# N‑Alkylamino-Functionalized Multiwalled Carbon Nanotubes for Advanced Grease Applications: Stability and Tribological Enhancement

## TL;DR

This paper explores how amino-functionalized carbon nanotubes can improve the performance of industrial greases by enhancing stability and reducing friction.

## Contribution

The novel contribution is the synthesis and application of N-alkylamino-functionalized MWCNTs as efficient nanoadditives for lubricants.

## Key findings

- Functionalized MWCNTs achieved a weld load of up to 490 kG in greases.
- Wear scar diameters were reduced by 11% compared to commercial additives.
- Friction coefficients were reduced by up to 84% while maintaining grease consistency.

## Abstract

Advanced lubricants play a critical role in modern industry
by
reducing friction, minimizing wear, and extending the service life
of heavily loaded mechanical systems. Addressing these challenges
requires the development of nanocomponents capable of simultaneously
improving multiple tribological parameters without compromising the
consistency or manufacturability. This study investigates the potential
of N-alkylamino functionalized multiwalled carbon
nanotubes (MWCNTs) as high-performance nanoadditives for industrial
grease formulations. The aim is to evaluate their impact on the dispersion
stability and key tribological properties under severe operating conditions. N-alkylamino MWCNTs were synthesized via one-step nucleophilic
addition of terminal n-alkylamines with chain lengths
of C6, C12, and C16 to pristine MWCNTs
yielding the functionalization degrees equal to 3.2, 2.8, and 10.3
wt %, respectively. This approach ensured atom economy, eliminated
side products and problematic wastes, and operated under relatively
mild conditions with high overall efficiency. The resulting nanoadditives
were dispersed in a base mineral oil and incorporated at as low as
0.02 wt % into lithium-based greases containing nanographite and MoS2 as the typical commercial additives. The functionalized MWCNTs
demonstrated excellent time and operational stability in the base
oil, with no observable sedimentation over 7 days. Greases formulated
with N-alkylamino-functionalized MWCNTs demonstrated
markedly superior tribological performance, achieving a weld load
of up to 490 kG (versus 250 kG for the commercial reference), reduced
wear scar diameters of 0.49–0.50 mm (approximately 11% lower),
and an exceptionally low SRV friction coefficient of 0.1030, representing
a reduction of up to 84% compared to the commercial grease. Notably,
these enhancements were achieved while maintaining an NLGI grease
consistency class of 2, ensuring practical applicability and processability.
This approach offers a scalable route to next-generation lubricants
suitable for highly loaded tribo–pairs, precision mechanical
assemblies, and energy-efficient drivetrains.