الفهرس 
Chapter One : Introduction And Literature ReviewOnly 14 pages are availabe for public view
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Abstract
The present work investigates the possibility to introduce new self-lubricating polymeric materials for dry sliding bearing applications. The proposed polymeric composites are consisting of high density polyethylene (HDPE), low density polyethylene (LDPE) and polystyrene (PS) filled by paraffin oil and reinforced by carbon nanotubes (CNTs). Experiments were carried out to find the friction properties of the proposed composites at dry sliding conditions.
The experiments showed that filling HDPE, LDPE and PS by paraffin oil and reinforcing them by CNTs decrease the friction coefficient and increase wear resistance significantly. This may be referred to the presence of oil in multipores that spread inside the polymer matrix, where they work as reservoirs of oil from which it leaks up to the sliding surface and causes friction decrease, where the contact will be between partially polymer composites/steel and oil/steel due to the mixed lubrication regime offered by the oil film. Besides, oil film can isolate the contacting asperities of the sliding surfaces from excessive wear, where high shear tearing and transfer of polymer to the steel surface were diminished. The self-lubricating mechanism of CNTs during sliding depends on the rolling movement of the CNTs, where they change friction and shear stress into rolling. This mechanism can be achieved when the nanotubes can have the medium in which they can move freely. Presence of oil can provide this facility that decreases both friction and wear.
It was observed that friction coefficient slightly increased with increasing CNTs content. The reason of friction increase is attributed to the abrasive action of CNTs. Besides, CNTs strengthened the polymeric matrix and increased its shear strength and consequently friction increased. Wear drastically decreases down to minimum then significantly increased with increasing CNTs content. Minimum wear values were observed at 0.6 wt. % CNTs. The reduction of wear can be explained on the basis that reinforcing the tested polymers by CNTs makes micro-crack propagation difficult and increases tensile strength. As CNTs content increases the tubes will agglomerate and decrease the interfacial adhesion between the CNTs and polymer, so that CNTs will be simply pull-out and will not contribute towards decreasing wear resistance of the composites. Friction displayed by the tested polymers filled by 5.0 wt. % paraffin oils and reinforced by CNTs showed lower values than that observed for composites free of oil. Friction coefficient slightly decreased with increasing CNTs content. It seems that, oil impregnation in the matrix helps the release of CNTs from the matrix during sliding, where they work as rollers on the contact surface. HDPE composites displayed minimum friction coefficient and wear, while PS showed the highest values.