WATER BLOWN

Semiflexible molded polyurethane foams are used in other automotive appHcations, such as instmment panels, dashboards, arm rests, head rests, door liners, and vibrational control devices. An important property of semiflexible foam is low resiHency and low elasticity, which results in a slow rate of recovery after deflection. The isocyanate used in the manufacture of semiflexible foams is PMDI, sometimes used in combination with TDI or TDI prepolymers. Both polyester as well as polyether polyols are used in the production of these water-blown foams. Sometimes integral skin molded foams are produced. 

For materials of equivalent density water-blown polyurethanes and the hydrocarbon-blown polystyrene foams have similar thermal conductivities. This is because the controlling factor determining the conductivity is the nature of the gas present in the cavities. In both of the above cases air, to all intents and purposes, normally replaces any residual blowing gas either during manufacture or soon after. Polyurethane foams produced using fluorocarbons have a lower thermal conductivity (0.12-0.15 Btu in fr h °F ) (0.017-0.022 W/mK) because of the lower conductivity of the gas. The comparative thermal conductivities for air, carbon dioxide and monofluorotrichloromethane are given in Table 27.3. 

Blowdown The water blown down from the boiler in order to maintain its total dissolved level below the specified limit. 

Journal of Applied Polymer Science 11, No. 12, 19th Sept. 2000, p.2646-56 DESAMINATED GLYCOLYSIS OF WATER-BLOWN RIGID POLYURETHANE FOAMS... 

Las Vegas, Nv., 20th-23rd Oct. 1996, p. 179-89. 43C6 LOW DENSITY ALL WATER-BLOWN RIGID FOAM FOR POUR-IN-PLACE APPLICATIONS Kaplan W A Neill P L Staudte L C Brink C J Stepan Co. 

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

Particulates are also classified as to their mode of formation. Some, designated sls primary particulates, are released directly to the atmosphere in the form of tiny particles or droplets. Droplets of salt and water blown off the surface of the ocean are examples of primary particulates. Other particulates are formed in the atmosphere as a result of chemical and/or physical reactions. For example, sulfur... 

Whether the one-shot process or prepolymer technique is used, the development of a foam involves the juxtaposition of gas generation and the development of tensile strength within the developing foam. The evolution of gas can be via the use of blowing agents or the in situ generation of CO2 from the reaction of water with an isocyanate to produce a water-blown foam. In any case, the gas evolution creates an internal pressure that must be resisted by the development of a gel structure via polymerization reactions as shown in Figure 3.13. 

Mutagens in natural waters (>10 L) (A) washed and Soxhlet extracted with acetone (16 h) (B) stored in acetone (1) washed with 3 bed volumes of distilled water (2) residual water blown out with dry nitrogen (3) elution with 4 bed volumes acetone (140 mL) 13... 

There are waters blown by changing winds to laughter And lit by the rich skies all day. And after Frost, with a gesture, stays the waves that dance And wandering loveliness. He leaves a white Unbroken glory, a gathered radiance,... 

The pumping out of the batch tank at the end of the cycle lowers the level in the batch tank which signals valve AV1 to open again and a new batch of undemineralized water comes into the system. The cycle is repeated automatically for an indefinite period. The salts removed in the stack from the dilute stream are absorbed in a concentrated stream loop being pumped by concentrating pump C. Enough water is continuously added under control of valve CV and rotameter R to make up for the amount of water blown down as brine. The proportion of water which must be wasted as brine is determined by the chemical composition of the water to be treated. The blowdown is adjusted so that the least soluble salt component in the feed water will remain in solution. 

Modesti, M. Lorenzetti, A. Improvement on fire behaviour of water blown PIR-PUR foams Use of an halogen-free flame retardant. Eur. Polym. J. 2003, 2, 263-268. 

Rogge, T.M., Stevens, C.V., Vandamme, A., Booten, K., Levecke, B., D hooge, C., Haelterman, B., and Corthouts, J., Application of ethoxylated inulin in water-blown polyurethane foams, Biomacromolecules, 6, 1992-1997, 2005. 

One way to do so is an extended overcharging period with the production of hydrogen and the undesirable loss of water. The hydrogen bubbles mix the electrolyte layers with different densities. The modern way replaces the function of hydrogen bubbles by purified compressed air (free of dust, oil, water), blown into the battery cells during the charging cycles (electrolyte circulation). 

M. Ravey and E. M. Pearce, Elexible polyurethane foam. 1. Thermal decomposition of a polyether-based, water-blown commercial type of flexible polyurethane foam, J. Appl. Polym. Sci., 63, 47-74 (1997). 

Careful studies of polyurea formations are generally quite difficult. Low-molecular-weight disubstituted ureas have such low solubility in most solvents that precipitation causes experimental difficulties the problem is even worse with many polyureas. In addition the rather limited thermal stability of polyureas at temperatures of about 200°C has detracted from what otherwise might have been a significant interest in these polymers for fibres. The major commercial interest has not been in pure polyureas, but rather in polymers containing polyurea blocks, as in water-blown polyurethane foams and in polyurea—urethane elastomers. The complexity of these commercial systems, which are nearly always crosslinked, has made kinetic studies difficult. 

An unusually valuable study of the kinetics of polyurea—urethane formation from systems normally used to prepare water-blown polyurethane foams was described by Hartley et al. [195]. Some typical systems were found to consist of a single phase initially, while certain others were complicated by the existence of two phases, with phase inversion occurring. Studies included measurements of the rate of heat evolution, gas evolution and viscosity increase, as well as analysis for the presence of reaction products after intervals of time. 

For flexible foams in which CFC s have typically been employed as auxiliary blowing agents, entirely water-blown foams can be achieved with the performance additives. 

Foams may be prepared by either one of two fundamental methods. In one method, a gas such as air or nitrogen is dispersed in a continuous liquid phase (e.g. an aqueous latex) to yield a colloidal system with the gas as the dispersed phase. In the second method, the gas is generated within the liquid phase and appears as separate bubbles dispersed in the liquid phase. The gas can be the result of a specific gasgenerating reaction such as the formation of carbon dioxide when isocyanate reacts with water in the formation of water-blown flexible or rigid urethane foams. Gas can also be generated by volatilization of a low-boiling solvent (e.g. trichlorofluoromethane, F-11, or methylene chloride) in the dispersed phase when an exothermic reaction takes places, (e.g. the formation of F-11 or methylene chloride-blown foams). 

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