Development of Soy Protein Plastics Using Functional Chemistry for Short-Life Biodegradable Applications

Soy protein plastic formulations were developed through iterative experimental stages to produce water-stable, soy protein isolate (SPI)-based plastic resins. The protein polymer-based materials are glycerol and water plasticized resins that have been described as thermoplastics [1] by some researchers and have been described as materials that behave similar to thermoplastics upon application of heat and pressure [2]. Previous researchers have developed SPI plastic for various applications, all of which were adversely effected by water absorption. The formulations in this research included anhydride chemistries, such as maleic anhydride (MA), phthalic anhydride (PA), and bifunctional chemistries, such as adipic acid in combination with glycerol as plasticizer. The mass content of the respective functional chemistries were varied between 3 and 10 w/w% (total mass). Formulations based on phthalic anhydride exhibited the lowest water absorption; in particular, PA10% formulation exhibited water absorption of 21% compared to 250% for the control formulation after 24 h of exposure to water. Anhydride-based formulations were characterized using Fourier transform infrared spectroscopy (FTIR) to verify the fundamental mechanisms of improved water stability. In addition, cotton-based composites were studied to enhance the mechanical strength. The inclusion of fiber reinforcements reduced the overall dry and wet state mechanical properties. The addition of adipic acid (AA) to PA5% reduced the tensile strength by 10-40%, depending on adipic acid concentration which was varied from 1.23-10%. Other cost effective formulations were developed and studied with varying levels of soy protein isolate (SPI) and soy flour (SF), which is a relatively inexpensive component compared to isolates (