Organosolv pretreatment of cocoa pod husks: isolation, analysis and use of lignin from an abundant waste product

Cocoa pod husks (CPHs) represent an under-utilised component of the chocolate manufacturing process. Whilst industry’s current focus is understandably on the cocoa beans, the husks make up around 75 weight percent of the fruit. Previous studies have been dominated by the carbohydrate polymers present in CPHs, but this work highlights the presence of the biopolymer lignin in this biomass. An optimised organosolv lignin isolation protocol was developed, delivering significant practical improvements. This new protocol may also prove useful for agricultural waste-derived biomasses in general. NMR analysis of the high quality lignin led to an improved structural understanding, with evidence provided to support deacetylation of the lignin occurring during the optimised pretreatment. Chemical transformation, using a tosylation, azidation, copper-catalysed click protocol, delivered a modified lignin oligomer with an organophosphorous motif attached. Thermogravimetric analysis was used to demonstrate the oligomers potential as a flame-retardant. Preliminary analysis of the other product streams isolated from the CPHs was also carried out