Intumescent Polypropylene Research Articles

Intumescent polypropylene in extreme fire conditions

The paper deals with intumescent polypropylene (PP) undergoing extreme fire (burn-through test with heat flux higher than 100 kW/m2). The purpose of this unusual approach is to explore the possibility to design intumescent plastic (here PP) resisting to burn-through test. A combination of commercial intumescent flame retardants (ammonium polyphosphate-based compounds containing a char former; AP766 (AP) and FlameOff (FO) of the companies Clariant and FlameOff Inc) with zinc borate (supplied by US Borax, ZB) or Kemgard (combination of ZB and molybdate supplied by Huber, KZ) was incorporated in PP. Use of ZB and KZ as synergists in FO formulations increases dramatically the time of piercing (formation of hole through the plaque of polymer at 80 s without ZB or KZ vs. 280 s with KZ) at the burn-through test (heat flux = 116 kW/m2, propane burner) while the combination with AP does not show any benefit. Analyses of the residues obtained at different times of combustion by solid state nuclear magnetic resonance (NMR) of 31P, 11B and 13C shows the formation of borophosphates creating a glass reinforcing the intumescent char: it acts as a ‘glue’ providing flexibility and cohesion to the char.

Intumescent polypropylene: Interactions between physical and chemical expansion

SummaryTo decrease the reaction to fire of a highly flammable plastic, polypropylene (PP), the concept of intumescence was applied. Two intumescent systems were designed on the basis of different mechanisms: physical expansion with expandable graphite (EG) and chemical expansion with modified ammonium polyphosphate (AP). Fire behavior of PP containing EG, AP, or an AP/EG mixture with a total loading of 10 wt% was evaluated by cone calorimetry at 35 kW·m−2. Thermocouples allowed measuring the temperature at the backside or inside samples over time and evaluating the thermal barrier of these intumescent materials. Two grades of AP (difference in composition) and several grades of EG (difference in expansion characteristics) were compared. Mixing AP and EG does not create a synergistic effect in studied conditions. Contrarily, the incorporation of small amount of EG in PP‐AP modifies heat transfer in the coating, creating a strong anisotropy. Graphite worms are trapped vertically into the expanded AP, which increases the transverse heat conductivity (lower efficiency of the thermal barrier) and decreases the fire performance. This phenomenon disappears in thicker specimens. While a higher expansion volume of graphite worms improves fire performances of PP with only small amount of EG (1 wt%), this effect is not noticeable with AP/EG mixtures.

Synergistic improvement of fire retardancy and mechanical properties of ferrocene‐based polymer in intumescent polypropylene composite

The ferrocene‐based polymer (PDPFDE) accompanied with traditional intumescent flame retardant (IFR) system (ammonium polyphosphate (APP)/pentaerythritol (PER) = 3/1, mass ratio) has been used as additive flame retardant in polypropylene (PP), aiming to lower the total loading amount. The thermal stability and fire retardant properties were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical combustion (UL‐94), and cone calorimetry (CONE). The fire retardant mechanism was studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The results showed that the PP1 with 25 wt% IFR only passed the UL‐94 V‐1 rating, but the PP6 loaded by 0.5 wt% PDPFDE and 22.5 wt% IFR possessed an LOI value of 28.5% and passed the UL‐94 V‐0 rating; the peak heat release rate (pHRR) and total heat release (THR) are decreased by 63% and 43%, respectively, compared with pure PP. In addition, the char residue of PP6 manifested a very compact and smooth surface, indicating a more effective barrier layer. Meanwhile, it was interesting that the addition of PDPFDE evidently improved the impact strength and elongation at break of PP/IFR composites.

The effects of POSS particles on the flame retardancy of intumescent polypropylene composites and the structure-property relationship

In the current study, the effects of four different POSS nanoparticles on the flame retardant properties of intumescent PP were investigated through mass-loss calorimetry (MLC), limiting oxygen index (LOI) test and UL-94 ratings. In addition, the structure-property relationship was enlightened via thermal, morphological and mechanical tests. The four different POSS types, namely aminopropyl isobutyl-POSS (A-POSS), octaphenyl-POSS (OP-POSS), octaammonium-POSS (OA-POSS) and trissulfonic acid propyl-POSS (TS-POSS), were used. The ratio of ammonium polyphosphate (APP) to pentaerythritol (PER) was kept constant and the POSS content was varied as 0.5%, 1% and 3%. The MLC, LOI and UL-94 tests revealed that the addition of POSS particles had adjuvant on the flame retardant properties of PP/IFR system. All POSS nanoparticles showed their highest adjuvant effect at the lowest concentration of 0.5 wt%. The highest UL-94 rating and the highest LOI values were achieved in the presence of OA-POSS and TS-POSS. The ceramic layer formation was monitored using scanning electron microscopy (SEM) and FTIR on the char residues. The thermal properties of PP/IFR/POSS composites were obtained via differential scanning calorimeter and thermo-gravimetric analysis. The inline melt flow properties were observed via vertical force measurements. The fracture morphology was investigated using SEM. Mechanical tests showed that the yield strengths of the composites were lower than that of pristine PP; in contrast, the elongation at break and the impact strength of composites enhanced in A-POSS and TS-POSS based composites.

Effect of carbon fiber amount and length on flame retardant and mechanical properties of intumescent polypropylene composites

The effects of carbon fiber amount and length were studied on the flame retardant, thermal, and mechanical properties of the intumescent polypropylene composites. The flame retardant properties of the intumescent polypropylene-based composites were investigated using limiting oxygen index, vertical burning test (UL-94), and mass loss calorimeter. The mechanical properties of the composites were studied using tensile test and dynamic mechanical analysis. According to the flammability tests results, the antagonistic interaction was observed between carbon fiber and ammonium polyphosphate. The limiting oxygen index value reduced steadily as the added amount of carbon fiber increased. Mechanical test results revealed that the addition of carbon fiber increased the tensile strength and the elastic modulus as the added amount increased. No effect of carbon fiber length was observed on the flammability, fire performance, and tensile properties of composites, whereas the elastic modulus increased as the carbon fiber initial length increased.

Dual Fire Retardant Action: The Combined Gas and Condensed Phase Effects of Azo-Modified NiZnAl Layered Double Hydroxide on Intumescent Polypropylene

A ternary nickel-substituted layered double hydroxide, ZnNiAl-CO3 LDH (C-LDH), was synthesized. It was intercalated with azobenzene-4,4′-dicarboxylic acid using an ion exchange method to obtain organically modified NiZnAl LDH (O-LDH). Both LDHs were melt-blended into polypropylene (PP) with an intumescent fire retardant (IFR). The structure, morphology, thermal stability, and combustible properties of intercalated LDH and its hybrid composite have been comprehensively characterized. Scanning electron microscopy and energy-dispersive X-ray mapping showed that O-LDH exhibits better dispersion than C-LDH. Cone calorimetry showed that the addition of IFR and LDH significantly reduces the smoke and heat release rates. The composite with 1 wt % O-LDH, which showed dual gas-phase and condensed-phase fire retardant action, exhibited the lowest flammability with an limiting oxygen index value of 29.3% and achieved a UL-94 V-0 rating. In addition, incorporation of LDH improved the mechanical properties compared wit...

Mechanism of enhancement of intumescent fire retardancy by metal acetates in polypropylene

The effects of cobalt acetate (CoAc), manganese acetate (MnAc), nickel acetate (NiAc) and zinc acetate (ZnAc) as fire retardant additive in intumescent polypropylene (PP) formulations containing PP/ammonium polyphosphate (APP)/pentaerythritol (PER) are reported. The limiting oxygen index (LOI) and vertical burning (UL94) tests and cone calorimetry were used to quantify the enhancement. Environmental chamber rheometry, thermal gravimetric analysis and the morphology of the residual char were used to investigate the mechanism of enhancement. The incorporation of small quantities of metal acetates had a significant influence on the fire behaviour. As an example, 0.7 wt% MnAc improved the UL 94 rating of PP/APP + PER (mass ratio 100/25, with APP/PER = 3/1) sample from V-2 to V-0, while 1 wt% MnAc reduced the peak heat release rate and the total heat release by 18% and 12% in the cone calorimeter. Rheological data, cone calorimetry, and photographs of the residual char showed how the fire retardancy of the systems were affected by the melt viscosity, which depended on the loading of metal acetate. During thermal decomposition, the metal acetates promote the crosslinking of the polymer and the fire retardant, reinforcing the protective intumescent layer. While, the effect is most potent at the optimal metal loadings. At higher MnAc loadings, the benefit of a stronger char is overwhelmed by the adverse effect of crosslinking on the transition char layer. Thus, this paper offers a new insight into the mechanism of the intumescent fire retarded PP system.

A new approach designed for improving flame retardancy of intumescent polypropylene via continuous extrusion with supercritical CO2

scCO2-aided IFR dispersion of PP/IFR composites and their improved flame retardancy.

A comprehensive study of the synergistic flame retardant mechanisms of halloysite in intumescent polypropylene

This work aims to evaluate the efficiency of halloysite as synergistic agent in an intumescent PP system based on a coated ammonium polyphosphate (IFR). The first part of the study analyses the thermal stability and fire performance of PP when using the intumescent formulation alone or in combination with the aluminosilicate nanotubes (HNTs). Cone calorimetry reveals that partial substitution of IFR by HNTs (3 wt.%) imparts substantial improvement in flame retardancy with reduced heat release rate and longer burning times. Additionally, a shift from V-1 to V-0 classification is achieved at the UL-94 test with only 1.5 wt.% HNTs. The second part provides a better understanding of the physical and chemical mechanisms of action of HNTs in the intumescent systems. The chemical evolution of the condensed phase during combustion is described by solid state NMR, and in particular using 2D NMR. Results indicate that halloysite speeds up the development of the intumescent shield, but also enhances its mechanical properties by physical reinforcement (i.e. aluminosilicate “skeleton-frame” for the phospho-carbonaceous structure) and/or by chemical interactions with IFR yielding to aluminophosphates. These new chemical species allow thermal stabilization of the char at high temperatures and provide good macro- and micro-structural properties. Both effects increase the mechanical strength of the protective layer during burning ensuring excellent heat and mass transfer limitations between gas and condensed phases.

Synergistic Effect of Organic Vermiculite on the Flame Retardancy and Thermal Stability of Intumescent Polypropylene Composites

Organic vermiculite (OVMT) prepared from vermiculite (VMT), with high aspect ratio and orderly arranged platelets intercalated by octadecyl trimethyl ammonum bromide (OTAB), was used as a synergistic agent on the flame retardancy of a polypropylene/intumescent flame retardant (PP/IFR) system. The flammability and thermal stability of PP/IFR/OVMT composites were investigated by limiting oxygen index (LOI), UL-94 testing, cone calorimetry tests, and thermogravometric analysis. The results of LOI and UL-94 testing showed that low loading of OVMT improved the flame retardancy and retarded dripping for PP/IFR composites. OVMT, with 1% loading, increased the char residue of PP/IFR composites and could act as an effective additive for improvement in flame retardancy, which was confirmed by the cone data. The char layer morphological structures observed by scanning electron microscopy (SEM) showed that OVMT with 1% loading can promote formation of a continuous and compact intumescent char layer. Raman spectroscopy results indicated that the OVMT or its pyrolytic products led to a decrease in size of the carbonaceous micro-domain during combustion, resulting in formation of more compact charred layers. Thus, OVMT with 1% loading showed a synergistic effect with IFR in the combustion of the PP/IFR composites.

Intumescent flame‐retarded building parts manufactured from polyolefines as well as from composites of polyolefines and bismaleinimides

AbstractCommercial intumescent flame retardants and intumescent compounds were tested as flame retardants for polypropylene. Their routes of decomposition were followed up by thermal gravimetric analysis, differential scanning calorimetry as well as thermal mechanic analysis and described by chemical formula, balances of weight, and heats of formation. These investigations showed that the combination of ammonium polyphosphate, polyols, and melamine exerted intumescence at 400°C and melamine was no blowing agent but reacted to melamine polyphosphate. Further they made clear that bisethylenediamine phosphate exerted intumescence at 350°C and degraded to piperazine phosphate. Intumescent flame‐retarded building parts exemplified the advantage of intumescent flame retardance by the time delay until they still fulfilled their function. F15 classification was achieved for thick walled intumescent polypropylene pipes and thin walled electrical boxes consisting of a flame‐retarded glass reinforced bismaleinimide core and an intumescent polyolefine shell in furnace fire tests. The difference in temperatures inside and outside of the building parts was calculated and compared with measurements in fire tests. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synergistic effect of boron containing substances on flame retardancy and thermal stability of clay containing intumescent polypropylene nanoclay composites

AbstractThe functions of nanoclay and three different boron containing substances, zinc borate (ZnB), borophosphate (BPO4), and boron silicon containing preceramic oligomer (BSi), were studied to improve the flame retardancy of polypropylene (PP)‐nanoclay‐intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated using limiting oxygen index (LOI), UL‐94 standard, thermogravimetric analysis (TGA), and cone calorimeter.According to the results obtained, the addition of 20 wt% intumescent flame retardant (IFR) improved the flame retardancy by increasing the char formation. Addition of clay slightly increases the LOI value and reduces the maximum heat release rate (HRR). Addition of clay also increases the barrier effect due to intumescent char, especially in thin samples. Boron compounds show their highest synergistic effect at about 3 wt% loading. According to UL‐94 test and LOI test, 3 wt% ZnB containing composite shows the highest rating (V0) and BPO4 containing sample shows the highest LOI value (26.5). Copyright © 2010 John Wiley & Sons, Ltd.

Effects of Aluminum Oxide on Combustion Behavior of Intumescent Fire-Retarded Polypropylene Composites

The melamine phosphate (MP) was synthesized from melamine and phosphate acid. Aluminum oxide (Al2O3) was added into the MP during its synthesis. Fourier transform infrared spectroscopy (FTIR) was used to characterize the reaction products. The composites were prepared from polypropylene (PP) and intumescent flame retardant (IFR) additives of MP and pentaerythritol (PER). The effect of Al2O3 content on the properties of the composites was investigated by the limiting oxygen index (LOI), thermogravimetry (TG) and scanning electron microscopy (SEM). The results indicated that the LOI value of the composites could be enhanced obviously with suitable content of Al2O3. When the Al2O3 content was 6 wt% in MP, the LOI value increased to 35.5% from 31.0% for the composite without Al2O3, the amount of residual char at 600°C increased from 8.9 wt% to 13.9 wt%.

Simulated Effects of Physical Parameters on Heat Transfer of Intumescent Fire-Retardant Polypropylene during Burning

Physical properties of intumescent materials are important parameters as input data in modeling the combustion behavior of intumescent materials in a fire. In this paper, effects of important physical properties on heat transfer of intumescent materials during burning are simulated based on a combustion model of intumescent fire-retardant polypropylene (IFR-PP) materials. Physical properties selected are thermal conductivity of virgin material and char layer, specific heat capacity of virgin material, density of virgin material, surface emissivity of virgin material and char layer, and intumescent temperature. Predicted temperature curves at a location 9 mm from the bottom of the IFR-PP material at an incident heat flux of 50 kW/m2 are shown for the varied physical parameters values. The results show that these varied parameter values can affect the heat transfer of materials remarkably.

Fire retardant properties of intumescent polypropylene composites filled with calcium carbonate

AbstractThis study was aimed to investigate the influence of calcium carbonate (CaCO3), a widely used filler, on the fire retardancy of intumescent polypropylene composites. Two intumescent systems based on (1) mixture of ammonium polyphosphate (APP) and pentaerythritol and (2) surface‐modified APP (m‐APP) were examined. In terms of steady heat release rate, total heat evolved, and fire growth index determined by mass loss calorimetry, m‐APP performed markedly superior to APP‐pentaerythritol. The presence of CaCO3 in both intumescent formulations caused significant losses in fire retardant performance assessed by mass loss calorimetry, limiting oxygen index and UL‐94 tests. Peak rates of heat release and mass loss during combustion, and total heat evolved on combustion were increased, whereas time to ignition was decreased. Characterization of fire residues ascribed the mechanism of deterioration in fire retardancy to the formation of porous and nonexpanded crystalline calcium phosphate/CaCO3 residues during combustion rather than the amorphous protective intumescent chars formed in the absence of CaCO3. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

San Antonio Statement on Brominated and Chlorinated Flame Retardants

We, scientists from a variety of disciplines, declare the following: Parties to the Stockholm Convention have taken action on three brominated flame retardants that have been listed in the treaty for global elimination. These substances include components of commercial penta-bromodiphenyl ether and commercial octa-bromodiphenyl ether, along with hexabromobiphenyl. Another brominated flame retardant, hexabromocyclododecane, is under evaluation. Many commonly used brominated and chlorinated flame retardants can undergo long-range environmental transport. Many brominated and chlorinated flame retardants appear to be persistent and bioaccumulative, resulting in food chain contamination, including human milk. Many brominated and chlorinated flame retardants lack adequate toxicity information, but the available data raises concerns. Many different types of brominated and chlorinated flame retardants have been incorporated into products even though comprehensive toxicological information is lacking. Brominated and chlorinated flame retardants present in a variety of products are released to the indoor and outdoor environments. Near-end-of-life and end-of-life electrical and electronic products are a growing concern as a result of dumping in developing countries, which results in the illegal transboundary movement of their hazardous constituents. These include brominated and chlorinated flame retardants. There is a lack of capacity to handle electronic waste in an environ-mentally sound manner in almost all developing countries and countries with economies in transition, leading to the release of hazardous substances that cause harm to human health and the environment. These substances include brominated and chlorinated flame retardants. Brominated and chlorinated flame retardants can increase fire toxicity, but their overall benefit in improving fire safety has not been proven. When brominated and chlorinated flame retardants burn, highly toxic dioxins and furans are formed. Therefore, these data support the following: Brominated and chlorinated flame retardants as classes of substances are a concern for persistence, bioaccumulation, long-range transport, and toxicity. There is a need to improve the availability of and access to information on brominated and chlorinated flame retardants and other chemicals in products in the supply chain and throughout each product’s life cycle. Consumers can play a role in the adoption of alternatives to harmful flame retardants if they are made aware of the presence of the substances, for example, through product labeling. The process of identifying alternatives to flame retardants should include not only alternative chemicals but also innovative changes in the design of products, industrial processes, and other practices that do not require the use of any flame retardant. Efforts should be made to ensure that current and alternative chemical flame retardants do not have hazardous properties, such as mutagenicity and carcinogenicity, or adverse effects on the reproductive, developmental, endocrine, immune, or nervous systems. When seeking exemptions for certain applications of flame retardants, the party requesting the exemption should supply some information indicating why the exemption is technically or scien-tifically necessary and why potential alternatives are not technically or scientifically viable; a description of potential alternative processes, products, materials, or systems that eliminate the need for the chemical; and a list of sources researched. Wastes containing flame retardants with persistent organic pollutant (POP) characteristics, including products and articles, should be disposed of in such a way that the POP content is destroyed or irreversibly transformed so that they do not exhibit the charac-teristics of POPs. Flame retardants with POP characteristics should not be permitted to be subjected to disposal operations that may lead to recovery, recycling, reclamation, direct reuse, or alternative uses of the substances. Wastes containing flame retardants with POP properties should not be transported across international boundaries unless it is for disposal in such a way that the POP content is destroyed or irreversibly transformed. It is important to consider product stewardship and extended producer responsibility aspects in the life-cycle management of products containing flame retardants with POP properties, including electronic and electrical products.

Synergistic effect of boron containing substances on flame retardancy and thermal stability of intumescent polypropylene composites

The synergistic effect of four different boron containing substances, zinc borate (ZnB), borophosphate (BPO 4), boron silicon containing preceramic oligomer (BSi) and lanthanum borate (LaB), were studied to improve the flame retardancy of a polypropylene (PP) intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated by limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis (TGA) and cone calorimeter tests. The addition of 20 wt% intumescent flame retardant (IFR) improves the flame retardancy by increasing the char formation. According to LOI and UL-94 test, boron compounds show their highest synergistic effect at 1 wt% loading. BPO 4 containing composite shows the highest LOI (30), lowest maximum heat release rate (HRR) and lowest total heat release rate (THR) value. Although the char yield increases as the amount of boron compounds increases, the flame retarding effect decreases. Cone calorimeter and TGA data indicate that the boron compounds are likely to show their synergistic effect by reinforcing the integrity of char which improves its barrier effect rather than increasing the char yield.

Effect of Fillers on the Fire Retardant Properties of Intumescent Polypropylene Compounds

The effects of fillers, including ammonium polyphosphate (APP), aluminium trihydrate (ATH) and talc, and the effect of polyethylene vinyl acetate (EVA) as an interfacial agent, were investigated on the flame retardant properties of intumescent polypropylene (PP), by using mechanical testing, to measure the tensile and Izod impact strengths, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and the limiting oxygen index (LOI) test method. SEM studies showed that the dispersion of flame retardant particles in the PP matrix improved with the use of EVA. Tensile strength decreased but elongation at break and impact resistance of PP/APP/EVA and PP/ATH/EVA composites increased by using 10 wt.% of EVA. Using 12 wt.% of talc in PP/APP/PA-6/EVA led to increasing impact resistance and decreasing tensile strength and elongation at break of the composite. EVA prevented the exudation of additives to the composite surface, and consequently the fire retardant properties of the composites improved. Talc increased fire protective performance due to the formation of a ceramic-like protective shield at the surface and increased residual mass at the end of the process. The results were interpreted by means of thermal decomposition, chemical reaction between components, and the formation of a protective layer at the surface on ignition.

Influence of talc on the fire retardant properties of highly filled intumescent polypropylene composites

AbstractIntumescent systems have been developed since many years for a wide range of applications, even if they are mainly used in coatings nowadays. The objective of this paper is to determine if the intumescent concept can be applied to highly filled reinforced polypropylene (PP) composites containing talc. Formulations that meet the electrical industry requirements have been developed, even if it has been observed that the addition of talc into intumescent PP leads to a decrease in the fire retardancy of the systems. A thermal stabilization of the material is noted at high temperature in the presence of talc. An increase in the crystallinity of the intumescent structure is suspected to be, at least partially, responsible for the decrease in the performance. Copyright © 2008 John Wiley & Sons, Ltd.

Modeling study on the combustion of intumescent fire-retardant polypropylene

The heat transfer and burning behavior of intumescent fire-retardant polypropylene were studied by cone calorimeter at heat flux levels of 50 kW·m -2 to establish an essential physical model for the intumescence process in fire. A mathematical model for the burning process of fire-retardant intumescent polymer was put forward based on the assump- tion that an intumescent front existed between the char layer and virgin layer. The model emphasizes the thermodynamic aspect of the intumescence process and a corresponding submodel is presented. Meanwhile the thicknesses and mass loss rates of the intumescent polypropylene during burning were measured for the validation of the modeling results. Thermal conductivity and heat capacity of polymer material were also measured as input parameters of the model. The validation results showed that the intumescent thicknesses and mass loss rates predicted by the model were in good agreement with the experimental results. The model was also used to predict the temperature distribution across the sample thickness during burning. The study shows that the present model can appropriately describe the intumescent behavior of the polymer and numerically predict its mass loss rates and temperature distribution in fire.