11 - Plastics Derived from Starch and Poly (Lactic Acids)

Abstract

Starch is a highly hydrophilic polymer that consists of linear amylose and highly branched amylopectin. Besides food and paper uses, starch has many application potentials as thermoplastics. However, starch is brittle, hydrophilic, and has low flowability in extrusion and molding processes. Blending with hydrophobic polymers, such as poly (lactic acid) (PLA) makes starch a useful material for disposable uses. PLA is a bio-based synthetic polymer derived from starch or sugar-based materials and has about 60 MPa tensile strength and 5% elongation. Simple blending of starch and PLA by mechanical method reduces mechanical properties of PLA to 50%. Small amounts of coupling reagents are helpful for improving mechanical properties. Methylenediphenyl diisocyanate (MDI) and maleic anhydride (MA) are two identified coupling reagents for the PLA and starch system. Triethyl citrate (TC) and dioctyl maleate (DOM) are compatible plasticizers of the starch and PLA system, so that the mechanical properties of the starch and PLA blends can be adjusted to meet application specifications. Application potential of the starch/PLA plastics includes packaging rigid or flexible containers, agriculture mulch film, packaging foam, service utensils, and other disposable items for single or short uses.