Session: 01-02 Sensor and Actuator Materials 1

Paper Number: 167786

167786 - Fabrication and Characterization of Flexible Strain Sensors via 3d Printing and Screen Printing of Conductive Tpu-Based Composites 

Flexible Electronics is a growing field due to the advancement of materials and production processes.  Numerous constructions, materials, and use cases for  flexible electronic circuits exist.  This work focuses on wearable resistance based stretch sensors to monitor human motion.  This study investigates the fabrication and characterization of screen-printed Thermoplastic Polyurethane (TPU) Carbon Nano Fiber (CNF) composites for use in flexible and wearable electronics.  TPU substrates were chosen for their flexibility and manufacturability using traditional additive processes such as fused deposition modeling (FDM) and screen printing.  In this work, two materials were compared, a new solvated TPU-CNF material and a traditional conductive TPU filament.   In this work, solvated TPU- CNF was screen-printed onto an FDM produced dielectric TPU substrate.  Solvated TPU-CNF was selected as an alternative to existing conductive materials in an effort to increase adhesion between the sensor, reduce mechanical stiffness of the sensor, and to address instability in electrical resistivity seen with off-the-shelf conductive filament.  

Sensors were fabricated in a two-step process.  Dielectric TPU samples were printed using a Prusa printer. Then, a mixture of solvated (TPU-CNF) was constructed by mixing a solvent, CNFs, and pelletized TPU.  This mixture was then screen-printed onto the dielectric TPU surface in different designs.  For the commercial material, conductive Filaflex was 3D printed using the same Prusa printer in the same patterns onto the surface of the FDM produced dielectric TPU. Sensors were fabricated using both screen printing with TPU-CNF and 3D printing on TPU substrates for comparison.

 Standardized dogbone-shaped substrates (ASTM D638 Type IV) were employed to ensure reproducible mechanical and electrical testing.  In order to assess the impact of geometry on the sensor’s functionality, three conductive electrode patterns were assessed.  These include parallel lines, zigzag, and interdigitated structures.  The dogbone samples were used to test electrical resistivity of the two materials as well as the stress-strain response using a mechanical testing system.  The addition of conductive particles to the polymer matrix increases the stiffness of these materials.  Therefore, there is a trade-off to be made in increasing material conductivity while also maintaining the flexibility seen in the base polymer.  TPU materials are also known to exhibit hysteresis. Due to this hysteresis, the dynamic performance of the composites was also assessed.  All experiments were done in triplicate and conducted following ASTM standards for repeatability.  The findings contribute to understanding the potential of TPU-CNF composites as a stable conductive material for wearable applications.

Presenting Author: Brittany Newell Purdue University

Presenting Author Biography: Dr. Brittany Newell is an associate professor at Purdue University in the Purdue Polytechnic Institute School of Engineering Technology. Brittany received her B.S. in Biomedical Engineering from Purdue University and her M.S. and Ph.D. in Agricultural and Biological Engineering from Purdue University. She then worked in industry from 2013-2015 before joining the Purdue faculty. Brittany completed her Ph.D. work in the field of electroactive polymers for industry applications. She is expanding upon this research to include manufacturing techniques along with development of dielectric electroactive polymer devices.