Extrusion plastometry processing of poly(3-hydroxybutyrate)/ground wool fiber blends

Authors: Yosief, Hailemichael; LIU, CHENG KUNG - Retired ARS Employee; Ashby, Richard - Rick; Strahan, Gary; Latona, Nicholas - Nick; CHEN, NUSHENG - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Green Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2022
Publication Date: 1/11/2023
Citation: Yosief, H.O., Liu, C., Ashby, R.D., Strahan, G.D., Latona, N.P., Chen, N. 2023. Extrusion plastometry processing of poly(3-hydroxybutyrate)/ground wool fiber blends. Green Materials. https://doi.org/10.1680/jgrma.22.00026.
DOI: https://doi.org/10.1680/jgrma.22.00026

Interpretive Summary: Poly(3-hydroxybutyrate) (PHB) is a bacterially-derived bioplastic and is the most well-known member of the polyhydroxyalkanoate (PHA) family of biopolymers. It can be naturally degraded to carbon dioxide and water in microbially-active environments and its properties are analogous to some petroleum-based materials, making PHB a potentially beneficial, environmentally friendly substitute in many applications. Unfortunately, the practical application of PHB has been challenging due to some of its inherent limitations such as a high cost to produce, a relatively narrow processing window, high brittleness, and low thermal stability. In this study, a melt flow extrusion plastometer, which measures melt flow as a function of temperature, was used to investigate the thermal processability of PHB. The melt flow rate and mechanical properties of the extruded monofilaments produced upon exposure to different processing temperatures, heating times and after blending with ground raw wool were evaluated. The melt flow rates of PHB were not significantly affected when blended with different amounts of ground wool fibers but, the mechanical properties of the PHB monofilaments differed significantly depending on the fraction of wool, temperature, and heat exposure time. The study also revealed that the molecular weight of the PHB test material decreased as the heat exposure and duration of heat treatment increased. Understanding thermal processing of PHB will be vital for selecting appropriate conditions to produce PHB-based blends/composites with desirable properties for a variety of applications.

Technical Abstract: Poly(3-hydroxybutyrate) (PHB) is the most well-known member of the polyhydroxyalkanoate (PHA) family of biopolymers. Because of its ubiquitous nature among many bacterial strains, PHB has been extensively investigated as an environmentally-benign replacement for petrochemical-based polymers in biomedical and food packaging applications. The practical application of PHB in the biomedical field and in packaging has been limited because of its relatively narrow processing window, high brittleness, and low thermal stability. In this study, a melt flow extrusion plastometer was used to investigate the processability of PHB by evaluating its melt flow rate and the mechanical properties of its monofilament extrudates. The monofilament extrudates were collected after exposure to different processing temperatures (180°C and 190°C) and heating times as well as after blending the biopolymer with different fractions of ground raw wool (1, 2, 5 and 10 wt%). The melt flow rate of PHB was not significantly affected when blended with different amounts of wool fiber. However, the melt flow rate increased significantly (from around 9 g/10 min to 14 g/10 min) as the heat duration and temperature increased. The mechanical properties of the monofilament extrudates from the parental PHB and PHB/wool blends were influenced by the fraction of wool, temperature, and heat duration. The tensile strength and the Young’s modulus of the PHB/wool blends decreased by more than 10% as the wool content, temperature, and duration of heat treatment increased. Diffusion Ordered Spectroscopy (DOSY)-NMR analysis revealed that the molecular weight of PHB decreased as the heat exposure and duration of heat treatment increased. The results of this study will be useful in selecting appropriate conditions to produce PHB-based blends/composites with desirable properties for a wide range of applications.