Synthesis and Characterization of Carbon Nanotube-Doped Thermoplastic Nanocomposites for the Additive Manufacturing of Self-Sensing Piezoresistive Materials

Pawan Verma; Jabir Ubaid; Kartik M Varadarajan; Brian L Wardle; S Kumar

doi:10.1021/acsami.1c20491

Synthesis and Characterization of Carbon Nanotube-Doped Thermoplastic Nanocomposites for the Additive Manufacturing of Self-Sensing Piezoresistive Materials

ACS Appl Mater Interfaces. 2022 Feb 16;14(6):8361-8372. doi: 10.1021/acsami.1c20491. Epub 2022 Feb 4.

Authors

Pawan Verma¹, Jabir Ubaid², Kartik M Varadarajan³, Brian L Wardle^{4

5}, S Kumar²

Affiliations

¹ Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77840, United States.
² James Watt School of Engineering, University of Glasgow, Glasgow G12 8LT, U.K.
³ Department of Orthopedic Surgery, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.
⁴ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
⁵ Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

PMID: 35119271
DOI: 10.1021/acsami.1c20491

Abstract

We present carbon nanotube (CNT)-reinforced polypropylene random copolymer (PPR) nanocomposites for the additive manufacturing of self-sensing piezoresistive materials via fused filament fabrication. The PPR/CNT feedstock filaments were synthesized through high shear-induced melt blending with controlled CNT loading up to 8 wt % to enable three-dimensional (3D) printing of nanoengineered PPR/CNT composites. The CNTs were found to enhance crystallinity (up to 6%) in PPR-printed parts, contributing to the overall CNT-reinforcement effect that increases both stiffness and strength (increases of 56% in modulus and 40% in strength at 8 wt % CNT loading). Due to electrical conductivity (∼10^-4-10^-1 S/cm with CNT loading) imparted to the PPR by the CNT network, multifunctional in situ strain and damage sensing in 3D-printed CNT/PPR bulk composites and lattice structures are revealed. A useful range of gauge factors (k) is identified for strain sensing (k_s = 10.1-17.4) and damage sensing (k_d = 20-410) across the range of CNT loadings for the 0° print direction. Novel auxetic re-entrant and S-unit cell lattices are printed, with multifunctionality demonstrated as strain- and damage-sensing in tension. The PPR/CNT multifunctional nanocomposite lattices demonstrated here exhibit tunable strain and damage sensitivity and have application in biomedical engineering for the creation of self-sensing patient-specific devices such as orthopedic braces, where the ability to sense strain (and stress) can provide direct information for optimization of brace design/fit over the course of treatment.

Keywords: additive manufacturing; melt blending; orthopedic braces; piezoresistivity; self-sensing.