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One of the current challenges in the development of flame retardants is the preparation of an environmentally friendly multi-element synergistic flame retardant to improve the flame retardancy, mechanical performance, and thermal performance of composites. This study synthesized an organic flame retardant (APH) using (3-aminopropyl) triethoxysilane (KH-550), 1,4-phthalaadehyde, 1,5-diaminonaphthalene, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials, through the Kabachnik-Fields reaction. Adding APH to epoxy resin (EP) composites could greatly improve their flame retardancy. For instance, UL-94 with 4 wt% APH/EP reached the V-0 rating and had an LOI as high as 31.2%. Additionally, the peak heat release rate (PHRR), average heat release rate (AvHRR), total heat release (THR), and total smoke produced (TSP) of 4% APH/EP were 34.1%, 31.8%, 15.2%, and 38.4% lower than EP, respectively. The addition of APH improved the mechanical performance and thermal performance of the composites. After adding 1% APH, the impact strength increased by 15.0%, which was attributed to the good compatibility between APH and EP. The TG and DSC analyses revealed that the APH/EP composites that incorporated rigid naphthalene ring groups had higher glass transition temperatures (Tg) and a higher amount of char residue (C700). The pyrolysis products of APH/EP were systematically investigated, and the results revealed that flame retardancy of APH was realized by the condensed-phase mechanism. APH has good compatibility with EP, excellent thermal performance, enhanced mechanical performance and rational flame retardancy, and the combustion products of the as-prepared composites complied with the green and environmental protection standards which are also broadly applied in industry. [ABSTRACT FROM AUTHOR]

• The strength of chars was heightened significantly by the bi-component flame retardant (PODSE/APP). • 20 wt% PODSE/APP led to an 88.1 % and 87.0 % reduction in pSPR and TSP. • The char residue was substantially increased by 89.2 % with 20 wt% PODSE/APP. • PODSE/APP changed the internal structure of chars into honeycomb with higher expanded ratio. The intrinsic flammability and high smoke production are two major defects that epoxy resin (EP) must overcome during the practical application. However, few current studies have acknowledged in both fire resistance and smoke suppression performance, which is vitally interrelated with quality of char layers. Herein, a P/S-containing compounds (PODSE) was prepared via esterification and then supplemented with ammonium polyphosphate (APP) to develop an intumescent flame retardant for heightening the strength of char. With 20 wt% PODSE/APP, the peak of smoke produce rate (pSPR) and total smoke production (TSP) of EP3 reduced by 88.1 % and 87.0 %, respectively, indicative of superior smoke suppression performance. It attained a limited oxygen index (LOI) value of 40.0 % with V-0 rating during vertical burning test (UL-94) and the char residues at 700 °C increased from 15.8 % to 29.9 % compared with pure EP. More importantly, in order to figure out the reason for such highly-improved performance, the residual chars after cone calorimeter (CC) test were comprehensively investigated. The result showed that the internal chars of the samples modified by PODSE/APP exhibited honeycomb-like structure instead of irregular network structure of the one modified with single PODSE, endowing the char layers with higher expanded ratio and strength, which responded to excellent insulation effect. This finding provided theoretical and experimental basis for further exploration of P/S synergistic intumescent flame retardant. [ABSTRACT FROM AUTHOR]

With the specialization and diversification of the use environment of composite products, composite materials should have good comprehensive properties. Abiding by this target, we successfully prepared a transparent epoxy resin (EP) composite with flame retardancy, low smoke, enhanced toughness, high glass transition temperature by blending the flame-retardant POI synthesized in this work. POI was synthesized from phosphophenanthrene, vanillin and histidine, and the combination of these three raw meticulously selected endowed POI molecule with excellent versatility. EP composite modified with 10 wt% POI (EP/POI-10) obtained a limiting oxygen index (LOI) of 30.5% and received the V-0 grade (UL-94). The reduction of total smoke production by 78.1% via cone calorimeter tests was obtained. The impact strength of EP/POI-7 increased by 48.2% due to the energy dissipation of cracks from POI. The comprehensive analysis of the dual-phase revealed that the improvement of flame retardance was attributed to the joint action of the gaseous phosphorus free radicals quenching and the protecting of condensed coke. Moreover, EP/POI obtained high glass transition temperature as well as good transparency. [Display omitted] • A bio-based flame retardant molecule POI was synthesized. • High-performance composites of EP/POI with high T g , toughened and transparent were prepared. • The EP/POI showed a remarkable smoke suppression effect with a 78.1% reduction in TSP. [ABSTRACT FROM AUTHOR]

A novel diaminodiphenylmethane (DDM) modified ammonium polyphosphate (APP) flame retardant, DDP, was successfully synthesized via ion-exchange reaction. DDP was introduced into epoxy resins (EPs) to reduce flammability. A comparable level of DDP exerts better flame-retardant and smoke suppression efficiencies in EP than APP. An EP blend containing 15 wt% DDP displays a limiting oxygen index (LOI) value of 37.1% and a UL 94 V-0 rating, and further exhibits a 32.3% reduction in total heat release and a 48.0% reduction in total smoke production compared with pure EP. The presence of DDP greatly facilitates char formation during combustion, and the char mass from thermal decomposition of an EP blend is 37.8% smaller than that of an EP blend containing 15 wt% DDP at 800 °C. The incorporation of DDP into EP blends has a smaller impact on the glass transition temperature and tensile strength than those of a comparable level of APP. This reflects the better compatibility of DDP with the EP matrix compared with that for APP. [ABSTRACT FROM AUTHOR]

• A phosphaphenanthrene/benzimidazolone-containing flame retardant (POBDBI) was synthesized successfully. • POBDBI imparted excellent flame retardancy and smoke suppression to EP. • POBDBI exerted flame-retardant effect both in condensed phase and gaseous phase. A novel flame retardant POBDBI was generated by the reaction of p-dibenzaldehyde, 5-amino-2-benzimidazolinone and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and employed to epoxy resin. The structure of POBDBI was measured by FT-IR and NMR tests. Then flame-retardant EP was fabricated by using POBDBI as a flame-retardant. The thermal stability, flame-retardant performance and fire behavior were investigated by a serious of comprehensive instruments. Combustion tests show the flame-retardant performance of composite materials has been significantly improved. For example, the EP/POBDBI-1.0 with the phosphorus content of 1.0% accorded a V-0 rating and its limiting oxygen index (LOI) value increased to 36.5%. Besides, total smoke production (TSP), peak heat release rate (PHRR) and total heat release (THR) of EP/POBDBI-1.0 dropped significantly, and the corresponding values were decreased by 48.4%, 48.9% and 8.7%, respectively. At the same time, the composition, morphology of chars and gaseous products of POBDBI were studied by X-ray photoelectron spectroscopy (XPS), FT-IR, scanning electron microscope (SEM) and Py-GC/MS. These results presented that POBDBI could not only exerted free radical capture effect, but also enhanced the density of char residue. [ABSTRACT FROM AUTHOR]