Improving the physical, mechanical and energetic properties of <i>Quercus</i> spp. wood pellets by adding pine sawdust

Abstract

The moisture content and fixed carbon content differed significantly (<i>p</i> < 0.05) between the groups of pellets (i.e., pellets made with different sawdust mixtures). The moisture content of all pellets was less than 10%. However, volatile matter and ash content did not differ significantly between groups (<i>p</i> ≥ 0.05). The ash content was less than 0.7% in all mixtures. The addition of <i>P. durangensis</i> sawdust to the mixtures improved the bulk density of the pellets by 18%. Significant differences (<i>p</i> < 0.05) in particle density were observed between species, mixtures and for the species × mixture interaction. The particle density was highest in the 80:20 and 60:40 mixtures, with values ranging from 1,245 to 1,349 kg m^-3. Bulk density and particle density of the pellets were positively correlated with the amount of <i>P. durangensis</i> sawdust included. The mechanical hardness and impact resistance index (IRI) differed significantly (<i>p</i> < 0.05) between groups. The addition of pine sawdust decreased the mechanical hardness of the pellets, up to 24%. The IRI was highest (138) in the <i>Q. sideroxyla</i> pellets (100:0). The mechanical hardness and IRI of the pellets were negatively correlated with the amount of <i>P. durangensis</i> sawdust added. The bulk density of the pellets was negatively correlated with mechanical hardness and IRI. The calorific value of mixtures and the species × mixture interaction differed significantly between groups. Finally, the mean calorific value was highest (19.8 MJ kg^-1) in the 20:80 mixture. The calorific value was positively related to the addition of <i>P. durangensis</i> sawdust.