## 4 Discussion
[51] and [PERSON] and [PERSON] [52] reported that MCC undergoes an increase in crystallinity when a pressure is induced, whereas [PERSON] et al. [53] reported an initial slight increase followed by a decrease in crystallinity. The tablets they produced were of 12 g weight, \(50\times 50\) mm square shape, and 0.5 g weight, 17 mm circular shape. When examining the cases for the increase in crystallinity, it was noticed that compression was carried out on tablets of thickness and/or surface area (punch diameter) much higher than that provided by roller compactors. In the current work, the compactor had a roller gap of 2.0 mm, which suggests a mechanically rendered intensive distribution of the compaction force, i.e., 25 MPa, onto individual powder particles. This hypothesis is supported by the findings of [PERSON] et al. [53], who compressed thinner and smaller tablets (estimated not greater than 100 mg tablet weight, 5.5 mm circular shape) than those of the two aforementioned cases which are associated with the increase in crystallinity with pressure. In contrast, the broadening of the diffraction peak at \(20=13\)-\(17\) is equivalent to a previous finding by [PERSON] et al. [54] who applied high stress/pressure conditions to powdered cellulose. In this regard, the aforementioned broadening was explained on the basis of amorphization of the specimen or a decrease in the degree of polymerization of cellulose [54]. From the foregoing results and discussion, it is evident that multiple compaction cycles using a roller compactor are capable of altering some of the physical parameters of the tested powder of Avicel PH101. This was evident due to the significant increase in bulk density from 0.18 g/mL to over 0.6 g/mL. This improves powder flow and facilitates its passage in a tableting machine. It can be noted that granules from the first and second compaction cycles behaved similarly but differently from granules of the third compaction cycle. The pore diameters for Avicel PH-101 and from the first and second cycles of compaction were larger than those of granules resulting from the third cycle of compaction. This can be an indication of the appearance of a new surface of MCC fiber. Indeed, pore diameter was smaller than the non-compacted Avicel PH-101 pore diameter, which was evident from porosity measurements. Such observations lead to the conclusion that new fiber surfaces appear due to the applied mechanical stress during roller compaction. This force is capable of destroying or disintegrating the outer layer of MCC fibers exposing the internal layer in the same fashion as used in obtaining nanosize crystalline cellulose fibers. This was reported by [PERSON] who confirmed the appearance of NCF upon wet grinding [55]. It can be safely concluded that the intense compaction acted as a mechanical force leading to the appearance of smaller sized grains of cellulose fibers (NCFs) and is clearly demonstrated by giving rise to new surfaces capable of bonding. This results in a crushing strength that is even higher than that of non-compacted MCC (Avicel PH-101). In contrast, SEM after the 1 st compaction cycle shows a consolidation of individual particles appearing on the surface and forming bigger granules. For the 2 nd compaction cycle, consolidation becomes intensified as the individual particles of Avicel PH-101 cannot be seen on the surface of the particles. For the 3 rd compaction cycle, the surface of the particles is, again, highly consolidated and consists of individual particles with high surface deformation. Such overall behavior visualized using SEM for Avicel PH-101 under roller compaction is somehow different than that seen in other mechanical stress-inducing techniques such as homogenization, extrusion, blending, and ball milling. These techniques are capable of providing sufficient shear forces necessary to induce delamination of the fibers in the form of nanofibers (nanofibrilated cellulose).