Synergistic improvement of fire retardancy and mechanical properties of ferrocene‐based polymer in intumescent polypropylene composite

Abstract

The ferrocene-based polymer (PDPFDE) accompanied with traditional intumescent flame retardant (IFR) system (ammonium polyphosphate (APP)/pentaerythritol (PER) = 3/1, mass ratio) has been used as additive flame retardant in polypropylene (PP), aiming to lower the total loading amount. The thermal stability and fire retardant properties were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical combustion (UL-94), and cone calorimetry (CONE). The fire retardant mechanism was studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The results showed that the PP1 with 25 wt% IFR only passed the UL-94 V-1 rating, but the PP6 loaded by 0.5 wt% PDPFDE and 22.5 wt% IFR possessed an LOI value of 28.5% and passed the UL-94 V-0 rating; the peak heat release rate (pHRR) and total heat release (THR) are decreased by 63% and 43%, respectively, compared with pure PP. In addition, the char residue of PP6 manifested a very compact and smooth surface, indicating a more effective barrier layer. Meanwhile, it was interesting that the addition of PDPFDE evidently improved the impact strength and elongation at break of PP/IFR composites. KEYWORDS ferrocene-based polymer, fire retardancy, mechanical properties, polypropylene, synergistic effect 1 | INTRODUCTION Polypropylene (PP) is of numerous applicability in packaging, construction, electronics, automotive, and chemical industries due to its low density, easy processing, chemical resistance, high-cost performance, and good mechanical properties. 1-3 However, its high flammability limits its application in fire-required fields, where most manufacturers are looking for halogen-free alternatives to replace small molecule halogenated flame retardants, which released from their host polymer, and have been shown to be persistent, bioaccumulative, and toxic (PBT). 4-8 In recent years, a mounting number of environment-friendly intumescent flame retardants (IFRs) have been widely used in polyolefin. 9-14 However, the low efficiency and poor compatibility of IFRs lead to the high-loading amount, inevitably deteriorate the mechanical properties of the flame retardant PP composites. 15-18 To figure out these shortcomings, Wang et al added adenine (A), guanine (G), cytosine (C), and uracil (U) as gas sources into IFR flame retardant PP system, respectively, in order to improve the flame retardant efficiency of IFR. PP composites containing 17 wt% IFR and 1 wt% C or U can pass the UL-94 V-0 rating and achieve a limiting oxygen index (LOI) value of 27.9%. 16 Chen et al synthesized a charring agent called PETAT and used it to synergize with ammonium polyphosphate (APP) to flame retardant PP. When APP/PETAT = 2/1(mass ratio) and the total loading is 25 wt%, the PP composites can pass the UL-94 V-0 rating, and the LOI value reaches 30.3%. Moreover, the tensile strength is not further damaged, and the bending strength is remarkably improved. 17

A strategy to construct multifunctional ammonium polyphosphate for epoxy resin with simultaneously high fire safety and mechanical properties

“…Whereas comparing with the calculated curve of APP and ZIF-67, the thermal decomposition started early and maximum weight loss rate of ZIF-67@APP at first decomposition step increased both N2 and O2 atmosphere. The phenomenon indicated that the ZIF-67 could accelerate the decomposition of APP and formation of the series structures of P-OH and Co 2+ -APP [52][53]. When the temperature increased from 450 °C to 700 °C under N2 atmosphere, the thermal decomposition step was divided into two steps and the maximum weight loss rate decreased obviously, and ZIF-67@APP displayed more residue up to 52.6 wt% from 27.9 wt% for APP at 700 °C, indicating that the synergistic effect existed between ZIF-67 and APP, which could promote the formation and the thermal stability of phosphorylation cross-linking structures at high temperature.…”

The effect of boric acid on flame retardancy of intumescent flame retardant polypropylene composites including nanoclay

“…When IFR was added to PP0, the tensile and flexural strengths of PP1 were decreased by 8.7% and 5.7%, respectively, due to the partially poor compatibility, poor dispersion, and agglomeration of IFR in the polypropylene matrix. 36,[120][121][122] However, 2% MMT addition into PP1(PP/IFR) enhanced the mechanical properties. The tensile strength of PP2 became 41.3 MPa and the flexural strength increased to 54.7 MPa.…”

Preparation and performance of waterborne polyurethane coatings based on the synergistic flame retardant of ferrocene, phosphorus and nitrogen

“…Therefore, in practical application, ferrocene is often used as a synergistic agent, and plays a synergistic effect together with other flame retardants. At present, studies have shown that there is a synergistic flame retardant and smoke suppression effect between ferrocene and halogen, 34 phosphorus, 35,36 nitrogen, 37 silicon 38 as well as intumescent 39 flame retardants.…”