Study of the Effect of Processing Temperature on the Properties of Recycled Polypropylene from Sachet Water Packaging

Sachet water packaging constitutes a significant component of plastic waste in Nigerian urban environments, with discarded polypropylene sachets presenting both a waste management challenge and a recoverable polymer resource. This study examines the effect of processing temperature on the mechanical and rheological properties of polypropylene recycled from sachet water packaging collected in Ibadan, Oyo State, South West Nigeria. Polypropylene sachets were sorted, washed, granulated, and reprocessed by injection moulding at barrel temperatures of 200, 220, and 240 degrees Celsius. Tensile strength, elongation at break, melt flow index, and Vicat softening point were evaluated for each processing temperature condition. Thermal analysis using thermogravimetric analysis assessed degradation behaviour relative to virgin polypropylene controls. Results indicate that processing at 220 degrees Celsius yielded optimal tensile strength retention at 87 percent of virgin material values, with melt flow index increasing from 8.4 to 11.2 g/10 min, indicative of moderate chain scission. Processing at 240 degrees Celsius resulted in measurable colour darkening and further melt flow index elevation to 16.7 g/10 min, reflecting more extensive thermal degradation. Thermogravimetric analysis confirmed that recycled specimens exhibited slightly earlier onset degradation temperatures compared to virgin controls. The study establishes practical processing temperature guidelines for sachet polypropylene recyclers in South West Nigeria, supporting improved product quality from the informal recycling sector. Recommendations include antioxidant stabiliser addition during reprocessing to mitigate thermal degradation effects. Keywords: polypropylene recycling, sachet water, processing temperature, melt flow index, thermal degradation