Cellulose Nanocrystals Proposed as Eco-Friendly Lubricant Additive

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The design of environmentally benign lubricant additives is critical for preserving the environment. In a paper available as a pre-proof in the journal Carbohydrate Polymers, the lubricating process and administration methodology of cellulose nanocrystal (CNC) in greases was investigated.

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​​​​​​​Study: Tribological behavior of cellulose nanocrystal as an eco-friendly additive in lithium-based greases. Image Credit: Tony Duy/Shutterstock.com

Nano-additives in Lubricants

In industrial settings, lubrication oils and greases are commonly utilized to prevent energy dissipation and part failures. Nonetheless, with increasing concern for ecosystems, traditional lubricant additives containing environmentally detrimental components, such as phosphorus, sulfur, or halogens, are facing replacement by nanoparticle (NP) additives like graphene, nano-copper, and nano-diamond.

Despite this, the hefty expense of NPs restricts their realistic usage in industrial settings. Moreover, although certain nanoscale additives featuring heavy metals such as copper are not immediately dangerous, they accumulate in living things. As a result, it is critical to investigate nanoscale additives made from more cost-effective and environmentally benign components.

Cellulose Nanocrystals may be the Perfect Nano-additives for Lubricants

The rod-like NP generated by eliminating the amorphous areas of organic cellulose is known as cellulose nanocrystal (CNC). Aside from being non-toxic and biodegradable, cellulose nanocrystal benefits from great mechanical strength with small density. Furthermore, CNC has already been widely employed in numerous industries because of the abundance of cellulose materials and its sophisticated industrial production process. CNC has gained increasing study interest in the field of lubricants in the last five years. Many investigations have proven CNC to be a potential contender as an environmentally benign additive for oil as well as water lubricants.

Challenges to be Addressed

Previously, surface-altered cellulose nanocrystal was integrated in polyalphaolefin (PAO) base oil and showed good performance in reducing friction and resisting abrasion on steel structures. Nonetheless, the unsatisfactory dispersing stability of cellulose nanocrystal in base oil remains a difficulty for industrial uses. This is also a common issue for nanoscale additives owing to their considerable surface energy and large disparity from the base oil in terms of density.

One possible approach is to use nanoscale additives in greases, where the NPs may be firmly held in the 3D framework of soap fibers and dispersed uniformly. That being said, the loading level of NPs must be carefully evaluated to prevent significant alterations in the fundamental physical characteristics (i.e., consistency and perceived viscosity) of the parent greases. Moreover, it is necessary to thoroughly examine which types of greases nanoscale additives might work more effectively.

Methodology Followed in the Study

This research was the first to try to incorporate cellulose nanocrystal into greases as a lubricant additive. CNC NPs were synthesized from cotton using an acid hydrolyzing procedure and were then inserted in Li-based grease with different consistencies and perceived viscosities.

The inclusion of cellulose nanocrystal is predicted to improve lubricating function without causing substantial modification in the fundamental physical characteristics of the parent greases. As a result, the effect of cellulose nanocrystal on grease firmness and rheological characteristics was investigated, and the appropriate cellulose nanocrystal loading concentration was recommended. The frictional and abrasive behavior of hybrid greases was then examined, and the lubricating process of cellulose nanocrystal additive was also explored.

Important Findings

To investigate environmentally benign lubricant additives, this study synthesized cellulose nanocrystal and attempted for the first time to use it as a nanoscale additive in four Li-based greases of different consistencies and perceived viscosities.

The effect of integrated cellulose nanocrystal on the greases’ fundamental physical characteristics and tribological activity has been studied. According to the findings, the addition of 15% cellulose nanocrystal had a significant impact on the viscosity-temperature attributes as well as the consistency of pure greases. As a result, the loading amount of cellulose nanocrystal must be kept at a tolerable level.

Cellulose nanocrystal in 421 grease with poor consistency and large viscosity base oil operated most effectively in terms of tribological activity owing to its adequate coating on the moving surface.

The friction minimization and anti-abrasive performance of the hybrid grease were clearly improved with the help of surface restoration and preservation by cellulose nanocrystal. Based on their strong application prospects, the performance of environmentally benign CNC additives and traditional phosphorus or sulfuric additives must be researched and compared in future studies.

Reference

Li, J., Lin, N. et al. (2022). Tribological behavior of cellulose nanocrystal as an eco-friendly additive in lithium-based greases. Carbohydrate Polymers. Available at: https://www.sciencedirect.com/science/article/pii/S0144861722003836?via%3Dihub


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