High-performance sustainable piezoresistive sensors based on Pebax/CNT composites with multi-stage linearity

Research summary

Wearable strain sensors typically rely on flexible polymers such as PDMS or TPU mixed with conductive fillers, but these base polymers are petroleum-derived and raise sustainability concerns. This study explores a more sustainable alternative: Pebax (poly(ether-block-amide)), a bio-derived polymer, combined with very small amounts (0.4 wt%) of carbon nanotubes (CNTs), graphene oxide (GO), or a hybrid of the two, to create piezoresistive sensors — materials whose electrical resistance changes measurably when stretched.

What the study examined

• Solution-cast Pebax films loaded with 0.4 wt% CNTs, GO, or a CNT/GO hybrid, compared against pure Pebax
• Tensile strength and elongation of each composite, measured with standardized dog-bone specimens
• Electrical current and resistance response as each film was stretched, and how that response evolved over repeated stretch-release cycles
• The underlying conduction mechanisms responsible for each composite’s sensing behavior

Main findings

Adding just 0.4 wt% CNTs to Pebax created a conductive network (about 1320 ohms) and increased tensile strength by 19.3%, to 225.4 MPa, while the film retained over 100% elongation — a combination the authors describe as a hierarchical network that reinforces the polymer while also making it conductive. Pure GO, in contrast, badly weakened the film’s strength and ductility, though combining CNTs and GO together mitigated most of this weakening.

Under strain, the Pebax/CNT sensor showed a distinctive multi-stage response: current initially decreased as the strain disrupted contact between CNTs, then increased again as further stretching caused the polymer to neck and locally realign and densify the CNTs, before finally declining once micro-cracks began to form. This behavior remained stable over 1000 stretch-release cycles. The GO-based sensors, by comparison, relied on electron “hopping” between sliding graphene oxide sheets, which produced weaker and much less stable signals, and could only tolerate smaller strains before failing.

Why it matters

The study shows that a bio-derived polymer can be turned into a mechanically robust, sensitive strain sensor using only a minimal amount of conductive filler, offering a more sustainable alternative to petroleum-based elastomer sensors without sacrificing performance. The multi-stage sensing response and long-term cycling stability suggest the Pebax/CNT composite is well suited to wearable health-monitoring applications, where sensors need to withstand repeated stretching over time.