Challenges and opportunities in manufacturing highly filled polymers

Abstract Processing highly filled polymers (>50 vol%), whether with particle or short fiber additives, is needed for many applications, such as pharmaceuticals, ceramics, batteries, coatings, etc. Forming these materials into more complex geometries with graded properties is necessary to meet the growing demand for structures with increasingly specialized functions. However, there are many poorly understood processing effects that must be studied to enable the reliable forming of new structures and the qualification of said structures for new applications. Here, we highlight four challenges that impede the processing of highly filled polymers, with a stronger emphasis on additive manufacturing and extrusion processes. They are: (1) understanding process-induced porosity, (2) understanding the solid-liquid interface during the manufacturing process, (3) overcoming equipment limitations, and (4) appropriate use of in-situ monitoring and measurement. We anticipate that by highlighting these research gaps and identifying paths forward, the processing science necessary to form highly filled polymer will advance.