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Effects of the presence of recycled tire powders on the kinetics of the radical polymerization of styrene and the properties of the resulting materials

Abstract : Recycling of end-of-life tire-derived materials is considered a sustainable approach to managing these wastes. The rubber phase of these tires is considered as a valuable source because it consists of a sulfur-crosslinked reinforced elastomer phase which displays interesting mechanical properties such as high extensibility and elasticity. One of the alternatives for used tire rubber recycling consists in grinding it into fine powders, commercially called ground tire rubber or GTR. The latter can be dispersed in thermoplastic polymers in order to improve some of their properties such as impact strength. This work aims to use GTR as a reinforcing agent to toughen brittle polymers such as polystyrene (PS). It is composed of three parts. In the first part, the effect of the presence of GTR on the kinetics of the free-radical polymerization of styrene is studied by DSC. During the polymerization of styrene in the presence of GTR, styrene is partly homopolymerized, leading to free PS, and partly grafted onto GTR, leading to PS grafted onto GTR. Benzoyl peroxide and 2,2-azobis(2-methylbutyronitrile) are used as free radical initiators. In general, the presence of GTR shows a negative effect on the ultimate monomer conversion to polymer. Moreover, it may have a positive or negative impact on the rate of polymerization. These effects can be more or less pronounced, depending on the type of initiator used. In the second part of the work, a mechanistic model is developed to describe the free-radical polymerization of pure styrene in a batch reactor. The model allows predicting the evolution of the total monomer conversion and that of the average molecular weight of PS. The validity of the model is demonstrated via comparison with experimental data generated through a series of DSC analyses as well as pilot-scale reactor runs. Subsequently, the same model is modified to take into account the reactions occurring in the presence of GTR. The third part of the work addresses the development of a new methodology combining two processes to prepare GTR toughened PS. These processes involve the free-radical polymerization of styrene in the presence of GTR and compounding of the resulting product in a twin-screw extruder. The grafting of styrene onto GTR ensures good interfacial adhesion between PS and GTR and compounding favors fine dispersion of GTR in the PS matrix. Results show that the notched Charpy impact strength of neat PS can be increased by a factor of 2 by adding 50 wt% of GTR. Moreover, a PS/GTR blend containing 70 wt% of GTR displays a performance similar to that of a thermoplastic elastomer vulcanizate (TPV) and its strain at break can reach 120%.
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Submitted on : Friday, October 23, 2020 - 3:34:14 PM
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  • HAL Id : tel-02976726, version 1



Daniela Carolina Florez Parra. Effects of the presence of recycled tire powders on the kinetics of the radical polymerization of styrene and the properties of the resulting materials. Chemical and Process Engineering. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0347⟩. ⟨tel-02976726⟩



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