Since they first appeared at the end of the 19th century, plastic materials have gradually become an integral part of our daily lives. While the benefits of these materials are undeniable, there is increasing concern about what happens to them at the end of their life. Therefore, in addition to reducing them at their source, the recycling of these polymer materials is now a major environmental priority. Among the various possible solutions, chemical recycling by purification makes it possible to return to a virgin polymer, free of additives or other impurities, via a dissolution and precipitation operation. IFPEN has already embarked on several research projects to this end for the recycling of two polyolefins, polyethylene (PE) and polypropylene (PP), which together account for more than half of all plastic packaging produced worldwide.
Developing a dissolution recycling process that can be used for all types of feedstocks1is an arduous undertaking and a long-term research theme. One of the prerequisites for being able to monitor the dissolution and precipitation stages is better description of the materials constituting these feedstocks.
1 Polymer introduced into the recycling process: in our case: PE and PP, alone or mixed, from various objects collected at sorting centers
In addition, in the case of polyolefin recycling, it is important to continuously characterize the feedstocks concerned, due to their variability, as well as the diversity of solvents and operating conditions that may be used during the recycling process. For this purpose, spectroscopic techniques have great potential, since they are fast, non-destructive, sensitive to chemical (as well as physical) properties, and easy to implement online.
Within the framework of PhD research conducted at IFPEN [1], several PP and PE dissolution/precipitatio operations were carried out at different temperatures, with different solvents and under different operating conditions (with or without stirring, in the presence or absence of oxygen). All these operations were subject to in situ monitoring using near-infrared spectroscopy (NIRS) and Raman spectroscopy (PP example, Figure 1). In parallel, samples were taken in order to calibrate these online monitoring results with a view to determining the characteristics of the reaction medium2 in real time.
2 Typically dissolution rate and molar mass
Thanks to this work, a database containing spectra and characteristics of the reaction medium was built up, enabling the development of chemometric prediction models3. A key advantage of one of the models developed is that it is not dependent on the variability of polymers from sorting centers, nor on that of solvents. Thanks to this breakthrough, it is now possible to monitor the dissolution and precipitation rates of PP [2] and PE online, irrespective of the feedstock involved and the solvent used.
Grâce à ces actions, une base de données contenant des spectres et les caractéristiques du milieu réactionnel a été constituée,
3 These models use mathematical tools to relate measured data (e.g. spectra) to known results (e.g. concentration). Once trained, they predict these results for new samples.
Spectroscopic techniques used in the research also enabled the in situ monitoring of the degradation rate of a PP via changes in its molar mass [3]. This represents an additional benefit for process optimization and control (temperature, residence time).
These models can be used to support the development of the chemical polymer recycling process, by assessing the impact of operating parameters on the dissolution and precipitation of different polyolefins.
‘in red’ in xylene, ‘in blue’ in decalin, ‘in green’ in decane and ‘in violet’ in tetra chlorobenzene
The figure demonstrates that 10% PP dissolves faster in xylene than in the three other solvents studied. This illustrates the benefit of online monitoring for process optimization, in this case solvent selection.
References :
- Thèse de Sofiane Ferchichi « Méthodes spectrales pour le suivi en ligne de procédés de recyclage de polyoléfines par dissolution-précipitation » (Spectral methods for online monitoring of dissolution-precipitation-based polyolefin recycling processes)
- S. Ferchichi et al., "In situ dissolved polypropylene prediction by Raman and ATR-IR spectroscopy for its recycling," Analytical methods : advancing methods and applications, vol. 16, no. 19, pp. 3109–3117, 2024,
>> DOI: https://www.doi.org/10.1039/d4ay00667d
- S. Ferchichi, N. Sheibat-Othman, O. Boyron, S. Norsic, M. Rey-Bayle, and V. Monteil, "Monitoring Polypropylene Chain-Scission for Dissolution-Based Recycling by In Situ Near Infrared and Raman Spectroscopy", Macromolecular rapid communications, e2400748, 2025,
>> DOI: https://www.doi.org/10.1002/marc.202400748
Scientific contact: Maud Rey-Bayle