Recently we have discussed some of the key concepts for applying spray foam insulation. Now over the next few weeks, we are going to discuss some concepts related to processing SPF chemicals before and during application.
To better understand processing and SPF application, let’s start this week with a brief introduction to the fundamentals of spray foam insulation.
SPF is a cellular plastic created by the mixture of isocyanate and a polyol-based, resin blend. Foam plastic is a solid polymeric structure, with tiny gas bubbles inside, and derives properties from both phases. The gas contributes primarily to the thermal insulation properties and the polymeric structure affects the mechanical and chemical properties.
Isocyanate, identified in most cases by the letter “A”, at least in North America, is a highly reactive organic chemical, and is a basic component in SPF systems and some polyurethane coating systems. The isocyanate generally used for spray foam systems is polymeric MDI.
Since most SPF system manufacturers use a similar isocyanate, the difference in SPF systems is mainly associated with the manufacturers proprietary resin blend. The resin blend, or polyol blend, is usually identified by the letter “B”, and consists of at least five components: polyols, catalysts, surfactants, fire retardants and blowing agents.
The timing of three key reactions is critical to SPF creation: plastic formation reaction, blowing reaction and cell formation reaction. The polyol reacts with iso to create the plastic formation, the blowing agent triggers the blowing reaction and expansion of the foam and, combined with the surfactant, impacts the cell formation. Several factors affect these reactions including the chemical formulations being used, ambient conditions and the mechanical heat and pressure of the proportioning units, this is known as processing conditions.
Now that you have a better understanding of the role of the different raw materials, join us next week as we continue to discuss Processing SPF.
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