Studio sperimentale sull'impatto del processo di spray freeze-drying sulla morfologia del prodotto finito = Experimental study on the product morphology obtained by spray freeze-drying

Industrial dying processes have been developed for little more than a century and increasing standards have moved the scientific community to find better, innovative ways to achieve minimum moisture. Among many drying techniques, spray-drying and freeze-drying have become an industry standard because they provide satisfactory results across multiple fields and are easily scaled-up, however, the two of them have some limitations regarding their energy usage and the kind of substances they can be applied to. To compensate for these limitations, a novel process called spray freeze-drying has captured the attention of researchers because of its potential to produce better results than the other two techniques while spending less energy. This thesis is done with the scope of studying the behavior of the particle’s size distribution and morphology when the power used for an ultrasonic atomizer is changed for different types of solution, therefore identifying which are the relevant parameters that guide the process. The experiment consisted of atomizing mannitol solutions at different values of power and flowrates, as well as sucrose solutions at different concentrations and flowrates, and then make them go through a freeze-drying process to study the influence these parameters have on the final morphology of different products. The morphology of the particles that resulted from this process was obtained through SEM and BET analysis. The results obtained show that increasing the power decreases the average particle size up until a certain value which, after exceeding it, will cause the samples to not atomize properly. It was also found that every solution has a peak flowrate value that depends on the concentration of the solution and the nature of the solute. After this value is reached the particle size will plummet and, if the power limit was exceeded and the flowrate is indiscriminately increased, the sample will not atomize. Another finding was that increasing the concentration of a solution will increase its particle size and will move the peak value. Regarding the specific surface area, it was found that amorphous solutions like sucrose tend to aggregate at low flowrates and concentrations, lowering their measured specific surface area and causing issues like multi-molecular adsorption, while at higher concentrations and flowrates this trend was corrected and resulted in a larger area. For crystalline components like mannitol, the specific surface area decreases with an increase in flowrate except for the peak value.