Mamdouh A. Al-Harthi

Electrical properties of natural rubber nanocomposites: effect of 1-octadecanol functionalization of carbon nanotubes

This article reports the results of studies on the effect of 1-octadecanol (abbreviated as C18) functionalization of carbon nanotubes (CNT) on electrical properties of natural rubber (NR) composites. Dispersion of CNT in NR matrix was studied by transmission electron microscopy (TEM) and electrical resistivity measurements. Fourier transform infra red spectrometry (FTIR) indicates characteristic peaks for ether and hydrocarbon in the case of C18 functionalized CNT. Dielectric constant increases with respect to the filler loading for both unmodified and functionalized CNTs, the effect being less pronounced in the case of functionalized CNT due to its better dispersion in the matrix. Stress–strain plots suggest that the mechanical integrity of the NR/CNT composites, measured in terms of tensile strength, increases on C18 functionalization of the nanofiller. TEM reveals that the functionalization causes improvement in dispersion of CNT in NR matrix, which is corroborated by the increase in electrical resistivity in the case of the functionalized CNT/NR composites.

Removal of Chromium (III) from water by using modified and nonmodified carbon nanotubes

This study was carried out to evaluate the environmental application of modified and nonmodified carbon nanotubes through the experiment removal of chromium trivalent (III) from water. The aim was to find the optimal condition of the chromium (III) removal from water under different treatment conditions of pH, adsorbent dosage, contact time and agitation speed. Multi wall carbon nanotubes (MW-CNTs) were characterized by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The diameter of the carbon nanotubes produced varied from 20-40 nm with average diameter of 24nm and 10 micrometer in length. Adsorption isotherms were used to model the adsorption behavior and to calculate the adsorption capacity of the absorbents. The results showed that, 18% of chromium (III) removal was achieved using modified carbon nanotubes (M-CNTs) at pH 7, 150 rpm, and 2 hours for a dosage of 150 mg of CNTs. The removal of Cr (III) is mainly attributed to the affinity of chromium (III) to the physical and chemical properties of the CNTs. The adsorption isotherms plots were well fitted with experimental data.

Reinforcement of starch/polyvinyl alcohol blend using nano‐titanium dioxide

The article reports the results of the studies on the effect of nano‐titanium dioxide (TiO2) on the morphology, thermal, and mechanical properties of 1:1 starch/polyvinyl alcohol (PVA) composites. Degree of crystallinity of the starch/PVA blends increases with increase in the amount of nano‐TiO2 as determined by differential scanning calorimeter and X‐ray diffraction studies. Results of stress–strain studies indicate an increase in the tensile properties and a decrease in the percentage of elongation and energy at break particularly at higher amount of nano‐TiO2. Increase in peak width in the differential thermogram plot for the maximum decomposition temperature is indicative of increased blend heterogeneity in the presence of nanofillers. The degree of swelling in water decreases with increase in filler loading due to filler–matrix bonding.

Radiation Vulcanization of Natural Rubber Latex Loaded with Carbon Nanotubes

The radiation vulcanization of natural rubber latex (NRL) has been carried out with 150 keV electrons beam with the presence of carbon nanotubes. The NRL/CNTs were prepared by using solving casting method by dispersing carbon nanotubes in a polymer solution and subsequently evaporating the solvent. The load of the carbon nanotubes in the rubber was varied from 1–7wt%. Upon electron beam irradiation, the tensile modulus of the nanocomposites increases with the increase of carbon nanotubes content up to 7wt%. The nanotubes were dispersed homogeneously in the SMR‐L matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, tear strength, elongation at break and hardness were studied.

Easy one-pot method to control the morphology of polyethylene/carbon nanotube nanocomposites using metallocene catalysts

AbstractAn easy one pot method is demonstrated for the controlled periodical surface coating of polyethylene over multiwalled carbon nanotubes (MWCNT) by insitu polymerization of ethylene using highly active metallocene catalysts (Cp2ZrCl2 and Cp2TiCl2) in combination with methylalumoxane. The crystallinity of the nanocomposite was increased and its morphology could be tuned from “sausage” like to “shish-kebab” in the presence of CNT depending on the experimental condition and choice of metal atom. FigureA convenient one-pot method is illustrated to control the morphology of polymer nanocomposite by simple mixing of metallocene catalyst (Cp2ZrCl2 or Cp2TiCl2) and MWCNT in toluene at normal conditions followed by the activation with MAO. The crystallinity of the nanocomposite is increased and the polymer morphology could be tuned from “sausage” like to “shish-kebab”, depending on the experimental conditions.

Synthesis, characterization and crystallization kinetics of nanocomposites prepared by in situ polymerization of ethylene and graphene

High-density polyethylene (HDPE)/graphene nanocomposites were synthesized by in situ polymerization. Zriconocene was used as a catalyst and methylaluminoxane as a co-catalyst. The effect of graphene on the activity of the catalyst and on chain microstructure, crystallization kinetics, mechanical and thermal characteristics of HDPE was investigated. Both the thermal and mechanical properties of HDPE were enhanced. The catalyst showed a slight reduction in the activity. The molecular weight of the polymer was analyzed by gel permeation chromatography, and a significant increase in weight-average molecular weight (MW) of HDPE was observed in the presence of graphene. Isothermal crystallization kinetics was studied by differential scanning calorimetry. The crystallization rate was increased with the addition of graphene. Microcalorimetric analysis indicated a major decrease in the peak decomposition temperature as well as the total heat released for the HDPE/graphene nanocomposites.

The Synthesis and Characterization of Microporous, High Surface Area Activated Carbon from Palm Seeds

A high surface area, microporous activated carbon was prepared from palm seeds using chemical and physical activation methods. Samples of powdered palm seeds were treated with different concentrations of phosphoric and nitric acid at 160°C, followed by physical activation using CO2 at 550°C. The Brunauer-Emmett-Teller surface area analysis of the carbon treated with acids has a low surface area (27 cm2/g) using nitrogen at 77.35 K, whereas only mesopore structures were opened by an acid mixture. Further physical treatment by CO2 provided a high surface area of 1,440 m2/g and the pore volume distribution illustrated a micropore structure with a mean pore of 1 nm. Fourier transform infrared spectroscopy analysis illustrated the presence of carboxylic, phenolic, and lactoine groups on the surface of these activated carbon samples where the obtained zero point of charge (pHZPC) for this material was 4.89.

Thermal and mechanical properties of polyethylene/doped-TiO 2 nanocomposites synthesized using in situ polymerization

Ethylene polymerization was carried out using highly active metallocene catalysts (Cp2ZrCl2 and Cp2TiCl2) in combination with methylaluminoxane. Titanium (IV) oxide containing 1% Mn as dopant was used as nanofillers. The effects of filler concentration, reaction temperature, and pressure on the thermal and mechanical properties of polymer were analyzed. The improvement of nanoparticles dispersion in the polyethylene matrix was checked byWAXD. The thermal properties were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The filler impact on the melting temperature of polyethylene synthesized using Cp2ZrCl2 was very minimal which is due to the degree of short-chain branching. The ash content was also analyzed for each nanocomposite and found to be in line with the activity of the catalyst. There was a significant increase in the mechanical properties of the polyethylene by addition of filler.

Influence of water immersion on the single-lap shear strength of aluminum joints bonded with aluminum-powder-filled epoxy adhesive

Durability of adhesively-bonded aluminum joints was investigated by measuring the joint strength using the single-lap shear test before and after exposure to distilled water and seawater. Fractured specimens were examined by photography and scanning electron microscopy to determine the failure modes. Addition of Al particles as much as 50 wt% did not cause any significant decrease in adhesive joint strength. Moreover, varying the Al filler content in the adhesive did not have a significant effect on adhesive behavior in either of the two environments studied. The unexposed adhesive joints failed almost completely in a cohesive (in the adhesive) failure mode. Some decrease in strength was observed in adhesive joints after exposure to both distilled water and seawater for 6 months. The decrease in adhesive joint strength was more significant for specimens immersed in distilled water than those immersed in seawater, probably due to the higher amount of moisture in the adhesive in distilled water than in seawater, as observed in a related moisture diffusion study. The joints exposed to distilled water or sea water failed in more than one mode. The interior part of the adhesive lap area failed in a cohesive mode while an adhesion failure mode was observed near the edges of the adhesive lap area, which is believed to be a result of moisture diffusion through the edges.

Ethylene homo- and copolymerization chain-transfers: A perspective from supported ( n BuCp) 2 ZrCl 2 catalyst active centre distribution

AbstractPolymerization chain termination reactions and unsaturation of the polymer backbone end are related. Therefore, in this study, the parameters resulting from the modelling of the active centre distribution of the supported catalyst—silica/MAO/(nBuCp)2ZrCl2—were applied to evaluate the active-centre-dependent ethylene homo- and copolymerization rates, as well as the corresponding chain termination rates. This approach, from a microkinetic mechanistic viewpoint, elucidates better the 1-hexene-induced positive comonomer effect and chain transfer phenomenon. The kinetic expressions, developed on the basis of the proposed polymerization mechanisms, illustrate how the active site type-dependent chain transfer phenomenon is influenced by the different apparent termination rate constants and momoner concentrations. The active centre-specific molecular weight Mni (for the above homo- and copolymer), as a function of chain transfer probability, pCTi