Evaluation of the Role of Devulcanized Rubber on the Thermo-mechanical Properties of Polystyrene

In this paper, different amounts of both devulcanized rubber (DR) and non-devulcanized rubber (NDR) were melt compounded and compression moulded with a brittle thermoplastic matrix such as polystyrene (PS). Scanning electron microscopy observations of the prepared blends showed that the PS/rubber interfacial adhesion, although rather limited, was improved in the case of DR, and that DR domains within the PS matrix had a lower size than NDR particles. Thermogravimetric analysis highlighted that the onset degradation temperature decreased upon the addition of rubber, and the maximum mass loss rate temperature increased. Differential scanning calorimetry tests showed that the glass transition temperature slightly decreased upon addition of DR and NDR. This increase also enhanced the maximum service temperature determined by measuring the Vicat grade. The surface hardness, the tensile modulus and stress at break were negatively affected when recycled rubber was added, because of the limited compatibility between PS and rubber particles and the relatively large size of the rubber domains. A notable increase in material ductility, with an enhancement of the tensile strain at break and of the impact resistance, was detected at elevated rubber amounts. Quite interestingly, mechanical properties of the blends with DR were systematically higher than those of the corresponding blends with NDR.