Tuning the thermodynamic trajectory in thermally induced phase separation to guide formation of polypropylene powders to upcycle polymeric post-consumer waste

Limited options for feedstocks have historically inhibited the growth of polymer powder bed fusion (PBF), a promising additive manufacturing (AM) technology, and created a demand for versatile, low-cost, and sustainable feedstock powders. In this study, we report the creation of a high-value feedstock for PBF from post-consumer polymeric waste, where PBF-adoptable polypropylene (PP) powders were produced via the facile thermally induced phase separation (TIPS) technique. We also elucidate the critical thermodynamic interplay between liquid-liquid phase separation (LLPS) and crystallization-which plays a significant role in dictating the final powder properties. In TIPS, LLPS forms droplets, where crystallization halts their growth to preserve and provide the final particle morphology. Our study demonstrates that control of the temporal window, i.e., the time that droplets stay between LLPS and crystallization during the particle formation process, manipulates the thermodynamic trajectory of the polymer solution and enables control of the crucial final powder properties such as particle size, shape, and flowability. By using the solution batch size as a process control variable, the temporal window is tuned, which regulates powder properties and fabricates a series of powders from post-consumer PP pill bottle waste. Therefore, this study not only presents an in-depth understanding and control of the fundamental processes that tune the structure of the final powders but also provides a mechanistic framework for a scalable route to upcycle versatile semi-crystalline polymer waste into high value AM feedstock by controlling these processes.