**3. Cellulose**

Cellulose has stood out in the last 20 years as a study material for several applications, as it is the most abundant, renewable and natural polymer on the face of the Earth [15], and can be found mainly in woody plants (wood), annuals and in grasses [16]. Cellulose is located mainly in the secondary cell wall, corresponding to approximately 40 to 45% of the wood mass [17].

Cellulose (C6H10O5) n is a polysaccharide, linear chain containing from hundreds to thousands of chemical bonds involving carbon, hydrogen and oxygen atoms (**Figure 1**) [18]. The cellulose chain is of high molecular weight, which tends to form hydrogen bonds between the molecules [19, 20]. The hydroxyl groups of cellulose molecules form hydrogen bonds that can be intramolecular or intermolecular,

**Figure 1.** *Chemical structure of cellulose.*

directing the crystalline packaging, and it is these bonds that make cellulose a stable polymer and appreciated as reinforcement in composites [21, 22].

Its organized structure is formed by cellulose microfibrils, which due to intermolecular bonds form the fibrils, which in turn are composed in an orderly fashion in order to form cellulosic fibers. Cellulose fibers are made up of two regions, the crystalline region, in which the microfibrils are presented in an extremely orderly manner, and the amorphous region, in which they are arranged in a less ordered manner [17], and for some lignocellulosic sources the amorphous regions can reach 50% of the structure [22].

Despite the hygroscopic nature of the individual cellulose molecules, the absorption of water molecules is only possible in the amorphous zones, since there is a lack of empty spaces in the crystalline structure. Hydroxy groups are the most abundant groups in the cellulose molecule, followed by the acetal bonds that form the ring of pyraneses [23].

In the crystalline regions of cellulose, we also have that the intra and intermolecular interactions can vary, giving rise to the various polymorphs [18]. The degree of polymerization and the crystallinity of cellulose vary according to the lignocellulosic source [1]. Due to the presence of crystalline and amorphous regions, cellulose can be classified as a semicrystalline fibrillar material [24].

Using cellulosic materials has several advantages, such as: its low cost, low density, high mechanical resistance and high elastic modulus. Due to the stable structure of their crystalline regions, cellulose fibrils have high mechanical properties along the longitudinal direction [24]. It is also possible to benefit from the high stiffness of the cellulose crystal which, when used on a nanometer scale for the production of composite materials, makes it possible to preserve the optical properties of the original material while improving the mechanical properties [25].

#### **3.1 Colloidal stability of cellulose**

Cellulosic pulp is a material whose characteristics and properties are determined by its origin. Cellulose modification methods are used when carrying out processes carried out in an aqueous medium, but cellulose is an amphiphilic polymer, that is, it presents a hydrophilic region that dissolves in water, and another hydrophobic region that does not dissolve in water, due to the presence of crystalline and amorphous regions.

The geometry, size and surface density of the particles are also properties that interfere with the processes of coagulation and flocculation. The polymers used with water retention agents increase the forces of colloidal attraction and induce flocculation through different mechanisms, based on different effects. We can mention: flocculation by bridge effect, flocculation by depletion effect and flocculation by reinforced bridge effect [1].

In the case of cellulose fibers, these properties are not well defined due to the variety in the size and shape of the fibers. However, it is known that cellulose fibers when dispersed in water have a pH of around 6, which indicates the acidic character of the surface, therefore a tendency to preferentially adsorb OH- group. In this way, the aqueous dispersions of cellulose fibers are influenced in their colloidal stability by the presence of a double electrical layer under their surface, resulting from the dissociation of different functional groups, such as carboxylics [26].

The pure cellulose fiber in suspension has a high tendency to aggregate and form clots by the action of gravity. However, studies show that through the addition of symmetrical or asymmetric electrolytes the tendency to coagulate the cellulose fiber suspension can be maximized or minimized depending on the final objective. The addition of cationic starch and calcium carbonate to the cellulose fiber suspension

**129**

**Author details**

Marina Stygar Lopes

Federal University of Paraná, Curitiba, Brazil

provided the original work is properly cited.

my training from undergraduate to doctorate.

**Notes/Thanks/Other declarations**

\*Address all correspondence to: marinastygar@gmail.com

*Colloidal Stability of Cellulose Suspensions DOI: http://dx.doi.org/10.5772/intechopen.94490*

**3.2 Cellulose used in paper production**

of operational problems.

**4. Conclusions**

of cellulose.

fiber [1].

causes a change in the charge signal of the fiber surface, resulting in phenomena of fiber-fiber interaction that guarantees greater stability in relation to pure cellulose

In the refining process, for example for the production of paper, cellulose fibers are immersed in water. The fibrils, which make up the cells, are composed of crystalline regions that, when immersed in water, absorb a quantity of this water across all exposed crystalline surfaces, causing their swelling and decreased attraction between the fibrils. The mechanical action of shearing the fibers through refiners speeds up this swelling, as it exposes the surfaces previously located inside the fibers, causing an increase in surface exposure, which promotes a greater number of contacts and connections between the fibers, resulting in this stronger paper [1]. The steps of converting cellulose to paper involve many surface chemical interactions, interactions between fibers and colloidal particles. Understanding these interactions is useful for product development and improving the resolution

This chapter sought to define the main characteristics of colloids, as well as their classification, methods of preparation and finally to address characteristics of colloid stability. Cellulose, the most abundant biopolymer in the world, is a colloid widely used in several industries. This colloid proves challenging for some segments due to its detailed characteristics throughout of the chapter. Studies continue to be carried out on this topic in order to bring solutions to improve the colloidal stability

I thank IntechOpen for the opportunity and the Federal University of Paraná for

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Colloids - Types, Preparation and Applications*

50% of the structure [22].

the ring of pyraneses [23].

**3.1 Colloidal stability of cellulose**

culation by reinforced bridge effect [1].

phous regions.

directing the crystalline packaging, and it is these bonds that make cellulose a stable

Its organized structure is formed by cellulose microfibrils, which due to intermolecular bonds form the fibrils, which in turn are composed in an orderly fashion in order to form cellulosic fibers. Cellulose fibers are made up of two regions, the crystalline region, in which the microfibrils are presented in an extremely orderly manner, and the amorphous region, in which they are arranged in a less ordered manner [17], and for some lignocellulosic sources the amorphous regions can reach

Despite the hygroscopic nature of the individual cellulose molecules, the absorption of water molecules is only possible in the amorphous zones, since there is a lack of empty spaces in the crystalline structure. Hydroxy groups are the most abundant groups in the cellulose molecule, followed by the acetal bonds that form

In the crystalline regions of cellulose, we also have that the intra and intermolecular interactions can vary, giving rise to the various polymorphs [18]. The degree of polymerization and the crystallinity of cellulose vary according to the lignocellulosic source [1]. Due to the presence of crystalline and amorphous regions, cellulose

Using cellulosic materials has several advantages, such as: its low cost, low density, high mechanical resistance and high elastic modulus. Due to the stable structure of their crystalline regions, cellulose fibrils have high mechanical properties along the longitudinal direction [24]. It is also possible to benefit from the high stiffness of the cellulose crystal which, when used on a nanometer scale for the production of composite materials, makes it possible to preserve the optical properties of the original material while improving the mechanical properties [25].

Cellulosic pulp is a material whose characteristics and properties are determined by its origin. Cellulose modification methods are used when carrying out processes carried out in an aqueous medium, but cellulose is an amphiphilic polymer, that is, it presents a hydrophilic region that dissolves in water, and another hydrophobic region that does not dissolve in water, due to the presence of crystalline and amor-

The geometry, size and surface density of the particles are also properties that interfere with the processes of coagulation and flocculation. The polymers used with water retention agents increase the forces of colloidal attraction and induce flocculation through different mechanisms, based on different effects. We can mention: flocculation by bridge effect, flocculation by depletion effect and floc-

In the case of cellulose fibers, these properties are not well defined due to the variety in the size and shape of the fibers. However, it is known that cellulose fibers when dispersed in water have a pH of around 6, which indicates the acidic character of the surface, therefore a tendency to preferentially adsorb OH- group. In this way, the aqueous dispersions of cellulose fibers are influenced in their colloidal stability by the presence of a double electrical layer under their surface, resulting from the

The pure cellulose fiber in suspension has a high tendency to aggregate and form clots by the action of gravity. However, studies show that through the addition of symmetrical or asymmetric electrolytes the tendency to coagulate the cellulose fiber suspension can be maximized or minimized depending on the final objective. The addition of cationic starch and calcium carbonate to the cellulose fiber suspension

dissociation of different functional groups, such as carboxylics [26].

polymer and appreciated as reinforcement in composites [21, 22].

can be classified as a semicrystalline fibrillar material [24].

**128**

causes a change in the charge signal of the fiber surface, resulting in phenomena of fiber-fiber interaction that guarantees greater stability in relation to pure cellulose fiber [1].
