Chocolate By-product Studied For Use as Flame Retardants

Millions of cocoa pods are harvested annually for the production of chocolate. While the beans and pulp go to make chocolate, about 24 million pounds of husks are usually discarded. Researchers reporting in ACS Sustainable Chemistry & Engineering show that cocoa pod husks could be a useful starting material for flame retardants.

Why husks? Cocoa pod husks contain lignin, a tough lipid polymer found in many woody plants. Lignin could be a renewable replacement for some substances typically derived from petroleum, such as flame retardants. While most methods to produce lignin have centered on hardwood trees, some scientists have processed other plant materials that would otherwise go to waste. Nicholas J. Westwood and coworkers wanted to see if high-quality lignin could be extracted from cocoa pod husks and determine whether it has the potential to make valuable, practical materials.

The researchers obtained cocoa husks and milled them into a powder. After rinsing to remove fatty residues, they boiled the powdered husks in a mixture of butanol and acid, a standard lignin extraction method called the butanosolv process. They next confirmed the isolated lignin’s quality and high purity, finding no evidence of carbohydrates or other contaminants.

Then, over the course of three chemical steps, the team modified the pure lignin biopolymer to have flame-retardant properties. They attached 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, which is a fire suppressant molecule called DOPO, into the backbone of the lignin polymer. In experiments, when the modified lignin was heated, it charred, but did not burn up, a sign that it could act as a flame retardant. 

It's possible that in the future renewable materials like these could be used in fire resistant adhesive foams, caulks, sealants, and adhesives.

Additionally, the researchers of cocoa pod husks recognize that safety tests are important and plan to conduct them after the next phase of testing. In the future, the researchers say they will optimize the properties of their cocoa pod husk-based flame-retardant materials for a variety of uses.

Source: ACS Sustainable Chemistry