Scaled-up Processing of Multi-functional Polymer Matrix Composites

Abstract

This dissertation provides a comprehensive framework for the scalable fabrication and characterization of multi-functional polymer composites prepared by electric-field alignment of carbon nanotubes (CNT) within the epoxy matrix. The core aim of this research is to enable the controlled network formation to achieve tailored microstructures with intrinsic damage sensitivity. Two themes underpin this study: a) linking local microstructural features to overall static and fatigue behavior using full-field infrared thermography (IRT), and b) electric-field alignment of nanomaterials for microstructure control. The first key finding of this work is the establishment of a novel IRT-based thermoelastic stress analysis (TSA) framework, developed to characterize multi-wall (MW) CNT/epoxy and graphene nanoplatelets (GNP)/epoxy nanocomposites at 0.1 and 0.2 wt%, offering a rapid and non-destructive alternative for microstructural discernment. The thermoelastic constant (K₀) determined graphically using the TSA approach provides a basis for mapping the nanocomposite microstructural characteristics with concentration. As a next step, the fatigue behavior of multi-functional composites, z-threaded carbon nanofiber (CNF)/carbon fiber reinforced polymer (CFRP), was investigated using IRT. Z-threaded specimens, with CNF electrically aligned in the z-direction, exhibit enhanced fatigue strength, signifying the effect of alignment on the composite performance. Finally, a scalable manufacturing technique for processing multi-scale composites using the electric-field alignment method and the effect of parameters on the duration of the alignment procedure has been described. Design of experiments (DOE) based study has been conducted to determine the optimized parameters required for the electric field alignment of MWCNT and single wall (SW) CNT. Electric-field alignment of SWCNT in epoxy matrix demonstrated significant improvements in mechanical performance, achieving up to 37% higher tensile strength at concentrations as low as 0.05 wt%. Optimization study using response surface methodology (RSM) and analysis of variance (ANOVA) confirmed that both voltage and electrode distance critically influence the alignment duration in the electric field alignment method. These studies provide important information about the parameters required to control during the scalable manufacturing process and to align CNT in the matrix to get enhanced damage sensing properties. Ultimately, the research paves the way for a scalable process to develop the next generation of multi-functional composite materials through electric-field-enabled microstructural tailoring and rapid non-destructive characterization based on IRT.