Since the dawn of the plastics industry, billions of tons of polymers have been produced – a dump truck of plastic for each living human. Most of this plastic is ultimately landfilled, incinerated, or lost to the environment with only a small fraction being recycled. Heterogeneous catalysis could help recycle plastics into fuels, lubricants, or even re-polymerizable monomers, but current models for catalytic depolymerization with a distribution of initial chains, intermediates, and products are too primitive for mechanistic analysis and design. I will describe several models and computational frameworks that we have developed in the Institute for Cooperative Upcycling of Plastics (iCOUP-EFRC). These include (i) a universal catalyst-agnostic equation for the average molecular weight as a function of time during depolymerization, (ii) a population balance framework for predicting concentrations and molecular weight distributions of reactants, co-reactants, products, and adsorbed intermediates, (iii) integration of microkinetic models, multistep scission mechanisms, adsorption isotherms, and mass transfer effects into the population balance framework, and (iv) models that help us extract driving forces and kinetics of polymer adsorption from 2D-NMR spectra. I will highlight results for “polyethylase”, a robust core-shell Pt/SiO2 catalyst with a geometry inspired by nature’s cellulase enzymes. This catalyst, designed, synthesized, and tested in iCOUP, can processively hydrolyze polyethylene into C10 – C25 fragments with sustained activity and no significant buildup of intermediates.