HOPE/carbon nanofiller composites, at loadings lower than 4 wt%, was increased due to the deagglomeration of nanofillers and increased inter-particle distance. Blown films of the HOPE/MWCNT composites were manufactured at blow-up-ratios (BURs) of 2 to 3. The stress at break and strain at break of the composite films increases steadily with increasing BURs. Blown film extrusion also has a destructive effect on the conductive network of MWCNTs. However, there is no significant increase in the resistivity of the composite containing 8 wt% MWCNTs after film blowing at increasing BURs due to a sufficient density of nanotubes forming a robust conductive network .