Synergistic interactions in the thermal decomposition of leather and PVC mixtures

The problem of mixed leather waste (natural and artificial) is recognized as a significant issue in industrial recycling, since the separation of these materials is challenging. However, thermochemical conversion is widely researched as a feasible method for dealing with such a complex waste stream. Deeper understanding of the interactions between the components during thermal decomposition and the effect of the reactive hydrogen chloride evolving from PVC (a usual component of artificial leather) should be considered in the planning of thermal recycling processes, and therefore, these findings can be of interest to users and manufacturers. In this paper, co-pyrolysis of PVC and natural leather was investigated by thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) methods. The study revealed the mutual influence of PVC and proteinaceous materials, such as leather, during thermal decomposition. The thermal stability of PVC decreased in the presence of leather, as the dehydrochlorination step shifted to lower temperatures by 20–30 °C, regardless of the tanning type of leather. Conversely, the thermal decomposition of leather was altered by the presence of PVC, favoring fragmentation reactions over depolymerization, which resulted in the formation of more hydrogen cyanide and acetonitrile but less diketopiperazines (DKPs). The effect of hydrogen chloride released by PVC in these processes was further studied by the pyrolysis of a model sample, which confirmed the primary role of hydrogen chloride in the increased hydrogen cyanide and acetonitrile evolution. The formation of mono- and polyaromatic compounds was increased slightly during pyrolysis of leather–PVC mixtures, which could contribute to the decreased char yields of the mixtures measured by TGA.