Thesis (M.Sc.)--Chulalongkorn University, 2008

The effects of extrusion conditions on physical properties of high density polyethylene (HDPE) compound for pressurized pipe application were studied. For extrusion of HDPE with typical bimodal molecular weight distribution, the studied variables were extrusion temperature profile, feed rate and screw speed as well as screw configurations. The physical properties of HDPE compound, full notch creep test (FNCT) for evaluating slow cracking growth (SCG) resistance, impact resistance, white spot area and morphological analyses for evaluating gel dispersion, and oxidative induction time (OIT) for evaluating thermal stability were investigated. For extrusion of bimodal high density polyethylene pipe grade compound, the barrel temperature of 200℃ and an optimized screw configuration were found appropriate. The decrease in material feed rate resulted in an increase in SCG resistance and impact energy of high pressure pipe. The higher barrel temperature (240℃) promoted the degradation leading to the decrease in OIT and impact resistance of HDPE pipe. However, the screw speed had no significant effect on the physical properties of high pressure pipe.