Cellulose acetate foams fabricated by solvent-assisted foaming via plasticization and enhanced CO2 diffusion

In this study, a solvent-assisted foaming method via plasticization of ethyl lactate and enhanced CO2 diffusion was proposed to prepare microcellular cellulose acetate (CA) foams. Under the plasticization effect of ethyl lactate on CA, the glass transition temperature of CA30 (CA containing 30 wt% ethyl lactate) precursors was decreased to approximately 100 °C, thus decreasing the foaming temperature and broadening the foaming temperature window to 60 °C. By adjusting the foaming temperature and pressure, the expansion ratio of CA30 foams ranged from 2.3 to 21.6-fold. Samples with a smaller cell size (15 μm) achieved a compressive strength of 0.17 MPa, which was four times higher than that of foams with larger cell size (50 μm), when they had a similar expansion ratio. As the expansion ratio increased from 2.3 to 9.8-fold, the thermal conductivity of CA30 foams decreased rapidly, and then remained relatively stable. When the expansion ratio was 21.6-fold, the thermal conductivity was as low as 41.0 mW/(m·K).