Understanding Creep Resistance in Pigmented Polymer Composites

Creep, the deformation of a material under a constant load over time, is a problem that affects all classes of materials including polymers. It has been estimated by the Society of Plastics Engineers that creep is the cause of nearly a quarter of plastic component failures. Palygorskite nanoclay was the basis for the renowned Maya Blue pigment, which was used to color murals in Mesoamerican temples. These murals have shown remarkable resilience over many centuries. Motivated by this fact, this award supports fundamental research in the use of modern palygorskite-based pigments to improve creep resistance of various types of polymers. The knowledge generated by this project will potentially lead to mitigation strategies for creep in plastics, lessening the number of plastic component failures, thus leading to a decrease in plastic waste. Additionally, the project will support integration of research outcomes into existing courses, an annual camp on materials sciences for local high school and middle school STEM educators, development of hands-on demonstrations at outreach exhibitions, and undergraduate research experiences, among other efforts. Though the phenomena of creep in polymers have been studied for decades, new models describing creep mechanisms continue to be developed and purveyed in literature. Despite the large body of research in this area, creep remains a major cause of polymer component failures. This project will utilize palygorskite nanoclay-based pigments with a fibrous morphology as an additive to mitigate creep in polymers. The claim here is that high tensile strength does not necessarily correlate with an improvement in creep response of polymer nanocomposites, which is the prevalent conjecture. Instead, the hypothesis is that manipulation of amorphous domains within the polymer structure by the nanoscale, fibrous pigment particles is responsible for a reduction in creep. Materials characterization at multiple size scales including small-angle and wide-angle X-Ray scattering, in-situ, temperature controlled tensile testing in a scanning electron microscope, and micro tensile testing coupled with digital image correlation will be used to elucidate the roles and relationships of crystalline and amorphous domains as well as the interaction between the nanoclay filler and these domains. A data science approach utilizing Python-based processing of creep test and other generated data is central to this project. The early stages of the effort will involve polyolefins, but as the project expands, other polymer classes such as polyesters and polyamides will be explored. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.