Flame-retarding polylactic-acid composite formed by dual use of aluminum hydroxide and phenol resin

Flame retardancy of polylactic acid (PLA) was improved by dual use of aluminum hydroxide (AH) and phenol resin as safe flame retardants to allow PLA to be widely applied in durable products including electronic devices. Adding more than 50 weight-percent (wt%) of a specific AH which contains a low concentration of alkali elements sufficiently improved the flame retardancy of PLA. However, other important characteristics of the resulting PLA composites, such as flexural strength and fluidity, were decreased owing to the high concentration of AH. On the other hand, the simultaneous addition of phenol resins (including phenol novolac resin and tri-phenol methane resin) and the specific AH improved the flame retardancy of the PLA composites. This enhancement effect on flame retardancy, which was mainly due to the formation of homogeneous char layers produced by the phenol resins on the surface of the PLA composites during combustion, permitted the specific AH concentration to be reduced, thereby improving these characteristics of the composites. In particular, a high-molecular-weight phenol novolac resin (HMw PN resin) showed highly flame-retarding effect. While using phenol resins adversely affected the action of an organic crystalline nucleus agent for PLA, the use of HMw PN resin improved the problem because its concentration in the PLA composite was reduced due to its highly flame-retarding effect.