Corn stover and switchgrass are two important feedstocks considered for producing renewable fuels and
energy in the US. Densification of these biomass feedstocks into briquettes/pellets would help reduce the
problems and costs of bulk transportation, handling, and storage of biomass feedstocks. In this study, the
role of the natural binders in corn stover and switchgrass to make durable particle–particle bonding in
briquettes/pellets was investigated by micro-structural analyses. Scanning Electron Microscopy (SEM)
images of briquettes made by using a uniaxial piston-cylinder densification apparatus in the laboratory,
briquettes made by using a pilot-scale roll-press briquetting machine, and pellets made by using a pilotscale
conventional ring-die pelleting machine were analysed. The SEM images showed that the bonding
between particles was created mainly through solid bridges. The solid bridges between particles were
made by natural binders in the biomass expressed during the densification process. UV auto-fluorescence
images of briquettes and pellets further confirmed that the solid bridges were made mainly by natural
binders such as lignin and protein. It was found that activating (softening) the natural binders using
moisture and temperature in the range of glass transition is important to make durable particle–particle
bonding.