Assessment of PHB with varying hydroxyvalerate content for potential packaging applications

Poly-(hydroxybutyrate) (PHB) is biodegradable aliphatic polyester that is produced by a wide range of microorganisms. Basic PHB has relatively high glass transition and melting temperatures. To improve flexibility for potential packaging applications, PHB is synthesized with various co-polymers such as poly-(3-hydroxyvalerate) (HV) leading to a decrease of the glass transitions and melting temperatures. In addition, the HV broadens the processing window since there is improved melt stability at lower processing temperatures. In this study, PHB synthesized with different valerate contents (5%, 12%, and 20%) and varying in molecular weights were characterized. All PHBV materials displayed a glass transition between −10 and 20 °C. The two melting transitions found for Aldrich 5%, 12%, and Tianan 20%, resulted from crystals formed during cooling of the samples. The complex viscosity decreased with increasing temperature due to a decrease in molecular weights of the samples. These results suggest that processing the co-polymer below 160 °C would be beneficial with low screw speed. The mechanical results indicate all PHBV materials had high elastic modulus and flexural strength with low tensile strength and elongation at break. The WVTR results indicated the polymer to be very hydrophilic, resulting in higher water transmission rates.