Effect of polymer plastic binder on mechanical, storage and combustion characteristics of torrefied and pelletized herbaceous biomass

Currently one of the main challenges of the wood pellet industry is the limitation of raw materials. The solution to this limitation can be either increasing the efficiency of the materials or finding new sources to replace them. To maintain the sustainability of global production and consumption, extra resources can be found in waste instead of natural resources. Plastic wastes may be considered as a replacement source due to their effect on environmental pollution which is caused by changing production and consumption patterns of the human population in addition to population increase. Linear low density polyethylene (LLDPE), one of the extractable plastics from municipal solid wastes (MSW) was investigated as an additive and binder for torrefied biomass pellets. Non-ground wheat and barley straws were torrefied at 250 °C for 15 min. The torrefied biomass was mixed with LLDPE as an additive at four levels (1, 3, 6 and 10%). The results showed that addition of 6% LLDPE to the biomass pellets led to a maximum increase in density by 1.8% for wheat and 1.7% for barley. Adding 10% LLDPE to the torrefied biomass pellets resulted in a 280% and 253% increase in tensile strength for wheat and barley pellets, respectively. Adding LLDPE from 1% up to 10% resulted in increasing higher heating values and a decreasing ash content for both torrefied wheat and barley straw pellets. The higher heating value (HHV) of the pellets at all levels of added LLDPE except 10% meet the current standard specifications of DIN 51731 for commercial pellets. The ash content of the torrefied barley pellets at all levels of LLDPE addition except at 1% were in agreement with the requirement of the Pellet Fuels Institute Standard Specification for Residential/Commercial Densified Fuel (⩽6.0%).