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This article has been devoted to investigation of the tribological properties of ultra-high molecular polyethylene/graphene oxide nanocomposite. The nanocomposite of ultra-high molecular polyethylene/graphene oxide was prepared with 0.5, 1.5, and 2.5 wt% of graphene oxide and with a molecular weight of 3.7 × 106 by in-situ polymerization using Ziegler-Natta catalyst. In this method, graphene oxide was used along with magnesium ethoxide as a novel bi-support of the Ziegler-Natta catalyst. Analyzing the pin-on-disk test, the tribological properties of the nanocomposite, such as wear rate and mean friction coefficient, were investigated under the mentioned contents of graphene oxide. The results showed that an increase in graphene oxide content causes a reduction in both wear rate and mean coefficient friction. For instance, by adding only 5 wt% graphene oxide to the polymeric matrix, the wear rate and mean coefficient friction decreased about 34% and 3.8%, respectively. Also, the morphological properties of the nanocomposite were investigated by using X-ray diffraction and scanning electron microscopy. In addition, thermal properties of the nanocomposite were analyzed using differential scanning calorimetry, under various contents of graphene oxide. The results of the morphological test indicated that the graphene oxide was completely exfoliated into the polymeric matrix without any agglomeration. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this research, ultrahigh-molecular-weight polyethylene (UHMWPE)/multiwalled carbon nanotube (MWCNT) nanocomposites with different nanotube concentrations (0.5, 1.5, 2.5, and 3.5 wt %) were prepared via in situ polymerization with a novel, bisupported Ziegler-Natta catalytic system. Magnesium ethoxide [Mg(OEt)2] and surface-functionalized MWCNTs were used as the support of the catalyst. Titanium tetrachloride (TiCl4) accompanied by triethylaluminum constituted the Ziegler-Natta catalytic system. Preparation of the catalyst and the polymerization were carried out in the slurry phase under an argon atmosphere. Support of the catalyst on the MWCNTs was investigated with Fourier transform infrared spectroscopy. The results confirmed the interaction between the catalyst and the MWCNT hydroxyl groups. Intrinsic viscosity measurements showed an ultrahigh molecular weight in the produced samples. Scanning electron microscopy images confirmed the good dispersion of MWCNTs throughout the polyethylene (PE) matrix. The crystallization behavior of the samples was examined with differential scanning calorimetry. Its results showed that the crystal content of the samples increased with increasing MWCNT concentration up to 1.5 wt %. The same trend was observed for the crystallization temperature, whereas the melting temperature did not change with increasing MWCNT concentration up to 1.5 wt %, but it decreased beyond this concentration. In addition, thermogravimetric analysis results showed that the addition of MWCNTs noticeably improved all of the investigated thermal stability factors of the UHMWPE/MWCNT nanocomposites compared to those of pure PE. The results obtained from tensile testing revealed significant increases in the Young's modulus, yield stress, and ultimate tensile strength. This indicated a tremendous improvement in the mechanical properties of the PE/MWCNT nanocomposites compared to those of pure PE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125:453-461, 2012 [ABSTRACT FROM AUTHOR]

In this research the radical chlorination reaction of polyethylene has been carried out in perchloroethylene solvent under atmospheric pressure, using chlorine gas and UV light. In order to characterize the structural configuration of chlorinated polymer and study the reaction rate, different samples have been taken in equal periods of time during the reaction time. The FT-IR and H NMR spectra of these samples have been recorded and interpreted. The sequences of methylene groups between two subsequent chloromethylene groups in the polymeric chains have been determined through H NMR spectra and the obtained results have been confirmed with the data of some model compounds. The relative percentage of these methylene groups, which have been calculated from their integrated values in their H NMR spectra have been plotted vs. percentage of chlorination and discussed. Also H NMR spectra have been used for calculating the chlorine percentage of each sample and the results have been compared with data obtained from an elemental analyzing technique namely flask combustion method. Using the results of these two techniques, the reaction rate has been plotted versus reaction time and compared. [ABSTRACT FROM AUTHOR]

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE's molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE's thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett's. The "Model-Fitting Method" showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (Ea) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content. [ABSTRACT FROM AUTHOR]