level due to melting of ice is also a serious problem that can lead to catastrophic disasters on the sea‐neighbor lands, which would negatively affect the environment. Natural fibers are considered renewable resources and can be recycled from many industrial process wastes. These natural fibers are obtained from plant sources, such as hemp, or from animal sources [12, 13]. Natural fibers of plant sources comprise cellulose, hemicellulose, and lignin; natural fibers of animal sources consist of mainly proteins. Natural fibers can be utilized in various sizes from macro‐ to nanoscale fibers. For instance, the nanocellulose fibers can be utilized in a wide range of applications as indicated in Figure 1.1.
Figure 1.1 Nanocellulose applications.
Figure 1.2 Illustration for the structure of cellulose extracted from plants.
Figure 1.2 illustrates the structure of cellulose extracted from plants as a 3D illustration showing the plant cross‐sectional walls, hemicellulose, lignin, fibril, microfibrils, the amorphous region, and cellulose.
In general, the natural fibers are used in polymer composites as reinforcement [14–17]. Hence, the properties of these composites will directly be influenced by the type of fibers used, their aspect ratio (length/width), their extraction processes, and their interaction with the matrix material [18–20].
1.2 Biodegradable Materials
Biodegradable materials are increasingly demanded to replace the conventional materials. Thermoplastic starch, for instance, is obtained from corn, potatoes, or other cereals. It mainly consists of amylose and amylopectin. As thermoplastic starch has highly sensitivity toward hydrolysis, and due to its low mechanical performance, it is usually used as a matrix for composites and not as a reinforcement. However, the starch phase is blended with polyesters to produce very interesting biodegradable products [21–23]. Examples of such products are commercially available in many fields such as the food packaging industry and in the manufacture of disposable items and films. Biomaterials are more and more in demand to replace the conventional materials and products in some applications. Thus, more efforts are still required to include their use in many industrial fields such as automobile, aerospace, construction, electronic, and food industries. However, before using the biodegradable materials in these industries, their reactions and performance with fire should be carefully assessed with various tools as well as with most newly established materials [24–29]. Thermoplastic starch has demonstrated good flame retardancy by including aluminum trihydroxide and coconut fibers; fire growth rate and the total heat release were significantly suppressed. This is due to the increase in carbonaceous char accompanied by the reduction of carbon content in the pyrolysis products. Also, using coconut fibers replaced a significant portion the aluminum trihydroxide causing its overall reduction in the thermoplastic starch. These results of flame retardancy opened the gate for researchers to explore alternatives from natural fibers to replace the current flame‐retardant additives for the thermoplastic starch biocomposites [30]. Thermoplastic starch‐blend materials are mainly produced for compostability. Hence, the organic wastes will be reduced, and the biogases will be decreased.
1.3 Polymers in Tissue Engineering
With the increasing trend toward using biomaterials in tissue engineering, great efforts are taken to develop biomaterials with desired characteristics, such as the ease of production, the compatibility with the host tissues, and the improvement of the healing rates. Polymeric‐based biomaterials are increasingly replacing the metallic and ceramic‐based biomaterials. As the latter type possesses high elastic modulus, the distribution of the stresses on the host bones will change completely, leading to alterations in the stress concentrations as well as relocating their locations [31]. In addition, polymeric materials are generally easier to be manufactured or shaped, and compatible with the host tissues [32]. Some classifications of polymers are illustrated in Figure 1.3. Moreover, some characteristics such as their mechanical performance and degradations can be controlled easily. Hence, they can perfectly be dedicated to a certain purpose once they are implanted in the host tissues.
For the last 50 years, many researchers have been concerned in investigating and developing potential natural and synthetic polymers for different applications in medical engineering such as biodegradable sutures, tissue scaffolds, and cardiovascular stents [33–35]. Polymers of natural resources are biocompatible and biodegradable in nature. Thus, they are readily suited for many medical applications such as tissue engineering applications and drugs production. Commonly used forms of scaffolds in tissue engineering are illustrated in Figure 1.4. Biobased composites are gaining more and more attention, and they are a concern for many researchers internationally due to their availability, recyclability, degradability, sustainability, low cost, light weight, and most importantly their high mechanical performance. The continuous improvements of the biocomposites will surely lead to new materials with a high potential to replace the conventional composites in the current applications or for future applications. In biocomposites, a material which is strong and similar to cement is made by the natural merging of different cells of hard plant fibers by lignin. These composites also possess high electric resistance due to the presence of cellulose fibrils embedded in lignin.
Figure 1.3 Classification of polymers.
Figure 1.4 Commonly used forms of scaffolds in tissue engineering.
1.4 Environmental Realization
Due to the severe environmental impact of the petro‐based plastics which are produced from nonrenewable resources, biobased composites of renewable resources with relatively fast biodegradability are preferred as ecofriendly alternatives. Thus, natural fibers as reinforcement of polymeric based composites can offer excellent ecofriendly alternatives and good environmental indices at a low cost. This is due to the fact that most of the natural fibers have specific reasonable mechanical properties comparable to the traditional synthetic fibers [16–19, 36–41]. Because of this, several researchers have considered the natural fibers in biomaterials as environmental alternatives of low cost materials. The number of researches that considered natural fibers as reinforced materials in polymeric based composites in three years from 2016 to 2018 is illustrated in Figure 1.5. However, the aspect of the biobased composites is challenging and huge efforts are still required to replace the petro‐based composites with these biobased composites. Nevertheless, biobased composites have already been commercialized in many industrial applications such as the automotive and packaging industries.
More promising aspects and applications are under development using biobased composites, and the
