Synergistic Flame Retardant Effect between Ionic Liquid Functionalized Imogolite Nanotubes and Ammonium Polyphosphate in Epoxy Resin

Ionic liquid functionalized imogolite nanotubes (INTs-PF6-ILs) were introduced into the epoxy resin (EP)/ammonium polyphosphate (APP) system to investigate the flame retardant performance and thermal properties using the limiting oxygen index (LOI) test, the UL-94 test, and the cone calorimeter test (CCT). The results suggested that a synergistic effect exists between INTs-PF6-ILs and APP on the char formation and anti-dripping behavior of EP composites. For the EP/APP, an UL-94 V-1 rating was obtained for the loading of 4 wt% APP. However, the composites containing 3.7 wt% APP and 0.3 wt% INTs-PF6-ILs could pass the UL-94 V-0 rating without dripping behavior. In addition, compared with the EP/APP composite, the fire performance index (FPI) value and fire spread index (FSI) value of EP/APP/INTs-PF6-ILs composites were remarkably reduced by 11.4% and 21.1%, respectively. Moreover, the char formed by EP/APP composites was intumescent, but of poor quality. In contrast, the char for EP/APP/INTs-PF6-ILs was strong and compact. Therefore, it can resist the erosion due to heat and gas formation and protect the inside of the matrix. This was the main reason for the good flame retardant property of EP/APP/INTs-PF6-ILs composites.

An Effective Method for Preparation of Liquid Phosphoric Anhydride and Its Application in Flame Retardant Epoxy Resin

A novel liquid phosphorous-containing flame retardant anhydride (LPFA) with low viscosity was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and methyl tetrahydrophthalic anhydride (MeTHPA) and further cured with bisphenol-A epoxy resin E-51 for the preparation of the flame retardant epoxy resins. Both Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS) and nuclear magnetic resonance (NMR) measurements revealed the successful incorporation of DOPO on the molecular chains of MeTHPA through chemical reaction. The oxygen index analysis showed that the LPFA-cured epoxy resin exhibited excellent flame retardant performance, and the corresponding limiting oxygen index (LOI) value could reach 31.2%. The UL-94V-0 rating was achieved for the flame retardant epoxy resin with the phosphorus content of 2.7%. With the addition of LPFA, the impact strength of the cured epoxy resins remained almost unchanged, but the flexural strength gradually increased. Meanwhile, all the epoxy resins showed good thermal stability. The glass transition temperature (T_g) and thermal decomposition temperature (T_d) of epoxy resin cured by LPFA decreased slightly compared with that of MeTHPA-cured epoxy resin. Based on such excellent flame retardancy, low viscosity at room temperature and ease of use, LPFA showed potential as an appropriate curing agent in the field of electrical insulation materials.

Study on flame retardancy and smoke suppression of PET by the synergy between Fe2O3 and new phosphorus-containing silicone flame retardant

To reduce the environmental hazard from the flame retardant, a halogen-free phosphorus-containing silicone flame-retardant poly N, N dimethylene phosphate aminopropyl siloxane (PDPSI) was prepared following the Mannich reaction. Then, PDPSI and ferric oxide (Fe2O3) were used for the preparation of synergistic flame-retardant polyethylene terephthalate (PET). The flame-retardant test results revealed that at 2% PDPSI/Fe2O3 content and 1:2 mass ratio of PDPSI to Fe2O3, the limit oxygen index value of the PDPSI/Fe2O3/PET composite material was 27.9%, reaching the flame-retardant level and passing the V-0 rating in the UL-94 test. In addition, the PDPSI/Fe2O3/PET composites had a char residue content of 17.5% at 700°C, an increase of 30.6% compared to that of the pristine PET. In the cone calorimeter test, the addition of PDPSI/Fe2O3 significantly reduced the peak heat release rate (PHRR), total heat release (THR) rate, and total smoke production (TSP) value of the resulting PET composites. PHRR and THR decreased by 66.05% and 14.3%, respectively. The TSP value decreased from 14.4 m2 to 8.1 m2, a decrease of 43.8%. The scanning electron microscopy images and Fourier-transform infrared spectra of the char residue showed a significant synergy between Fe2O3 and PDPSI, changing the structure of the carbon layer in continuous and dense form, thus the flame retardancy and smoke suppression of the PET composites improved. In addition, the tensile strength of the PET composite was 42.11 MPa, which was only 1.84% less than that of the pristine PET.

Effective Biobased Phosphorus Flame Retardants from Starch-Derived bis-2,5-(Hydroxymethyl)Furan

A series of biobased phosphorus flame retardants has been prepared by converting starch-derived bis-2,5-(hydroxymethyl)furan to the corresponding diacrylate followed by Michael addition of phosphite to generate derivatives with phosphorus moieties attached via P–C bonds. All compounds behave as effective flame retardants in DGEBA epoxy resin. The most effective is the DOPO derivative, 2,5-di[(3-dopyl-propanoyl)methyl]furan. When incorporated into a DGEBA blend at a level to provide 2% phosphorus, a material displaying a LOI of 30, an UL 94 rating of V0 and a 40% reduction in combustion peak heat release rate compared to that for resin containing no additive is obtained. The analogous compounds generated from bisphenol A and tetrabromobisphenol A exhibit similar flame-retarding properties.