Study of the Effect of Polymer Additive Selection on the Mechanical and Thermal Properties of Injection-Moulded Polypropylene Products in Aba, Abia State

Polymer additives including antioxidants, ultraviolet stabilisers, nucleating agents, and processing aids are critical to achieving specified performance characteristics in injection-moulded polypropylene products for consumer and industrial markets. This study investigates the effect of additive package selection on the mechanical and thermal properties of injection-moulded polypropylene household products manufactured by processors in Aba, Abia State, South East Nigeria. Polypropylene resins from three domestic suppliers were compounded with varying additive combinations at a local compounding facility and characterised by melt flow index, Vicat softening point, notched impact strength, and tensile modulus. Products moulded from each compound were subjected to accelerated weathering for 200 hours in a UV-B weatherometer, and post-weathering mechanical property retention was assessed. Results show that products manufactured without ultraviolet stabiliser exhibited tensile strength retention of only 54 percent after 200 hours of UV exposure, compared to 88 percent for fully stabilised compounds. Impact strength declined most severely in unstabilised samples, with 62 percent reduction after weathering, representing a critical failure mode for outdoor applications. Nucleating agent addition improved Vicat softening point by 4.2 degrees Celsius on average, enhancing thermal resistance for hot-fill product applications. Melt flow index sensitivity to antioxidant type was minimal under typical processing conditions. The study recommends standardised minimum additive package specifications for outdoor-use polypropylene products manufactured in South East Nigeria and provides a practical additive selection guide for compounders serving Aba's plastics processing industry. Keywords: polymer additives, polypropylene, injection moulding, UV stabiliser, Aba