Glow Wire Research Articles

Uncertainty determination of glow-wire test for ignition of materials

The glow-wire test has been one of the basic electrotechnical material fire tests since the 1970 s. Although the test exists in a large number of versions, only one is internationally standardized as IEC 60695-2, Parts 10–13. Test results are ignition or flame persistence of a material in contact with a glow wire at a given temperature. Since the measurement is qualitative, uncertainty can only be performed on the temperature measurement itself. This article demonstrates the main verifications needed to ensure trueness and repeatability of the test and proposes a method to calculate test uncertainty. It also summarizes the results of various round-robin inter-laboratory studies and presents an example application of uncertainty determination.

Study of Glow Wire Ignition Temperature (GWIT) and Comparative Tracking Index (CTI) performances of engineering thermoplastics and correlation with material properties

Recent regulation IEC 60335-1 ed.4 (2008) was introduced for materials used in electric appliance, establishing new limits in Glow Wire Ignition Temperature (GWIT) performance for materials used for electric connectors. Development of new products with high GWIT is possible, but the main issue is to keep good mechanical properties and processability, as well as tracking resistance (Comparative Tracking Index-CTI). Only a few patents and scientific publications exist about glow wire test performance of polymers. In this work we report GWIT and CTI properties for three engineering thermoplastic polymers (PBT, PET and PC). We have also studied the phenomena involved in this test, treating the phenomena with the parameterisation approach already used in the studies of the fire behaviour of polymers. PC, PBT and PET filled with 30% w/w glass fibres have been tested, and material properties that can be related to GWIT and CTI performance have been measured by TGA, Laser Flash Thermal Diffusivity (LFTD), Pyrolysis-GC/MS. CTI seems to be correlated with the char formation tendency of the materials, so PBT show a higher tracking resistance than PET and PC. Polycarbonate was the only material that passed the glow wire test (GWIT higher than 775°C) but generally GWIT performance is not directly related with degradation temperature, since PET is thermally more stable compared with PBT, but less stable in glow wire test. The ignition process, together with the unsteady heat and mass transfer process characteristic of glow wire testing, are affected by many parameters at the same time. That’s why it is not easy to relate results of TGA, Laser flash, Pyrolysis-GC/MS with the glow wire ignition temperature of the materials tested, but the whole of these properties can give useful indication.

Uso da cinza da casca de arroz como carga em matrizes de poliamida 6 e poliamida 6.6

Este trabalho avalia a utilização da cinza da casca de arroz como carga estrutural em poliamida 6 e poliamida 6.6. Estas matrizes poliméricas são importantes plásticos de engenharia com aplicações em várias áreas. Fez-se uma comparação das propriedades mecânicas de resistência à tração, resistência à flexão, resistência ao impacto e a propriedade térmica de fio incandescente entre compostos de poliamida 6 e poliamida 6.6, com 30% de cinza da casca de arroz, e compostos de poliamidas com 30% de talco. Os resultados das propriedades mecânicas e térmica mostraram um comportamento semelhante entre as poliamidas com 30% de cinza da casca de arroz e as poliamidas com 30% de talco. Assim sendo, o uso da cinza da casca de arroz é uma alternativa viável para a substituição do talco como carga, como foi comprovado ao confeccionar um conector elétrico injetado com poliamida 6.6 com 30% de cinza da casca de arroz. Portanto, este trabalho contribui para a diminuição de um problema ambiental, possibilitando o uso da cinza da casca de arroz em processos industriais.

Thermal behaviour of compatibilised polypropylene nanocomposite: Effect of processing conditions

The thermal properties and fire behaviour of polypropylene (PP) nanocomposites were investigated using differential scanning calorimetry, dynamic-mechanical analysis, thermogravimetric analysis and glow wire test. In order to study the morphological structure of the materials obtained, TEM and XRD analyses were also carried out. The nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. Particular attention was given to studying the influence of different processing conditions (barrel temperature profile and screw rate) and compositions of PP–nanoclay blends (clay content, use of compatibiliser) on the thermal properties of the nanocomposites. The results show that all the properties analysed were strongly influenced by the nanocomposite composition; instead, the processing conditions greatly affect only the dynamic-mechanical properties. DSC curves show that the crystallinity is deeply influenced by the presence of the clay in the matrix, owing to the fact that the filler acts as nucleating agent. DMA curves show that materials processed at low temperature profile and high shear stress, i.e. when a good clay dispersion is achieved, are characterised by an enhanced modulus, thus indicating that the incorporation of clay into the PP matrix remarkably enhances its stiffness and has good reinforcing effects. TGA traces in oxidizing atmosphere show a drastic shift of the weight loss curve towards higher temperature and no variation of the onset temperature (i.e. the temperature at which degradation begins). The TGA analyses in inert atmosphere show instead marked increase of this parameter (about 200 °C) and no shift of weight loss curves. Glow wire results highlight that polymer nanocomposites are characterised by enhanced fire behaviour.

Fire retardancy of polypropylene/flax blends

A comprehensive characterization of the thermal and the fire behaviour is presented for polypropylene (PP) flax compounds containing ammonium polyphosphate (APP) and expandable graphite as fire retardants. Thermogravimetry coupled with an evolved gas analysis (TG-FTIR) was performed to ensure a significant thermal analysis. The fire response under forced flaming conditions was studied using a cone calorimeter. The external heat flux was varied between 30 and 70 kW m −2 so that the results could be evaluated for different fire scenarios and tests. Different flammability tests (UL 94, limiting oxygen index, glow wire test, GMI 60261) were performed and the results compared with the cone calorimeter data. The different char forming mechanisms are described and the resulting fire retardancy is classified. The successful and ecological friendly fire retardancy is a technological breakthrough for PP/flax biocomposites.

Clariant lays foundation for new flame retardants plant

The effect of changing the ratio of aluminium diethyl phosphinate (as Exolit OP1230) and zinc stannate (as Flamtard S) present within a glass-reinforced high temperature polyamide (HTPA/GF) at a constant total flame retardant level of 15 wt% is shown to have fire performance properties that depend on the ratio of both these agents. Aluminium diethyl phosphinate (AlPi) alone at 15 wt% gives LOI > 40 vol% and a V-0 rating. The introduction of zinc stannate (ZS) at levels up to 3.75 wt% maintains the LOI at about 40 vol% and the V-0 rating. Similarly, glow wire ignition temperatures and cone calorimetry results, in terms of minimal peak heat release rate, show that optimum fire performance also occurs at the [ZS] ≤ 3.75% and [AlPi] ≥ 11.25% condition.Smoke generation reduces only slightly when highest levels of AlPi are present compared with the HPTA/GF sample and then reduces further as the ratio [ZS]/[AlPi] increases. Tensile and impact properties are also optimal for the [ZS] ≤ 3.75 wt% and [AlPi] ≥ 11.25 wt% condition.At the mechanistic level, TGA studies show that for HPTA/GF, the presence of oxygen increases char residue in the 450–550 °C region compared to when heated under nitrogen. Air oxidation further increased residues above 450 °C when AlPi is present and confirms other published work that the reported volatilization occurring during pyrolysis under nitrogen is now in competition with its oxidation to aluminium phosphate. Thus residues above 450 °C in air comprise both increased char from HTPA plus residual aluminium phosphate with the latter remaining above 600 °C after the former has oxidized.

Fire retardant mechanism of aliphatic bromine compounds in polystyrene and polypropylene

This paper deals with the effective flame retardance of polystyrene and polypropylene with aliphatic bromine compounds. By studying glow wire and UL94 V2 performance of aliphatic hexabromocyclododecane in polystyrene and the mixed aliphatic/aromatic compound tetrabromobisphenol A bis (2,3-dibromopropyl ether) in polypropylene with and without synergists like antimony trioxide and dicumene, it is made plausible that the combination of chain scission and flame poisoning mechanisms causes these compounds to be so effective. The effectiveness of a synergist depends on the use ratio and can be negative depending on the FR test. Also the effect of neutral fillers like talc is studied and it is shown that particle size has the strongest effect on the FR test which depends most on polymer flow. The effect of polymer molecular weight is in line with the mechanisms involved.

The use of thermographic technique in the evaluation of polymers combustion and fire retardants performance

AbstractThe combustion behaviour of polymeric materials either fire retarded or not, burning in the Glow Wire and UL 94 tests, was characterised by means of thermography. It is shown that the distribution of temperatures in the gas and condensed phase of the burning specimen thus recorded, supplies fundamental complementary information for the characterisation of the combustion process.

Evaluation of polymer combustion and fire retardance by using thermography

AbstractThe temperature distribution in the condensed and gas phase during combustion of polymer materials in fire tests was measured by means of thermography. It is shown that these data are very useful for mechanistic rationalization of the diagnostically poor, fail‐pass rating of most of these tests. Preliminary data were obtained for polymer materials, fire retarded or not, burning in the widely used Glow Wire and UL 94 tests. It is shown that the relative fire hazard and test rating may depend strongly on the combustion parameter on which the rating is based. Furthermore, detailed data on temperature distribution are helpful in eliminating intrinsic ambiguity of the UL 94 classification in the case of fire‐retarded materials burning with dripping.