Mirigul Altan

Mechanical and Antibacterial Properties of Injection Molded Polypropylene/TiO2 Nano-Composites: Effects of Surface Modification

Polypropylene (PP)/titanium dioxide (TiO2) nano-composites were prepared by melt compounding with a twin screw extruder. Nanoparticles were modified prior to melt mixing with maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MA) and silane. The composites were injection molded and mechanical tests were applied to obtain tensile strength, elastic modulus and impact strength. Antibacterial efficiency test was applied on the injection molded composite plaques by viable cell counting technique. The results showed that the composites including SEBS-g-MA and silane coated TiO2 gave better mechanical properties than the composites without SEBS-g-MA. Antibacterial efficiency of the composites varied according to the dispersion and the concentration of the particles and it was observed that composites at low content of TiO2 showed higher antibacterial property due to the better photocatalytic activity of the particles during UV exposure.

Optimization of Residual Stresses in the Surface Regions of Injection Moldings

The present study focused on the optimization of the injection molding process parameters to minimize thermal residual stresses in the surface regions of the polystyrene and high density polyethylene parts. Process parameters such as melt temperature, mold temperature and cooling time were considered as variables and their effects on residual stresses in surface regions of the parts were investigated by utilizing design of experiment (DOE), Taguchi and analysis of variance (ANOVA) methods. As a result, the most important parameters for residual stresses in surface regions of the PS and HDPE parts were found melt temperature and mold temperature, respectively.

Effects of compatibilizers on mechanical and antibacterial properties of injection molded nano-ZnO filled polypropylene

Polypropylene (PP)/zinc oxide (ZnO) nanocomposites were prepared by melt compounding. Prior compounding, surface of the particles were modified with different compatilibizers such as silane and stearic acid. Modification was also done by coating the particles with maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MA) block copolymer dissolved in toluene. Specimens of tensile test, impact test, and antibacterial efficiency test were obtained by injection molding. The results showed that stearic acid and silane containing composites gave structures with fine distributed particles while the presence of SEBS-g-MA induced agglomerates. The presence of stearic acid increased tensile strength and impact strength but reduced elastic modulus. Silane was more effective in increasing elastic modulus. Despite the elastomeric nature of SEBS-g-MA, it did not rise impact strength due to its limited amount of usage in coating of the particles. Antibacterial properties of the composites reduced with the increment of ZnO loading because of the weak UV absorption and insufficient photocatalytic activity of the particles. On contrary, at low ZnO content, satisfactorily high antibacterial effect was observed especially in well dispersed structures including stearic acid and silane.

Residual stresses determination in injection molded virgin and recycled HDPE blends: mechanical properties and morphology

Abstract An experimental study of residual thermal stresses has been carried out in injection molded virgin and recycled high density polyethylene (HDPE) blends. Effects of blend concentrations on residual stresses were investigated under different injection conditions such as melt temperature, mold temperature and cooling time. Layer removal technique was used for measuring residual stresses. In order to determine the relation between the residual stresses and material characteristic of HDPE blends, mechanical and morphological properties of the blends were also investigated. Elastic modulus and impact strength were important key factors for determining the blend characteristics. As a result, it was found that HDPE blends gave higher residual stresses but lower impact strength with higher elastic modulus when recycled concentration was increased. Furthermore, it was seen that shape and size of the crystallites were also effective on residual stresses. Small and spherulitic crystallite structured blends such as 30 % recycled HDPE induced reduction in residual stresses due to easier relaxation with lower elastic modulus and higher impact strength while lamellar crystallite structured blends such as 50 % recycled HDPE gave higher elastic modulus but lower impact strength with higher residual stresses.