The effect of the conditioning process parameters on the properties of the pellets was
investigated. Maize residues were collected locally from the field and crushed into small
sizes, dried, and separated for compaction. The effects of the variation of the die temperature
(30e80 C), the compaction pressure (150e250 MPa), and the biomass type (cob,
husk, and stalk) on compact density, relaxed density, and durability index were investigated.
It was found that the compact density increased with pressure and temperature to
around 950e1100% higher than the residue density. The relaxed density was stable at 60
e80 C, but at 30 C, it was found to decrease from 800e1000 kg m3 to 660e700 kg m3
. The
durability index was observed to improve with increasing pressure and temperature by 30
e60% and 70e90%, respectively. This corresponded well with the lignin glass transition
temperatures being in the range of 60e80 C at moderate pressure values between 150 MPa
and 250 MPa. Pellet density was also found to increase with increasing compression
pressure and temperature. Pellet density was three times higher than bulk density and
similar to the particle density. Heating the feed materials during compression decreased
the compaction pressure from 250 MPa to 150 MPa, resulting in the formation of pellets
with a higher durability index and more stable relaxed density.