الفهرس 
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Abstract
Polymeric nanocomposites (PNCs) have been widely applied in numerous engineering and medical fields such as coatings, automobiles, and aerospace due to their appropriate and good thermal, mechanical, electrical, physical, and optical properties. Polymethylmethacrylate (PMMA) resin is the most acrylic material widely used for denture applications because it possesses a combination of suitable characteristics including inexpensive fabrication, light weight, ease of laboratory manipulation, and stability in the oral environment. Although PMMA resin has better mechanical and physical properties than other polymeric materials, it has poor physical and mechanical performance when used alone. Recently, there has been an increasing attention toward incorporating ceramic nanofillers into denture-base acrylic to act as a strengthening material.
Therefore, the main objective of this study is to study the effect of Al2O3 nanowires (Al2O3 NWs) and ZrO2 nanoparticles (ZrO2 NPs) content on the mechanical and tribological properties of PMMA. Two methods were used to fabricate the composites, there were cold (self) and heat-cured methods. For the cold-cured method, specimens were fabricated directly without any heat treatment. Two groups of specimens were fabricated, the first group added ZrO2 NPs to PMMA with different weight fractions (wt.%) of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 wt.%. For the second group, Al2O3 NWs were added to PMMA at the same wt.%. For the heat-cured method, the specimens were fabricated and immerged in water bath at least for one hour.
Effect of ZrO2 NPs and Al2O3 NWs content on the elastic modulus, Vickers microhardness number (VHN), wear rate, and coefficient of friction (COF) of all nanocomposites have been investigated. Tribological properties have been investigated by pin-on-disc tester under applied loads of 10, 20, 30, 40, and 50 N at constant sliding speed and sliding distance of 1.256 m/s and 226 m, respectively. Then, the worn surfaces after wear test were characterized by scanning electron microscope (SEM).
For cold and heat-cured nanocomposites, experimental results revealed that the elastic modulus, microhardness, wear rate, and COF were enhanced with increasing nanofiller content up to 0.5 and 0.7 wt. % of Al2O3 NWs and ZrO2 NPs, respectively. Also, wear rate increased with increasing applied loads up to 50 N, while COF decreased with increasing applied loads up to 40 N.
SEM examination showed that the worn surface of unfilled PMMA contains many deep grooves and ploughed marks. After adding of 0.5 wt. % Al2O3 NWs and 0.7 wt. % ZrO2 NPs into PMMA, mechanical strength of the specimen’s surface was enhanced and showed dramatically decreased wear grooves. Also, after adding of Al2O3 NWs and ZrO2 NPs to PMMA more than 0.5 wt.% and 0.7 wt., respectively up to 1 wt. %, there were more ploughed marks and porosity formation on worn surfaces than those of PMMA at 0.5 wt.% Al2O3 NWs and 0.7 wt.% ZrO2 NPs.