4 Recent developments in nanofillermodified natural fiber composites

Abstract

The use of natural (cellulose) fibers presents various benefits due to their many positive characteristics, such as biodegradability, low density, good acoustic isolation and low cost, when compared to the synthetic fibers. However, their main shortcomings are the variability in fiber quality and absorption of humidity due to the hydrophilic characteristic of the fiber, which leads to low interfacial adhesion between the fiber and the hydrophobic matrix, consequently leading to relatively low mechanical properties. Different techniques as reported in literature are used to surpass these shortcomings, such as chemical treatments of the fibers and hybridization techniques. One method explored in the literature to improve the properties of cellulose fiber-reinforced composites is the use of fillers (either on the fiber surface or into the matrix as the second reinforcing phase). The fillers can be organic, inorganic, metallic, and ceramic and they can be in macro-, micro-, or nanoscale. Generally speaking, microsized fillers are defined as those between 1 and 1,000 μm, while the nanosized fillers defined as those that have at least one dimension in the range of 1 to 100 nm. The fillers may contribute to water resistance (lowered hydrophilic nature) of polymeric composites, increased dimensional stability and shrinkage reduction, thermal stability, machinability, and vibrational damping. However, these properties depend on many factors such as shape, size, and orientation of filler reinforcement, filler content, filler/matrix/fiber adhesion, and agglomeration. Another important benefit derived from filler reinforcements is the possible improvement in fracture toughness of the composites, due to crack arrestment mechanisms such as crack bridging, microcracking, filler debonding, and shear banding. This chapter presents recent developments in the field of cellulose composites reinforced with nanofillers. The main challenges met in the production of nanofillerreinforced cellulose composites (agglomeration of nanofillers during manufacture, insufficient interfacial compatibility between fillers and the matrices, and degradation of the fillers during processing, etc.) are briefly discussed.