Physical Properties of Two Biological Cushioning Materials from Wheat and Corn Starches'

Cereal Chem. 72(1):38-41 Physical properties of two biological cushioning materials made from dates were significantly higher than those of the wheat starch extrudates. wheat and corn starch extrudates were compared with those of commercial Both biological cushioning materials showed similar water absorption plastic foam cushioning material. Characteristics measured included isotherms at three temperatures when the equilibrium moisture contents dimensions, bulk and true densities, and water absorption isotherms at significantly increased as relative humidities increased. The S-shaped 15, 25, and 400C. Their properties under simple compression tests and plastic foam exhibited lower bulk and true densities. Simple compression stress relaxation tests were also examined. The C-shaped extrudate from tests and stress relaxation tests showed that the biological materials had corn starch showed more radial expansion than that of the wheat starch more unrecoverable plastic deformation than the plastic foams and also extrudate. But the bulk density and true density of the corn starch extruindicated a difference between the two extruded cushioning materials. Loose-fill cushioning materials provide cost-effective protection for relatively lightweight products against shock or vibration during shipping and handling (Torok 1990). In addition to the important energy absorbing properties of cushioning materials, characteristics such as light weight, stability in ambient conditions, good resilience, and stress dissipation rate also should be considered. As cushioned packages play an increasing role in world commerce, flexible, closed-cell, expandable polystyrene foam materials are being used more and more. Disposal of used plastic cushioning materials, which are derived from petroleum sources, has become a public concern (Larson 1989, 1990). Biological cushioning materials, such as extrudates from wheat and corn starches, are now available. The objective of this study was to compare the physical properties of two biological cushioning materials with those of plastic foam materials by measuring dimensions, bulk and true densities, water absorption isotherms, and compression properties. MATERIALS AND METHODS Materials Wheat starch (Midsol 50) manufactured by Midwest Grain Products (Atchison, KS) and corn starch (pearl corn starch) manufactured by A. E. Staley (Decatur, IL) were mixed with 3% polyethylene glycol and 0.5% silicon dioxide for 0.5 hr in a doubleribbon mixer (Wenger Mixer Mfg., Sabetha, KS) and sealed tightly in plastic bags for 12 hr before the extrusion process. The total mix was 50 kg for each type of starch. A Wenger X20 single-screw extruder with a C-shaped die was used to process both the wheat and the corn starches under the operational conditions listed in Table I (Neumann and Seib 1993). The final formulation of feed material, extruder screw configuration, feed rate, die dimension, die zone temperature, and plate cutter were determined from previous runs conducted in the extrusion laboratory (Department of Grain Science and Industry) and in the physical properties laboratory (Department of Biological and Agricultural Engineering) at Kansas State University, Manhattan, KS. The loose-fill plastic foam used in the comparisons was an 'Contribution 94-459-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan. 2 Graduate student. Current address: Biological and Agricultural Engineering, University of California, Davis. 3 Associate professor. Current address: Agricultural and Biosystem Engineering, Iowa State University, Ames. 4 R&D manager. Heinz-UFE Ltd., Yan Tang, Shade, Guangzhou, People's Republic of China. © 1995 American Association of Cereal Chemists, Inc. expandable polystyrene material manufactured by Dow Chemical Company (PELANSPAN-PAC). This S-shaped foam is one of the most commonly used commercial cushioning materials. Methods Dimensions, bulk and true densities, and water absorption isotherms at 15, 25, and 400C were determined. Resilience and stress dissipation properties of the materials were measured using simple compression and stress relaxation tests. A digital reading caliper (Manostate, Switzerland) was used TABLE I Operational Conditions of the Extruder Wheat Corn Starch Starch Extrusion Condition Mix Mix Feed screw speed (rpm) 15.0 15.0 Mixing cylinder speed (rpm) 150.0 150.0 Discharge temperature (IC) 90.0 96.0 Discharge moisture (%) 19.34 17.78 Shaft speed (rpm) 300 300 Motor load (%) 24.0 24.0 Knife drive speed, two blades (%) 40-50% 40-50% Extrudate bulk density (wet) 18.58 kg/iM 20.50 kg/im Pressure (psig) 4,237 kPa 5,650 kPa Barrel jacket conditions 2nd to 4th Cold water Cold water 5th Steam Steam 6th Cold water Cold water