Showing papers on "Charring published in 2020"

Renewable vanillin-based flame retardant toughening agent with ultra-low phosphorus loading for the fabrication of high-performance epoxy thermoset

Abstract: The poor impact toughness and flame retardant performance have greatly restricted the engineering application of epoxy thermoset. To obtain the high-performance epoxy composites, the renewable vanillin-based flame retardant toughening agent (PVSi) was synthesized and incorporated into epoxy. The use of PVSi macromolecules can significantly enhance the impact toughness of epoxy. With 5 wt% of PVSi, the impact strength of the epoxy was maximally raised by 189.69%, from 12.42 kJ/m2 of the neat EP to 35.98 kJ/m2 of EP/PVSi5 composites. The toughening effect of PVSi macromolecules on epoxy was closely linked to its structural features, such as the flexible phenylsiloxane, active imine and polar phosphaphenanthrene groups. Simultaneously, the EP/PVSi5 composites reached up to the V-0 rating in vertical burning test (UL-94) and 29.5% in limiting oxygen index (LOI), with only 0.27 wt% ultra-low phosphorus loading. Additionally, the suppressed heat release, the evidently reduced toxic pyrolytic volatiles, and the promoted charring capability of EP/PVSi composites can be obtained, with phosphaphenanthrene, phenylsiloxane and diaminodiphenylsulfone groups in PVSi macromolecules jointly playing a role. These results indicated the improved fire safety of epoxy. Furthermore, the free radical scavenging effect of P· and PO·, the fuel dilution effect of nonflammable NH3 and SO2, the catalytic charring effect of the pyrophosphoric acid and metaphosphoric acid, the charring-stability effect of phenylsiloxane group and the suppression effect of high-quality carbon layers were analyzed and summarized. It was expected that PVSi would pave the way for the development of more highly efficient flame retardant toughening agents and high-performance epoxy thermoset.

Bioinspired iron-loaded polydopamine nanospheres as green flame retardants for epoxy resin via free radical scavenging and catalytic charring

Abstract: The versatile coating capability of polydopamine (PDA) has received much research interest in numerous fields, including flame retardant functionalization of fillers for polymers. However, the understanding of flame retardant actions of PDA materials in combustion still remains incomplete, limiting its practical applications and future designs as polymer reinforcing fillers. In this study, iron-loaded polydopamine (Fe-PDA) nanospheres were introduced into epoxy resin (EP) as green flame retardant additives. The resultant EP nanocomposites exhibited remarkably reduced flammability, reflected by the high LOI value of 31.6%, V-0 rating in the UL-94 test, as well as a 41% reduction in the peak heat release rate at 5 wt% Fe-PDA loading. More importantly, for the first time, it is clearly revealed that the flame inhibition action in the gas phase was owing to the free radical scavenging ability of Fe-PDA. In addition to the gas phase action, Fe-PDA also promoted the charring process in the condensed phase, leading to the formation of integrated char layers that effectively delayed the mass and heat transfer of combustion. Based on these actions (free radical scavenging and catalytic charring), Fe-PDA acted as the nontoxic and highly efficient flame retardant in EP.

Novel alkynyl-containing phosphonate ester oligomer with high charring capability as flame retardant additive for thermoplastic polyurethane

Abstract: Phosphonate esters may be used as flame retardants for flammable polymers, but always face low flame-retardant efficiency and melt dripping. Until now, no remarkable progress was made in solving the above two defects, thus tremendously affecting their applications as flame retardants. In current work, from the chemistry viewpoint, we designed and synthesized poly(2-butyne-1,4-diol phenylphosphonate) (PPBP) containing alkynyl group to break through above-mentioned defects. Compared with the corresponding control sample poly(1,4-butanediol phenylphosphonate) (PPBOP) without alkynyl, thermal analysis revealed that residual char of the PPBP with C C bonds increased to 45.0%, much higher than 1.6% for the PPBOP without C C bonds, and greatly increased by 27 folds. Various measurements and kinetic analysis were used to investigate the underlying cause for the leap in charring. It turns out that PPBP was involved in a unique decomposing and crosslinking process upon heating, which played a vital role in the leap in charring for PPBP. The leap in charring might afford polymers better flame retardancy through condensed phase. After incorporation of the PPBP into thermoplastic polyurethane (TPU), burning tests illustrated that PPBP not only endowed TPU with excellent flame retardancy and anti-melt dripping performance, but also resulted in extremely low heat release rate and smoke production rate, correspondingly decreased by 70.7% and 53.9% compared with those of TPU. Various measurements further confirmed that the charring caused by PPBP itself and the enhanced charring of TPU induced by PPBP played a crucial role in the remarkable superior flame retardancy of TPU/PPBP.

Flame retardant effect of cytosine pyrophosphate and pentaerythritol on polypropylene

Abstract: Cytosine pyrophosphate (PPA-C) was prepared by using pyrophosphoric acid (PPA) and cytosine (C). The structure, morphology and thermal stability of PPA-C were analyzed by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermogravimetric analysis (TGA). The PPA-C was used as acid and gas source and pentaerythritol (PER) as charring agent to form an intumescent flame retardant (IFR) system which was applied to improve the flame retardancy of polypropylene (PP). The flame retardancy and thermal degradation behaviors of PP/IFR composites were investigated by vertical combustion (UL-94), limiting oxygen index (LOI) and cone calorimeter (cone), TGA etc. The PPA-C and PER have good synergistic effects on improving the flame retardancy of PP which is better than that of commercial ammonium polyphosphate (APP) and PER system. The PP/IFR composites with 18 wt% PPA-C/PER (3:1) achieves the UL-94 V-0 rating and a LOI value of 28.8 vol%. The PPA-C reacts with PER to form -P-O-C and -P-C- during combustion which helps the formation of intumescent char layer. In addition, the IFR makes PP degrade in advance and form more char residues at high temperature. Proper ratio and amount of PPA-C/PER promotes the formation of intumescent char layer without defects during combustion, reduces the heat release rate and delays the thermal degradation of PP composites, thus improves the flame retardancy of PP.

Surface engineering of magnesium hydroxide via bioinspired iron-loaded polydopamine as green and efficient strategy to epoxy composites with improved flame retardancy and reduced smoke release

Abstract: Functionalized magnesium hydroxide (MDH@Fe-PDA) by polydopamine (PDA) and iron chloride (FeCl3) were designed by one-pot method, aiming at improving flame retardancy and reducing smoke release of epoxy resin. The structure of MDH@Fe-PDA was confirmed via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). MDH and MDH@Fe-PDA with different ratio were introduced into epoxy resin (EP) as flame retardant additives. The enhanced flame retardancy and smoke suppression of EP composites were evaluated by limiting oxygen index (LOI), UL-94 test and cone calorimetry. The resultant EP composites exhibited remarkably reduced flammability, reflected by high LOI value of 29.3%, V-0 rating, as well as a 57% reduction of peak heat release rate for 7 wt% MDH@Fe-PDA loading. In addition, EP/MDH/MDH@Fe-PDA composites decreased the evolution of volatiles significantly. The char structure of EP composites revealed that char with a more intact and continuous structure. A probable mechanism was proposed which involved catalytic charring behavior at the interface and intensive protection by char and strong radical scavenging activity. Notably, this work provided an attractive method to organo-modified MDH, and enriched its practical applications of MDH as functional fillers to polymers.

Thermal Analysis and Cone Calorimeter Study of Engineered Wood with an Emphasis on Fire Modelling

Abstract: Engineered wood products (EWPs) are a group of materials having a very similar chemical composition but having different and non-uniform thermo-physical properties throughout their thickness. Such materials present a significant challenge from the pyrolysis modelling point of view. The main focus of the paper is to study and compare the differences between six EWPs—oriented strand board (OSB), plywood, particle board (PB), low-density (LDF), medium-density (MDF) and high-density (HDF) fibreboard—in terms of their pyrolysis and burning behaviour. Vertical density profiles (VDPs), thermal degradation behaviour, and burning behaviour were studied and compared. There is a considerable need for a consistent and systematic approach in estimating pyrolysis model complexity and model input parameters. A systematic method to determine the minimum level of the EWPs decomposition model complexity to reproduce the thermal degradation behaviour as measured using thermogravimetric analysis and using the set of parallel reactions was applied. EWPs were found to have similar thermal decomposition onset and range. Maximal decomposition rates were within 25%. OSB, PB, LDF and HDF decomposition can be modelled using three-step parallel reactions scheme, MDF using four parallel reactions. A set of parallel reactions cannot describe the thermal degradation behaviour of plywood. Cone calorimeter tests at heat flux levels of 20 kW/m2, 50 kW/m2 and $$80\, \hbox {kW}/\hbox {m}^{2}$$ revealed that influence of the different thermo-physical properties on time to ignition and time to peak heat release rate (HRR) is not significant except LDF and HDF due to their very different density. Peak HRR varies between EWPs, which is attributed primarily to charring and different thermo-physical properties of the EWPs char. EWPs gas phase combustion parameters for the fire models were derived.

Thermal Expansion for Charring Ablative Materials

Abstract: A mesh moving scheme is developed and tested in a finite-volume thermo-mechanical solver to investigate the effects of geometry deformation on thermal protection system materials. Verification case...

A Case Study of Polyether Ether Ketone (I): Investigating the Thermal and Fire Behavior of a High-Performance Material

Abstract: The thermal and fire behaviors of a high-performance polymeric material—polyether ether ketone (PEEK) was investigated. The TG plots of PEEK under different oxygen concentrations revealed that the initial step of thermal decomposition does not greatly depend on the oxygen level. However, oxygen concentration plays a major role in the subsequent decomposition steps. In order to understand the thermal decomposition mechanism of PEEK several methods were employed, i.e., pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), thermogravimetric analysis (TGA) coupled with a Fourier-transform infrared spectrometer (FTIR). It was observed that the initial decomposition step of the material may lead to the release of noncombustible gases and the formation of a highly crosslinked graphite-like carbonaceous structure. Moreover, during the mass loss cone calorimetry test, PEEK has shown excellent charring and fire resistance when it is subjected to an incident heat flux of 50 kW/m². Based on the fire behavior and the identification of pyrolysis gases evolved during the decomposition of PEEK, the enhanced fire resistance of PEEK was assigned to the dilution of the flammable decomposition gases as well as the formation of a protective graphite-like charred structure during its decomposition. Moreover, at 60 kW/m², ignition occurred more quickly. This is because a higher rate of release of decomposition products is achieved at such a heat flux, causing a higher concentration of combustibles, thus an earlier ignition. However, the peak of heat release rate of the material did not exceed 125 kW/m².

Numerical Simulation of Coupled Pyrolysis and Combustion Reactions with Directly Measured Fire Properties.

Abstract: In this study, numerical simulations of coupled solid-phase reactions (pyrolysis) and gas-phase reaction (combustion) were conducted. During a fire, both charring and non-charring materials undergo a pyrolysis as well as a combustion reaction. A three-dimensional computational fluid dynamics (CFD)-based fire model (Fire Dynamics Simulator, FDS version 6.2) was used for simulating the PMMA (non-charring), pine (charring), wool (charring) and cotton (charring) flaming fire experiments conducted with a cone calorimeter at 50 and 30 kW/m2 irradiance. The inputs of chemical kinetics and the heat of reaction were obtained from sample mass change and enthalpy data in TGA and differential scanning calorimetry (DSC) tests and the flammability parameters were obtained from cone calorimeter experiments. An iso-conversional analytical model was used to obtain the kinetic triplet of the above materials. The thermal properties related to heat transfer were also mostly obtained in house. All these directly measured fire properties were inputted to FDS in order to model the coupled pyrolysis–combustion reactions to obtain the heat release rate (HRR) or mass loss. The comparison of the results from the simulations of non-prescribed fires show that experimental HRR or mass loss curve can be reasonably predicted if input parameters are directly measured and appropriately used. Some guidance to the optimization and inverse analysis technique to generate fire properties is provided.