Formation Of Intumescent Char Layer Research Articles

An eco-friendly cellulose-based flame retardant with high expansibility and carbonization efficiency

Cellulose nanocrystals (CNCs) with flame-retardant property attract considerable attention as multifunctional reinforcing nanofillers for the polymers. Herein, a novel eco-friendly CNC-based (CTP) flame retardancy (FR) had been developed by modifying CNC with tannic acid (TA) and phytic acid (PA). The CTP with spherical morphology displayed good thermal stability and high char residue up to 59.3 % at 600 °C. Notably, the CTP can be carbonized rapidly to form the dense and continuous intumescent char layer, which height increased from 2 mm to 16 mm. The quick dehydration and carbonization of TA under the catalysis of PA contributed to the high expansibility and carbonization efficiency of CTP. The formation of intumescent char layer acted as a strong barrier, significantly improving the flame retardancy and inhibiting the dense smoke release. This eco-friendly and high flame-retardant CNC-based FRs can be widely used for developing multifunctional polymers.

Zinc hydroxystannate anchored PAP-activated carbon spheres for enhancing flame protection of aqueous epoxy coatings

Here, carbon spheres (CS), a carbonaceous spherical material with a wide source and easy preparation, were used as enhanced nano-fillers to reinforce the flame retardancy of aqueous epoxy intumescent coatings. To overcome the defects of CS themselves during combustion, polydopamine (PDA) was co-deposited with adenosine triphosphate (ATP) on its surface to obtain activated carbon spheres with C-N-P structure (CS/PAP), which can contribute to the formation of intumescent char layer. Meanwhile, zinc hydroxystannate (ZHS), as a non-halogen, environmentally friendly, and efficient flame retardant, was introduced to the surface of carbon phosphide spheres to obtain a composite functional hybrid reinforcement (CS/PAP@ZHS). Adiabatic performance tests indicated that the backside temperature of the CS/PAP@ZHS filler-reinforced EP expansion specimen was maintained at the minimum fig. (168.8 °C), confirming its highest resistance to heat penetration. Compared to the CS-based EP, the CS/PAP-loaded EP showed reduced smoke emission, indicating the effectiveness of the PAP intumescent phosphate modification for smoke suppression. By comparison, the CS/PAP@ZHS-based EP showed the largest char residue (29.1 % in N2, 12 % in air), expansion height (23.1 mm), and minimal smoke density grade (40.7 %). Additionally, compared with pure EP, the peak heat release rate (PHRR), total heat release rate (THR), peak smoke production rate (PSPR), and total smoke production (TSP) of CS/PAP@ZHS/EP are reduced by 33.3 %, 28.2 %, 37.4 %, and 23.6 % respectively, demonstrating its best fire and smoke suppression properties.

Flame retardancy and mechanical properties of glass fibre reinforced polyethylene composites filled with novel intumescent flame retardant

A novel intumescent flame retardant (IFR) system composed of ammonium polyphosphate and poly (1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (APP/PDTBP) was mixed with polyethylene to prepare the continuous glass fibre reinforced polyethylene (CGF/PE) unidirectional prepregs by melt impregnation process, and then the CGF/PE/IFR composite laminate were consolidated by hot compression moulding method. The flame retardancy, thermal stability and mechanical properties of CGF/PE/IFR composite laminates were investigated by limiting oxygen index, vertical burning test, cone calorimetric test, thermogravimetric analysis, tensile and flexural strength tests, mode I interlaminar fracture toughness test, and scanning electron microscopy (SEM). The flame retardancy of CGF/PE composite laminates increased with the increase of IFR system loading, which attributes to the formation of intumescent char layer from flame retardants and the weakening of wicking actions of glass fibres. The mechanical properties increased and then decreased with addition of flame retardants, except for the flexural strength with continuous increase. The SEM images showed that IFR system had toughening effect and could improved the strength of fibre-matrix interface. Based on the mechanical properties and the flame retardancy, when the matrix contains 30 wt% IFR system, the CGF/PE/IFR composite laminate had the best comprehensive performance.

Flame retardant effect of cytosine pyrophosphate and pentaerythritol on polypropylene

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.

Highly Effective Flame Retardancy of a Novel DPPA-Based Curing Agent for DGEBA Epoxy Resin

The flame retardancy, thermal, and mechanical properties of the cured epoxy resins are difficult to be simultaneously improved. In the present work, a novel DPPA-based curing agent, 10-[(4-hydroxyphenyl)(4-hydroxyphenylimino)methyl]-5,10-dihydrophenophosphazine 10-oxide (H-DPPA), is successfully synthesized to serve as a co-curing agent of 4, 4′-diaminodiphenylmethane (DDM) for bisphenol A diglycidyl ether (DGEBA) epoxy resin. With the aid of 3.0 wt % of H-DPPA, the cured epoxy resin, in which the phosphorus content is as low as 0.22%, passes V-0 rating of UL-94 test with limiting oxygen index (LOI) of 31.8%. The high flame retardancy of epoxy resin modified by H-DPPA originated mainly from the formation of intumescent char layer during combustion. This new type of flame retardant containing both phosphine oxide structure and nitrogen moieties provides epoxy resins with excellent integrated performances.

High performance fire-retarded epoxy imparted by a novel phenophosphazine-containing antiflaming compound at ultra-low loading

A novel phenophosphazine-containing compound, HD-DPPA, was successfully synthesized via the addition reaction between 5,10-dihydro-phenophosphazinine-10-oxide and Schiff base obtained in advance by condensation of 4,4′-dimninodiphenylmethane (DDM) and 4-hydroxybenzaldhehyde, and used as a co-curing agent of DDM and a flame retardant for DGEBA epoxy resin. The cured epoxy resin passed UL-94 V-0 rating with limiting oxygen index (LOI) of 31.3% at only 2.5wt% HD-DPPA, where phosphorus content was as low as 0.19wt%. The formation of intumescent char layer and blowing-out effect during combustion are responsible for high flame retardancy of epoxy resin. The flame-retarded epoxy resin exhibited the improved tensile and impact strength compared with the pristine epoxy resin.

Synthesis and characterization of aluminum poly-hexamethylenephosphinate and its flame-retardant application in epoxy resin

A flame retardant additive, aluminum poly-hexamethylenephosphinate (APHP) with a polymeric structure was synthesized from 1,5-hexadiene, hypophosphorous acid and aluminum ions. The molecular structure of APHP and thermal stability were characterized by solid nuclear magnetic resonance, Fourier transform infrared and thermogravimetric analysis. Then, APHP was applied into diglycidyl ether of bisphenol-A cured by 4,4′-diamino-diphenylmethane. APHP showed flame-retardant effect on the epoxy thermosets in limited oxygen index (LOI), UL94 vertical test and cone calorimeter. The thermosets with only 4 wt.% APHP obtained an LOI value of 32.7% and reached the UL94 V-1 rating. The APHP/EP thermosets decreased the pk-HRR, THR and av-EHC values, decreased CO2Y and enhanced the COY ratios, and also reserved more residual char comparing with neat thermoset. The less incorporation of APHP in thermosets will impose the better flame retardancy to epoxy thermosets. The flame-retardant effect of APHP was resulted by its two main pyrolyzed contents phosphorus and alkyl-phosphinic fragments. In condensed phase, the phosphorus-containing contents facilitated to the higher char yields and the formation of intumescent char layer, which led to a reduction of the released fuel and a strong barrier effect to weaken the combustion intensity. In gas phase, the PO, PO2 and alkyl-phosphinic fragments with quenching effect were released from the phosphorus-containing contents, and can decrease the heat release and weaken the combustion intensity.

Influence of molecular weight of PEG on thermal and fire protection properties of PEPA-containing polyether flame retardants with high water solubility

Abstract A series of novel PEPA-containing polyether (PAPEG) flame retardants with high water solubility were synthesized by pentaerythritol phosphate (PEPA), phosphorus oxychloride (POCl3) and polyethylene glycol (PEG) with different molecular weight. Their chemical structures were confirmed by 1H nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The influence of molecular weight of PEG on the thermal property of PAPEGs was investigated by thermogravimetric analysis (TGA) and a possible thermal degradation mechanism was speculated to illustrate the char-forming ability of PEG. Afterwards, the influence of molecular weight of PEG on the fire protection of the transparent fire resistant coatings (FRC) was investigated in detail by fire protection test, intumescence ratio, scanning electron microscopy (SEM) and TGA. The fire protection test found that the coatings with low molecular weight PEG presented good fire retardancy, supplying effective fire protection for the plywood boards. The intumescence ratio and SEM results well demonstrated that the fire protection of coatings and foam structure of char layers were significantly improved when the molecular weight of PEG was low. TGA result showed that the residual weights of the fire resistant coatings presented the order of FRC200 > FRC150 > FRC400 > FRC600. It indicated that low molecular weight PEG could enhance the char-forming ability of the coatings. TGA and real-time FTIR results proved that blowing agent and carbon source degraded in the same temperature range, which resulted in the formation of intumescent char layer.

Effect of hexaphenoxycyclotriphosphazene combined with octapropylglycidylether polyhedral oligomeric silsesquioxane on thermal stability and flame retardancy of epoxy resin

A novel phosphazene-based compound called hexaphenoxycyclotriphosphazene (HPCTP) was synthesized and characterized by Fourier transform infrared spectroscopy as well as proton and phosphorus nuclear magnetic resonance spectroscopies. Epoxy (EP) resin composites containing HPCTP and octapropylglycidylether polyhedral oligomeric silsesquioxane (OGPOSS) were prepared using 4,4′-diamino diphenylmethane as curing agent. Differential scanning calorimetry, thermogravimetric analysis, UL 94 vertical burning test, and cone calorimetry test were used to assess thermal stability and flame retardancy of the composites. Evaluation of thermal properties demonstrated that the resulting composites achieved less thermal stability compared with control EP resin but possessed high char yields at high temperatures. It indicated that both HPCTP and OGPOSS could induce the formation of intumescent char layer that retarded the degradation and combustion process of EP resin. The peak heat release rate of EP resin composite containing 15 wt% HPCTP was 61% less than that of control EP resin. Meanwhile, other flame-retardant parameters were also improved. Results of scanning electron microscopy and energy-dispersive x-ray spectroscopy of residual chars confirmed that both HPCTP and OGPOSS can enhance thermal stability and flame retardancy of EP resin.

Synthesis and characterization of a novel organophosphorus flame retardant and its application in polypropylene

A novel organophosphorus containing spiro and caged bicyclic phosphate, 3,9‐Bis‐(1‐oxo‐2,6,7‐trioxa‐1‐phospha‐bicyclo[2.2.2]oct‐4‐ylmethoxy)‐2,4,8,10‐tetraoxa‐3,9‐diphospha‐spiro[5.5]undecane 3, 9‐dioxide (SBCPO), was synthesized and characterized by Fourier transform infrared (FTIR), hydrogen‐1 nuclear magnetic resonance (NMR) and phosphorus‐31 NMR. The flame retardancy of polypropylene (PP) containing the novel intumescent flame retardant (IFR) based on the combination between SBCPO and melamine (MA) was studied by limiting oxygen index (LOI), UL‐94 test and cone calorimeter test. Results indicated that this combination showed the excellent flame retardancy for PP at appropriate proportions (with the total loading of 30 wt. % and SBCPO: MA = 4:1). The value of LOI was as high as 31.6, and the rating in UL94 reached to V‐0. Moreover, the HRR and THR of IFR/PP decreased significantly in comparison with that of neat PP. The scanning electron microscopy results indicated that the incorporation of SBCPO could induce the formation of intumescent char layer, which retarded the degradation and combustion process of PP. The thermal oxidative degradation of the PP samples at different temperature was analyzed by FTIR. The thermal stabilities of the composites were further investigated by thermogravimetric analysis. It was found that the amount of residues was increased greatly with the addition of SBCPO that remained in the form of polyaromatic stacks and phosphoric or polyphosphoric acid at the residual chars. Copyright © 2013 John Wiley & Sons, Ltd.