Blowing Agents CBAs

CBAs can be used in almost any thermoplastic and can be either inorganic or organic. The most common CBA is sodium bicarbonate, but its use is limited in plastics because its decomposition cannot be controlled as can the organic CBAs. The following are the most popular organic CBAs for plastics usage (8)  

Widely used for foaming HDPE, PP, HIPS, PVC, EVA, acetal, acrylic, and PPO-based plastics. Decomposes at 400°-415°F (204°-213°C). Non-plateout grades are available to eliminate formation of cyanuric acid, which can attack molds. 

Additives, Fillers and Reinforcements 283 Commonly used in LDPE, EVA and 

---

Chemical blowing agents (CBAs). These are solids that decompose to give a gas at the processing temperature. In addition to the demands above, the CBA must possess the following ... 

Chemical blowing agents (CBAs) decompose at various processing temperatures to form a gas (Table 8.3). The most important criterion for selection of a chemical blowing agent is that the decomposition temperature matches the processing temperature of the plastic. Little or... 

In either case, the gas, if evenly dispersed, expands to form the cells in the plastic. There are a number of different ways to bring about the formation of cells, depending on the gas being used, the chemical blowing agent (CBA) the type of plastic resin, and/or the particular process being used (7). 

On the other hand, the use of chemical blowing agents (CBAs) has increased. These agents generate the gas necessary for stractural foam by either decomposition or chemical reaction in the melt. Factors to consider when selecting a blowing agent for a particular thermoplastic stmctural foam are (21) ... 

For example, in profile foam operations, where higher density foams are desired, it is general practice to use chemical blowing agents (CBA). These materials, which decompose under polymer melt processing conditions to yield gases to expand the polymer, are usually dry-blended with the resin and then fed to the extruder. They can also be compounded directly into the resin by the polymer supplier and provided as a ready-to-use masterbatch. 

---