**3.1 Moisture absorption**

Humidity aging is well acknowledged as a significant contributor to the longterm degradation of an organic matrix subjected to the environment or in contact with an aqueous medium. Moreover, humidity aging has a detrimental influence on the mechanical characteristics and dimensional stability of composites [24].

*Utilizing Photocatalysts in Reducing Moisture Absorption in Composites of Natural Fibers DOI: http://dx.doi.org/10.5772/intechopen.106543*

**Figure 2.** *Schematic representation of impact of moisture on Fiber-Matrix Interface.*

Consequently, it is critical to research the moisture absorption behavior of NFr composites to determine the possible impacts of the absorbed water and the durability of the NFr composites utilized in the humidity environment [25, 26]. The majority of studies believe that moisture penetrates composite materials through three distinct mechanisms. The primary process is due to water molecules diffusing into the microgaps between polymer chains. The second mechanism includes capillary transportation through the holes and defects caused by insufficient wettability at the interfaces between the fiber and matrix. The third mechanism is the transfer through microcracks formed in the matrix during the combining process with fiber or due to fiber swelling [26, 27]. Moisture quickly hydrolyzes matrixes such as polyester, resulting in a reduce in molecular weight of polymer [24, 28]. Temperature and humidity have an impact on the rate of decomposition of NFr [28]. In a humid climate, this would significantly lose mechanical characteristics for NFr [29]. The loading of NFr has a significant impact on the moisture absorption characteristics. IAS et al. [30] evaluated the impact of fiber loading (10–40 wt%) on the moisture absorption capacity of a kenaf/polyester composite at ambient temperature. Moisture absorption increased with increasing fiber volume in composites, it was reported. The water uptake process of a NFr is shown in **Figure 2**.
