Vulcanization kinetics and reinforcement behaviour of natural rubber-carbon black composites: Addition of Shea-butter versus aromatic oil as plasticizers.

This work is a comparative study between Shea butter (SB) and treated distillate aromatic extract oil (TDAE) as plasticizers in the vulcanization of natural rubber (NR)- carbon black (CB) vulcanizates (-CB-S-NR-). The plasticized -CB-S-NR- composites extended scorch (Ts2) and optimum (T90) curing times. The delays in crosslinking reaction were suspected to be due to the increased viscosity (ML) and insulation of the reacting species (NR, CB, Sulfur and other curing aids) by the films of plasticizers. This effect increased the activation energy (Ea (KJ/mol)) for vulcanization. The -CB-S-NR- without plasticizer SB (SBO), showed higher ML, crosslinking density index (ΔM), rheological strength (MH) and low cure reversion properties than others. In comparison, the SB loaded -CB-S-NR- composites showed improvement in ML, ΔM, T90, with lowers Ea (KJ/mol) than TDAE samples. Also, the SB compounds exhibited higher Young's modulus Eo(MPa) than SBO and TDAE compounds. For instance, the Eo(MPa) of SB5 was over 7 and 1200 % higher than SBO and STD5 respectively. However, -CB-S-NR- filled with TDAE generally showed higher strength(MPa), attributed to stronger CB-NR interactions. Therefore, environmentally friendly SB could replace petroleum based oils for compounding rubbers.

Stacking Interactions of Poly Para-Phenylene Vinylene Oligomers with Graphene and Single-Walled Carbon Nanotubes: A Molecular Dynamics Approach.

This study is meant to address the understanding of the interactions between poly para-phenylene vinylene (PPV) oligomers, graphene and single-walled carbon nanotubes (SWCNT). To this end, the binding energies of the PPV oligomers with graphene and SWCNTs were investigated. Calculations are performed and the parameters related to van der Waal vdW interactions are discussed to achieve and confirm the crystallization of oligomers of PPV into herringbone (HB) structure arrangement, which is known to be the most stable conformation at 300 K. Finally, the interfacial interactions between crystal PPV, graphene and SWCNT are carried out. According to the results, the intramolecular potential energies of PPV chains are found to increase linearly with each extending PPV monomer unit by approximately 50 kcal/mol. Moreover, the interfacial interaction properties analysis using radial distribution functions (RDFs) for PPV-graphene and PPV-SWCNT show significant disordering of the arrangement of molecules, which is more pronounced for PPV-SWCNT than that in PPV-graphene. The radius of gyration (Rg) profiles show a net decrease of ∼-0.8, for PPV-graphene with different surface coverage, and, a net increase of ∼+0.6, for PPV-SWCNT; meaning that, the binding between PPV-graphene is much stronger than with PPV-SWCNT.

Development and Characterization of Clay-Nanocomposites for Water Purification.

In this work we propose a facile method of preparing cost-effective clay-metaloxide/metal (CuO/Ag and ZnO/Ag) composite pellets for an efficient water purification technique. Clay, with intrinsic antibacterial activity, served as a membrane support for different metaloxide/Ag nanoparticles (NPs) concentrations (2.5, 5 and 10 wt.%), as the active fillers. The effect of time (24 and 48 h) on the bactericidal activity of these pellets was also monitored. The clay-nanocomposite pellets were characterized using: X-ray diffraction, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible (UV-Vis) spectrophotometry and nitrogen desorption analysis. The antibacterial activity performance was tested using E. coli and S. aureus strains of ATCC25922 and ATCC25923, respectively, in two aqueous media (nutrient broth and nutrient-free) by the colony-forming unit method. The results showed that the clay-CuO/Ag composite with a bandgap (1.24 eV) exhibited overall best performance under all conditions and time factors of ~100% efficiency in nutrient-free medium for all concentrations and times and 20-40% efficiency in nutrient broth for 24 h. The clay-ZnO/Ag with a bandgap of 2.88 eV showed no bactericidal activity in both media, except for that with 10 wt.% ZnO/Ag which showed 100% efficiency in nutrient-free medium after 24 h. All the synthesized composites showed 100% bactericidal efficiency in nutrient free medium after 48 h. These results indicate that, the clay/metaloxide/Ag could serve as efficient water purification technique, with a potential for large-scale commercialization.

Ag2CO3-halloysite nanotubes composite with enhanced removal efficiency for water soluble dyes.

The release of water soluble dyes into the environment is an utmost concern in many countries. This paper presents the effects of Ag2CO3-halloysite composites on the efficient removal of water soluble dyes. In this study, NaHCO3 solution was added dropwisely to halloysite nanotubes (HNTs) dispersed in aqueous AgNO3 to form Ag2CO3-HNTs composite. The synthesized Ag2CO3-HNTs composite was characterized with Diffused Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDX) and Fourier Transform Infra-Red (FT-IR) spectroscopy. The photocatalytic activity and the adsorption capacity of Ag2CO3-HNTs on methylene blue and rhodamine b dyes were dependent on pH and the amount of HNTs used in the synthesis. The photodegradation efficiency of Ag2CO3 was lower when compared with that of the composite material. This observation is due to the reduction in the electron-hole recombination with the HNTs acting as electron trapping site and the enhanced aqueous dispersity of Ag2CO3-HNTs. The enhanced adsorption of water soluble dyes by the Ag2CO3-HNTs resulted from the electrostatic attraction of cationic dyes to the surface of the HNTs (negatively charged). The Ag2CO3-HNTs therefore removed dye pollutants through a combination of photocatalytic and adsorption processes. The results obtained during the study confirmed the potential application of Ag2CO3-HNTs composite in water treatment technologies.