Conductive polymer composites (CPCs) have attracted intensive attention for several decades because they can endow the materials with not only good processability but also various functionalities except the electrical conductivity. It is known that the electrical resistance of the CPCs is dominated by the conductive networks in the polymer matrix. Therefore, tiny change of the conductive networks can lead to remarkable changes in the output electrical signal of the CPCs. Utilizing this stimulus-response behavior of conductive networks to the environment conditions, CPCs can be used to design sensitive sensors to detect or monitor the environment conditions, such as the strain/stress, pressure, temperature, solvent or vapor. This review systematically outlines the preparation, microstructures, properties, and the stimulus-response mechanisms to the environment conditions of the CPCs as well as their applications in various sensitive sensors, including strain sensors, pressure sensors, liquid sensors, vapor sensors, and temperature sensors. Finally, the open question and future challenge of utilizing the stimulus-response behavior of CPCs to design versatile sensors are discussed.

Plant oil-based epoxy resins are of great interest due to their ecological and economic necessity. In this study, the relationship between the crosslinking density and the thermo-mechanical properties of tung oil-based epoxy resins was established.

Conductive epoxy composites are of great interest in industrial applications. The electrical properties of these composites, however, often come at the expense of mechanical properties, particularly toughness. Herein, we report a simple, facile, and universal fabrication method for a strong, stiff, and extremely tough conductive epoxy composite with an ultralow percolation threshold. By tuning the interaction between multi-walled carbon nanotubes (MWCNTs) and epoxy components, they spontaneously assembled into a “cellular structure”, with the MWCNTs selectively located in the continuous domain of the diglycidyl ether of bisphenol A (DGEBA) epoxy. These cellular structures dramatically improved the toughness of the epoxy resin and the electrical properties of the MWCNT/epoxy composites while maintaining an excellent tensile strength and modulus. A 26.83-fold increase in toughness (to 3.25 ± 0.12 GJ m⁻³) was seen in the MWCNT/DGEBA/tung oil-based diglycidyl ester (TODGE) epoxy composite (0.75 wt% MWCNTs). The elongation at break of the composite increased 33.93 times (to 112.84 ± 4.25%) over that of neat DGEBA epoxy (toughness: 116.76 ± 7.84 MJ m⁻³; elongation at break: 3.23 ± 0.25%). The tensile strength and modulus remained at 37.09 ± 1.28 MPa and 2.88 ± 0.14 GPa, respectively. Moreover, composites with the cellular structure exhibited an ultralow electrical percolation threshold (∼0.032 wt%). The outstanding toughness and good electrical properties of the MWCNT/epoxy composites with cellular structures are attributed to the synergistic toughening effects of TODGE and MWCNTs as well as volume exclusion from the cellular structure. This work provides a new strategy for designing mechanically robust multifunctional thermoset composites, which have important applications in various fields.

Polyurethane is widely used to toughen epoxy resins due to its excellent comprehensive properties and compatibility. However, some demerits of polyurethanes limit their applications, such as the harsh storage condition of isocyanate-terminated polyurethane (ITPU), the limited amount of ITPU in epoxy resin, and using solvents during the preparation of polyurethane-modified epoxy resins. To address these issues, in this study, we reported a facile and green approach for preparing epoxy-terminated polyurethane (EPU)-modified epoxy resins with different EPU contents. It was found that the toughness of the epoxy resin was significantly improved after the addition of EPU. When the EPU content was 30 wt%, the elongation at break and toughness were improved by 358.36% and 73.56%, respectively. In comparison, the toughening effect of EPU outperformed that of ITPU. Moreover, the high content of EPU did not significantly decrease the glass transition temperature and had little effect on the thermal stability of the epoxy resin.