What doesn’t smell good is hard to recycle. This simple rule also applies to the world’s growing plastic waste. One way to recycle them in an environmentally sound manner as high-quality post-consumer recyclate is through improved sorting and reprocessing.
Until now, the reduced material quality has significantly limited the reuse of plastic recyclates, and this is mainly due to their odor. Scientists at the Fraunhofer Institute for Structural Durability and System Reliability LBF have developed a new environmentally friendly process on a laboratory scale to remove odors from plastic packaging.
The new process is based on pressurized water extraction. It removes the tracer fragrance limonene from commercial HDPE packaging and does not require organic solvents. In this way, the material quality of processed plastic waste can be increased within one hour, the scientists explain.
In-process analyses using infrared spectroscopy and mass spectrometry provide the research team with data on the chemical composition of the samples as a result of different extraction conditions. These analytical data show that significantly less limonene is present in the samples after extraction. Furthermore, in addition to the fragrance, other impurities and short-chain HDPE are removed from the samples that were originally contained in the packaging. With this database as a basis, the Darmstadt experts determined process parameters for the pressurized water extraction of fragrances from HDPE packaging. “The project results demonstrate the benefits of a systemic approach to solving current plastics technology issues of great relevance to society,” emphasizes Dr.-Ing. Guru Geertz, who is in charge of the project at Fraunhofer LBF.
Material analysis with machine learning methods
To develop the process, detailed insights into the chemical kinetics of the extraction process were necessary, which were made possible with the help of an innovative approach to in-process analytics: by evaluating the data using machine learning methods, it was possible to optimize the extraction parameters in terms of economical process control. At the current stage of development, an application scenario for improved processing of plastic waste is emerging for the new process. “The extraction process we have developed shows a path to reprocessed single-use plastics with an increased range of applications, and this serves to protect the environment,” says Geertz.