**1. Introduction**

Environmental concerns and escalating social demand for the adoption of less hazardous composites materials have prompted a paradigm shift toward employing NFr as a replacement for synthetic and non-renewable reinforcements. This has led to the development of what are usually known as "Green Composites," or composites made from biodegradable or renewable raw materials with lower environmental effect [1]. The application of NFr in polymer composites is expanding in many sectors such as automotive, furniture, packaging and construction. The utilization of NFr is based on its advantages including decreased tool wear, inexpensive, light weight, high toughness, good specific strength characteristics, ease of separation, improved energy recovery, carbon dioxide sequestration, and biodegradability, as well as

their sustainable renewable characteristics, and having competitive mechanical performance are just some of the significant properties that make them suitable for us. NFr are available in a broad multitude of types and are often used as fillers and reinforcement [2].

However, NFr reinforced composites have a number of disadvantages, including limited wettability, poor fiber/polymer matrix performance, and the ability to absorb more water and moisture [3]. For the majority of NFr users, the influence of moisture absorption properties on NFr-reinforced composites became a warning signal. In reality, this absorption destroys the adhesion force between the fiber and matrix in an enormous manner. Subsequently, it diminishes the composite's strength in a manner proportional to the absorption duration or nature. In addition, it results in inadequate stress transfer and ultimately specimen fracture over time. The moisture absorption involves the following mechanisms: at first, the water molecule penetrates the micro gaps that are present within the chains, then the penetrated water diffuses deep within the chain via the capillary transport mechanism, and finally, the fibers swell due to the micro gaps [4]. The hydrophilic nature of NFr and the presence of components such as wax and pectin preclude an efficient reaction with the thermoset or thermoplastic polymer, therefore preventing the reinforcement and matrix from bonding better. Improved bonding between NFr and resin is critical for stress transmission from the matrix to the reinforcement. As a result, a weak interface reduces the physical and mechanical characteristics of composites [5].

To resolve this concern, chemical treatments of NFr are utilized to enhance the physical, mechanical, and thermal characteristics of the composites. According to Edeerozey et al. and Baiardo et al., chemical treatments can increase interfacial interaction between NFr and polymer matrix by diminishing the hydrophilicity of NFr, cleaning the surface of NFr, augmenting fiber roughness, and lowering moisture content of NFr [6, 7]. The numerous chemical processes were conducted for NFr, such as alkaline, silane, and stearic acid. Further studies have shown that the chemically treated NFr composite materials have superior tensile, bending, impact, and interlaminar shear strengths and hardness levels compared to untreated composites.

According to Njuguna et al., PHNPs are a promising filler material for improving the mechanical and physical characteristics of NFr polymer composites while lowering moisture absorption [8]. Since nanoscale fillers are often defect-free, their applications in polymer composite area setup can overcome the limitations of the traditional/conventional micrometer scale. Owing to the uniform and homogenous dispersion of PHNPs, a large matrix-PHNPs interfacial area is formed, which influences relaxation behavior and ensues the mechanical, molecular mobility, and thermal characteristics [9, 10]. PHNPs are often found in the minor zone., whereas just a few microparticles contribute to the deformation of the plastic area. This enables PHNPs to enhance the fracture and mechanical characteristics of fragile matrixes. PHNPs with a higher surface area are of particular interest because they provide superior reinforcement for the production of nanocomposites [9]. PHNPs are typically included as a percentage of the total weight of the composite for nanocomposite advancement [11]. The particular surface area of PHNPs has a significant effect on the composite characteristics, which is continuous. The basic principle behind nanocomposites is to make a high interface between the PHNPs and the matrix. The homogenous dispersion of PHNPs is frequently problematic [12]. Nanocomposites are a type of high-performance material that has exceptional characteristics, combinations, and design options [13].

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


#### **Table 1.**

*The implications of integration of PHNPs into NFr.*

Despite the fact that review papers and even books have been published on the totality impact of surface treatment on NFr in terms of moisture absorption, mechanical performance, and morphology [2, 14], the researchers believe that a precise book or review papers on the overall surface treatment with PHNPs is an essential first step in providing immunity to NFr polymer composites against quick and unnecessary degradation, resulting in the production of NFr polymer composites with high water repellency and strength properties, has not yet been published; nevertheless, it is anticipated that such a book will be of considerable importance to the composite scientific community. In the published literature, we found no review or book has been written to evaluate the impact of surface treatment with inorganic PHNPs on the hydrophobicity of NFr and relate that with improving the mechanical, physical, and chemical attributes of its composite. In order to achieve this goal, we tabulated in **Table 1**, the effects of the incorporation of PHNPs into NFr on moisture absorption and mechanical properties. The findings will serve as a scientific benchmark for developing high-performance polymer composites incorporating NFr as reinforcement, particularly for use in building applications such as floor decking, door and window frames.
