Prasun Kumar Roy

Quantitative risk assessment for accidental release of titanium tetrachloride in a titanium sponge production plant

This paper outlines the quantitative risk assessment for storage and purification section of a titanium sponge production facility. Based on qualitative HAZAN technique, which involves a detailed FETI and HAZOP study of the entire plant, the storage and the purification section were found to be the most hazardous sections. Titanium tetrachloride (TiCl(4)) is the major reactant used in this plant. TiCl(4) is a toxic, corrosive water reactive chemical and on spillage from containment creates a liquid pool that can either boil or evaporate leading to the evolution of toxic hydrogen chloride (HCl). Fault tree analysis technique has been used to identify the basic events responsible for the top event occurrence and calculate their probabilities. Consequence analysis of the probable scenarios has been carried out and the risk has been estimated in terms of fatality and injuries. These results form the basic inputs for the risk management decisions.

Polyurea coatings for enhanced blast-mitigation: a review

Elastomeric coatings are being advocated as excellent retrofit materials for strategic applications, particularly for blast mitigation and ballistic protection. Polyurea, an elastomer formed by the reaction of isocyanate and amine, possesses hard domains dispersed randomly within the soft domains, forming a heterogeneous landscape with a nano-segregated microstructure, with each domain exhibiting its own characteristic glass transition temperature. Commercialised in the late eighties, this relatively new entrant in the field of elastomers has received enormous attention in view of its excellent blast mitigation properties and ballistic protection. Although the literature is abundant with studies demonstrating the potential of polyurea for retrofitting applications, the underlying mechanism behind its exceptional properties has not yet been fully comprehended. The ballistic protection ability is attributed to the dynamic transition from “rubber to glass”, which occurs when the material is subjected to extremely high strain rates, while the blast mitigation potential is attributed to a phenomenon more commonly referred to as “shock wave capture and neutralization”. Since the blast mitigation and ballistic protection ability is decided by the hard and soft domains of polyurea, respectively, the polymer needs to be tuned for a particular application through judicious choice of the raw materials. The current article reviews the relevant publications in the field of polyurea-based retrofits including their preparation, characterization, properties and applications in the context of blast mitigation and ballistic protection.

Synthesis of mesoporous bimetallic Ni–Cu catalysts supported over ZrO2 by a homogenous urea coprecipitation method for catalytic steam reforming of ethanol

The synthesis of mesoporous Ni–Cu bimetallic oxides supported over ZrO2 by the homogenous urea co-precipitation technique and its catalytic efficacy towards steam reforming of ethanol has been explored. The amount of NiO was kept constant and that of CuO was varied to obtain bimetallic supported oxides which were characterized using different techniques like N2 adsorption–desorption measurements, XRD, H2-TPR, ICP-OES, TGA and SEM analyses. The results were compared with those obtained by alkali coprecipitation. The oxides prepared by urea coprecipitation were found to exhibit a type IV isotherm and a characteristic H2 type hysteresis, while those prepared by alkali precipitation were found to be nonporous. The studies reveal that this facile route of urea-coprecipitation can generate mesoporosity in zirconia based compositions and because of its simplicity, it holds enormous potential as a soft-templating technique for large scale preparation. The surface area increased on introduction of Cu, exhibits maxima at 3% w/w CuO, and subsequently decrease at higher loadings. The reducibility and the metal support interactions were altered in the presence of Cu, which reflected on its improved catalytic activity towards steam reforming of ethanol. The introduction of Cu species enhances the water gas shift reaction and favors acetaldehyde decomposition and reforming over the ethanol dehydrogenation reaction, as indicated by the reduced levels of acetaldehyde in the product stream. On increasing the reforming temperature, H2 and CO2 selectivity and ethanol conversion increased significantly. Bimetallic oxides containing 3% w/w CuO were found to be most effective towards ethanol steam reforming, exhibiting complete ethanol conversion and 84% H2 selectivity at 600 °C, indicating their potential to be used as stable ESR catalysts.

Hydrolytically stable ZIF-8@PDMS core–shell microspheres for gas–solid chromatographic separation

Metal organic frameworks (MOFs) with exceptionally high surface areas, shape selectivity and availability of multiple active sites are suitable materials to serve as solid stationary phase for chromatographic applications. Packed columns filled with conventionally prepared MOFs result in high pressure drops and low column efficiency, mainly due to the presence of small irregular shaped crystals and broader size distribution. In this paper, we report the successful utilization of the hydrolytically stable microcrystalline zinc imidazolate (ZIF-8), a well-known MOF immobilized on a thermally stable polymer i.e., polydimethylsiloxane (PDMS) for application as a stationary phase towards gas–solid chromatographic separations. A gas chromatography (GC) column (2 m × 2.5 mm) packed with the ZIF-8@PDMS core–shell microspheres demonstrate efficient separation of liquid and gas mixtures including xylene isomers and natural gas mixtures. We also successfully used the stationary phase for quantification of ethanol concentration in aqueous samples; the column did not undergo any structural change suggesting its excellent hydrolytic stability.

Curing kinetics of self-healing epoxy thermosets

The curing kinetics of self-healing epoxy compositions was investigated by non-isothermal differential scanning calorimetric (DSC) studies. Cycloaliphatic epoxy resin was encapsulated in urea–formaldehyde (UF) using emulsion polymerisation technique to prepare epoxy-loaded UF microcapsules. Triethylene tetramine (TETA) hardener was immobilised on a mesoporous siliceous substrate (SBA 15) and both these additives were dispersed into an epoxy resin, which was subsequently cured using TETA. DSC studies revealed the autocatalytic nature of epoxy curing, which remained unaltered due to addition of the above-mentioned fillers, responsible for introducing self-healing functionality. The kinetic parameters of the curing process were determined using both Friedman and Kissinger–Akahira–Sunose (KAS) method. The activation energy at different degrees of conversion (Eα) was found to decrease with increasing degree of cure (α). Although UF resins possess secondary amine functionalities, which have the potential to react with the epoxy groups, no significant differences in the curing kinetics of the base resin were observed. Kinetic parameters were used to predict the curing behaviour of compositions at higher heating rates using KAS method. As expected, the onset curing temperature (Tonset) and peak exotherm temperature (Tp) of epoxy shifted towards higher temperatures with increased heating rate; however, introduction of fillers does not affect these characteristic temperatures significantly. Also, the overall order of reaction does not vary significantly which supports the autocatalytic nature of curing reaction. The results suggests that although 2° amino groups are available with the UF resin, these do not directly participate in the curing reaction, as the primary amino groups in TETA are more easily accessible.

Toughening of epoxy resin using Zn4O (1,4-benzenedicarboxylate)3 metal–organic frameworks

In this paper, we have demonstrated the potential of the well-known microporous MOF 5 towards toughening of a cycloaliphatic epoxy resin by preparing Epoxy–MOF 5 composites (0.1–0.7% w/w). Introduction of MOF 5 led to significant stiffening and improvement in dynamic properties as indicated by a 68% increase in impact strength and a 230% increase in fracture energy at an optimal loading of 0.3% w/w. A comparison of the mechanical response under different strain rates established the strain rate sensitivity of the composites, which is of relevance under blast loading conditions. We also performed fractographic analysis of the ruptured surface to understand the underlying mechanism behind the improvement in toughness.

Core–shell polysiloxane–MOF 5 microspheres as a stationary phase for gas–solid chromatographic separation

Core–shell poly(dimethylsiloxane) (PDMS)–MOF 5 microspheres were prepared by directed crystallization of MOF 5 on thermally stable PDMS beads. The microspheres were evaluated for their potential use as a stationary phase for gas-chromatographic separation of permanent gases and liquids, where the issues associated with pressure drop were circumvented. The successful demonstration of this simple and versatile methodology widens the scope for large-scale application of Metal–Organic Frameworks (MOFs) in chromatographic separation.

Investigating the Degradation Behavior of LDPE-grafted Maleic Anhydride for Use as Compatibilizer in Environmentally Degradable Compositions

In this paper, we report the degradation behavior of a LDPE-grafted Maleic anhydride polymer prepared using a reactive extrusion technique. 70 ± 5 µm blown films were exposed to oxidative environments, and the degradation was followed by monitoring physico-chemical and morphological changes. The studies indicated that grafting with Maleic anhydride does not affect the degradation characteristics of the base polymer. Kinetic parameters of degradation, as estimated using non-isothermal TGA, were used to estimate the theoretical lifetime of the polymers, which remained unaltered due to grafting. The results, however, indicated that cobalt stearate, a typical pro-oxidant, led to massive degradation during thermal processing.

Application of microencapsulated unsaturated polyester toward temperature-triggered healing in epoxy composites

In this article, we demonstrate the potential of encapsulated unsaturated polyester resin toward introduction of temperature-triggered healing functionality in a representative cycloaliphatic epoxy matrix. Unsaturated polyester resin was encapsulated in poly(urea–formaldehyde) shell by dispersion polymerization technique which resulted in the formation of free-flowing microcapsules (diameter ∼130 ± 49 µm) with a core content 58 ± 4%. Calorimetric studies confirmed the chemical activity of the encapsulated unsaturated polyester resin, which spontaneously polymerized in the presence of a free radical initiator, 2,2′-azobis(2-methylpropionitrile), at temperature as low as 80°C. Temperature-triggered healing of epoxy-microcapsule composites was performed at 110°C and the healing efficiency was quantified as the ratio of impact strength of healed and virgin specimens. The healing efficiency was found to increase with the increasing amount of microcapsule in the formulation and reached a maximum (100 ± 2%) at 20% (w/w) loading. Fractographic analysis of the surface revealed the flow pattern of chemically active resin from the ruptured microcapsules, which subsequently cured in the presence of 2,2′-azobis(2-methylpropionitrile) pre-dispersed in the matrix.

Toughening of Epoxy with Preformed Polyethylene Thermoplastic Filler

The potential of polyethylene as a thermoplastic filler towards improving the fracture properties of epoxy resin was explored. Oxo-degradable films were subjected to thermo-oxidative exposure, and the oxidized polyethylene (OPE) was extracted with acetone to remove low molecular weight products (APE). The presence of functionalities led to its homogenous dispersion in the epoxy matrix. Blending of epoxy with OPE and APE led to significant improvement in both quasi-static and impact properties, as evidenced by 44% increase in GIC and 21% increase in impact strength at loadings of 3% w/w. The strain rate sensitivity of the composites was also investigated. GRAPHICAL ABSTRACT