## 4 Discussion  
The direct recycling of postconsumer plastics, such as PS, would lead to products of poor quality, with a loss of properties due to aging during the service-life and any thermo-mechanical degradation during reprocessing [52]. By using prodegraded PS as a carbon source to produce biodegradable plastics, waste PS gains an extended usefulness time-span, rather than becoming a hazardous material. The results of Table 1 and the FTIR data (Figure 3) clearly show that the thermal pretreatment with ozone increased the presence of ketone or aldehyde groups, further increasing the acid number of samples PS1-3. A treatment time of 20 h at 60 \({}^{\circ}\)C was even more effective than the treatment at 80-100 \({}^{\circ}\)C for the same period and when 120 \({}^{\circ}\)C was used for 20 h the samples are rendered useless for bacterial fermentation. The GPC results showed a progressive decrease in the average molecular mass of the PS samples when heat exposure was extended. This was expected, however, it was not known that PS4 samples, although possessing the lowest molecular mass, would produce the least biomass and no PHAs after 48 h fermentation. The dispersity (_D_) between the samples was mostly consistent, apart from PS4 (_D_ = 3.8), possibly showing a higher range of polymers in the sample that could have been produced by the thermal treatment itself. As there was very little growth and no product, these particles could be hazardous so further analysis, or simply avoiding the more extreme conditions used to produce the PS4 samples, is suggested if this kind of pretreatment is utilized by laboratories in the future. It is known that the presence of mixed polymeric fractions, such as impurities in recycled polymeric materials, can affect the macroscopic performance of recyclates [23]. By using thermal analysis as part of the characterization analysis, it has been observed that the PS fragments were able to pass  
Figure 12: ESI-MS/MS spectrum acquired for the selected potassium adduct of oligomers at _m_/z 583.  
through the extraction into the PHA because PS readily dissolves in chloroform. If this process was to be adopted in an industrial setting, further filtration steps would have to be added. From these results in Section 3.6, it does appear that the treated PS samples significantly increased the biomass and percentage yield of the PHA. Comparisons of PS1, PS2, and PS3 (the successfully oxidized PS specimens) against BSM showed the greatest significance (\(P\) = 0.001), with PS1 showing a 48% yield. The combination of increased hydrophilicity and reduced average molecular mass undoubtedly contributed to the better emulsification and absorption of the PS carbon chains by the bacteria into the \(\beta\)-oxidation pathway, producing PHBV rather than PHB as in the TSB only controls. PS1 sample fermentations also produced relatively low average molecular mass PHAs of 35,000 Da, with the highest distribution value of 12.1 (\(M_{\rm w}/M_{\rm n}\)), compared to PS2 (113,000 Da with \(D\) = 6.0) and PS3 (100,000 Da with \(D\) = 7.0). When these data are compared to the \(M_{\rm n}\) results for polyesters synthesized using TSB only, the PHAs synthesized showed a \(M_{\rm n}\) of 52,000 Da with a distribution of 5.7 (\(M_{\rm w}/M_{\rm n}\)) [5]. This shows that PS1 samples had the greatest dispersity value, and more varied ranges of polyesters were generated in all prodegraded sample fermentations, but PS1 was the only pretreated sample to give a dispersity value greater than the original prodegraded (PS0) specimen. Again, this is likely due to the higher AN value. \({}^{1}\)H-NMR was used to determine the molecular structure of the copolymers produced using fermentation. The \({}^{1}\)H-NMR spectra of PSx-PHA revealed the presence of characteristic signals corresponding to the protons of 3-hydroxybutyrate (3-HB) and 3-hydroxyvalerate (3-HV) repeating units. It was found that PHB was produced by bacteria in the TSB only fermentations.