Mechanical properties of graphene films enhanced by homo-telechelic functionalized polymer fillers via π-π Stacking interactions

© 2015 Elsevier Ltd. All rights reserved. Most researches on graphene/polymer composites are focusing on improving the mechanical and electrical properties of polymers at low graphene content instead of paying attention to constructing graphene's macroscopic structures. In current study the homo-telechelic functionalized polyethylene glycols (FPEGs) were tailored with π-orbital-rich groups (namely phenyl, pyrene and di-pyrene) via esterification reactions, which enhanced the interaction between polyethylene glycol (PEG) molecules and chemical reduced graphene oxide (RGO) sheets. The π-π stacking interactions between graphene sheets and π-orbital-rich groups endowed the composite films with enhanced tensile strength and tunable electrical conductivity. The formation of graphene network structure mediated by the FPEGs fillers via π-π stacking non-covalent interactions should account for the experimental results. The experimental investigations were also complemented with theoretical calculation using a density functional theory. Atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), UV-vis and fluorescence spectroscopy were used to monitor the step-wise preparation of graphene composite films.

Epoxy nanocomposites with aligned carbon nanofillers by external electric fields

This paper presents systematic studies on aligning carbon nanofillers in epoxy by external fields, either electric fields or magnetic fields, to create nanocomposites with greatly improved mechanical and electrical properties. Carbon nanofibers (CNFs) and graphene nanoplatelets (GnPs) were observed to align along the field direction in the epoxy resin. Compared to the unmodifed epoxy and those with randomly-oriented carbon nanofillers, the nanocomposites with aligned carbon nanofillers showed significantly higher fracture toughness and electrical conductivity along the direction of the external field. Compared with randomly-oriented nanofillers, aligned GnPs and CNFs produced 40% and 27% improvement in fracture energy at 1.0 wt%, bringing the total increase in fracture energy over the neat polymer to more than 10 times. Several key toughening mechanisms were identified through fractographic analysis, which was used to develop predictive models to quantify the increases in the value of GIc as a result of 1-D and 2D carbon nanofillers. The present findings suggest that aligning carbon nanofillers presents a very promising technique to create multi-scale reinforcement with greatly increased electric conductivity and fracture toughness.

One-pot synthesis of aminated multi-walled carbon nanotube using thiol-ene click chemistry for improvement of epoxy nanocomposites properties

A non-oxidative method based on thiol-ene click chemistry for functionalization of multi-walled carbon nanotube (CNT) was performed in order to improve the interfacial interactions between epoxy matrix and CNT. In this way, the CNT was aminated using 2-aminoethanethiol hydrochloride radicals thermally produced by a peroxide radical initiator. The aminated CNT (CNT-NH2) was characterized by FTIR, TGA, and solubility evaluations, confirming that thiol radicals are successfully grafted onto the CNT surface with a proper yield. Various percentages of pure CNT (p-CNT) and CNT-NH2 were then incorporated into epoxy matrix to evaluate the effect of the functionalization of CNT on thermal, mechanical, and morphological properties. The nanocomposites were characterized by DMA, tensile testing, and TGA. Results showed that glass transition temperature, tensile properties and thermal stability of epoxy nanocomposites containing CNT-NH2 improves significantly compared to those containing unmodified CNT. These results prove the role of amino-functionalization in improving the interfacial adhesion between epoxy and CNT, which was further confirmed by morphological observations of fracture surfaces of the nanocomposites.

The role of SEBS in tailoring the interface between the polymer matrix and exfoliated graphene nanoplatelets in hybrid composites

Nanocomposites of polypropylene (PP) and polypropylene/styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) blends with exfoliated graphene nanoplatelets (xGnP) were prepared by melt-mixing method. The incorporation of xGnP increased the stiffness and crystallinity of PP at the expense of toughness and the molecular mobility. The effect of addition of SEBS on the mechanical, viscoelastic, thermal degradation and crystallization properties of PP/xGnP composites was studied. The addition of SEBS into PP transformed the phase structure and distribution of xGnP in the PP matrix. SEM micrographs revealed that SEBS polymer chains formed a coating over the graphene nanoplatelets, which strengthened the interface between the filler and the matrix, and improved the dispersion and distribution of the filler throughout the matrix.