Date of Award

1-31-2023

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Nanocomposite coatings, Dropcasting, Poly(methyl methacrylate), Graphene nanoplatelets, Thermoplastics

Supervisor

A.T. Algas

Supervisor

R.Riahi

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Graphene/polymer nanocomposite coatings are being considered as corrosion resistant coatings on aluminum alloy surfaces. In certain applications in vehicles these composites should also show good tribological and mechanical properties. In this study, graphene nanoplatelets (GNP) (0.5, 1.0, 3.0, and 5.0 wt. %) were incorporated into poly(methyl methacrylate) (PMMA), and deposited on the surfaces of 6061Al alloy using a dropcasting method. The incorporation of 1 wt. % GNP increased the tensile strength of PMMA from 33 MPa to 49 MPa. Further increase of GNP to 3 and 5 wt. % reduced the tensile strength to 43 and 36 MPa, respectively. The composites with 1, 3, and 5 wt. % GNP showed lower fracture strain compared to neat PMMA and 0.5G-PMMA. Permeability studies showed a reduction in the water vapour transition rate (WVTR) from 707.66 g/(m2.d) for the neat PMMA to 412.19 g/(m2.d) for 1G-PMMA, then an increase occurred for composites with higher GNP contents. Electrochemical Impedance Spectroscopy (EIS) was used to evaluate corrosion properties of the coatings. According to the Nyquist and Bode plots, nanocomposite coatings showed an increase in coating resistance (Rcoat), charge transfer resistance (RCT), and value of impedance modulus at the lowest frequency (|Z|0.01 Hz) compared to neat PMMA. The results also showed that 1G-PMMA had the highest values of Rcoat, RCT, and |Z|0.01 Hz, which were 37105 Ω, 1.84 × 105 Ω, and 85113.82 Ω, respectively. Raman images of nanocomposite revealed that an increase in the amount of GNP caused graphene agglomeration, which resulted in the formation of defects at the graphene-matrix interfaces. Also a higher number of shear fronts on the fracture surface of 3G-PMMA was observed compared to 1G-PMMA. Defects was suggested to reduce corrosion resistance of G-PMMA coatings. Incorporation of 1.0 wt.% GNP decreased friction and specific wear rate in comparison with neat PMMA. However, the specific wear rate increased significantly with the further addition of GNP. Agglomeration of GNPs at high concentrations likely accelerated wear. The average steady-state COF of neat PMMA was 0.25 while the lowest average steady-state COF of 0.19 was obtained for 5G-PMMA. But, this was due higher amount of composite material being transferred to the counterface. In summary, 1G-PMMA had a high tensile strength and showed the lowest permeability to water vapour, and provided good resistance to corrosion and wear.

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