Non-Halogenated Flame Retardant Polymeric Additive Synthesized from a Renewable Byproduct

The toxicity and environmental persistence of halogenated flame retardant (FR) compounds has led to reduction in their usage cross the globe. There is a need for the development of alternative non-halogenated FR compounds especially for highly flammable plastics such as polypropylene. Here we present a new type of non-halogenated polymeric FR synthesized from a renewable and biodegradable byproduct of cashew nut processing namely cardanol. Polymerization of cardanol (Cashew nut shell liquid) was carried out in predominantly aqueous media using common oxidants. The thermal properties and FR characteristics of the resulting polymers were investigated. Polycardanol exhibits good thermal stability with moderate heat release capacity (HRC). To ensure that polycardanol was not toxic, appropriate toxicity studies were carried out in accordance with the Organization for Economic Co-operation and Development (OECD) 425 guidelines for the testing of chemicals. The results of this study indicated that LD50 values for polycardanol was greater than 2000 mg/kg. To investigate the possibility of using Polycardanol as an FR additive, this material was melt-blended into commercially available polypropylene (PP) resin. In PP-polycardanol blends, polycardanol increased the thermal stability and char-forming ability. Polycardanol also lowered the HRC of PP by over 20%. These results clearly demonstrate the possibility of utilizing renewable waste/co-product of the food industry (Cashew nut shell liquid) as a feedstock for the synthesis of safer FR materials.