Nylon 12/graphene nanocomposites

A unique combination of excellent mechanical, thermal and barrier properties has made graphene a multifunctional reinforcement for polymers. The goals of this research were to prepare exfoliated functionalized graphene sheets (FG) from expanded graphite, the uniform dispersion of these graphene sheets in the nylon 12 matrix, and understanding the effect of graphene on mechanical, thermal and barrier properties of nylon 12. FG were successfully prepared from various methods and was confirmed by XPS and TEM analysis. FG were melt blended with nylon 12 and their dispersion in the matrix was characterized by SEM. Crystallization behaviour of Nylon 12/ FG was investigated by means of differential scanning calorimetery (DSC). Non isothermal crystallization analysis revealed that the addition of only 1wt% FG in nylon 12 improved its crystallinity to about 67%. Application of Avrami analysis; to study isothermal crystallization kinetics; disclosed an unchanged nucleation mechanism and growth geometry. Polarized optical microscopy (POM) results indicated that FG did act as nucleating agent but hindered the formation of larger size crystals. Study of mechanical performance revealed that the incorporation of very small amount (about 0.6wt %) of the FG caused a significant improvement in ultimate tensile strength, elongation, impact strength and toughness of the nylon 12. With 0.6wt% FG ultimate tensile strength and elongation at break of the nylon 12 is improved by ～ 35% and ～200%, respectively. FTIR confirmed the hydrogen bonding between nylon 12 and FG, which contributed towards strengthening of the interface. The KIc of the nylon 12 is ～1.28 MPa.m0.5 and the incorporation of 0.6wt% FG causes a significant increase of 72 % (～2.2 MPa.m0.5). 0.6wt% FG causes also a significant improvement of 175 % in impact failure energy of the nylon 12. The incorporation of FG caused the increase in amount of γ phase of nylon12 and decreased its crystal size which could be the direct reason for the enhancement of the toughness. Nano-graphite, MWCNTs and carbon black were surface functionalized and their effect on the toughness was investigated. The results proved graphene to be the best nanofiller among three for the toughening of nylon 12. Oxygen and water permeability of nylon 12 was decreased to ~40%, implying the high aspect ratio of graphene which forced the permeant to pass through longer path.