**6. Conclusions**

This chapter reviewed the research on NFr-reinforced composites and the constraints that have emerged in their development and serviceability. These constraints must be addressed in order to utilize the potential of NFr successfully. To begin, a suitable surface treatment of the fiber should be performed. Additionally, the study discusses the literature on NFr treatments that researchers have employed to decrease the moisture absorption of NFr composites and increase the compatibility of NFr with the polymer matrix. Many surface treatments are available, such as sodium chlorite, methacrylate, silane, peroxide, enzyme, plasma, ozone treatment, etc. Furthermore, the study describes how surface treatments-based photocatalysts nanoparticle could increase NFr adhesion to their matrix and reduce NFr moisture absorption. Therefore, surface treatments with PHNPs can be regarded for modifying the characteristics of NFr. Moisture resistance and fiber-matrix adhesion can be improved by including specific PHNPs, such as Zinc oxide, titanium dioxide, and copper oxide, inside the cell wall and on the surface of NFr. In addition, these PHNPs exert a high electric static attraction on the nonpolar polymer surface, enhancing the compatibility of the fibers with the polymer matrix. Water-repelling inorganic PHNPs are projected to cover the cell wall components, which could prevent water molecules from accessing the wall components, delaying their swelling and decreasing moisture absorption rate of NFr. The review is given here will aid researchers in better comprehending the many characteristics of NFr composites, therefore facilitating the development of novel green materials with enhanced performance. However, research in this field is extensive, and the current literature discusses using photocatalysts nanoparticle in reducing the moisture uptake by NFr. As a result, it is essential to do a thorough analysis of the current literature to understand the pros and cons of photocatalysis treatment for the specific requirements. In light of this review, it is advised that more research be conducted to determine the impact of matrix modification and fiber length on the characteristics of NFr composite materials.
