Biobased flame-retardant poly(lactic acid) / cork / melem phytate composites

A B S T A R C T The bio-based, compostable poly(lactic acid) (PLA) is difficult to flame-retard without degrading its molar mass and physical properties, impeding ambitious technical applications. Furthermore, the demand for using bio-based flame retardants (FRs) in PLA increases. As a novel approach, cork, derived from Quercus suber L., is incorporated into PLA at three particle sizes to examine whether cork’s charring and heat barrier effects can be strengthened to achieve superior flame retardancy. At 20 wt.%, cork reduced the peak heat release rate from 703 kW/m 2 to 280 kW/m 2 . The preserved cork cellular structure scales its efficacy as FR with increased particle size. While the flame retardancy effect improves, molar mass and physical properties of PLA composites remain constant across cork particle sizes. Mechanical properties of the PLA/cork composites deteriorated compared to PLA. A novel bio-based FR, melem phytate (PhytM), is compounded with PLA to address the FR performance in PLA/cork composites and compared with commercial phosphorus-based FRs: 10 wt.% barrier-forming ammonium polyphosphate (APP); and flame-poisoning 6,6′- (Ethylendiamin-N,N′-diyl)bis(6H-dibenzo[c,e][1,2]oxaphosphinin-6-oxid) (EDA-DOPO). Flammability decreased to UL 94 V0, physical properties and molar mass were preserved in PLA/FR composites. PLA/cork/APP composites decreased flammability to UL 94 V0 without dripping. In PLA/cork/PhytM composites, the addition of 10 wt.% PhytM reduced fire load by 36% compared to PLA/cork. PLA/cork/FR composites maintain PLA’s molar mass and physical properties while providing excellent flame retardancy. PLA/cork and PLA/cork/PhytM benchys were 3D-printed and investigated with a needle burner test, demonstrating the application potential. PLA/cork/PhytM composites pave the way for bio-based flame-retarded technical polymers.