The objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co-rota-twin-screw extruder and a Buss co-Kneader single-screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%. with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n-butylmethacrylate (BMA), t-butylamino ethylmethacrylate (TBBMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half-lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration. EXPERIMENTAL Raw Material and AdditiveaThe waste polymer used in these experiments consisted of shredded and washed shampoo bottles provided by =KO, lot 2360, sample M043210. DSC was used to determine the relative melting enthalpies of both the PP and the HDPE fraction. From the melting enthalpies of the bottle waste, the HDPE fraction was determined to be 90% ( 2 2%). This material was compounded in the twin-screw extruder and the mechanical properties of compression-molded samples were determined as shown in Table 1 (abreviations and symbols are explained in the Nomenclatura section).