Characteristics of biodegradable Mater-Bi®-starch based foams as affected by ingredient formulations

Abstract

Expanded polystyrene (EPS) foams are widely used to provide protection to merchandise during shipping and handling. The disposal of EPS foams, however, causes pollution to the environment. Starch based loose fill packaging foams are commercially available to replace the EPS foams. Starch foams dissolve readily in water, and do not possess satisfactory physical and mechanical properties. To improve the functional properties and water resistance of starch foams, regular (25% amylose) and waxy corn starches blended with Mater-Bi® ZF03U (MBI) were extruded into loose-fill packaging foams using a co-rotating twin screw extruder. MBI contents of 10, 25 and 40% and starch moisture contents of 19, 22 and 25% (d.b.) were used. Waxy starch produced foam with greater radial expansion and lower unit and bulk densities than regular starch. Higher levels of MBI reduced radial expansion and increased unit and bulk densities. Foam made with regular starch had a lower water solubility index than foam made with waxy starch. The addition of MBI improved the water solubility. Higher starch moisture contents increased foam water solubility indices. Foams made from both types of starch possessed acceptable mechanical properties. Regular starch produced more rigid foams than the waxy starch as indicated by the higher compressibility values based on both single-piece and bulk samples. Moisture content affected the compressibilities. Higher moisture contents produced more rigid foams. The spring indices of bulk samples were excellent (>95%) for all MBI contents.