(291a) Upcycling of Polypropylene through Thermal Pyrolysis Using Mechano-Chemical Methods

Polypropylene is ubiquitous in plastics manufacturing where waste practices lack a sustainable approach and current efforts to recycle polypropylene diminish its mechanical properties. Plastic upcycling of polypropylene through chemical methods offers a promising path to a sustainable solution and adds value into waste that would otherwise be incinerated or landfilled. One example of an upcycling method uses degraded product from polypropylene pyrolysis as a building block to synthesize copolymers that exhibit enhanced properties over homopolymers. Previous studies to chemically recycle polypropylene have been done to target oligomeric units, primarily in liquid and gaseous form, while focus on solid residue formation remains underexplored. Low temperature thermal pyrolysis of polypropylene has been tuned to selectively yield a solid degraded product with controlled molecular weight and therefore, preservation of physical and mechanical properties. Mild degradation for a solid residue product involves less energy input and a lower reaction barrier for oligomeric polypropylene units. However, during conventional high temperature pyrolysis, the generation of low molecular weight residues results in higher concentrations of functional end groups. In order to develop functionalization and molecular weight control as independent parameters of the degradation process, we assess the efficiency of functional group formation through mechano-chemical pathways. Here, we establish a robust protocol to control the oligomerization of isotactic polypropylene through temperature control and ultrasonication. An experimental apparatus for thermal pyrolysis has been modified to include an ultrasonication probe. Our work here describes the understanding of the combination of thermal, mechanical and chemical degradation of polypropylene to result in functional, controlled molecular weight polypropylene moieties to be integrated in upcycling of polypropylene. Mild polypropylene pyrolysis coupled with ultrasonication at temperatures less than 350°C has given controlled molecular weight and control over product distribution. These studies aim to investigate the properties of chemically recycled, functionalized polypropylene and establish a foundation for the design of a new class of polymers.