## 3 Results and Discussion
### Comparison of Grindability for Treatment Samples  
The particle size distribution of PSD and Kenaf showed a high distribution in region of 0.6-0.425 mm and 0.85-0.6 mm (Figure 5). Among them, the largest particle size distribution of 1.0-1.18 mm or more had a large distribution of R. PSD and R. Kenaf, as well as a smaller distribution of T. PSD, A. PSD, and T. A PSD. As the torrefraction process, the smaller particle distribution is hisheR. This is  
Figure 4: Hydrophobic properties of raw and pretreated biomasses.  
indicated that torrefraction lead to improved grindability as shown in the torrefraction of Kenaf samples. This trend is consistent with those reported in similar studies investigating the grinding of torrefied biomass [30]. This indicates that during torrefraction, continuous decomposition of hemicellulose causes weakening and destruction of the highly interlinked cellulose-hemicellulose matrix, which no longer can support the cellulose fibers [31]. In addition, [PERSON], [PERSON], and [PERSON] are mainly distributed in areas below the smallest size distribution (0.15-0.075 mm). Thus, kenaf shows a smaller size distribution than that of PSD when samples are pretreated.  
When examining cumulative particle mass (%), the slowest rising curve was observed in R. PSD, followed by R. Kenaf, which implies that R. Kenaf had better grindability than that of raw material  
Figure 5: Particle size distributions of PSD samples (**a**) and kenaf samples (**b**)’s raw and pretreated biomasses.  
(Figure 6). For pretreated PSD, torrefraction led to improved grindability and the ashless process showed further improvement. The curves of cumulative particle mass clearly shifted towards smaller particles. Similar changes of particle size distribution of ground biomass have been reported in other studies [7].  
T. A PSD shows better grindability than that of A. PSD. The same trend is observed in pretreated kenaf. However, the pretreatment of kenaf resulted in a large increase in grindability. To further examine this point, the cumulative particle mass by the range of 0.075 \(\sim\) 0.6 mm was compared with each other (Figure 7). R. PSD comprised of 11% of the total particles, while R. Kenaf comprised of 26%. This indicates that the smaller particle sizes of R. Kenaf were distributed more in this range. For pretreated PSD, the values were raised in the order T. PSD, A. PSD, and T. A PSD, with respective values of 42%, 57%, and 70%. The same trend was observed in the pretreated kenaf; however, the values increased rapidly to 67%, 58%, and 76%, respectively, and the rate of grindability also increased. This indicates that pretreated kenaf had a greater grindability characteristic than that of PSD.  
Torrefraction and ashless processes of biomass led to the decomposition and breakdown of the hemicellulose-cellulose interlinked matrix caused by heating and the chemical treatment. This considerably simplifies the grinding of pre-treatment samples. For torrefraction biomass, the degradation of the hemicellulose and cellulose components is larger through the pre-treatment process. As a result, torrefraction biomass has a greater grindability compared with ashless biomass.  
Featured Application: torrefraction and ashless techniques in this work were used to upgrade physicochemical properties of woody and herbaceous biomass. The ashless technique combining torrefraction process provided a promising application in herbaceous biomass especially.  
Figure 6: Cumulative particle mass of raw and pretreated biomasses.