# Valorization of Insulation Cellulose Waste as Solid Biomass Fuel
## 3 Results and Discussion
### Mechanical Durability  
As stated previously, pellets' mechanical durabilities were characterized by the loss of mass by sieving after the abrasion and knocking test and the decrease in their length. Figure 4 shows the pellets' loss of mass after testing as a percentage of the initial samples' masses.  
Mixes with 5% of moisture content showed the highest losses of mass in this test. Thus, C-0-5W, C-1S-5W, C-2S-5W, C-1L-5W and C-2L-5W combinations lost 22.32%, 6.31%, 6.30%, 17.66% and 4.40% of the initial mass, respectively. For higher moisture contents the loss of mass decreased, reaching the mixes' lowest losses in the range of 10-20% of moisture content, showing the existence of an optimum moisture content for particle bonding. Thus, C-0-20W, C-1S-20W, C-2S-15W, C-1L-15W and C-2L-10W combinations lost 2.95%, 1.67%, 1.84%, 0.94% and 1.10% of the initial mass, respectively. For values of moisture content above the optimum for each mix, all the combinations showed a slight increase in the loss of mass, probably due to an excess of water that hampered the particles' contact and bonding mechanisms. Combinations between 10% and 30% of moisture content showed a loss of mass under the limits stated in the Standard ISO 17225-6.  
Figure 3: Bulk dry densities.  
Figure 5 shows the pellets' lengths before and after the abrasion and knocking test.  
CFP produced the longest pellets for all the moisture contents. Thus, for the combination of C-0-5W the pellets' mean lengths reached 18.5 mm. For higher water contents, pellet lengths increased up to mean values close to 30 mm for the 10-40% moisture content range. After the abrasion and knocking test, CFP pellet lengths decreased to about 54-69% of the initial value of each combination. For the sugar-containing combinations, pellets reached mean length values between 17.8 for the combination C-15-5W and 23.1 mm for the C-15-15W. After the abrasion and knocking test, pellet lengths decreased, oscillating the final lengths between 70% and 96% of the initial values for the C-25-10W and C-15-40W combinations, respectively.  
No relationship was observed between the pellet lengths and the sugar dosage or the moisture content. It is remarkable that after the abrasion and knocking test, only sugar pellet lengths clearly overcame the CFP results for 5% of moisture content mixes. On the other hand, 1% of lignocellulosic combinations required a minimum moisture content of 15% to reach these mixes' potential lengths of about 20 mm. The pellet length obtained its higher value of 20.7 mm for a 20% moisture content and slightly decreased for higher moisture contents, showing the existence of a possible adverse effect of the excess water, in accordance with the loss of mass results. The 2% lignocellulosic mixes showed a much better result than the 1% dosage for the 5 and 10% moisture contents. The best pellet length was reached by combination C-2L-15W, at 22.0 mm. For higher moisture contents results slightly decreased, demonstrating the existence of an optimum moisture content of 15% for the combinations containing a dosage of 2% of this binder. These combinations' pellet lengths after the abrasion and knocking test remained in the range of 88-98% of the initial values. It is remarkable that all the combinations reached the pellet lengths stated by the ISO 17225-6 Standard before and after the abrasion and knocking test. The results obtained after this test highlight the complexity of the relationship between the binder kinds, their dosages or the moisture content and the pellets' durability.