Method to improve natural rubber (hevea/guayule)-toughened poly-(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) for food packaging applications
Nearly all plastics that are used to produce packaging materials are petroleum-based and non-biodegradable. This makes their use undesirable to consumers in an increasingly sustainability-focused market. Therefore, the development of biologically-derived, biodegradable plastic for packaging materials is a growing priority. Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bioplastic that could supplant widespread plastics such as polypropylene, which has a similar tensile strength. However, the primary obstacle to PHBV product development is brittleness after cooling. Previous efforts revealed that blending PHBV with high molecular weight natural rubber (HMW-NR), a processed form of natural rubber that has a viscosity similar to PHBV, mitigates these problems. However, HMW-NR is not commercially available and standard weight NR cannot substitute for HMW-NR due to its differing viscosity. As a result, blends of PHBV and NR cannot overcome the pitfalls of PHBV plastic as blends of PHBV and HMW-NR do. Further, the conventional method to blend NR and PHBV despite their differing viscosities, sulfur vulcanization, is inappropriate for most consumer products as the resulting blends retain sulfur odors from processing. Therefore, if a method for blending PHBV/NR is developed that results in blends with the characteristics of PHBV/HMW-NR blends, then there will be an opportunity to replace petroleum-derived plastics with a comparable bioplastic.
Yael Vodovotz and her colleagues at The Ohio State University have invented a method to combine PHBV and NR that produces a blend comparable to PHBV/HMW-NR blends. By incorporating organic peroxides into the blending process, the researchers establish a method that overcomes the obstacles that prevented successful blending of PHBV and NR. As opposed to sulfur vulcanization, the organic peroxides do not produce any undesirable side effects and are FDA-approved for food-contact applications. Relative to standard PHBV, this PHBV/NR blend minimizes the material drawbacks of PHBV relative to conventional plastics. Specifically, this new PHBV/NR blend increases flexibility by 59% and toughness by 20%. Therefore, this new PHBV-based bioplastic overcomes the pitfalls associated with PHBV, and has the potential to supplant petroleum-based plastics currently in use.