Functional properties of extruded acetylated starch-cellulose foams

Acetylated starches, with degrees of substitution (DS) of 2, 2.5 and 3, were blended with 3%, 7.5% and 12% α-cellulose and 14%, 17% or 20% (d.b.) ethanol and twin-screw extruded at 165°C barrel temperature and 225 rpm screw speed. A response surface methodology experimental design was applied to the sub-plot and a completely randomized design to the whole plot design to test the differences among the acetylated starches and the effects of cellulose and ethanol. DS, cellulose and ethanol contents significantly affected the functional properties and specific mechanical energy requirement. DS had positive effects on radial expansion ratio (RER), compressibility and specific mechanical energy requirement and a negative effect on bulk density. Highest (RER) was obtained from 20% ethanol content. Extrudates containing 12% cellulose had the highest bulk density and the highest compressibility. Higher cellulose contents required more specific mechanical energy.