Table 2.

Approaches used to make polylactic acid (PLA) flame-retardant.

Source	Authors	Short Description	Findings
[95]	Kimura and Horikoshi	Tried to improve flame retardancy of PLA by blending with virgin polycarbonate (PC), but results showed not very significant improvement in flame retardancy of the blend.	To achieve better results, silicon-comprising PC was blended with PLA, but still only a V-2 rating could be achieved in UL-94 vertical burning test.
[96]	Nishida et al.	Studied flame-retardant properties of PLA by compounding Alumina trihydrate (ATH) in the polymer.	However, they found that, in order to get superior results, a relatively higher amount of ATH (about 40 to 50%) needs to be added to the PLA matrix.
[97]	Yanagisawa et al.	Incorporated ATH together with phenolic resins in PLA matrix to improve its flame retardancy for electronic applications. A significant char formation during combustion on the surface of the composite was observed.	The addition of phenolic resin not only resulted in improved flame retardancy, reinforced by alumina from ATH on the surface of composite, but also reduced the loading content of ATH to 35% (w/w).
[98]	Kubokawa et al.	Determined flame retardancy of PLA based fabrics by using bromine containing additives, and tri-phenyl phosphates and tested LOI of the fabrics.	Limiting oxygen index (LOI) of untreated fabrics was 24%; however, after treatment with FR additives, LOI of the fabrics increased to 28% with tri-phenyl phosphate and to 26% with bromine-containing FR additives.
[99]	Wang et al.	Prepared composites containing pentaerythritol (PER) and melamine cyanurate (MC) by controlling the weight ratio of 2:2:1 and organo-modified zinc-aluminum-layered double hydroxide (Zn-Al-LDH).	Microscale combustion calorimeter (MCC) and cone calorimetry results revealed substantial progresses in flame retardancy of the nanocomposites. A significant reduction in heat release rate and total heat release was observed.
[100]	Wei et al.	Investigated the effect of aryl poly-phenyl phosphonate together with PLA. LOI, UL-94 vertical burning and cone calorimetry tests were carried out together with the investigation of thermal and mechanical behavior of the composites.	PLA composites containing 7 wt % and 10 wt % of poly phenyl phosphonate achieved V-0 rating in UL-94 vertical burning test. However, not much improvement in HRR and THR of the FR composites were observed in comparison to neat PLA.
[101]	Bourbigot et al.	Studied flame-retardancy of different polymer nanocomposites such as polylactides, polyurethane and polyamides. Different nano-fillers such as carbon nanotubes and organoclay were incorporated in these polymers and their flame retardancy was investigated.	Found that nano-dispersion play a vital role in improving flame retardancy of nanocomposites and nano-fillers give better results when they are used in combination with inorganic flame retardants due to better synergistic effects.
[102]	Solarski et al.	Developed PLA/clay nanocomposites and studied their thermal and fire properties. Four different formulations ranging from 1 wt % to 4 wt % of the organo clay (C30B) were prepared. The nanocomposites were melt spun to produce multifilament yarns.	Yarns with better mechanical properties were used to produce knitted structures. The fire properties of the knitted fabrics were tested by cone calorimetry. It was observed that pHHR of the fabrics containing only 2 wt % of the clay were reduced up to 38%.
[17]	Suardana et al.	Prepared bio-composites containing natural fibers together with di-ammonium phosphate and investigated their mechanical and fire related properties.	By increasing wt % of di-ammonium phosphate, fire properties, flexural modulus, and weight loss rate of the composites were improved; however, tensile and flexural strengths of the composites were reduced.
[59]	Qian et al.	Prepared aluminated mesoporous silica and used it as an FR additive in PLA resin. Different formulations of fumed silica and aluminated mesoporous silica were compounded in PLA resin.	Achieved UL-94 V-0 rating and LOI value also increased quite significantly. pHHR of FR composites decreased to about 15% compared to neat PLA by the addition of only 0.5 wt % of aluminated mesoporous silica.
[103]	Wang et al.	Developed an inherently fire-resistant PLA polymer using a chain-extending procedure of pre-polylactic acid (PPLA). PPLA was produced by direct condensation reaction of L-lactic acid and its fire properties were tested.	Here, 5 wt % of PPLA in PLA polymer would be sufficient to achieve remarkable FR properties as LOI value of 35% and UL-94 V-0 rating was achieved with delayed ignition time compared to pure PLA.
[104]	Mngomezulu et al.	Investigated FR properties of PLA and expandable graphite (PLA/EG) composites. EG was compounded in PLA with different wt % to produce PLA/EG composites and their surface morphology, filler dispersion, dynamic mechanical behavior and crystallization rate were studied.	The presence of graphite layers with not so good filler dispersion resulted in poor bonding between PLA resin and EG. The crystallization rate of PLA was increased with an increase in the glass transition temperature. Furthermore, lower modulus of the composites with higher wt % of EG was observed.
[105]	Shumao et al.	Used ramie fibers together with PLA to reinforce the polymer and to enhance the mechanical properties. Used different formulations together with ramie fibers.	At 40 wt %, loading the LOI value could only be reached at 30%. Resulted phosphoric acid contributed in intermolecular dehydration of ramie fibers followed by dehydrogenation.
[63]	Zhan et al.	Investigated the combustion and thermal degradation behavior of PLA with a special flame-retardant consisting of spirocyclic-pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) and melt compounded with different wt % in PLA.	Attained UL-94 V-0 rating at 25 wt % loading and LOI value was 38%. A significant reduction in weight loss rate of PLA was observed after addition of SPDPM in PLA as confirmed by thermogravimetric analysis.
[106]	Fox et al.	Polyoligomeric Silsesquioxane (POSS) modified cellulose was melt blended with PLA to prepare PLA/POSS composites. Thermal and fire related properties of as prepared composites were tested by thermogravimetric analysis, dynamic mechanical analysis and cone calorimetry.	pHHR of the composites was reduced to 45% by the introduction of 15 wt % of modified cellulose in comparison to pHHR of neat PLA. Total heat release (THR) was also reduced to 20% and lesser smoke generation was observed in comparison to non-modified cellulose.