This study presents a new approach for the recycling of bilayered PET waste in an efficient, continuous process with a depolymerization degree >97%. The complex PET waste was converted by chemolysis into its monomers ethylene glycol (EG) and the corresponding salt of terephthalic acid (TA) in a twin-screw extruder (TSE). Via this method, the starting materials for PET production were recovered, and highly contaminated PET waste and PET composite materials were transformed into valuable starting materials. The PE layer of the composite PET/PE material remained inert under depolymerization conditions and could be separated by filtration. An increase in the rotational speed by 200 rpm in the TSE reduced the residence time, but the degree of depolymerization was not affected in a proportional manner. Thus, the results indicate that a shorter residence time can be compensated with intensified mechanical agitation due to higher rotational speeds to obtain a similar degree of depolymerization. These results support the potential of this recycling concept to substantially contribute to the implementation of a circular PET economy.

Due to the presence of dyes and additives, textile recycling is challenging, therefore the majority of textile waste is downcycled to low‐value products, incinerated or landfilled. In this study, a continuous depolymerization of post‐consumer polyester textiles was conducted by alkaline hydrolysis. The degree of depolymerization was assessed and found to be 94 %. After recovering and analyzing the terephthalic acid and ethylene glycol the monomers were successfully polymerized to regain a food grade quality recycled polyethylene terephthalate. The presented recycling approach allows a closed‐loop recycling of textiles.

The alkaline depolymerization reaction of poly(ethylene terephthalate) (PET) under quasi-solvent-free conditions was investigated. This is a new approach for recycling PET waste to its monomer building blocks: terephthalic acid and ethylene glycol. The influence of base particle size, reaction temperature, and rotational speed of the employed laboratory kneader on terephthalic acid yield in the quasisolid-solid reaction was investigated. PET is depolymerized almost quantitatively in a reaction time of 5 min at moderate reaction temperatures, with intense mixing affecting the yield of terephthalic acid. The quality of the terephthalic acid monomer, assessed by color index measurements, indicated that the reaction temperature primarily influences the color index of the monomer. By balancing terephthalic acid yield versus color index, optimum reaction conditions were proposed.

Plastic waste is one of the major challenges facing modern society. Against the background of climate change and finite fossil resources, the realization of a true circular economy for plastics is imperative. Mechanical recycling processes offer a short‐cut path for the recycling of clean, single material waste while they are not capable to handle mixed material or colored feeds. Complementary technologies are necessary to recover pure monomers, hydrocarbon mixtures or syngas from mixed secondary raw material to continuously close the loop in a circular plastics economy. Using the example of PET, this contribution discusses the benefit of integrating a back‐to‐monomer recycling for closing the loop aiming at a holistically approach integrating technological, ecological and economic aspects.

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