الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Outdoor applications of polymers are increasing rapidly. So the ability of polymers to withstand environmental degradation became very important for many researchers. The effect of accelerated weathering and hardening on the stability of high-density polyethylene (HDPE) with and without stabilizers has been studied in this work. HDPE samples were prepared with UV absorbers (UVA) and hindered amine light stabilizers (HALS) at different concentrations. The samples were placed in Xenon-Arc Weather-Ometer (WOM) to simulate outdoor weathering conditions. The exposed samples were tested by a universal tensile testing machine at regular time intervals till 1300 hours to study the changes in mechanical properties such as tensile strength, modulus of elasticity, elongation at break, and toughness The results indicate that non-stabilized HDPE was affected after 300 hours of exposure, where it lost most of its toughness from 36.9 J to 0.5 J, and the percentage of elongation at break decreased from 1223% to 21%. It was found that stabilizers sustain the mechanical properties of samples efficiently until 900 hours. However, the best performance was observed by samples containing 0.15% of UVA and 0.45% of HALS, which retain most of its properties until 1300 hours. The hardening test was performed by heating the samples to 125 °C then suddenly cooled at 0 °C, 25 °C, and, 50 °C. The mechanical properties of HDPE were significantly affected by hardening. The effect of cross-head speed, initial crack length, and hardening on the fracture toughness of HDPE was investigated in this thesis, the results show that the fracture toughness decreases with the increase of the cross-head speed and increases with the increase of the initial crack length. Also, the hardening shows a sharp effect on fracture toughness as the material became very brittle.