Polyhydroxyalkanoates – Linking Properties, Applications and End-of-life Options

Abstract

When it comes to “bioplastics”, we currently notice an immense complexity of this topic, and, most of all, a plethora of contradictory legislations, which confuses or even misleads insufficiently informed consumers. The present article therefore showcases microbial polyhydroxyalkanoate (PHA) biopolyesters as the prime class of “bioplastics” sensu stricto. In particular, biodegradability of PHA as its central benefit in elevating the current plastic waste scenario is elaborated on the biochemical basis: this covers aspects of the enzymatic machinery involved both in intra- and extracellular PHA degradation, and environmental factors impacting biodegradability. Importantly, PHA degradability is contextualized with potential fields of application of these materials. It is further shown how the particularities of PHA in terms of feedstocks, mode of synthesis, degradability, and compostability differ from other polymeric materials sold as “bioplastics”, highlighting the unique selling points of PHA as “green” plastic products in the circular economy. Moreover, current standards, norms, and certificates applicable to PHA are presented as basis for a straight-forward, scientifically grounded classification of “bioplastics”.

Laser Processing of Polymer Films Fabricated from PHAs Differing in Their Monomer Composition

“…Polyhydroxyalkanoates (PHAs), degradable polyesters of microbial origin, are promising “green” plastics, which are degraded by natural microflora to CO 2 and H 2 O, causing no harm to biota and the entire environment [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. PHAs are synthesized by prokaryotes from various substrates, including waste products [ 18 , 19 , 20 , 21 ].…”

The First Insight into Polyhydroxyalkanoates Accumulation in Multi-Extremophilic Rubrobacter xylanophilus and Rubrobacter spartanus

“…The results are shown in Table 4 . Copolymers usually have better mechanical properties than pure P3HB, which results in advantages in their eventual processing and applications [ 13 ]. For this reason, the capability of producing copolymers for production strains is very important and it depends on the available metabolic apparatus of the culture and predominantly on the substrate specificity of the PHA synthase.…”

“…Moreover, its melting temperature of about 170 °C is very close to the degradation temperature (about 200 °C), which complicates its processing. However, a supplementation of the culture with appropriate structural precursors can result in the incorporation of other monomer units such as 3HV or 4HB into the polymer chain, which substantially improves its mechanical as well technological properties [ 13 ]. As shown in Table 1 , R. xylanophilus DSM 9941 possesses two PHA synthases belonging to class I and class III.…”

“…The homopolymer of 3-hydroxybutyrate, poly(3-hydroxybutyrate) (P3HB), is the most widespread and best-studied member of the PHA family. Actually, due to their technological and mechanical properties, biodegradability, biocompatibility, and renewable origin, PHA are considered to be a “green” alternative to petrochemical “plastics” [ 13 ]. From a biological point of view, the main purpose of PHA in bacterial cells is the storage of carbon and energy.…”

Polyhydroxyalkanoates (PHAs): Biopolymers for Biofuel and Biorefineries

“…When PHAs-based products are left in the environment, they degraded into CO 2 , H 2 O, and CH 4 , which facilitate the natural cycle of circulatory and renewability. In addition, the spent PHAs can undergo hydrolysis and produce optically pure building blocks which can be used as synthons for pharmaceuticals, organic synthesis, and fragrances [ 10 ]. Moreover, the structural diversity of PHAs allows them to readily undergo methyl esterification and to be used as biofuels, which further extends the application value of PHAs.…”