An intumescent flame retardant system using β-cyclodextrin as a carbon source in polylactic acid (PLA)

In this paper, β‐cyclodextrin (CD) was used as effective “green” carbon source to replace pentaerythritol (PER) in an intumescent flame retardant (IFR). The combination of CD with traditional acid resource ammonium polyphosphate (APP) and/or blowing agent melamine (MA) at different weight ratios exhibited outstanding char‐forming ability. It was demonstrated that strong interactions occurred in APP‐CD and MA‐CD systems through thermogravimetric analysis (TGA). Mechanisms of esterification between APP and CD or dehydration between MA and CD were discussed. The APP/MA/CD complexes showed doubled char residue of those calculated based on three single components in nitrogen atmosphere. For instance, the char residue of CD‐APP (at the weight ratio of 1:1) complex was 38 wt% at 700°C, while the calculated char formation was only 19 wt% in N2. After addition of these complexes into polylactic acid (PLA), the flammability of these PLA resins was evaluated by limited oxygen index (LOI) and vertical combustion (UL‐94). The TGA results indicated that the cyclodextrin mixed with APP and MA as a “green” char agent demonstrated outstanding char formation ability for PLA. When the complex contained CD/APP/MA at weight ratio of 1/2/1 and the addition amount of complex in PLA was 20 wt%, the PLA composites showed LOI values of 34.2 and passed UL 94 V0 rating, and the char residue of the PLA composite was 17.4 wt% at 700°C while only 7.4 wt% was achieved for the calculated composition. Copyright © 2011 John Wiley & Sons, Ltd.