Flame retarded poly(lactic acid) using POSS-modified cellulose. 1. Thermal and combustion properties of intumescing composites

POSS-modified nanofibrillated cellulose (PNFC) was used as a carbon source in intumescing flame retardants (IFRs) for melt-blended poly(lactic acid) (PLA) composites. The POSS moeities were found to inhibit reactions between ammonium polyphosphate (APP) and cellulose during extrusion. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) indicated this was due to cross-linking between the silanol groups on PNFC and phosphate groups on APP. Composite properties were assessed using viscometry, thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC), cone calorimetry, and dynamic mechanical analysis (DMA). Viscosity average molar masses of PLA decreased during extrusion, which was accelerated in the presence of APP based flame retardants. The use of PNFC resulted in the highest PLA molar mass of all flame retarded composites. Extruding the neat PLA lowered onset and peak decompositions, but the addition of APP based flame retardants modestly increased these temperatures. PCFC was found to be inconclusive in assessing beneficial flammability characteristics of the composites. The addition of 15% by mass IFR reduced the peak heat release rate by 45% and the total heat released by 20%, regardless of the carbon source. PNFC led to reduced smoke production compared to unmodified nanofibrillated cellulose (NFC) or pentaerythritol (PER). Use of APP-PER reduced composite stiffness and the glass transition temperature. The use of APP-NFC and APP-PNFC slightly increased composite stiffness, and did not significantly affect the glass transition temperature.