Polyamide‐enhanced flame retardancy of ammonium polyphosphate on epoxy resin

Abstract

An attractive intumescent flame retardant epoxy system was prepared from epoxy resin (diglycidyl ether of bisphenol A), low molecular weight polyamide (cure agent, LWPA), and ammonium polyphosphate (APP). The cured epoxy resin was served as carbonization agent as well as blowing agent itself in the intumescent flame retardant formulation. Flammability and thermal stability of the cured epoxy resins with different contents of APP and LWPA were investigated by limited oxygen index (LOI), UL-94 test, and thermogravimetric analysis (TGA). The results of LOI and UL-94 indicate that APP can improve the flame retardancy of LWPA-cured epoxy resins. Only 5 wt % of APP can increase the LOI value of epoxy resins from 19.6 to 27.1, and improve the UL-94 ratings, reaching V-0 rating from no rating when the mass ratio of epoxy resin to LWPA is 100/40. It is much interesting that LOI values of flame retardant cured epoxy resins (FR-CEP) increase with decreasing LWPA. The results of TGA, FTIR, and X-ray photoelectron spectroscopy (XPS) indicate that the process of thermal degradation of FR-CEP consists of two main stages: the first stage is that a phosphorus rich char is formed on the surface of the material under 5008C, and then a compact char yields over 5008C; the second stage is that the char residue layer can give more effective protection for the materials than the char formed at the first stage do. The flame retardant mechanism also has been discussed according to the results of TGA, FTIR, and XPS for FR-CEP.

Water resistance, thermal stability, and flame retardation of polypropylene composites containing a novel ammonium polyphosphate microencapsulated by UV-curable epoxy acrylate resin

“…In comparison with PP/APP, the T onset of PP/EA‐APP was 282°C, much higher than that of PP/APP. This illustrates that the shell of EA resin delayed the pyrolysis process of APP in the initial temperature range . In the whole process of thermal decomposition, the amount of the residue for PP/EA‐APP was more than that of PP/APP, indicating that the thermal stability of PP/EA‐APP was improved to some extent after being microcapsulated by EA.…”

“…At 290°C, the peaks at 284.5 eV could be assigned to C–H and C–C in aliphatic and aromatic species in the material. The bands around 286.1 eV were the contributions of C–O–C, C–OH, C–N, and C–O–P . Interestingly, new peak around 288.8 eV appeared at 312°C and became stronger at 550°C, which could be ascribed to the bonds of CO, CC, and CN, indicating that more steady cross‐links were further formed by aromatization at relatively high temperature.…”

“…c. As can be seen, the bonds at 531.6 eV can be assigned to double binding = O in phosphate and carbonyl groups (CO, PO); the other peak around 533.0 eV can be assigned to –O– in C–O–C, P–O–C, P–O–P, and/or C–OH groups . The relative intensity of 533.0 eV had a raise at high temperature, demonstrating the reaction between EA resin and the phosphoric acid(s).…”

“…During this process, cross‐linked reaction might occur and then led the formation of a three‐dimensional network structure. The EA resin containing a large number of hydroxyl groups could promote the dehydration reaction in EA‐APP, which facilitated the stabilization of APP and reduced the volatility of phosphorus, and thus more APP would be available for phosphorylation and the formation of char . This would certainly enhance the stabilization of the three‐dimensional network structure.…”

“…Ammonium polyphosphate (APP, (NH 4 ) n + 2 P n O 3n + 1 ), as a very common and popular inorganic phosphorus/nitrogen flame retardant (FR), has been extensively investigated because of its being inexpensive, low toxicity, and higher thermal stability . Generally, APP can improve the flame retardancy of cured epoxy resins and coatings effectively when it is used alone . Several physical modes of FR action of APP have been suggested in the literatures, such as the formation of polyphosphoric acid as a surface coating, dilution of the combustible pyrolysate by less combustible gas products, and the reduction of melt viscosity that suppresses melt dripping.…”