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

Experiments were performed to evaluate the mechanical and water barrier properties of corn-protein-based materials that were compression molded from thermoplastic resins. The influence of varying concentrations of water, glycerol, and octanoic acid was studied. At 0% relative humidity, the material exhibited a linear elastic deformation and a brittle fracture at any glycerol or octanoic acid content. Raising relative humidity from 0% to 97.3%, progressively decreased the tensile strength (from 24.1 to 2.2 MPa and 19.4 to 1.0 MPa), and the modulus of elasticity (from 1.67 to 0.03 GPa and 1.87 to 0.13 GPa), respectively, for the octanoic acid- or glycerol-plasticized materials. Increasing water content did not increase the tensile strain at break of the glycerol-plasticized material, whereas this parameter changed from 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 mmolmm^-2 s ^-1. Differences in water absorption were related to plasticizer solubility and material structure.