Synthesis of phosphazene‐triazine bi‐base sulfonate and its applications in flame‐retardant modified polycarbonate

Abstract

A phosphazene‐triazine bi‐base sulfonate compound (CPNS) was synthesized using hexachlorocyclotriphosphazene, cyanuric chloride, and sodium p‐hydroxybenzene sulfonate as raw materials. The chemical structure was determined by FTIR, 1H NMR 31P NMR (NMR stands for nuclear magnetic resonance), and elemental analysis of P, Na. To study the flame retardant properties of CPNS, a series of modified polycarbonate (MPC) with different ratios of CPNS were prepared. The flame retardant performance and thermal stability of CPNS/MPC were characterized by limiting oxygen index (LOI), UL‐94 vertical burning test, cone calorimetry test, and TG. Results show that when CPNS is added to 0.3%, the CPNS/MPC can pass the UL94 V‐0 level with an LOI value of 35.3% and reduce the peak heat release rate by 16.89% during the combustion. TG results show that adding 0.1% CPNS can decrease the initial decomposition temperature of the MPC by 68°C in nitrogen and 27°C in air. The reduction of the initial decomposition temperature means that the flame retardant promotes the isomerization reaction of polycarbonate accelerates the formation of an intermediate char on the surface. Investigation of intermediate char residue's morphology and chemical structure demonstrates that CPNS promotes the formation of more complete and compact char residue, which acts not only there is increased opportunity for radical recombination reactions in the condensed phase but also as physical barriers to inhibit the transfer of heat and oxygen, resulting in good flame retardant properties.

Preparation and Characterization of Transparent Polycarbonate with High Flame Retardancy and Smoke Suppression

“…When 0.04 wt % HSPP was added, the T onset of PC/HSPP-2 declined to 467 °C, while pristine PC had a T onset of 489 °C. This was because the organosulfonate groups in HSPP could promote chain isomerization and rearrangement of PC in high temperature. , A similar trend was also found for T max . Although the thermal stability of PC/HSPP composites decreased to some extent, the sulfonate moieties from HSPP could catalyze the isomerization and Fries rearrangement of PC and promote the formation of intermediate chars at a lower temperature, which favored the self-extinguishment of flame. ,, The final char residues at 700 °C for PC/HSPP were almost the same as those of PC due to the low loading of HSPP (less than 0.06 wt %), which suggested that the char forming effect could not play a dominant role in the following flame retardancy behaviors.…”

“…With the temperature increasing, the residual phosphazene moieties began to degrade at temperature from ca. 520 to 620 °C, which resulted in the following second mass loss . Interestingly, although the final residues were almost the same, the first mass loss of HSPP in air was lower than that in N 2 , which could be caused by the oxidative scission of sulfonate groups …”

“…The TCT of PC/HSPP-2 was just 400 s, while that of PC was as long as 855 s. The shorter the TCT, the better is the flame retardancy. This phenomenon could be explained that the presence of sulfonates and phosphazene moieties in HSPP promoted the forming of a protective carbon layer on the surface of PC and released in advance the radical scavenger containing P element in gas …”

“…Although the thermal stability of PC/HSPP composites decreased to some extent, the sulfonate moieties from HSPP could catalyze the isomerization and Fries rearrangement of PC and promote the formation of intermediate chars at a lower temperature, which favored the self-extinguishment of flame. 8,17,27 The final char residues at 700 °C for PC/HSPP were almost the same as those of PC due to the low loading of HSPP (less than 0.06 wt %), which suggested that the char forming effect could not play a dominant role in the following flame retardancy behaviors.…”

“…This phenomenon could be explained that the presence of sulfonates and phosphazene moieties in HSPP promoted the forming of a protective carbon layer on the surface of PC and released in advance the radical scavenger containing P element in gas. 27 The toxic smoke is mainly responsible for over 70% of people killed by fires. One disadvantage for PC is the heavy smoke release and high CO yield (COY) during combustion.…”