**1. Introduction**

Cellulose, a fibrous carbohydrate found in all plants, is the most abundant natural polymer with biomass production of 50 billion tons per year [1]. Cellulose is a linear polymer of glucose. Based on solubility in alkaline, cellulose is divided into three groups which are alpha, beta, and gamma celluloses. Microcrystalline cellulose (MCC) is a purified, partially depolymerized cellulose having the formula (C6H10O5)n. It is prepared by treating alpha cellulose with mineral acids (type Ib). This polysaccharide polymer consists of a linear chain of several hundred to over ten thousand β(1 → 4) linked D-glucose units, consisting of linear chains of *β*-1,4-d anhydroglucopyranosyl units. Raw material used for MMC preparation is a pulp from a fibrous plant such as conifer wood. Cotton is also a possible cellulose source for MCC [2, 3]. Pharmaceutical grade MCC, which needs a high-quality pulp, used wood as the most common source. From such wooden source, cellulose chains are packed in layers and held together by strong hydrogen bonds from lignin, a cross-linking polymer. For that purpose, both softwoods (evergreen conifer) and hardwoods (deciduous broadleaf) can be used [4]. These woods differ not only in chemical composition including cellulose proportions, hemicelluloses, and lignin

but also in structural organization, i.e., regions which are relatively more crystalline or amorphous. The amorphous regions are more prone to hydrolysis by acid resulting in shorter and more crystalline fragments.

Non-woody lignocellulosic materials have also been developed as source of MCC such as cotton linters [5], cotton stalks [6], cotton rags [5], cotton fabric waste [7], cotton wool [8], soybean husk [9], corn cob [10], water hyacinth [11], coconut shells [12], oil palm biomass residue [13, 14], oil palm fronds [15], rice husk [6, 16], sugar cane bagasse [6, 16–20], jute [21, 22], ramie [23], fibers and straw of flax [24], wheat straw [25], sorghum stalks [26], sisal fibers [27] and mangosteen [28], alfa grass fibers [29, 30], soybean hulls [31], orange mesocarp [32], Indian bamboo [33], roselle fiber [34], and alfa fiber [35]. Seed flosses from milkweed pods (*Calotropis procera*), shrubs, and kapok (*Ceiba pentandra*) trees are also known as cellulosic resources. Due to its high purity of alpha cellulose, most seed flosses must be treated to remove impurities including lignin, pectin, and wax [36].

Wooden sources contain cellulose chains which are packed as layers held by cross-linking hydrogen bonds [37]. Chemically it consists of polymeric matrix of lignin, hemicelluloses, and pectin [38]. Different woods considerably possessed different chemical composition of cellulose (including allocations of cellulose, hemicelluloses, and lignin in cell wall) and structural organization as well. Relatively different crystallinity in particular regions is observed as more amorphous according to softwoods (evergreen conifer) and hardwoods which are termed as deciduous broadleaf [4, 37]. The amorphous regions of cellulose provide a more susceptible property for depolymerization by acid hydrolysis. At optimum acid concentration, the process gave shorter and more crystalline fragments such as the MCC [2, 37].
