Effect of graphene oxide coating on mechanical, thermal, moisture and morphological behaviour of alkali-treated coconut tree primary flower leaf stalk fibre-reinforced polymer composites

In this study, the effect of graphene oxide (GO) coating on the mechanical, thermal, moisture and morphological properties of alkali-treated coconut tree primary flower leaf stalk fibre (CPFLSF)-reinforced epoxy composites has been investigated. Compression moulding was used to prepare composite laminates using different fibre lengths (2, 4, 6 and 8 mm) referred to as GO-2CPFLSFC, GO-4CPFLSFC, GO-6CPFLSFC and GO-8CPFLSFC, respectively, and neat epoxy resin (LY556) as a control. Tensile, flexural, impact and hardness tests showed notable enhancement of the mechanical properties due to GO coating, with GO-4CPFLSFC being the best-performing composite. Tensile strength and modulus were enhanced to 74 MPa and 6.8 GPa, respectively, and flexural strength and modulus were improved to 135 MPa and 9.4 GPa. The impact and hardness properties also improved significantly, suggesting enhanced toughness and abrasion resistance. But, with longer fibre lengths (GO-6 and GO-8), there was a slight decrease in properties due to agglomeration. Thermogravimetric analysis (TGA) studies showed improved thermal stability, with a higher onset degradation temperature (Tonset = 215 °C) for GO-4CPFLSFC, due to the barrier effect and thermal stability of GO. Water absorption tests confirmed that the GO coating significantly decreased water absorption by blocking hydrophilic channels and strengthening fibre -matrix interactions. Fractured surface scanning electron microscopy studies showed a shift from fibre pull-out (lower GO content) to fibre breakage, indicating enhanced bonding. The incorporation of GO and surface functionalisation was confirmed by EDAX analysis, which found carbon and oxygen, with 78.13 wt% carbon and 21.87 wt% oxygen. The optimised GO-4CPFLSFC composite may be used for lightweight automotive interior parts, construction panels, furniture parts, sports parts, protective parts and other semi-structural parts with the demand for low weight, low-temperature resistance, mechanical strength and resistance to the environment.