Basics Fig. 1: Cropping
Basics Fig. 1: Cropping system using protein based bioplastic pots Bioplastics from proteins By David Grewell Associate Professor and Chair of Biopolymers and Biocomposites Research Team Iowa State University, Agricultural and Biosystems Engineering Ames, Iowa, USA Fig. 2: Golf Tees, wood composites with protein adhesives, animal toys and lubrication sticks (transparent samples are renewable oil based samples from Dr. Kesslers group at Iowa State University) The concept of using protein as a plastic is not novel. While nature has been using protein for structural purposes, Henry Ford was one of the first to make automotive components, such as body panels, from soy protein plastics. Proteins are naturally occurring polymers that consist of amino acids linked together to form a long globular molecular structure. In nature, these proteins can have a wide range of properties and functions. Today, research efforts at Iowa State University (ISU) as well as at other institutions are building on Ford’s idea and turning protein plastics into commercial products tailored to the demands of the current economy. These materials have many inherent benefits compared to petrochemical plastics, including being biorenewable and biodegradable. However, as with any new technology, researchers have had to overcome many challenges to the successful implementation and use of these new materials, such as optimization of formulations to meet market needs, development of processing, and testing and characterization to determine their performance. Because they are readily available, plant proteins have been the primary feedstock for producing protein plastics, in particular corn and soy proteins. While widely available, these proteins have a globular molecular structure, which is not conducive to load bearing applications, unlike collagen that gives bones their strength and integrity. To overcome this shortcoming, researchers have developed chemistries, processing conditions, and benign solvents (e.g., water, glycerin, ethanol) to linearize (denature/plasticize) the molecular structures to enhance mechanical performance through molecular reconfirmation. The plastics formulations are relatively easy and involve only a few steps: 1) protein extraction (denaturing); 2) plasticization through heat, benign solvents (such as water, ethanol, or polyethylene glycol), 3) shearing (through a conventional plastic extruder); and 4) pelletization. The pellets are similar to those already used by the plastics industry and can be processed using existing polymer processing equipment. They can be injection molded, extruded, blown into films, and, with slight modification to the formulations, even sprayed. Researchers at the ISU Biopolymers and Biocomposites Research Team (BBRT) along with other institutes have been working on a cropping system, made in part or in whole, of protein plastics. These cropping systems, pots (Fig. 1) are not only sustainable, renewable and biodegradable, they have an added feature: Once the plant is in the soil together with the pot, the pot degrades and inherently releases nitrogen into the soil because of the protein’s natural nitrogen content. This selffertilizing effect allows gardeners and growers to be ‘green.’ Similar applications under development at ISU include golf tees, protein-based adhesive composites panels, animal toys and lubrication sticks (Fig. 2) as well as temporary lawn and garden markers. According to Dr. James Schrader (Assistant Scientist, Department of Horticulture) at ISU, “Horticulture plant containers (pots) made from corn- and soy-protein polymers have potential to provide a fertilizer effect for plants grown in them.” 40 bioplastics MAGAZINE [04/12] Vol. 7
Bioplastics from Protein Fig. 4: Temporary lawn flags / markers Fig. 3: Erosion control products “Administrative, communications, and grant development assistance from the Center for Crops Utilization Research (CCUR) have enabled BBRT researchers to focus on science,” said Dr. Darren Jarboe, program manager for the CCUR and BioCentury Research Farm. “This focus and the diversity of participating researchers, for example artists, chemists, and engineers, have allowed the group to identify unique opportunities and develop proposals, such as the cropping systems project.” Other applications include plastics for erosion control and ground cover matting as seen in Fig. 3. The sheets can be made as matting or as a weave to allow plant growth. Research suggests that nitrogen amounts released from pots made of 100% corn and soy plastics may be too high to sustain healthy plant growth and that blending these protein polymers with biopolymers that have lower nitrogen contents may help optimize the inherent fertilizer effect of protein-based containers for horticulture crop production. In addition, researchers at ISU have been working with companies such as Creative Composites, Ankeny, Iowa, USA, to develop environmentally friendly, temporary lawn flags/ markers (Fig. 4). Researchers at the University of Illinois, led by Dr. Graciela Padua, have been using these natural polymers as food additives, even replacing petrochemical rubber in chewing gum. This biorenewable, non-stick gum is environmentally friendly. In addition, Dr. Padua has developed edible food packages based on corn protein. Dr. Jinwen Zhang at the University of Washington has been developing degradable foams produced from soy protein and polylactic acid (PLA). Dr. Zhang has been able to produce relatively homogeneous mixtures of soy protein and PLA to produce relatively high-strength plastics. In addition to soy and corn protein (both plant based), a team of Iowa State researchers, including Drs. Permenus Mungara and Jay-lin Jane, also investigated feather protein for plastic production. Results of the study demonstrated that chicken or turkey feathers can be used for bioplastics production. A drawback of this approach was the odor transferred to the product due to the current process used in the slaughterhouse. Feather protein has good potential for making bioplastics, once the process of feather harvesting can be improved. Another example for animal based protein are casein proteins. These are extracted from milk and are composed of glutamic acid, proline, valine, leucine and lysine, which account for more than 60 % of the amino acid residues. They are unique in comparison to plant proteins because of their randomly coiled structure and the lack of cysteine and resulting crosslinking disulfide bonds. These properties and their excellent barrier properties make casein a promising base material for coatings. Similar to other protein polymers, casein shares the shortcoming of water sensitivity and inferior mechanical properties compared to petroleum plastics. Historically, aldehyde was used as a crosslinking agent to stabilize casein; these resins were utilized to manufacture buttons, imitation ivory and other novelty items as early as at the beginning of the last century. Recent research has explored the utility of these proteins as a plastic foam material utilizing glyceraldehyde as a crosslinker. Within the United States much of this fundamental research and development has been supported by the national grower associations such as the United Soybean Board (USB) and National Corn Growers Association. According to Russ Carpenter, Chair of the United Soybean Board’s New Uses Committee and a soybean farmer from Trumansburg, N.Y., soy protein research characterizes a key component of USB’s Long Range Strategic Plan. “Investments in novel applications for soy proteins help the United Soybean Board address its strategic objectives of meeting customer demand for a wide range of quality soy products,” Carpenter said. “By capitalizing on the demand for biobased, sustainable products, the soy checkoff can increase the value of U.S. soy oil across the entire value chain.” www.biocom.iastate.edu/ bioplastics MAGAZINE [04/12] Vol. 7 41
