Flammability and Thermal Kinetic Analysis of UiO-66-Based PMMA Polymer Composites

Metal–organic frameworks (MOFs) are emerging as novel flame retardants for polymers, which, typically, can improve their thermal stability and flame retardancy. However, there is a lack of specific studies on the thermal decomposition kinetics of MOF-based polymer composites, although it is known that they are important for the modeling of flaming ignition, burning, and flame spread over them. The thermal decomposition mechanisms of poly (methyl methacrylate) (PMMA) have been well investigated, which makes PMMA an ideal polymer to evaluate how fillers affect its decomposition process and kinetics. Thus, in this study, UiO-66, a common type of MOF, was embedded into PMMA to form a composite. Based on the results from the microscale combustion calorimeter, the values of the apparent activation energy of PMMA/UiO-66 composites were calculated and compared against those of neat PMMA. Furthermore, under cone calorimeter tests, UiO-66, at only 1.5 wt%, can reduce the maximum burning intensity and average mass loss rate of PMMA by 14.3% and 12.4%, respectively. By combining UiO-66 and SiO2 to form a composite, it can contribute to forming a more compact protective layer, which shows a synergistic effect on reducing the maximum burning intensity and average mass loss rate of PMMA by 22.0% and 14.7%, respectively.

Environmentally Benign Phytic Acid-Based Nanocoating for Multifunctional Flame-Retardant/Antibacterial Cotton

Environmentally benign layer-by-layer (LbL) deposition was used to obtain flame-retardant and antimicrobial cotton. Cotton was coated with 8, 10, and 12 phytic acid (PA) and chitosan (CH)-urea bilayers (BL) and then immersed into copper (II) sulfate (CuSO4) solution. Our findings were that 12 BL of PA/CH-urea + Cu2+ were able to stop flame on cotton during vertical flammability testing (VFT) with a limiting oxygen index (LOI) value of 26%. Microscale combustion calorimeter (MCC) data showed a reduction of peak heat release rates (pHRR) of more than 61%, while the reduction of total heat release (THR) was more than 54%, relative to untreated cotton. TG-IR analysis of 12 BL-treated cotton showed the release of water, methane, carbon dioxide, carbon monoxide, and aldehydes, while by adding Cu2+ ions, the treated cotton produces a lower amount of methane. Treated cotton also showed no levoglucosan. The intumescent behavior of the treatment was indicated by the bubbled structure of the post-burn char. Antibacterial testing showed a 100% reduction of Klebsiella pneumoniae and Staphylococcus aureus. In this study, cotton was successfully functionalized with a multifunctional ecologically benign flame-retardant and antibacterial nanocoating, by means of LbL deposition.

Improvement of Flame Retardancy of Polyurethane Foam Using DOPO-Immobilized Silica Aerogel

In this work, silica aerogel was modified by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-1-oxide (DOPO). Then DOPO-immobilized silica aerogel nanoparticles were used as a flame retardant to prepare flame-retardant polyurethane foams. Microscale combustion calorimeter and cone calorimeter tests were employed to evaluate the flame retardancy of polyurethane foams. It was found that both the heat release rate and the total heat release of the composites were reduced with the incorporation of DOPO immobilized silica aerogel. It is speculated that the DOPO-immobilized silica aerogel nanoparticles can inhibit the degradation of polyurethane and catalyze the formation of carbonaceous carbon on the surface.

Environmentally-Benign Phytic Acid-Based Multilayer Coating for Flame Retardant Cotton

Chemically bleached cotton fabric was treated with phytic acid (PA), chitosan (CH) and urea by means of layer-by-layer (LbL) deposition to impart flame retardant (FR) behavior using only benign and renewable molecules. Samples were treated with 8, 10, 12 and 15 bilayers (BL) of anionic PA and cationic CH, with urea mixed into the aqueous CH solution. Flammability was evaluated by measuring limiting oxygen index (LOI) and through vertical flame testing. LOI values are comparable to those obtained with commercial flame-retardant finishes, and applying 10 or more bilayers renders cotton self-extinguishing and able to pass the vertical flame test. Microscale combustion calorimeter (MCC) measurements show the average reduction of peak heat release rate (pHRR) of all treated fabrics of ~61% and the reduction of total heat release (THR) of ~74%, in comparison to untreated cotton. Decomposition temperatures peaks (T1max) measured by thermogravimetric analyzer (TG) decreased by approximately 62 °C, while an average residue at 650 °C is ~21% for 10 and more bilayers. Images of post-burn char indicate that PA/CH-urea treatment is intumescent. The ability to deposit such a safe and effective FR treatment, with relatively few layers, makes LbL an alternative to current commercial treatments.

Flammability testing of wool/cellulosic and wool/synthetic fiber blends: Vertical flame spread and heat release results

Wool is a natural fiber with lower heat release/flammability than some synthetic fabrics, but it has not been well studied for its heat release when other fibers such as cotton, linen, and nylon are present in the woven fabric. In this article, the heat release and vertical flame spread of six commercially available natural color fabrics is reported. This includes 100% wool, 80% wool/20% nylon, 70% wool/30% linen, 45% wool/55% cotton, and 40% wool/38% cotton/12% nylon/10% metallic thread fabric. Heat release was measured through cone calorimetry (ASTM E1354) as a function of the sample mounting method, through microscale combustion calorimetry (ASTM D7309), and flame spread was measured by ASTM D6413. The type of insulated backing used greatly affected the cone calorimeter results, and fabric types did show some effects in vertical flame spread and microscale combustion calorimeter testing.

Application of microscale combustion calorimeter to characterize protective properties of bovine leather

The quality and properties of fire resistance are crucial to the selection of leather for the production of protective fire fighting boots, which has a primarily protective role. During fire extinguishing it is exposed to extremely high and low temperatures, chemicals (acids and alkalis), mechanical loads, etc. The properties of fire resistance were tested on two samples of bovine leather (BL1, BL2). Burn resistance test has been carried out in accordance with the requirements of the technical standards for the burn resistance test: HRN EN ISO 15090: 2012, t, 7.3 - Firefighters and rescue services. The mentioned two samples were individually tested according to HRN EN ISO 15025: 2003. The test procedure was carried out by the "Flame Expansion Testing Method". Moreover, in this research used Microscale Combustion Calorimeter (MCC) Govmark, UK because that was designed for produce the maximum heating rate capability similarly the heating rates in fires and give as a lot of flammability parameters. The analysis of physicochemical properties of samples was performed using Fourier transform infrared (FTIR) spectroscopy. The surface morphology of the samples was studied using a Field Emission Scanning Electron Microscopy (FE-SEM). The measurement of the above samples on MCC was performed according to ASTM D7309. From the obtained HRR results, it is evident that BL1 sample has a better thermal stability than the BL2 sample.

Microwave Assisted Preparation of Flame Resistant Cotton Using Economic Inorganic Materials

Innovative approaches for preparing flame retardant cotton fabrics were employed by utilizing a microwave-assisted technique with a minimum amount of co-solvent. Our attempts at flame retardant cotton fabrics treated with low cost inorganic formulations, such as urea and diammonium phosphate, were done successfully. The evidence of flame retardant chemical penetrations or surface modification of cotton fabrics was confirmed by scanning electron microscope (SEM) and the treated cotton fabrics were evaluated by flammability tests, such as 45° angle (clothing textiles test), vertical flame (clothing textile test) and limiting oxygen index (LOI). For formulations with urea only, LOI values of treated fabrics were 21.0–22.0% after add-on values for the formulation were 5.16–18.22%. For formulations comprising urea with diammonium phosphate, LOI values were greater than 29.0% after add-on values for the formulation were 1.85–7.73%. With the formulation comprising urea and diammonium phosphate, all treated fabrics passed the vertical flame test for add-on values 5.34–7.73%. Their char lengths were less than half the length of the original fabric and after-flame and after-glow times were less than 3.2 s. Additional thermal properties of desired products will be discussed using thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC).

Some Key Factors Influencing the Flame Retardancy of EDA-DOPO Containing Flexible Polyurethane Foams

The role of various additives (emulsifier, anti-dripping agent) and formulation procedures (pre-dispersion of solid additives in polyol via milling) which influence the flame retardancy of 6,6′-[ethan-1,2-diylbis(azandiyl)]bis(6H-dibenzo[c,e][1,2]oxaphosphin-6-oxid) (EDA-DOPO) containing flexible polyurethane foams has been investigated in this work. For comparison, the flame retardancy of two additional structurally-analogous bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based compounds, i.e., ethanolamine-DOPO (ETA-DOPO) and ethylene glycol-DOPO (EG-DOPO) were also evaluated together with EDA-DOPO in flexible PU foams of various formulations. The flame retardancy of these three bridged-DOPO compounds depends on the type of PU formulation. For certain PU formulations containing EDA-DOPO, lower fire performance was observed. Addition of emulsifier and polytetrafluoroethylene (PTFE) to these PU formulations influenced positively the flame retardancy of EDA-DOPO/PU foams. In addition, dispersion of EDA-DOPO and PTFE via milling in polyol improved the flame retardancy of the PU foams. Mechanistic studies performed using a microscale combustion calorimeter (MCC) and its coupling to FTIR showed no difference in the combustion efficiency of the bridged-DOPO compounds in PU foams. From MCC experiments it can be concluded that these bridged-DOPO compounds and their decomposition products may work primarily in the gas phase as flame inhibitors. The physiochemical behavior of additives in PU formulation responsible for the improvement in the flame retardancy of PU foams was further investigated by studying the dripping behavior of the PU foams in the UL 94 HB test. A high-speed camera was used to study the dripping behavior in the UL 94 HB test and results indicate a considerable reduction of the total number of melt drips and flaming drips for the flame retardant formulations. This reduction in melt drips and flaming drips during the UL 94 HB tests help PU foams achieve higher fire classification.

Sensitivity analysis on the microscale combustion calorimeter for polyurethane foam using a full factorial design methodology

A sensitivity analysis on test outcomes from the microscale combustion calorimeter was performed using flexible polyurethane foam as the sample material. Three input factors were investigated: sample preparation, heating rate and pyrolysis chamber atmosphere. The experiments were setup according to the principles of design of experiments and a full factorial design was implemented. In total, 39 experiments were performed as part of this study: 27 unique tests and 12 repeat experiments. Results from the microscale combustion calorimeter showed excellent repeatability in most cases. Sample inhomogeneity was suggested as a possible explanation for the variation observed. A statistical analysis was performed to quantitatively assess how each input factor affected the test results. Analysis showed that all three factors had some effect on the test outcomes, with heating rates and pyrolysis chamber atmosphere proving to be the most influential in regard to the analysed output quantities. Increasing the heating rate from 15 to 180°C/min illustrated the effects of thermal lag, increasing the temperatures at which the sample reactions took place. Interaction effects between input parameters were also observed. The pyrolysis chamber atmosphere, either inert or oxidative, was observed to have the largest effect on the tested output parameters. The energy release was observed to decrease with the introduction of 20% oxygen. Increasing the oxygen levels also produced a drop in the peak reaction temperatures; this was consistent for all tested atmospheres (from 0% to 10% and 10% to 20% oxygen). This study illustrated that outcomes from this apparatus, for materials such as flexible polyurethane foam, can be dependent on sample preparation as well as heating rate and testing atmosphere. In addition, it highlights the importance of apparatus characterisation for less homogeneous materials to understand how input factors choices can influence the outcomes of the tests performed.