Abstract
Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of organic montmorillonite (OMMT) on the structure and properties of flame-retardant PA6 nanocomposites were systematically investigated. The X-ray diffraction and transmission electron microscopy results suggested that the introduction of OMMT improved the dispersion of the flame retardant particles independently of the type of OMMT. The derivative thermogravimetry (DTG) curve transformed to one peak from two peaks (representing the degradation of ABPA and PA6, respectively) after incorporation of the OMMT, which further confirmed better ABPA dispersion. Viscoelastic measurements demonstrated that a mechanically stable network structure was formed with the introduction of OMMT or ABPA and OMMT, while PA6/ABPA/PMMT presented the highest storage modulus and viscosity, suggesting a more efficient network structure. From UL-94 and limited oxygen index (LOI) tests, PA6/ABPA/PMMT presented the best flame performance, with a UL-94 of V-0 and a LOI of 33%. In addition, the PA6/ABPA/PMMT presented the lowest peak heat release rate (pHRR) among the investigated samples. Combined with the char layer analysis, it can be deduced that the introduction of PMMT improved the dispersion of ABPA, and promoted the formation of more efficient network structure, before promoting more compact char structures, which finally resulted in improved flame retardancy.
Highlights
Apart from dramatic improvements in mechanical, thermal, and barrier properties, polymer/clay nanocomposites have been rendered even more attractive by recent demonstrations of their flame-retardant properties, which is namely diminution of the heat release rate
Compared to the PA6/clay nanocomposites, a more compact protective layer was formed in the case of flame-retardant PA6/clay nanocomposites. We examined whether such a relationship can be generalized to flame-retardant polymer nanocomposites based on different types of organic montmorillonite and explored how the different types of OMMT influence the microstructure of the flame retardant nanocomposites and the flame retardancy
PA6, platelets are obtained for both PA6/aluminium salts of diisobutylphosphinic acid (ABPA)/CMMT and PA6/ABPA/phosphonium salt intercalated MMT (PMMT)
Summary
Apart from dramatic improvements in mechanical, thermal, and barrier properties, polymer/clay nanocomposites have been rendered even more attractive by recent demonstrations of their flame-retardant properties, which is namely diminution of the heat release rate This effect is mainly attributed to the formation of a char barrier on the surface of the polymer, which insulates the underlying materials and slows the mass loss rate of decomposition products during pyrolysis and combustion [1,2]. It has been shown that nanocomposites based on nanoclay and flame-retardant particles formed a continuous network structure in the initial samples, before formation a protective solid layer on the burning surface made of clay and carbonaceous material. We examined whether such a relationship can be generalized to flame-retardant polymer nanocomposites based on different types of organic montmorillonite and explored how the different types of OMMT influence the microstructure of the flame retardant nanocomposites and the flame retardancy
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