Enhanced flame retardancy of polylactic acid with aluminum tri-hydroxide and phenolic resins

Abstract

Improvement of the flame retardancy of polylactic acid (PLA) was investigated by the combined use of aluminum tri-hydroxide (ATH) and phenolic resins as safe flame retardants in order to apply PLA to housings of electronic products which are required to meet standards of high flame retardancy. The addition of more than 50 wt% of a specific ATH, the alkali elements of which were reduced, sufficiently improved the flame retardancy of the resulting PLA composite. However, other important characteristics of the composite, such as bending strength, bending strain, impact strength and fluidity, were reduced owing to the high concentration of the ATH. On the other hand, the simultaneous addition of the ATH and the specific phenolic resins including phenol novolac resin and tri-phenol methane resin improved the flame retardancy of the composite. The effect on flame retardancy was mainly due to the formation of homogeneous char layers produced by these phenol resins on the surface of the composite during ignition. This enhancement of flame retardancy allowed us to reduce the ATH, and as a result, these other characteristics were improved. Furthermore, these phenolic resins were effective in increasing the bending strength and fluidity of the composites. In addition, the combined use of a copolymer composed of PLA and aliphatic polyester as a biomass-based flexibilizer increased the bending strain, the impact strength and the fluidity of the composite. © 2009, The Society of Polymer Science, Japan.