# Mechanical Properties of Green Synthesized Graphene Nano-Composite Samples
## 1 Introduction
Adding different weight fractions of graphene nanoplatelets to epoxy resin remarkably increases the fatigue life of the epoxy. The best fatigue life was obtained by adding 0.25 wt.% graphene [12]. Additionally, adding carbon nanofibers (hybrid nanocomposites of graphene, carbon nanofibers and epoxy resin) will significantly improve the epoxy resin's fatigue life compared with the results obtained by adding 0.25 wt.% graphene [16]. [PERSON] and [PERSON] [18] fabricated a composite consisting of polyacrylamide(PAN) and polyaniline (PANI) polymers and green synthesized graphene quantum dots. The graphene quantum dots were 2-50 nanometer-sized particles which had superior electrical properties, and hence it has been utilized in many energy harvesting and storage applications. The prepared composites were used to fabricate a prototype supercapacitor cell which could deliver a significantly higher current density compared with other polymeric capacitors. Graphene nanoplatelets and nanosheets are used in the fabrication of polymeric composites. Another type of graphene nanoparticle is graphene quantum dots. Graphene quantum dots have been used extensively in recent years due to their unique structure-related properties. Graphene quantum dots can be obtained from the green synthesis of alternative sources of carbon-like glucose powder [19], citric acid [20], corn powder [21]and rice husks [22]. Several studies have been conducted for reducing graphene oxide and improving the production process of graphene on a large scale [23; 24]. Graphene quantum dots are environmentally friendly due to their nontoxic and biologically inert properties. Graphene quantum dots are stable chemically and physically because of their intrinsic inert carbon properties. [PERSON] et al. [25] published a review paper. They discussed different methods of graphene quantum dot preparation such as the hydrothermal method, microwave-assisted hydrothermal method, soft template method, liquid exfoliation method, metal-catalyzed method and electron beam lithography method. [PERSON] et al. [26] also published a review paper, and the differences between graphene quantum dots and other nanomaterials, including nano carbons, were discussed. Good mechanical, electrical and photosensitive applications can be obtained using graphene quantum dots by fabricating nanocomposite polymers. [PERSON] et al. studied the effect of adding graphene quantum dots to epoxy resin. The results showed that the tensile strength, Young's modulus and nominal strain at break increased by 125%, 153.4% and 18.1%, respectively [27]. The graphene-based nanocomposites will be a starting point for new and more sophisticated composite materials. The literature survey shows different aspects of using graphene in nanocomposite fabrication. Graphene was used as nanoplatelets and nanosheets at first. Then, by introducing graphene quantum dots, new ways for using this type of carbon atom were found. Several studies have been carried out on lemon extract to reduce the graphene oxide and graphene quantum dot synthesis. However, the synthesis of graphene quantum dots directly from the lemon extract is very novel. In this article, the effect of different weight percentages of graphene quantum dots on polyester nanocomposite fabrication will be investigated. The main difference between the current work and other implemented research is the way of preparing graphene quantum dots: green synthesis and the usage of graphene quantum dots to enhance the mechanical properties of polymer-based nanocomposites. The flexural strength, strain at the failure point and elastic modulus of the nanocomposites were measured and discussed. The flame retardancy of fabricated nanocomposites will be carried out against fire.