Polyamide 4 with long-chain fatty acid groups – Suppressing the biodegradability of biodegradable polymers

Abstract Polyamide 4 (PA4) is a biodegradable polymer that can be produced from biomass. We found that modifying the terminal group of PA4 with a long-chain fatty acid resulted in the suppression of its biodegradation. PA4 modified with various acyl compounds from acetyl (C2) to stearoyl (C18) chlorides were prepared and used for biodegradation tests. The biodegradation of the PA4s was evaluated using PA-4-degrading bacteria ( Pseudomonas sp. ND-11) and activated sludge. The PA4-degrading bacteria grew and formed a clear zone around the colonies on the media containing PA4s with C2, C3, C6, and C10 end groups. On the other hand, PA4s with C12, C14, C16, and C18 end groups were not significantly degraded. Similar results were obtained using activated sludge. These results showed that the biodegradability of PA4 could be controlled by the molecular design of the polymer end group. Blending PA4 with fatty acid-functionalized PA4 decreased its biodegradability depending on the blend ratio. From the results of the contact angle measurements on the PA4 surfaces, it was suggested that the biodegradability was correlated to the hydrophilicity of the polymers. This method of controlling the biodegradability by adding a fatty acid group could be applied to other biodegradable polymers such as poly(butylene succinate adipate)s, e-poly(caprolactone), and poly(lactic acid).