For this work, solid-state shear pulverization (SSSP) was used to create polymer composites with starch-based materials. This process utilizes a modified twin-screw extruder which is cooled to keep the polymer below the glass or melt transition temperature. Consequently, all processing occurs in the solid state. This eliminates any thermodynamic limitations associated with blend formation, providing the opportunity for a well dispersed system. In addition, SSSP has the potential to eliminate the need for solvents, organic modifiers, and plasticizers necessary in conventional processes.

Granular starch has been added to several polymer matrices as an inexpensive, abundant filler. Blends were created using polyethylene, and poly(caprolactone). Pulverization was found to damage the starch granules in the polyethylene systems, i.e. increase starch surface area and crack the outer starch casing. When the same composition blends were produced by melt-mixing, the starch granules maintained the neat polyhedral granule shape. The breakdown of the granular structure from pulverization resulted in improved mechanical and oxygen barrier properties of the composites.

Additional blends were created using thermoplastic starch (TPS) as the filler. The TPS was prepared from a premix containing 68 wt% starch, 23 wt% glycerol, and 9 wt% water. While this material has fairly poor mechanical properties, the low permeability to oxygen (oxygen permeability coefficient = 0.2 (cc*mm)/(m2*day*atm)) suggests the addition of TPS as a minor component should decrease the permeability of the matrix materials.

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