Hongqiang Yan

Effect of graphene nanosheets and layered double hydroxides on the flame retardancy and thermal degradation of epoxy resin

The effects of graphene nanosheets (GNS) and layered double hydroxides (LDH) on morphology, flame retardancy and thermal degradation of epoxy resin (ER) were investigated. LDH was exfoliated in ER/GNS/LDH nanocomposites, while GNS was partially exfoliated and partially agglomerated into small clusters. Since not all of the GNS had good dispersion, the compactness and barrier properties of residual char in ER/GNS/LDH were inferior to ER/GNS and ER/LDH. However, the simultaneous addition of GNS and LDH created an additional GNS–LDH interface, which could increase interaction in the melt and inhibit the flammable drips of ER and thus limit the flame propagation during combustion. As a result, a synergistic effect of simultaneous addition of GNS and LDH to improve the flame retardancy of ER was realized. The LOI value of ER was increased from 15.9 to 23.6 by adding 0.5 wt% of GNS and 0.5 wt% of LDH. In comparison, the LOI value was 19.5 and 21.7 when GNS or LDH was added separately, at the same level, 1 wt%. Furthermore, both GNS and LDH can increase the thermal stability of ER; there was a synergistic effect between them to decrease the THR of ER from 33.4 to 24.6.

Superior flame retardancy of epoxy resin by the combined addition of graphene nanosheets and DOPO

In this paper, the thermal stability and fire retardant behavior of epoxy resin (ER) composites filled with graphene nanosheets (GNS) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were investigated. Addition of GNS and DOPO changed the decomposition pathway of ER. During combustion, DOPO played a key flame retardancy role in the gas phase and the char enhancement in the condensed phase, while GNS played an effect in the condensed phase. Addition of 5 wt% GNS and DOPO separated, the peak heat release rate (PHRR) of ER was reduced from 1194 kW m−2 to 513.9 kW m−2 and 937.1 kW m−2, respectively. With the combined addition of GNS and DOPO, the flame retardancy of ER composites was significantly improved. The PHRR was reduced to 396 kW m−2 at the addition of 2.5% GNS and 2.5% DOPO. The same tendency was obtained for the total heat release (THR), showing a synergistic effect between GNS and DOPO in improving the flame retardancy of ER composites. The combined addition of GNS and DOPO extended the diffusion path for heat and combustible gas while DOPO captured the free radicals which further retarded ER degradation.

A phosphorus-, nitrogen- and carbon-containing polyelectrolyte complex: preparation, characterization and its flame retardant performance on polypropylene

A new polyelectrolyte complex (PEC), containing phosphorus, nitrogen and carbon elements, has been prepared from positively charged polyethylenimine (PEI) and negatively charged phytic acid (PA). The PEC shows good performance in improving the thermo-oxidative stability and flame retardancy of pristine polypropylene (PP). When the content of PEC is 20 wt%, the char residues at 600 °C for the PP/PEC composites (PP/20PEC) are 10 wt% higher than those of pristine PP under an air atmosphere. Meanwhile, the peak heat release rate and total heat release of PP/20PEC are 314 W g−1 and 7.7 kJ g−1 lower than those of pristine PP, respectively. In comparison, PEI or PA is less effective than PEC in improving the thermo-oxidative stability and flame retardancy of pristine PP. Furthermore, the char residues of PP/20PEC are more full and compact, the surfaces of which are covered with a perfect intumescent layer. This work proposes a new guideline for designing and fabricating an intumescent flame retardant system.

Effect of iron acetylacetonate on the crosslink structure, thermal and flammability properties of novel aromatic diamine-based benzoxazines containing cyano group

Iron acetylacetonate (Fe(AcAc)3) was chosen as the catalyst for a novel aromatic diamine-based benzoxazine, containing cyano group (BAPBACP). Its effect on the curing process, thermal and flammability properties of BAPBACP were investigated. The results indicated that without Fe(AcAc)3, the ring-opening polymerization of the BAPBACP monomer occurred and an arylamine Mannich bridge structure was formed at the low curing temperature stage; and then the cyclotrimerization of the cyano group followed at the high curing temperature stage, but the cyano group was not fully cyclotrimerized even after curing at 350 °C for 0.5 h. The addition of 3.5% Fe(AcAc)3 speeded up the curing reaction and the cyano group was fully cyclotrimerized at 350 °C. Thermogravimetric analysis and microscale combustion calorimetry results showed that the poly(BAPBACP) resins possess excellent thermal and flammability properties due to the existence of the arylamine Mannich bridge structure and triazine ring in their crosslinked structure.