Sjang's research examines the phenomena of disciplinarity and interdisciplinarity from historical and philosophical points of view. His work mainly focuses on the similarities, differences, and interactions between the humanities and natural sciences, with particular attention to shared concepts such as “facts,” scholarly virtues and vices, and practices of evaluation.

He has published widely on these themes in journals including Isis, Historical Studies in the Natural Sciences, History of Humanities, History of Science, and Science in Context. His forthcoming book Disciplinary Connections (University of Pittsburgh Press, March 2027) examines the relationship between history and physics in nineteenth-century Germany. In a related, new research project, he investigates past and present collaborations between humanities scholars and natural scientists in the study of climate.

Alongside these individual research projects, Sjang has been collaborating with Herman Paul (Leiden University) on the history of scholarly virtues and vices, and with Marie-Gabrielle Verbergt (Ghent University) on the history of peer review and other forms of scholarly evaluation. Another of his current research projects includes working with Annemarie Horn (Utrecht) on the historical origins and transformations of the interrelated concepts of “integration,” “interdisciplinarity,” and “transdisciplinarity.”