Unsaturated polyester was modified with dioctyl phthalate (DOP) and used as matrix in glass fiber reinforced composite. The effect on the thermal stability of the composite was studied in this work. The results of the modification showed that modified matrix had the best thermal stability at 5 wt% DOP with temperature of 373°C at 20% weight loss as compared with unmodified of temperature of 346°C at the same weight loss. The analysis of the resultant composites also indicated that the composite with modified matrix had better thermal stability having 65% of its weight left at 897°C as compared with unmodified matrix with 53% of its weight at the same temperature. The drop weight impact test conducted did not show any significant difference in the properties of the modified composite and unmodified.
Key words: Thermal stability, glass fiber, impact test, unsaturated polyester.