Extrusion Coating of Poly(Hydroxyalkanoates) (PHAs) and Blends: Modifying the Mechanical Properties and Water Vapor Barrier Performance

Poly(hydroxy alkanoates) PHAs are a family of bio-based and biodegradable polyesters, which are potential sustainable alternatives to fossil-based and nondegradable plastics. The interest in PHAs ascends from their renewable origin, unique properties, and fast degradation rates in soil and marine conditions. This study focuses on properties of commercially available PHA grades using extrusion coating and cast film extrusion processes. The relation between PHA crystallinity and properties was studied by blending crystalline poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV and amorphous poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P34HB. Consequently, processability, mechanical properties, and water vapor permeation could be tailored with blending ratio. By increasing amorphous content in the blend, material flexibility and elongational values were increased significantly; whereas Young's modulus and maximum stress at break were decreased. Moreover, the increase in amorphous content was found to increase water vapor permeability slightly. Hence, the balance between processability, mechanical properties, and barrier performance needs to be compromised when selecting the optimal blending ratio. This publication provides novel insights on the processability and properties of commercially available PHA grades and demonstrates that homogeneous PHA blends with tailorable properties can be formed by mixing crystalline and amorphous PHA grades.