1. Background

#### 1.1 Biopolymers

As the name suggests, biopolymers are polymers synthesized by living organisms. Therefore, they are polymeric biomolecules i.e. long chain biomolecules comprised of covalently linked repeating monomeric units [1]. Living organisms (plants, animals, bacteria, fungi and yeast) synthesize a wide range of biopolymers such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, cellulose, chitin, starch, etc. Biopolymers carry out countless number of vital functions, such as storage of energy, preservation and transmittance of genetic information, and cellular construction, in vivo. DNA and RNA are the hereditary materials for the storage and passage of the genetic information in all living organisms, and thus making perpetuation of life possible in the planet. Proteins not only catalyze reactions (e.g. enzymes) and take part in cell signaling (e.g. hemoglobin) but also

provide structural support (e.g. collagen). Cellulose is the major structural component of the plant cell walls.

sustainable bioproducts, the so called "green products" [3]. It is a linear homopolymer of β-D glucose monomers covalently linked together by 1!4 glycosidic bonds i.e. the ringed glucose monomers are joined together via polycondensation reaction between hydroxyl groups at C1 of a glucose unit and C4 of the neighboring glucose unit. Since, every glucose unit is rotated 180° with respect to its neighbors along the fiber axis, dimer of glucose, called cellobiose, is considered as a repeating unit of cellulose polymer (Figure 1a) [15]. However, the convention of considering cellobiose as a repeating unit has been challenged and a recent review in this regard makes a cogent argument that glucose is the repeating unit rather than the cellobiose [16]. Cellulose is a long chain molecule and the degree of polymerization (DP) differs with source and the treatments employed during its extraction. The DP of cellulose is reported to be as

Biopolymer-Based Materials from Polysaccharides: Properties, Processing, Characterization…

Cellulose in nature is not found as an isolated molecule, but rather possesses an intriguing multi-level assembly, popularly known as hierarchical structure [18]. It is usually agreed that, during biosynthesis, approximately 36 individual cellulose molecules are assembled together to form elementary fibrils, which have dimensions in nano-scale (a square cross section, 3–5 nm in size). Elementary fibrils further undergo packing into a larger entity called microfibrils with a cross section of �20 nm � 8 nm. These microfibrils further assemble into macro sized cellulose fibers (e.g. wood fiber, cotton fiber) [14, 15]. However, specific packing of cellulose

Chemical structure and hydrogen bonding in cellulose: (a) chemical structure of cellulose, (b) hydrogen bonding in cellulose, and (c) schematic of cellulose microfibrils showing crystalline and amorphous structure.

high as 10,000 and 15,000 in wood and cotton fibers [14, 17].

may be different based on the source.

DOI: http://dx.doi.org/10.5772/intechopen.80898

Figure 2.

5

Figure 1.

Chemical structure chitin.

There are three main classes of biopolymers owing to their universal occurrence and abundance: (i) polynucleotides, (ii) polypeptides/poly amino acids, and (iii) polysaccharides. Polynucleotides (DNA and RNA) are long polymers composed of 13 or more nucleotide monomers [1]. Polypeptides are the short polymers comprised of amino acids as monomeric units and amide bonds link the monomeric units together [2]. Polysaccharides are composed of monomeric sugars linked together by O-glycosidic linkages. Among hundreds identified polysaccharides, cellulose, starch, chitin, chitosan are some of the important examples [3–5]. In contrast to the often simpler and more random structure of the synthetic polymers, biopolymers, in their natural states, are complex molecular assemblies that assume defined 3D structure and shapes, often known as hierarchical levels of structure.

Since biopolymers possess material properties suitable for various industrial and medical applications, they have garnered a great deal of interest both in academia and industry. Primarily, the interest and increasing trend of application of biopolymers as commodity products stems from their renewability, biodegradability and, often, their biocompatibility. Even though traditional plastics (petroleum based polymer products) are still indispensable in our daily life, there is a growing concern about their environmental impacts as they are non-biodegradable and as a consequent, accumulate in the environment. Furthermore, petroleum is not a renewable resource and its reserve is dwindling at a fast pace. Thus, biopolymers derived from renewable resources possess competitive advantage over synthetic non-renewable polymers. However, the cost of production of biopolymers and biopolymer based commodity products is of prime importance if they are to compete with oil-based synthetic polymers in the market.

Exploiting biopolymers, which are abundant and can be obtained from source material at lower cost, as a main component of biopolymeric products can be a smart strategy in the first place to mitigate the cost related issues. To that end, polysaccharides, the biopolymers comprised of monosaccharides (sugars) linked together by Oglycosidic linkages are of obvious choice. Both the most abundant natural resource, cellulose, and the second most abundant biopolymer, chitin, are polysaccharides [3, 6]. Additionally, polysaccharides are widely distributed in nature as they can be derived from plants, animals and microorganisms. Furthermore, variation in physicochemical properties, such as mechanical properties, solubility, viscosity, gelling potential, surface and interfacial properties, governed by monosaccharide composition, chain length (degree of polymerization), linkage types and patterns, provide polysaccharides versatility in preparation of materials with diverse applications. In fact, polysaccharides based materials in different forms including fibers, films, food casing, membranes, hydrogels, aerogels and sponges, with applications in several important commercial areas such as food, pharmaceuticals, biomedical, electronics, and adsorption have been developed [7–13]. Thus, polysaccharide-based biopolymers are promising candidates in the preparation of materials that can meet the much coveted dual requirements of environmental friendliness and economic sustainability. In this book chapter we focus on three important polysaccharide based biopolymers: cellulose, chitin, and chitosan.

#### 1.2 Cellulose

Cellulose, the most abundant renewable resource in the planet with an annual yield of 1.5 1012 tons, is the major structural component in plant cell walls. Besides plants, some species of bacteria, algae also biosynthesize cellulose. Tunicates are the only known animals capable of biosynthesizing cellulose [3, 14]. Because of its abundance, cellulose can serve as a virtually inexhaustible source of raw material in production of

Biopolymer-Based Materials from Polysaccharides: Properties, Processing, Characterization… DOI: http://dx.doi.org/10.5772/intechopen.80898

sustainable bioproducts, the so called "green products" [3]. It is a linear homopolymer of β-D glucose monomers covalently linked together by 1!4 glycosidic bonds i.e. the ringed glucose monomers are joined together via polycondensation reaction between hydroxyl groups at C1 of a glucose unit and C4 of the neighboring glucose unit. Since, every glucose unit is rotated 180° with respect to its neighbors along the fiber axis, dimer of glucose, called cellobiose, is considered as a repeating unit of cellulose polymer (Figure 1a) [15]. However, the convention of considering cellobiose as a repeating unit has been challenged and a recent review in this regard makes a cogent argument that glucose is the repeating unit rather than the cellobiose [16]. Cellulose is a long chain molecule and the degree of polymerization (DP) differs with source and the treatments employed during its extraction. The DP of cellulose is reported to be as high as 10,000 and 15,000 in wood and cotton fibers [14, 17].

Cellulose in nature is not found as an isolated molecule, but rather possesses an intriguing multi-level assembly, popularly known as hierarchical structure [18]. It is usually agreed that, during biosynthesis, approximately 36 individual cellulose molecules are assembled together to form elementary fibrils, which have dimensions in nano-scale (a square cross section, 3–5 nm in size). Elementary fibrils further undergo packing into a larger entity called microfibrils with a cross section of �20 nm � 8 nm. These microfibrils further assemble into macro sized cellulose fibers (e.g. wood fiber, cotton fiber) [14, 15]. However, specific packing of cellulose may be different based on the source.

Figure 1.

provide structural support (e.g. collagen). Cellulose is the major structural compo-

Exploiting biopolymers, which are abundant and can be obtained from source material at lower cost, as a main component of biopolymeric products can be a smart strategy in the first place to mitigate the cost related issues. To that end, polysaccharides, the biopolymers comprised of monosaccharides (sugars) linked together by Oglycosidic linkages are of obvious choice. Both the most abundant natural resource, cellulose, and the second most abundant biopolymer, chitin, are polysaccharides [3, 6]. Additionally, polysaccharides are widely distributed in nature as they can be derived from plants, animals and microorganisms. Furthermore, variation in physicochemical properties, such as mechanical properties, solubility, viscosity, gelling potential, surface and interfacial properties, governed by monosaccharide composition, chain length (degree of polymerization), linkage types and patterns, provide polysaccharides versatility in preparation of materials with diverse applications. In fact, polysaccharides based materials in different forms including fibers, films, food casing, membranes, hydrogels, aerogels and sponges, with applications in several important commercial areas such as food, pharmaceuticals, biomedical, electronics, and adsorption have been developed [7–13]. Thus, polysaccharide-based biopolymers are promising candidates in the preparation of materials that can meet the much coveted dual requirements of environmental friendliness and economic sustainability. In this book chapter we focus on three important polysaccharide based biopoly-

Cellulose, the most abundant renewable resource in the planet with an annual yield of 1.5 1012 tons, is the major structural component in plant cell walls. Besides plants, some species of bacteria, algae also biosynthesize cellulose. Tunicates are the only known animals capable of biosynthesizing cellulose [3, 14]. Because of its abundance, cellulose can serve as a virtually inexhaustible source of raw material in production of

There are three main classes of biopolymers owing to their universal occurrence and abundance: (i) polynucleotides, (ii) polypeptides/poly amino acids, and (iii) polysaccharides. Polynucleotides (DNA and RNA) are long polymers composed of 13 or more nucleotide monomers [1]. Polypeptides are the short polymers comprised of amino acids as monomeric units and amide bonds link the monomeric units together [2]. Polysaccharides are composed of monomeric sugars linked together by O-glycosidic linkages. Among hundreds identified polysaccharides, cellulose, starch, chitin, chitosan are some of the important examples [3–5]. In contrast to the often simpler and more random structure of the synthetic polymers, biopolymers, in their natural states, are complex molecular assemblies that assume defined 3D structure and shapes, often known as hierarchical levels of structure. Since biopolymers possess material properties suitable for various industrial and medical applications, they have garnered a great deal of interest both in academia and industry. Primarily, the interest and increasing trend of application of biopolymers as commodity products stems from their renewability, biodegradability and, often, their biocompatibility. Even though traditional plastics (petroleum based polymer products) are still indispensable in our daily life, there is a growing concern about their environmental impacts as they are non-biodegradable and as a consequent, accumulate in the environment. Furthermore, petroleum is not a renewable resource and its reserve is dwindling at a fast pace. Thus, biopolymers derived from renewable resources possess competitive advantage over synthetic non-renewable polymers. However, the cost of production of biopolymers and biopolymer based commodity products is of prime importance if they are to compete with oil-based

nent of the plant cell walls.

Advanced Sorption Process Applications

synthetic polymers in the market.

mers: cellulose, chitin, and chitosan.

1.2 Cellulose

4

Chemical structure and hydrogen bonding in cellulose: (a) chemical structure of cellulose, (b) hydrogen bonding in cellulose, and (c) schematic of cellulose microfibrils showing crystalline and amorphous structure.

Prevalence of hydroxyl groups in cellulose (three hydroxyl groups per glucose monomer) results in extensive intra-and interchain hydrogen bonding in cellulose (Figure 1b). Intra-and interchain hydrogen bonding and the stacking interactions mainly originating from Van der Waals forces facilitate highly ordered arrangement (crystalline regions) of cellulose fibrils although there are also amorphous regions present (where arrangement of cellulose chains is disordered) as depicted in Figure 1c [19]. In general, cellulose, regardless of the source, is highly crystalline and high molecular weight biopolymer and is, usually, a fibrous, tough and hydrophilic but insoluble in water and other common solvents [20]. However, important properties such as DP, crystallinity and fibrillar organization are dependent on the source. For example, cellulose from cotton fiber is more crystalline (�80% crystallinity) as compared to wood cellulose (�50% crystallinity). Similarly, quite different from plant derived cellulose, bacterial cellulose has ultrafine nanofibrous network structure, high hydrophilicity, and moldability [21].

cellulose derivatives such as acetylated (e.g. cellulose acetate), carboxy methylated (e.g. carboxymethyl cellulose), and phosphorylated (e.g. cellulose diphenylphosphate) and cationized cellulose [27–30]. Cellulose acetate (CA) is one of the most important commercially available cellulose derivatives with many applications such as fiber, film, and osmotic membrane. CA is a cellulose ester in which hydroxyl groups in cellulose are esterified with acetate groups to varying degrees [31]. Similarly, chitin and chitosan can be derivatized through O- and N-substitution to obtain carboxyalkyl derivatives such as O-carboxymethyl chitin, O-carboxymethyl chitosan and N,N-dicarboxymethyl chitosan [21, 24]. Derivatization not only eases the processing of these biopolymers since derivatives can be solubilized in common solvents and even in water based on degree and type of substitution [21, 29, 32], but also imparts some novel chemical and physical properties to cellu-

Biopolymer-Based Materials from Polysaccharides: Properties, Processing, Characterization…

lose. For instance, phosphorylation of cellulose can impart enhanced flame retardancy and bioactivity [21, 32]. Similarly, carboxyalkylation of chitosan enhances its affinity towards metal ions and has application in metal ions collec-

Due to their high molecular weight and complex biopolymeric network (extended hydrogen bonding and crystallinity), processing of cellulose and chitin into desirable forms, such as films, membranes, fibers, and gels, via dissolution is generally considered as nontrivial task as they are insoluble in water and other common organic solvents [13, 33]. Therefore, although studied for a long time, cellulose and chitin dissolution in cost effective and environmentally friendly manner remains an active area of research. A number of solvents/solvent systems have been developed over the course of time. Derivatizing solvent (carbon disulfide/ aqueous sodium hydroxide used in "Viscose" process), and other non-derivatizing solvents such as aqueous alkali solution (e.g. aqueous solution of 7% sodium hydroxide/12% urea), N,N-dimethylacetamide/lithium chloride (DMAC/LiCl), Nmethylmorpholine-N-oxide (NNMO) (used in "Lyocell" process), and ionic liquids (ILs) have been some of the important cellulose solvents [34–38]. Aqueous sodium hydroxide/urea solution, DMAc/LiCl and ILs such as 1-allyl-3-methylimidzolium bromide, 1-butyl-3-methylimidzolium chloride and 1-butyl-3-methylimidazolium acetate have been reported to be capable of dissolving chitin [33]. Although they are yet to find significant industrial breakthrough, ionic liquids are thought to have advantages over other solvents due to their chemical and thermal stability, tunability, non-flammability, negligible low vapor pressure, high efficiency in dissolution of both cellulose and chitin. Regenerated cellulose products such as fibers, film, aerogels and beads have been prepared from biopolymer solutions in different

Aerogels are broadly defined as sol–gel derived materials, which are highly porous, low density and predominantly mesoporous (pore diameter: 2–50 nm) [43]. They are derived from hydrogels followed by the removal of liquid component using super critical point drying or freeze-drying to avoid damage to the original gel micro-structure prepared from biopolymers solution. Because of their very low density, high porosity and high specific surface area, aerogels have potential applications in separation, adsorption, catalyst, photo-electricity, and biomedicine [13].

) [44], chitin

) [46] have been prepared.

High surface area aerogels from cellulose (400–500 m<sup>2</sup> g<sup>1</sup>

) [45], and chitosan (248 m<sup>2</sup> g<sup>1</sup>

2.2 Dissolution of cellulose, chitin and chitosan

DOI: http://dx.doi.org/10.5772/intechopen.80898

tion [24].

solvents [39–42].

2.3 Aerogels

(560 m<sup>2</sup> g<sup>1</sup>

7

#### 1.3 Chitin

Chitin is another important polysaccharide and the most abundant biopolymer on the planet after cellulose. It is a structural biopolymer, contributing in strength and reinforcement, present in the exoskeleton of arthropods (i.e., in the shells of shrimps and crabs), and the cuticle of insects. It is also found in the cell walls of fungi, yeast and other organisms in lower plant and animal kingdoms [4]. Structurally, it is similar to cellulose except the presence of acetamide or amine functional groups at C2 position of the glucose monomer unit. Therefore, chitin is a linear polymer of 2-acetamido-2-deoxy-D-glucopyranose linked together by β(1!4) glycosidic bond [22] (Figure 2). The degree of acetylation (DA) which is the share of nitrogen sites occupied by acetyl group is typically �90% in chitin after extraction and purification from source material since alkali treatment applied for the removal of protein also lowers DA [23].

Similar to cellulose, native chitin is arranged in highly crystalline microfibrils because of the extensive hydrogen bonding among the polymer chains. It is tough, hydrophobic, and insoluble in water and other common organic solvents. Chitin is even more recalcitrant to solubilization and consequently harder to process than cellulose [6].

#### 1.4 Chitosan

Chitosan is the most important partially deacetylated derivative of chitin with degree of acetylation (DA) <50%. Typically chitin has DA <35% [24]. Chitin can be deacetylated by treating it with concentrated alkali at elevated temperature. Enzymatic hydrolysis in the presence of chitin deacetylase can also be employed for deacetylation purpose [21]. Therefore, chitosan can be represented by the same chemical structure as chitin. While chitin is insoluble in common solvents, chitosan can be dissolved in weak acidic solutions (aqueous solutions with pH < 6.5). It is soluble in hydrochloric acid and aqueous organic acids such as formic, acetic, oxalic and lactic acids. Protonation of the free glucosamine in acidic condition facilitates chitosan solubility [25, 26]. Chitin and chitosan are reported to have inherent antimicrobial properties.

### 2. Processing of cellulose, chitin and chitosan

#### 2.1 Derivatization of cellulose, chitin and chitosan

Because of the abundance of hydroxyl (OH) groups present in cellulose, it can be derivatized through esterification, etherification, and other reactions to produce

Biopolymer-Based Materials from Polysaccharides: Properties, Processing, Characterization… DOI: http://dx.doi.org/10.5772/intechopen.80898

cellulose derivatives such as acetylated (e.g. cellulose acetate), carboxy methylated (e.g. carboxymethyl cellulose), and phosphorylated (e.g. cellulose diphenylphosphate) and cationized cellulose [27–30]. Cellulose acetate (CA) is one of the most important commercially available cellulose derivatives with many applications such as fiber, film, and osmotic membrane. CA is a cellulose ester in which hydroxyl groups in cellulose are esterified with acetate groups to varying degrees [31]. Similarly, chitin and chitosan can be derivatized through O- and N-substitution to obtain carboxyalkyl derivatives such as O-carboxymethyl chitin, O-carboxymethyl chitosan and N,N-dicarboxymethyl chitosan [21, 24]. Derivatization not only eases the processing of these biopolymers since derivatives can be solubilized in common solvents and even in water based on degree and type of substitution [21, 29, 32], but also imparts some novel chemical and physical properties to cellulose. For instance, phosphorylation of cellulose can impart enhanced flame retardancy and bioactivity [21, 32]. Similarly, carboxyalkylation of chitosan enhances its affinity towards metal ions and has application in metal ions collection [24].

#### 2.2 Dissolution of cellulose, chitin and chitosan

Due to their high molecular weight and complex biopolymeric network (extended hydrogen bonding and crystallinity), processing of cellulose and chitin into desirable forms, such as films, membranes, fibers, and gels, via dissolution is generally considered as nontrivial task as they are insoluble in water and other common organic solvents [13, 33]. Therefore, although studied for a long time, cellulose and chitin dissolution in cost effective and environmentally friendly manner remains an active area of research. A number of solvents/solvent systems have been developed over the course of time. Derivatizing solvent (carbon disulfide/ aqueous sodium hydroxide used in "Viscose" process), and other non-derivatizing solvents such as aqueous alkali solution (e.g. aqueous solution of 7% sodium hydroxide/12% urea), N,N-dimethylacetamide/lithium chloride (DMAC/LiCl), Nmethylmorpholine-N-oxide (NNMO) (used in "Lyocell" process), and ionic liquids (ILs) have been some of the important cellulose solvents [34–38]. Aqueous sodium hydroxide/urea solution, DMAc/LiCl and ILs such as 1-allyl-3-methylimidzolium bromide, 1-butyl-3-methylimidzolium chloride and 1-butyl-3-methylimidazolium acetate have been reported to be capable of dissolving chitin [33]. Although they are yet to find significant industrial breakthrough, ionic liquids are thought to have advantages over other solvents due to their chemical and thermal stability, tunability, non-flammability, negligible low vapor pressure, high efficiency in dissolution of both cellulose and chitin. Regenerated cellulose products such as fibers, film, aerogels and beads have been prepared from biopolymer solutions in different solvents [39–42].

#### 2.3 Aerogels

Prevalence of hydroxyl groups in cellulose (three hydroxyl groups per glucose monomer) results in extensive intra-and interchain hydrogen bonding in cellulose (Figure 1b). Intra-and interchain hydrogen bonding and the stacking interactions mainly originating from Van der Waals forces facilitate highly ordered arrangement (crystalline regions) of cellulose fibrils although there are also amorphous regions present (where arrangement of cellulose chains is disordered) as depicted in

Figure 1c [19]. In general, cellulose, regardless of the source, is highly crystalline and high molecular weight biopolymer and is, usually, a fibrous, tough and hydrophilic but insoluble in water and other common solvents [20]. However, important properties such as DP, crystallinity and fibrillar organization are dependent on the source. For example, cellulose from cotton fiber is more crystalline (�80% crystallinity) as compared to wood cellulose (�50% crystallinity). Similarly, quite different from plant derived cellulose, bacterial cellulose has ultrafine nanofibrous network struc-

Chitin is another important polysaccharide and the most abundant biopolymer on the planet after cellulose. It is a structural biopolymer, contributing in strength and reinforcement, present in the exoskeleton of arthropods (i.e., in the shells of shrimps and crabs), and the cuticle of insects. It is also found in the cell walls of fungi, yeast and other organisms in lower plant and animal kingdoms [4]. Structurally, it is similar to cellulose except the presence of acetamide or amine functional groups at C2 position of the glucose monomer unit. Therefore, chitin is a linear polymer of 2-acetamido-2-deoxy-D-glucopyranose linked together by β(1!4) glycosidic bond [22] (Figure 2). The degree of acetylation (DA) which is the share of nitrogen sites occupied by acetyl group is typically �90% in chitin after extraction and purification from source material since alkali treatment applied for the removal of protein also lowers DA [23]. Similar to cellulose, native chitin is arranged in highly crystalline microfibrils because of the extensive hydrogen bonding among the polymer chains. It is tough, hydrophobic, and insoluble in water and other common organic solvents. Chitin is even more recalcitrant to solubilization and consequently harder to process than

Chitosan is the most important partially deacetylated derivative of chitin with degree of acetylation (DA) <50%. Typically chitin has DA <35% [24]. Chitin can be deacetylated by treating it with concentrated alkali at elevated temperature. Enzymatic hydrolysis in the presence of chitin deacetylase can also be employed for deacetylation purpose [21]. Therefore, chitosan can be represented by the same chemical structure as chitin. While chitin is insoluble in common solvents, chitosan can be dissolved in weak acidic solutions (aqueous solutions with pH < 6.5). It is soluble in hydrochloric acid and aqueous organic acids such as formic, acetic, oxalic and lactic acids. Protonation of the free glucosamine in acidic condition facilitates chitosan solubility [25, 26].

Chitin and chitosan are reported to have inherent antimicrobial properties.

Because of the abundance of hydroxyl (OH) groups present in cellulose, it can be derivatized through esterification, etherification, and other reactions to produce

2. Processing of cellulose, chitin and chitosan

2.1 Derivatization of cellulose, chitin and chitosan

ture, high hydrophilicity, and moldability [21].

Advanced Sorption Process Applications

1.3 Chitin

cellulose [6].

1.4 Chitosan

6

Aerogels are broadly defined as sol–gel derived materials, which are highly porous, low density and predominantly mesoporous (pore diameter: 2–50 nm) [43]. They are derived from hydrogels followed by the removal of liquid component using super critical point drying or freeze-drying to avoid damage to the original gel micro-structure prepared from biopolymers solution. Because of their very low density, high porosity and high specific surface area, aerogels have potential applications in separation, adsorption, catalyst, photo-electricity, and biomedicine [13]. High surface area aerogels from cellulose (400–500 m<sup>2</sup> g<sup>1</sup> ) [44], chitin (560 m<sup>2</sup> g<sup>1</sup> ) [45], and chitosan (248 m<sup>2</sup> g<sup>1</sup> ) [46] have been prepared.

### 2.4 Nanofibrillation/nanoparticles (nanocellulose, nanochitin, nanochitosan)

3.2.3 Scanning electron microscopy (SEM)

DOI: http://dx.doi.org/10.5772/intechopen.80898

Japan) with an accelerating voltage of 15 kV.

the wavenumber range of 4000 to 650 cm<sup>1</sup>

least 48 h prior to their characterization.

4.1 X-ray diffraction (XRD) analysis

Figure 3.

9

PerkinElmer Spectrum software.

3.2.4 Fourier transform infrared (FTIR) spectroscopy

spectra were collected at a spectral resolution of 4 cm<sup>1</sup>

4. Characterization of cellulose, chitin and chitosan

Wide angle X-ray diffraction curves for cellulose, chitin and chitosan powder.

The morphology of cellulose, chitin and chitosan samples was studied on a Hitachi S-4700 field emission scanning electron microscope (TM-100, Hitachi,

Biopolymer-Based Materials from Polysaccharides: Properties, Processing, Characterization…

FTIR spectra of the cellulose, chitin and chitosan samples were recorded using a PerkinElmer Spectrum-400 FTIR spectrometer equipped with a universal attenuated total reflectance (UATR) accessory (PerkinElmer, Waltham, MA). All FTIR

All samples were conditioned in an environmentally-controlled laboratory maintained at a relative humidity of 65 2% and temperature of 21 1°C for at

Wide-angle X-ray diffraction measurements were collected for raw cellulose, chitin, and chitosan powder samples. Figure 3 shows the X-ray diffraction curves for cellulose, chitin, and chitosan. The XRD pattern of cellulose exhibits five major diffraction peaks at 14.9 (101), 15.8 (10ī), 21.8 (021) 22.5 (002) and 34.6 (004) which are in agreement with the literature values reported for cellulose I<sup>β</sup> [52]. The XRD patterns of chitin showed two strong reflections at 9.2° (020) and 19.1° (110) and minor reflections at 12.6° (021), 22.9° (130) and 26.2° (013) corresponding to α-chitin [53]. Chitosan shows two distinct peaks at 10.67 (020) and 19.92° (110) [54]. Our results suggest that chitin has the highest crystallinity as compared

, with 32 co-added scans in

. The spectra were analyzed using

The term "nanocellulose"/"nanochitin"/"nanochitosan" encompasses various materials derived from respective biopolymers, which possess at least one dimension in the nanometer range [14, 47]. Nanoparticles from cellulose and chitin are usually prepared by destructing the native hierarchical structure of these biopolymers [48]. Cellulose and chitin nanofibers, in general, are obtained by subjecting purified cellulose and chitin substrates to multiple mechanical shearing actions, which disintegrate the native microfibril structure and release enmeshed individual or bundle of fibrils. Chitosan nanofibers are typically produced by electrospinning [49].

Highly crystalline elongated rod like (or needle-like) nanoparticles called nanocrystals can be obtained when cellulose and chitin substrates are subjected to a strong acid hydrolysis treatment due to preferential dissolution of amorphous domains. For acid hydrolysis to produce nanocrystals, sulfuric acid and hydrochloric acid are usually employed [50, 51]. Biopolymer nanoparticles can be directly processed into films and aerogels by drying from the suspension or they can be utilized as reinforcement agents in other polymer matrices.
