Effect of water on the mechanical and thermal properties of natural fibre reinforced hybrid composites

Research and development on natural fibre-reinforced composites (NFRCs) is constantly increasing and their use is expanding into new areas of applications. One of the main problems is the absorption of humidity due to the hydrophilic characteristic of the natural fibre, which leads to low interfacial adhesion between the fibre and the hydrophobic matrix and consequently, relatively low mechanical properties. One method to reduce the sensitivity of mechanical and thermal properties of NFRCs to water uptake is the hybridization by using synthetic fibres and/or fillers. This research investigates the effect of ageing on the mechanical and thermal properties of different natural fibre and hybrid composites. Pure jute, pure jute modified with two different types of fillers (micro glass and nano TiO2) and interlaminar hybrid jute/glass fibre-reinforced polymer composites were fabricated. Bulk specimens were used to measure the diffusion coefficient of water in the composites, and tensile and flexural specimens were used to measure the mechanical properties of the conditioned specimens. A thermogravimetric technique (TGA) analysis was used to measure and compare the degradation temperature of all composites studied as a function of ageing. Finally, a scanning electron microscopy (SEM) analysis was performed to examine the fracture surfaces of the specimens tested. It was found that the water uptake decreases by adding the synthetic fibres and the fillers to the NFRCs. The mechanical properties of the composites (the tensile and flexural strength and modulus) tend to decrease with the increase of water content, and they are partially recovered after desorption at the same temperature as the absorption. The thermal properties of natural fibre composites are affected by water absorption and by the hybridization. The hybridization of the composites increased the maximum degradation temperature when compared to the pure jute, while the addition of fillers improved the thermal properties of aged specimens (the initial degradation temperature values were higher than those for the pure jute composites).