Emission of nanoparticle aerosols from composites functionalized with Multi-Wall Carbon Nano Tubes (MWCNTs) subjected to sliding wear: the influence of matrix material

A comprehensive investigation was conducted to evaluate the impact of the matrix material on the mechanical properties, microstructure, and triboemission of nanoparticle aerosols in polymer-matrix and cement-matrix composites functionalized with multi-walled carbon nanotubes (MWCNTs). The cementitious specimens were subjected to abrasion using a 20 mm diameter alumina ceramic ball, which was pressed against the sample using a constant dead load of 2.94 N. For the polymer composites, an inverse configuration was utilized to simulate the sliding conditions of a top-of-rail friction modifier, wherein a stationary composite specimen was pressed against a rotating steel disk under a constant dead load of 10 N. The sliding velocity was maintained at 1 m/s for the cement composite, while for the polymer materials, it ranged between 3.0 and 3.5 m/s. A systematic quantitative methodology was implemented to evaluate the deposition rate, emission rate, and emissivity. For cementitious materials, characterized by more pronounced porosity compared to polymers, the pore structure was analyzed using a Dynamic Vapor Sorption (DVS) system and mercury intrusion porosimetry. Raman spectroscopic analysis, utilizing a 780 nm excitation laser wavelength, was performed on both the worn surfaces and the adjacent pristine areas. The matrix material plays a critical role in nanoparticle aerosol generation and triboemission from MWCNT-functionalized composites. In polymer-matrix composites, MWCNT incorporation reduces surface damage and promotes transfer layer formation. While MWCNT addition has no impact on triboemission kinetics, it slightly modifies the aerodynamic characteristics of aerosol particles by narrowing the range of relaxation times across particle sizes. In the cement-matrix composite, the addition of MWCNT significantly increased crystallite size, reduced surface damage, and improved wear resistance. The observed differences in triboemission behaviors can likely be attributed to the primary wear mechanisms: abrasion in the cement-matrix composite and adhesion in the polymer-matrix composite, rather than any direct mechanical or structural changes induced by the MWCNT additive.