Espumas de celulose microfibrilada obtidas pelo método freeze-thawing-dryin

Abstract

This study explored the manufacturing of microfibrillated cellulose (MFC) foams using the freeze-thawing-drying (FTD) method as a more sustainable and scalable alternative compared to conventional methods such as supercritical drying and lyophilization. The technique involves the formation of highly porous and low-density structures from an MFC suspension. The aim of this study was to investigate production parameters affecting the quality of MFC foams. MFC was prepared by defibrillating pulp with distilled water and used at concentrations of 0.7% and 1.1%. Mechanical strength, density, and porosity of the foams were evaluated, along with their volumetric shrinkage. Results showed that MFC concentration and ethanol content in the solvent exchange process significantly impacted the compressive strength of the foams. Foams with lower ethanol concentration (96% and 90%) exhibited greater strength due to slower evaporation. Foam density was also affected by MFC concentration and ethanol content, with denser foams being less porous. Foam porosity ranged from 96.6% to 98.7%, with apparent densities between 0.0202 and 0.0519 g/cm³. The obtained foams are highly porous and lightweight, similar to aerogels produced by lyophilization. The relationship between density and porosity was inversely proportional, where lighter foams displayed higher specific compressive strength. Volumetric shrinkage of the foams was significantly affected by MFC concentration, with lower concentrations leading to less volumetric shrinkage due to depletion of bonds between fibers.