Paper Number
AC19 

Session
Additive Manufacturing and Composites

Title
Determining stable curing recipes for printed thermoset materials via rheo-Raman microscopy

Presentation Date and Time
October 13, 2022 (Thursday) 9:05

Track / Room
Track 7 / Ontario

Authors (Click on name to view author profile)

1. Romberg, Stian K. (National Institute of Standards and Technology, Materials Science and Engineering Division)
2. Kotula, Anthony (National Institute of Standards and Technology)

Author and Affiliation Lines (in printed abstract book)
Stian K. Romberg and Anthony Kotula
National Institute of Standards and Technology, Gaithersburg, MD 20899

Speaker / Presenter 
Kotula, Anthony

Keywords
experimental methods; additive manufacturing; composite rheology; spectroscopy

Text of Abstract
With their ability to be extruded at room temperature and excellent compatibility with fibers, thermoset composite resins show potential to expand the material properties and scale offered by direct ink write (DIW) additive manufacturing. However, the factors governing structural stability during printing and curing are a key challenge to successful thermoset DIW. Recent work linked the storage modulus and yield stress to the height at which printed thermoset structures collapse under their own weight but did not investigate structural stability during post-curing at elevated temperatures. At elevated temperatures, rheological properties of thermosets are governed by a competition between the temperature dependence of the resin and the progression of the curing reaction, impeding characterization with conventional techniques. The rheo-Raman microscope, which can simultaneously measure rheological properties and probe reaction progress via the Raman spectrum, can provide critical insight into the dependence of these properties on temperature and degree of reaction. This work uses the rheo-Raman microscope to track rheological properties that have been shown to affect stability at a range of isothermal cure temperatures. High temperatures can cause the storage modulus and yield stress to drop before these properties increase due to the crosslinking reaction. Lower cure temperatures can mitigate this initial drop in properties but increase the time needed to reach the final extent of reaction. By combining the results from the temperature tests on the rheo-Raman microscope with previously developed mechanical models, recipes can be designed to maintain the structural stability of printed parts during curing and post-processing while minimizing the time required to reach full cure. This study demonstrates a new way to evaluate and design thermoset composites for post-cured DIW and provides an understanding of the limits of these materials for thermoset additive manufacturing applications.