Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

Synergistic effects of cerium phosphate and intumescent flame retardant on EPDM/PP composites

An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system

The effects of lanthanum oxide (La₂O₃) as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (IFR-PP) were studied, and the new IFR system mainly consisted of the charring-foaming agent (CFA) and ammonium polyphosphate (APP). The limiting oxygen index (LOI), UL-94 test, thermogravimetric analysis (TGA), cone calorimeter (CONE) and scanning electron microscopy (SEM) were used to evaluate the synergistic effects of La₂O₃. It was found that when IFR was fixed at 20 wt% in IFR-PP composites, only a little amount of La₂O₃ could enhance LOI value and pass the UL-94 V0 rating test (1.6 mm). The TGA data showed that La₂O₃ could enhance the thermal stability of the IFR-PP systems at high temperature and effectively increase the char residue formation. The CONE results revealed that La₂O₃ and IFR could clearly change the decomposition behavior of PP and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSP), ignition time (IT) and so on. The morphological structures observed by SEM demonstrated that La₂O₃ could promote to form the homogenous and compact intumescent char layer. Thus, a suitable amount of La₂O₃ plays a synergistic effect in the flame retardancy and smoke suppression of IFR composites.     

Synergistic effects of aluminum hypophosphite on intumescent flame retardant polypropylene system

The effects of aluminum hypophosphite(AHP) as a synergistic agent on the flame retardancy and thermal degradation behavior of intumescent flame retardant polypropylene composites(PP/IFR) containing ammonium polyphosphate(APP) and triazine charring-foaming agent(CFA) were investigated by limiting oxygen index(LOI), UL-94 measurement, thermogravimetric analysis(TGA), cone calorimeter test(CONE), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). It was found that the combination of IFR with AHP exhibited an evident synergistic effect and enhanced the flame retardant efficiency for PP matrix. The specimens with the thickness of 0.8 mm can pass UL-94 V-0 rating and the LOI value reaches 33.5% based on the total loading of flame retardant of 24 wt%, and the optimum mass fraction of AHP/IFR is 1:6. The TGA data revealed that AHP could change the degradation behavior of IFR and PP/IFR system, enhance the thermal stability of the IFR and PP/IFR systems at high temperatures and promote the char residue formation. The CONE results revealed that IFR/AHP blends can efficiently reduce the combustion parameters of PP, such as heat release rate(HRR), total heat release(THR), smoke production rate(SPR) and so on. The morphological structures of char residue demonstrated that AHP is of benefit to the formation of a more compact and homogeneous char layer on the materials surface during burning. The analysis of XPS indicates that AHP may promote the formation of sufficient char on the materials surface and improve the flame retardant properties.     

Effects of organo-clay and sodium dodecyl sulfonate intercalated layered double hydroxide on thermal and flame behaviour of intumescent flame retarded polypropylene

The thermal and flame performances of intumescent flame retarded polypropylene (PP/IFR) composites with organically modified clay or sodium dodecyl sulfonate intercalated layered double hydroxide (SDS-LDH) were studied. The organo-clay particles were partially exfoliated in the PP matrix, while intercalation and aggregation was obtained for SDS-LDH. Incorporation of SDS-LDH improved the thermal stability and flame retardancy of the intumescent flame retarded PP composite in the early stage of heating and combustion; while the effects of organo-clay came into play in the middle-later stage. Differences in degradation pathway of clay and LDH were responsible for the above phenomenon which bore important implication for the barrier mechanism. The introduction of organo-clay into PP/IFR not only increased the char residue, but also formed compact and folded morphology of char residue which provided more effective protect for underlying materials against heat and oxygen relative to LDH, thus improved the flame retardancy of intumescent flame retarded PP samples more efficiently.     

Synergistic effect of zeolite 4A on thermal,mechanical and flame retardant properties of intumescent flame retardant HDPE composites

The combination of synergistic agent with intumescent flame retardant (IFR) systems provides a promising way to prepare high performance IFR composites. In this study, the effects of the synthetic zeolite 4 A in combination with the IFR system consisting of ammonium polyphosphate (APP) and tris (2-hydroxyethyl) isocynurate (THEIC) on thermal degradation, mechanical properties, flame retardancy and char formation of high-density polyethylene composites were investigated by limiting oxygen index (LOI) measurement, cone calorimetry, scanning electron microscopy and laser Raman spectroscopy. The LOI value of HD/FR/Z-0.5 composite with an optimum content of 0.5 wt. % zeolite 4 A and 25 wt. % of total flame retardant reaches 26.3 %. A low loading of zeolite 4 A can improve the bench-scale combustion performance as determined by cone calorimetry, and promote the formation of more compact char residue with a highly graphitic structure. However, a low loading of zeolite in combination with the IFR system consisting of APP and THEIC produces no significant changes in mechanical performance.     

Synthesis and thermal stability of a novel phosphorus-nitrogen containing intumescent flame retardant

A novel phosphorus-nitrogen containing intumescent flame retardant （P-N IFR） was prepared via the reaction of dichlor-opentate with N-methylaniline. The structure of the product was confirmed by ^1H NMR, ^31p NMR, MS and IR. TGA analysis showed it has effective thermal stability.     

Synthesis of a novel hybrid synergistic flame retardant and its application in PP/IFR

A novel inorganic-organic hybrid synergistic flame retardant was prepared by sol-gel reaction and characterized by NMR and FT-IR. It showed that the fire resistance of polypropylene/intumescent flame retardant (PP/IFR) composites could be improved with the combination of hybrid synergistic flame retardant. The char morphology and structure of PP composites were characterized by SEM and Raman spectra. The influence of the hybrid flame retardant on the thermal degradation process of PP composites was analyzed by FT-IR and the rheological behavior of the PP composites was also evaluated. The thermal stability of PP composites was characterized by TGA, weight loss difference and integral procedural decomposition temperature (IPDT). It indicated that the hybrid synergistic flame retardant had good synergistic effect with IFR.     

Synergistic effect of ammonium polyphosphate and layered double hydroxide on flame retardant properties of poly(vinyl alcohol)

A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1-1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.     

Synergistic effect of nanoflaky manganese phosphate on thermal degradation and flame retardant properties of intumescent flame retardant polypropylene system

Nanoflaky manganese phosphate (NMP) was synthesized from manganese nitrate and trisodium phosphate dodecahydrate, and used as a synergistic agent on the flame retardancy of polypropylene (PP)/intumescent flame retardant (IFR) system. The thermogravimetric analysis (TGA), real time Fourier-transform infrared (RTFTIR) spectroscopy measurements, cone calorimeter (CONE) and microscale combustion calorimeter (MCC) were used to evaluate the synergistic effects of NMP on PP/IFR system. When IFR + NMP was fixed at 20 wt% in flame retardant PP system, the TGA tests showed that NMP could enhance the thermal stability of PP/IFR system at initial temperature from about room temperature to 440 °C and effectively increase the char residue formation. The RTFTIR results revealed that NMP could clearly change the decomposition behavior of PP in PP/IFR system, which promotes decomposition at the initial temperature from about room temperature to 260 °C and forms more effective barrier layer to protect PP from decomposing at high temperature from about 260 °C to 500 °C. The CONE tests indicated that the addition of NMP in PP/IFR system not only reduced the peak heat release rate (HRR), but also prolonged the ignition time. The MCC results revealed that PP/IFR/NMP system generated less combustion heat over the course of heating than that of PP/IFR system. And scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to explore the char residues of the PP/IFR systems with and without NMP.     

Synergistic effects and mechanism of multiwalled carbon nanotubes with magnesium hydroxide in halogen-free flame retardant EVA/MH/MWNT nanocomposites

The synergistic effects and mechanism of multiwalled carbon nanotubes (MWNTs) with magnesium hydroxide (MH) in halogen-free flame retardant EVA/MH/MWNT nanocomposites have been studied by cone calorimeter test (CCT), limiting oxygen index (LOI), thermogravimetric analysis (TGA), torque test, morphological evolution experiment, and scanning electron microscopy (SEM). The data obtained from the CCT, LOI, and TGA show that suitable amount of MWNTs has synergistic effects with MH in the EVA/MH/MWNT nanocomposites. The MWNTs can considerably decrease the heat release rates and mass loss rate by about 50-60%, prolongate the combustion time to near two times, and increase the LOI values by 5% when 2 wt% MWNTs substitute for the MH in the EVA/MH/MWNT samples. The TGA data also show that the synergistic effects of MWNTs with MH apparently increase the thermal degradation temperatures and final charred residues of the EVA/MH/MWNT samples. The experimental observations from the torque, morphological evolution tests, and SEM give positive evidences that the synergistic mechanism of MWNTs with MH can be described to: (i) the increase of melt viscosity because of network structure formation of MWNTs in the EVA/MH matrix; (ii) the enhancement of thermo-oxidation stability due to the MWNTs' mechanical strength and integrity of the charred layers in the EVA/MH/MWNT nanocomposites; (iii) the formation of compact charred layers promoted by MWNTs acted as heat barrier and thermal insulation. All the above-mentioned factors efficiently enhance thermal and flame retardant properties and protect the EVA/MH/MWNT nanocomposite materials to be burning.     

Intumescent flame retardation and silane crosslinking of PP/EPDM elastomer

This study deals with the silane crosslinking and intumescent flame retardation of polypropylene/ethylene‐propylene‐diene copolymer (PP/EPDM) elastomers. The effect of silane crosslinking on the flame retardancy of the PP/EPDM composites containing melamine phosphate (MP) and dipentaerythritol (DPER) was studied by limiting oxygen index, UL 94 and cone calorimetry tests. The chemical composition of the silane crosslinked and flame retarded PP/EPDM composites treated at different temperatures was studied by X‐ray photoelectron spectroscopy and real time Fourier transform infrared (FTIR) spectrometry. Thermal decomposition and crystallization behavior of the PP/EPDM composites were investigated using thermogravimetric analysis and differential scanning calorimetry, respectively. Moreover, the mechanical properties of the composites were also studied. It is found that the flame retardancy, mechanical properties, and thermal decomposition behavior of the composites are influenced by silane grafting and crosslinking. Copyright © 2008 John Wiley & Sons, Ltd.     

Combustion properties and thermal degradation behavior of polylactide with an effective intumescent flame retardant

An intumescent flame retardant spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) has been synthesized and its structure was characterized by Fourier transformed infrared spectrometry (FTIR), ¹H and ³¹P nuclear magnetic resonances (NMR). A series of polylactide (PLA)-based flame retardant composites containing SPDPM were prepared by melt blending method. The combustion properties of PLA/SPDPM composites were evaluated through UL-94, limiting oxygen index (LOI) tests and microscale combustion calorimetry (MCC) experiments. It is found that SPDPM integrating acid, char and gas sources significantly improved the flame retardancy and anti-dripping performance of PLA. When 25 wt% flame retardant was added, the composites achieved UL-94 V0, and the LOI value was increased to 38. Thermogravimetric analysis (TGA) showed that the weight loss rate of PLA was decreased by introduction of SPDPM. In addition, the thermal degradation process and possible flame retardant mechanism of PLA composites with SPDPM were analyzed by in situ FTIR.     

Synergistic effects of 4A zeolite on the flame retardant properties and thermal stability of a novel halogen‐free PP/IFR composite

The synergistic effects of 4A zeolite (4A) on the thermal degradation, flame retardancy and char formation of a novel halogen‐free intumescent flame retardant polypropylene composites (PP/IFR) were investigated by the means of limiting oxygen index (LOI), vertical burning test (UL‐94), digital photos, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), cone calorimeter test (CCT), laser Raman spectroscopy (LRS) and X‐ray photoelectron spectroscopy (XPS). It was found that a small amount of 4A could dramatically enhance the LOI value of the PP/IFR systems and the materials could pass the UL‐94 V‐0 rating test. Also, it could enhance the fire retardant performance with a great reduction in combustion parameters of PP/IFR system from CCT test. The morphological structures observed by digital and SEM photos revealed that 4A could promote PP/IFR to form more continuous and compact intumescent char layer. The LRS measurement, XPS and TGA analysis demonstrated that the compactness and strength of the outer char surface of the PP/IFR/4A system was enhanced, and more graphite structure was formed to remain more char residue and increase the crosslinking degree. Copyright © 2013 John Wiley & Sons, Ltd.     

Synergistic flame retardant effects of nano-kaolin and nano-HAO on LDPE/EPDM composites

A novel flame retardant system composed of nano-kaolin and nano-HAO (nano-sized hydroxyl aluminum oxalate) was used for flame retarding the low density polyethylene (LDPE)/ethylene propylene diene rubber (EPDM) blends. Results of fire testing showed that nano-kaolin and nano-HAO exhibited excellent synergistic effects on the flame retardancy of the LDPE/EPDM composites. When 12 wt% nano-kaolin took the place of 12 wt% nano-HAO in the composites, the LOI of the composites increased from 31.0% to 35.5% and the composites could meet the UL94V-0 standard. Through thermogravimetric and differential thermal analysis (TG-DTA) it was found that nano-HAO mainly affected the degradation of the experimental composites chemically. Meanwhile, results of scanning electronic microscope (SEM) and Fourier transformation infrared spectra (FTIR) of the composites on the char layer revealed that nano-kaolin mainly affected the transfer process physically by aggregating with nano-HAO and thus the synergistic effect on flame retardancy appeared.     

Polymer nanocomposites using zinc aluminum and magnesium aluminum oleate layered double hydroxides: Effects of the polymeric compatibilizer and of composition on the thermal and fire properties of PP/LDH nanocomposites

A series of five oleate-containing layered double hydroxides with varied ratios of zinc to magnesium, i.e., with the general formula Zn_2−yMg_yAl(OH)₆ [CH₃(CH₂)₇CHCH(CH₂)₇COO]·nH₂O, were synthesized and used to prepare nanocomposites of polypropylene (PP). The nanomaterials were characterized by elemental analysis, attenuated total reflection-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the composites were characterized by XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. The zinc-containing LDH showed better dispersion in the polymer at the micrometer level than did the magnesium-containing LDH while both are equally well-dispersed at the nanometer level. The magnesium-containing composites led to more thermally stable systems in TGA experiments, while the zinc systems gave greater reductions in heat release rate during combustion. Dispersion was also affected by the amount of PP-g-MA which was present. More PP-g-MA gave better dispersion and a significantly reduced peak heat release rate, i.e., enhanced fire performance.     

Synergistic effects of novolac-based char former with a phosphorus/nitrogen-containing flame retardant in polyamide 6

The synergistic effect of phosphorus oxynitride（PON） with a novolac-based char former modified by salification （NA-metal salt） on the flame retardance of polyamide 6（PA6） was investigated.For this purpose,various flame-retardant PA6 systems were melt-compounded with PON,PON/NA,PON/NA-V₂O₅ and PON/NA-Fe₂O₃,and their flame retardance was evaluated by measuring the limiting oxygen index（LOI） values and UL-94 vertical burning ratings.The results showed that,compared with the PA6/PON/NA system,the combination of two char formers（NA-V₂O₅,NA-Fe₂O₃） with PON could obviously improve the char formation and flame retardance of PA6.The flame retardance and cone calorimetric analyses showed the stronger synergism as well as the better flame retardant performance of PON/NA-Fe₂O₃ flame retardant system. The effects of different char formers on the flame retardance and thermal stability of this system were also discussed.     

Layered double hydroxide/polyethylene terephthalate nanocomposites. Influence of the intercalated LDH anion and the type of polymerization heating method

Conventional and microwave heating routes have been used to prepare PET–LDH (polyethylene terephthalate–layered double hydroxide) composites with 1–10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate had been previously intercalated in the LDH. PXRD and TEM were used to detect the degree of dispersion of the filler and the type of the polymeric composites obtained, and FTIR spectroscopy confirmed that the polymerization process had taken place. The thermal stability of these composites, as studied by thermogravimetric analysis, was enhanced when the microwave heating method was applied. Dodecyl sulphate was more effective than terephthalate to exfoliate the samples, which only occurred for the terephthalate ones under microwave irradiation.     

Structural characterization and thermal decomposition of layered double hydroxide/poly(p-dioxanone) nanocomposites

Nanocomposites based on layered double hydroxides (LDH) and poly(p-dioxanone) (PPDO) were prepared by melt processing using dodecylbenzene sulfonate (DBS) and 4-hydroxybenzene sulfonate (HBS) as organic modifiers. The incorporation of organic anions in LDH was demonstrated by wide-angle X-ray scattering (WAXS) and Fourier transform infrared (FTIR). The dispersion degree of the organically modified LDHs in the PPDO matrix was analyzed by WAXS, indicating that only the LDH modified with HBS was exfoliated. The effect of the organically modified LDHs on the thermal stability of PPDO was studied using thermogravimetric analysis (TGA). The thermal stability of PPDO matrix was enhanced by the incorporation of the LDH modified with HBS due to the shielding effect of the exfoliated layers. In contrast, the LDH modified with DBS produced a decrease of the thermal stability of PPDO, probably due to hydrolytic decomposition of ester group. The thermogravimetric analysis also showed that the organo-modified LDH did not modify the thermal decomposition mechanism of the polymer, but had an effect on the thermal stability.