Microstructure of spray freezing dried powders affected by the presence of inert particles

Spray freeze-drying is a process to directly produce high quality powders with short drying time. The difference of microstructures has a great influence on the physical properties of powders. However, during the spray freeze-drying process, the freezing degree of droplets in the drying chamber will change the product structure and affect the powder quality. In this study, the surface structure and morphology of dry powders were observed using scanning electron microscopy. The formation mechanism of droplet morphology during spray freeze-drying was analyzed. The results show that the rapid freezing process can produce finer microstructures.

A Simple Method to Synthesize Lignin Nanoparticles

The self-assembly of lignin (molecular and supramolecular) is driven mainly by non-covalent interactions, and the nature of the solvents and antisolvents directly affect the driving forces. The lignin particle is usually formed by noncovalently bonded cylindrical subunits. In this paper, we report a simple method which can be used to synthesize lignin nanoparticles by using spray freezing. The method is based on two properties of dimethyl sulfoxide (DMSO) that are excellent lignin solubility and a high melting point. Based on these two properties, kraft lignin solution in DMSO was sprayed onto liquid nitrogen-cooled copper plates using a handheld spray. The high melting point of DMSO caused immediate freezing and particle formation. The obtained particles were characterized for their size and morphology using dynamic light scattering (DLS), as well as scanning electron microscopy (SEM). Nano-range polydispersed particles were obtained by spraying 0.05% of lignin onto DMSO. This method can avoid lignin–solvent–antisolvent interactions, and can also be used to study lignin–lignin (subunits) and lignin–DMSO interactions.