Twin-screw extrusion production and characterization of starch foam products for use in cushioning and insulation applications

Cylindrical starch foam shapes were produced on a small scale (∼11–12 kg/hr) Werner Pfleiderer ZSK-30 twin-screw extrusion (TSE) process using water, which functions as a plasticizer as well as a blowing agent. The properties of the starch foams depend on the type of starch used (hydroxypropylated high amylose corn starch, 70% amylose), the amount of water and additives (poly(hydroxyamino ether)) (PHAE) used, and extrusion conditions such as temperature and the screw configuration. PHAE offers the adhesion and durability of epoxy resins with the flexibility and processibility of thermoplastic resins. PHAE was successful in imparting mechanical strength and toughness, cell integrity, weather and water resistance to the foam structure. The purpose of this work was to study the effects of the extrusion (melt) temperature, amount of water added and the screw configuration on the density of starch foams. The water externally added was varied from 3% to 12%, while the PHAE content was varied from 3% to 15% of the starch used (on a wet basis). The foaming was carried out at melt temperatures in the range from 85 to 145°C. A match of material properties with process engineering conditions was achieved to facilitate the control of expansion to a structure with valuable commercial properties. The effects of processing conditions on the foaming process were studied using a Werner Pfleiderer ZSK-30 twin screw extruder. The optimum temperature, blowing agent content, and PHAE content were determined. The density of the cylindrical foam extrudates obtained was 22–25 kg/m3. The screw configuration, temperature and pressure profiles, and additives affected the morphology, expansion ratio (ER), resilience, and compressibility of the product. These results were then employed on an industrial scale (410–420 kg/hr) twin-screw food extruder, a Wenger-80, to manufacture foam sheets. The density of the foam sheets was 27–30 kg/m3. The cushioning and insulation properties were studied and are reported. POLYM. ENG. SCI., 46:438–451, 2006. © 2006 Society of Plastics Engineers