Recycling the 460 million tons of plastics produced each year is a major environmental and energy challenge of the 21st century. The use of recycled plastics is an important lever for reducing the overall CO2 emissions associated with the production and processing of new plastics. However, our ability to recycle plastics remains severely limited by the appearance of new chemical compounds during the aging of the materials to be recycled. In this thesis, we propose to study the aging of plastic additives by combining a historical study and an experimental approach. In a first approach, we will document the compositions and transformation processes of plastics from 1950 onwards, and, from dated samples, the new compounds formed during aging. In a second approach, we will simulate the aging processes by controlled irradiation, in order to reconstitute the reaction chains. The products of natural and artificial aging will be studied in terms of toxicity.