Moisture resistance treatments of natural fiber-reinforced composites: a review

This article extensively explores moisture resistance treatments for natural fiber-reinforced composites (NFRCs), aiming to mitigate the hindrance posed by their high moisture absorption and limited applications. The study delves into five distinct fiber treatments, emphasizing their roles in improving fiber separation, wettability, homogeneity, and crucial fiber/matrix adhesion by removing surface impurities. Chemical treatments applied are instrumental in inducing hydrophobic behavior in treated fibers, validated by Fourier-transform infrared spectroscopy (FTIR) analysis and an observed increase in water contact angle. Scanning electron microscopy (SEM) analysis underscores the treated NFRCs' superior mechanical properties, showcasing extensive fiber breakage and enhanced energy-dissipating mechanisms. The article employs a 2D finite element (FE) model to visually represent the impact of moisture resistance treatments on NFRCs using the thermal-moisture analogy. Treated samples initially exhibit faster moisture absorption than untreated epoxy, creating a moisture gradient. However, over time, treated NFRCs demonstrate reduced moisture absorption compared to neat epoxy, with the hydrophobic interphase actively attracting and subsequently retarding moisture progression. This comprehensive study identifies effective moisture resistance treatments for NFRCs. It explains their mechanisms, helping to understand how these treatments improve the performance of natural fiber-reinforced composites in practical applications.