Liquid carbon dioxide blowing

Demands on Surfactants in Polyurethane Foam Production with Liquid Carbon Dioxide Blowing... 

The polyurethane dosing and foaming section of this plant is equipped with a moulding technology that allows chlorofluorocarbon (CFC) blowing agents to be replaced with liquid carbon dioxide. This helps reduce the density of the polyurethane considerably and thus saves on material costs. 

In the manufacture of flexible foams, carbon dioxide generated from the water-isocyanate reaction has replaced the external blowing agent, yet methylene chloride is still widely used with acetone and liquid carbon dioxide. Cyclopentane has become the main blowing agent for refrigeration appliances, w-pentane has only been exploited for sandwich panels and other building insulation. 

Rather than pre-blending the blowing agent with a polyol before injection into the foam mixing chamber, the process uniquely introduces a stream of liquid carbon dioxide directly into the mixing head. This allows the moulder to stop and start injections of short duration, without altering the concentration of carbon dioxide in the reacting mixture, and without the need to re-circulate the gas back to the day tank of the machine. 

In the liquefied-gas system, liquid carbon dioxide or nitrogen is atomized through a nozzle in the blow pint into the bottle immediately after the parison has been expanded. The liquid quickly vaporizes, removing heat, and exhausts at the end of the cycle. This method has increased production rates by 25-35%. A disadvantage is the cost of the liquefied gas. If consumption is not precisely controlled, the cost saving is small. 

Polyethylene terephthalate is injection blow molded to make water and carbonated drink bottles, and other liquid food packages. High stiffness, excellent clarity, and good resistance to carbon dioxide permeation are the principal attributes of these bottles. We carefully control molding conditions to promote transparency and surface gloss, which are prized for food... 

The second, much more often applied, method of foam manufacture, is the generation of gas bubbles within the liquid. This requires the presence of blowing agents, which exist in two types physical and chemical ones. To the first category belong substances which are soluble in the polymer at a high pressure or at a lower temperature, but which leave the polymer upon pressure reduction and/or temperature increase (for comparison carbon dioxide gas escapes from beer when... 

Crosslinked Polystyrene. Polystyrene lightly crosslinked during polymerization by 0.01-0.25% divinylbenzene provides foams, expanded by carbon dioxide or other gases, with greater expandability and resistance to collapse at elevated temperatures (102, 103). Other divinylbenzene copolymers are reported, employing as blowing agent saturated aliphatic or fluoroaliphatic volatile liquids, tetramethylsilane, and azobis-isobutyronitrile (99,106, 108). 

Another technique to generate a gas in the liquid phase is the thermal decomposition of chemical blowing agents which generate either nitrogen or carbon dioxide, or both. 

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