## 1 Introduction  
Cellulose is a linear polymer which consists of hundreds to thousands of linked D-glucose units having \(\beta\)-(1-4)-glycosidic bonds with a general formula (C\({}_{6}\)H\({}_{10}\)O\({}_{5}\))n. These units are inter-connected through hydrogen bonding and van der Waals forces to form fibrils [1]. This polysaccharide is found in cells of all plants, in addition to hemicellulose, lignin, and other comparably small amounts of extractives. Cellulose exists in plant cells in the form of fibers with a high axial stiffness and which can be separated into nanocellulose fibers (NCF). This transformation can be carried out either by chemical or mechanical treatments; the former use enzymes or chemicals such as mineral acidse.g., sulfuric or hydrochloric acids, while the latter using mechanical stress methods such as ball milling or homogenization. These mechanical stressing methods may be preceded by chemical or enzymatic treatment as has been described by [PERSON] et al. [2]. However, these methods generally produce fibrils with different dimensions. The same transformation may occur during industrial processing that applies mechanical stress e.g., ball milling [3; 4; 5]. This structure renders the cellulose polymer with crystalline and amorphous parts. The balance between these two parts and the de-polymerization of the biopolymer have played a key role in the manufacturing of microcrystalline cellulose (MCC) as the most widely used excipient in pharmaceutical applications [6; 7; 8]. MCC is manufactured by de-polymerization using acid hydrolysis (HCl or H\({}_{2}\)SO\({}_{4}\)) of \(\alpha\)-cellulose obtained from the pulp of fibrous plant materials, such as cotton wool [9]. Hydrolysis in this manner produces a hydrocellulose which is subjected to filtration then to spray drying to form dry, porous particles of various sizes with increased crystallinity compared to the original raw cellulose [10]. The high recognition of MCC is attributed to its distinctive multifunction and direct compression features. From this perspective, MCC shows superiority with strong binding, flowability, and disintegrant characteristics and uniform particle size, in addition to compatibility with other excipients or drugs [11]. The motivation for using MCC in various solid dosage form preparations is its ability to be compressed and compacted, which is due to its extended porous structure, surface roughness, and plastic deformation [12]. High porosity results in a higher interior particle space which in turn facilitates higher compactibility in the resulted product. This is an advantage compared to other available non-cellulosic direct compression (DC) excipients used in pharmaceutical solid dosage form preparations [13; 14]. For a plastically deforming material with such high porosity, an applied pressure facilitates bonding and interlocking between its differently sized and irregularly shaped particles [15; 16; 17; 18]. This observation was outlined by [PERSON] et al. [19] who showed that the degree of deformation of MCC granules is substantially increased upon increasing their original intra-granular porosity. Despite numerous benefits of MCC in compactibility of solid powders, a number of shortcomings in the processing of powder mixtures containing MCC exist. These are mostly related to MCC low bulk density, high sensitivity to lubrication, and loss of excipient functionality upon re-workability [20; 21; 22]. Low bulk density, which has been attributed to the highly porous structure of MCC, leads to a decrease in flowability [23]. This is regarded as a major processing drawback when preparing solid dosage forms because processing of powder mixtures containing Active Pharmaceutical Ingredients (API) must have a certain bulk density to facilitate their processing. Thus, volume reduction techniques through slugging or roller compaction are necessary. These processes may need to be repeated where such repetition causes a reduction in powder binding in compacts [24].