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An innovative phosphorus‐nitrogen flame retardant (ZrMP) is fabricated by reacting a‐zirconium phosphate (a‐ZrP), phenylphosphinic acid with melamine, and applied to improve the flame retardancy of rigid polyurethane foam/expandable graphite (RPUF/EG) composites. The synergistic effect of ZrMP and EG on the flame retardancy and thermal stability of RPUF was examined by the limiting oxygen index (LOI), UL‐94 vertical burning test, and thermogravimetric analyses. Benefiting from the P and N elements of ZrMP and the expanded char layer of EG, the synergistic effect of ZrMP and EG endows FPUF with excellent flame retardant and thermal properties. The RPUF composites containing 12.5% EG and 2.5% ZrMP can achieve a V‐0 level and its LOI value increases to 26.7%. RPUF/EG/ZrMP composites exhibit good thermal stability compared with pure RPUF. Accordingly, the flame‐retardant mechanism of RPUF composites is proposed by thermogravimetric analyses/infrared, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The results indicate a combination of physical barriers in condensed‐phase and gaseous‐phase dilution activity during combustion. Therefore, this study provides a scalable and promising strategy for constructing flame‐retardant RPUF composites. [ABSTRACT FROM AUTHOR]

Silica (SiO2) nanohybrid expandable graphite (nEG) particles fabricated through one‐step method are used as an efficient flame retardant for polypropylene (PP)/polyamide 6 (PA6) blends. The effect of nEG on the flammability, thermal stability, crystallization behaviors, and mechanical properties of PP/PA6 composites is investigated by using limit oxygen index (LOI), UL‐94 test, cone calorimeter test (CCT), thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared, scanning electron microscopy, and mechanical tests. Compared with pure expandable graphite (EG), nEG improves the flame retardancy of composites. The results of LOI show that LOI of PP/PA6/nEG10 and PP/PA6/nEG15 composites are 26.0% and 27.2%, respectively. But the LOI values of PP/PA6/EG10 and PP/PA6/EG15 composites are 25.7% and 26.9%, respectively. The UL‐94 test results show that PP/PA6/nEG10 composites reach V‐1 level when the nEG content is only 10%. However, the PP/PA6 composites with 10% EG does not pass the UL‐94 test. In addition, PP/PA6 composites with 15% nEG can reach V‐0 level. The CCT results further show that nEG has a higher flame‐retardant efficiency than pure EG for PP/PA6 blends. The thermal stability of PP/PA6/nEG composites is better than that of PP/PA6/EG composites. The mechanical property tests indicate that nEG is more conducive to maintain the tensile and impact strengths of PP/PA6 blends than EG due to the enhanced compatibility and interfacial adhesion. [ABSTRACT FROM AUTHOR]

The flammability, thermal properties, and synergistic effects of modified expandable graphite (MEG) with magnesium hydroxide (MH) and aluminum hydroxide (ATH) on the linear low-density polyethylene/ethylene vinyl acetate (LLDPE/EVA) blends are investigated by Underwriters Laboratories-94 (UL-94) vertical combustion test, limiting oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter test (CCT), and scanning electron microscopy (SEM). The results show that the MEG improves the flame-retardant efficiency of LLDPE/EVA blends. The addition of MEG apparently improves the LOI values and the UL-94 rating of LLDPE/EVA composites. The data obtained from the CCT show that the heat release rate (HRR), the total heat release (THR), and the gas production rate of composites with MEG decrease remarkably with increasing the content of MEG. When 10 phr of MEG is added, the char residues of LEMEG10 increase to 38.2% from 2.7% of LLDPE/EVA. The results of SEM and CCT present that MEG can improve the quality of char layers. The rate of char formation is enhanced also due to the existence of MEG, which plays an important role to improve the flame retardancy of the LLDPE/EVA composites. [ABSTRACT FROM AUTHOR]

An efficient approach has been proposed for improving the flame retardancy of low‐density polyethylene (LDPE) by organic‐inorganic intumescent interfacial flame retardants, avoiding the damage to intrinsic performances of LDPE caused by high loading of flame‐retardant additives. The expandable graphite (EG) particles are successfully functionalized by a grafting process containing phosphorous, exhibiting the excellent thermal stability and high flame‐retardant efficiency. Then a battery of flame‐retardant LDPE composites with different content of grafted EG (GEG) are fabricated and investigated. The results indicate that the Underwriters Laboratories‐94 V‐0 is achieved, and the limiting oxygen index is as high as 25.1% when 12 wt% GEG particles are filled into LDPE matrix. The residues of the flame‐retardant LDPE composites observably increase with the addition of GEG. The results of cone calorimeter test also verify that GEG is an efficient flame retardant for LDPE due to the interfacial effect between graphite and inorganic flame retardant. Besides, the microtopography of residual char shows that the LDPE/GEG composites are more compact and integrated after burning. This interfacial grafting flame retardant exhibits excellent flame‐retardant efficiency and will be promising for the development of organic‐inorganic intumescent flame retardants for polymer materials. [ABSTRACT FROM AUTHOR]

In this work, modified expandable graphite (MEG) and zinc borate (ZB) are melt‐blended with metal hydroxide/aluminum hydroxide flame retardant linear low‐density polyethylene/ethylene vinyl acetate (LLDPE/EVA) blends. The synergistic effects of MEG with ZB on the flammability, thermal stability and crystallization behaviors of LLDPE/EVA composites are characterized and discussed by UL‐94 vertical burning, limiting oxygen index (LOI), thermogravimetric analysis, cone calorimeter test (CCT), carbon layer morphology, and differential scanning calorimetry (DSC). The addition of ZB and MEG apparently increases the LOI values and improves the UL‐94 rating of the flame retardant LLDPE/EVA composites. The data obtained from the CCT indicate that the heat release rate, the total heat release and the gas production rate of the flame retardant LLDPE/EVA composites decrease remarkably with increasing the MEG content and the residues of the composites increase to 38.2% from 2.7% of the LLDPE/EVA blends, which indicates that MEG enhances the thermal stability and layer carbon capacity of the composites. The DSC results describe that MEG can act as a nucleating agent to accelerate the crystallization rate of the flame retardant composites, but the crystallinity of polypropylene of the flame‐retardant composites firstly increases and then decreases with increasing the content of MEG. POLYM. COMPOS., 40:E687–E694, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this work, the flame-retardant high-density polyethylene/ethylene vinyl-acetate copolymer (HDPE/EVA) composites have been prepared by using expandable graphite (EG) as a flame retardant combined with ammonium polyphosphate (APP) and red phosphorus masterbatch (RPM) as synergists. The synergistic effects of these additives on the flammability behaviors of the filled composites have been investigated by limiting oxygen index, UL-94 test, cone calorimeter test, thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), and scanning electron microscopy. The results show that APP and RPM are good synergists for improving the flame retardancy of EG-filled HDPE/EVA composites. The data from TGA and FTIR spectra also indicate the synergistic effects of APP and RPM with EG considerably enhance the thermal degradation temperatures but decrease the charred residues of the HDPE/EVA/EG composites because the flame-retardant mechanism has changed. The morphological observations present positive evidences that the synergistic effects take place in APP and RPM with EG in flame-retardant EG-filled HDPE/EVA/EG composites. The formation of stable and compact charred residues promoted by APP and RPM with EG acts as effective heat barriers and thermal insulations, which improves the flame-retardant performances and prevents the underlying polymer materials from burning. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work, the flammability behaviors and synergistic effects of red phosphorus masterbatch (RPM) with expandable graphite (EG) in flame-retardant high-density polyethylene/ethylene vinyl-acetate copolymer (HDPE/EVA) composites have been investigated by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) and scanning electron microscopy (SEM). The data obtained from LOI, UL-94 test and CCT showed that suitable amount of RPM had synergistic effects with EG in the HDPE/EVA/EG/RPM composites. The addition of RPM greatly increased the LOI values by 3.4%, obtained UL-94 V-0 rating, decreased the heat release rates and total heat release, and prolongated the ignition time when 6.7 phr RPM substituted for EG in the HDPE/EVA/EG/RPM composites. The data from TGA and FTIR spectra also indicated the synergistic effects of RPM with EG considerably enhanced the thermal degradation temperatures. The morphological observations after UL-94, CCT, and SEM images presented positive evidences that the synergistic effects took place for RPM with EG, and the flameretardant mechanism has been changed in flameretardant HDPE/EVA/EG/RPM composites. The formation of stable and compact charred residues promoted by RPM acted as effective heat barriers and thermal insulations, which improved the flame-retardant performances and prevented the underlying polymer materials from burning. [ABSTRACT FROM AUTHOR]

In this article, high-density polyethylene/ethylene vinyl-acetate copolymer (HDPE/EVA) composites filled with two different particle sizes (45 and 150 µm) of expandable graphite (EG) were prepared by using a twin-screw extruder. The thermal stability, flammability, and mechanical properties of HDPE/EVA/EG composites were investigated by thermogravimetric analysis (TGA), cone calorimeter test (CCT), tensile test, and scanning electron microscopy (SEM). The results from TGA and CCT indicated that EG significantly enhanced the thermal stability and fire resistance of HDPE/EVA blend. The thermal stability and flame retardancy of HDPE/EVA/EG composites were improved with decreasing particle size of EG. Although the onset of weight loss of the flame-retardant composites occurred at a lower temperature than that of HDPE/EVA blend, the flame-retardant composites produced a large amount of char residue at a high temperature. The consolidated char layer formed a barrier, which could reduce heat, low-molecular transfer, and air incursion, and thus enhanced the flame retardancy. The data from the tensile test showed that the addition of EG deteriorated the mechanical properties; however, the tensile stress and strain of HDPE/EVA/EG composites increased with decreasing the particle size of EG owing to the strong interface adhesion between polymer matrix and inorganic particles. POLYM. ENG. SCI., 54:1162-1169, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Polypropylene/thermoplastic polyurethane (PP/TPU) blends filled with two different particle sizes (45 and 150 μm) of expandable graphite (EG) were prepared by melt blending. Thermogravimetric analysis (TGA) was carried out to explain the effect of EG on the thermal stability of PP/TPU blends. In addition, the fire behavior of PP/TPU and PP/TPU/EG was investigated by a cone calorimeter. The char morphology and carbonation of the above systems were also characterized. The experimental results indicated that intumescent EG significantly enhanced the thermal stability and fire resistance of these blends. With the smaller particle size of EG, the thermal stability and flame retardancy were improved. The results from TGA and cone calorimeter demonstrated that the addition of EG could retard the degradation of the polymer materials above the temperature of 500°C by promoting the formation of a compact char layer. This char layer prevented further degradation of the polymer matrix and protected it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame-retarded performances. [ABSTRACT FROM AUTHOR]

In this study, polypropylene (PP)/thermoplastic polyurethanes (TPU) filled with inorganic intumescent flame retardant expanded graphite (EG) was prepared by melt blending in a twin-screw extruder. The thermal stability, fire retardancy, mechanical properties, and fracture morphology of PP/TPU composites with treated and untreated EG were investigated by thermogravimetric analysis, cone calorimeter, and scanning electron microscope. The results showed that both untreated and treated EG can greatly enhance the thermal stability and fire resistance of polymer matrix materials. Compared with untreated EG, treated EG can further improve the flame retardancy of the composites. For example, treated EG can further reduce the heat release rate, total heat release, and CO emissions of the composites in the combustion. Surface treatment of EG could significantly improve elongation at break and impact strength of PP/TPU/EG composites due to its enhanced interfacial adhesion and the good dispersion of EG particles in the polymer matrix. [ABSTRACT FROM AUTHOR]

The flammability and the thermal oxidative degradation kinetics of expandable graphite (EG) with magnesium hydroxide (MH) in flame-retardant polypropylene (PP) composites were studied by limiting oxygen index (LOI), UL-94 test, and thermogravimetric analysis (TGA). The results show that EG is a good synergist for improving the flame retardancy of PP/MH composite and the effect is enhanced with decreasing EG particle size. The Kissinger method and Flynn-Wall-Ozawa method were used to determine the apparent activation energy (E) for degradation of PP and flame retarded PP composites. The data obtained from the TGA curve indicate that EG markedly increases the thermal degradation temperature of PP/MH composites and improves the thermal stability of the composites. The kinetic results show that the values of E for degradation of flame retarded PP composites is much higher than that of neat PP, especially PP/MH composites with suitable amount of EG, which indicates that the flame retardants used in this work have a great effect on the mechanisms of pyrolysis and combustion of PP. [ABSTRACT FROM AUTHOR]

The flammability, thermal properties, and synergistic effects of modified expandable graphite (MEG) with magnesium hydroxide (MH) and aluminum hydroxide (ATH) on the linear low-density polyethylene/ethylene vinyl acetate (LLDPE/EVA) blends are investigated by Underwriters Laboratories-94 (UL-94) vertical combustion test, limiting oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter test (CCT), and scanning electron microscopy (SEM). The results show that the MEG improves the flame-retardant efficiency of LLDPE/EVA blends. The addition of MEG apparently improves the LOI values and the UL-94 rating of LLDPE/EVA composites. The data obtained from the CCT show that the heat release rate (HRR), the total heat release (THR), and the gas production rate of composites with MEG decrease remarkably with increasing the content of MEG. When 10 phr of MEG is added, the char residues of LEMEG10 increase to 38.2% from 2.7% of LLDPE/EVA. The results of SEM and CCT present that MEG can improve the quality of char layers. The rate of char formation is enhanced also due to the existence of MEG, which plays an important role to improve the flame retardancy of the LLDPE/EVA composites. [ABSTRACT FROM AUTHOR]

In this work, modified expandable graphite (MEG) and zinc borate (ZB) are melt‐blended with metal hydroxide/aluminum hydroxide flame retardant linear low‐density polyethylene/ethylene vinyl acetate (LLDPE/EVA) blends. The synergistic effects of MEG with ZB on the flammability, thermal stability and crystallization behaviors of LLDPE/EVA composites are characterized and discussed by UL‐94 vertical burning, limiting oxygen index (LOI), thermogravimetric analysis, cone calorimeter test (CCT), carbon layer morphology, and differential scanning calorimetry (DSC). The addition of ZB and MEG apparently increases the LOI values and improves the UL‐94 rating of the flame retardant LLDPE/EVA composites. The data obtained from the CCT indicate that the heat release rate, the total heat release and the gas production rate of the flame retardant LLDPE/EVA composites decrease remarkably with increasing the MEG content and the residues of the composites increase to 38.2% from 2.7% of the LLDPE/EVA blends, which indicates that MEG enhances the thermal stability and layer carbon capacity of the composites. The DSC results describe that MEG can act as a nucleating agent to accelerate the crystallization rate of the flame retardant composites, but the crystallinity of polypropylene of the flame‐retardant composites firstly increases and then decreases with increasing the content of MEG. POLYM. COMPOS., 40:E687–E694, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Researchers have widely focused on the high flammability and releasing toxic gases of rigid polyurethane foam (RPUF) under fire attack. In this work, the hybrid expandable graphite (EG) intumescent flame retardant is designed and fabricated for the fire safety of RPUF. Hexachlorocyclotriphosphazene (HCCP) is self-assembled on the surface and interlamination of EG (HCCP@EG) via water bath method and incorporated into RPUF matrix to improve the flame retardant efficiency of EG and the interfacial adhesion between EG particles and RPUF matrix. The structural morphological characterization indicates that HCCP@EG is successfully synthesized. HCCP@EG also exhibits good thermal stability and high char residues. Compared with neat RPUF, RPUF composites with 15% HCCP@EG show excellent flame-retardant properties and achieve a UL-94 V-0 level and a limiting index higher than 27.0%, which is due to the construction of a network structure of HCCP in the graphite lamellas and its synergistic and barrier effect. In addition, compared with EG, the presence of HCCP enhances interface compatibility between EG and RPUF, resulting in improving the mechanical property of RPUF composites. In summary, this work provides a facile approach to manufacturing high-performance RPUF products with outstanding fire safety. [Display omitted] • A novel and high-efficient flame-retardant (HCCP@EG) is designed and fabricated for rigid polyurethane foams (RPUF). • The RPUF/HCCP@EG flame retardant composites exhibit outstanding flame retardancy. • The compatibility and interfacial adhesion between EG and RPUF are enhanced obviously by HCCP. • The flame-retardant mechanism is also proposed accordingly. [ABSTRACT FROM AUTHOR]