PHAs are polyesters synthesized by micro-organisms as an energy reserve from renewable, and possibly non-food, feedstock. They are non-toxic, biocompatible and quickly biodegradable in different natural environments, ensuring not to pollute and jeopardize our ecosystems unlike conventional plastics. They are good candidates to replace conventional plastics such as polypropylene for their functional properties during the usage stage of their life cycle. However, expanding their eco-efficiency and circularity by adding cycles, such as reuse or recycling, to their life-cycle requires to improve their thermal stability and mechanical properties. Here we offer to discuss on how improving their thermomechanical properties while preserving their crucial biodegradability. The review focuses on a well-known type of stabilizer, the polyphenols and their impacts on PHAs’ thermomechanical properties and biodegradability. It has mainly been concluded that the presence of polyphenols, at a certain amount, contributes to the improvement of the physical-chemical properties of PHAs, whereas there is no evidence that polyphenols have an inhibitory effect on the biodegradation of PHAs.