Compounding plastics by the combination of virgin and recycled material is a complex processing problem. In the specific case of polypropylene, the recycled material is contaminated, partially degraded, has different pigments and a wide distribution of molar mass. In this work we used a statistical response surface method to obtain a compound of virgin and recycled polypropylene on a competitive basis with the pure virgin material (MFI 10 g/10 min) used for injection molding. Adjusting the linear and quadratic models produced equations relating the ratio of virgin and recycled material and the stabilizer (Recyclostab 411(TM)) concentration with the expected properties (melt flow index, oxidation induction time and mechanical properties). The extruded pellets of the compound containing a 1:1 ratio of the polymers and 0.20% (m/m) Recyclostab 411(TM) had properties similar to non-stabilized virgin polypropylene in relation to thermo-oxidative stability and melt flow index, both containing 1% (m/m) of carbon black. However, injection molded test samples of the compound showed higher elongation at break and lower modulus and stress at break in comparison to the virgin material. (C) 2001 Elsevier Science Ltd. All rights reserved.712293298