Viability of cascading application of polyamide waste into lubricant basestock by partial hydrolysis

Polyamide waste is difficult to recycle in part due to its chemical resistance. In this study, partial hydrolysis of PA10.10 was performed under several types of aggressive environment seeking high yields of a PA10.10 trimer, see Fig. 1, where R=H.
Fig. 1 Structure of the target products: PA10.10 trimer (R=H), basestock (R=C8H17) and wax (R=CH3).
Other polyamides, e.g. PA6.6 (a.k.a. Nylon 6.6), can also be hydrolyzed using the same concept, which involves esterification of the trimer with 2-ethyl hexanol (2EH) in order to produce a basestock for lubricants (R=C8H17). PA10.10 was selected, since 1,22-di-2EH-docosenedioate had pour point of -57°C [1], so it was reasonable to expect the trimer diester with 2EH (R=C8H17) to show good fluidity. Two hydrolytic pathways were tested. High pressure hydrolysis of PA10.10 pellets resulted in reduction of the pellet size and increase in surface roughness. Both effects were more pronounced in neutral media, while size reduction was not as evident in basic media. Unfortunately, hydrolysis generated a mix of highly polymeric materials with monomers of diamino decane and sebacic acid. Yields of PA10.10 trimer appeared negligible. The second hydrolysis pathway under ambient pressure in 50% H2SO4 resulted in heavy froth on the surface. After adding 20% acetic a. the froth dissolved, splitting the mix into two phases. Products from the high-pressure pathway were also blended with sulfuric and acetic acids. The pellets which had been partially hydrolyzed in neutral media yielded a dark homogeneous solution, while those of basic media produced two phases.
Concurrently, organic synthesis of the proposed basestock was attempted in order to verify that fluidity and other lubricant properties of the target product (R=C8H17) were acceptable. Monomethyl sebacate chloride was reacted with diaminodecane at 2:1. But the resulting wax (R=CH3) was extremely tough with its melting point at 163°C. Due to very poor solubility in organic solvents transesterification with 2EH could not be performed. Most likely, the trimer is excessively linear and fluidity would be problematic even after the transesterification with 2EH. Molecular architecture should include more branching for viscometric and other lubricant properties to be satisfactory. Therefore, trimers from partial hydrolysis of PA10.10 or larger monomer polyamides cannot be employed for a cascading
application into a lubricant basestock. Nevertheless, the monomers
such as sebacic acid could be considered for recycling once isolated.
Acknowledgment
The project COSMOS has received funding from the European Union’s Horizon
2020 research and innovation programme under grant agreement No 645405.
Reference
1. S.R.Yasa, S.Cheguru, S.Krishnasamy, P.V.Korlipara, A.K. Rajak, V.Penumarthy, Ind.
Crops Prod. 103 (2017) 141-151