**5. Natural fibers composites—Some salient features and associated challenges**

Fiber reinforced polymeric composites consist of reinforcement fibers held by surrounding resin matrix. Continuous filaments or short fibers comprise the reinforcement fibers. Reinforcement preforms like nonwoven mats, yarns, fabrics and 3D fabrics are obtained from fibers.

The biological origin of at least one of the components of natural fiber composite make them potential sustainable candidates with long textile fibers (e.g., flax, hemp, kenaf, jute, ramie and sisal), short fibers (wood fibers, by-products from long fiber processing, and recycled fibers) and fiber fibrils being used as reinforcement. Biomaterials like various epoxidized plant oils and soy protein serve as matrix materials. The fabrication of natural fiber composites is accomplished in a similar manner as manufacturing methods namely resin transfer molding (RTM), vacuum infusion, compression molding, direct extrusion and compounding, and injection molding deployed for conventional composites comprising thermoset matrix and thermoplastic composites. The pre-treated process of fiber and manufacturing techniques of composites primarily govern the properties of natural fiber reinforced polymer composites. Composites with diverse properties can be obtained by varying the manufacturing techniques and the constituents of composite materials. Thus it can be inferred that precise selection of fibers, matrix, additives and manufacturing method enables tailoring the properties of natural fiber composites for varied applications.

Natural fiber composites offer several environmental benefits in contrast to their synthetic counterparts as the former result in less pollution during fabrication, lower fuel consumption and CO2 emissions during transport to the constructions sites and lastly, considerable reduction of the disposal and energy-consuming disposal efforts.

Natural fiber composites owing to replacement of synthetic materials by bio-base and renewable sources are classic examples of sustainable resources for industrial applications. The materials exhibit the potential of being cost effective for identical

#### *Natural Fibers: The Sustainable Alternatives for Textile and Non-Textile Applications DOI: http://dx.doi.org/10.5772/intechopen.106393*

structural characteristics, can be grown in controlled facilities or farms and can substantially bring down the carbon footprints. The problems posed by synthetic fibers and resins in their disposal accounts for approximately 20% of the total landfill space thereby fostering ardent replacement of synthetic composites with natural fiber composites.

Nevertheless, the applications of natural fibers are restricted to interior structures owing to their hydrophilic nature thereby demanding chemical treatment for improving their moisture related properties. The variability in fiber properties namely apparent variability and actual property variability presents a challenge in their usage as reinforcement in composite materials. Apparent variability arises due to experimental methods, measurement and testing techniques while the actual property variability is the inherent variability present in fiber. Moreover, the structural defects in the fibers leads to fiber deformation which also restrict the usage of natural fibers.

The inherent property of moisture absorption on exposure to different temperatures and humidity conditions by natural fibers presents a key challenge for their usage in different environmental conditions [2, 3]. The presence of hydrophilic group affects the interfacial bonding between polymer matrix and the fiber in composite structures owing to hydrophobic characteristics of matrix. The interaction between fibers and polymer matrix can be optimized by chemical treatment of natural fibers by reduction in hydroxyl functional groups on the fiber surface thereby increasing surface roughness and the interfacial interaction between the matrix and the fibers [6, 7].
