Synthesis and Characterization of Cardanol Based Epoxy Systems
Emre Kinaci1, Giuseppe R. Palmese1
1Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA, 19104 USA.
Polymeric materials are mainly derived from petroleum feed-stocks. With the petroleum production facing exhaustion day by day, the use of renewable plant based feed-stocks for making polymers offers both economic and environmental advantages. Thermosetting materials are highly cross-linked polymers that are cured or set using heat, heat and pressure, and/or light irradiation. Among the renewable resources that can be used to prepare thermosetting polymers, the Cashew nut shell liquid (CNSL) is an important one due to its composition of phenolic compounds that offer many routes for chemical modification. The main component of thermally treated CNSL is cardanol which is a phenol derivative mainly having a meta substituent of a C15 unsaturated hydrocarbon chain with one to three double bonds. In this study, three commercially available CNSL based resins, NC 514 which is a bisphenol type commercially available epoxy resins with approximately two epoxies per molecule, LITE 2513HP (epoxy cardanol) with approximately one epoxy per molecule on the benzene ring and LITE 2020 which is a cardanol molecule with an ethanol moiety on the benzene ring were used. LITE 2513HP epoxy resin and LITE 2020 cardanol resin were chemically modified from the double bonds on the side chain to increase the functionality of the molecules by means of epoxidation. Epoxidation of the resins have been carried out in the presence of formic acid and hydrogen peroxide at lower temperatures where toluene used as inert carrier liquid. The side chain epoxidized products as well as commercially available NC 514 resin were characterized via epoxy equivalent titration and spectroscopic techniques including FT-IR and 1H-NMR spectroscopy. The rheological properties of the liquid resins were also evaluated. The modified resins and NC 514 di-epoxy resin have been thermally cured with four different synthetic and cardanol based epoxy hardeners and the cure temperatures and the reactivity of the resins towards four different epoxy hardeners were analyzed via Differential Scanning Calorimetry (DSC). After the cure of these resins, the thermo-mechanical properties were determined via Dynamic Mechanical Analysis (DMA), mechanical properties were determined via tensile tests and the thermal stabilities of the resins were examined by thermal gravimetric analysis (TGA) method. Finally, the effect of the different final structures of the different epoxy monomers as well as different epoxy hardeners in these systems on both liquid resin properties and cured resin properties were evaluated.
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