Mechanical and water barrier properties of corn-protein-based biodegradable plastics

Experiments were performed to evaluate the mechanical and water barrier pro perties of corn-protein-based materials that were compression molded from t hermoplastic resins. The influence of varying concentrations of water, glyc erol, and octanoic acid was studied. At 0% relative humidity, the material exhibited a linear elastic deformation and a brittle fracture at any glycer ol or octanoic acid content. Raising relative humidity from 0% to 97.3%, pr ogressively decreased the tensile strength (from 24.1 to 2.2 MPa and 19.4 t o 1.0 MPa), and the modulus of elasticity (from 1.67 to 0.03 GPa and 1.87 t o 0.13 GPa), respectively, for the octanoic acid- or glycerol-plasticized m aterials. Increasing water content did not increase the tensile strain at b reak of the glycerol-plasticized material, whereas this parameter changed f rom 1.6 to 52.3% for octanoic-acid-plasticized material. This last material was waterproof during 21 h and its water transmission rate was then 0.05 m u mol m m(-2) s(-1). Differences in water absorption were related to plasti cizer solubility and material structure.