One of the most ubiquitous materials in today's society is synthetic polymers (plastics). The accumulation of plastic waste causes serious environmental and public health problems. Furthermore, to reach a circular economy, plastic waste needs to be reused or recycled.

Recycling techniques are classified into physical (melting, extrusion, etc.) and chemical (depolymerization) methods. When plastic waste cannot be treated using the existing technologies, it ends up in landfills or is incinerated for energy.

Multilayer plastics, composed of two or more layers of various materials, are one of the most difficult plastic wastes to recycle. They are essential for food packaging due to their barrier properties, mechanical strength, lightness, flexibility, and functional properties (antimicrobial and/or antioxidant). They are also used for packaging, making up a large proportion of non-recyclable plastic waste. It is therefore urgent to develop new technologies for simple and efficient recycling of the various types of plastic waste.

The use of supercritical fluid (SCF) in plastic recycling is gaining attention [1-3]. SCF have solvation powers similar to liquids, but transport properties (diffusivity, surface tension) similar to gases. Supercritical CO₂ stands out because it is cheap, non-combustible, non-toxic and it has moderate critical parameters (31 ºC and 73.8 bar). Furthermore, CO₂ is a gas at ambient temperature and after depressurization, it does not leave any residue. CO₂ solubilizes very well in polymers, causing a decrease in their glass transition temperature (Tg) and melting temperature (Tm), which can be used in the physical recycling or separation processes of plastic composites. In addition, it can improve mass transfer processes, increasing the conversion yield in chemical recycling [2]. Supercritical CO₂ is also an excellent extraction agent that can be used for decontamination [3]. Finally, thanks to its sterilizing properties supercritical CO₂ can be used to decontaminate biological waste.

In our lab, we research the recycling of polymer using supercritical fluids. We investigate both physical and chemical recycling processes. In physical recycling, we investigate the delamination of multilayer plastics, including food packaging films comprising different polymers.  We also research the chemical recycling of condensation polymers. Finally, we propose using supercritical CO₂ to sterilize Personal Protective Equipment made out of plastics for its reuse or safe recycling.

 

[1] Goto, M., Chemical recycling of plastics using sub- and supercritical fluids. The Journal of Supercritical Fluids, 47, 500 (2009).

[2] Li, X.-K., et al., Reaction kinetics and mechanism of catalyzed hydrolysis of waste PET using solid acid catalyst in supercritical CO₂. AIChE Journal, 61, 200 (2015).

[3] Alassali, A., et al., Assessment of supercritical CO₂ extraction as a method for plastic waste decontamination. Polymers, 12, 1347 (2020)

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SuRePlas-CM: Nuevas Tecnologías Sostenibles de Reciclado de Plásticos utilizando Fluidos Supercríticos

PROYECTO PRESENTADO A LA CONVOCATORIA DE TECNOLOGÍAS DE LA CAM

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Proyecto Art 83-Título del contrato/proyecto: 613-2019, Reciclado de envases plásticos mediante el uso de Fluidos Supercríticos

Empresa/Administración financiadora: Instituto Tecnológico del Embalaje, Transporte y Logística, ITENE

Duración,  Diciembre 2019   

Investigador responsable: Albertina Cabañas Poveda/Lourdes Calvo Garrido