How Vazo™ Free Radical Initiators Are Applied in Polymer Foams
Rigid polymer foams can be used in building insulation, appliances, furniture, packaging, and food containers. Flexible foams are used in carpet underlays, textiles, sporting equipment, furniture, bedding, and for absorbing shock or sound.
Polymer foams are generally created by injecting a gas (i.e., "a blowing agent") inside a molten thermoplastic or thermoset resin, and cooling the resin below its melting point to trap the gas bubbles. This blowing agent is commonly a volatile liquid that evaporates upon heating to create foam.
Physical blowing agents have their challenges as well, namely:
- It is often not easy to work with a liquid.
- There are a host of environmental and regulatory issues to consider, depending on the chosen agent.
- "Greener" alternatives often require high pressure to control when and the extent to which foaming occurs.
Vazo™ free radical initiators represent an entirely different class of blowing agent. Known as a chemical blowing agent, Vazo™ free radical initiators decompose to produce one mole of nitrogen gas for every mole of azo compound used. Thus, Vazo™ initiators generate benign nitrogen gas in situ to create polymer foams. Moreover, being solids themselves under common handling conditions, Vazo™ initiators can be easily, and homogeneously, compounded into the resin prior to foam expansion.
In the world of polymer foams, Vazo™ initiators are most often employed in the production of polyol, polyurethane, and silicone foams.
Uniquely, two different Vazo™ initiators having different reactivity can be blended without fear of incompatibility. This is useful for initiating polymerization and, later, creating foam expansion using a singular batch addition.
Combine a more reactive azo compound with a less reactive one and run the reaction in thermal stages. When run in stages, the lower temperature polymerization stage is followed by a higher temperature expansion phase, which allows the less-reactive azo to be used as a blowing agent.
The Vazo™ initiator brand is the longest lived and most established azo brand. Vazo™ 67 is the most commonly used grade for polymer foam expansion, followed by Vazo™ 88 and Vazo™ 64.
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