Richard Yuen

Melamine-containing polyphosphazene wrapped ammonium polyphosphate: A novel multifunctional organic-inorganic hybrid flame retardant

To achieve superior fire safety epoxy resins (EP), a novel multifunctional organic-inorganic hybrid, melamine-containing polyphosphazene wrapped ammonium polyphosphate (PZMA@APP) with rich amino groups was prepared and used as an efficient flame retardant. Thanks to the cross-linked polyphosphazene part, PZMA@APP exhibited high flame retardant efficiency and smoke suppression to the EP composites. Thermogravimetric analysis indicated that PZMA@APP significantly enhanced the thermal stability of EP composites. The obtained sample passed UL-94 V-0 rating with 10.0wt% addition of PZMA@APP. Notably, inclusion of incorporating PZMA@APP leads to significantly decrease on fire hazards of EP, for instance, bring about a 75.6% maximum decrease in peak heat release rate and 65.9% maximum reduction in total heat release, accompanied with lower smoke production rate and higher graphitized char layer. With regards to mechanical property, the glass transition temperature of EP/PZMA@APP10.0 was as high as 184.5°C. In particular, the addition of PZMA@APP did not worsen the mechanical properties, compared to pure APP. It was confirmed that the participation of melamine-containing polyphosphazene could significantly enhance the quality of char layer and thereby resulting the higher flame retardant efficiency of PZMA@APP.

An experimental study about the effect of arrangement on the fire behaviors of lithium-ion batteries

Safety problem is always a significant consideration before wider field of application such as mobile phones, computers and new energy vehicles. However, the knowledge on the battery combustion behavior is limited. To increase the safety margin, the fire hazard of lithium-ion batteries should be considered. An experimental study of different arrangements: horizontal 4xa0×xa01, horizontal 2xa0×xa02 and vertical 2xa0×xa02 lithium-ion batteries fire behaviors was conducted. The photographs of fire processes and the batteries before and after the fire tests were directly shown to describe the fire hazard. The mass loss rate, heat release rate and heat flux were used to analyze the combustion behavior more detailed. Based on the results, lithium-ion batteries are volatile and burning with potentially deadly explosions. The arrangements can affect the ignition time, heat release rate, released heat and the heat flux, while the way of mass loss and the total mass loss are similar. The results indicate that batteries with bigger heating area have more risky and fierce fires compared with others.

Effect of different humectants on the thermal stability and fire hazard of nitrocellulose

In order to ensure the thermal safety of nitrocellulose (NC) mixtures in the process of handing, storage, and usage, it is necessary to obtain the thermal stability and fire hazard of NC with different humectants. In this study, the thermogravimetry experiments with four heating rates (5, 10, 15, 20xa0Cxa0min−1) under nitrogen and air atmospheres were performed to investigate the thermal stability of two NC-humectants, namely NC-water and NC-ethanol mixtures, and pure NC. Moreover, the influence of humectants on the fire hazard of NC was evaluated by the ISO 5660 Cone Calorimeter test. The humectant, water or ethanol, can increase the activation energy and reduce the fire risk of NC. Compared with the NC with water, the NC with ethanol exhibits lower activation energy and higher fire hazard.

Experimental study on the fire characteristics of typical nitrocellulose mixtures using a cone calorimeter

To further understand the safety performance of energetic materials such as nitrocellulose (NC) mixtures, it is necessary to obtain the fire properties of commonly used NC mixtures. In the present study, an in situ calorimeter was employed to investigate the fire characteristics of pure NC, NC-plasticizer mixture and two NC-humectant mixtures, namely NC-isopropanol and NC-ethanol mixtures. The plasticizer (dibutyl phthalate) and humectants (ethanol or isopropanol) can effectively reduce the fire risk of NC. NC-plasticizer is more risky than NC-humectants in the burning process. Compared with the NC with isopropanol, the NC with ethanol exhibits higher fire risk. Also, the thermogravimetric (TG) curves of four NC samples were measured by a TG analyzer. The curves indicate that the decomposition of pure NC is more dramatic than NC mixtures, and the NC with plasticizer dibutyl phthalate can decompose in advance.

A novel boron–nitrogen intumescent flame retardant coating on cotton with improved washing durability

A series of boron–nitrogen polymers (PEIPAs) were synthesized to provide a green alternative for flame retardant finishing on cotton fabrics. An organic boron compound, phenylboronic acid (PA) was successfully bonded to the branched polyethylenimine, which was confirmed by 1H NMR and FTIR analysis. Thermogravimetric analysis showed that the polymer with molar ratio 1:1 of ethylenimine:PA (PEIPA 1:1), presented the optimal thermal-oxidative stability. PEIPA 1:1 was easily applied on cotton fabrics through a simple dipping method with high uptake in acetone medium. The fabric with 33.8xa0wt% add-on got self-extinguishing ability. SEM analysis on the char morphology of the treated fabrics revealed the fire protection by the coating through intumescent flame retardant mechanism. TGIR analysis showed the coated fabric has significant reduction in the flammable volatiles production. Further improvement of the coating washing durability was achieved by a novel formaldehyde-free cross-linking treatment. The new washing stable coating achieved LOI values 29.6 and 23.2% before and after repeated launderings respectively with 30xa0wt% add-on. Cone calorimetry analysis showed that the total heat releases of PEIPA 1:1 treated sample and cross-linked sample (PEIPA 3:1/NeoFR treated) were decreased by 30.3 and 45.5% respectively. Smoke analysis revealed that the treated fabrics have significant decrease in CO2/CO ratio, indicating an effective flame inhibition in gas phase. The novel coatings, simple to synthesize and easy to apply with low waste, are suitable alternative to toxic halogenated flame retardants for cellulosic products.

Constructing 3D Polyphosphazene Nanotube@Mesoporous Silica@Bimetallic Phosphide Ternary Nanostructures via Layer-by-Layer Method: Synthesis and Applications

A novel ternary nanostructure polyphosphazene nanotube (PZS)@ mesoporous silica (M-SiO2)@bimetallic phosphide (CoCuP) was facilely fabricated, using PZS as the template, where large amount of cetyltrimethylammonium bromide molecules were anchored to PZS via a similar layer-by-layer assembly strategy, and then uniform M-SiO2 shells can be formed successfully by Hyeons coating method. Subsequently, the three-dimensional (3D) nanostructure on the basis of bimetallic phosphide (CoCuP) interconnected with PZS@M-SiO2 was synthesized via a convenient, mild hydrothermal route. It is noted that incorporating well-designed PZS@M-SiO2@CoCuP led to significant decrease on fire hazard of thermoplastic polyurethane (TPU), that is, 58.2% and 19.4% reductions in peak heat release rate and total heat release, respectively, as well as lower toxic hydrogen cyanide and carbon monoxide yield accompanied by higher graphitized char layer. In the case of TPU/PZS@M-SiO2@CoCuP system, the storage modulus at -97 °C was dramatically improved by 62.6%, and glass transition temperature was shifted to higher value, compared to those of pure TPU. The enhanced fire safety and mechanical property for TPU composites can be ascribed to tripartite cooperative effect from respective parts (CoCuP and M-SiO2) plus the PZS.

Experimental study of high altitude effect on heat release rates of pool fires using calorimeters

With the aid of same configured calorimeters as dimensions of 40% of that in ISO 9705 in Hefei (24xa0m, 100.8xa0kPa) and Lhasa (3650xa0m, 64xa0kPa), the influence of high altitude on heat release rate and combustion efficiency were investigated. Two groups of liquid pool fires of moderate sizes (Dxa0=xa00.15, 0.25xa0m) with fuel level maintaining system were tested at two sites, respectively. Typical fuels with different sooting levels, i.e., N-heptane and Jet-A, were selected. The ambient air pressure effects were introduced by modifying the standard calculation method of heat release rate in ISO 9705. Experimental results indicated that the dimensionless burning intensity in the quasi-steady stage for both fuels could be accorded to pressure modeling with acceptable accuracy. And it could be correlated with radiation modeling well for Jet-A, while that of n-heptane failed and this may be explained by the flame convection feedback which could not be neglected for moderate sooty fuel of moderate sizes. The combustion efficiency at high altitude is slightly higher than that at atmospheric pressure, and it will gradually increase with the decreasing pool dimension regardless of the ambient pressure.

Spatial memory enhances the evacuation efficiency of virtual pedestrians under poor visibility condition

Spatial memory is a critical navigation support tool for disoriented evacuees during evacuation under adverse environmental conditions such as dark or smoky conditions. Owing to the complexity of memory, it is challenging to understand the effect of spatial memory on pedestrian evacuation quantitatively. In this study, we propose a simple method to quantitatively represent the evacueeʼs spatial memory about the emergency exit, model the evacuation of pedestrians under the guidance of the spatial memory, and investigate the effect of the evacueeʼs spatial memory on the evacuation from theoretical and physical perspectives. The result shows that (i) a good memory can significantly assist the evacuation of pedestrians under poor visibility conditions, and the evacuation can always succeed when the degree of the memory exceeds a threshold (); (ii) the effect of memory is superior to that of follow-the-crowd under the same environmental conditions; (iii) in the case of multiple exits, the difference in the degree of the memory between evacuees has a significant effect (the greater the difference, the faster the evacuation) for the evacuation under poor visibility conditions. Our study provides a new quantitative insight into the effect of spatial memory on crowd evacuation under poor visibility conditions.