Bench Scale Tests on Controlling Plastic Fires with Water Mists

Bench scale tests are proposed to study the performance of a water mist fire suppression system on plastic fires. The effects of water mist on burning solid polymethylmethacrylate (PMMA) and polyvinylchloride (PVC) are compared with a cone calorimeter. A scaled nozzle developed earlier for discharging water mist in a cone calorimeter was used. Operating pressures of 0.2–0.7 MPa, corresponding to water flow rates of 68 mL/min and 134 mL/min, were used. It was observed that PMMA samples could be ignited easily and liberated significant amounts of heat at high release rates. PVC was more difficult to ignite, but gave out large quantities of smoke. Discharging water to both did not increase the heat release rate significantly. However, both smoke quantity and carbon monoxide concentration increased. This was more obvious for PMMA fires. Hazard assessment parameters for thermal aspects and smoke were measured and presented as a ‘hazard diagram' to understand the action of water mist and the potential for re‐ignition. It is suggested that bench scale tests can also give useful results for designing water mist systems. The discharging time of water mist is a key factor in controlling PMMA fires. If the discharging time is not long enough, re‐ignition might occur once the discharging of water stops.     

Study on the suppression mechanism of water mist on poly(methyl methacrylate) and poly(vinyl chloride) flames

In this study, the action of water mists on poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) in a confined space under different external radiant heat fluxes was studied. Water mist was generated by a downward‐directed single pressure nozzle. Physical characteristics of the water mist were measured by laser doppler velocimetry and the adaptive phase doppler velocimetry system. The heat release rate, oxygen, carbon dioxide, and carbon monoxide concentrations, and other important parameters of the interaction under various experimental conditions were measured with cone calorimeter. To explain experimental results, the chemical suppression mechanisms of water mist extinguishing PMMA and PVC flames are investigated from literatures, and the corresponding proposed chemical reactions with water mist are presented. The investigation shows that aromatic compounds are formed by light hydrocarbon products with water mist for PMMA flame. Otherwise, for PVC flame, the decrease of temperature with water mist prevents aromatic compounds from oxidation and degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1130–1139, 2006     

Near‐surface vapour bubble layers in buoyant low stretch burning of polymethylmethacrylate

Large‐scale buoyant low stretch stagnation point diffusion flames over a solid fuel (polymethylmethacrylate) were studied for a range of aerodynamic stretch rates of 2–12 s⁻¹ which are of the same order as spacecraft ventilation‐ induced stretch in a microgravity environment. An extensive layer of polymer material above the glass transition temperature was observed. Unique phenomena associated with this extensive glass layer included substantial swelling of the burning surface, in‐depth bubble formation, and migration and/or elongation of the bubbles normal to the hot surface. The bubble layer acted to insulate the polymer surface by reducing the effective conductivity of the solid. The reduced in‐depth conduction stabilized the flame for longer than expected from theory neglecting the bubble layer. While buoyancy acts to move the bubbles deeper into the molten polymer, thermocapillary forces and surface regression both act to bring the bubbles to the burning surface. Bubble layers may thus be very important in low gravity (low stretch) burning materials. As bubbles reached the burning surface, monomer fuel vapours jetted from the surface, enhancing burning by entraining ambient air flow. Popping of these bubbles at the surface can expel burning droplets of the molten material, which may increase the fire propagation hazards at low stretch rates. Published in 1999 by John Wiley & Sons, Ltd.     

Bench‐scale studies of poly(vinyl chloride) fires with water mist

Bench‐scale tests to study the effect of water mist on burning solid poly(vinyl chloride) (PVC) were carried out with a cone calorimeter. Water mist was discharged from a small nozzle under two operating pressures, 0.4 and 0.7 MPa. The corresponding water flow rates were 103.5 and 134 mL/min, respectively. The cone angle of the discharged water spray was 90°, and the volume mean diameter of the mist was about 90 μm. The results were useful in understanding the effects of discharging water mist to suppress the diffusion flame from burning PVC. The reignition process also was studied. The testing method was appropriate for studying the interaction between water mist with smaller droplets and the diffusion flame in a confined space. There, the combined effects of oxygen displacement, gas phase, and fuel surface cooling were the key extinguishing mechanisms. The critical water mist application rate on burning PVC under different thermal radiative heat fluxes was able to be determined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2520–2527, 2006     

Oxygen index and minimum limiting rates of polymer combustion

The influence of the initial temperature and thermal loss upon the oxygen index and burning rates of polymethylmethacrylate (PMMA), polystyrene (PS) and polyoxymethylene (POM) has been studied. It has been shown that the temperature profiles in the proximity of the burning surface are identical under the critical conditions for each of the polymers. Direct measurements of flame–polymer heat flows have shown that with an increase in initial temperature from 25° up to 200°C the heat flow decreases approximately by a factor of 2. An analogous situation is also observed with change in the thermal loss value in the condensed phase. These data are confirmed by linear pyrolysis experiments. In all experiments under critical conditions the oxygen concentration indicates the constant mass decomposition rate for each polymer. With a decrease in the outlet velocity of the combustibles below this value, which is specific to each polymer, extinction occurs.     

Poly(methyl methacrylate) membranes

Uniform and symmetric membranes were formed from poly(methyl methacrylate) (PMMA) by making use of the stereocomplex phenomenon which characteristically occurs in the solution of a mixture of isotactic PMMA and syndiotactic PMMA. The water permeability of the membrane was very high compared to a commercially available cellulosic membrane, whereas their NaCl permeabilities were the same. The permeabilities of the membranes are explained by a simple capillary model. By varying the tacticity of the polymer it was found that the finest membrane structure is formed at the isotactic polymer ratio of ca. 30%. This shows the close relationship between complex formation and membrane permeability.     

Microencapsulation of stearic acid with polymethylmethacrylate using iron (Ⅲ) chloride as photo-initiator for thermal energy storage

Aiming to identify the validity of fabricating microencapsulated phase change material (PCM) with polymethylmethacrylate (PMMA) by ultraviolet curing emulsion polymerization method using iron (Ⅲ) chloride as photoinitiator,SA/PMMA microcapsules were prepared and various techniques were employed to determine the ignition mechanism,structural characteristics and thermal properties of the composite.The results shown that the microcapsules containing SA with maximum percentage of 52.20 wt％ formed by radical mechanism and only physical interactions existed in the components both in the prepared process and subsequent use.The phase change temperatures and latent heats of the microencapsulated SA were measured as 55.3 ℃ and 102.1 J.g-1 for melting,and 48.8 ℃ and 102.8 J.g-1 for freezing,respectively.Thermal gravimetric analysis revealed that SA/PMMA has good thermal durability in working temperature range.The results of accelerated thermal cycling test are all shown that the SA/PMMA have excellent thermal reliability and chemical stability although they were subjected 1000 melting/freezing cycles.In summary,the comparable thermal storage ability and good thermal reliability facilitated SA/PMMA to be considered as a viable candidate for thermal energy storage.The successful fabrication of SA/PMMA capsules indicates that ferric chloride is a prominent candidate for synthesizing PMMA containing PCM composite.     

Effect of pore solution calcium and substrate calcium on PMMA/cement paste interface during early stages of hydration

The interfacial shear strength of polymer thin film coating on calcium–silicate–hydrate (C–S–H) or cement paste significantly depends on the time-point, from addition of water, when the polymer is coated. This is because the physico-chemical properties of C–S–H surface evolve over time as hydration progresses. The instant of coating thus determines the interfacial performance of a thin film coating in an organic-inorganic material system. In this work, we provide molecular insights into the interactions of poly(methyl methacrylate) (PMMA) functional groups with the pore solution calcium and bound substrate calcium present in hydrating C–S–H. The experimental observation reveals that PMMA thin film coated on second day of hydration exhibits larger interfacial shear strength than when coated on the 28th day. The possible reasons for this observations are: a) chemical crosslinking of two oxygen atoms from two different PMMA polymer chains by pore solution calcium ions and b) the physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium. In this work, physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium and substrate calcium in C–S–H is addressed.     

Zur unverträglichkeit von polymergemischen. VII. Lichtstreuungsmessungen an quaternären und quintären polymer-systemen polymer(1)/polymer (2)/polymer(3)/benzol und polymer(1)/polymer(2)/polymer(3)/polymer (4)/benzol

A polystyrene of high molecular weight was investigated by means of light scattering in isoerefractive polymer/benzene mixtures. Two or three of the following polymers are used, which are isorefractive with benzene: polymethylmethacrylate (PMMA), polybutadienne (PB), and polyisobutene (PIB). It is possible to determine the degree of incompatibility of the ?unvisible”? polymers by a comparison of the ?-points of PS in the multi-component systems with the ?-points PS in the ternary systems PS/polymer(2)/benzene. In all cases it turned out, that the degree of compatibility of PS with the other polymers increased by a further addition of a chemical different polymer.     

Synthesis and friction properties of copper/PMMA composites by soapless emulsion polymerization

Copper (Cu)‐doped polymethylmethacrylate (PMMA) composites were prepared by soapless emulsion polymerization. In this process, copper nanoparticles were modified by sodium oleate (SOA) and the surface property of Cu nanoparticles changed from hydrophilic to hydrophobic. The hydrophobic Cu nanoparticles could not only avoid the oxidation of Cu in air but also improve the compatibility between Cu nanoparticles and PMMA. The TEM micrographs revealed that Cu nanoparticles were encapsulated in PMMA polymer microspheres. In addition, the uniform Cu/PMMA composite microspheres could be synthesized in such a soapless emulsion polymerization process. It was worth mentioning that the friction property in oil was well improved when little nanocomposites were added into the base oil, which indicated that the composites can be widely used in lubricating oil. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface initiated graft polymerization from carbon-doped TiO2 nanoparticles under sunlight illumination

A simple and efficient method is presented for the preparation of polymer-grafted TiO₂ by a photocatalytic polymerization. PMMA chains are directly grafted from the surface of the TiO₂ nanoparticles in water under sunlight illumination. FT-IR and TEM results demonstrate that there existed strong chemical bonding at the interface of TiO₂ nanoparticles and PMMA chains. The thermal stabilities of the grafted polymer are dramatically elevated relative to that of pure PMMA according to TGA results. Moreover, the resulted polymer exhibits much higher melting temperature compared with traditional stereoregular PMMA by controlling the conformation of polymer chains growing in the highly restricted space on the surface of nanoparticles.     

Altering a polymer surface chemical structure by an ion-assisted reaction

A new surface modification technique, the so-called ion-assisted reaction (IAR), has been developed; such modification of polymer surfaces offers many industrial applications. The addition of new functional groups on polymer surfaces and permanent hydrophilic polymer surfaces (water contact angle below 30° and surface energy 60-70 mJ/m²) have been accomplished by IAR treatment. The formation of functional groups is significantly dependent on the flow rate of the reactive gas, the irradiating ion dose, and the ion beam energy. Improvements in wettability and surface energy are primarily attributed to the increase of polar characteristics due to the formation of functional groups such as —(C=O), —(C=O)—O—, —(C—O)—, etc. The characteristics of the IAR treatment have been reviewed, with outstanding results regarding the wettability and adhesion of various polymers such as PMMA, PC, PP, PS, PI, PVDF, and PTFE.     

Improved adhesion of PMSQ hard coatings on polymer substrates

Various surface treatment methods were investigated to improve the adhesion of abrasion-resistant polymethylsilsesquioxane (PMSQ) coatings on the optical resins. The adhesion of PMSQ films was improved on polymethylmethacrylate (PMMA), polycarbonate (PC), and PC/acrylonitrile butadiene styrene (ABS) by pretreating their surface with O₂ plasma or chromic acid followed by surface grafting with trimethyl ethoxysilane (TMES). After the O₂ plasma and the subsequent TMES treatments, the adhesion of PMSQ coating on PMMA substrate was significantly enhanced by the reduction of the percentage of peeling area from ~100% to <1% in cross cut tests. After the chromic acid and the subsequent TMES treatments of PC and PC/ABS substrates, the adhesion of PMSQ coatings was also significantly enhanced by reducing the percentages of peeling areas from nearly 100% to 50% and <1%, respectively, for PC and PC/ABS. The PMSQ coating might increase the hardness of the polymer by two to three levels.     

Mechanism of Action of Phosphorus-based Flame Retardants in Nylon 6. III. Ammonium Polyphosphate/Manganese Dioxide

Partial substitution of ammonium polyphosphate (APP) by manganese dioxide (MnO₂) in polyamide 6 (PA-6) fire retarded with 20% of APP strongly increases the fire retardant effect. ‘Linear pyrolysis’ experiments, which are modified cone calorimeter tests, show an increase in the amount and an improvement of the shielding properties of the intumescent char formed on the surface of burning polymer. The enhancement of the yield of aliphatic–aromatic char stable to oxidation was observed in thermogravimetry under air. The fire retardant action of an APP/MnO₂ mixture in PA-6 is twofold. On the one hand, this additive promotes involvement of the polymer in the charring and, on the other, the formed manganese phosphate glasses improve the thermo-insulating properties of the intumescent char on the surface of burning PA-6.     

Possible mechanism of interaction among the components in MAPP modified layered silicate PP nanocomposites

Model reactions were carried out with components frequently used for the preparation of intercalated or exfoliated polypropylene (PP) nanocomposites. The results prove that maleinated polypropylene (MAPP) can react chemically with the surfactant applied for the organophilization of the filler, if this latter contains active hydrogen groups. The reaction of hexadecylamine (HDA) and MAPP was detected by MALDI-TOF spectroscopy, DSC measurements and FTIR spectroscopy. Anhydride groups are consumed and mainly amide groups form in the reaction. The formation of cyclic imides could not be proved by the techniques used. MAPP reacts also with the surfactant adsorbed on the surface of the silicate in ionic form. On the other hand, N-cetylpyridinium chloride (CPCl) not containing active hydrogen atoms does not react with maleinated PP. Intercalated or exfoliated composites could be prepared from the silicate organophilized with HDA, while microcomposites formed from the filler treated with CPCl. Chemical reactions remove the surfactant from the surface of MMT and hydrogenated silicate sites are left behind. The high energy surface interacts either with the anhydride or the amide groups by dipole-dipole interactions. Even the unmodified polypropylene chains may be attached much stronger to the surface by London dispersion forces than to the silicate covered with aliphatic chains. Although the effect of competitive adsorption (MAPP, HDA) and mutual solubility of the components (PP, MAPP, surfactant, reaction products) cannot be neglected, chemical reactions play a crucial role in structure formation in PP nanocomposites containing a functionalized polymer. Direct interaction of the silicate surface and the functionalized polymer as well as the formation of hydrogen bridges seem to play a lesser role, but the relative influence of processes may change with the type of surfactant, functionalized polymer, surface coverage and processing conditions.     

Ceramic Surface Reactions and Carbon Retention during Non-Oxidative Binder Removal Al2O3/Poly(methyl methacrylate) at 20°–700°C

Neat poly(methyl methacrylate) (PMMA) thermally decomposes in oxygen-free environments with negligible production of nonvolatile residue. Compacts of α-alumina powder containing PMMA that are fired in a non-oxidative ambient, however, retain appreciable amounts of char. Fourier transform infrared (FTIR) spectroscopy and evolved gas analysis utilizing mass spectral detection were employed to probe the chemical mechanism that initiates the production of organic residue from non-oxidatively fired PMMA/alumina bodies. We find that binding of organic groups to alumina particles is caused by a sponification reaction between either the ester groups of PMMA or thermally evolved PMMA fragments (including MMA) and hydroxyl groups on alumina particle surfaces. Isolated alumina surface hydroxyl groups were found to be much more reactive than mutually hydrogen-bonded alumina surface hydroxyl groups in producing surface-bound organic groups. This surface-carboxylate-forming reaction anchors organic residue to the inorganic surfaces to temperatures above the unzipping temperature of the polymer and leads to retention of organic fragments in the compacts at temperatures where neat PMMA has completely volatilized. Subsequent transformations of these surface-bound organic fragments at high temperatures produce the nonvolatile carbonaceous residues, which are retained in the fired alumina compacts. We demonstrate that unsaturation in the carboxylate side chain plays an important role in this stage of the process in increasing the char yield. We also show that the char yields are proportional to surface carboxylate coverage but that it is difficult to control surface carboxylate coverage by thermal pretreatments of the alumina powders.     

Evaluating the performance of a portable water–mist fire extinguishing system with additives

This study investigates how high‐pressure water–mist system discharge methodologies influence the fire extinction performance for pan pool fires and the corresponding mechanisms of restraining fire. The fire source is a pool‐fire burner. Fine water spray is injected using a portable device. The additive in the water–mist is neither toxic nor corrosive. All the tests are regarded as fuel controlled. The fire test parameters are fuel type, nozzle discharge angle, and additive solution volume. The fuels used are heptane, gasoline, and diesel. Nozzle discharge angles are 30, 45, and 60° with respect to the ground. Additive solution volumes are 0% (pure water), 3, 6, and 10%. Test results indicate that the nozzle discharge angle and additive solution volume in a water–mist fire extinction system play a significant role. Fire extinguishing efficiency is influenced by mist effects and the additive. Furthermore, the water–mist system can reduce radiation and can provide good protection for operators using portable fire extinguishing equipment. Copyright © 2008 John Wiley & Sons, Ltd.     

聚合物表面改性方法概述

聚合物表面改性方法多种多样,结合聚乙烯、聚苯乙烯、聚碳酸酯、聚甲基丙烯酸甲酯这些具体材料详细介绍目前应用广泛的溶液处理法、低温等离子体处理法、表面接枝法、离子注入法和一种新兴的原子力显微探针震荡法。前几种方法都是化学处理法,在基底上形成的新的极性表面层与体相结合一体,非常牢固;最后一种方法为物理过程,能够精确控制改性区域,对于改善材料表面微摩擦性能有重要作用。     

Plasma treatment of polymers: the effect of the plasma parameters on the chemical,physical, and morphological states of the polymer surface and on the metal-polymer interface

The results of the characterization of plasma-treated polypropylene (PP) and polymethylmethacrylate (PMMA) by X-ray photoelectron spectroscopic, atomic force microscopic (AFM), and surface resistivity measurements are presented. Chemical, physical, and morphological modifications of the polymer surface were investigated. The importance of the neutral gas of the electron cyclotron resonance-radio frequency (ECR-RF) plasma treatment is principally demonstrated. Large differences between the effects of noble and reactive gas plasmas were observed by AFM and surface resistivity measurements. However, the maximum sticking coefficient of evaporated Mg on PP is similar for both Ar and N₂ plasma treatments.     

Interphase effects in polymer-modified hydraulic cements

Earlier work has indicated the importance of interphase adhesion within these systems. The work here reported shows that, with reactive polymers, substantial chemical modification occurs at the surface of the polymer latex particle. With certain polymer types, such as polyethylene and polystyrene homopolymers, no evidence is found of such reactions; with others, such as poly(vinylidene chloride, vinyl chloride) and poly(ethyl acrylate, methyl methacrylate), substantial reaction occurs. Crosslinking and insolubilization frequently accompany these reactions, and the nature of the polymer is significantly altered.