# Valorization of Agri-Food Waste into PHA and Bioplastics: From Waste Selection to Transformation
## 3 Production of Bioplastics from Volatile Fatty Acids
### Physico-Chemical Properties of Bioplastics and Their Applications  
PHA biopolymer is the focus of this section; nevertheless, it is essential to mention other bioplastics for its suitable classification. Bioplastics can be classified into distinct categories based on their synthesis, which can be microbiological or involve a synthetic polymerization process. This classification is represented in Figure 5.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Strain** & **Fermentation Conditions** & **Yield** & **Type** \\ \hline _Cipreridus reactor_ & -Mix of volatile fatty acids. & 1.5 g/L of biomass and & PHBV with 91-96\% of \\ _DSM_ 545 [147] & -pH 7 & 56\% of PHA & \\ _DSM_ 545 [147] & -C/N 6 & accumulation & hidroxybutyrate content. \\ \hline _Bacillus megaterium_ & -Biogas digestate. & 0.360 g/L of PHA and & \\ _LVN01_[153] & -pH 7 & 0.133 g/L of DCW. & PHBV \\ \hline _Haloferaxmidertareni_ [156] & -Phosphate limitation (KH\({}_{2}\)PO\({}_{4}\)). & 0.95 g/Lwith 15.6\% dry biomass & PHBV \\ \hline _Pseudomonas oleoverants DSM 1045_[157] & -Synthetic medium (8.4 g/L glucose \(\pm\) 5.7 g/L & \\  & sodium ammonium & 1.7 g/L of biomass & mcl-PHA \\  & phosphate +35.44 mM & & \\  & phosphate buffer) & & \\  & -30 \({}^{\circ}\)C & & \\ \hline \multirow{4}{*}{_Aeronomas hydrophilic_ _4 AK4_} & -Sodium gluconate & 4.63 g/L of biomass with & \\  & -P limitation & 35.1\% of PHA & P(3 HB) \\ \cline{1-1} \cline{2-5}  & -Lauric acid + glucose & 16.2 g/L of biomass with & \\ \cline{1-1} \cline{2-5}  & -P limitation & 51.5\% of PHA & \\ \cline{1-1} \cline{2-5}  & -Undecanoic acid & 5.01 g/L of biomass with & \\ \cline{1-1} \cline{2-5}  & 45.2\% of PHA & & P(3 HV) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary of microorganisms producing different types of PHA, fermentation conditions, and yields achieved.  
Figure 5: Bioplastic polymers, and their monomers, produced by microbial fermentation combined with chemical synthesis. Modified from [PERSON] and [PERSON] [162].  
These monomers have been used to produce a range of bio-based plastics, including polyhydroxyalkanoates (PHAs), polylactic acid (PLA), poly(butylene succinate) (PBS), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), poly(propylene carbonate) (PPC), and poly(trimethylene terephthalate) (PTT) [163; 164]. Apart from PE, PP, PTT, PET, and bio-based polyamides, all the other bio-based polymers mentioned above are biodegradable to varying degrees. Moreover, PHA is a unique biopolymer that can be fully obtained from the biological transformation of a residual carbon source, i.e., other biopolymers require a chemical synthesis step.  
Another bioplastic not shown in Figure 5 is biopolyurethane, which can be synthesized from the bioproduced precursor 2,3-butanediol. Nowadays, the biological conversion of renewable carbon sources with bacteria, such as _Klebsiella pneumoniae_ or yeast is a sustainable method to produce 2,3-BDO. Different carbon sources, such as glucose, glycerol, molasses, and lignocellulosic hydrolysate, have been used [165]. Furthermore, their biosynthesis is currently being investigated as part of the European PROMOFER project [28].  
Because they are bio-based and biodegradable, PBS, PHA, PLA, and PPC have been proposed as environmentally friendly, sustainable, less fossil-fuel-dependent, and low-carbon fingerprint bioplastics for future applications [164; 165]. The physicochemical properties of each bio-based and biodegradable one are described in detail below.