Dripping Behavior Research Articles

A novel organic-inorganic hybrid SiO2@DPP for the fire retardance of polycarbonate

To enhance the fire retardance of polycarbonate (PC), a novel organic-inorganic hybrid particle containing phosphorus and silicon (SiO2@DPP) was synthesized through a facile hydrothermal reaction. Different measurements verified that the SiO2@DPP was prepared successfully. After incorporation of the SiO2@DPP into PC, it was found that the flame retardancy of PC was greatly affected by only small amount of SiO2@DPP. The PC containing only 0.8 wt% SiO2@DPP passed the UL-94 V-0 rating in vertical combustion test and had the limiting oxygen index (LOI) of 29.3%. Moreover, the dripping behavior of PC was also restricted in this case. In cone calorimetry test, the peak heat release rate (PHRR) and the peak smoke production rate (PSPR) of PC were correspondingly remarkably reduced by 41.6% and 15.4% in the presence of only 0.8 wt% SiO2@DPP. Moreover, the flame-retardant mechanism of the SiO2@DPP was also investigated in detail through different measurements. The results demonstrated that the phosphorus-containing substances and SiO2 left in the condensed phase and some structures containing phosphorus in gaseous phase had great contribution to excellent fire retardance of PC/SiO2@DPP. All these results demonstrate that the SiO2@DPP is an efficient organic-inorganic hybrid material for preparing fire-retardance PC.

Development of a pendant experiment using melt indexer for correlation with the large‐size dripping in the UL‐94 test

SummaryThe dripping phenomena affect fire hazards significantly. In the UL‐94 test, the dripping has been classified into the small‐size dripping due to surface melting and the large‐size dripping originating from bulk softening. Both types of dripping result from the gravity resisted by the forces including the viscous force. Based on the mechanical mechanism, a pendant experiment to reflect the ability of polymer melt to resist the gravity and a simple model equation were developed. The pendant experimental data of 7 polymers verified the model equation, and the regressed model parameter values of activation energy were close to reported data to some extent for most polymers. Correlations between the predicted pendant mass and the dripping behavior featured by the maximum drop mass showed that the pendant mass predicted at the glass transition temperature was proportional to the maximum drop mass. For polymers of large‐size dripping, the pendant mass predicted at typical decomposition temperatures such as the onset decomposition temperature was generally proportional to the maximum drop mass. Moreover, the model equation indicated that for the large‐size dripping the product of drop mass and first dripping time should be proportional to the specimen thickness, which was verified by reported dripping data.

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

AbstractIncorporation 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.

The effect of hBN on the flame retardancy and thermal stability of P-N flame retardant PA6

ABSTRACTA novel thermally conductive Polyamide 6 (PA6) with good fire resistance was prepared by introducing a phosphorous-nitrogen flame retardant (FR) and platelet-shaped hexagonal boron nitride (hBN) into the matrix. With high thermal conductivity and good flame retardancy, the material is suitable for applications in electronic and electrical devices. The limiting oxygen index (LOI) changes for various loadings content of FR. However this formulation still does not show an ideal fire resistance, due to the appearance of melt dripping behavior during the UL 94 test. With the extra introduction of 3 vol% and 5 vol% hBN, the melt dripping behavior during the burning process completely disappeared. The hBN also increased the thermal conductivity. Furthermore PA6 compounded with FR and hBN showed a better thermal stability than neat PA6. The morphology of the char residues was investigated by scanning electron microscopy (SEM). The flaky hBN acted as the framework in the char structure and the rigid hBN could effectively break the bubble-shaped char on the surface of the residues which resulted in the enhancement of the strength and compactness of the char.

Dripping behavior of vertical burning thermally thin PMMA with different spacings to wall

Experiments were carried out to study the dripping behavior of vertical burning thermally thin poly(methyl methacrylate) (PMMA) with different spacings between the wall and PMMA. The dripping behavior was studied by infrared video image analysis with spacings of 7, 10, 13, 16, 19, 22, and 25 mm. As the spacing increased, the dripping time and mass and burnout growth distance first increased and then decreased. The critical value was observed at the 13 mm case. The dripping behavior is assumed to correspond to the net heat flux to the surface, extensional viscosity, and gravitational force of melting PMMA. After the dripping, the pyrolysis and burnout spread rates become asymptotically equal. In this study, the effects of spacing between the wall and fuels on the dripping behavior were investigated for the first time using uniform PMMA samples with 200 mm height, 50 mm width, and 2 mm thickness.

Molten thermoplastic dripping behavior induced by flame spread over wire insulation under overload currents

The dripping behavior of the molten thermoplastic insulation of copper wire, induced by flame spread under overload currents, was investigated for a better understanding of energized electrical wire fires. Three types of sample wire, with the same polyethylene insulation thickness and different core diameters, were used in this study. First, overload current effects on the transient one-dimensional wire temperature profile were predicted using simplified theoretical analysis; the heating process and equilibrium temperature were obtained. Second, experiments on the melting characteristics were conducted in a laboratory environment, including drop formation and frequency, falling speed, and combustion on the steel base. Third, a relationship between molten mass loss and volume variation was proposed to evaluate the dripping time and frequency. A strong current was a prerequisite for the wire dripping behavior and the averaged dripping frequency was found to be proportional to the square of the current based on the theoretical and experimental results. Finally, the influence of dripping behavior on the flame propagation along the energized electrical wire was discussed. The flame width, bright flame height and flame spreading velocity presented different behaviors.

Development of a physiologically relevant dripping analytical method using simulated nasal mucus for nasal spray formulation analysis

Current methods for nasal spray formulations have been elementary evaluating the dripping characteristics of a formulation and have not assessed the behavior of the nasal formulation in the presence of varying types of mucus depending on the indication or diseased state. This research investigated the effects of nasal mucus on the dripping behavior of nasal formulations and focused on developing an improved in vitro analytical test method that is more physiologically relevant in characterizing nasal formulation dripping behavior. Method development was performed using simulated nasal mucus preparations for both healthy and diseased states as coatings for the dripping experiment representing a wide range of viscosity. Factors evaluated during development of this in vitro test method included amount of mucus, application of mucus, drying times, and compatibility of the mucus on a C18 Thin Layer Chromatography (TLC) substrate. The dripping behavior of nasal formulations containing a range of 1% Avicel to 3.5% Avicel was assessed by actuating the nasal spray on a perpendicular TLC plate coated with either healthy or diseased simulated nasal mucus. After actuation of the nasal spray, the dripping of the formulation on the coated TLC plate was measured after the plate was repositioned vertically. The method that was developed generated reproducible results on the dripping behavior of nasal formulations and provided critical information about the compatibility of the formulation with the nasal mucus for different diseased states, aiding in nasal spray formulation development and physical characterization of the nasal spray.

Experimental studies on the effects of spacing on dripping behavior of thin polymethyl-methacrylate slab

Experiments were carried out to study the dripping behavior of vertical burning thermally thin polymethyl-methacrylate (PMMA) with different spacings parallel to the wall. With spacings of 7, 10, 13, 16, 19, 22, and 25mm, the dripping behavior was studied by infrared video image analysis, and the mass retention was recorded by the load cells. As the spacing increased, the dripping time, dripping mass, and burnout growth distance first increased and then decreased. The minimum value was observed at the 13mm case. The dripping behavior is assumed to correspond to the net heat flux to the surface, extensional viscosity, and gravitational force of melting PMMA. In this study, the dripping behavior was investigated using uniform PMMA samples with 200mm height, 50mm width, and 2mm thickness.

Preparation and Characterization of a Novel Anti-Dripping Flame Retardant PET/Phosphate Glass Nanocomposite

In the present study, the effect of phosphorus flame retardation (FR) agent, 2-carboxyl ethyl (phenyl) phosphinic acid (CEPPA), incorporating phosphate glass (Pglass) on the flame retardation and melt dripping behavior of poly (ethylene terephthalate) (PET) has been investigated. The Pglass/FR-PET nanocomposites (P/FR-PET) were prepared by melt blending. The morphology, thermal degradation behavior and flamability of the nanocomposites were investigated by means of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), limiting oxygen index test (LOI) and vertical combustion test. SEM micrographs showed that as the increasing of Pglass contents the morphologies of Pglass in the FR-PET matrix changed from nanoparticles (50 nm to 100 nm) to network structures. The thermal stability of nanocomposites at high temperature increased with the addition of Pglass contents. Meanwhile, the LOI values of the nanocomposites increased from 33.6 for neat FR-PET to 36.1 for 50% P/FR-PET nanocomposites. The vertical combustion test revealed that the P/FR-PET nanocomposites had excellent anti-dripping flame retardant property which can achieve UL-94 V-0 level. The formation of the Pglass network-structured protective layer, which acted as a supporting and heat shield layer, must be crucial for the large reduction in melt dripping. In a word, the experimental results showed that the CEPPA in combination with Pglass has excellent flame retardation and anti-dripping effect.

Thermal and Flame Resistant Properties of Poly (Lactic Acid)/Poly (Methyl Methacrylate) Blends Containing Halogen-free Flame Retardant

Flame retarded poly(lactic acid)/poly(methyl methacrylate) (PLA/PMMA) blend was prepared using melt compounding technique in the presence of isopropylated triaryl phosphate ester flame retardant [FR; 20 parts per hundred resins (phr)]. The effect of FR on the thermal and flame resistant properties of PLA/PMMA blend was studied. The flammability of PLA/PMMA blends was evaluated by UL-94 vertical burning test while the morphology of the residues was analyzed using field emission scanning electron microscope (FESEM). Thermogravimetric analyzer (TGA) was utilized to characterize the thermal decomposition behaviors of PLA/PMMA blends. The UL-94 result revealed that the inclusion of FR has shorten the after-flame time and improved dripping behavior of PLA/PMMA blend, achieving V-0 ranking in the test. An extensive and continuous carbonaceous char-like layer was found on the surface of the PLA/PMMA/FR residue, indicating the existence of condensed phase mechanism by FR. The incorporation of FR has accelerated the thermal degradation of PLA/PMMA blend at low temperature, but enhanced thermal stability of the blend at elevated temperature.

Adding the combination of CNTs and MoS2 into halogen-free flame retarding TPEE with enhanced the anti-dripping behavior and char forming properties

In this paper, the nanocomposites thermoplastic polyester-ether elastomer (TPEE) with phosphorus–nitrogen (P–N) flame retardants, carbon nanotubes (CNTs) and molybdenum disulfide (MoS2) was prepared by melt blending. TPEE containing P–N flame retardant, CNTs and MoS2 achieved UL94 V-0 rating due to the better barrier effect of the special structure. The structure was supported by the result of rheological properties. The thermal stability was studied by thermal gravimetric analysis (TGA) and char residue characterization was investigated by SEM–EDX measurements. The results demonstrated that the combination of CNTs and MoS2 results in the increase of char yield and the formation of the thermally stable char which can effectively prevent in the dripping behavior during the burning process.

Synergistic effect of aluminum hypophosphite and intumescent flame retardants in polylactide

Aluminum hypophosphite (AHP) was introduced into polylactide/intumescent flame retardant (PLA/IFR) systems by melt blending. The flame retardant and thermal properties of the PLA composites were investigated. The results suggest that a synergistic effect exists between IFR and AHP on the char formation and anti‐dripping behavior of PLA composites. The PLA/IFR composites containing 10 wt% IFR can pass the UL‐94 V‐0 rating but the test is accompanied by heavy melt dripping. For the PLA/AHP a UL‐94 V‐2 rating is obtained for the same loading of IFR. However, the composites containing 7 wt% IFR and 3 wt% AHP pass the UL‐94 V‐0 rating with modified dripping behavior. Moreover, the char from combustion of PLA/IFR is flexible but of poor quality. That for PLA/AHP is brittle with many cracks. In contrast, that for PLA/IFR/AHP is strong and compact. Thus it can resist the erosion due to heat and gas formation and protect the inside of the matrix. In addition, AHP causes the crosslinking among APP, which promotes the char formation and prevents the melt dripping. This is the main reason for the good flame retardant properties of PLA composites. Copyright © 2015 John Wiley & Sons, Ltd.

Characterization of Liquid Trickle Flow in Poor-Wetting Packed Bed

A low coke rate operation of a blast furnace tends to cause deterioration of the gas permeability. The liquid iron and molten slag dripping under the melting zone influences the gas flow and permeability in the lower part of the furnace. A computational fluid dynamic model, using a particle-based simulation, is presented for characterization of the melt dripping behavior in a packed bed. In this work, the validity of the liquid passing conditions based on the gravity to surface tension ratio was confirmed. The melt shape produces an “icicle,” “droplet,” and “dome” forms based on the change of the surface tension and density absolute values. Even with an identical liquid volume passage, the form of the liquid flow changed by the pressure from the liquid’s upper portion. Even if it has identical gravity and surface tension ratios, the liquid flow changes with the volume of the liquid phase and its form.

Layer by layer assembly of flame retardant thin films on closed cell PET foams: Efficiency of ammonium polyphosphate versus DNA

The present work aims to investigate the layer by layer deposition of flame retardant thin coatings on closed cell polyethylene terephthalate foams. To this aim, two coating architectures have been selected in order to evaluate the efficiency of ammonium polyphosphate (APP) versus the freshly proved flame retardant deoxyribonucleic acid (DNA). Both the selected architectures were able to homogeneously coat the external surface of the foams; APP-based coatings yielded average thicknesses around 450 nm while DNA based counterparts reached 340 nm. Flammability and cone calorimetry tests clearly demonstrated the superior performances of APP-based coatings. Indeed, only these latter were capable of suppressing the melt dripping behavior typical of PET and reducing the heat release rate peak by 25%.

Preparation, characterization, and flame retardance of high-density polyethylene/sulfur-free expandable graphite composites

In this work, a hydrothermal method was used to prepare a novel, sulfur-free expandable graphite (EG), which was added to high-density polyethylene (HDPE) to improve the flammability and the dripping behavior of composites. Phosphoric acid (H3PO4) was utilized as the intercalating agent, and potassium permanganate and nitric acid were used as the oxidizing agent. EG was investigated using Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectrometry, energy dispersive spectrometry, and scanning electron microscopy. Thermogravimetric analysis, the limiting oxygen index (LOI) and UL-94 were used to examine the thermal and flame-retardant properties of the composites. The results demonstrated that the EG composite exhibited much better thermal stability than pure polymer. Additionally, at 30 wt% EG loading, the LOI value of HDPE/ EG fabrication by H3PO4-hydrothermal method (PEG) was 30, and the flammability standard of UL-94 reached the V0 level, verifying that the EG that was prepared using the H3PO4-hydrothermal process can effectively be used in fireproof composites. The tensile modulus of the composites increased with increasing filler content, while the tensile strength decreased. EG enhanced flexural strength and flexural modulus of HDPE composites but not with high EG loading. The impact strength of the composites was diminished due to the incorporation of EG into HDPE matrix.

Dripping behavior of burning polymers under UL94 vertical test conditions

This article studied the dripping behavior of eight polymers under UL94 vertical test conditions. The results suggested two different dripping behaviors: Type I, dripping with uniform- and small-sized drops with the short first dripping time, and Type II, dripping with irregular- and large-sized drops with the long first dripping time. Polymers of Type I dripping had dominant decomposition mechanism of random-chain scission, low activation energy of viscous flow, and high ratio of effective heat of combustion to heat of gasification. Otherwise, Type II dripping dominates. The surface tension at ambient temperature and the melt flow index at processing temperatures were not as important to dripping as expected. It was found that talc could convert the dripping of low-density polyethylene from Type I to Type II at a critical talc loading level of 20 wt%, which was ascribed to the reduction in the burning rate and the formation of an integral residue. Finally, a generalized model was presented, and a derived correlation showed that the drop mass was a power law function of the dripping time.

Modeling of Dripping Behavior in Particles Packed Bed Filled with Immiscible Fluid

Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.

Modeling of Dripping Behavior in Particles Packed Bed Filled with Immiscible Fluid

Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.

Development of Production and Utilization Technology of Coke with High Strength and High Reactivity

Coke in a blast furnace has many significant functions such as a heat source, a spacer for a stable gas and liquid flow, a carburization agent for modifying the dripping behavior of metal and a reducing agent of iron ore. As the blast furnace operation moved into a more difficult stage where a high productivity and a high level of pulverized coal injection is demanded in a large volume blast furnace, coke strength has been considered important. On the other hand, the blending ratio of slightly caking coal has been increased in cokemaking process to meet cost reduction. With the development of cokemaking technology, reactivity of coke is attracting attention in terms of improving blast furnace reaction efficiency and reducing CO2 emission. In this paper, reviewed are how production technology of highly reactive coke and improvement in blast furnace reaction efficiency through the use of highly reactive coke have developed.

LDPE/Mg–Al layered double hydroxide nanocomposite: Thermal and flammability properties

Layered double hydroxides (LDHs) are new nanofillers which exhibit improved thermal and flammability properties in various kinds of polymer matrices. These materials have certain advantages over conventional metal hydroxides and also layered silicates so far as the flame retardancy is concerned. In this article, flammability and thermal properties of the nanocomposite based on low density polyethylene (LDPE) and Mg–Al based layered double hydroxide (Mg–Al LDH) are reported in detail. The nanocomposites containing different LDH concentrations were prepared by melt-compounding using a tightly intermeshing co-rotating twin-screw extruder. The morphological analysis reveals an exfoliated/intercalated type LDH particle morphology in these nanocomposites. The thermogravimetric analysis (TGA) shows that even a small amount of LDH improves the thermal stability and onset decomposition temperature in comparison with the unfilled LDPE. The heat release rate (HRR) and its maximum (PHRR) during cone-calorimeter investigation are found to be reduced significantly with increasing LDH concentration. The nanocomposites not only exhibit reduced total heat released (measure of propensity to produce long duration fire), but also lower tendency to fast fire growth (measured by the ratio of PHRR and time of ignition). The limited oxygen index (LOI) and the dripping behavior are also improved with increasing LDH concentration.