Reactive supercritical fluid extrusion for development of moisture resistant starch-based foams

The main objective of this work was to reduce barriers that prevent the usage of starch‐based foams by understanding the effect and the sequence of dual‐modification of crosslinked (XL) and acetylated (Ac) starch in one continuous supercritical fluid reactive extrusion (SCFX) process on wetting properties, physicochemical properties, and cellular structure of solid foam. The starch was reacted with epichlorohydrin (EPI) and acetic anhydride (Ac) under alkaline conditions in a twin‐screw extruder in the presence of supercritical carbon dioxide (SC‐CO2). An increase in EPI concentration from 0.00 to 3.00% increased the degree of crosslinking as measured by DSC and confirmed by the quantification of the glucose units in the solution after acid hydrolysis. We observed a reduction of the glucose units from 93.07% for 0.00% EPI to 6.73% when 3.00% EPI was added. With crosslinking/acetylation processing, contact angle was higher for modified starches, indicating that chemical treatments induced dramatic changes in their surface polarity. Compared with native, the contact angle for dual modified starch increased from 43.1° to 91.7° which indicated their lower wettability. The addition of SC‐CO2, EPI, and Ac to the formulation reduced the density of the extrudates and increased the expansion ratio. The average cell size in the extrudate determined by scanning electron microscopy was also found to decrease from 150 to 34 μm by the addition of the two reagents. Moreover, the dual‐modification of starches provided more hardness and adhesiveness to the extrudates than was observed for the unmodified starches. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011