Dr. Brian Ralston, - Associate
Exponent Failure Analysis Associates
149 Commonwealth drive
Menlo Park, CA 94025
650-688-7222 fax: 650-328-2990
Abstract
Viable bio-based materials will one day contribute to a more sustainable economy. Plastics derived from renewable resources are one piece of the puzzle in reducing fossil fuel dependence. Many bio-based materials, including soy protein-based plastics, are biodegradable as well as renewable, offering an outlet for overflowing solid waste streams.
Many potential applications of soy protein plastics take advantage of the biodegradability of this material, including protective tubes for nursery trees, agricultural mulch films, plantable flowerpots and garden cell packs. Upon degradation, soy protein plastics can provide nutrients to the soil. Additional applications include more complex extruded, injection molded and thermoformed parts such as compostable food trays, containers, flatware and packaging. Soy protein plastics also could be used in biomedical applications such as tissue scaffolding, implants and drug delivery.
The ranges of mechanical performance of soy protein plastics (e.g., tensile strength, elongation, modulus) are comparable to commodity resins such as polypropylene (PP), polystyrene (PS), and polyethylenes (PE). However, soy protein plastics with high modulus and strength have extremely low elongation, and vice versa. Soy protein plastics also display substantial water sensitivity. Moisture content of the resin affects behavior during processing. The properties of finished parts can fluctuate with humidity. Improving mechanical properties and reducing water sensitivity are the two most urgent challenges facing soy protein plastics. One method to meet these challenges and bring soy protein plastics to market is blending soy proteins with other bio-based polymers, including poly(lactic acid) (PLA) and cornstarch. Natural fiber composites of these blends can yield further property improvements.
The work reported here includes viscosity data from capillary rheometry and mechanical properties and water sensitivity from injection molded and extruded samples of soy-cornstarch blends. Capillary rheometry data shows the viscosities of soy protein plastics are comparable to commodity resins, allowing soy protein plastics to be processed on conventional plastics processing equipment. The objective of this work is to gain an understanding of how soy protein plastics can be processed in order to manufacture commercially viable parts from these materials.
Five formulations of soy protein-cornstarch plastics were compounded
and injection molded. The effects of soy protein-to-cornstarch ratio, addition
of sodium sulfite, addition of a titanate coupling agent, recycling and
ambient relative humidity on tensile properties were evaluated. Material
with a soy protein-to-cornstarch ratio of 2:3 showed the best overall tensile
properties, with tensile strength of 4.8 MPa, modulus of 154 MPa and elongation
at break of 120%. Titanate coupling agent also improved tensile properties.
Recycling led to slightly decreased tensile performance. Higher relative
humidity led to gel formation and substantial decreases in strength, modulus
and elongation.
Speaker details:
Dr. Brian Ralston recently received his Ph.D. in Mechanical Engineering with a minor in Industrial Engineering from the University of Wisconsin-Madison. The focus of Dr. Ralston's dissertation research was to formulate, process, and characterize biodegradable, renewable soy protein plastics. His polymer processing experience includes extrusion, compounding, injection molding, compression molding, and thermoforming. For the past year, he has performed failure analysis of plastic parts as a Plastic Consulting Engineer with The Madison Group. Dr. Ralston also earned a B.S. and M.S. in Entomology from The Ohio State University where he studied the toxicity of PCBs and dioxins to aquatic invertebrates.