Hybrid biocomposites

Composites are primarily made using matrix and reinforcement as major components but may also contain several other fillers or additives. A majority of the composites are made using synthetic fibers and polymers. However, in the last few decades, focus has been on developing biocomposites using renewable resources. Conventionally, biocomposites are developed using natural fibers such as jute, Kenaf, or Ramie as reinforcement and synthetic resins such as polyethylene, polypropylene and epoxy as matrix. Typically, biocomposites contain either the reinforcement or matrix which makes the composites partially degradable. Such partially degradable composites provide good properties, but the presence of a nonbiodegradable component, particularly as a matrix limits their biodegradability. Alternatively, composites that contain both the matrix and reinforcement from renewable resources which make the composites completely degradable have also been developed. However, these completely biodegradablebiocomposites do not have the desired mechanical properties and stability at high humidities or in aqueous environments which restricts their application. In addition, natural fibers and resins used in biocomposites have inherent limitations and also not easily processable. To overcome limitation of using a single reinforcement or matrix derived from bioresources, hybrid composites that contain more than one reinforcement or matrix are developed. Such hybrid composites are manufactured by either intimately mixing two or more fibers or other reinforcing materials or by placing different layers of the reinforcement and molding them into composites using one or more resins. Conventionally, hybrid composites refer to metallic and ceramic based reinforcement, matrix and fillers. Although hybrid biocomposites are gaining significant attention, the presence of multiple reinforcements and/or matrix makes it difficult to process and also to predict the properties of such composites. Hence, understanding the properties and potential of using multiple reinforcements and/or matrix materials from renewable resources to develop biobased hybrid composites is highly desirable. This article discusses hybrid composites that contain a major proportion of renewable materials. Hybrid composites not only provide better properties but could also lead to substantial cost reduction due to the incorporation of inexpensive raw materials. These composites show potential for use in aeronautical, sporting goods, wind power turbine blades, helmets and civil construction such as pedestrian bridges and many other applications. This review provides an overview of the biobased materials used to develop hybrid composites, their processability and their potential applications. POLYM. COMPOS., 39:E30-E54, 2018. (c) 2017 Society of Plastics Engineers