**5.4 Addition of nanoparticles**

The use of nanoparticles to enhance the properties of NFPCs have been widely reported [99, 153, 154]. Nanoparticles are inorganic materials which possess a very high surface to volume ratio in which one or its entire dimension is less than 100 nm [155]. The addition of these nanoparticles influences the crystallization process during the solidification of the polymer composites leading to improved mechanical and thermal properties. These particles can be modified to selectively interact with a particular phase of the composites in a controlled manner [23, 156–158]. They can also be modified to act as a compatibilizer and react with both the matrix and the fibers to bring about good interaction and a better composite with stress transfer behavior.

Vargas et al. [159] reported the influence of nanofilters on some properties of polypropylene including mechanical properties. Their findings revealed that the nanofilters, in the presence of PP grafted MA, improved the tensile strength and Young's modulus properties which are indicative of the synergistic effect between the nanoparticles and compatibilizers. According to Lee and Youn [160], the addition of layered silicates worsened tensile properties of PP nanocomposites prepared by them. Similar investigation was presented by Rault et al. revealing that the addition of a maximum 1 wt% led to improvement in tensile properties but above the maximum, the silicate nanoparticle caused difficulties for processing the composites due to the formation of aggregates [161]. However, Joshi et al. [162] has reported improvement in tensile properties of PP/nanoclay composites. Therefore, we can conclude with certainty that there are other factors interfering in the positive influence expected from the addition of nanoparticle such as clay. According the Vargas et al. [159], fibers geometry plays a vital role in determining the composites eventual properties. Nanoparticles of different shapes and sizes were used to prepare polyamide 6 (PA6) composites in some research work conducted by Vlasveld et al. [163]. Their findings revealed that the rheological properties of the composites samples were highly dependent on the aspect ratio of the nanoparticle used. Therefore utmost care must be taken when the option of nanoparticles are being considered. Other nanoparticles have been used and their influence on the mechanical properties have been positive and very encouraging [164, 165].

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*Improving the Mechanical Properties of Natural Fiber Composites for Structural and Biomedical…*

Hybrid composites involve the combination of two or more different types, shapes or sizes of reinforcement in one composite material [166]. The hybrid composite properties have been reported to depend on many factors such as; fibers individual property, fiber-matrix compatibility, roughness of fiber surfaces, orientation of fibers and the extent of their intermingling [167]. Recently, investigations on the hybrid composites properties were based on the natural/synthetic fibers, natural/natural fiber and natural/synthetic/additive modified reinforced polymer composites. The popularity of these types of composites are increasing rapidly owning to their capability to provide freedom to tailor the composites and realizing properties that cannot be obtained in fabricated composites containing singular

Fiber-based hybrid composites have been reported to have improved properties compared with the unhybridized composites having single reinforcement [168–170]. Many research reports have shown that the addition of synthetic fibers at various amount to form hybrid fibers have composites of better-quality, especially in respect to their mechanical properties [171–179]. According to Ashik and Sharma [180], in one of their reviews, they listed some factors that may impact the mechanical properties of natural fiber hybrid polymeric composites, with the processing parameters featuring as one of the factors. Also, Nunna et al. [181] listed fiber content, fiber treatment, and the environmental conditions as some of the conditions that affect the properties of hybrid composites. For hybrid natural/ synthetic fibers, it has been reported that as wt% of the synthetic fiber rises, the mechanical properties also rises. However, at a certain wt% of the synthetic fiber content added, the properties of the composites mechanical properties starts dropping and this may be ascribed to poor interfacial adhesion, high fiber-to-fiber

Mishra et al. [182] prepared hybrid glass fiber (GF) and pineapple leaf fiber (PLF) polyester composite with a total fiber content of 25 wt%. The tensile strength

was observed to have increased as the GF was increased from 0 to 7.5 wt% to approximately 70 MPa, after which the strength started dropping. The flexural strength kept increasing as glass content increased from 4.3 to 12.9 wt%, in the hybrid biocomposite. The authors also prepared a similar hybrid biocomposite, but this time with 30 wt% total fibers (sisal and glass fibers). They reportedly observed

a major improvement in tensile strength as the GF content was increased to

5.7 wt%. After this, the tensile strength was almost static even as the GF content was increased above this value. A similar trend was observed for the flexural strength. However, comparing the hybrid biocomposites with the biocomposites containing only pineapple or sisal fibers, the hybrid showed better improvement. Nevertheless, more evidence is available to show that the overall properties of hybrid composites depend greatly on (i) the percentage elongation at break and (ii) Young's modulus

Shahzad [183] presented the impact and fatigue properties of hybrid biocomposites of hemp and chopped strand mat glass fibers using unsaturated polyester resin as the matrix. Two different variations of hybrids composites were prepared. The first denoted with "A" containing 35.8 wt% hemp fiber and 11.1 wt% GF, while the second denoted with "B" had 36.6 wt% and 11.3 wt% hemp and glass fibers respectively. From the results, "A" had 70.1 ± 10.2 MPa, 8.3 ± 0.4 GPa and 1.31 ± 0.25% for tensile strength, Young's modulus and strain to failure respectively, while "B" showed 81.6 ± 3.7 MPa, 7.7 ± 0.3 GPa and 1.73 ± 0.08% for tensile strength, Young's modulus and strain to failure improvement respectively when compared with biocomposites reinforced only with hemp fibers, having

*DOI: http://dx.doi.org/10.5772/intechopen.85252*

**5.5 Hybridization**

type reinforcement [21, 79].

contact, and poor wettability.

of the reinforcing fibers present.

*Improving the Mechanical Properties of Natural Fiber Composites for Structural and Biomedical… DOI: http://dx.doi.org/10.5772/intechopen.85252*
