Key Engineering Materials Vols. 334-335

Abstract: Polymer nanocomposites are recognized as the next generation of polymer composites due to their exceptional properties. Understanding the molecular origin of the reinforcement mechanism is crucial to the development of such promising materials. This paper reports our recent molecular dynamic study on clay-based polyurethane nanocomposites. The effect of clay platelets on phase separation behavior of polyurethane, at the clay-polyurethane interface, is quantified in terms of molecular interactions, structure and dynamics. The results show that the nanoconfinement of polyurethane chains in clay gallery impedes the development of phase separation commonly observed in bulk polyurethane. The absence of phase separation of intercalated polyurethane is believed to be related to the competitive interactions among clay platelet, polyurethane and surfactant.

Abstract: Surface defects cause the measured tensile strength of glass and other brittle materials significantly lower than their theoretical values. Here, we describe an on-line process to ‘heal’ surface flaws and functionalise surface properties. A nanometer-scale hybrid coating layer based on styrene-butadiene copolymer with mutiwalled carbon nanotubes (MWCNTs) and/or nanoclays, as mechanical enhancement and environmental barrier layer, is applied to alkali-resistant glass fibres (ARG). The nanostructured and functionalised traditional glass fibres with low fraction of nanotubes or nanoclay (1 wt% in sizing) show significant improvement in both mechanical properties and environmental corrosion resistance. We introduce a healing efficiency factor and conclude that the coating modulus, thickness and roughness are responsible for the mechanical improvement of fibres. Furthermore, we show that the hybrid coating layer is essential for enhanced interfacial adhesion strength of the glass fibre reinforced cement composites.

Abstract: Young’s modulus of nanohoneycomb structures in the vertical direction relative to the pore (generally along the beam length) is measured according to the porosity from bending tests in atomic force microscopy (AFM). The pore diameters of the nanohoneycomb structures are from about 30 to 60 nm. To determine the Young’s modulus of the nanohoneycomb structures, the area moment of inertia of the nanohoneycomb structure is determined according to the arrangement of the pores. The area moment of inertia of the nanohoneycomb structure is found to be affected by the porosity of the nanohoneycomb structures. The Young’s modulus of the nanohoneycomb structures decreases as a function of the porosity in a large range.

Abstract: Carbon nanotubes have excellent mechanical and electrical properties such as high stiffness, light weight, heat stability, excellent heat conductivity, and excellent electrical conductivity. This study was aimed into investigate the properties of composites consisting of adding several different proportions of carbon nanotubes to phenolic resin, which contained tensile strength, fatigue life and electrical properties. The experimental results showed that the electric resistance decreases as the weight percentage of the nanotubes increases, also the tensile strength increased as the nanotubes increased. After the different moisture-temperature circumstances and thermal cycling, the increase of the electric resistance was compared to the pristine composites. The experimental results hoped to be understood from the fracture surface observations by scanning electron microscope (SEM).

Abstract: This research focuses on the fabrication of glass fiber/epoxy organoclay nanocomposites as well as on the investigation of organoclay effect on transverse tensile strength and in-plane shear strength of the nanocomposites. To demonstrate the organoclay effect, three different loadings of organoclay were dispersed respectively in the epoxy resin using a mechanical mixer followed by sonication. The corresponding glass/epoxy nanocomposites were produced by impregnating dry glass fiber with organoclay epoxy compound via a vacuum hand lay-up procedure. For evaluating transverse tensile strengths, the unidirectional coupon specimens were prepared and tested in the transverse direction. Results indicate that with the increment of organoclay loadings, the glass/epoxy nanocomposites demonstrate higher transverse tensile strength. On the other hand, the in-plane shear strengths were measured from [± 45]s laminates. It is revealed that when the organoclay loadings increase, the in-plane shear strength of glass/epoxy nanocomposites also increases appropriately. Scanning Electron Microscopy (SEM) observations on the failure surfaces indicate that the increasing characteristics in transverse and in-plane failure stresses may be ascribed to the enhanced fiber/matrix bonding modified by the organoclay.

Abstract: This research is aimed to fabricate the nano and micron particle reinforced composites as well as to understand the particulate size effect on the mechanical behaviors of the composites. The stiffness, strength and fracture toughness were investigated in this study. Spherical alumina particles with diameters of 5 microns and 10-20 nano meters were dispersed respectively into the epoxy resin using the mechanical mixer followed by the sonication. To measure the stiffness and strength of the composites, coupon specimens were prepared and then tested in tension. On the other hand, the fracture toughness was evaluated by performing three point bending tests on the single edge notch bending specimens. Experimental results revealed that the Young’s modulus of composites basically is not affected by particulate size; while, the tensile strength of the composites containing nano particles is higher than that with micron particles. From the fracture tests, it was indicated that the composites containing nano particles possess superior fracture toughness than the composites with micron inclusions.

Abstract: A full 3D finite element method has been used to understand how nano-clay particles affect the mechanical properties of an epoxy/clay nanocomposite. The epoxy/clay nanocomposite has been modelled as a representative volume element (RVE) containing intercalated clay platelets that internally delaminates at the gallery layer upon satisfying an energy criterion, and an epoxy matrix that is elastic-plastic. A cohesive traction-displacement law is used to model the clay gallery behaviour until failure. For clay volume fractions >1%, clay particle interaction is observed to develop during uniaxial tension, the nanocomposite stiffness becomes non-linearly dependent on the clay volume fraction, and the Mori-Tanaka model overestimates the stiffness. Failure of the clay gallery is not observed and is believed to have no influence on the ultimate tensile strength of the nanocomposite.

Abstract: The functionalized multiwall carbon nanotubes (MWNTs) have been prepared by free radical reaction with maleic acid and maleic anhydride. The functionalized MWNT was further blended with poly(dimethylsiloxane) (PDMS) based Poly(urea-urethane) (PUU). Both maleic acid modified MWNT (Maa-g-MWNT) and maleic anhydride modified MWNT (Mah-g-MWNT) showed enhanced dispersion compared with that of pristine MWNT and PUU.For MWNT/PUU nanocomposites containing 5 phr functionalized MWNT, the maximum microwave absorption was -19.2 dB for Maa-g-MWNT/PUU nanocomposites and was -22 dB for Mah-g-MWNT/PUU nanocomposites.