A facile strategy to construct multifunctional microencapsulated urea ammonium polyphosphate for epoxy resins towards satisfied fire safety, thermal stability and compatibility

Abstract

Enhancing the fire safety of epoxy resin (EP) concomitant with less mechanical performance degradation is still a challenge for traditional flame retardants. Hence, polypyrrole (PPy) was used as a film material to fabricate microencapsulated urea ammonium polyphosphate (UAPP) for simultaneously improving the fire safety, thermal stability and compatibility of epoxy composites. The obtained polypyrrole-coated urea ammonium polyphosphate (PPy-UAPP) at a load of 10 wt% endows the EP with a UL94 V-0 rating and a limiting oxygen index (LOI) value of 32.3%, while 10 wt% ammonium polyphosphate (APP) only endows EP with a LOI of 28.5%. Furthermore, the peak heat release rate (PHRR) and peak smoke production rate (PSPR) of EP containing 10 wt% PPy-UAPP are decreased by 12.3% and 21.4% compared to EP containing 10 wt% APP. The decreased fire hazard of EP/PPy-UAPP is attributed to the reduction of hazardous gases including CO 2 and CO and the generation of more incombustible gases including H 2 O and NH 3 to reduce the combustion intensity. Meanwhile, the good compatibility between EP matrix and PPy-UAPP endows the resulting EP composites with a superior balance between fire safety and mechanical properties.

Combination effect of ADP‐intercalated kaolinite and ammonium polyphosphate on simultaneously enhancing the flame retardancy and smoke suppression of epoxy resins

“…By comparing Figure 10A, clearly see from Figure 10B that there is little difference in the type of chemical groups between the EP/APP and EP/APP/K‐ADP when the temperature is below 350°C. As temperature rises, the CC (1608 cm −1 ) and POC (991 cm −1 ) peaks are remarkably stronger while the band of CH 3 and CH 2  (2800–3000 cm −1 ) still remains at 400°C, suggesting that K‐ADP can promote the formation of more aromatic and phosphorus‐rich crosslinking structures to protect the matrix 15 . Besides, the exfoliated Kaol could migrate to the surface of the matrix to form a ceramic‐like silica‐phosphate structure.…”

“…34,35 By comparing Figure 10A, clearly see from Figure 10B that there is little difference in the type of chemical groups between the EP/APP and EP/APP/K-ADP when the temperature is below 350 C. As temperature rises, the C C (1608 cm À1 ) and P O C (991 cm À1 ) peaks are remarkably stronger while the band of CH 3 and CH 2 (2800-3000 cm À1 ) still remains at 400 C, suggesting that K-ADP can promote the formation of more aromatic and phosphorus-rich crosslinking structures to protect the matrix. 15 Besides, the exfoliated Kaol could migrate to the surface of the matrix to form a ceramic-like silica-phosphate structure. The special structure provides not only the physical insulation of inorganic materials but also the chemical interaction with aromatic and phosphorus-rich crosslinking structures to improve the thermal insulation of the char layer and enhance the flame retardancy of EP.…”

“…[12][13][14] Significantly, adding individual APP to polymers is not efficient for flame retardancy. 15 For the purpose of reducing fire damage and casualties, it is necessary to modification or adding synergist to effectively promote the flame resistance of APP in polymeric materials. 16 Nowadays, layered silicate depends on its special elemental composition and structural characteristics being a fancy and revolutionary flame retardant synergist.…”

“…Ammonium polyphosphate (APP), as a typical intumescent flame retardant (IFR), is widespread used in the flame retardancy of EPs and other polymers by virtue of the advantages of halogen‐free, heat and smoke resistance and low toxicity 12–14 . Significantly, adding individual APP to polymers is not efficient for flame retardancy 15 . For the purpose of reducing fire damage and casualties, it is necessary to modification or adding synergist to effectively promote the flame resistance of APP in polymeric materials 16 …”