Mechanical and electrical properties of hybrid carbon nanotubes and graphene nanoplatelet polymer nanocomposites

  • Niall Doherty

Student thesis: Master of Science by Research

Abstract

The directive of this research was to substantiate whether the hybridisation of carbon nanotubes and graphene nanoplatelets (GNP) in polypropylene (PP) nanocomposites (NC) could synergise to create both mechanically and electrically enhanced NC relative to the individual composite of CNT/PP and GNP/PP. Multiwall Carbon Nanotubes (CNT) and (GNP) were incorporated into a (PP) matrix through melt compounding and injection moulding, as individual fillers and in tandem. This was pursued to demonstrate if synergy CNTs and GNPs could create a middle ground between having both strong mechanical and electrical properties. PP/CNT and PP/GNP NC were fabricated to establish a baseline for the morphology, their mechanical and electrical properties, each individually filler induced in PP. This was then compared to hybrid NC, created to indicate if their synergy had a positive effect. Three different hybrid compositions were created, Composition A, a CNT dominant composition (3:1), B a 1:1 ratio and composition C a GNP dominant composition (1:3). All hybrid NC had filler weight fractions (wt.%) of 2.5, 5, 7.5, and 10%. SEM imaging was used to assess the dispersion states of each NC and how they progressed with increasing wt.%. PP/CNT composites dispersed as small clusters or bundles and PP/GNP showed a moderate dispersion. Both formed filler networks at higher wt.%. CNT dispersion was improved with the addition of GNP which reduced cluster sizes. GNP dispersion was improved in all hybrid compositions. XRD profiles of CNT, GNP, A and B hybrid NC display typical 𝝰-phase PP patterns, with a graphitic plane at 2𝞡 =26.6°. While hybrid C at 10wt.% produced different peaks at 2𝞡 = 21.43° and 2𝞡 = 23.71°, either indicating the presence of a β-phase or contamination. CNTs propagate stronger 𝝰1-phase growth while GNPs promote stronger 𝝰2-phase growth. These effects are cancelled out in hybrid NC. DSC found that the mono composites had little and inconsistent effects on the crystallinity of PP, whereas all the hybrid composites increased the crystallinity and crystallisation temperature. Hybrid C showed a second melt point at 127℃, further indicating contamination. Hybrid C displayed a double recrystallisation peak and lower 2nd melt temperature of 150℃ also indicating the presence of a β-phase. Whilst the rest showed consistent 𝝰-phase properties. Tensile testing of the NC found that Hybrid B produced the strongest enhancement to Young’s Modulus;105% compared to neat PP, a 9.5% improvement compared to PP/CNT and a 4.5% improvement compared to PP/GNP. While NC A and C did enhance PP’s YM, they were not more effective than the mono NC. Most composites produced did not improve the tensile strength of PP. Resistance impedance spectroscopy of the NC found the percolation threshold of PP/CNT and PP/GNP NC to be between 5-7.5wt.% and 10-15wt.%, respectively. Hybridisation was shown to lower the percolation threshold, with A and C percolating at 2.5-5wt.% and B between 5-7.5wt.%. Hybrid conductivity was also increased relative to PP/GNP where predictions placed compositions C conductivity 2 factors higher at 15wt.%. However, relative to the PP/CNTs, conductivity was reduced for hybrid NC. Composition B enhanced both mechanical and electrical properties relative to PP/GNP composites. Aspects of PP/CNT can be improved by hybridisation of filler but not in tandem. Composition B at 10wt.% improved its mechanical properties but not its electrical and while composition A did the opposite.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorArthur Wilkinson (Supervisor) & Ian Kinloch (Supervisor)

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