By Annel K. Greene, PhD
Center Director, Clemson University
Animal Co-Products Research and Education Center
Polymer scientist Dr. Igor Luzinov, a member of the Clemson University Animal Co-Products Research and Education Center (ACREC) team, is working to find new solutions for making biodegradable plastics from animal co-products. Luzinov specializes in nanofabrication of thin polymer films and multi-component polymer systems. In his research, Luzinov works to custom design submicron polymeric films with specific structure and properties. He also investigates the correlation between polymeric structure and the properties of films. His work bridges the study of traditional polymer systems with new materials for advanced applications.
Various research studies have indicated that thermoplastic material and composites can be produced from plant and animal-based proteins. Luzinov’s work for ACREC concentrates on finding methods for making plastic and fiber reinforced composite materials from various animal proteins such as feather meal, poultry meal, and blood meal, which would be available on a renewable basis from the rendering industry. These proteinaceous materials are high protein agricultural commodities that are currently used primarily as animal feed. The most important protein properties for making plastics are good processability, both in aqueous media and in the melt; good film forming properties and good mechanical properties of films; adhesion to various substrates; high resistance toward ultraviolet radiation and oils/organic solvents; high barrier properties for gases such as oxygen and carbon dioxide; and surface active properties.
Protein-based plastic materials have potential for various applications such as trash bags, pet food containers, planter boxes, composting bags, fishing nets, mulch films, dog chew toys, and mesh for temporary retaining and reinforcing soil. The current research would help the rendering industry to exploit these proteins beyond traditional use in animal feed.
In the manufacture of biodegradable plastics, two major processes may be used. The “wet process” involves formation of a film by dispersion in a solution. The “dry process” involves the use of thermoplasticity of protein materials that are extruded, molded, or roll milled. Biodegradable soy protein-based plastics have been achieved that possess high strength; however, because these plastics are brittle, research is continuing. One method of altering properties of plastics is to blend polymers. In some instances, a third component known as a compatibilizer is added to assist in blending incompatible polymers and, thus, improve the mechanical properties of the blended polymer.
There are three main stages of protein processing for making thermoplastic materials. The first stage is the solubilization or dispersion in water or other solvents, or mixing with water or plasticizer. At this stage, structural change (denaturing) is evident. The second stage is structure formation, where protein molecules become rearranged in a new order. The last stage is structure fixation by either physical and/or chemical means, which happens by decreasing the temperature of the polymer to below the so-called “glass transition temperature” (e.g., after extrusion) or by decreasing the water content (e.g., drying).
As associate professor in the Clemson University School of Material Science and Engineering, Luzinov has been evaluating methods to translate commercial and experimental processes developed for soy proteins for use on proteins generated by the rendering industry. In his initial trials using defatted feather meal, Luzinov, his graduate student Suraj Sharma, and his undergraduate student researcher James Hodges have developed a plastic material that is brittle but comparable in certain aspects to polystyrene plastics. This early part of their research demonstrated that plastic samples could be produced from feather meal proteins under the application of heat and pressure through compression molding. However, the researchers realized that although the modulus (stiffness) of the formed plastic is comparable with synthetic material, its strength and elongation may be improved further to increase the physical properties of the material.
Using an evaluation technique known as differential scanning calorimetric (DSC) thermography, Luzinov measured the heat-induced denaturation of proteins. As protein molecules are placed under pressure and absorb heat, the molecules unfold. Scans conducted using DSC thermography revealed the denaturation temperature of the polymer and indicated the irreversible thermal set of the polymer. Luzinov’s results using feather meal were in agreement with soy protein plastics.
Other parameters Luzinov measured during the study were described by such terminology as stress and strain at break, modulus, dynamic elastic modulus, and glass transition temperature by dynamic mechanical analysis. For evaluating performance properties of polymers, researchers create a standard shape of polymer known as a “dog bone.” These elongated dog bone shapes are then placed on equipment that measures a variety of parameters that describe the strengths and weaknesses of the polymer. Standard dog bone samples of the feather meal polymer were molded through compression molding. The stress at break (strength), strain at break, and modulus (stiffness) were measured on the unmodified defatted feather meal proteins. Using scanning electron microscopy, the surfaces of the materials were examined and micrographs indicated a brittle fracture surface. Overall, the initial results indicated encouraging and comparable results between the polymers generated from feather meal to those from soy proteins.
Luzinov’s team is now working to test a variety of additives such as “nano impact modifiers,” “reactive rubbery copolymers,” and polymer blends to modify the physical properties of the bioplastic generated from feather meal. Studies on the use of “acrylic core-shell impact modifiers with and without reactive epoxy groups” did not improve the mechanical properties of feather meal plastic samples. In this study, it was observed that these modifiers obstructed the unfolding (denaturing) of protein polymers.
Luzinov and his team recognize that further investigation is needed to make these additives compatible with the protein molecules from the feather meal. With the addition of “reactive rubbery copolymers,” the strength and toughness properties of the feather meal plastics were improved, although there was a little bit of compromise with modulus (stiffness). Using scanning electron microscopy, the team observed uneven fracture surfaces that further supported the ductile behavior. Work is continuing in this area.
From a literature search, Luzinov’s team noted that whey (by-product from cheese making) and albumin (egg white) proteins have good adhesive properties. Therefore, research is underway to prepare blends of feather meal proteins with other natural proteins. Preliminary research indicates that blends of feather meal protein with other natural proteins improve the mechanical and thermal properties in comparison to unmodified feather meal. The study is continuing.
Luzinov’s team also intends to develop biodegradable composites, reinforced with natural fibers such as hemp fiber and fillers such as natural rubber latex and silica, for delaying biodegradability, enhancing toughness, and increasing the water resistance of the final samples.
Rising oil and gas prices as well as concerns over landfill space are driving interest in biodegradable plastics. By investigating varying processing and material parameters such as pressure, temperature, moisture, and time, Luzinov and his research team are working to improve mechanical properties of polymers generated from rendered animal co-products. Luzinov’s methods for making unique polymers will offer another potential market for rendered animal products.
ACREC Solutions - April 2007 Render