The effects of exfoliated varmiculite nanoflakes on the flame retardancy of polyamide 11

What is it about?

Polyamide 11-based bionanocomposites were preparedby melt compounding with 10 wt% clays of different chemistry and morphology. This included vermiculite nanoflakes obtained by consecutive thermal and ultrasonic exfoliation in both neat and organo-modified form.The mechanical reinforcement- and flame-retardant performance of the vermiculite clays were compared to organo-modified montmorillonite (Cloisite 30B) and needle-shaped sepiolite (Pangel S9). Electron microscope investigations revealed different structures and dispersion levels of the clay nanoparticles in the polymer matrix. Tensile tests showed that the addition of clays led to considerable improvements in Young’s modulus without compromising the elongation at break. Compared to the neat polymer, all clays reduced the peak heat release rate and the smoke production rate in cone calorimeter testing. Surprisingly, the needle-shaped sepiolite clay and the two vermiculites outperformed the montmorillonite organoclay in the fire testing even though it featured the highest degree of exfoliation in the polymer matrix.

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Why is it important?

Polyamide 11 is a bio-based polymer derived from a renewable resource, i.e. castor oil [26, 27]. It can be flame retarded with phosphorus-based modifications [27]. However, the use of clay nanofillers is expected to simultaneously improve the mechanical performance. The present investigation considered vermiculite-based bionanocomposites prepared by surfactant-free organo-modification approaches as flame retardant for polyamide 11. Vermiculite exfoliates in a worm-like manner when heated to elevated temperatures. This form exfoliates easily using ultrasonic means. Good dispersion of such extensively delaminated vermiculite sheets are expected to significantly improve fire properties of polyamides.

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