The banana fruit is a renewable agricultural product packed with high nutritional value. Once we peel the banana to reveal and consume the superfood, the external peel is worthless to us. In banana processing factories, tons and tons of the banana peels are discarded as waste. Now, imagine if we could recycle these banana peels to make paper. Not just one type of paper, but various kinds of speciality papers – waterproof paper, ink-erasable paper, untearable paper, etc. This would not only reduce and repurpose our waste, but also provide a sustainable and high-performance alternative to traditional paper, which requires felling trees.

Similar to how banana peel is an agro-waste of the banana processing industry, cashew nutshell is an agro-waste of the cashew producing industry. Earlier, these non-edible cashew nutshells were simply discarded as waste or burnt as fuel, rather inefficiently. Later, it was discovered that the shell could be thermally treated to obtain Cashew Nut-Shell Liquid (CNSL), a dark-brown oily liquid extracted after roasting the cashew nutshell.

CNSL is a mixture of various phenolic oils and among these is Cardanol, a natural, bio-derived monomer with diverse functionalities and excellent inherent properties. Cardanol has a very interesting structure where a phenolic ring is meta-substituted with a long 15 carbon aliphatic chain. The long aliphatic chain imparts hydrophobicity, flexibility and low viscosity. Its low volatility, high boiling point, and lack of aggressive odors make Cardanol easy to handle, process, and store. The phenolic moiety, on the other hand, aids in adhesion, chemical resistance and low-temperature curing.

Phenalkamines – The Workhorse of Sustainable Epoxy Curing Agents

Among the materials derived from Cardanol, Phenalkamines  have found the most success. Due to the diverse functionalities of Cardanol mentioned above, it can undergo Mannich Reactions to form Phenalkamines. Simply put, Mannich Reactions are a type of organic reaction where a compound with acidic hydrogen is reacted with an aldehyde and amine to release water and form a Mannich Product. When Cardanol is used as the acidic compound, the resultant Mannich Product is Phenalkamine.

Phenalkamines make excellent epoxy curing agents that can rapidly react with epoxy resins at low temperatures or even in humid and damp conditions. Faster cure allows for quicker return to service, crucial for manufacturing efficiency. Cardanol’s presence in Phenalkamines ensures excellent water and moisture resistance during film formation. Resultantly, the coating system can adhere to challenging substrates such as poorly prepared surfaces or even wet surfaces.

This hydrophobicity of Cardanol, along with its phenolic nature, and its ability to form highly crosslinked films with epoxy resins translate to excellent corrosion resistance. Thereby, they are well suited for the most demanding applications such as marine  and industrial  protective coatings.

Furthermore, the long aliphatic chain of Cardanol provides flexibility to coatings, which is vital for contoured substrates with complex structures. The chain also imparts low viscosity, allowing Phenalkamines to be 100% solids. This means that solvents are not required to reduce their viscosity for ease of handling. The complete elimination of petro-derived organic solvents is essential for a sustainable future.

Specialized Phenalkamines

The properties of Phenalkamines can be tailored based on the purity of Cardanol, type of amines, type of aldehydes, and reaction conditions. NSPC’s experienced R&D team has been working on specialized Phenalkamines for over 20 years, tailoring their structure to meet customers’ specific end-use applications. As a leading manufacturer and exporter of epoxy resins and curing agents, NSPC is committed to balancing performance and sustainability.

Following is a list of some of our high-performance Phenalkamines (and Phenalkamine Adducts) that have been specifically developed for their intended use case.

Conclusion

One man’s trash is another man’s treasure. Cashew nut shells, once discarded as waste, have found new life in high-performance coatings suited for the most challenging of applications. Phenalkamines not only repurpose waste but also support local rural communities near cashew plantations. NSPC takes pride in contributing to their development while producing specialized resins that add value to our customers.

Further Reading

1. NadkarniSPC – CURE-O-POXY for our wide range of Epoxy Curing Agents.
2. Wikipedia-Cardanol for more on Cardanol.
3. UCLA to learn about sustainability.
4. World Population Review for Cashew Production by Countries.
5. Research and Markets for a report on Epoxy Curing Agents Market.