Foto düzenleyicilerin pamuk lifi takviyeli düşük yoğunluklu polietilen kompozit malzemelerin mekanik özelliklerine ve yüzey analizine etkisinin incelenmesi

Fiber reinforced composites have gained much acceptance in recent years. Synthetic fibers like glass, carbon and aramid are widely being used in polymer based composites because of their high stiffness and strength properties. However, these fibers have serious disadvantages in terms of their biodegradability, costs, recyclability, energy consumption etc. Although synthetic fibers currently dominate the polymer industry, the use of natural fibers as reinforcing substance in the thermoplastic industry has become more accepted. The use of cotton fiber could be an alternative reinforcement in the replacement of wood fiber, especially in the outdoor environment. The natural fiber composites expose outdoors undergo expecially photo-oxidation degradation caused by ultraviolet radiation. This degradation takes place primarily in the lignin substance, which is responsible for the characteristic color changes. The presence of 0.7-1.6% lignin content in the cotton structure is advantage for the cotton fiber. Cotton fiber have very promising physical properties as a fiber in plastic/fiber composites but there have been few studies about plastic/cotton fiber composites. Thermal stability, moisture resistance, fungal resistance and ultraviolet exposure (UV) are included in the outdoor durability of composites. UV exposure is one of the important concern about the durability of these composites when exposed to outdoor environment. For example, UV exposure can cause the composites to undergo photo-degradation leading to undersirable effects, including a loss in mechanical properties and surface quality, i.e. surface micro-cracking and color change. To prevent the photodegradation and extend service life of cotton fiber reinforced polyethylene (CF/LDPE) composites, various stabilizers were introduced to eliminate or delay the UV light exposure on the CF/LDPE composites, or dissipate the enegry of molecules in the excited state. In this study, the use of photo-stabilizers such as UV absorbers (UVA), hindered amine light stabilizers (HALS-free radical scavengers) and antioxidants were used to minimize the effect of UV exposure in the cotton fiber reinforced low density polyethylene composites.. Cotton fiber reinforced LDPE (CF/LDPE) composites were manufactured by using a custom made single screw extruder. After the manufacturing process, composite plates were pressed to maintain constant thickness and flatness. Samples were cut out by using a desktop CNC milling machine for tensile and impact testing. Composite materials were exposed to both Ultraviolet (UV) light exposure for the time periods of up to 240h. To investigate the effect of photostabilizers on mechanical properties of stabilized and unstabilized CF/LDPE composites, tensile testing was applied to the all composites and compared to each other. Tensile strength, modulus of elasticity and strain at break were calculated from the tensile testing. Fourier transform infrared (FTIR) spectroscopy has been used to study changes in the surface of chemistry of polyethylene. Carbonyl index of all composites were determined to investigate the degradation of composites upon UV weathering. DSC analysis were determined for obtaining the thermal properties of CF/LDPE composites. The crystallinity values were calculated from DSC curves. The crystallinity values of composites indicates that the chain scission mechanism of polyethylene matrix during photo-degradation. Color measurement of CF/LDPE composites were determined. The lightness (L*) and chromaticy coordinates (a* and b*) were measured and color change (∆E*) was calculated.