## 6 Thermal Behaviour of Epoxy-Based NFRCs  
When NFRCs are exposed to high temperatures, they degrade due to the thermal damage of the composite components. The thermal degradation of NFRCs is mostly reflected due to the natural fiber degradation as its thermal stability is lower than epoxy [122; 123]. Natural fibers have hemicellulose, cellulose, and lignin as primary components. The thermal degradation of the natural fiber is divided into four phases. The first stage involves water loss and low-molecular-weight component degradation at a temperature ranging from 50 to 150 \({}^{\circ}\)C for water that is not chemically bound to the fiber. The second step involves hemicellulose breakdown at temperatures ranging from 200 to 350 \({}^{\circ}\)C. The third stage is associated with cellulose degradation (typically between 320 and 400 \({}^{\circ}\)C), whereas the fourth stage is associated with lignin degradation which can occur at temperatures ranging from 100 to 900 \({}^{\circ}\)C [124]. [PERSON] et al. [125] studied the effect of bagasse fiber (20 mm) and cardanol-epoxy resin wt.% on the thermal strength of the reinforced composites. They reported higher thermal strength of the reinforced composite than pristine polymer. In a similar study, [PERSON] et al. [94] studied banana fiber-reinforced epoxy composites' mechanical, thermal, and morphological characteristics. They chopped the banana fibers into similar average lengths of 10 and 20 mm and prepared two sets of bio-composites by compression moulding with different wt.% of epoxy resin (0-20%). The composites' thermogravimetric analysis (TGA) showed high thermal stability up to 220 \({}^{\circ}\)C.  
Figure 3: Effect of fiber loadings and length on the mechanical characteristics of the banana fiber-reinforced epoxy composites.  
Since thermal degradation depends upon the NFRC components, the chemical treatment affects these components. In this connection, [PERSON] et al. [126] studied the effect of fiber treatment (NaOH), boiling water, and their combination on the thermal stability of composites. Alkali-treated fibers exhibited higher thermal stability with improved tensile strength and modulus of elasticity compared to untreated fiber-reinforced composites. [PERSON] et al. [41] found that 6 wt.% NaOH-treated bamboo fiber-reinforced composites exhibited higher thermal stability than untreated bamboo fiber-reinforced composites. Although bamboo fiber composites disintegrated at lower temperatures than neat epoxy, the thermal stability of the bamboo fiber composites was still good. As a result, bamboo fiber composites have the potential to be used in engineering applications. [PERSON] et al. [127] investigated the influence of clay content on the thermal behaviour of cellulose fiber-reinforced epoxy composites. The addition of nano-clay improved the heat resistance of the composite while increasing the char residue over plain epoxy, since the coefficient of thermal expansion (CTE) of epoxy resin is significantly greater than reinforcing cellulose fibers. Therefore, the CTE falls as the fiber concentration increases. Adding some filler also increases the thermal stability of the NFRCs [128]. [PERSON] et al. [76] investigated the effect of adding Al(OH)\({}_{3}\) on thermal behaviour and found that composite became more fire resistant. [PERSON] et al. [129] added clay as filler in kenaf fiber-reinforced composite and reported that the addition of clay increased thermal stability.  
Thermal characteristics of NFRCs improve with fiber treatments with NaOH and boiling water. Furthermore, adding filler can improve the thermal properties of the NFRCs. Thermal degradation of the NFRCs also depend on fiber loadings. However, fiber loadings beyond certain limits harm the thermal characteristics of NFRCs.