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Large amounts of acidic waste are produced on the industrial scale during hydrolysis of partially amorphous cellulose to produce microcrystalline cellulose (MCC). The essential disposal and treatment of this highly acidic liquid wastes the acid feedstock and increases the production cost. To maximize the use of acid without sacrificing the MCC product quality, this project reports a successful attempt to recycle the acid hydrolysis waste liquid, focusing on the impact of waste recycling on MCC morphology and reducing sugar in the hydrolysate. The results showed that when the waste liquid is recycled 1-5 times, no metal accumulation occurred while cellulose particles remained intact, maintaining their shape and size. Their extent of crystallinity remained nearly constant, even increasing slightly with up to three cycles. The concentration of reducing sugar showed growth when recycling the waste liquid up to three times, although not quite to the levels that would allow for its cost-effective fermentation. The acid amount to be added at the start of each cycle was near 50% of that used on the first stage.

Low-density foams based on nanofibrillated cellulose (NFC) made from Pinus massoniane softwood pulp were prepared from NFC aqueous suspensions containing one of four C2–C4 alcohols followed by freeze-drying, with the goal of controlling their pore structure and reducing the shrink rate. The foams prepared from NFC suspensions containing ethanol, isopropanol and n-butanol exhibited highly porous structures with a honeycomb-like cellular texture featuring well-defined “cell walls” between the layers. By contrast, the tert-butanol/NFC foam featured a higher number of smaller size pores with irregular shape. The foams prepared by freezing at −196 °C with ethanol also revealed small size pores, with no layered pore structure. The results obtained suggested that freeze-drying could be used to control the key foam parameters by adding different alcohols into an NFC suspension and adjusting the freezing temperature. Combining the obtained information, a possible formation mechanism was proposed. The microstructure, density, porosity, shrinkage, mechanical properties and thermal properties of NFC foams were determined. The obtained NFC foams feature low shrinkage upon formation and thermal conductivity. Smaller Young’s modulus and energy absorption yet similar yield stress values compared to the blank indicate that the freeze-drying in the presence of alcohols tends to generate “soft” foams.

Nanofibrillated cellulose (NFC)-based foam materials have broad prospects in replacing traditional foams, due to its facile natural biodegradation. This study addressed the relationship between the foam preparation process parameters and resulting pore structure. An aqueous NFC suspension was freeze-dried while adding an organic solvent, ethanol, to adjust the curing process. The effects of the solid content and freeze-drying temperature on the microstructure and mechanical stability as well as heat transfer performance of the produced NFC-based foam were investigated. The foam obtained at a 3%–5% solid content featured a well-defined lamellar and interlayer pillar support structure. With an increase in the solid content, the average wall thickness increased whereas the average pore area decreased. Yet the pore density increased with the pore distribution becoming non-uniform. With a decrease in freezing temperature, the wall thickness decreased (with no wall structure at −196 °C) but the pore density increased, with the pores being distributed more uniformly. The foam mechanical strength and thermal conductivity were found to be linked to porosity. The foam material had the most suitable mechanical and thermal insulation properties when prepared with a 5% solid content at a freeze-drying temperature of −55 °C.