The influence of layered, spherical, and tubular carbon nanomaterials' concentration on the flame retardancy of polypropylene

Abstract

The characteristic influences of increasing concentrations of graphene, expanded graphite (EG), carbon black (CB), and multiwall carbon nanotubes (MWNT) are investigated on pyrolysis, reaction to small flame, burning behavior, and on electrical, thermal, and rheological properties of flame retarded polypropylene (PP-FR). The property-concentration dependency is different for the various material properties, as threshold, linear, and leveling off functions were observed. Increasing concentrations of carbon nanoparticles resulted in a decrease in the electrical resistivity of the polymer by crossing the percolation threshold. The developing nanoparticle network changes melt flow behavior for small shear rates, increases thermal conductivity and therefore, affects the UL 94 classification and oxygen index. The onset temperature of PP decomposition is shifted to temperatures up to 37 C higher; the peak heat release rate is reduced by up to 74% compared to PP-FR. Both effects leveled off with increasing particle concentration. Among the four carbon nanomaterials tested, graphene presents superior influence on composite properties over the tested concentration range and outperforms commercial CB, MWNT, and EG.

Flame-Retardancy Properties of Intumescent Ammonium Poly(Phosphate) and Mineral Filler Magnesium Hydroxide in Combination with Graphene

“…Despite their success in the cone calorimeter, nanoparticles are often not efficient in reducing the overall flammability of polymers. The UL 94 classification and oxygen index remain similar or are even worsened by the addition of nanoparticles [19][20][21][22][23]. An increase in nanocomposites' melt viscosity hinders the polymer material from dripping or flowing away from the pyrolysis zone and thus from cooling it.…”

“…Increasing amounts of TRGO increased the melt viscosity of the already optimized commercial intumescent system APP in PP (Figure 4a). The increase in melt viscosity by nanoparticles is a generally known feature and has already been observed for many particles like TRGO, carbon nanotubes and layered silicate [16,[19][20][21]. Nevertheless, the increase in viscosity for low concentrations of 0.5 wt% TRGO appears to be tolerated without altering the swelling behavior of APP.…”

“…The residue consisting of MgO and TRGO was not effective in hindering the diffusion of the gaseous pyrolysis products. The effect of a shift in only Tonset is also known for TRGO and other carbon particles like carbon black and carbon nanotubes [16,19,20]. The combination of 59 wt% MH with TRGO shifted the entire decomposition step to higher temperatures.…”

“…An increase in nanocomposites' melt viscosity hinders the polymer material from dripping or flowing away from the pyrolysis zone and thus from cooling it. The latest proposals for flame-retardant nanofillers are graphene particles, which have already proved to have the strongest influence on non-charring polymer properties and especially on the burning behavior within the group of carbon (nano)particles [16,19,20].…”

Polylactic acid biocomposites: approaches to a completely green flame retarded polymer

“…By contrast, much lower concentrations (3-10 wt%) of nanomaterials can be used to achieve improved fire behavior under forced-flaming conditions, because they influence the properties of the protecting residual layer formed upon combustion (34)(35)(36)(37). Naturally, it would be of great interest to combine these additives in a synergistic system exploiting the advantages of each component, while keeping the overall additive concentrations as low as possible.…”