Abstract
AbstractThis work aims to study the synergistic effect of aluminum/magnesium hydroxide microfillers and organomodified fumed silica nanoparticles as flame retardants (FRs) for linear low-density polyethylene (LLDPE), and to select the best composition to produce a fire-resistant polyethylene-based single-polymer composite. The fillers were added to LLDPE at different concentrations, and the prepared composites were characterized to investigate the individual and combined effects of the fillers on the thermo-oxidation resistance and the fire performance, as well as the microstructural, physical, thermal and mechanical properties. Both filler types were homogeneously distributed in the matrix, with the formation of a network of silica nanoparticles at elevated loadings. Melt flow index (MFI) tests revealed that the fluidity of the material was not considerably impaired upon metal hydroxide introduction, while a heavy reduction of the MFI was detected for silica contents higher than 5 wt%. FRs introduction promoted a noticeable enhancement of the thermo-oxidative stability of the materials, as shown by thermogravimetric analysis (TGA) and onset oxidation temperature (OOT) tests, and superior thermal properties were measured on the samples combining micro- and nanofillers, thus evidencing synergistic effects. Tensile tests showed that the stiffening effect due to a high content of metal hydroxide microparticles was accompanied by a decrease in the strain at break, but nanosilica at low concentration contributed to preserve the ultimate mechanical properties of the neat polymer. The fire performance of the samples with optimized compositions, evaluated through limiting oxygen index (LOI) and cone calorimetry tests, was strongly enhanced with respect to that of the neat LLDPE, and also these tests highlighted the synergistic effect between micro- and nanofillers, as well as an interesting correlation between fire parameters and viscosity.
Highlights
The massive employment of polymers and polymer-matrix composites has been driven by their combination of low density, high processability and interesting mechanical and physical properties [1, 2]
linear low-density polyethylene (LLDPE)-based micro/nanocomposites were prepared by using surface functionalized fumed silica nanoparticles and two kinds of metal hydroxides at different relative amounts
scanning electron microscopy (SEM) images revealed that both metal hydroxide microparticles and fumed silica aggregates were homogeneously distributed within the matrix, and silica created a percolative network at elevated concentrations
Summary
The massive employment of polymers and polymer-matrix composites has been driven by their combination of low density, high processability and interesting mechanical and physical properties [1, 2]. Polyolefins, and polyethylene (PE) in particular, are among the most widely used thermoplastic polymers, due to the remarkable combination of high chemical resistance, good mechanical properties and cheapness. One of the major drawbacks of polymers and polymer composites is represented by their high flammability, and the improvement of flame resistance of polymers is crucial to broaden their useand meet the increasingly stringent safety requirements [2, 5, 6]. To reach this goal, the most common approach is to add flame retardants (FRs). FRs operate physically and/or chemically in the solid, liquid or gas phase and hinder combustion at different levels [7]
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