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Manipulating the melt dripping of thermoplastics makes a fire scenario more or less dangerous. Yet, a detailed understanding of this phenomenon has remained a question mark in studies of the flammability of plastics. In this work, the individual and collective impacts of additives on the dripping behaviour of polyamide 6 (PA6) were studied. A set of materials compounded with melamine cyanurate (MCA) and glass fibre (GF) was investigated. Under UL 94 vertical test conditions, the dripping during first and second ignition was quantified and investigated in detail. The number, size and temperature of the drops were addressed, and the materials and their drops evaluated with respect to such aspects as their averaged molecular weight, thermal decomposition and rheological properties. PA6 with V-2 classification improved to V-0 with the addition of MCA, and achieved HB in the presence of GF. PA6/GF/MCA achieved V-2. Non-flaming drops of PA6/MCA consisted of oligomeric fragments. Flaming drops of PA6/GF showed a more pronounced decomposition of PA6 and an increased GF content. The dripping behaviour of PA6/GF/MCA can be understood as a combination of the influence of both additives. The results showed nicely that dripping under fire is neither a straightforward material property nor a simple additive influence, but the complex response of the material influenced by the interaction and competition of different phenomena.
The individual and collective impacts of additives in melt dripping behaviour were studied under UL 94 vertical test conditions. A set of polyamide 6 (PA6) based materials compounded with melamine cyanurate (MCA) – a ˝dripping agent˝ – and glass fibre (GF) – a ˝non-dripping agent˝ - was investigated in detail. Dripping quantification was carried out during first and second ignition. The materials and their drops were investigated with respect to thermal decomposition, melt viscosity, and others properties. PA6 with V-2 classification improves to V-0 when MCA is added; and is worsened to HB in presence of glass fibre. Together, PA6/GF/MCA achieved V-2. The non-flaming drops of PA6/MCA are formed by oligomeric fragments. The flaming drops of PA6/GF contain a high amount of glass fibre. The dripping behaviour of PA6/GF/MCA under fire is a complex response of the specimen, but not explained by an easy superposition of the materials’ properties. The dripping behaviour is influenced by the interaction and concurrence of the different phenomena.
Since thermoplastics’ melt dripping is connected directly with their ability to make a fire scenario more or less dangerous, it has been investigated in greater detail. However, it has still remained a question mark in the field of the flammability of plastics. Once it was recognized that each polymer has its own dripping characteristics under equal, standardized conditions, efforts were made to better understand the specifics of this phenomenon. Several different polymers were tested under fire in order to study the relations between molecular structure and the dimensions of the drops. In particular, the relationship between the polymer decomposition mechanisms and their drops was investigated. New quantification methods helped to study drop yields from materials upon exposure to fire or heat. Polymers and flame-retarded polymers showed variations in dripping, indicating that this behaviour is a combination of melting and the decomposition of the polymer and additives. From this, the main material characteristics that influence dripping under fire were highlighted: temperature, viscosity and decomposition.
As Polyamide 6 (PA6) is a thermoplastic polymer used in a wide range of products, including electronic devices, interest in enhancing the fire retardancy of this type of polymer is high. Melamine cyanurate (MCA) has been reported to be the most important nitrogen-containing flame retardant used in polyamides, and is especially attractive because it is halogen-free. In addition, glass fibres (GF) are commonly used in PA6 to improve its mechanical properties, mainly for engineering applications. In order to contribute to the scientific discussion on dripping behaviour, this work reports on an experimental investigation of a set of PA6 materials compounded with different amounts of MCA and GF content. In UL 94 conditions, dripping quantifications were carried out during First Ignition (FIG) and Second Ignition (SIG). These flammability tests were recorded with an infrared camera. The thermal decomposition and rheological properties of all of the materials and collected drops were evaluated.
Dripping behaviour under fire is controlled by the polymer, the flame retardant and the reinforcement filler. Pure PA6 achieved a V-2 classification in UL 94 test, PA6/MCA V-0, PA6/GF HB, and the flame-retarded composites are also classified as V-2. In spite of these classifications, dripping behaviour observed during the flammability test was distinct for each type of samples, as described in the paper. As for decomposition, the PA6 drops collected had a starting decomposition temperature lower than pure PA6 (Figure 1.a), indicating partly decomposed PA6. PA6/MCA shows a clear, early decomposition step for MCA in thermogravimetry, which vanishes for the collected PA6/MCA drops, proving the complete decomposition of MCA during the UL 94 test. In PA6, glass fibres acted as inert filler, prolonging the time to dripping, and leading to a constant flaming flow (Figure 1.b) in the samples with high concentrations. When GF and MCA were combined in PA6/GF/MCA, the modes of action of both the GF and the MCA interfered with each other (Figure 1.c). GF reduces the effectiveness of MCA and tends to force its main action into the condensed phase. There the dripping behaviour is well restricted through the formation of thermally stable residues. Rheological properties and scanning electron microscopy images are consistent with these results.
FIGURE 1. Thermal decomposition of samples and drops of: a) PA6, b) PA6/30GF, and c) PA6/20GF/20MCA
Polyamide 4.6 (PA46) is a high-heat-resistant polymer, but it has no dripping resistance under fire. Three commercial grades of PA46 are investigated under UL 94 vertical fire test conditions. Their performances are discussed based on the materials’ structural, thermal, and rheological properties. PA46 presents flaming drops, whereas dripping is prevented in the flame-retarded PA46.
Friction-modified PA46 has increased flaming dripping. Temperature profiles of the specimens under fire and the temperature of the drops are measured by thermocouples. A UL 94 vertical test configuration consisting of two flame applications is designed to assess the quantitative dripping behavior of the set of materials by the particle finite element method (PFEM). Polymer properties (activation energy and Arrhenius coefficient of decomposition, char yield, density, effective heat of combustion, heat of decomposition, specific heat capacity, and thermal conductivity) in addition to rheological responses in high temperatures are estimated and measured as input parameters for the simulations. The dripping behavior obtained by simulated materials corresponds with the experimental results in terms of time and drop size. A consistent picture of the interplay of the different phenomena controlling dripping under fire appears to deliver a better understanding of the role of different materials’ properties
The dripping behaviour of polymers is often observed experimentally through the UL94 flammability standard test. In this work, polymeric dripping under fire is investigated numerically using particle finite element method. A parametric analysis was carried out to observe the influence of a single property on overall dripping behaviour via a UL94 vertical test model. Surrogates and property ranges were defined for variation of the following parameters: glass transition temperature (Tg), melting temperature (Tm), decomposition temperature (Td), density (ρ), specific heat capacity (Cp), apparent effective heat of combustion of the volatiles, char yield (μ), thermal conductivity (k), and viscosity (η). Polyamide, poly(ether ether ketone), poly(methyl methacrylate), and polysulfone were used as benchmarks. Simulated results showed that specific heat capacity, thermal conductivity, and char yield allied with viscosity were the properties that most influenced dripping behaviour (starting time and occurrence).