Graphene and Nanotube Coating Makes PET Fibres Conductive

Researchers in China have developed a method to transform ordinary polyester fibers into electrically conductive, temperature-sensitive textiles by coating them with graphene oxide and carbon nanotubes. Published in the Journal of Materials Science, this study addresses challenges in conductive polymer composites, such as ensuring carbon nanomaterials adhere, disperse, and form continuous electrical pathways without compromising the mechanical properties of the fiber. Led by Wenguang Yu and colleagues at Zhejiang Jiaren New Materials and Nanjing Tech University, the team reports fibers that are not only conductive but also ten percent stronger than unmodified polyester.

The substrate used in this study is polyethylene terephthalate (PET), a common polymer in drink bottles and clothing. PET is inexpensive and durable but acts as an electrical insulator and interacts poorly with carbon-based nanofillers. To address this, researchers employed a hybrid fiber strategy, blending PET with thermotropic liquid crystal polyester (TLCP), which self-orients during melt spinning, enhancing the composite fiber's stiffness and strength and providing a compatible surface for nanomaterial deposition.

The study's distinctive contribution lies in interfacial chemistry. Graphene oxide, with its oxygen-containing functional groups, is dispersible in water and reactive with polymers but bonds weakly to PET. The team used functionalized graphene oxide to improve compatibility with the polyester matrix, using polyketone as a compatibilizer between PET and carbon nanomaterials. This approach reduced agglomeration and interfacial slippage, common issues in carbon-nanomaterial-reinforced polymer composites.

The coating process involves a two-stage impregnation of PET/TLCP fibers. Initially, fibers are soaked in a dispersion of large-lateral-sized graphene oxide (LGO), which forms a highly oriented coating framework. Ultrasonic agitation ensures intimate contact with the fiber surface and maximizes overlap between sheets, essential for electron transport. A second stage involves impregnation with small-lateral-sized graphene oxide (SGO) and carbon nanotubes, filling gaps between LGO sheets and creating a continuous architecture.

The electrical performance of these coatings is sensitive to processing conditions. Optimizing the LGO and SGO concentrations and ultrasonic impregnation time resulted in a resistivity of 2.3 x 10^3 ohm centimeters, a significant reduction from the insulating nature of pristine PET. This demonstrates that a conductive network can be established with modest nanomaterial loadings and a short treatment time.

Importantly, the coating does not compromise mechanical integrity. The treated fibers achieved a tensile strength of 560 megapascals, ten percent higher than pure PET fibers. This is attributed to the synergy between the TLCP phase and the interfacial interactions between carbon nanomaterials and polymer groups. The coating reinforces the fiber, transferring stress across a well-bonded interface, crucial for wearable applications where fibers undergo bending and stretching.

The fibers also exhibit temperature sensitivity, with electrical resistance changing measurably with temperature, functioning as built-in thermal sensors. The team measured a temperature sensitivity of -0.66% per degree Celsius, indicating a consistent resistance decrease as temperature rises. This stable, linear response is ideal for flexible temperature-sensing devices, enabling smart garments that monitor skin temperature or detect overheating.

This research aligns with the growing demand for flexible, wearable electronics and smart textiles. Conventional conductive fabrics often suffer from durability and cost issues. Carbon nanomaterials offer a lightweight, robust alternative, but their tendency to clump and weak adhesion to polymers have limited their use. The demonstrated strategy, using functionalized nanofillers and a size-segregated coating process, provides a scalable solution.

The study builds on previous work by the same group, extending from mechanical reinforcement to electrical functionality. Supported by a project on recycling and high-value reuse of waste polyester textiles, the research suggests that polyester fibers could become integral to wearable electronics, conducting electricity and sensing temperature.