Novel Dihydroxy-Containing Ammonium Phosphate Based Poly(Lactic Acid): Synthesis, Characterization and Flame...

Area of Science:

• Materials Science
• Polymer Chemistry
• Flame Retardancy

Background:

• Poly(lactic acid) (PLA) is a widely used biobased polymer.
• Developing effective flame-retardant PLA is crucial for expanding its applications.
• Existing flame retardants can negatively impact PLA's properties.

Purpose of the Study:

• To synthesize and incorporate a novel flame retardant, dihydroxy-containing ammonium phosphate (DAP), into biobased poly(lactic acid) (PLA).
• To evaluate the flame-retardant properties and thermal stability of the modified PLA materials.
• To elucidate the flame-retardant mechanism of DAP in PLA.

Main Methods:

• Synthesis of DAP from 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphinane-2-oxide (DOP) and 2-amino-2-methyl-1,3-propanediol (AMPD).
• Incorporation of DAP into PLA to create flame-retardant composites.
• Evaluation of flame retardancy using UL-94 tests and limiting oxygen index (LOI) measurements.
• Analysis of thermal stability using thermogravimetric analysis (TGA).
• Investigation of the flame-retardant mechanism through decomposition analysis.

Main Results:

• PLA modified with only 0.5% DAP achieved a UL-94 V-0 rating.
• The limiting oxygen index (LOI) reached 24.6% with 0.5% DAP and increased with higher loadings.
• DAP showed minimal impact on PLA's thermal stability.
• The degree of crystallization in PLA increased due to DAP's plasticized effect.
• The heat release rate (HRR) did not show significant improvement at low DAP loadings.

Conclusions:

• The novel DAP is an effective flame retardant for biobased PLA, even at low concentrations.
• DAP functions by releasing incombustible gases (water, ammonia) and phosphorus-containing fragments, interrupting radical reactions and promoting char formation.
• DAP's plasticizing effect enhances PLA's crystallization, while its flame-retardant action is primarily gas-phase and char-based.