The synergistic role of acidic molecular sieve on flame retardant performance in PLA/MF@APP composite

Intumescent flame retardant (FR) system containing acid source, foaming agent and carbonizing agent becomes popular to improve flame suppression. It is still challenging to improve FR performance by directly utilizing polymer matrix as carbonizing agent. Herein, we selected polylactide (PLA) matrix as carbonizing agent, APP encapsulated with melamine formaldehyde (MF) resin (MF@APP) as FR system, and acidic molecular sieve (HZ) as a synergist to improve the flame suppression performance in PLA/MF@APP composites. The APP surfaces were encapsulated with MF particles to protect APP from moisture, which could be supported by scanning electron microscopy (SEM) and Fourier transform infrared spectrometer spectra (FTIR). Temperature-programmed desorption of ammonia (NH3-TPD) measurement proved that HZ particle exhibited more weak and strong acid sites. As an effective synergist, PLA/MF@APP composites with 0.5% synergist exhibit higher (similar to 60%) limited oxygen index (LOI) of 28.8% and lower (50%) peak heat release rate (pHRR) of 211 kW/m(2) than that of neat PLA. In order to investigate the acidic role of molecular sieve synergist, we exploit neat molecular sieve as a control sample for the comparative study. As a result of protective char layer formation, the total smoke release (TSR) value further decreased from 130.4 to 76.6 m(2)/m(2) in the PLA/MF@APP composites with acidic synergists.

Automated summary

Intumescent flame retardant system with polylactide as carbonizing agent, melamine formaldehyde encapsulated ammonium polyphosphate as flame retardant system, and acidic molecular sieve as synergist, showed improved flame suppression performance in PLA composites. The addition of acidic synergist reduced the total smoke release and increased the limited oxygen index of the composites.