**6.3 Processing condition**

During the processing of NFPCs, the processing temperature, mixing speed and residence time are all important for any melt blending process while for in-situ polymerization; the temperature and curing time are of importance [58, 78, 79]. For NFPCs to be prepared via melt blending, the temperature must not be too high to avoid the degradation of the natural fibers. Since natural fibers are thermally stable below 200°C, above this temperature, the integrity of the fibers cannot be guaranteed. Therefore, polymers with higher melting temperature may not be used in the preparation of NFPCs or alternative processing methods are applied. One factor to bear in mind is that the polymer must be molten enough to wet the fibers. This means that the Gibb's free energy of interaction tend towards negative. As the fibers are added, the viscosity increases. This increase is dependent on weight percentage of fibers added [13]. However, if the shear rates are increased it could minimize the effect of the increased viscosity [75, 77, 111–113]. Good fiber-matrix interaction can only be achieved if the polymer can wet the fiber surfaces properly. The resident time for processing the NFPC is also very important, one cannot use the same processing time as used for the neat polymer or blends, for NFPC, if other parameters are to remain the same. As mentioned earlier, the addition of fibers leads to change in viscosity; therefore NFPC will require more time to achieve good wettability. However, the option of increasing the shear rate or mixing speed might compensate for the change in viscosity. Therefore it may be possible to use the same resident time during processing. It must be mentioned that every option has its advantages and disadvantages. For example, longer time and increased mixing speed may lead to thermomechanical degradation [75].

**19**

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

In the preparation of composites, additives are added to help improve specific properties. For example, nanoparticles are added to enhance the mechanical and thermal properties through better crystallinity growth and stabilization of phase

Compatibilizers are added to increase interfacial interactions amongst polymer-

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)

polymer in blends and polymer-fibers in composites [10, 41, 116]. The use of compatibilizers to improve interfacial interaction is widely reported [117]. In a series of works by Kamaker and other co-researchers [118–120], it was reported that Jute/PP composites' mechanical properties were improved drastically, when 3 wt% maleic anhydride grafted polypropylene (MAHgPP) was used to treat the Jute/PP composites as coupling agents. The tensile strength increased from 29.82 to 59.13 MPa, a 98% increase. Also, the bending strength was reported to increase from 49.97 to 87.66 MPa, a 75.4% increase. In related work, the tensile, flexural and dynamic strength of Jute/PP composites were enhanced by approximately 50% when the jute fibers are treated with 0.1 wt% MAHgPP solution of toluene, although the impact strength was negatively affected [121, 122]. Li et al., investigated two different kinds of silanes as coupling agents to treat sisal fibers surfaces [15]. The coupling agents were diluted in acetone to 6% concentration before use. A 24 h immersion of the sisal fibers was done using the coupling solution after which it was washed with acetone and dried up in the oven for 4 h at 60°C. Their results showed that the sisal surfaces were etched and they were very rough, which led the unbundling of the fiber bundle into smaller fibers, as seen in **Figure 3**. This increased the operative surface area presented for contact with the polymer matrix. Although, it was reported that the interaction at the interface was more of mechanical interlocking with less of chemical bonding. Therefore, the observed increase in load was due to frictional shear stress transferal across interface. Other coupling agents which had performed relatively well, have also been reported by other researchers [11, 123, 124]. However, to chemically modify the surface properties of the cellulose fibers to the extent that they can in turn influence the polymer composites properties significantly, it is suggested that the fibers should

**6.4 Addition of other materials**

be modified to its nanoscale [125, 126].

*6.4.2 Nanocellulose and nanoparticles*

morphology [114, 115].

*6.4.1 Compatibilizers*
