An Investigation towards Coupling Molecular Dynamics with Computational Fluid Dynamics for Modelling Polymer Pyrolysis.

Building polymers implemented into building panels and exterior façades have been determined as the major contributor to severe fire incidents, including the 2017 Grenfell Tower fire incident. To gain a deeper understanding of the pyrolysis process of these polymer composites, this work proposes a multi-scale modelling framework comprising of applying the kinetics parameters and detailed pyrolysis gas volatiles (parent combustion fuel and key precursor species) extracted from Molecular Dynamics models to a macro-scale Computational Fluid Dynamics fire model. The modelling framework was tested for pure and flame-retardant polyethylene systems. Based on the modelling results, the chemical distribution of the fully decomposed chemical compounds was realised for the selected polymers. Subsequently, the identified gas volatiles from solid to gas phases were applied as the parent fuel in the detailed chemical kinetics combustion model for enhanced predictions of toxic gas, charring, and smoke particulate predictions. The results demonstrate the potential application of the developed model in the simulation of different polymer materials without substantial prior knowledge of the thermal degradation properties from costly experiments.

Peanut Shell Derived Carbon Combined with Nano Cobalt: An Effective Flame Retardant for Epoxy Resin.

Biomass-derived carbon has been recognised as a green, economic and promising flame retardant (FR) for polymer matrix. In this paper, it is considered that the two-dimensional (2D) structure of carbonised peanut shells (PS) can lead to a physical barrier effect on polymers. The carbonised sample was prepared by the three facile methods, and firstly adopted as flame retardants for epoxy resin. The results of thermal gravimetric analysis (TGA) and cone calorimeter tests indicate that the carbon combined with nano Cobalt provides the most outstanding thermal stability in the current study. With 3 wt.% addition of the FR, both peak heat release rate (pHRR) and peak smoke production rate (PSPR) decrease by 37.9% and 33.3%, correspondingly. The flame retardancy mechanisms of the FR are further explored by XPS and TG-FTIR. The effectiveness of carbonised PS can be mainly attributed to the physical barrier effect derived by PS's 2D structure and the catalysis effect from Cobalt, which contribute to form a dense char layer.

Experimental and numerical perspective on the fire performance of MXene/Chitosan/Phytic acid coated flexible polyurethane foam.

Recent discoveries of two-dimensional transitional metal based materials have emerged as an excellent candidate for fabricating nanostructured flame-retardants. Herein, we report an eco-friendly flame-retardant for flexible polyurethane foam (PUF), which is synthesised by hybridising MXene (Ti[Formula: see text]) with biomass materials including phytic acid (PA), casein, pectin, and chitosan (CH). Results show that coating PUFs with 3 layers of CH/PA/Ti[Formula: see text] via layer-by-layer approach reduces the peak heat release and total smoke release by 51.1% and 84.8%, respectively. These exceptional improvements exceed those achieved by a CH/Ti[Formula: see text] coating. To further understand the fundamental flame and smoke reduction phenomena, a pyrolysis model with surface regression was developed to simulate the flame propagation and char layer. A genetic algorithm was utilised to determine optimum parameters describing the thermal degradation rate. The superior flame-retardancy of CH/PA/Ti[Formula: see text] was originated from the shielding and charring effects of the hybrid MXene with biomass materials containing aromatic rings, phenolic and phosphorous compounds.

A Review on Lithium-Ion Battery Separators towards Enhanced Safety Performances and Modelling Approaches.

In recent years, the applications of lithium-ion batteries have emerged promptly owing to its widespread use in portable electronics and electric vehicles. Nevertheless, the safety of the battery systems has always been a global concern for the end-users. The separator is an indispensable part of lithium-ion batteries since it functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of separators have direct influences on the performance of lithium-ion batteries, therefore the separators play an important role in the battery safety issue. With the rapid developments of applied materials, there have been extensive efforts to utilize these new materials as battery separators with enhanced electrical, fire, and explosion prevention performances. In this review, we aim to deliver an overview of recent advancements in numerical models on battery separators. Moreover, we summarize the physical properties of separators and benchmark selective key performance indicators. A broad picture of recent simulation studies on separators is given and a brief outlook for the future directions is also proposed.

MXene/chitosan nanocoating for flexible polyurethane foam towards remarkable fire hazards reductions.

MXene/chitosan nanocoating for flexible polyurethane foam (PUF) was prepared via layer-by-layer (LbL) approach. MXene (Ti3C2) ultra-thin nanosheets were obtained through etching process of Ti3AlC2 followed by exfoliation. The deposition of MXene/chitosan nanocoating was conducted by alternatingly immersing the PUF into a chitosan solution and a Ti3C2 aqueous dispersion, which resulted in different number of bilayers (BL) ranging from 2, 5 and 8. Owing to the utilization of ultra-thin Ti3C2 nanosheets, the weight gain was only 6.9% for 8 BL coating of PUF, which minimised the unfavourable impact on the intrinsic properties of PUF. The Ti3C2/chitosan coating significantly reduced the flammability and smoke releases of PUF. Compared with unmodified PUF, the 8 BL coating reduced the peak heat release rate by 57.2%, alongside with a 65.5% reduction in the total heat release. The 8 BL coating also showed outstanding smoke suppression ability with total smoke release decreased by 71.1% and peak smoke production rate reduced by 60.3%, respectively. The peak production of CO and CO2 gases also decreased by 70.8% and 68.6%, respectively. Furthermore, an outstanding char formation performance of 37.2 wt.% residue was obtained for 8 BL coated PUF, indicating the excellent barrier and carbonization property of the hybrid coating.

Novel 3D Network Architectured Hybrid Aerogel Comprising Epoxy, Graphene, and Hydroxylated Boron Nitride Nanosheets.

A novel three-dimensional (3D) epoxy/graphene nanosheet/hydroxylated boron nitride (EP/GNS/BNOH) hybrid aerogel was successfully fabricated in this study. This was uniquely achieved by constructing a well-defined and interconnected 3D network architecture. The manufacturing process of EP/GNS/BNOH involved a simple one-pot hydrothermal strategy, followed by the treatment of freeze-drying and high-temperature curing. In comparison with EP/GNS-3, EP/GNS/BNOH-3 demonstrated improvement of 97% for compressive strength at 70% strain. Through compression tests, fracture occurred for EP/GNS-3 at ninth compression cycles, whereas EP/GNS/BNOH-3 retained its original form after twenty compression cycles, with a residual height of 97% (i.e., only 3% reduction). By the addition of BNOH in the polymer matrix, the dynamic heat transfer and dissipation rates of EP/GNS/BNOH aerogels were also considerably reduced, indicating that the aerogel with BNOH additive possessed excellent thermal insulation properties. Thermogravimetric analysis results revealed that the thermal stabilities of EP/GNS and EP/GNS/BNOH aerogels were improved with increasing loading of EP, and EP/GNS/BNOH aerogels exhibited a better thermal stability at high temperatures. Through the elevated levels attained in the compressive strength, superelasticity, and thermal resistance, EP/GNS/BNOH aerogels has the great potential of being a very effective thermal insulation material to be utilized across a board range of applications in building, automotive, spacecraft, and mechanical systems.

Comparative Studies on Thermal, Mechanical, and Flame Retardant Properties of PBT Nanocomposites via Different Oxidation State Phosphorus-Containing Agents Modified Amino-CNTs.

High-performance poly(1,4-butylene terephthalate) (PBT) nanocomposites have been developed via the consideration of phosphorus-containing agents and amino-carbon nanotube (A-CNT). One-pot functionalization method has been adopted to prepare functionalized CNTs via the reaction between A-CNT and different oxidation state phosphorus-containing agents, including chlorodiphenylphosphine (DPP-Cl), diphenylphosphinic chloride (DPP(O)-Cl), and diphenyl phosphoryl chloride (DPP(O3)-Cl). These functionalized CNTs, DPP(Ox)-A-CNTs (x = 0, 1, 3), were, respectively, mixed with PBT to obtain the CNT-based polymer nanocomposites through a melt blending method. Scanning electron microscope observations demonstrated that DPP(Ox)-A-CNT nanoadditives were homogeneously distributed within PBT matrix compared to A-CNT. The incorporation of DPP(Ox)-A-CNT improved the thermal stability of PBT. Moreover, PBT/DPP(O3)-A-CNT showed the highest crystallization temperature and tensile strength, due to the superior dispersion and interfacial interactions between DPP(O3)-A-CNT and PBT. PBT/DPP(O)-A-CNT exhibited the best flame retardancy resulting from the excellent carbonization effect. The radicals generated from decomposed polymer were effectively trapped by DPP(O)-A-CNT, leading to the reduction of heat release rate, smoke production rate, carbon dioxide and carbon monoxide release during cone calorimeter tests.