(614b) Enhancing Thermo-Oxidative Stability of Polymers Using Natural and Synthetic Melanins

Melanins are well known for their intriguing chemical structure and physiological functions including photoprotection, radical scavenging and metal-ion chelation. However, compared to other biopolymers such as cellulose, chitosan or collagen, they have received little attention in exploiting these properties to create technologically relevant composite materials. To this end, we report here on the potential of natural and synthetic melanins as thermal stabilizers for common polymers. Synthetic melanin-like polymers, synthesized by oxidation of L-3-(3,4-dihydroxyphenyl) alanine (L-Dopa), significantly reduced the radical initiated chain scission behavior of poly(methyl methacrylate) (PMMA) with only 0.5-5 wt% incorporation. As a consequence, the onset decomposition temperature of PMMA was increased by 50-90 °C in both inert and air atmospheres. Parallel studies with natural melanin that was extracted from the ink sac of Sepia officinalis also revealed significant thermal stabilization effects on PMMA and polypropylene at similar loadings. The associated delay in the molecular weight decrease of PMMA and other polymers at elevated temperature could be potentially beneficial for high temperature processing or increasing their upper use temperature in demanding applications. This interesting biopolymer is ubiquitous in nature and easily accessible in large quantities. Since natural and synthetic melanin additives are macromolecules, they are also less likely to leach from the base polymer in the same way that small molecule additives often do.