Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends

Thermal stability and combustion behavior of flame-retardant polypropylene with thermoplastic polyurethane-microencapsulated ammonium polyphosphate

In this article, thermoplastic polyurethane-microencapsulated ammonium polyphosphate (MTAPP) is prepared and well characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis (TGA). MTAPP and APP are added onto polypropylene (PP) as a novel intumescent flame-retardant system to improve the flame retardancy of PP. The flammability, thermal stability, and mechanical properties of the flame-retardant PP composites are investigated by limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimeter test (CCT), TGA, and mechanical properties tests. The results show that MTAPP exhibits better flame retardancy and thermal stability than that of the APP in the flame-retardant PP composites. The LOI value of the PP/MTAPP composite at the same loading level is higher than that of PP/APP composite. The dripping of MTAPP system disappears compared with APP system from UL-94 test. The results of the CCT also indicate that MTAPP is an effective flame retardant in PP. The improvement may be attributed to the better charring capacity of MTAPP from TGA. Additionally, the mechanical properties of MTAPP are better than those of APP in PP.

Study of different-sized sulfur-free expandable graphite on morphology and properties of water-blown semi-rigid polyurethane foams

In this paper, EG with different nominal particle sizes (70 μm, 430 μm and 960 μm) and different loadings from 0 to 50 pphp were considered to investigate the effect of expandable graphite on the morphology and properties of water-blown semi-rigid polyurethane foams (SPFs).

Influence of Aluminum Hydroxide and Expandable Graphite on the Flammability of Polyisocyanurate-Polyurethane Foams

The aim of this work was to verify the influence of expandable graphite (EG) and aluminum hydroxide (ATH) fillers on the flammability of polyisocyanurate-polyurethane (PIR). Limited oxygen index increased to 72.5 with an incorporation of 16 phr (parts per hundred of matrix) EG and 50 phr ATH into the matrix (total weight percent was 39.76%). Cone calorimetry was employed to study the flammability properties of these PIR/ATH/EG composites. Scanning electron microscopy analysis was conducted to study the char characteristics of the composites after the cone calorimetry tests. It was found ATH could effectively induce villi like particles, which made the intumescent char denser, on the surface of EG. The compact char layer could effectively impede the transport of bubbles and heat. ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface. Thus, degradation products of the composite were slowed down and the diffusion of volatile combustible fragments to flame zone was delayed.

Analysis on Properties of Water-Based Fire-Retardant Nano-Coatings

The study explores the effects of the flame-retardant properties of nano-particles on water-based fire-retardant coatings, which include the effects on thermal stability and combustion properties. The coating used by the paper is acrylate resin (VAC), which is added with 3 basic components, including fire-retardant ammonium polyphosphate, pentaerythritol and melamine (APP-PER-MEL), to form an itumescent fire retardant (IFR). Then the fire retardent is added with magnesium hydroxide (Mg(OH)2, MH) nano-particles, multiwall carbon nanotubes (MWNT) and zinc borate (ZB) nano-powders of different concentrations, to form water-based fire-retardant coatings. By adjusting and controlling the concentration ratios of flame retardant to the 3 kinds of nano-particles with different profiles, the study analyzes the fire-retardant multiplying effect of nano-particles on water-based coatings. The nano-coatings mixed in special proportion are coated on plywood. Through thermogeavimetric analyzer (TGA) and cone calorimeter (CCT), the study inspects the thermal stability and combustion properties of water-based fire-retardant nano-coatings. The experimental results show that when the fire-retardant nano-coating composed of MH of concentration 28% and MWNT of concentration 2% is compared with the fire-retardant coating added with flame retardant only, the amount of residue can be increased by around 80% at combustion temperature 580°C. Besides, when the fire-retardant nano-coating composed of MH of weight concentration 28% and MWNT of weight concentration 2% is compared with the fire-retardant coating added with flame retardant only, the maximum heat release can be decreased by about 15%. The time required for this fire-retardant nano-coating to achieve maximum heat release is delayed by around 70 seconds when compared with other samples. Besides, the char-layered structure formed during thermal decomposition of nano-coating is more compact than the char-layered structure of water-based coating composed of the flame-retardant APP-PER-MEL components only. Therefore, nano-coatings can effectively decrease the transfer of heat and inflammable volatiles to plywood surface, and can enhance the flame retardant performance of plywood.

C(60) reduces the flammability of polypropylene nanocomposites by in situ forming a gelled-ball network

The thermal and flame retardancy properties of polypropylene/fullerene (PP/C(60)) nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cone calorimetry with the C(60) loading varied from 0.5 to 2% by weight. Dispersion of C(60) in the PP matrix was characterized by transmission electron microscopy (TEM) and optical microscopy (OM). TGA and DSC results showed that the presence of C(60) could remarkably enhance the thermal property and cone calorimeter measurements suggested that C(60) could to some extent reduce the flammability of PP, with a significant reduction in peak heat release rate and a much longer time to ignition. Furthermore, the larger the loading level of C(60), the better the flame retardancy property of PP/C(60) nanocomposites. The flame retardation mechanism and corresponding model were proposed with the help of rheological measurements, TEM and x-ray diffraction. C(60) reduced the flammability of PP by trapping free radicals in the gas phase and in situ forming a gelled-ball crosslink network to improve the flame retardancy of PP in the condensed phase. Finally, this suggested mechanism was supported by the results of advanced rheological extended systems (ARES), gel content, infrared spectrum, OM, and atomic force microscopy (AFM) measurements.

Substituição de amianto por silicato de alumínio e grafite expansível em compósito de poliuretano utilizado em motor-foguete

Compósitos de poliuretano e amianto (liner) são utilizados como revestimento interno em paredes de motor-foguete, conferindo proteção térmica e garantindo a adesão entre o propelente e as paredes do motor. No entanto, o uso do amianto tem sido restringido devido à sua toxidade. No presente trabalho, o amianto foi substituído por um silicato de alumínio hidratado (SA) e pelo grafite expansível (GE) em diferentes teores no liner. Resultados de análise termogravimétrica (TG) mostraram que a estabilidade térmica do liner praticamente não é afetada pela substituição das cargas, embora a energia de ativação (Ea) obtida para a decomposição tenha mudado, mostrando maiores valores para as amostras contendo as cargas SA e GE. A análise termomecânica (TMA) mostrou que o coeficiente de expansão térmica linear do liner contendo SA foi menor que aquele encontrado para o liner contendo amianto. O liner contendo a carga SA também apresentou os maiores valores de tensão nos testes mecânicos de tração.