## 4 Physical Properties of the Natural Fibers Reinforced Epoxy Composites
### Wear Behaviour  
The sliding wear resistance of the NFRCs shows its ability to resist fiber breakage, polymer degradation, thinning, and separation. The wear characteristics of NFRCs also depend upon the fiber orientation and interfacial adhesion between the reinforced fibers [72; 73; 74]. The wear properties of the epoxy matrix can be significantly improved by incorporating \begin{table}
\begin{tabular}{c c c c c} \hline \hline
** Composites** & \begin{tabular}{c} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Porosity/Volume of** \\ **Void Fraction** \\ \end{tabular} &
\begin{tabular}{c} **Water Absorption \%** \\ **(Till Steady State)** \\ \end{tabular} & **Ref.** \\ \hline Jute/epoxy (25/75) & 1.08 & 7.50 & - & [31] \\ \hline Jute/epoxy (35/65) & 1.276 & 1.09 & 10 & [67] \\ \hline Bagasse/epoxy (3/97), \(5\) mm fiber length & 1.14 & 1.02 & 7.12 & [26] \\ \hline Bagasse/epoxy (3/97), \(10\) mm fiber length & 1.13 & 1.94 & 8.11 & [26] \\ \hline Bagasse/epoxy (3/97), \(15\) mm fiber length & 1.12 & 2.62 & 16 & [26] \\ \hline Hemp/epoxy (9/91) & 1.275 & 3.40 & 0.7 & [18] \\ \hline Hemp/epoxy (25/75) & 1.10 & 6.12 & - & [31] \\ \hline Nettle/epoxy (9/91) & 1.283 & 5.17 & 1 & [18] \\ \hline Hemp + nettle/epoxy (18/82) & 1.35 & 2.46 & 1.2 & [18] \\ \hline Prosopis julifora/epoxy (20/80) & 1.14 & - & - & [68] \\ \hline Abutilion indicium/epoxy (20/80) & 1.12 & - & - & [68] \\ \hline Tapsi/epoxy (20/80) & 1.31 & - & - & [68] \\ \hline Coir/epoxy (30/70) & 1.28 & - & 0.09 & [69] \\ \hline Banana/epoxy(30/70) & 1.10 & - & 0.1 & [69] \\ \hline Sisal/epoxy (30/70) & 1.16 & - & 0.05 & [69] \\ \hline Flax/epoxy (25/75) & 1.07 & 8.09 & - & [31] \\ \hline Jute + hemp/epoxy (25/75) & 1.08 & 7.52 & - & [31] \\ \hline Jute + hemp + flax/epoxy (25/75) & 1.10 & 6.30 & - & [31] \\ \hline (Kevlar + Jute)/epoxy ((20 + 20)/60 \(0^{\circ}\) fiber orientation & 1.23 & 4.27 & - & [70] \\ \hline (Kevlar + Jute)/epoxy ((20 + 20)/60 \(30^{\circ}\) fiber orientation & 1.22 & 5.20 & - & [70] \\ \hline (Kevlar + Jute)/epoxy ((20 + 20)/60 \(45^{\circ}\) fiber orientation & 1.20 & 6.75 & - & [70] \\ \hline (Kevlar + Jute)/epoxy ((20 + 20)/60 \(60^{\circ}\) fiber orientation & 1.20 & 6.75 & - & [70] \\ \hline Agave raw fiber & 1.20 & - & 7.69 & [71] \\ \hline Agave fiber with 5\% NaOH & 1.30 & - & 8.74 & [71] \\ \hline Agave fiber with 10\% NaOH & 13.2 & - & 8.64 & [71] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Physical properties of natural fiber-reinforced epoxy compositesdifferent natural fibers because fiber addition increases mechanical strength [68; 75]. The wear characteristics of the NFRCs improve with the fiber loadings; however, the higher fiber loading reduces the wear characteristics as the formations of voids occur during the fabrications of the composites. Composites of a high degree of wear resistance and coefficient of static friction (CoF) can be used as the bearing materials in automobiles or other applications. [PERSON] et al. [76] investigated the wear behaviour of the banana fibers (short length) and Al(OH)\({}_{3}\) particulate (filler) composites in an epoxy matrix. The findings indicated that combining fiber and filler in an epoxy matrix has a synergistic effect that improves the wear resistance of the composites. Similar observations have also been seen by [PERSON] et al. [77]. [PERSON] and [PERSON] [78] investigated the wear behaviour of NFRCs of agave fiber of different lengths (3, 5, and 7 mm). They found that with an increase in the wt.% of the filler in the composite, the maximum CoF increased, leading to better friction properties of the composites. [PERSON] et al. [79] observed that the Napier fiber-based epoxy composite CoF was higher than the hemp and pineapple fiber-based epoxy composite at each wt.% of filler due to the lower penetration depth in Napier fiber-based epoxy composites. The effect of nanoclay (1, 3, and 5 wt.%) on the mechanical behaviour ofisal fiber-reinforced epoxy composites was investigated by [PERSON] and [PERSON] [80].