Pollution due to petroleum-based plastic is a growing problem all over the world. Petroleum-based plastics that fill landfills and oceans take hundreds of years to degrade. One possible solution to this growing problem is to increase the use of bioplastics. Polyhydroxybutyrate (PHB) is a widely studied bioplastic that is biodegradable in both soil and marine environments. However, PHB use is limited due to its poor mechanical properties. Past researchers have investigated the use of natural additives, primarily different types of plant fibers, to enhance both the mechanical properties and degradation rates of bioplastics. The purpose of this project was to develop a composite bioplastic using PHB and algal biomass in order to enhance the mechanical and degradation properties of PHB.
Composite bioplastic films were formed using a solvent casting method with algal biomass to PHB ratios of 0, 5, 10, and 20% on a weight-to-weight basis. To test the mechanical properties of the biocomposites using a tensile testing machine, the films were cut into dogbones, 3 cm in length. The films were also cut into 2.5 x 3 cm ships that were placed into gas-tight serum vials filled with seawater to measure the degradation rate through CO2 evolution.
The mechanical properties of the biocomposite that were tested include ultimate tensile strength, modulus of elasticity, and percent elongation at break. The ultimate tensile strength and modulus of elasticity of the 20% algae biocomposite were found to be significantly lower than those of the neat, 5, and 10% algae biocomposite. The percent elongation at break of the different biocomposite blends, however, were not significantly different. For the rate of degradation, the neat , 5, and 10% algae biocomposites were found to degrade at significantly different rates, with the 10% blend having the highest rate of degradation followed by the 5% blend and then the neat PHB. The 20% algae biocomposite degraded at a rate that was not significantly different from the degradation rate of the 10% algae biocomposite.
From the results of the mechanical properties and degradation rate testing, the 10% algae biocomposite was found to have mechanical properties similar to those of neat PHB and a degradation rate that was much higher than that of neat PHB. Therefore, it can be concluded that the addition of algal biomass to PHB on a 10% weight-to-weight basis enhances both the mechanical properties and degradation rate of PHB
