Fabricating and Characterizing Multifunctional Graphene Nanoplatelets-based Polylactide Nanocomposites

• Author / Creator

  Zhang, Qi

• With rising environmental concerns related to plastic pollution and dependency on petrochemical resources, biopolymers have been gaining attention. Polylactide (PLA) as one biopolymer option has attracted much interest. However, the low thermal and electrical conductivities limit its full application in advanced engineering devices. The main objective of this thesis was to fabricate multifunctional PLA polymers with high conductivity and mechanical properties comparable to pure PLA polymer by incorporating graphene nanoplatelet (GNP).
  Heat conduction in polymer nanocomposites is mainly controlled by the transport of phonons. A weak interfacial compatibility between filler and polymer may result in high interfacial thermal resistance and robust phonon scattering, resulting in low thermal conductivity. To improve the
  dispersion of pure graphene nanoplatelet (pGNP) and interfacial bonding between pGNP and PLA matrix, the surface of pGNP was non-covalent modified with tannic acid to obtain functionalized graphene nanoplatelet (fGNP). Moreover, phonon and heat transfer are more pronounced for
  nanofiller alignment. Therefore, in this work, the two-step processes solution-blending followed by hot compression molding was applied to prepare aligned pGNP/PLA and fGNP/PLA nanocomposites.
  The analysis of Fourier transform infrared spectroscopy and X-ray diffraction of fGNP and pGNP powders suggested the success of non-covalent modification. Scanning electron microscopy results indicated improved interfacial adhesion. Moreover, alignment of pGNP and fGNP in PLA specimens was revealed by transmission electron microscopy and thermal conductivity testing. Therefore, PLA nanocomposites exhibited anisotropic thermal conductivity perpendicular and
  parallel to the in-plane direction of the samples. Anisotropy indices (the ratio of thermal conductivity in parallel to perpendicular direction) of 18.5 and 21.6 were ascertained for samples with 16 wt% pGNP and 16 wt% fGNP loading, respectively. A greatly enhanced in-plane thermal
  conductivity of 8.65 W/mK was achieved for PLA nanocomposite with 16 wt% fGNP, which was a 43-fold and 1.5-fold increase compared to neat PLA and nanocomposite reinforced by 16 wt% pGNP, respectively.
  Moreover, in-plane electrical conductivity was substantially increased, with the electrical percolation threshold of GNP between 6 and 8 wt%. With the incorporation of 16 wt% fGNP and pGNP, respective conductivities of 0.8 S/cm and 0.5 S/cm reached more than 13 orders of magnitude higher than the value of pure PLA. Besides, embedding 12 wt% GNP in
  nanocomposites can impart an average total electromagnetic interference shielding effectiveness of 20.71 dB (pGNP/PLA) and 27.91 dB (fGNP/PLA), respectively, which exceeds the required minimum value (20.0 dB) for commercial electromagnetic interference shielding application.
  Other testing revealed nanocomposites exhibiting improvement in the Young’s modulus (3.51 GPa at 16 wt% fGNP) and storage moduli (12.1 GPa at 40°C for 16 wt% fGNP) as well as better thermal stability upon fGNP incorporation accompanied by strong adhesion to PLA matrix.
  Overall, the simple hot-compression process combined with the non-covalent modification was effective in manufacturing multifunctional fGNP/PLA nanocomposites with improved electrical and thermal conductivity, better thermal stability, as well as mechanical properties, which may enable the applications of GNP/PLA nanocomposites in electric/electronic, automobile devices, and other potential fields requiring efficient directional thermal management.

• Subjects / Keywords

  • Polylactide
  • Anisotropic Thermal Conductivity
  • Alignment
  • Graphene Nanoplatelets

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-0c1v-zp86

• License

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