CO2 Gas Blowing

Keywords Magnesium phosphate, morphological control, microwave heating, CO2 gas blowing... 

Foams can be made by releasing a gas within a foamable liquid. For example, the opening and pouring of a bottle of soda releases pressurized CO2 gas, producing foam bubbles. Chemical reactions can also generate bubbles within the liquid. Other methods of foam production are to force both liquid and gas through a packed column (Khan et al. 1988), to spray foamable liquid onto a screen on which a fan is blowing (Aubert et al. 1986), or to use the foam-extrusion process (Han 1981). 

On the contrary, the gas dissolution foaming process, and in particular the high-pressure or supercritical CO2 gas dissolution foaming, allows obtaining micro-and nanoporous polymers. In this technique CO2 is used as a physical blowing agent [39,57-59] this gas is one of the best options for this kind of process because of its excellent characteristics of diffusion in the supercritical state and the mild conditions to reach this state (31°C and 7.3 MPa). Last but not the least, carbon dioxide is a green solvent that can be removed without residue or production of any pollutant compound [60,61]. 

When an isocyanate reacts with water, CO2 is given off. When just the right amount of water is added to the polymerization, the CO2 gas that is generated in situ acts as a "blowing agent" and creates the cavities in the final material that make it a foam. 

Research and development programs have been initiated by the cellular plastics industry to develop viable substitute blowing agents. These must have similar or improved properties to their CFC counterparts at a reasonable cost. Emphasis was initially placed on HCFC 123 and HCFC 141b, both having much shorter lifetimes and considerably less effect (up to 50 times) on o2one layer depletion (22). However, various options, including gas mixtures, water, or CO2 blown foams, continue to be studied ultimately to eliminate all CFCs and HCFCs. 

Azocarbonamide (I) Carbonamide N2, CO, CO2 190-230 220 Most widely used blowing agent in PVC and polyolefins. High decomposition temperature reduced by a variety of metal salts and oxides such as lead carbonate, lead phosphite and zinc oxide. High gas yield. Reaction products show little odour or discoloration. ... 

Foams are commercially produced several ways. Some polymerization processes produce their own foam. Polyurethanes, for example, are very exothermic. When they are formed, if a little water is present, CO2 will be a by-product. As the polymer forms, the CO2 will cause closed cell foam. As another example, a blowing agent can be injected into the molten polymer. The agent will later decompose, giving off a gas when the polymer is heated to melting. Epoxy resins are expanded into foams this way. 

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. 

Total acidity includes, in addition to [H" ] and strong acids, the weak acids. The latter acids can be titrated with strong base if their pJ values are less than — 10. CO2 is usually removed from the samples by blowing it out with an inert gas. The end point of total acidity is characterized by the volume V2 of strong base added. After this end point, further additions of strong base are linearly related to an increase in [OH"] ... 

Figure 6 Emissions of Oj, CO and CO downstream of the grate in the large rig. Data as in Figure 5. The peaks in Oj with corresponding dips in CO2, CO and THC originate from back-blowing the gas analysis system.

Flexible Foams CO2 obtained in situ by the reaction of water with isocyanate has been the chief blowing agent for all commercially produced flexible urethane foams. The amount of water and tolylene diisocyanate (TDI) used determines foam density, providing most of the gas formed is used to expand the urethane polymer. Because water participates in the polymerization reactions leading to the expanded cellular urethane polymer, it has a very pronounced influence on the properties of foams. For better control of the foaming process most foam manufacturers employ distilled or deionized water (16). 

C02 blown foam - A polyurethane foam in which all of the gas from expanding or blowing is carbon dioxide (CO2) generated by the chemical reaction between water and isocyanates also called water-blown foam (3). cold-cure foam - See Cold molding. 

CO 26.0, CO2 13.4. Although,its Btu is only 87 per cu foot, it Is suitable for several purposes, such as to raise steam for the driving of the blowing engines, as internal gas fuel for the gas engine driving the air compressor, to heat the stoves so that by means of the latter the incoming blast may be heated. 

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