Advanced PP/CNT Monofilaments for Sensory SHM Applications: Influence of Additives and Processing Parameters

Melt‐spun polypropylene/carbon nanotube (PP/CNT) monofilaments hold great promise for use in structural health monitoring (SHM) due to their low density, mechanical flexibility, and piezoresistive properties. However, achieving homogeneous CNT dispersion, optimizing processing parameters, and enhancing strain sensitivity remain key challenges for their practical implementation. This study systematically examines the influence of CNT and carbon black (CB) content as extrinsically conductive fillers, the incorporation of polyethylene glycol (PEG) as processing aids, and the effect of extruder screw speeds on the morphology, mechanical properties, and electrical behavior of PP/CNT monofilaments. Spinning pressure measurements reveal PEG effectively reduces spinning pressure. Morphological analysis indicates that higher CNT content results in rougher filament surfaces, while PEG enhances fiber uniformity. Tensile testing demonstrates a strong dependence of Young′s modulus and tensile strength on CNT content and processing parameters, with PEG‐modified samples exhibiting improved ductility. Electrical characterization confirmed a stable strain‐dependent resistance variation, with gauge factors up to 1.5. Mechanical testing showed that Young’s modulus could be tailored from 0.8 to 16 GPa depending on CNT and PEG content. These results demonstrate the feasibility of producing lightweight PP/CNT monofilaments with tunable electromechanical properties for scalable SHM sensor integration.

Background:

Melt‐spun polypropylene/carbon nanotube (PP/CNT) monofilaments hold great promise for use in structural health monitoring (SHM) due to their low density, mechanical flexibility, and piezoresistive properties. However, achieving homogeneous CNT dispersion, optimizing processing parameters, and enhancing strain sensitivity remain key challenges for their practical implementation.

Methods:

This study systematically examines the influence of CNT and carbon black (CB) content as extrinsically conductive fillers, the incorporation of polyethylene glycol (PEG) as processing aids, and the effect of extruder screw speeds on the morphology, mechanical properties, and electrical behavior of PP/CNT monofilaments.

Results:

Spinning pressure measurements reveal PEG effectively reduces spinning pressure. Morphological analysis indicates that higher CNT content results in rougher filament surfaces, while PEG enhances fiber uniformity. Tensile testing demonstrates a strong dependence of Young′s modulus and tensile strength on CNT content and processing parameters, with PEG‐modified samples exhibiting improved ductility. Electrical characterization confirmed a stable strain‐dependent resistance variation, with gauge factors up to 1.5.

Data Summary:

Mechanical testing showed that Young’s modulus could be tailored from 0.8 to 16 GPa depending on CNT and PEG content. Gauge factors up to 1.5 were observed.

Conclusions:

These results demonstrate the feasibility of producing lightweight PP/CNT monofilaments with tunable electromechanical properties for scalable SHM sensor integration.

Practical Significance:

Melt‐spun polypropylene/carbon nanotube (PP/CNT) monofilaments hold great promise for use in structural health monitoring (SHM) due to their low density, mechanical flexibility, and piezoresistive properties.