**2.4. Starch**

Starch comprises of two main components: (1) amylose (**Figure 2a**), a nonbranching helical polymer consisting of α‐1, 4 linked D‐glucose monomers and (2) amylopectin (**Figure 2b**), a highly branched polymer consisting of both α‐1,4 and α‐1,6 linked D‐glucose monomers. All starches are biosynthesized as semicrystalline granules with small amount of water [16]. There are amorphous and crystalline growth rings arranged alternately encircling hilum which is the point of initiation of the granule. Starch gelatinization is done by heating native starch in water [17]. After heating, starch granules start to swell and burst. The semicrystalline structure is disrupted and smaller amylose molecules start to leach out of the granules. Gelatinization irreversibly dissolves starch granule in water where water acts as a plasticizer. It forms network that holds water and increase the solution viscosity.

Starch is a resourceful natural polymer where it can be found in many plant roots, crop seeds, stalks, and staple crops. Main sources of native starch are maize (82%), wheat (8%), cassava (5%), and potatoes (5%) [18]. Starch is produced by all green plants as source of stored energy. They were used in many applications in the form of native and modified starches. Starches are popular in food making including bakery, dairy products, confectionery, and processed foods. Other nonfood industries using starches are papermaking, adhesives, clothing, and cosmetics. Starch also involves in production of antibiotics, vitamins, penicillin, and dialysis solutions.

**Figure 2.** Structures of (a) amylose and (b) amylopectin [17].

#### **2.5. Cellulose**

and act as binder of flux in welding rod production. Alginates are also established as bioma‐ terials in the pharmaceutical industry where they can be compounded into tablets to accelerate disintegration of tablet for faster release of drugs. In cosmetic field, alginate can help to retain

Chitosan is a natural aminopolysaccharide produced from partial alkaline deacetylation of chitin. Chitin, the second largest natural polymer after cellulose, is the structural element found in the exoskeleton of crustaceans, insects, and fungi. Just like plants produce cellulose in their cell walls, insects and crustaceans produce chitin in their shells. Chitosan is composed of linear copolymer of β (1–4) linked 2‐acetamido‐2‐deoxy‐β‐D‐glucopyranose and 2‐amino‐2‐deoxy‐ β‐D‐glycopyranose. Different factors, such as alkali concentration, incubation time, ratio chitin to alkali, temperature, atmosphere, source of chitin, and particle size, play a role in affecting the properties of chitosan [10]. Chitin possesses poor solubility in aqueous solution and organic solvents mainly because of the highly extended hydrogen bonded semicrystalline structure of chitin, thus limiting its practical application in biomaterials [11]. Chitin has the degree of acetylation (DA) of 0.90 [12]. Whereas chitosan possess primary amino groups with pKa value of 6.3. These amines get protonated and form water‐soluble and bioadhesive chitosan which

Unlike chitin, chitosan has highly sophisticated functionality and wide range of applications in biomedical and other industrial areas. The advantage of chitosan over other polysaccharides is because of its cationic character and primary amino group [14]. Although they exhibit similar structure, chitosan display different properties from that of cellulose. When the degree of deacetylation of chitin reaches about 50%, it becomes chitosan and soluble in aqueous acidic media [15]. Chitosan has been applied in agriculture, water and waste management, food and

Starch comprises of two main components: (1) amylose (**Figure 2a**), a nonbranching helical polymer consisting of α‐1, 4 linked D‐glucose monomers and (2) amylopectin (**Figure 2b**), a highly branched polymer consisting of both α‐1,4 and α‐1,6 linked D‐glucose monomers. All starches are biosynthesized as semicrystalline granules with small amount of water [16]. There are amorphous and crystalline growth rings arranged alternately encircling hilum which is the point of initiation of the granule. Starch gelatinization is done by heating native starch in water [17]. After heating, starch granules start to swell and burst. The semicrystalline structure is disrupted and smaller amylose molecules start to leach out of the granules. Gelatinization irreversibly dissolves starch granule in water where water acts as a plasticizer. It forms network

Starch is a resourceful natural polymer where it can be found in many plant roots, crop seeds, stalks, and staple crops. Main sources of native starch are maize (82%), wheat (8%), cassava (5%), and potatoes (5%) [18]. Starch is produced by all green plants as source of stored energy.

the color of lipstick on lip surface by forming gel network.

68 Composites from Renewable and Sustainable Materials

readily bind to negatively charged surfaces [13].

beverages, cosmetics and toiletries, and biopharmaceutics.

that holds water and increase the solution viscosity.

**2.3. Chitosan**

**2.4. Starch**

Cellulose is a linear chain of ringed glucose molecules and has a flat ribbon‐like conformation. It has the formula (C6H10O5)*n* where *n* depended on the source of cellulose linked by β(1→4) glycosidic bonds. Cellulose is an essential structural component of cell walls in higher plants and is the most abundant organic polymer on the Earth. It is relatively stiff and rigid because of the intramolecular hydrogen bonding that can be reflected from its tendency to crystallize, high viscosity, and ability to form fibrillary strands [19]. Cellulose is insoluble in water and indigestible by the human body [20]. The glucose units in cellulose are linked by β glycosidic bonds, different than the α glycosidic bonds found in glycogen and starch. Cellulose has more hydrogen bonds between adjacent glucose units, both within a chain and between adjacent chains, making it a tougher fiber than glycogen or starch. This is why wood is so tough. Wood, paper, and cotton are the most common forms of cellulose. The purest natural form of cellulose is cotton. Other than these, cellulose can also be produced by certain types of bacteria and they are called bacterial cellulose. While cellulose is a basic structural component in most plants, it is also produced in *Acetobacter*, *Sarcina ventriculi*, and *Agrobecterium*. Bacterial cellulose contains higher purity and water uptake capability compared to plant cellulose [21]. It has a tensile strength that is almost comparable to the Kevlar and steel and it can achieve stress‐strain behavior resembling that of a soft tissue in never dried form [22].

Being the largest natural polymer available is the most advantageous character for material sustainability and renewability. Cellulose has been tremendously applied in the production of cardboard and paper [19]. Current development of cellulose shows its potential in biomedical and biotechnological implementation. It is used in bioseparation, adsorbent for sewage treatment, cell suspension culture, and wound healing system.
