## 3 Results and Discussion
### TGA Analysis of Biomass Fuels

Table 2: Fuel and fuel ash properties of untreated (U) and acid leached (L), cassava (CasP), yam (YamP), coconut (CocH), comrcob (CorC) and corn husk (CorH). Inorganic species are specified on fuel ash basis. Abbreviations wb, db, and n.d. stand for wet basis, dry basis and not detected. Oxygen is calculated by difference. VM: volatile matter; AC: ash content; MC: moisture content; and LHV: lower heating value. In the second stage (307-381 \({}^{\circ}\)C), a simultaneous degradation process was observed, owing primarily to the presence of cellulose [58], which accounts for approximately 20.25-30.69 wt.% db of mass loss. In yam and coconut biofuels, the second devolatilization stage (i.e., decomposition of cellulose) was not observed. The decomposition of the organic compounds occurred in parallel, in a super-compositional manner, as shown in the DTG curves. However, cellulose decomposition was observed in cassava, corncob, and cornhusk with the maximum decomposition rate at a temperature between 307-381 \({}^{\circ}\)C. Because cellulose is a high-molecular-weight substance with a long linear chain formed of D-glucosyl groups [62], and a portion of cellulose has a crystal structure composed of organized microfibrils, it degrades more slowly than hemicellulose [63]. Figure 2: TG (black curve and y-axis on the left side) and DTG (red curve and y-axis on the right side) profiles of untreated residues of (**a**) cassava, (**b**) yam, (**c**) coconut, (**d**) corncob, and (**e**) cornhusk. The third stage only accounts for a minor portion of mass loss (6.14-7.81 wt.% db) with a maximum decomposition rate at a temperature range of 408.3-454.7 \({}^{\circ}\)C. This stage might be attributed to the degradation of lignin, which is the most stable component of lignocellulosic biomass. It is difficult to decompose and requires higher decomposition temperatures, as the decomposition occurs slowly along the whole combustion temperature range [61]. From Figure 2, the distinct weight loss peaks in the DTG curves of cassava, yam and coconut were considerably different from corncob and cornhusk, which presented only one distinct peak and an additional \"shoulder\" peak. This could be a result of a low lignin content compared to the residues of cassava, yam and coconut. Lignin is an amorphous substrate that resides in the minute spaces between cellulose microfibrils. It is covalently bonded to hemicellulose and crosslinked to polysaccharides and contributes to the crystallinity of biomass fuels [58-60]. It is conceivable that there is a higher lignin content in cassava, yam, and coconut. Thus, they were thermally degraded more slowly than the other biomass residues, corncob and cornhusk, resulting in distinct mass losses of hemicellulose and cellulose [64]. [PERSON] et al. [65] observed a similar result of two discrete mass-loss maxima in hazelnut husk with a high lignin concentration (39%). Similar observations for other biomasses that showed only one distinct peak in the DTG curve (such as pinewood [66], bamboo [67] and corn stover [68] or with a minor \"shoulder\" (e.g., wheat straw [68]) have been reported in the literature. In addition, charring of the biomass fuels has been reported to occur at this stage due to lignin breakdown [69,70]. Therefore, it can be concluded that the overall decomposition behaviour of cassava, yam, coconut, corncob, and cornhusk is due to the decomposition of the primary organic materials: cellulose, hemicellulose, and lignin, with the extent of complexity of the TGA curves depending on the definite compositions of the individual components of the lignocellulosic biomasses [61]. Similar decomposition behaviours of cellulose, hemicellulose and lignin have been reported in the study of [PERSON] et al. [60]. They noted that the degradation of hemicellulose and cellulose showed the highest mass loss rate at 268 \({}^{\circ}\)C and 355 \({}^{\circ}\)C, respectively, and lignin was the most difficult of the three to disintegrate [60,61]. According to [PERSON] et al.