Flame Retardant PLA Research Articles

The influence of nano ZnO coated by phosphazene/triazine bi-group molecular on the flame retardant property and mechanical property of intumescent flame retardant poly (lactic acid) composites

Nano zinc oxide (nano ZnO) and phosphazene/triazine bi-group flame retardant in situ doping nano zinc oxide (A4-d-ZnO) were used as synergists in intumescent flame retardant poly (lactic acid) (PLA) composites, respectively. The results showed that nano ZnO endowed flame retardant PLA excellent flame retardant properties, such as the higher LOI value, the lower pk-HRR, av-HRR, THR, mass loss rate, TSR and more final mass than A4-d-ZnO. It was because that nano ZnO catalyzed PLA decomposed into low molecular segments, which acted as a char-forming agent. However, it destroyed the mechanical properties seriously. By contrast, although the flame retardant properties of PLA/IFR/A4-d-ZnO was not better than PLA/IFR/nano ZnO, owing to the weakened catalytic effect of A4-d-ZnO coated by the phosphazene/triazine bi-group flame retardant, A4-d-ZnO improved the flame retardant properties, the thermal stability and the mechanical properties at the same time, which was important and necessary for application.

Flame retardant poly (lactic acid) biocomposites based on azo‐boron coupled 4,4′‐sulfonyldiphenol and its combination with calcium lignosulfonate—Crystalline and mechanical properties

Poly (lactic acid) (PLA) has become an important biopolymer with excellent properties but has limited engineering applications where fire safety is ultimate. An efficient flame retardant (FR) for PLA biocomposites based on azo‐boron coupled with 4,4′‐sulfonyldiphenol‐(((1E,1′E)‐(sulfonylbis(6‐hydroxy‐3,1‐phenylene))bis (diazene‐2,1‐diyl))bis(3,1‐phenylene))diboronic acid (SBDA) was synthesized and characterized by FTIR, 1H and 13C NMR spectra. SBDA was combined with calcium lignosulfonate (Calig) and compounded with PLA, and the FR, crystallization, and mechanical properties were investigated. The addition of 15 wt% FR (10 wt% Calig and 5 wt% SBDA) into PLA led to important reductions in peak heat release rate (PHRR) approximately 54%, total heat release (THR) approximately 28.6%, and the average effective heat of combustion (AEHC) approximately 29.4%. The fire performance index and fire growth index improved by approximately 56.4% and 33.1%, respectively. A V‐0 rating (vertical burning test) and a limiting oxygen index value of 28.8% were achieved for the FR PLA biocomposites. The combinatory SBDA/Calig reduced the segmental mobility of PLA in the organic‐inorganic interface with insignificant changes in the elongation at break and the Young Modulus. TG‐IR study showed significant reductions in pyrolysis gaseous products for the composites compared with PLA. This research work will expand the frontiers of knowledge on use of boron and calcium functionalized polyaromatic polyols for reducing the flammability of PLA.

Enhanced flame-retardant performance of poly (lactic acid) (PLA) composite by using intrinsically phosphorus-containing PLA

The intrinsically phosphorous-containing flame-retardant poly (lactic acid) (P-PLA) was synthesized through the chain extension of L-lactide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative, then P-PLA was melt blended with neat PLA to produce flame-retardant PLA composite (FR-PLA). The flame-retardant properties of FR-PLAs were investigated by Limiting Oxygen Index (LOI), UL-94, and Cone Calorimeter Tests, the results indicated that the flame-retardant properties of PLA composites were significantly improved with the addition of P-PLA due to its excellent ability to carbonize and dilute combustible gases. The LOI value of FR-PLA10 composite (consisting of 90 wt% neat PLA and 10 wt% P-PLA) increased from 20.5 to 27.8 and UL-94 rating reached up to V-1, the peak heat release rate and total heat release of FR-PLA composite were lower than those of neat PLA. The flame-retardant mechanism of FR-PLA depended on both condensed and gaseous phases, which was confirmed by the FTIR, Raman and TG-FTIR. Besides, the tensile strength of FR-PLA10 slightly decreased from 72.4 to 61.8 MPa, which met the requirements of most practical applications. Therefore, the modification method used in this work presented a feasible approach to prepare FR-PLA composite with satisfactory mechanical property.

Fire safety enhancement of a highly efficient flame retardant poly(phenylphosphoryl phenylenediamine) in biodegradable poly(lactic acid).

Flame-retarded poly(lactic acid) (PLA) biodegradable materials are viewed as promising as sustainable alternatives to petroleum-based commodity polymers. A new highly efficient flame retardant, poly(phenylphosphoryl phenylenediamine) (PPDA), was synthesized by the condensation of phenylphosphoryl dichloride with p-phenylenediamine and its structure was confirmed by 1H nulear magnetic resonance and Fourier-transform infrared spectroscopy. When 3 wt% PPDA was incorporated into PLA, the limited oxygen index increased from 20.0% of neat PLA to 25.5% and its UL-94 vertical burning testing achieved V-0 rating. Moreover, the total heat release and peak heat release rate values of PLA/3 wt% PPDA material were decreased from 109.1 MJ/m2 and 643.7 kW/m2 of PLA to 98.3 MJ/m2 and 570.0 kW/m2, respectively, and the fire performance index increased from 0.081 of PLA to 0.132 m2 s/kW. The high fire safety of PPDA in PLA is mainly attributed to the combined effects of the phosphorous-containing radical inhibition and inert gases and the barrier action of the formed char layer. The addition of less than 3 wt% PPDA has little influence on the tensile and impact properties of PLA. The flame retardant PLA blends have great application potential in electrical casing, automobile interiors and three-dimensional printing materials.

Mechanical Properties and Degrading Behaviors of Aluminum Hypophosphite-Poly(Lactic Acid) (PLA) Nanocomposites

ABSTRACTThe flame retardancy of poly(lactic acid) (PLA)/aluminum hypophosphite (AHP, phosphorous content = 41.87 wt.%) nanocomposites (PLA/(AHP-x), x = 15%, 20%, 25%; and x denotes the weight percentage content of AHP) was greatly enhanced by melt blending of AHP into PLA through twin-screw extruder and injection-molding process. The UL 94 V-0 flammability rating can be reached for PLA/(AHP-20%) with the LOI value over 28.8. The well dispersion of the AHP in PLA/(AHP-x) was investigated by FT-IR spectra under the line mapping model. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of PLA/(AHP-x) composites were studied by Kissinger’s, Ozawa’s and Flynn-Wall-Ozawa’s (FWO’s) methods. And those thermal degradation dynamic analyses showed lower activation energy (EK or EO) (from 155 to 122 kJ·mol–1) corresponded to higher content of AHP (from 15 to 25 wt.%) for PLA/(AHP-x) nanocomposites. Kissinger’s, FWO’s and Coast-Redfern’s methods were used to discriminate the kinetic models and kinetic parameters for the thermal degradation of PLA/(AHP-x), which suggested conversion function G (α) = [-ln(1-α)]2/3 or G (α) = α for the investigated process. The flame retardant PLA nanocomposites obtained in this study will become safety environment-friendly potential candidates in household and automobile engineering with high performance.

Preparation of Polylactide Composite with Excellent Flame Retardance and Improved Mechanical Properties

Despite the good biodegradable and mechanical properties, poly(lactic acid) still suffers from a highly inherent flammability, which restricts its applications in the electric and automobile fields. In order to improve the flame retardancy of PLA, in this work, melamine polyphosphate (MPP) and zinc bisdiethylphosphinate (ZnPi) were firstly incorporated into PLA, and the synergistic effect of them on flame retardance of PLA was investigated using limiting oxygen index (LOI), UL-94 vertical measurement, scanning electron microscopy (SEM) and cone calorimeter tests etc. The results showed that PLA composite with 15 wt% of MPP/ZnPi (3:2) had the best flame-retardant efficiency with LOI value of 30.1 and V0 rating in UL-94 tests, which was far better than using MPP or ZnPi alone. What is more, although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical properties of PLA. On the premise of maintaining good flame-retardant performance, we improved the toughness of flame-retardant PLA composite, and the impact strength of flame-retardant PLA composite was more than tripled (8.08 kJ/m2) by adding thermoplastic urethanes (TPU). This work offers an innovative method for the design of the unique integration of extraordinary flame retardancy and toughening reinforcement for PLA materials.

Mechanically Robust, Flame-Retardant Poly(lactic acid) Biocomposites via Combining Cellulose Nanofibers and Ammonium Polyphosphate.

Expanding the application range of flame-retardant polymer biocomposites remains a huge challenge for a sustainable society. Despite largely enhanced flame retardancy, until now the resultant poly(lactic acid) (PLA) composites still suffer reduced tensile strength and impact toughness due to improper material design strategies. We, herein, demonstrate the design of a green flame retardant additive (ammonium polyphosphate (APP)@cellulose nanofiber (CNF)) via using the cellulose nanofibers (CNFs) as the green multifunctional additives hybridized with ammonium polyphosphate (APP). The results show that PLA composite with 5 wt % loading of APP@CNF can pass the UL-94 V-0 rating, besides a high limited oxygen index of 27.5%, indicative of a significantly enhanced flame retardancy. Moreover, the 5 wt % of APP@CNF enables the impact strength (σi) of the PVA matrix to significantly improve from 7.63 to 11.8 kJ/m2 (increase by 54%), in addition to a high tensile strength of 50.3 MPa for the resultant flame-retardant PLA composite. The enhanced flame retardancy and mechanical strength performances are attributed to the improved dispersion of APP@CNF and its smaller phase size within the PLA matrix along with their synergistic effect between APP and CNF. This work opens up a facile innovative methodology for the design of high-performance ecofriendly flame retardants and their advanced polymeric composites.

Functionalized MWCNTs modified flame retardant PLA nanocomposites and cold rolling process for improving mechanical properties

10-hydroxy-9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-OH) has been successfully covalently grafted onto the surfaces of multi-walled carbon nanotubes (MWCNTs) to obtain DOPO-functionalized MWCNTs (MWCNT-DOPO-OH) by a three-step process. The resultant core-shell nanostructured MWCNT-DOPO-OH was introduced into aluminum hypophosphite/poly(lactic acid) (AHP/PLA) flame retardant systems via melt blending to improve both flame retardancy and mechanical properties. AHP/PLA/MWCNT-DOPO-OH nanocomposites with synergistic effect of 1 wt.% MWCNT-DOPO-OH and 14 wt.% AHP were shown to be effective in improving flame retardancy with UL 94 V-0 rating and limiting oxygen index (LOI) value of 28.6. And these flame-retardant nanocomposites show a usable Tg higher than 57.8 °C and much higher char yield for preventing the anti-dropping. Moreover, a cold rolling process was performed for AHP/PLA/MWCNT-DOPO-OH nanocomposites to further improve the mechanical properties for secondary processing. For 1 wt.% MWCNT-DOPO-OH loading PLA nanocomposites, the tensile strength increased from 69.5 MPa to 77.9 MPa and 82.0 MPa, and the fracture strain increased from 17.9% to 27.5% and 120%, at rolling ratios of 30% and 50%, respectively, indicating that MWCNT-DOPO-OH modified PLA was homogenized plastic deformation during the rolling process.

Crystallization, Mechanical and Flame-retardant Properties of Poly(lactic acid) Composites with DOPO and DOPO-POSS

Poly(lactic acid) (PLA) composites with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and DOPO-containing polyhedral oligomeric silsesquioxane (DOPO-POSS) were prepared via melting extrusion and injection molding. The crystallization, mechanical, and flame-retardant properties of PLA/DOPO and PLA/DOPO-POSS were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), tensile testing, thermogravimetric analysis (TGA), limiting oxygen index (LOI), and cone calorimeter test. The DSC results showed that the DOPO added could act as a plasticizer as reflected by lower glass transition temperature and inhibited crystallization of part of the PLA; the DOPO-POSS acted like a filler in the PLA matrix and slightly improved the crystallinity of the PLA matrix. The XRD and DSC analyses indicated that the PLA composites by cold molding injection were amorphous, and the PLA composites following a heat treatment in an oven at 120 °C for 30 min achieved crystallinity. All the PLA and its composites after heat treatment had improved mechanical properties. The thermogravimetric analysis (TGA) tests showed that the PLA, DOPO and DOPO-POSS decomposed separately in the PLA/DOPO and PLA/DOPO-POSS, respectively. The cone calorimeter tests offered clear evidence that addition of the DOPO-POSS resulted in an evident reduction of 25% for the peak of heat release rate (p-HRR). It was also confirmed that the crystalline flame-retardant PLA composites after heat treatment had better flame retardant properties than the amorphous PLA composites prepared by the cold molding.

Effect of NiFe2O4@graphene in intumescent flame‐retarded poly(lactic acid) composites

NiFe2O4 nanoparticles loaded on graphene layers (NiFe2O4@GR) were prepared by the hydrothermal method, and they first combined with intumescent flame retardant (IFR) consisting of polyphosphate (APP) and pentaerythritol (PER) was used to prepare poly(lactic acid) (PLA) composites. Effect of NiFe2O4@GR and IFR on thermal stability and flame retardancy of PLA was investigated. Limit oxygen index (LOI) value of all the PLA composites increased, and the results of UL‐94 tests passed V0 ratings. With the presence of NiFe2O4@GR in intumescent flame‐retarded PLA composites, the initial degradation temperature had a big increase and char residue increased apparently. The ratio of graphite crystalline carbon was increased. The denser and more intumescent char layer was formed. In addition, NiFe2O4@GR had the reinforcing effect for PLA. Therefore, NiFe2O4@GR and IFR had a good synergistic effect in improving thermal stability and flame retardancy of PLA. POLYM. COMPOS., 40:652–656, 2019. © 2018 Society of Plastics Engineers

Synthesis of a novel polyphosphate and its application with APP in flame retardant PLA

A phosphorus-containing flame retardant was synthesized via an A2 + B3 type reaction of bisphenolic acid-based monomer and phosphorus oxychloride. Then, intumescent flame retardant systems were prepared by combining PFRS with ammonium polyphosphate.

Intercalation of phosphotungstic acid into layered double hydroxides by reconstruction method and its application in intumescent flame retardant poly (lactic acid) composites

Phosphotungstic acid is a typical kind of superior catalysts, and it is hardly to intercalate into the layered double hydroxides (LDH) by ion-exchange process because of its low negative charge. In this work, a phosphotungstic acid intercalated MgAl-LDH (PWA-LDH) was prepared by reconstruction method, and it was then introduced into poly (lactic acid) (PLA) resin in association with intumescent flame retardant (IFR) by melt blending to prepare a flame-retardant biodegradable PLA composite. The effects of PWA-LDH on the flame retardancy of PLA composites were characterized by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. The results showed that the composite sample containing 18.0 wt% IFR and 2.0 wt% PWA-LDH achieved the maximal LOI value of 48.3%, passed the UL-94 V-0 rating, and significantly decreased the peak heat release rate from 306.3 kW/m2 of neat PLA to 40.1 kW/m2. Thermogravimetric analysis showed that both the thermal stability and the char formation were enhanced. The char morphology observation revealed that PWA-LDH was beneficial to form dense and compact char layers. It was demonstrated that there existed a synergistic effect between IFR and PWA-LDH in promoting the char formation and enhancing the fire resistance.

Preparation and characterization of intumescent flame retardant biodegradable poly(lactic acid) nanocomposites based on sulfamic acid intercalated layered double hydroxides

A novel sulfamic acid intercalated MgAl-LDH (SA-LDH) was prepared by intercalating NH3SO3− into MgAl-layered double hydroxides (LDH), and it was then introduced into poly(lactic acid) (PLA) resin in association with intumescent flame retardant (IFR) by melt blending to prepare a flame-retardant biodegradable PLA composite. The effects of SA-LDH on the flame retardancy of PLA composites were characterized by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test (CONE). The results showed that the composite sample containing 19.0 wt% IFR and 1.0 wt% SA-LDH achieved the maximal LOI value of 48.7 %, passed the UL-94 V-0 rating, and significantly decreased the peak heat release rate from 306.3 kW/m2 of neat PLA to 58.1 kW/m2. Thermogravimetric analysis showed that both the thermal stability and the char formation were enhanced. The char morphology observation revealed that SA-LDH was beneficial to form dense and compact char layers. It was demonstrated that there existed a synergistic effect between IFR and SA-LDH in promoting the char formation and enhancing the fire resistance. The mechanical and crystallization properties were also tested and discussed.

Flame retardant and mechanically tough poly(lactic acid) biocomposites via combining ammonia polyphosphate and polyethylene glycol

Although the flammability of biodegradable poly(lactic acid) (PLA) has been effectively addressed so far, the resultant flame retardant PLA still displays a high brittleness, extremely restricting its wide applications in electrical, automobile and aerospace fields. In this work, we have demonstrated the fabrication of flame retardant and tough PLA composites by combining ammonia polyphosphate (APP) and poly(ethylene glycol) (PEG) with a molecular weight of 20,000 via the melt-blending strategy. The results show that the peak heat release rate of PLA can reduce by 14% in cone tests and a V-0 rating is achieved in vertical burning tests by adding 7 wt% of APP and 14 wt% PEG. Moreover, such PLA composite shows a high strain at break of 280% and impact strength of 14.9 kJ/m2, respectively increasing by thirty-eight-fold and two-fold relative to the PLA bulk. The results strongly indicate that flammability and brittleness of the PLA are strikingly reduced. This work provides an integrated strategy for creating advanced green polymer composites with exceptional flame resistance and toughness.

Synergistic effect of lanthanum oxide on the flame retardant properties and mechanism of an intumescent flame retardant PLA composites

The synergistic effect of lanthanum oxide (La2O3) on the flame retardant properties and mechanism of a novel intumescent flame retardant polylactide composites (PLA/IFR) was investigated by the means of limited oxygen index (LOI), catalytic effectivity analysis (CAT-EFF), vertical burning test (UL-94), microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). La2O3 enhanced the LOI value of the PLA/IFR composite dramatically and all the composites passed the UL-94 V-0 rating test. PLA/IFR/1% La2O3 had the highest CAT-EFF, and the LOI value of the composite increased from 32.8 to 42.2% according to catalytic affectivity (CAT-EFF) analysis. 1%La2O3 enhanced the fire retardant performance of PLA/IFR, resulting consequently in reduction of heat release rate (HRR), total heat release (THR), heat release capacity (HRC) and degree of flammability (Findex) of the PLA/IFR. The TGA test revealed that La2O3 changed the degradation behavior of the PLA/IFR, enhanced the thermal stability of the PLA/IFR at high temperature and increased the char residue. The morphological structures observed by SEM demonstrated that La2O3 effectively help to form more continuous and compact intumescent char layer on the surface. The LRS results indicated that higher graphitization degree of the residue char was formed. The EDS and XPS results illustrated that the existence of La2O3 promoted to remain more P and O in the char layer to form more crosslinking structure to improve barrier properties of the char layer.

Improvement of flame retardancy of poly(lactic acid) nonwoven fabric with a phosphorus- containing flame retardant

A cyclic phosphonate ester flame retardant was applied to improve the flame retardancy of poly(lactic acid) (PLA) nonwoven fabric by a pad-dry-cure technique. The effects of curing temperature and flame retardant dosage on the flammability of PLA fabric were analyzed. The burning behavior, thermal stability and flame-retardant mechanism of the flame-retardant PLA fabric were investigated by limiting oxygen index (LOI), vertical burning test, microscale combustion calorimetry (MCC), thermogravimetric (TG) analysis and scanning electron microscopy (SEM) with energy dispersive spectrum (EDS). The treated PLA fabric exhibited good flame retardancy, and its LOI was about 35%, whereas this value was 26.3% for the untreated fabric. No obvious difference of the MCC test results between the untreated and treated fabrics was found. The results from TG analyses indicated the formation of a very small amount of char during the thermal degradation process of the treated PLA fabric. The SEM-EDS analysis showed an obvious decrease in the phosphorus content of the flame retardant fabric after burning. These indicate that the gas-phase flame-retardant mechanism during combustion is dominant, and results in the good flame retardancy of the treated fabric in the presence of a very small amount of char residue.

Highly-effective Flame Retardancy of Poly(lactide) Composite Achieved Through Incorporation of Amorphous Nickel Phosphate Microparticle

In this study, amorphous nickel phosphate (NiPO) was prepared through urea-assisted hydrothermal process. The composition of NiPO was investigated via X-ray photoelectron spectrum (XPS). And the structure of NiPO was characterized by Fourier transform infrared spectrometer (FTIR) and X-ray diffraction measurement (XRD).Then poly(lactide) (PLA) was melt blended with the resulting NiPO to prepare flame retardant PLA composites. The flame retardant property of PLA composites was probed using limiting oxygen index test (LOI), UL-94 vertical burning test (UL-94), cone calorimeter test (CCT). And the thermal combustion property was analyzed through pyrolysis combustion flow calorimeter test (PCFC). In the meantime, the thermal stability of NiPO microparticles and PLA composites was analyzed through thermogravimetric analyzer (TGA) and integrated procedural degradation temperature (IPDT). In the meantime, the melting and crystallization property of PLA composites was investigated through DSC analysis. Results showed that NiHPO3 was the main component of NiPO. PLA composite with only 2 wt.% NiPO powder exhibited excellent flame retardancy (LOI = 27.5% and UL-94 V-0 rating). In the CCT and PCFC test, it showed that HRR of PLA composites was higher in the early stage of combustion and lower in the late stage of combustion than that of pure PLA. Moreover, a slightly increased CO production rate (COP) and obviously decreased total smoke production (TSP) were found in PLA composites containing 2 wt.% NiPO in CCT. In the DTG curve, the similar weight derivation trend to HRR in CCT and PCFC test was also observed. Additionally, the intrinsic thermal stability was enhanced significantly by 19°C with 2 wt.% NiPO into PLA composites. DSC results showed that NiPO could also improve the crystallization property of PLA composites.

Synthesis of a hyperbranched poly(phosphamide ester) oligomer and its high-effective flame retardancy and accelerated nucleation effect in polylactide composites

In this article, a hyperbranched poly(phosphamide ester) oligomer HBPE was prepared via A3 + BB′ method. FTIR spectrum, 1H and 31P NMR spectrum and GPC were utilized to characterize HBPE. Then HBPE was melt blended with PLA to fabricate flame retardant PLA composites. The integrated flame retardant property of PLA composites was investigated by LOI, UL-94, pyrolysis combustion flow calorimeter test (PCFC) and cone calorimeter test (CCT). The thermal stability of PLA composites was investigated by TGA, weight loss difference analysis and integral procedural decomposition temperature (IPDT). Results showed that PLA composite with only 2 wt% HBPE exhibited excellent flame retardancy (LOI = 33% and UL-94 V-0 rating) and 10 wt% HBPE imparted PLA composites largely increased LOI value of 43%. The incorporation of 10 wt% HBPE increased CO production rate (COP) and prolonged time to ignition (TTI) in CCT. Furthermore the thermal stability of PLA composites was enhanced from IPDT analysis. Meanwhile, DSC analysis of PLA composites showed Tg of PLA composites decreased slightly with the addition of HBPE, which indicated the limited plasticizing ability of HBPE in PLA composites. Finally, the accelerated nucleation effect was also detected in PLA composites using POM observation. Results showed HBPE was a high-effective flame retardant of PLA, exhibiting good nucleating property and limited plasticizing ability in PLA composites.

Inherent flame retardation of bio-based poly(lactic acid) by incorporating phosphorus linked pendent group into the backbone

The molecular design for inherently flame-retardant poly(lactic acid) (IFR-PLA) was outlined and achieved by chemically incorporating an effective organophophorus-type flame retardant (FR) into the PLA backbone via the chain extension of the dihydroxyl-terminated prepolymer with 1, 6-hexamethylene diisocyanate (HDI). The structure of IFR-PLA was characterized by 1H- and 31P-nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. IFR-PLA was further blended with the commercial PLA to prepare flame retardant PLA blends (PLA-FR blend). The relevant properties of IFR-PLA and PLA-FR blends were evaluated by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), limiting oxygen index (LOI) measurements and UL-94 tests. The thermal analysis revealed that the char yield of IFR-PLA and PLA-FR blend above 400 °C was greatly enhanced compared to that of pure PLA. The LOI value was significantly improved from 19 for pure PLA to 29 when 1 wt% of phosphorus content was introduced and all IFR-PLA samples achieved V-0 rating in the UL-94 tests. PLA-FR blends had an LOI value of 25–26 and UL-94 V-2 rating at 20 wt% of IFR-PLA content. The tensile strength of all the FR PLA systems was ca. 60 MPa. The method used in this study provided a novel route to permanently flame retard PLA.

Effect of a phosphorus-containing flame retardant on the thermal properties and ease of ignition of poly(lactic acid)

An aryl polyphenylphosphonate, poly(9-oxa-10-(2,5-dihydro-xyphenyl) phospha-phenanthrene-10-oxide) phenylphosphonate (WLA-3), was used to prepare a flame-retardant poly(lactic acid) (PLA) by direct melt compounding. The thermal behaviour, burning behaviour and mechanical properties of the flame-retardant PLA systems have been investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), vertical burning test (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT) and tensile test. The flame retardance mechanism has been studied via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and P content analysis. The UL-94 ratings of PLA’s containing 7phr (W 7P) and 10phr (W 10P) of WLA-3 were enhanced to V-0 from no rating for neat PLA. However, the cone calorimetry of flame-retardant PLA (W 7P) only showed a little decrease in heat release rate (HRR), peak of heat release rate (PHRR) and total heat release (THR) compared to neat PLA. TGA results showed that the PLA containing different amounts of WLA-3 presented more complicated thermal decomposition behaviours than neat PLA. Additionally, the results from DSC and tensile tests showed that the addition of WLA-3 into PLA had a slight impact on the crystallization behaviours and tensile properties.