**7. Possible applications of NFPCs with improved fiber-matrix adhesion**

The application of NFPCs comes with different requirements. These requirements are specific to application demands which include mechanical properties, thermal stability, transparence, conductivity and operational temperature. These factors are not unconnected to the factors considered before processing. For mechanical and thermal stability, the design of the NFPCs are considered from the point of improved interfacial interaction, using compartibilizers, fiber surface modification, addition of other chemical components and lastly reducing the fibers to nanosizes.

The automotive industry is one of the major end user playing a key role in the utilization of NFPCs. In the early '90s, Mercedes-Benz was the first, as a carmaker, to use NFPC, by building panels for doors with jute fibers [160]. This resulted in other car makers following suite, utilizing natural fibers comprising polymer composites for parcel shelves, headrests, upholstery, door panels, etc. The widespread adoption can be linked to the advantages of NFPCs, relating to the impact on the environmental, cost, elastic modulus and weight. No matter the applications, it was always a necessity to increase the mechanical properties of the composites via pre-treatment techniques (as discussed earlier). The fibers which have been treated were used in several ways, in order to obtain non-woven structures, mats, etc. [9]. Researchers have shown that subjecting natural fibers to some form of distinct treatment could lead to the development of high-quality composites with mechanical properties which are similar to those of glass fiber composites [160]. An outcome that would have ordinarily been very difficult to achieve because of natural fibers' hydrophilic nature which encourages water molecule absorption and agglomeration with no adhesion to the polymer matrix; This is the challenge and much works is ongoing to overcome this challenges [160, 161].

For conductivity, the addition of inorganic nanoparticles has been used and this has served a dual purpose of also improving the mechanical and thermal properties. Transparency is best impacted on NFPCs by the use of nanocellulose modified or not, with careful selection of the matrix. Some of the biodegradables are considered as having transparent properties including PLA. For water and gas permeability, applications are numerous with good water permeability. Such composites can be applied in water filtration processes, while for low water permeability composites; can be applied in packaging.

Researchers have reported positive impact of cellulose fibers on moisture and gas barrier performances for biodegradable polymers after modification with nanosize celluloses [162, 163]. Ambrosio-Martin and his colleagues prepared biodegradable composites of PLA using CNCs [164]. They reported improvements of barrier properties of oxygen and water which was due to the addition of welldispersed OLLA-BCNCs. The researchers hypothesized that the nanofillers were able to make a tortuous path for the permeation of gas and water, thereby acting as blocking agents inside the polymeric matrix and hence, causing an increase to the barrier properties of the material. In these materials, the CNCs good level of dispersion within the polymer matrix, the morphology and its orientation led to enhanced tortuosity effects, thereby, heightening the barrier properties of the materials [165, 166]. Sanchez-Garcia and co-workers did similar work on PLA biodegradable materials and reported a decrease in the water permeability capacity and oxygen of approximately 82 and 90% respectively on addition of CNC to the PLA matrix [167]. In contrast, Espino-Pérez et al., highlighted results that were entirely opposite after compounding PLA with n-octadecyl-isocyanate-grafted-CNCs [168]. In their publication, it was clear that there was no reduction in oxygen permeability on adding CNCs into PLA. Apart from investigations about the tortuosity effects and barrier properties, researchers have tried to relate the improvement observed for the barrier properties to the materials crystallinity changes on addition of the nanofillers to the polymer matrix [169]. Fortunati et al, highlighted the improvements in barrier properties of PLA/CNC nanocomposites as well as increased crystallinity simultaneously, which was attributed to the addition of CNCs [170]. Espino-Pérez and co-workers investigated CNC/PLA nanocomposites using a high D-lactic acid content (a material which under normal processing conditions cannot crystallize) as matrix [171]. In conclusion, they indicated that the tortuosity effect of CNC on the oxygen barrier properties is limited. Although, after addition of modified CNS, significant improvement in the water vapor barrier properties was observed. They reported the swelling of unmodified CNCs due to absorption of water as a result of their hydrophilicity, which encouraged the pathway for mass transport and this property was not demonstrated when modified CNCs were employed because the surface modification caused the reduction in the hydrophilicity of the nanoparticles [172]. Follain et al., also reported that other elements can be considered to be significant in moisture and gas barrier performances of CNC-based nanocomposites [173]. They indicated that the formation of a 3D network and close interfacial adhesion between PCL chains and CNC can result in the matrix having structural defects, which encourage transfer of gas. Hence, their results highlighting the barrier properties of CNC-based nanocomposites allow for the conclusion that the tortuosity effect is influenced by CNCs, CNC surface chemistry, the structure of the nanocomposite. Also, that change(s) in crystallinity of the host matrix play a vital role on moisture and gas barrier performances of the material.

Biodegradation has been described as a vital prerequisite for biomedical materials, agricultural mulches and the packaging industry, as a result of the high level of consumption of these materials. Thus, the preparation of biodegradable polymers with improved properties is necessary but not without its own challenges. However, it will be exceptional to alleviate the concerns of landfills, chiefly in countries which are yet to adopt the technique of composting. A lot of research output has shown enhanced biodegradation for a number of polymer matrices when cellulosic fibers are added to them [174, 175]. However, the surface modification of the cellulose fibers negatively influences the matrix degradation because it reduces the number of OH group on the cellulose surface and so decreases the hydrophilicity [176]. Pinheiro and co-workers prepared poly (butylene adipate-co-terephthalate) PBAT-based composites with modified and unmodified cellulose fibers [174]. They presented from their results that the addition of unmodified cellulose fibers caused more weight reduction and this was attributed to the hydrophilic properties of the nanocrystals that hastened the hydrolysis of PBAT. In another related work, Monhanty et al, reported similar findings and also highlighted that the hydrophilic properties of the reinforcement encourages the degradation of the polymer [177]. The crystal size [178] and crystallinity of the polymer matrix [179, 180] have also been reported to playing a vital role in the degradation degree of the matrix, considering that regions which are crystalline are relatively unaffected by hydrolysis [178–182].

The use of other methods such as micro-fibrillation, laser, and ionomer to enhance the mechanical properties of materials have been reported. Choudhury and co-workers highlighted the capacity to improve the tensile and flexural properties of NFPCs by ionomer treatment of natural fibers [183]. The improvement was as a result of uniform stress dissemination and good dispersion of the fibers inside the matrix. This enhancement in mechanical properties by the microfibrillation was largely ascribed to the larger interaction observed between the polymer and fibers after the treatment by micro-fibrils and aggregates.

**25**

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

attack, thereby making them biodegradable.

factors discussed above are properly considered.

**Acknowledgements**

Chair for Nanotechnology.

**8. Conclusion**

The selection of polymer matrix in all these areas of application becomes very important and sensitive. Although there are general purpose polymers with little or no health concerns for examples PP, PE, HDPE. When these polymers are compounded with NFs, their composites become more susceptible to microorganism

The dependence of performance properties on a strong fiber-matrix interface cannot be over emphasized. Fiber-matrix interfacial interactions are very important properties of all polymer composites. The performance properties are highly dependent on the kind of fiber-matrix interfacial bonds formed. These bonds can be physical or chemical in natural. The physical interaction includes interlocking between the matrix and the fibers, which is as a result of the rough edges of splits caused by the various surface treatments subjected to the fibers. While chemical interactions include the formation of bonds from the weak Van der Waal force to a strong covalent bond. The chemical bonds can be induced by (i) the type of surface treatment given to the fibers, which be either be a chemical or biological treatment and (ii) the deliberate addition of selected compatibilizers which confirm specific functionality on either the fibers or the polymer matrix. Furthermore, the addition of nanoparticles has been reported to help improve interfacial interactions through the direct participation in the crystallization processes which increases rigidity of the polymer matrix and thus enhances the physical interlocking at the interface. The use of hybrid fibers of polymer blends is another way of improving the interfacial interaction in NFPCs. Hybrid fibers can be natural/natural or natural/synthetic. While the natural/ synthetic hybrid fibers clearly have better thermal and mechanical properties, their effect on the environment will always be of great concern. With appropriate surface treatments, natural/natural hybrid fibers have been reported to display improved thermal stability and good mechanical properties. Also, the use of polymer blends has resulted in improved interactions. The choice of processing methods and conditions can undermine the kind of and extent of interaction formed. While the in-situ polymerization is used for thermosets, it mostly leads to the formation of covalent interactions. The thermoplastics are prepared using melt blending which mostly gives rise to interlocking or at most Van der Waal force types of interaction at the interphases, although compatibilizer can be added the form covalent interactions. However, melt blending processes are more prone to thermomechanical degradation, which is likely to affect the blends performance properties. In conclusion, to ensure that the materials with the required properties are developed, it is necessary that the

The financial assistance of the University of Zululand and the National Research

Foundation, South Africa through the South African Research Chair Initiative (SARChI) is hereby acknowledged. OSJ thanks the National Research Foundation (NRF) for a postdoctoral fellowship and funding under South African Research

The selection of polymer matrix in all these areas of application becomes very important and sensitive. Although there are general purpose polymers with little or no health concerns for examples PP, PE, HDPE. When these polymers are compounded with NFs, their composites become more susceptible to microorganism attack, thereby making them biodegradable.
