*6.4.2 Nanocellulose and nanoparticles*

Nanocellulose particles are derived from rigorous chemical modification of plant fibers using a combination of alkaline and acidic solution in phases. At the nanoscale chemical modification is relatively easier; large numbers of the OH groups at the surface are more exposed; the amorphous components of the fibers have been eliminated, leaving only the crystalline part of the cellulose material. The nanoscale cellulose fibers when modified have wide application [127, 128]. Filler or additives can be described as materials which are added to the matrix in low percentages ranging from 0.1 to 5 wt% in order to improve performance and impact some special properties [129]. Some of the fillers are low-cost, allowing for a cost effective measure for the enhancement of performance properties. In addition, they can improve the processing of the material by controlling the viscosity of the resin [130]. Common fillers used in NFPCs include metal particles, nanosize cellulosic materials (CNCs), silica, nano-clay, maleic anhydride (MA)

and carbon nano-tubes (CNT) [131]. Mohanty et al. showed that better interfacial adhesion existed amongst the fiber/matrix owing to filler addition in the NFPC as evident from the SEM micrographs of the fractured tensile samples; this resulted in the improvement of the mechanical properties [132]. Mechanical properties enhancement were resultant from the adding of fillers at low wt% which has led to the consistent assembly observed and enhanced stress transfer amongst the fiber and the matrix [1]. Meanwhile, at higher wt% of fillers, there was deterioration in the properties of the NFPCs, due to agglomeration of the fillers and the interfacial adhesion between the polymer matrix and fiber were noticed to be weak. Furthermore, it was suggested that the rise in tensile modulus and the fall in impact strength of the NFPCs with clay fillers were as a result of the polymer matrix improved cross-link density, which led to a decrease in the stiffness of the composite, hence reduced the impact strength [130, 133]. While in other studies, aluminum powder was used as fillers and in others, modified clay improved the impact strength of the composite, as the SEM micrographs revealed the existence of less voids and rise in density along with improvement in stiffness resultant from better interfacial adhesion amongst the fiber and the matrix in the presence of the modified clay [134, 135]. Other advantages of filler addition to sisal fiber reinforced polymer composites are increased moisture absorption or reduced water uptake as reported by [135, 136].

The addition of nanoparticles to NFPC to improve their interfacial properties has gained more popularity in recent time. Nanoparticles incorporation into polymer composites has been reported to improve their strength and young's modulus, as can be seen from earlier discussion. The addition of these nanoparticles at very low concentration of approximately 0.1–1.0% had influenced the mechanical properties of the NFPCs [137]. The modifications of the particles by some researcher have led to improved chemical interactions when added to the composites. Thereby improving interfacial bonding and by extension, mechanical and thermal properties [138–140]. Moreover, the addition of inorganic nanoparticles has helped to improve both thermal and mechanical [131]. This has influenced the crystallization process during processing of the composites. The improved crystallinity can encourage superior mechanical interlocking of the polymer-fiber interface.

### *6.4.3 Hybrid fibers*

Hybrid fibers are a combination of two or more different fibers to make a composite. The addition of glass and/or carbon fibers to form hybrid fibers has also contributed to improving the composite properties. Allamraju et al., reported an increase in the compression and tensile strength of Jute/glass hybrid fibers epoxy composite, as a result of percentage increase in mass fraction of jute fibers [141]. Their results showed that the measured strengths increased as the fiber load increases from 6 to 9%, after which there was a decrease. The 9 wt% jute fibers that was reported as the optimal loading was attributed to higher stiffness of the composites and an improved fiber-matrix adhesion.

Hybrid composites are prepared by the combination of two or more different type, shape or size of reinforcement [142]. The crossbreed composite properties is completely dependent on many elements such as, extent of intermingling of fibers, fibers orientation, fiber surface roughness, compatibility between the fibers and their matrix, and the property of the individual fibers [143]. Recently, investigations on the properties of the crossbreed composites were centered on the natural/ synthetic fibers, natural/natural fiber and natural/synthetic/additive modified reinforced polymer composites. Essentially for applications that required such

**21**

improvement.

*6.4.3.1 Natural/natural hybrids*

decreased the possibility of fiber pullout.

performance characteristic property [151].

hybrid in a composite [142].

*Fiber-Matrix Relationship for Composites Preparation DOI: http://dx.doi.org/10.5772/intechopen.84753*

of pure natural fiber polymer composites is difficult.

hybrid/crossbreed composites with stiffness and high strength, but the employment

The popularity of these crossbreed types of composites is increasing rapidly owning to their capability to provide freedom to tailor the composites and achieving properties that cannot be acquired in composite encompassing only one kind of material [13, 144]. One of the major reasons for creating crossbreed NFPCs is to utilize the pluses of the fibers and lessen some drawbacks [145]. Another reason is based on economy, which is to decrease the cost of the finished composite product. Even though the usage of natural fibers in composites is less costly in comparison to the orthodox reinforcements, there are significant differences in the costs of natural fibers. Therefore, partially substituted cotton fibers in a composite made with wood fibers could offer very huge benefits in terms of the performance of the composite and also in the manufacture prices. The hybridization of wood flour- polypropylene composites with waste cone flour (20–40 wt%) was reported the composite was said to have been negatively affected in terms of their flexural properties and water resistance of the composite [146]. However, adding pine cone flour (10 wt %) to the composite revealed no substantial consequence on the measured properties, i.e. water absorption and flexural strength properties. This means it is economically advantageous. Further research showed that reducing the amount of pine cone flour added to the composite lead to positive

Hybrid composites of sisal fibers and short banana fibers were also prepared using a polyester [147, 148]. From the result obtained, the tensile strength of the polyester composite was observed to rise as the volume fraction of the banana fiber was increased. On the other hand, the impact strength of the composites was affected negatively with increasing volume fraction of the banana fibers. Nevertheless, the impact strength improved with rise in total content of the fibers used. The observed properties were ascribed to two factors: (i) the lower microfibrillar angle of the banana fibers (11°) as compared to that of sisal (20°) and (ii) the better compatibility between the polymer matrix and banana fibers, which

In the same vain, Venkateshwaran et al., prepared the same hybrid of banana and sisal fibers using epoxy resin in order to determine the optimal quantity of banana fibers with regard to its tensile properties [149]. The results revealed that about 50% of the complete fiber content added was good enough to impact significantly on the tensile strength of the composite. The differences in the morphologies of the different fibers have been shown to be of significant advantage when used as

Furthermore, Fernandes et al., prepared hybrid composites of cork and coir fiber using high density polyethylene (HDPE) matrix [150]. With a coupling agent present, adding 10 wt% coir fibers to the composite caused a 30% rise in tensile maximum strength and a 39% rise in the tensile modulus. The overall effect of the coir fiber on the hybrid composites was very evident when compare to the single fiber composite, even with the coupling agent. Therefore, it can be said that the hybridization of NFPCs, most especially with natural/natural fibers, presented an efficient, sustainable and high economical way of improving the performance of the composites at a reduced cost. Also the addition of compatibilizers is still a necessity in order to create the needed covalent interactions required to enhance the

### *Fiber-Matrix Relationship for Composites Preparation DOI: http://dx.doi.org/10.5772/intechopen.84753*

*Renewable and Sustainable Composites*

uptake as reported by [135, 136].

*6.4.3 Hybrid fibers*

posites and an improved fiber-matrix adhesion.

and carbon nano-tubes (CNT) [131]. Mohanty et al. showed that better interfacial adhesion existed amongst the fiber/matrix owing to filler addition in the NFPC as evident from the SEM micrographs of the fractured tensile samples; this resulted in the improvement of the mechanical properties [132]. Mechanical properties enhancement were resultant from the adding of fillers at low wt% which has led to the consistent assembly observed and enhanced stress transfer amongst the fiber and the matrix [1]. Meanwhile, at higher wt% of fillers, there was deterioration in the properties of the NFPCs, due to agglomeration of the fillers and the interfacial adhesion between the polymer matrix and fiber were noticed to be weak. Furthermore, it was suggested that the rise in tensile modulus and the fall in impact strength of the NFPCs with clay fillers were as a result of the polymer matrix improved cross-link density, which led to a decrease in the stiffness of the composite, hence reduced the impact strength [130, 133]. While in other studies, aluminum powder was used as fillers and in others, modified clay improved the impact strength of the composite, as the SEM micrographs revealed the existence of less voids and rise in density along with improvement in stiffness resultant from better interfacial adhesion amongst the fiber and the matrix in the presence of the modified clay [134, 135]. Other advantages of filler addition to sisal fiber reinforced polymer composites are increased moisture absorption or reduced water

The addition of nanoparticles to NFPC to improve their interfacial properties has gained more popularity in recent time. Nanoparticles incorporation into polymer composites has been reported to improve their strength and young's modulus, as can be seen from earlier discussion. The addition of these nanoparticles at very low concentration of approximately 0.1–1.0% had influenced the mechanical properties of the NFPCs [137]. The modifications of the particles by some researcher have led to improved chemical interactions when added to the composites. Thereby improving interfacial bonding and by extension, mechanical and thermal properties [138–140]. Moreover, the addition of inorganic nanoparticles has helped to improve both thermal and mechanical [131]. This has influenced the crystallization process during processing of the composites. The improved crystallinity can encourage superior mechanical interlocking of the polymer-fiber interface.

Hybrid fibers are a combination of two or more different fibers to make a composite. The addition of glass and/or carbon fibers to form hybrid fibers has also contributed to improving the composite properties. Allamraju et al., reported an increase in the compression and tensile strength of Jute/glass hybrid fibers epoxy composite, as a result of percentage increase in mass fraction of jute fibers [141]. Their results showed that the measured strengths increased as the fiber load increases from 6 to 9%, after which there was a decrease. The 9 wt% jute fibers that was reported as the optimal loading was attributed to higher stiffness of the com-

Hybrid composites are prepared by the combination of two or more different type, shape or size of reinforcement [142]. The crossbreed composite properties is completely dependent on many elements such as, extent of intermingling of fibers, fibers orientation, fiber surface roughness, compatibility between the fibers and their matrix, and the property of the individual fibers [143]. Recently, investigations on the properties of the crossbreed composites were centered on the natural/ synthetic fibers, natural/natural fiber and natural/synthetic/additive modified reinforced polymer composites. Essentially for applications that required such

**20**

hybrid/crossbreed composites with stiffness and high strength, but the employment of pure natural fiber polymer composites is difficult.

The popularity of these crossbreed types of composites is increasing rapidly owning to their capability to provide freedom to tailor the composites and achieving properties that cannot be acquired in composite encompassing only one kind of material [13, 144]. One of the major reasons for creating crossbreed NFPCs is to utilize the pluses of the fibers and lessen some drawbacks [145]. Another reason is based on economy, which is to decrease the cost of the finished composite product. Even though the usage of natural fibers in composites is less costly in comparison to the orthodox reinforcements, there are significant differences in the costs of natural fibers. Therefore, partially substituted cotton fibers in a composite made with wood fibers could offer very huge benefits in terms of the performance of the composite and also in the manufacture prices. The hybridization of wood flour- polypropylene composites with waste cone flour (20–40 wt%) was reported the composite was said to have been negatively affected in terms of their flexural properties and water resistance of the composite [146]. However, adding pine cone flour (10 wt %) to the composite revealed no substantial consequence on the measured properties, i.e. water absorption and flexural strength properties. This means it is economically advantageous. Further research showed that reducing the amount of pine cone flour added to the composite lead to positive improvement.

### *6.4.3.1 Natural/natural hybrids*

Hybrid composites of sisal fibers and short banana fibers were also prepared using a polyester [147, 148]. From the result obtained, the tensile strength of the polyester composite was observed to rise as the volume fraction of the banana fiber was increased. On the other hand, the impact strength of the composites was affected negatively with increasing volume fraction of the banana fibers. Nevertheless, the impact strength improved with rise in total content of the fibers used. The observed properties were ascribed to two factors: (i) the lower microfibrillar angle of the banana fibers (11°) as compared to that of sisal (20°) and (ii) the better compatibility between the polymer matrix and banana fibers, which decreased the possibility of fiber pullout.

In the same vain, Venkateshwaran et al., prepared the same hybrid of banana and sisal fibers using epoxy resin in order to determine the optimal quantity of banana fibers with regard to its tensile properties [149]. The results revealed that about 50% of the complete fiber content added was good enough to impact significantly on the tensile strength of the composite. The differences in the morphologies of the different fibers have been shown to be of significant advantage when used as hybrid in a composite [142].

Furthermore, Fernandes et al., prepared hybrid composites of cork and coir fiber using high density polyethylene (HDPE) matrix [150]. With a coupling agent present, adding 10 wt% coir fibers to the composite caused a 30% rise in tensile maximum strength and a 39% rise in the tensile modulus. The overall effect of the coir fiber on the hybrid composites was very evident when compare to the single fiber composite, even with the coupling agent. Therefore, it can be said that the hybridization of NFPCs, most especially with natural/natural fibers, presented an efficient, sustainable and high economical way of improving the performance of the composites at a reduced cost. Also the addition of compatibilizers is still a necessity in order to create the needed covalent interactions required to enhance the performance characteristic property [151].
