How to Identify and Quantify Different Plastic Compositions in the Recycling Stream 

Last week, we explained, how multi-layer packaging films can be investigated with regard to their composition by means of Differential Scanning Calorimetry (DSC) and the NETZSCH PeakSeparationAdvanced Soft­ware Package.

However, these products should not only to be oxygen-tight, transparent, printable and possessed to a certain flexibility. Because plastics are poorly biodegradable, but should remain a valuable resource after their useful life, the focus on recycling pathways is more important than ever.

The majority of plastics used in packaging are polyole­fins; namely PP and PE like HDPE, LDPE and LLDPE. Thus, a combination of these materials is found in our recy­cling streams. This poses a challenge, because PE and PP are immiscible and incompatible both in molten and in solid state.

Differential Scanning Calorimetry (DSC) has been proven to be suitable for the analysis of mixed plastic waste and recycled polyolefin blends. It utilizes the ther­mal fingerprint of a material, which is, among other fac­tors, determined by their backbone structure, molecular weight, side groups and branching. The significantly different melting temperatures of the materials can be used to identify the different components of a mixture, while their weight percentage is estimated based on the melting enthalpy.

In many cases, the peak areas of PP and PEs found in such mixtures overlap, which requires that the peaks are being separated for a reliable determination of the individual components. For this purpose, the PeakSeparation analysis in the Proteus^® software comes into play. Read our latest Application Note to learn more: