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a gas into an extruder barrel or a die, or into injection molding barrels or nozzles and allowing the shear/mix action of the screw to disperse the gas uniformly to form very fine bubbles or a solution of gas in the melt. When the melt is molded or extruded and the part is at atmospheric pressure, the gas comes out of solution expanding the polymer melt immediately before solidification. Frothing (akin to beating egg whites making a
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Soluble fillers, e.g. solid sodium chloride crystals mixed into a liquid urethane system, which is then shaped into a solid polymer part, the sodium chloride is later washed out by immersing the solid molded part in water for some time, to leave small inter-connected holes in relatively high density
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Mechanically made foams and froths, involves methods of introducing bubbles into liquid polymerisable matrices (e.g. an unvulcanised elastomer in the form of a liquid latex). Methods include whisking-in air or other gases or low boiling volatile liquids in low viscosity lattices, or the injection of
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Mixed physical/chemical blowing agents are used to produce flexible PU foams with very low densities. Here both the chemical and physical blowing are used in tandem to balance each other out with respect to thermal energy released and absorbed, minimizing temperature rise. Otherwise excessive
185:. The bubble/foam-making process is irreversible and endothermic, i.e. it needs heat (e.g. from a melt process or the chemical exotherm due to cross-linking), to volatilize a liquid blowing agent. However, on cooling process, the blowing agent will condense, which is a reversible process.
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for thermoplastic foams. Gaseous products and other byproducts are formed by a chemical reaction of the chemical blowing agent, promoted by the heat of the foam production process or a reacting polymer's
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Blowing agents (also known as 'pneumatogens') or related mechanisms to create holes in a matrix producing cellular materials, have been classified as follows:
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is used for the same purpose. Once formed the low molecular weight compounds will never revert to the original blowing agent; the reaction is irreversible.
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exothermic heat because of high loading of a physical blowing agent can cause thermal degradation of a developing thermoset or
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heat. Since the blowing reaction occurs forming low molecular weight compounds acting as the blowing gas, additional
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material. For instance, to avoid this in polyurethane systems isocyanate and water (which react to form
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for vinyl, hydrazine and other nitrogen-based materials for thermoplastic and elastomeric foams, and
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362:"A Method for Evaluating the Effect of Blowing Agent Condensation on Sprayed Polyurethane Foams"
169:(replaced CFCs, but are still ozone depletants, therefore being phased out), hydrocarbons (e.g.
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Kumaran, M.K.; Bomberg, M.T.; Marchand, R.G.; Ascough, M.R.; Creazzo, J.A. (October 1989).
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process in a variety of materials that undergo hardening or
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122:is a substance which is capable of producing a
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409:"Manufacturing Routes for Metallic Foams"
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233:at elevated temperatures.
470:Technology Leaps Forward"
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297:Wypych, George (2017).
407:Banhart, John (2000).
235:Zirconium(II) hydride
221:in the production of
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425:2000JOM....52l..22B
506:Plastics additives
202:sodium bicarbonate
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179:cyclopentane
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96:October 2009
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38:Please help
33:verification
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274:vermiculite
223:metal foams
495:Categories
480:2012-01-20
466:"CarDio CO
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284:References
211:exothermic
207:exothermic
190:isocyanate
175:isopentane
165:of 1987),
134:, such as
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386:0148-8287
327:cite book
319:963394095
259:meringue
231:titanium
229:gas and
227:hydrogen
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136:polymers
421:Bibcode
270:fly ash
171:pentane
128:foaming
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