Polyhydroxyalkanoates are natural polyesters produced by certain bacteria. Depending on the type of bacteria and the cultivation conditions, a whole
range of PHAs with different properties can be obtained. Depending on the nature of the lateral carbon chain R and the number (x) of carbons in the repeating unit making up the main chain, it will be possible to modify their flexibility, extensibility or crystallinity. The most common PHAs are polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-valerate) (PHBV).