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Abstract
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 pilot-scale 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.