Binding mechanism in bio-briquette prepared with wheat straw and lignite by mechanical thermal expression process

In this study, bio-briquette was prepared with lignite and wheat straw by mechanical thermal expression (MTE) process and analyzed using an optical microscope (OM), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Under the combined action of thermal and mechanical energy, the binding mechanism between lignite and biomass in bio-briquette was discussed. Results showed that the compressive strength of bio-briquette increased with the increase of pressure and temperature, which positively affected the bonding of material particles. Lignite particles were wrapped into the network formed by interconnected fibers of different lengths. During the MTE process, the liquid bridges were built among the biomass undergoing glass transition, water, and partially melted lignite, which became solid bridges after briquette formation, enhancing the compressive strength of bio-briquette.