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

Abstract

In this study, different amounts of boric acid (BA, 1.25, 2.5, 3.75 and 5.0 wt%) were used to enhance the effectiveness of an intumescent flame retardant (IFR) system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) in polypropylene (PP) including 2 wt% montmorillonite nanoclay (MMT). Meanwhile, metaboric acid and boron oxide which were generated by the decomposition of BA appeared in the melt compounding and the burning processes, respectively. Extensive experimental studies were performed to investigate the effects of BA/boron oxide and MMT combinations on the properties of PP/IFR. The fire resistances of the composites were studied by UL 94, limiting oxygen index (LOI) and cone calorimetry tests. The thermal properties were determined by using thermogravimetric analysis, differential scanning calorimetry and thermal conductivity measurements. In addition, the mechanical properties of the composites were examined. The experimental results revealed that although the additions of 1.25 and 2.5 wt% BA with 2 wt% MMT significantly enhanced thermal and flame resistances of PP composites, 3.75 and 5.0 wt% BA additions generated antagonistic effects and deteriorated the fire resistance of the composites. The sample including 2.5 wt% BA addition achieved the best flame retardancy. The LOI value was increased from 18 to 31% with UL 94 V-0 rating. In addition, the peak heat release rate was reduced from 668.6 to 150.0 kW/m2 and the total heat release value was decreased from 247.9 to 98.4 MJ/m2. In the meantime, the thermal conductivity was increased from 0.22 up to 0.28 W/mK. Furthermore, CO, CO2 and the smoke productions were significantly decreased with respect to PP. NO generation was decreased with BA replacements. At the same time, although there was a slight decrease in the tensile strength, the flexural strength significantly increased with BA and MMT additions.

Synergistic Effect of 4A Molecular Sieve on Intumescent Ternary H-Bonded Complex in Flame-Retarding of Polypropylene

“…It can be seen that the decomposition of TH-IFR is divided into four stages ( Figure 2 b). The first stage is in the range of 150~258 °C, which could be attributed to water loss and degradation of the incompletely reacted PER [ 37 ]; the second stage is in the range of 280~350 °C, which could be caused by the release of water and ammonia due to the existence of hydroxyl and amine groups; the three stage is in the range of 350~427 °C, which is attributed to the formation of char layer; the four stage falls in the range of 427~650 °C, which could be ascribed to the further degradation of the char layer and the formation of the final intumescent carbon layer. Moreover, the char yield of TH-IFR at 700 °C is 38.29%, revealing a good char-forming capability.…”

“…The DSC melting and crystallization curves of samples are shown in Figure 6 , and the corresponding parameters are summarized in Table 4 , including the crystallization temperature (T c ), the crystallization enthalpy (ΔH c ), the melting temperature (T m ), the melting enthalpy (ΔH m ) and the crystallinity (X c ). The X c is calculated according to the following equation: where ΔH m is the melting enthalpy, f is the weight fraction of PP in the composite and ΔH 0 = 209 J/g is the theoretical melting enthalpy of the 100% crystalline PP [ 37 ]. It can be seen that the T c of all the FR PP composites is higher than that of pure PP, indicating that the incorporated TH-IFR fillers and TH-IFR/4A composite fillers both show the heterogeneous nucleation effects on the crystallization of PP macromolecular chains.…”

Insights into structural, thermal, electrical and mechanical properties of copper alumina reinforced chlorinated natural rubber nanocomposites

“…These properties have a great significance in restricting the fire by forming a swollen char or a protective covering on the surface of polymeric materials and thereby resisting further combustion. 46 Chlorinated NR shows the limiting oxygen index (LOI) value of 23.6%, which is higher than the oxygen content present in atmospheric air. It is found that the LOI value increases with filler loading in chlorinated NR, indicating the increased flame resistance of composites compared to chlorinated NR.…”

Experimental analysis of the effect of natural fibers and SiC filler on the thermal behavior of green biocomposites

“…The use of GBCs has been limited due to its poor flame retardancy. To address this issue, it is important to enhance their fire resistance to protect the structural integrity of the underlying materials 31–33 . One of the most used means is to apply Intumescent Fire Retardants (IFR).…”