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Processing, Structure and Properties of Polyamide 6/Graphene Nanoplatelets Nanocomposites
Mohd Halit, Muhammad Khairulanwar bin
[Thesis]. Manchester, UK: The University of Manchester; 2018.
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Abstract
Graphene Nanoplatelets (GNP) was incorporated into polyamide 6 (PA6) matrix by melt compounding method and the enhancements in the properties of the nanocomposites were studied. Response Surface Methodology (RSM) was employed to assist in the study of processing conditions in melt compounding. RSM analysis revealed that the GNP concentrations to be the most significant term to affect the tensile modulus and crystallinity followed by the screw speed whereas the residence time was found to be non-significant. GNP with 5 μm (G5) and 25 μm (G25) were used in the GNP aspect ratio study. The average flake size of G5 and G25 to was measured to be 5.07 μm and 22.0 μm, respectively with the G5 distributed narrowly whereas the G25 exhibit broad distribution. TGA analysis shown that HT25 is more thermally stable compared to G25 due to some remnants lost during thermal treatment and this was confirmed by EDX and CHNS analysis. XRD profiles of the PA6-G-NC illustrate typical peaks of PA6 crystals phase as well as pure graphite characteristic peak. PA6-G25-NC observed to exhibit slightly higher peak intensity compared to PA6-G5-NC suggesting more formation of PA6 crystals. Similar improvement was observed on PA6-HT25-NC compared to PA6-G25-NC indicating more formation of PA6 crystals due improved dispersion of HT25. DSC on PA6-G25-NC showed higher cooling temperature and crystallinity compared to PA6-G5-NC due to larger surface area of the G25. Similarly, PA6-HT25 showed better improvement in crystallinity over PA6-G25-NC due to increase nucleation sites by the HT25. The thermal conductivity of PA6-G25-NC is slightly higher than the thermal conductivity of PA6-G5-NC but not significant considering the G25 is 5 times larger than G5. Instead, no significant difference was observed between PA6-HT25-NC and PA6-G25-NC. Addition of GNP increased the thermal stability of the PA6-G-NC systems under both nitrogen and air atmospheres regardless of the GNP aspect ratio. The viscoelastic properties showed insignificant difference between PA6-G5-NC and PA6-G25-NC. The inefficient improvement by G25 might be due to agglomeration formed during processing. The storage modulus and tan δ of PA6-HT25-NC decreased but the Tg significantly improved compared to PA6-G25-NC. This was assumed to be because of improved dispersion of HT25 but reduced interfacial interaction after the heat treatment. The shear storage modulus, G’ and complex viscosity, |η*| were observed to increase with increasing GNP content with more pronounced improvement seen on PA6-G25-NC compared to PA6-G5-NC. However, no network percolation threshold was observed until 20 wt.% of GNP. The poor interfacial interaction of HT25 resulted in lower G’ and |η*| compared to G25. Tensile test results showed typical improvement with PA6-G25-NC having higher tensile modulus compared to PA6-G5-NC. Further enhancement was obtained with PA6-HT25-NC suggesting improved dispersion and volume of constrained chains mobility despite the poor surface interaction. Comparison with Halphin-Tsai modulus revealed that the effective modulus to be 150 GPa for G5 and 200 GPa for G25. The water uptake measurement results showed that GNP reduced the water uptake percentage and diffusion coefficient especially with G25. The test conducted on saturated PA6-G-NC results in improved thermal conductivity due to the high thermal conductivity of water but the viscoelastic and tensile properties severely reduced due to plasticisation effect.