Synergistic effects of metal hydroxides and fumed nanosilica as fire retardants for polyethylene

This 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.

Design and characterization of flame resistant blended nondrip PA6/Lenzing FR®/PBI fiber nonwoven fabrics

In current thermal protective clothing systems, maximizing the personal protection performance against fire and heat is in great demand. Additionally, minimizing the manufacturing cost by using low-cost materials is also a critical factor. In previous studies [1–3], a new type of low-cost inherently flame resistant (FR) non-drip Polyamide 6 (PA6) nanocomposite fiber was developed. In this paper, this FR non-drip PA6 fiber was tested in blends with two commercially available inherently FR fibers to form FR nonwoven fabrics. Different formulations of varying blending ratios were processed into nonwoven fabrics. The fiber morphology was observed by Scanning Electron Microscopy (SEM). The fabric flammability and combustion properties were characterized using a Microscale Combustion Calorimeter (MCC), and a vertical flame tester, as well as Thermogravimetric Analysis (TGA). Tensile tests were conducted to characterize mechanical properties of these FR nonwoven fabrics. The water vapor permeability test was also performed to measure the wearability of the fabric. Results of several nonwoven blends were compared to find the one with optimum blend ratio which has the potential to be used as low-cost thermal protective fabric.

Rubber toughened flame retardant (FR) polyamide 11 nanocomposites Part 2: synergy between multi-walled carbon nanotube (MWNT) and MMT nanoclay

In the previous study, flame retardant (FR) polyamide 11 (PA11) nanocomposites formulations designed for selective laser sintering (SLS)were prepared and characterized. The SEBS-g-MA elastomer successfully improved the material’s ductility. Although the nonhalogenated FR additives and montmorillonite (MMT) nanoclay successfully decreased the heat release capacity (HRC) and peak heat release rate (pHRR) as characterized by microscale combustion calorimeter (MCC). None of the rubber toughened formulations achieved UL 94 V0 rating, which is a bench mark for many FR polymer applications. As part two of this study, we explored the synergism between two nanoparticles, nanoclay and multi-walled carbon nanotubes (MWNTs), to see whether better FR properties can be achieved. TEM micrographs indicate that both nanoclay and MWNTs achieved high level of dispersion. Flammability results showed that all formulations achieved UL 94 V0 rating, which is a significant improvement from the previous formulations without MWNTs. Char morphology characterization indicated that a solid carbonaceous char layer was reinforced by nanoclay and MWNTs.

Synergistic flame-retardant effect between lignin and magnesium hydroxide in poly(ethylene-co-vinyl acetate)

In this study, we evaluated the interest of combining magnesium hydroxide (MDH) and lignin for developing complementary flame retardant actions in poly(ethylene-co-vinyl acetate) (EVA). Lignin was selected owing to its char forming ability thatwas supposed to reinforce the endothermic effect provided by MDH. The effect of lignin chemical modification by ammonium phosphate functions also evaluated as a way for enhancing its charring effect. Fire properties and thermal behavior of EVA composites were characterized using cone calorimeter, Pyrolysis Combustion Flow Calorimeter (PCFC) and thermogravimetric analysis (TGA). The effect of the incorporation of lignin alone on EVAcomposite thermal and fire behavior first evaluated. Results evidenced that the incorporation of lignin, whatever its nature, induced important reduction of composite thermal stability during TGA analysis as well as significant reduction of the time to ignition (TTI) in cone calorimeter test. However, a significant reduction of peak of heat release rate (pHRR), higher than that obtained with MDH was observed. The combination of lignin and MDH was led to further reduction of pHRR. Furthermore, it was concluded that the chemical modification of lignin is not required prior obtaining improved flame-retardant properties.

Flame retardant PP/PA6 blends: A recipe for recycled wastes

Disposal of plastics in the form of discarded scrap or waste is an environmental nightmare to the developed and under-developing countries. In this sense, modern technologies are every day growing; meanwhile recycling wastes are taking credit for higher performance to pave the way towards a cleaner planet. Recycling of polymer blends is associated with serious complexities in finding appropriate additives acting in each phase or at the interface of non-miscible polymers to attain materials with higher properties. A flame retardant system was designed and intended to play the role of typical recycled flame retardant polypropylene/polyamide (PP/PA6) blends by incorporation of two kinds of talc, sepiolite, and a phosphorus-based flame retardant. First, two types of talcs having different physical properties were added to PA6 in combination with melamine cyanurate (MC) or melamine pyrophosphate (MPP) to find the one acting as a barrier during combustion. Then, high-aspect-ratio talc that appeared more effective in the first-stage survey was then used in combination with MC, MPP and ammonium polyphosphate (APP) together with a compatibilizer for PP/PA6 blend. Then, thermogravimetric analysis (TGA), microcalorimeter of combustion (PCFC) and cone calorimeter measurements were performed to study thermal degradation and flammability behavior. The results are indicative of successful formulation of flame retardant system containing the aforementioned precursors to be intended to the recycled PP/PA6 blends.

Lignin fractionation as an efficient route for enhancing Polylactide thermal stability and flame retardancy

Due to its variable botanical origin, functionality, reactivity, and heterogeneity, using lignin in industrial application is not an easy task. In the present study, we investigate the effect of lignin fractionation as a simple way for reducing the variability in its properties. Kraft lignin was separated by ultrafiltration membranes in two fractions with a specific molecular weight and the properties of each fraction were characterized through FTIR, XPS, TGA and cone calorimeter test. Lignin fractions display different thermal and combustion behaviors. Thus, the two fractions have been evaluated as flame retardant additives for polylactide (PLA). PLA composites, containing well dispersed lignin (20 wt%), were produced by melt blending in an internal mixer. The thermo-degradant effect of each fraction on PLA during melt processing was investigated by rheological analysis and size exclusion chromatography while the composites thermal stability and fire properties were evaluated using TGA and cone calorimeter test. Results showed that using appropriate lignin fraction enables for obtaining PLA composites presenting enhanced properties

Rubber toughened flame retardant (FR) polyamide 11 nanocomposites Part 1: the effect of SEBS-g-MA elastomer and nanoclay

The objective of this research is to develop a multifunctional polyamide 11 (PA11) with balanced thermal, mechanical, and flammability properties for SLS. In this study, two sets of formulations were prepared by twin-screw extrusion: the first set examined the effect of maleic anhydride modified elastomers on flammability and the mechanical properties, whereas the second set added various amount of nanoclay and discussed thermal stability, flammability and mechanical properties. The addition of 20 wt.% elastomer brought the elongation at break up to 40%. Reduction in heat release capacity as high as 49% was achieved, all nanocomposite samples passed UL 94 V-1 rating. The addition of nanoclay improved the tensile modulus by up to 78%, the elongation at break for all the formulations were negatively affected by the addition of flame retardant and nanoclay.

Self-Extinguishing and Non-Drip Flame Retardant Polyamide 6 Nanocomposite: Mechanical, Thermal, and Combustion Behavior

Incorporation of flame-retardant (FR) additives and nanoclay fillers into thermoplastic polymers effectively suppresses materials flammability and melt dripping behavior. However, it largely affects other properties, such as toughness and ductility. In order to recover the lost toughness and ductility of flame retardant polyamide 6, various loadings of maleic anhydride modified SEBS elastomer were added and processed by twin screw extrusion. TEM images showed exfoliated nanoclay platelets and reveals that the clay platelets well dispersed in the polymer matrix. By balancing the ratio of flame retardants, nanoclay and elastomers, formulation with elongation at break as high as 76% was achieved. Combining conventional intumescent FR and nanoclay, UL-94 V-0 rating and the LOI value as high as 32.2 were achieved. In conclusion, effective self-extinguishing and non-drip polyamide 6 nanocomposite formulations with significant improvement in toughness and ductility were achieved.