# Utilization of Polymeric Materials toward Sustainable Biodiesel Industry: A Recent Review
###### Abstract  
The biodiesel industry is expanding rapidly in accordance with the high energy demand and environmental deterioration related to the combustion of fossil fuel. However, poor physico-chemical properties and the malperformance of biodiesel fuel still concern the researchers. In this flow, polymers were introduced in biodiesel industry to overcome such drawbacks. This paper reviewed the current utilizations of polymers in biodiesel industry. Hence, four utilizing approaches were discussed, namely polymeric biodiesel, polymeric catalysts, cold-flow improvers (CFIs), and stabilized exposure materials. Hydroxyalkanoates methyl ester (HAME) and hydroxybutyrate methyl ester (HBME) are known as polymeric biodiesel sourced from carbon-enriched polymers with the help of microbial activity. Based on the literature, the highest HBME yield was 70.7% obtained at 10% H\({}_{2}\)SO\({}_{4}\) ratio in methanol, 67 \({}^{\circ}\)C, and 50 h. With increasing time to 60 h, HAME highest yield was reported as 68%. In addition, polymers offer wide range of esterification/transesterification catalysts. Based on the source, this review classified polymeric catalysts as chemically, naturally, and waste derived polymeric catalysts. Those catalysts proved efficiency, non-toxicity, economic feasibility, and reusability till the 10 th cycle for some polymeric composites. Besides catalysis, polymers proved efficiency to enhance the biodiesel flow-properties. The best effect reported in this review was an 11 \({}^{\circ}\)C reduction for the pour point (PP) of canola biodiesel at 1 wt% of ethylene/vinyl acetate copolymers and cold filter plugging point (CFPP) of B20 waste oil biodiesel at 0.08 wt% of EVA copolymer. Polymeric CFIs have the capability to modify biodiesel agglomeration and facilitate flowing. Lastly, polymers are utilized for storage tanks and auto parts products in direct contact with biodiesel. This approach is completely exclusive for polymers that showed stability toward biodiesel exposure, such as polyoxymethylene (POM) that showed insignificant change during static immersion test for 98 days at 55 \({}^{\circ}\)C. Indeed, the introduction of polymers has expanded in the biodiesel industry to promote green chemistry. polymers; biodiesel; polyhydroxyalkanoates; polymeric catalyst; CFIs; biodiesel exposure materials +
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the other hand [3; 4]. Biodiesel is a good alternative for conventional diesel since it has physicochemical properties close to fossil fuel-based diesel, making it a suitable substitute in diesel engines [5]. In addition to the suitability of biodiesel fuel to be poured directly in diesel engines without modifications, its lubricants characteristics resist the engine wearing out, which can be considered as a privilege for biodiesel compared with conventional diesel [6]. Furthermore, the higher content of oxygen in biodiesel leads to complete combustion of the fuel inside engine that results in lower unfavorable emissions [7]. Thus, biodiesel is classified as an ecofriendly alternative to the conventional diesel [8]. Biodiesel fuel is conventionally sourced from four generations of feedstocks. These feedstock generations include edible oils, inedible oils, algae oil, and genetically modified crop oils. Currently, more than 75% of the global biodiesel production is produced from the first-generation feedstock which requires wide cultivation areas [9; 10]. In this case, first-generation biodiesel is not green enough since the total greenhouse gas footprint for both fuel combustion and cultivation emissions may exceed that of fossil fuel diesel [11]. Moreover, the accumulating costs of farming, cultivation, production, and treatment are not feasible economically since 70-80% of the biodiesel costs are accounted for by the feedstock expenses [12]. Beside the environmental impact and the economic feasibility, ethical issues concern researchers and decision makers.