Blowing agents concentration ranges

Foam density is largely a function of the concentration of blowing agents. There has been a strong development towards the use of less expanded, i.e. higher density rigid cellular polyurethanes. This includes not only the so-called structural foams for simulated wood but also unexpanded solid materials used for brush handles and gun stocks. This range is clearly indicated in Table 27.4. ... 

The concentration of blowing agent depends on the density required. The increase of blowing agent decreases the density of product but beyond certain level the cell structure becomes irregular and density cannot be reduced. If it is necessary to reduce density further, chemicals called "kickers" are used which lower the decomposition temperature ranges or accelerate the rate of decomposition. Kickers are mainly stabilizers such as tribasic lead phthalate, dibasic lead phthalate and dibasic lead phosphite which act as activators that reduce the temperature needed to produce the gas. 

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