# Utilization of Polymeric Materials toward Sustainable Biodiesel Industry: A Recent Review
## 2 Polymeric Biodiesel
### Characteristics and Limitations  
Polymeric biodiesel (HAME and HBME) has physicochemical properties almost close to biodiesel fuel. In spite of being sourced from low-cost feedstocks like sewage sludge or wastes, HAME and HBME offer valuable, ecofriendly, and sustainable biodiesel fuel. Unlike vegetative and animal-based biodiesel, the polymeric biodiesel does not require extensive purification process. The calorific value of this pure biologically derived fuel reached 20 and 30 MJ/kg for HBME and HAME, respectively. The heating value can be improved to 30 and 35 MJ/kg for HBME and HAME respectively by adding 10% ethanol [35]. The polymeric biodiesel has preferable performance characteristics. The start ignition is faster than vegetative and animal-based biodiesel. In addition, just short combustion time is needed to fully burn. Plus, this fuel produces very little trace amounts of exhaust smoke. The reason behind these preferable performance characteristics refers to the high oxygen  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Polymeric Biodiesel**} & \multirow{2}{*}{**Polymers Source**} & \multicolumn{6}{c}{**Reaction Parameters**} & \multirow{2}{*}{**Yield Source**} \\ \cline{3-4} \cline{6-9}  & & & & **Ratio \%** & & **Temperature (\%)** & **Time (h)** & **(\%)** \\ \hline HAME & mcl PHA & Methanol & H\({}_{2}\)SO\({}_{4}\) & 15 & 100 & 60 & 65 & [35] \\ \hline HAME & mcl PHA & Methanol & H\({}_{2}\)SO\({}_{4}\) & 10 & 67 & 60 & 68 & [20] \\ \hline HBME & P3 HB & Methanol & H\({}_{2}\)SO\({}_{4}\) & 15 & 100 & 60 & 52 & [35] \\ \hline HBME & P3 HB & Methanol & H\({}_{2}\)SO\({}_{4}\) & 10 & 67 & 60 & 40 & [57] \\ \hline HBME & P3 HB & Methanol & H\({}_{2}\)SO\({}_{4}\) & 10 & 67 & 50 & 70.7 & [21] \\ \hline HBME & P3 HB & Methanol & H\({}_{2}\)SO\({}_{4}\) & 10 & 67 & 60 & 65 & [22] \\ \hline \hline \end{tabular}  
* C in A: catalyst in alcohol.  
\end{table}
Table 2: Optimum values for polymeric biodiesel production HAME and MBME.  
Figure 3: Schematic production of polymeric biodiesel HAME and HBME.  
content of HAME and HBME fuels which helps to combust the full fuel within short time and produce neglectable smoke. Besides, the polymeric biodiesel contains neither nitrogen nor sulfur. That is why its emissions are more ecofriendly since it is free of nitrogen oxides and sulfur oxides. Thus, sustainable biodiesel fuel with favorable characteristics is offered by biopolymers materials derived from low-cost feedstocks which are not competitive with food resources [19]. Table 3 explores the characteristics of polymeric biodiesel HBME.  
Despite the preferable characteristics of biologically derived polymeric biodiesel, there are some drawbacks that may limit using HAME and HBME as an alternative fuel. The conversion percentage of mcl PHAs and P3 HB into alkyl esters is lower compared with vegetative and animal-based biodiesel. [PERSON] et al. [35] recorded conversion percentages for the first time as 52% and 65% for HBME and HAME, respectively. However, 70% recovery yield was recorded later by [PERSON] et al. [21], [PERSON] et al. [22], and [PERSON] et al. [20]. Beside the low conversion percentage, much time is required to reach the maximum yield. The optimized results of [PERSON] et al. [21] revealed that only 12.8% yield of HBME can be obtained from P3 HB after 10 h of esterification reaction. The yield increased to 70.7% once the reaction time was doubled five times into 50 h. However, the HBME yield was decreased beyond 50 h of reaction time. The polymeric synthesized esters of HBME and HAME have a lower cetane number compared with conventional diesel and biodiesel since they are highly oxygenated compounds. Moreover, their vaporization latent heat is high. Thus, much enhancement is needed before fueling engines with polymeric biodiesel [35].