Pelletization of biomass reduces its handling costs, and results in a fuel

The aim of this work was to study the mechanical fibrillation process for the preparation of cellulose nanofibers from two commercial hard-and softwood cellulose pulps. The process consisted of initial refining and subsequent high-pressure homogenization. The progress in fibrillation was studied using different microscopy techniques, mechanical testing, and fiber density measurements of cellulose films prepared after different processing stages. The mechanical properties of cellulose films showed an increase in strength and stiffness with decreasing fiber size, and this stabilized after a certain number of passes in the homogenizer. Atomic force microscopy studies showed that the obtained cellulose nanofibers had diameters in the 10-25-nm range. The significant difference between the two samples was that the ultimate failure strain for cellulose films made of softwood fibers increased during the process whereas it remained constantly low for hardwood cellulose films. This difference could be due to the presence of shorter fibers and more defects in the films. An important point to note is that excessive processing reduced properties, as seen by the decrease in failure strain of softwood fiber films, and could also decrease other properties such as strength if the number of processing steps were further increased.

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Torrefaction is a thermo-chemical conversion process improving the handling, storage and combustion properties of wood. To save storage space and transportation costs, it can be compressed into fuel pellets of high physical and energetic density. The resulting pellets are relatively resistant to moisture uptake, microbiological decay and easy to comminute into small particles. The present study focused on the pelletizing properties of spruce torrefied at 250, 275 and 300 °C. The changes in composition were characterized by infrared spectroscopy and chemical analysis. The pelletizing properties were determined using a single pellet press and pellet stability was determined by compression testing. The bonding mechanism in the pellets was studied by fracture surface analysis using scanning electron microscopy. The composition of the wood changed drastically under torrefaction, with hemicelluloses being most sensitive to thermal degradation. The chemical changes had a negative impact, both on the pelletizing process and the pellet properties. Torrefaction resulted in higher friction in the press channel of the pellet press and low compression strength of the pellets. Fracture surface analysis revealed a cohesive failure mechanism due to strong inter-particle bonding in spruce pellets as a resulting from a plastic flow of the amorphous wood polymers, forming solid polymer bridges between adjacent particles. Fracture surfaces of pellets made from torrefied spruce possessed gaps and voids between adjacent particles due to a spring back effect after pelletization. They showed no signs of inter-particle polymer bridges indicating that bonding is likely limited to Van der Waals forces and mechanical fiber interlocking.

13The purpose of the study was to investigate the influence of torrefaction on the grindability of wheat straw. 14 Straw samples were torrefied at temperatures between 200 ˚C to 300 ˚C and with residence times between 0.5 to 15 3 hours. Spectroscopic information obtained from ATR-FTIR indicated that below 200 ˚C there was no obvious 16 structural change of the wheat straw. At 200-250 ˚C hemicelluloses started to decompose and were totally 17 degraded when torrefied at 300 ˚C for 2 hours, while cellulose and lignin began to decompose at about 270-300 18 ˚C. Tensile failure strength and strain energy of oven dried wheat straw and torrefied wheat straw showed a clear 19 reduction with increasing torrefaction temperature. In addition, Hardgrove Grindability Index (HGI) of wheat 20Page 2 of 23 straw torrefied at different conditions was determined on a standard Hardgrove grinder. Both results showed an 21 improvement of grindability in the torrefaction temperature range 250-300 ˚C, which can be well explained by 22 the findings from FTIR analysis. At a torrefaction temperature of 260 ˚C and with a residence time of 2 hours, 23 wheat straw samples produced similar HGI values as coal (RUKUZN) with 0% moisture content. Under this 24 condition, the Anhydrous Weight Loss (AWL%) of the wheat straw sample was 30% on dry and ash free basis 25 (daf), and the higher heating value of the torrefied wheat straw was 24.2 MJ kg -1 (daf). The energy loss 26 compared to the original material was 15% (daf). 27

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The thermal transitions of the amorphous polymers in wheat straw were investigated using dynamic mechanical thermal analysis (DMTA). The study included both natural and solvent extracted wheat straw, in moist (8-9 % water content) and dry conditions,

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