In this study, silica from waste materials – rice husk (silica TT) and by-product of quartz stone grinding (silica TA) – modified with bis (3-ethoxy propylsilane) tetrasulphide (TESPT) were characterized. Their particle sizes are mostly under 30μm, quite suitable for plastic filling. Some factors influencing the properties of injectional compounds based on HDPE/LDPE blend and silica from waste materials were carried out. It is revealed processing conditions including a maximum temperature of 190-200oC and screw speed of 50-100 rpm are suitable for stable compound properties. Processing aid additives ratios such as stearic acid/zinc stearate and PE wax/paraffinic oil affect mostly compound melt flow index, but HDPE/LDPE ratio strongly affects both melt flow index and mechanical properties of compounds: change HDPE/LDPE ratio from 90/10 to 60/40 decrease tensile from 15.2MPa to 12.5MPa, bending strength from 15.5MPa to10.6MPa while melt flow index decrease almost twice but elongation at break increase from 34.4% to 72.2%. Also, using PE-g-MA as a compatibilizer may remarkably enhance the mechanical properties of compounds: the PE-g-MA content of 0.8-1.0 (%wt) increases tensile, bending strength, and impact resistance of compound by about 10-30% in comparison with the compound without PE-g-MA.
