Study On Synergistic Char-forming Behavior Of Green Flame Retardant Polymer Materials

In this paper, three kinds of polyoxometalates-based ionic liquids (PILs) hybrid materials ([BMIm]3PW (PIL1),[BMIm]3PMo (PIL2) and [BMIm]4SiW (PIL3)) were synthesized by using polyoxometalates and a room temperature ionic liquid. The PILs were introduced into polypropylene/intumescent flame retardants (PP/IFR) system to modify its flame retardant efficiency. The used IFR was a combination of ammonium polyphosphate (APP) and pentaerythritol (PER) with a weight ratio3:1. The PILs structures were verified by FT-IR,1H-NMR techniques. Analysis of the results showed that the basic structure and geometry of the polyoxometalates’Keggin anions entrapped in the [BMIm]+cations were preserved. In addition, the polyoxometalates lose crystalliferous water due to the introduction of organic fractions, it mean that the PILs were successfully achieved. The flame retardant and thermal properties of the PP/IFR/PILs composites were investigated. It is found that the presence of PILs play great roles in the flame retardant properties of PP/IFR composites. The synergistic effect in PP composites of PILs were ordinal and ordinal for PIL2> PIL1> PIL3. The PP composite with0.5wt%PIL2and14.5wt%IFR has a LOI28.0and passes the UL-94V-0test without melt-dripping, while that for PP/IFR is only23.7and not classified (NC) at the same content. It is because PILs promote charring reaction in IFR and improve the thermal stability of the PP composites. Investigated the morphology and structure of carbon residue, objective to know the intrinsic factors that affect the char formation and flame retardant performances of PP/IFR systems during combustion. The morphology of char residue reveals that the PIL2promoted the reaction between APP and PER, so more N element was kept in the condensed phase, accelerated the formation of compact and continuous charring layer and enhanced the char accumulating degree which is the inherent reason for good flame retardant properties. However, PIL1and PIL3also promoted the char-forming reaction, but they were more inclined to lead PP/IFR to degradation rather than charring. So PIL1and PIL3showed poor synergistic effects on charring behavior. The research of this paper offered a highly efficient intumescent flame retardant (IFR) system for PP by adding PIL2into conventional PP/IFR composites. This provided a feasible strategy for a highly efficient and environmentally friendly flame retardant system.