Submitted to: Polymer Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 2002
Publication Date: November 15, 2002
Citation: WILLETT, J.L., SHOGREN, R.L. PROCESSING AND PROPERTIES OF EXTRUDED STARCH/POLYMER FOAMS. POLYMER. 2002. v. 43. p. 5935-5947. Interpretive Summary: Foam packaging materials ("peanuts") which compete with nonbiodegradable polystyrene foams but produced with starch are commercially available. These starch foams are water-sensitive, and require modified or other high-cost starches. Blending biodegradable plastics with low-cost, unmodified starches may provide foams with acceptable properties, increased dwater resistance, and reduced costs. We blended unmodified starches from corn, wheat, and potato with biodegradable polymers and extruded low density foams. Several of the blend foams had densities comparable to commercially available foams. Some of the biodegradable polymers did not improve the foam properties, and did not make low-density foams suitable for packaging applications. These results are useful to manufacturers of starch-based foams, and to other researchers in the area of starch utilization.
Technical Abstract: Blends of starch and various thermoplastic resins were extruded into foams using a twin-screw extruder. Resins included poly(vinyl alcohol), cellulose acetate, and several biodegradable polyesters. Foams of corn starch with poly(lactic acid) (PLA), poly(hydroxyester ether) (PHEE), or poly(hydroxybutyrate-co-valerate) (PHBV) had significantly lower densities and greater radial expansion ratios than the control starch. Blends with other polyesters and cellulose acetate (CA) had densities and expansion ratios between those of the control starch and the other polyesters. Foams were also extruded using blends of PLA or PHEE with high amylose starch (70% amylose), wheat starch and potato starch. Addition of either resin significantly reduced the foam density and increased expansion. At constant relative humidity, compressive strength was a function of foam density only and not the type of resin or starch in the blend. Addition of fthe resins reduced the water sensitivity of the foams and increased the time needed for complete dissolution. Blends with PLA, PHEE, or PHBV produced foams with densities comparable to commercial starch-based loose-fill foams.