Poly (hydroxy alkanoates) (PHA), which belong to the biodegradable polyesters, can be synthesized from renewable resources by specific types of bacteria. Poly (3-hydroxy butyrate) (PHB) as well as poly (3-hydroxy butyrate-co-3-hydroxy valerate) (PHB-co-HV) are the most produced and investigated products under the PHA.
According to its high crystallinity, PHB has high tensile strength and modulus of elasticity, but only poor thermal stability and high brittleness. Conventional melt-processing is connected with molecular degradation and loss of mechanical properties. To avoid degradation of PHA during processing and to guarantee improved properties new routes have been developed to generate compact or porous materials, respectively.
So, the modification of PHB by external plasticizers and other polymer components was realized. Plasticizers were incorporated into PHB by melt mixing as well as a special solution technique.
A solid state processing route was realized for the production of compact parts: After production of a “green” body by cold compaction of PHB powder solid state extrusion of this specimen under plain strain compression in a channel die was realized that lead to products with high level of mechanical properties. Structure and properties of solid-state processed PHB are discussed in dependence on molecular parameters and processing steps.
Furthermore, a foaming process is presented, which avoids strong thermal exposure, i.e. degradation and property loss, but guarantees foamed PHA parts with definite porous structure and sufficient mechanical properties. The route is a non-thermal procedure characterized by use of a solvent casting/particle leaching (SCPL) technology. The influence of material components and processing parameters on structure and properties of PHB foam is discussed.
