Sorting multilayer packaging is still a major challenge in the recycling of post-consumer plastic waste. In a 2019 Germany-wide field study with 248 participants, lightweight packaging (LWP) was randomly selected and analyzed by infrared spectrometry to identify multilayer packaging in the LWP stream. Further investigations of the multilayer packaging using infrared spectrometry and microscopy were able to determine specific multilayer characteristics such as typical layer numbers, average layer thicknesses, the polymers of the outer and inner layers, and typical multilayer structures for specific packaged goods. This dataset shows that multilayer packaging is mainly selected according to the task to be fulfilled, with practically no concern for its end-of-life recycling properties. The speed of innovation in recycling processes does not keep up with packaging material innovations.

Compounding is the final processing step for quality adjustment and control before recycled thermoplastic polymer material can be introduced into production processes. Motivated by the need for higher recyclate shares, the research question is which quality problems recycling compounders are encountered in practice, where they occur, and which mitigation options might be reasonable. Therefore, an online survey with 20 recycling compounders based in Germany was conducted asking about typical processing steps and processed materials, test procedures for quality assurance, quality problems, and possibilities for reducing quality problems. Results show that compounders mainly name impurities and contaminations of the input material as challenging and the reason for quality problems. The study shows that the problems are not dependent on the material input type. Quality problems occur along the entire secondary value chain, with companies manufacturing components themselves being particularly affected. The composition determination of the input materials helps to minimize quality problems.

The material properties and stable chemical structure of PET make it a frequently used polymer, for example, for packaging applications, and allow multiple recycling processes. Fluorescent tracer additives in polymer waste management may enhance the sorting quality of packaging waste streams by using the fluorescent signal of tracer additives introduced into the polymer matrix. Prior to field application of tracer additives, it is necessary to investigate tracer influence on the polymer matrix in general and, more specifically, in multiple recycling cycles. Therefore, PET with mineral tracer concentrations of 0, 10, 100, and 1000 ppm was extruded up to six times. To investigate changes in material properties, differential scanning calorimetry, intrinsic viscosity, spectroscopic analysis, tensile testing, and color measurements were performed. In parallel, the up‐conversion photoluminescence of the tracer was quantified. Polymer degradation is generally induced by mechanical and thermal degradation during multiple processing cycles, leading to chain shortening, reduction of molecular weight, and the formation of new functional groups, as previously published in the literature. The results of the experiments indicate that tracer additives do not further affect the thermal, rheological, chemical, and optical polymer properties. Moreover, photoluminescent tracer properties are not affected by multiple polymer processing cycles.

Tracer additives as a polymer‐independent sorting criterion have recently been proposed as a solution to enhance the quality and quantity of polymer recycling. To date, scientific literature has not filled a research gap concerning the visual appearance of particulate tracer distribution fluorescence in a polymer matrix. This paper investigates the appearance of fluorescent tracers’ visual signals when activated, depending on their size and location in the polymer matrix, taking transparent PMMA as an example. Furthermore, a methodology is developed to differentiate tracer particle size distributions using imaging technology. Subsequently, an evaluation of the actual particle size distribution based on observed fluorescence areas is conducted. The results indicate that larger particles can be identified more deeply in the polymer matrix than smaller particles, and they emit a brighter luminescence. The utilization of five distinct tracer particle size distributions enabled their differentiation based on the D ₅₀ and D ₉₅ values, the fluorescence intensity, and the number of recorded particles. Applying a logistic function to describe the particle distribution, in conjunction with the implementation of a transformation matrix, allows approximation of the actual particle size distribution. This methodology is validated with tracer additives in a PET matrix.