Silk fibers and their unidirectional polymer composites

Natural fiber reinforced polymer composites have gained their popularity in the composite research because of versatility and diversified nature of their applications (Gay et al., 2003). This is due to a range of potential advantages of natural fibers, especially with regard to their environmental performance. Natural fibers are renewable resources and even when their composite wastes are incinerated, they do not cause net emission of carbon dioxide to the environment. They are inherently biodegradable, which may be beneficial (Aquino et al., 2007; Singleton et al., 2003; Verpoest et al., 2010). Among all the natural reinforcing fibrous materials, silk appears to be a promising fiber due to its high toughness and aspect ratio in comparison with other natural reinforcements. Moreover, the mechanical properties of silk fibers consist of a combination of high strength, extensibility, and compressibility. On the other hand, maleic anhydride grafted polypropylene (MAPP) and commercial grade polypropylene (PP) are commonly used matrices for fiber-reinforced composites due to their good interfacial bonding properties (Karmarkar et al., 2007; Wambua et al., 2003). In this chapter, both raw and alkali treated silk fibers are taken into consideration to characterize their properties first. The specific objective is to determine the modulus and strain to failure of the single silk fiber. Other aims of this work are to fabricate the unidirectional silk fiber reinforced polymer (MAPP and commercial grade PP) matrix composites by varying fiber volume fraction and to determine their mechanical properties such as tensile strength, flexure strength, impact strength, and hardness.