Mixed plastic waste streams are heavily dominated by polyolefin materials and their recycling is a challenge having a large societal significance. Chemical recycling via pyrolysis and steam cracking is seen as a promising technology for the recycling of mixed polyolefins into new plastics with identical properties to virgin grades. However, current technologies are not yet efficient from the economic and environmental standpoint. In fact, with only less than 1% of the collected plastic being recycled back to monomers, there is a big demand for more efficient monomer recovery developments. A lot of challenges are related to uncertainties and variations in compositions of waste streams. The current proposal introduces a transformational CIRCA concept of a controlled chemical recycling of polyolefin waste streams. In its core, the concept is based on the predictive modelling approach, where the composition of incoming polyolefinic waste streams is accurately characterized and used to steer the chemical recycling process via built-in structure-property relationships. To monitor complex polyolefin waste streams, the concept adopts an advanced analytical toolset that enables their unambiguous compositional characterization in a fast manner. The obtained data is then used to fine-tune the process parameters for boosting its efficiency. The CIRCA will be implemented at large-scale recycling lines.