Preparation and Characterization of Polypropylene/Carbon Nanotubes (PP/CNTs) Nanocomposites as Potential Strain Gauges for Structural Health Monitoring

Abstract

Polypropylene/carbon nanotubes (PP/CNTs) nanocomposites with different CNTs concentrations (i.e., 1, 2, 3, 5 and 7 wt%) were prepared and tested as strain gauges for structures monitoring. Such sensors were embedded in cementitious mortar prisms and tested in 3-point bending mode recording impedance variation at increasing load. First, thermal (differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA)), mechanical (tensile tests) and morphological (FE-SEM) properties of nanocomposites blends were assessed. Then, strain-sensing tests were carried out on PP/CNTs strips embedded in cementitious mortars. PP/CNTs nanocomposites blends with CNTs content of 1, 2 and 3 wt% did not show significant results because these concentrations are below the electrical percolation threshold (EPT). On the contrary, PP/CNTs nanocomposites with 5 and 7 wt% of CNTs showed interesting sensing properties. In particular, the best result was highlighted for the PP/CNT nanocomposite with 5 wt% CNTs for which an average gauge factor (GF) of approx. 1400 was measured. Moreover, load-unload cycles reported a good recovery of the initial impedance. Finally, a comparison with some literature results, in terms of GF, was done demonstrating the benefits deriving from the use of PP/CNTs strips as strain-gauges instead of using conductive fillers in the bulk matrix.

Thermal, Rheological, Mechanical, and Electrical Properties of Polypropylene/Multi-Walled Carbon Nanotube Nanocomposites

“…With regard to the melting and crystallization enthalpies ( Table 1 ), no dependency on the MWCNT loading could be identified, similarly with that observed for other PP/MWCNT nanocomposites [ 36 , 41 , 55 , 60 ]. The degree of crystallinity is influenced by the addition of MWCNTs; however, the trend is not consistent.…”

“…The DSC cooling scan ( Figure 2 a) displays a single crystallization peak, which shifts gradually to higher temperatures as the MWCNT loading increases, indicating that the crystallization process is facilitated in the presence of MWCNTs (i.e., the nucleation starts around CNTs) as reported by [ 27 , 36 , 41 , 43 , 50 , 55 , 60 , 61 ]. From Table 1 it can be seen that the ejection temperature (e.g., the temperature at which the molded part can be ejected from the mold without distortion) also increases with increasing MWCNT loading, indicating that cycle time can be reduced by the addition of MWCNTs as the molded part can be safely ejected at higher temperatures without compromising the quality of the part.…”

“…Moreover, PP/CNT nanocomposites have received extensive attention in the last years. The addition of CNTs into PP results in nanocomposites with changed properties; some of them are advantageous (superior mechanical properties-improved Young modulus and tensile strength [ 27 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], higher heat deflection, higher thermal [ 30 , 37 , 38 ] and electrical conductivity [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ], better warpage and shrinkage [ 33 , 48 ]), while others are less favorable (increased viscosity [ 29 , 31 , 39 , 40 , 42 , 44 , 49 , 50 , 51 ] or decreased ductility [ 30 , 31 , 32 , 33 , 34 , 35 ]).…”

“…Numerous research papers investigated different aspects of the structure–property–relationships of PP/CNT nanocomposites [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. However, as already underlined, less attention has been dedicated to investigate the materials property data that can be used for numerical simulation of PP/CNT nanocomposite manufacturing processes.…”

Time-Stability Dispersion of MWCNTs for the Improvement of Mechanical Properties of Portland Cement Specimens

“…Raman analysis showed the damage caused by the MWCNTs due to the sonication process for each energy used (see Figure 1 ). Three characteristic bands were observed—(i) the D band is due to the defect-induced phonon mode associated to the kinematic restriction disorders [ 38 ]. It means that this band contributed with a disorder, due to the presence of vacancies, defects or finite size of the MWCNTs structure, consisting of sp 2 and sp 3 bonds; (ii) G band is assigned to the phonon mode and it shows the vibration of the carbon-carbon sp 2 bonds of the graphite structure present in the MWCNTs [ 39 ]; (iii) the G’ band is related to second-order dispersion processes; here, two phonons can be involved in the same way (overtone) or phonons in different modes (combination).…”