Enhanced Char Formation Research Articles

Functionalized LDH via intercalation of gluconate anion and surface assembly of ultrafine copper hydroxide for improving mechanical properties and the fire safety of epoxy resin

To impart epoxy resin (EP) with outstanding mechanical properties and fire safety, LDH was systematically functionalized through gluconate anion (GA) intercalation followed by surface assembly of ultrafine Cu(OH)2, resulting in the LDH-GA@Cu(OH)2 hybrid. Comprehensive characterizations confirmed the successful synthesis of the desired product, with a uniform distribution of ultrafine Cu(OH)2 nanoparticles on the GA-intercalated LDH surface. The findings revealed that LDH-GA@Cu(OH)2 improved the mechanical properties of EP due to the increased LDH layer spacing, facilitating EP chain insertion, and the hydrogen bonding between the –OH of GA and the EP matrix. Fire retardancy tests indicated that the EP composite containing 7.5 wt% LDH-GA@Cu(OH)2 achieved a limiting oxygen index (LOI) of 30.1%. Furthermore, compared to pure EP, the composite demonstrated significant reductions in the peak heat release rate (PHRR) and peak CO production rate (PCOP) by 47.4% and 60.5%, respectively, underscoring its superior flame-retardant and toxic smoke suppression capabilities. Mechanistic studies further indicated that ultrafine Cu(OH)2 enhanced char formation through catalytic charring at the interface, which promoted compact and cohesive char layers. Overall, this work proposes a promising functionalization strategy for LDH to endow EP with excellent comprehensive performance.

Cellulose pyrolysis via liquid metal catalysis

Liquid metals are largely unexplored as catalytic media for biomass conversion. Unlike conventional solid-state catalysts which are prone to deactivation, liquid metals, i.e., low-melting metals operated above their melting point, can show resilience against coking, high thermal conductivity, and enhanced liquid-solid contact between catalyst and biomass feedstocks. This promise motivated the present investigation of liquid metals as catalysts for cellulose pyrolysis. Bismuth, tin, and indium were selected as liquid metal candidates, and their impact on cellulose devolatilization kinetics is studied via thermogravimetric analysis. The results indicate that all three metals show catalytic activity, with bismuth catalyzing volatiles formation, while indium and tin enhance char formation. Quantitative analysis of liquid product reveals that bismuth is selective to dehydration and functional rearrangement reactions, leading to anhydro sugars and functionalized furans formation. In contrast, indium and tin are selective towards dehydration, fragmentation reactions, and Diels Alder chemistry, leading to formation of C2-C4 fragments and aromatic compounds, as further confirmed via infrared spectroscopic analysis of the obtained chars. Finally, the Sn and Bi liquid metals’ stability against deactivation via coking is examined against conventional solid-state zeolite catalyst through multiple cellulose pyrolysis runs in the thermogravimetric analyzer (TGA) with the same batch of catalyst. While ZSM-5 zeolite catalyst's activity and selectivity declined and approached non-catalytic sand results (both the TGA curve and the liquid product distribution) within the first few runs, both Sn and Bi fairly maintained their robustness against coking for the conducted durability runs. Overall, the results show significant promise for this new class of catalysts for biomass pyrolysis.

Synergistic effect of phytic acid and eggshell bio-fillers on the dual-phase fire-retardancy of intumescent coatings applied on cellulosic substrates

Cellulosic substrates, including wood and thatch, have become icons for sustainable architecture and construction, however, they suffer from high flammability because of their inherent cellulosic composition. Current control measures for such hazards include applying intumescent fire-retardant (IFR) coatings that swell and form a char layer upon ignition, protecting the underlying substrate from burning. Typically, conventional IFR coatings are opaque and are made of halogenated compounds that release toxic fumes when ignited, compromising the roofing's aesthetic value and sustainability. In this work, phytic acid, a naturally occurring phosphorus source extracted from rice bran, was used to synthesize phytic acid-based fire-retardants (PFR) via esterification under reflux, along with powdered chicken eggshells (CES) as calcium carbonate (CaCO3) bio-filler. These components were incorporated into melamine formaldehyde resin to produce the transparent IFR coating. It was revealed that the developed IFR coatings achieved the highest fire protection rating based on UL94 flammability standards compared to the control. The coatings also yielded increased LOI values, indicative of self-extinguishing properties. A 17 °C elevation of the IFR coating's melting temperature and a significant ∼172% increase in enthalpy change from the control were observed, indicating enhanced fire-retardancy. The thermal stability of the coatings was improved, denoted by reduced mass losses, and increased residual masses after thermal degradation. As validated by microscopy and spectroscopy, the abundance of phosphorus and carbon groups in the coatings' condensed phase after combustion indicates enhanced char formation. In the gas phase, TG-FTIR showed the evolution of non-flammable CO2, and fire-retardant PO and P–O–C. Mechanical property testing confirmed no reduction in the adhesion strength of the IFR coating. With these results, the developed IFR coating exhibited enhanced fire-retardancy whilst remaining optically transparent, suggestive of a dual-phase IFR protective mechanism involving the release of gaseous combustion diluents and the formation of a thermally insulating char layer.

Enhancing char formation of flame retardant epoxy composites: Onigiri-like ZIF-67 modification with carboxymethyl β-cyclodextrin crosslinking

To enhance char formation of flame retardant epoxy (EP) composites, carboxymethyl β-cyclodextrin (CM-β-CD) is employed as an etchant for or ZIF-67 derivatives. In the early stage, etching plays a dominant role. The mismatch in size between CM-β-CD opening and ZIF-67 pore leads to the stacking of carboxyl cobalt complexes on the shell. When the reaction time is prolonged, crosslinking occurs between carboxyl and hydroxyl groups. Crosslinked CM-β-CD weakens and eventually stops the etching process. Triethyl phosphate (TEP), an additive to improve flame retardancy, is also absorbed on the shell in this one-pot synthesis. Herin, the synthesis of metal-organic framework (MOF) derivatives can impart multiple functions to MOF. This novel nanohybrid significantly improved flame retardancy of EP composites with only 2.0 wt% loading. The peak heat release rate (pHRR) and total smoke production (TSP) were reduced by 54.8 and 46.9%, respectively. The integrated multi-element system resulted in an expanded and reinforced char layer. This study proposes a simple and precise method for controlling the structure of MOF-carbohydrate hybrids through competition between chemical reactions.

Enhancing flame retardant and wrinkle-resistant performances of silk fabric with bio-based Maillard reaction products between glucose and poly(glutamic acid)

Bio-based materials have garnered considerable attention in the flame retardant field due to their inherent safety and environmental benefits. This study introduces a novel and eco-friendly flame retardant prepared through the Maillard reaction between glucose and poly(glutamic acid) for treating silk fabric. The study elucidates the synthesis of Maillard reaction products (MRPs) and verifies their deposition onto the silk fabric surface by observing changes in surface morphology, functional groups, and charged characteristics. The flammability tests demonstrate that MRPs treated silk fabrics had a high limiting oxygen index of over 27 % and a charred length of less than 12 cm, indicating effective flame retardancy. Moreover, the introduction of MRPs led to a significant decrease in smoke release when silk fabric underwent combustion. This observation can be attributed to the enhanced char formation and increased thermal degradation temperature of MRPs treated silk fabric. The electrostatic interaction between silk fiber and MRPs contributed to the fabric's resistance to repeated washing. Moreover, MRPs treated silk fabric retained their tensile properties and showed enhanced wrinkle-resistant performance. Generally, this research opens up a new path for the green preparation of halogen-free and phosphorus-free flame retardant protein fibers.

Solvent-Free Preparation of Thermally Stable Poly(urethane-imide) Elastomers

Polyurethanes (PUs) are widely used in many applications due to their versatile chemical and physical properties. To meet the increasing demands on PU with respect to intrinsic mechanical and thermal properties, they can be modified with thermally stable aromatic imide structures to form poly(urethane imide) (PUI). However, the preparation of PUI materials has been limited by the need for strong polar solvents, which hinder their industrial scale development. In this work, we prepared imide-containing isocyanate-terminated prepolymers via the reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic dianhydride in completely solvent-free conditions. The subsequent PUI elastomers made from these prepolymers exhibited enhanced char formation and stiffness in comparison to the reference elastomers without imide structures, among which the aromatic PUI elastomer shows improved flame retardancy according to the initial cone calorimetry measurement. This work demonstrates the potential use of imide prepolymers in other PU applications where high thermal stability and flame retardancy are required. The solvent-free synthesis also paves a way for the large-scale production of PUI materials.

The effect of phosphorus based flame retardants on the thermal and fire retardant properties of chicken feather/thermoplastic polyurethane composites

The aim of the study was to enhance the flame-retardant properties of chicken feather (CF) reinforced thermoplastic polyurethane (TPU) composites by incorporating three different phosphorus-based flame retardants, namely aluminum hypophosphite (AHP), ammonium polyphosphate (APP), and aluminum diethyl phosphinate (AlPi), at concentrations of 5, 10, and 20 wt%. The effectiveness of the additives was evaluated through various tests, including limiting oxygen index (LOI), vertical burning test (UL 94 V), thermogravimetric analysis (TGA), and mass loss calorimeter test (MLC). The results indicated that all three additives exhibited flame retardant properties in both the condensed and gas phases, but APP and AHP performed better than AlPi due to their enhanced char formation capabilities. The flame retardant effectiveness of the additives decreased in the order of APP > AHP > AlPi.

Bio-Based Flame-Retardant Coatings Based on the Synergistic Combination of Tannic Acid and Phytic Acid for Nylon-Cotton Blends.

Natural and synthetic polymeric fibers are used extensively in making fabrics for a variety of civilian and military applications. Due to the durability and comfort, nyco, a 50-50% blend of nylon 66 and cotton, is used as the material of choice in many applications including military uniforms. This fabric is flammable due to the presence of cotton and nylon but has good mechanical properties and is comfortable to wear. Here, we report a novel surface functionalization method that utilizes a synergistic combination of bio-based materials, tannic acid (TA) and phytic acid (PA), to impart flame-retardant (FR) properties to the nyco fabric. TA and PA were sequentially attached to nylon and cotton fibers through hydrogen bonding interactions and phosphorylation, respectively. The surface functionalization of the treated fabrics was confirmed using Fourier-transform infrared spectroscopy. Thermogravimetric analysis, microscale combustion calorimetry, cone calorimetry, and vertical flame testing were employed to study the effect of the functionalization on the thermal stability and flammability of the nyco fabric. Though reasonable durable functionalization is observed from elemental analysis, it is not enough to impart wash-durable FR treatment. These results indicate that flame retardancy is enabled through the enhanced char formation provided by the combination of TA and PA. The TA-PA system applied to nyco shows great promise as a bio-based FR system. This study for the first time also provides evidence for the selectivity of TA in imparting FR characteristics for nylon and PA in imparting FR properties for cotton. The combination of TA and PA provides promising FR characteristics to nyco.

Understanding enhanced char formation in the thermal decomposition of PVC resin: Role of intermolecular chlorine loss

Owing to the importance of controlling the decomposition products of plastic pyrolysis, in this study the mechanisms of char formation in the thermal decomposition of PVC were investigated quantitatively using a kinetic approach. Thermal decomposition behavior of pure PVC, PE, PP, and mixtures of PVC + NiO and PVC + TiO2 powders was probed using a thermogravimetry-differential scanning calorimetry analyzer under an Ar atmosphere from room temperature to 1073 K. Morphological and structural analyses of solid residues were conducted using X-ray diffraction, scanning electron microscopy-energy dispersive spectrometry and Raman spectroscopy. Chlorine was removed from PVC up to 673 K with an activation energy of 104.7 kJ/mol, resulting in 38 % mass of solid residue polyene. When temperature was further increased, the decomposition of polyene occurred almost in the same temperature range of PE and PP decomposition, leading to the final solid residue at 1073 K of 11 %, nil and 1 % for PVC, PE and PP respectively. Central to our examination, two competing routes of chlorine loss in the pyrolysis of PVC (involving intramolecular and intermolecular intermediates respectively) were compared, with respect to their contributions towards char formation. By juxtaposing the pyrolysis behavior of PVC against those of PE and PP, it was deduced that chlorine loss through intermolecular intermediates contributed overwhelmingly to char precursor formation. Theoretical calculations revealed around 35 % of PVC subject to pyrolysis underwent chlorine loss via intermolecular intermediates. This theoretically derived proportionality is in good agreement with experimental results, which indicated a char yield of 28.6 % in the thermal decomposition of PVC. This char formation mechanism was further confirmed by the co-pyrolysis results of PVC with each of two transition metal oxides, i.e. chemically reactive NiO and inactive TiO2, showing that the intermolecular chlorine loss was enhanced in the presence of NiO due to the formation of NiCl2, whereas no obvious change in char yield was observed in case of TiO2 because no chlorination of TiO2 was detected. This combination of experimental and theoretical considerations unanimously verifies that intermolecular mechanisms of chlorine loss in the pyrolysis of PVC play a leading role to the formation of net structures giving rise to char. These findings allude to the possibility of manipulating the decomposition products such as to synthesize net structured carbon based materials through the pyrolysis of waste plastics.

A Bio-derived Char Forming Flame Retardant Additive for Nylon 6 Based on Crosslinked Tannic Acid

Nylon is one of the most important engineering polymers used in textile, electronics, and automotive applications. In addition to good mechanical properties, flame retardancy is desirable in these applications. Nylon is typically processed at high temperatures and very few non-toxic synthetic flame-retardant (FR) additives are stable at these temperatures. Tannic acid (TA) - a naturally occurring polyphenol, has low heat release capacity (HRC) and good char forming capabilities but is not thermally stable and starts to degrade at the processing temperature of thermoplastics such as Nylon. Here we report the use of chemically modified TA (TAT) as a more stable char forming FR additive for Nylon. Upon thermal degradation, Nylon 6 blends containing 15 wt% TAT exhibit consistently lower peak heat release rate (pHRR) (52% reduction) and HRC (36% reduction) combined with enhanced char yield (about 9%). Evolved gas analysis through TGA-FTIR reveals that, in the presence of TAT, some of the primary amide/amine and secondary amide species in Nylon 6 degrade into less flammable moieties like ammonia while aromatic moieties in TAT enhance char formation in the condensed phase, thus reducing flammability. In the lab-scale flame tests, Nylon 6 blends containing 15 wt% TAT exhibited reduced afterflame time and self-extinguishing behavior. The oxygen index of the Nylon 6 - TAT blends also increased from 22% to 25%. This research opens new possibilities for modifying natural polyphenols to create melt-processable FR additives that can enhance char formation and lower HRC of Nylon.

Organophosphorus-hydrazides as potential reactive flame retardants for epoxy

For structural composites used in vehicles and aircraft, flame retardant chemistries which enhance char formation and reduce heat release are preferred. Phosphorus-based and phosphorus–nitrogen flame retardants for epoxies have been well studied to date, but phosphorus hydrazides have not been studied for their flame-retardant potential in epoxy. These hydrazides offer some novel structures and they can potentially offer a combination of vapor and condensed phase flame retardant action. A series of eight compounds were systematically investigated in this study as reactive flame retardants in a bisphenol F epoxy/aliphatic amine resin system at a level of 2.5 wt% phosphorus. Results suggest that the phosphorus hydrazides react with the epoxy during thermal decomposition, and they also release nitrogen during flaming combustion of the epoxy matrix. The observed reactions resulted in increased char yields and reduced total heat release, while simultaneously lowering heat of combustion and total smoke release.

Surface grafting of sepiolite with a phosphaphenanthrene derivative and its flame-retardant mechanism on PLA nanocomposites

Poly (lactic acid) (PLA), which is one of the most widely used biodegradable polymers, needs to be rendered flame retardant for use in textiles, automobiles, and electronics. Few environmentally friendly flame-retardant solutions exist for PLA mainly because of the nature of the additives (large amount introduced or the use of non-biodegradable organic additives). In this regard, natural sepiolite (SEP) is a known flame retardant for PLA mainly due to high loading (at least 25 wt %). In this study, SEP was surface-modified by grafting with 9, 10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) via the condensation between amino groups and salicylaldehyde with a grafting ratio of approximately 12.8%. DOPO-modified sepiolite (SEP-DOPO) was then introduced to PLA to improve the fire performance of the nanocomposites. PLA containing 10 wt % SEP-DOPO showed improved dispersion compared to a mixture of 10 wt % DOPO/SEP in a PLA matrix. Moreover, the peak of the heat release rate (pHRR) measured using mass loss calorimeter reduced by 40.7% for a loading of 10 wt % SEP-DOPO. The synergetic effect between DOPO and sepiolite was evaluated. The TGA-FTIR result showed that un-grafted DOPO was degraded before the polymer matrix, which cannot enhance the flame retardancy of the PLA composite. The solid-state nuclear magnetic resonance (NMR) spectra of the charred residues confirmed that the formed SiOSi, H3PO3, and PN crosslinking structure enhanced char formation in the condensed phase.

A novel bio-based flame retardant for polypropylene from phytic acid

Phytic acid mainly exists in seeds, roots and stems of plants, which has a potential value in flame-retarding polymers due to the high content of phosphorus. In this work, a novel bio-based phytic acid salt PHYPI was prepared through a salt formation reaction between phytic acid and piperazine. The structure of the bio-based PHYPI was verified using 1H NMR spectrascoppy. When PHYPI was used to fabricate flame-retardant polypropylene (PP), it showed high efficiency in combustion tests. The limiting oxygen index (LOI) value for PP containing 18.0 wt% PHYPI is 25.0%, showing a 38.9% increase compared to 18.0% for PP containing no additive. Moreover, it passed the UL-94 V-0 rating in the vertical burning test, superior to the no rating for pure PP. Obviously, the flame-retarding efficiency of PHYPI is higher than that of typical traditional intumescent flame retardant containing ammonium polyphosphate or pentaerythritol. Cone calorimeter test revealed that the heat release and smoke production of PP were efficiently restrained by the presence of PHYPI. The peak of heat release rate (PHRR), total heat release (THR), and the peak of smoke release rate (PSPR) for PP containing 20 wt% PHYPI were decreased by 65.6%, 13.5%, and 32.8%, respectively, compared to the same values for PP alone. Fourier transform infrared spectroscopy (FTIR) was used to investigate the changes which accompanied the thermal degradation of the polymer containing PHYPI. Changes in the infrared spectra for the polymer undergoing degradation indicate that structures containing C=C and P-N-C were formed as a consequence of the presence of PHYPI. These transformations enhanced char formation to provide condensed phase protective action. At the same time, non-combustion volatile gases such as water and carbon dioxide may be released to dilute the fuel load in the gas phase. All evidences illustrate that PHYPI is an effective flame retardant for PP.

The preparation of a bisphenol A epoxy resin based ammonium polyphosphate ester and its effect on the char formation of fire resistant transparent coating

This work reports the synthesis of an effective charring agent (ammonium polyphosphate ester (BAPPE)) and its application in preparing intumescent transparent fire resistive coatings. Bisphenol A epoxy resin reacted with diethanol amine to produce a waterborne epoxy resin (WEP), and then WEP was further reacted with orthophosphoric acid (PA) and urea (U) to obtain BAPPE. The chemical structure of BAPPE was confirmed by FT-IR and 1H NMR. Transparent fire resistive coating containing BAPPE and melamine urea formaldehyde (MUF) resin was prepared. The thermal gravimetric analysis showed that BAPPE could enhance char formation of the coating in the temperature range of 320–800 ℃. The flammability evaluation by simulated big panel method, smoke density test, and cone calorimeter (CONE) indicated that the presence of BAPPE significantly increased the fire resistant time, suppressed the smoke release amount, and remarkably reduced the peak heat release rate (pHRR) to 6.6 kW/m2. It was proved BAPPE could act as a three sources integrated reactive flame retardant in transparent coating. It is proposed that BAPPE can form cross-linking networks with MUF, thus enhancing the char formation upon heating and improving the fire resistance of the coating.

Eco-friendly Flame-Retardant Cellulose Nanofibril Aerogels by Incorporating Sodium Bicarbonate.

Cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties, but high flammability restricts their application. In this study, CNF aerogels were prepared by incorporating sodium bicarbonate (SBC), which effectively improved the fire retardancy without compromising the thermal conductivity of the aerogels, which was only 28 mW m–1 K–1. The minimum burning velocity of flame-retardant aerogels was 0.20 cm s–1 at 40 wt % of SBC, which is significantly lower compared to 5.84 cm s–1 of pure CNF aerogels. At the threshold concentration of 20 wt % SBC, the flame-retardant aerogel demonstrated flameless pyrolysis along with enhanced char formation. SBC additionally provides control over the microporosity and morphology, due to the concentration-dependent formation of lamellar layers during the preparation of aerogels. Overall, this work describes an efficient method for preparing flame-retardant CNF aerogels that could lay the foundation for next-generation bio-based insulation materials.

Fire resistant polyphenols based on chemical modification of bio-derived tannic acid

Utilization of renewable materials for the development of safer and nontoxic flame retardants has been of interest from environmental safety and sustainability perspective. Tannic acid (TA) is an abundantly available bio-based polyphenol that exhibits good intumescence and char forming characteristics upon being subjected to heat. Intumescence and char formation are important prerequisites for certain types of effective flame retardant (FR) additives. However, the potential for utilizing TA as an FR has been limited by its poor thermal stability. A single step chemical modification process that overcomes the limitations of TA while allowing the utilization of its beneficial properties is reported here. TA was crosslinked using interfacial polycondensation with terephthaloyl chloride to yield tannic acid terephthalate (TAT). The complex structure of TAT necessitated the synthesis of several model compounds based on methyl gallate (MG) to facilitate the complete structural characterization of TAT using FTIR and 1H NMR. TAT is thermally stable up to 230 °C (less than 3% weight loss) and shows 30% higher char yield and extremely low heat release capacity (<80 J/g-K) as compared to that for TA. Detailed thermal degradation studies combined with gas phase spectroscopy using thermogravimetric analysis - Fourier-transform infrared spectroscopy (TGA-FTIR) and pyrolysis - gas chromatography - mass spectrometry (Py-GC-MS) provide an understanding of the degradation process. Crosslinked phenolic species enhance char formation in the condensed phase and allow for utilization of these compounds as flame retardant coatings for polymers such as Nylon 66. TAT coating on Nylon 66 fabric significantly impedes flame propagation in the fabric, resulting in quick self-extinguishing behavior and reduced char length in vertical flame tests. Morphological characterization, thermo-oxidation studies and microscale combustion calorimetry (MCC) (at high heating rates) of TAT-coated fabric reveal the beneficial effects of char formation and its direct impact on flame retardancy.

Fire reaction properties of polystyrene-based nanocomposites using nanosilica and nanoclay as additives in cone calorimeter test

Using nanofiller additives in the polymer matrix to form nanocomposites is a potential way of reducing the flame spread and enhancing flame retardancy of polymeric materials during fire. To understand the fire reaction properties and the relative performance of flame-retardant additives in polymer during well-developed fire, neat polystyrene, polystyrene–silica and polystyrene–nanoclay (MMT) have been tested in a cone calorimeter. The neat polystyrene and the polystyrene nanocomposites have been prepared via an in situ polymerization method. An external heat flux of 50 kW m−2 was applied in the test, and parameters such as heat release rate, peak heat release rate, time to ignition, smoke toxicity, CO and CO2 yield have been investigated. Both neat polystyrene and polystyrene nanocomposites have shown the trend of a thermally thick charring polymer in the heat release rate over time data. The nanocomposites had an overall better flame retardancy than the neat polystyrene in terms of lower peak heat release rate, lower average mass loss rate and enhanced char formation. The nanocomposites had also reduced smoke emission with lower CO and CO2 yield compared to the neat polystyrene. The overall flame retardancy was enhanced as the nanofiller loading was increased for both the nanosilica and MMT nanocomposites.

Highly-efficient reinforcement and flame retardancy of rigid polyurethane foam with phosphorus-containing additive and nitrogen-containing compound

Flame retardant rigid polyurethane foam (RPUF) with a reactive melamine-derived polyol (MADP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were fabricated through free-rise technique. The thermal stability and fire behaviors of RPUF were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), and cone calorimeter. In comparison with the results of RPUF and RPUF/MADP, RPUF/MADP-DOPO displayed higher compressive strength, owing to the two stiff phenyl groups of DOPO. Moreover, with only 7.5 wt % MADP and 7.5 wt % DOPO loading, the MADP/DOPO system endowed RPUF with enhanced char formation, increased LOI value of 28.5% and reduced heat release. Scanning electron microscope (SEM) images, X-ray photoelectron spectroscopy (XPS) analysis and Raman spectra of the char residues suggested that the formation of compact, continuous char layer. The thermal degradation was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR) and chemical structure changes during the thermal degradation were monitored by real time Fourier transform infrared (RT-FTIR), these results demonstrated that the partial phosphorus from DOPO remained in the residual char, but the introduction of MADP significantly promoted generating more stable aromatic structure and enhanced the strength of the char layer formed. Furthermore, MADP facilitated the formation of more H2O and CO2 and diluted the flammable gases in gaseous phase. Based on the analysis, the introduction of MADP/DOPO can endowed excellent flame retardancy to RPUF depending on bi-phase flame-retardant mechanism.

Cone calorimeter analysis of flame retardant poly (methyl methacrylate)-silica nanocomposites

Nanocomposite is a promising method to reduce fire hazards of polymers. Specifically due to increased interfacial area between polymer and nanofillers, polymer nanocomposites have an advantage in reducing fire hazards efficiently even when the flame retardant additives are at a concentration of 5 mass% or less. In theory, crosslinking between the polymer chains can create a carbon-dense structure to enhance char formation, which can further promote the flame retardancy. However, little research has been done to explore the flammability of crosslinking polymer nanocomposites with a low concentration of nanosilica particles. In this study, crosslinked and non-crosslinked poly (methyl methacrylate) (PMMA) nanocomposites of a low concentration of nanosilica particles have been prepared via an in situ method. Their fire properties were tested by using the cone calorimeter at the heat flux of 50 kW m−2. Although silica-containing flame retardants tend to negatively affect the ignitability and soot production especially at a high concentration, through the condensed phase mechanism, the samples of high loading rate of nanosilica particles show better fire retardancy performance in the aspect of flammability, including decreased heat release rate, mass loss rate, and total heat release. Additionally, crosslinking indeed attributes to the less intensive combustion of crosslinked PMMA samples, especially at a low concentration of nanosilica. The combination of nanosilica particles with the modification of the internal structure of the polymer nanocomposites might be a good strategy to improve fire retardancy.

Flammability and thermal degradation of poly (lactic acid)/polycarbonate alloys containing a phosphazene derivative and trisilanollsobutyl POSS

Abstracts This work reports our recent efforts on improving the flame retardancy and thermal stability of biodegradable poly (lactic acid) (PLA) which is usually produced from corn and sugar beets. Hexa-(phosphaphenanthrene-methyl-(p-hydrobenzal)-amino-phenoxyl)-cyclotriphosphazene (HPHAPC) was synthesized by the classic Kabachnik-Fields reaction, and was then incorporated into PLA/polycarbonate (PC) alloys by melt blending. The flammability evaluation by limiting oxygen index (LOI), vertically burning (UL-94) and cone calorimeter tests has indicated that the LOI value can reach up to 31.5 and UL-94 grade can pass V-0 by the presence of only 3 wt% HPHAPC and 3 wt% polyhedral oligomeric silsesquioxane (POSS). The thermal behavior characterization by thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) shows that the char formation of PLA/PC alloys can be significantly enhanced by the presence of HPHAPC/POSS. The evolved gas of the alloys was analyzed by Fourier transform infrared spectroscopy-TGA (FTIR-TGA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Char morphology was observed by scanning electronic microscopy (SEM). It is demonstrated that HPHAPC can react with POSS during processing to form an intumescent char structure. It is proposed that the degradation products of HPHAPC/POSS can capture free radicals in the gas phase and enhance char formation in the condensed phase.