Metal catalysed Intumescence of Polyhydroxyl compounds

Fire presents a great risk to humans and their possessions. Polymeric compounds are highly flammable and compounds are added to increase their fire resistance. These additives are referred to as flame retardants. Intumescent flame retardants are systems that form a carbon rich foam on the surface of the polymer during thermal degradation. A new field of metal catalysed intumescence is discussed in this document. The influence of both the metal ion and organic backbone of polyhydroxylcarboxylic acid metal salts was studied. The intumescence and foaming properties of selected salts were studied in more detail. Gluconic acid proved to be the best intumescent and showed the best combination of carbon char yield, foam structure and volume, stability and open flame characteristics. As a general rule of thumb, the char volume and structure improved with an increased number of hydroxyl groups in the compound. Carbon char yield increased with an increase in the number of hydroxyl groups for a constant number of carbons in the complex. The number of acid groups in the compound played a lesser role in intumescence. Most metal complexes catalyse intumescent decomposition of polyhydric compounds such as polyhydroxylcarboxylic acids and pentaerythritol. The reduction in the volatilisation losses implies that the metal cations catalyse carbonisation reactions in the polyhydroxyl compound. Unfortunately, the resultant carbon-foams are unstable: the metal residues also catalyse the further oxidative degradation of the char. The low thermal stability of the compositions tested, as well as the afterglow effect makes them unsuitable for use as flame retardant additives in plastics. From the studies of the different metal complexes with acetylacetone and gluconic acid, it was concluded that the calcium ion exhibited the most promise. When pyrolysed in air with an open gas flame or in a furnace, calcium gluconate monohydrate produces voluminous foam. The foam is of a closed cell structure, densely packed and has no mechanical strength. The cell walls are very thin (5 to 50 nm) and the cells are between 50 µm and 200 µm in size. If the sample is compressed before heating, the resultant foam produced during pyrolysis is less voluminous than that of the loose powder. The BET surface area of the calcium gluconate monohydrate foamed at 300°C for 5 min. is 16.0 m2/g. The foam produced after 5 min heating at 300°C has a thermal conductivity similar to standard polystyrene foam. Adding leached silica to the calcium gluconate monohydrate increases mechanical strength of the foam, but influences the foam volume negatively. The optimum silica level was calculated to be 1:1 gluconate to silica on a mole ratio (11.8% SiO2 by mass). The mechanical strength of the foam can also be increased with the addition of expandable graphite. The graphite has a lesser influence on the foam volume than the silica, but also reduces the foam volume. However, the addition of the expandable graphite gives the sample more .opening. force, as the foam volume of a compressed sample pyrolysed, is similar to that of the heated loose powder. Calcium gluconate monohydrate starts to degrade at 120°C, losing its crystal water and shows a mass loss of 4% at 180°C. The exothermic peak (shown in the DSC/TGA data) associated with the metal catalysed carbon oxidation (afterglow) is observed at 570°C in air. For the calcium gluconate monohydrate the transition from CaCO3 to CaO occurs above 650°C in air. It has been shown that the foaming of polyhydroxylcarboxylic acids is due to the formation of water vapour during degradation. For calcium gluconate monohydrate, foaming starts due to the loss of crystal water and is continued by the loss of hydroxyl groups as water. The bulk of the foaming is due to the second reaction. It has been shown that compounds with crystal waters produce a more voluminous and lower density foam. The foam is an amorphous carbon rich residue. The molecular mass of the carbon residue increases up to a heating temperature of 300°C. This implies that the carbon residue crosslinks during formation, forming a stretchable cell wall for the foam. Compounds with a .free. hydroxyl group at the end of the carbon chain produce a foam of larger volume and lower density. This supports the crosslinking theory. The foam produced when calcium gluconate monohydrate is heated for 5 min at 300°C in air is of very low density . 2.5 kg/m3 based on residual mass. The density of the calcium gluconate monohydrate pyrolysed at 1000°C for 5 min in air yields a CaO with a density of 20 kg/m3 . This implies that the high temperature pyrolysis of calcium gluconate can produce an inorganic oxide of low bulk density and possible high specific surface area. The BET surface area of CaCO3 from the gluconate pyrolysed at 600°C is ~ 12 m2 /g. An intumescent coating containing calcium gluconate monohydrate, leached silica and expandable graphite as a system was prepared and compared to commercial formulations. This gluconate based system was at least as efficient as the commercial formulations when painted on balsa wood planks or aluminium plates. On cardboard sheets it did not perform as well as the commercial systems. More work should be done to overcome the afterglow effect observed with metal- based intumescent systems. The crystal structure of calcium gluconate monohydrate should be determined as to understand the decomposition better. It is unclear whether the decomposition is catalysed inter- or intramolecularly.Thesis (PhD(Chemical Engineering))--University of Pretoria, 2005.Chemical Engineeringunrestricte

Systematic literature review of the effect of layered double hydroxides on the mechanical properties of rubber

Layered double hydroxides (LDHs) have attracted interest as reinforcing fillers in elastomers due to their ease of synthesis and customisability. A systematic review was performed on the effect of LDHs on the mechanical properties of elastomers using the Scopus database. Of the 61 articles relevant to the search criteria, the majority were published on polyurethane (PU) and nitrile butadiene rubber (NBR). Mg-Al LDH was used in most of the studies and Zn-Al LDH was used second most common. LDH can act as a reinforcing filler, typically increasing tensile strength even at low concentrations, so it could be used as an alternative to traditional reinforcing fillers for elastomers. LDH can also be made a functional filler by selecting the right metals and interlayer anions. It was found that Mg-Al LDH and Zn-Al LDH can both participate in crosslinking reactions and can replace MgO and ZnO, respectively. Less Zn ions are required for crosslinking when LDH is used than when ZnO is used, making LDH more environmentally friendly. Organic modification is usually required to improve compatibility with the elastomer matrix, especially in non-polar elastomers. It enables exfoliation of the LDH and intercalation of polymer chains into the LDH interlayer to occur. Organic modifiers can also be used to functionalise the LDH. Stearic acid used in crosslinking systems can be replaced by stearate anions from stearate-modified LDH.The National Research Foundation of South Africa (NRF) postgraduate (master’s) scholarship and by Techsparks (Pty) Ltd., the Technology and Human Resources for Industry Programme (THRIP).https://www.mdpi.com/journal/polymersam2022Chemical Engineerin

Metal catalysed intumescence : characterisation of the thermal decomposition of calcium gluconate monohydrate

Calcium gluconate monohydrate is a member of a new class of base-catalysed intumescent compounds. It forms low-density closed-cell carbonaceous foam when exposed to heat. The volume expansion can be as high as two hundred times the original volume. At temperatures above 750°C this foam is transformed into a porous, yet cohesive, structure based on calcium oxide. The latter has only a slightly higher density and shows significant flame-resistance.http://link.springer.com/journal/10853hj2020Chemical Engineerin

Exploring the influence of milling parameters on the wet mechanochemical synthesis of mg-al layered double hydroxides

The synthesis of Mg-Al layered double hydroxide (LDH) was explored, through a one-step wet mechanochemical route, with the use of a NETZSCH LME 1 horizontal bead mill. Raw materials selected comprised of a mixture of metallic oxides/hydroxides promoting green synthesis. The research aims to expand on the understanding of the wet mechanochemical synthesis of Mg-Al LDH through variation in milling and synthesis parameters. The selected parameters investigated were rotational speed, retention time, solids loading, bead size and jacket water inlet temperature. Samples were collected, filtered and dried at 60 °C for 12 h. Unless stated otherwise, or under investigation, parameters were kept constant at pre-selected conditions adapted from existing literature. LDH synthesis was deemed to occur successfully at elevated jacket water temperatures of 50 °C and longer retention times. It was noted that Al(OH)3 XRD peak reduction occurred readily for increased rotational speeds and residence times, regardless of system temperature. MgO was deemed to react more readily at elevated temperatures. It was proposed that the amorphitisation and mechanochemical activation of Al(OH)3 contributed to its dissolution providing the relevant Al3+ ions necessary for Mg2+ isomorphic substitution. Increasing the system temperature promoted the hydration of MgO, with the absence of Mg(OH)2 attributed to its contribution as an intermediate phase prior to LDH formation.Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (THRIP).https://www.mdpi.com/journal/crystalsam2022Chemical Engineerin

Thermochemical models and data of layered double hydroxides, a review

DATA AVAILABILITY : Data will be made available on request.Applications and reports of unique properties displayed by layered double hydroxides (LDHs) are steadily increasing. Fundamental insight into LDH synthesis is essential to developing sustainable production processes, and this can be acquired through an improved understanding of their underlying thermochemistry. The collection of work presented introduces LDHs, describes essential terminology, and provides a review of currently available literature focused on modelling methods and measurement techniques used to describe and capture standard thermodynamic formation property data of LDHs. A table of standard thermodynamic formation property data of LDHs is also presented at the end of the review.http://www.elsevier.com/locate/cttaChemical EngineeringMaterials Science and Metallurgical Engineerin

Modelling the thermal degradation and stabilisation of PVC in a torque rheometer

A novel method for simulating the torque and temperature curves from a torque rheometer thermal stability test on poly(vinyl chloride) (PVC) was developed. A mathematical model was proposed which combines the chemical kinetics involved in the thermal degradation and stabilisation process of PVC with heat transfer and viscosity relationships within the torque rheometer. The model coefficients were fitted to data obtained from previous experiments with a program written in the Python programming language using the Levenberg-Marquardt Algorithm (LMA) with multiple starts. The mathematical model fits the torque rheometer data successfully depending on the characteristics of the torque curve. The model fit is successful when the torque curve follows the expected behaviour. An unsuccessful model fit occurs when the torque curve deviates from the expected shape in a very specific way. In the degradation phase the torque curve increases to a local maximum, decreases to a local minimum and then increases again. The exact reason for the dip in torque is unknown.https://www.degruyter.com/view/j/cppm2019-04-13am2019Chemical Engineerin

Towards understanding photon absorption and emission in MgAl layered double hydroxide

SUPPLEMENTARY INFORMATION : The Rietveld refinement, the bandgap determination, the deconvolution of the MIR spectrum, more information on the MgAl-LDH luminescence reproducibility, the comparison of luminescence intensity with excitation at 5.0 eV and 3.8 eV, the linear combination of luminescence spectra, a thorough description of deconvoluted excitable states, the X-ray photoelectron analysis of MgAl-LDH (O 1s), additional data on the calcined MgAl-LDH (luminescence at 298 K and MIR spectra), and the full spectrum luminescence of MgAl-LDH to 1000 nm.Please read abstract in the article.https://pubs.rsc.org/en/journals/journal/mahj2023Chemical EngineeringChemistr

Mechanochemical synthesis of layered double hydroxides

Hydrotalcite-like layered double hydroxide was successfully synthesised from metal oxides and hydroxides using a horizontal bead mill and was identified as a mixture of hydrotalcite and meixnerite. The final thermally aged material that was milled for three hours has a particle size distribution in the range 0.5µm to 12µm. XRD and FTIR both suggest that the synthesised material is phase-pure LDH but the amorphous halo present in the XRD results suggests that an amorphous compound is present as a contaminant.https://aip.scitation.org/journal/apchj2020Chemical Engineerin

Oxygen consumption as the definitive factor in predicting heat of combustion

Please read abstract in the article.The Paper Manufacturers Association of South Africa (PAMSA), as well as the guidance and resources provided by the Future Energy Cluster at the Mäladalens Högskola, Sweden.http://www.elsevier.com/locate/apenergy2020-02-01hj2018Chemical Engineerin

Statistical analysis of the effect of varying material and manufacturing conditions on the mechanical properties of high-density polyethylene/layered double hydroxide composites

DATA AVAILABILITY STATEMENT : The data that support the findings of this study are openly available in University of Pretoria Research Data Repository (Figshare) at https://DOI.org/10.25403/ UPresearchdata.22126433.v1.Polymers are used in various industrial applications due to their ease of production, light weight, and ductility. Fillers such as clays are added to polymers to improve a range of factors such as material processing, thermal properties, fire retardance and cost. However, adding clays may negatively impact the mechanical performance of the composite. In addition, manufacturing parameters, for example, number of extrusions, press time, and so forth may also have an influence on the resulting composite system. This study performs a statistical analysis on a set of previously obtained experimental results, which investigated the influence of various manufacturing, material, and testing parameters on the composite mechanical properties. Exploratory data and statistical analysis techniques are applied to the historical tensile test data to gain insight into the influence on mechanical properties as well as the relationships and interactions between the parameters. Specifically, it is shown that clay loading does not have a statistically significant effect on the composite mechanical properties, which is contrary to literature. Another surprising result is the poor performance of the clay that is compatible with high-density polyethylene compared to the clay that is compatible with poly vinyl chloride. The contribution of this paper is to demonstrate the usefulness of applying statistical analysis on a large volume of data to understand the diverse correlations between the different variables.http://wileyonlinelibrary.com/journal/pls2am2024Chemical EngineeringMechanical and Aeronautical EngineeringNon