Endothermic blowing agents

Kycerol, Chemical blowing agents, endothermic, Rit-Chem Co. Inc. 

Foam extrusion experiments are performed to study the effects of surrounding temperature variation on cell structure. LLDPE is used with endothermic chemical blowing agent on a single-screw extruder to exit from a capillary die into environments with different... 

The endothermic or exothermic nature of a blowing agent affects processing economics. One of the factors that frequently controls the cycle time of structural-foam parts, and therefore the number of parts that can be produced in an hour, is the post blow. Post blow results when a part is removed from a mold before the core is sufficiently cooled, causing swelling in areas with the greatest thickness. This swelling is caused by the presence of pressurized gas in the core of the part (21). 

Safoam. [Reedy Int l.] Chemical endothermic nucleating and blowing agent for thermoplastics. 

Endothermic and inorganic chemical blowing agents have included materials that degrade into carbon dioxide when heated, such as sodium bicarbonate. Sodium bicarbonate s low decomposition temperature (100°C-140°C) suits its use with POs, though it can decompose rapidly, forming open-cell stmctures. Other endothermic agents include citric acid, sodium borohydride, and polycarbonic... 

Sodium borohydride (NaBH4). Sodium borohydride is an effective endothermic blowing agent because its reaction with water produces 10 to 20 times the amoimt of gas produced by other CBAs that give off nitrogen. Sodium borohydride must be blended with the polymer to be foamed to prevent reaction with water during storage. 

Chemical blowing agents generate a gas, typically nitrogen, water, carbon monoxide or carbon dioxide, by a chemical reaction that can be either exothermic (i.e., heat is generated chemically and given out by the system, resulting in a rise in temperature) or endothermic (heat is absorbed... 

Sodium bicarbonate, with or without citric acid, is a blowing agent that decomposes endothermically at 150-230 °C. It is suitable for polystyrene, ABS, polyamides, the polyolefins and rigid PVC, but not plasticised PVC. The gases evolved include carbon dioxide and water, so there can be a rust problem with metal moulds. The type of foam obtained with sodium bicarbonate usually has a coarse structure, although tests with different manufacturers products, all using bicarbonate/citric acid as the active ingredient, show considerable differences in cell and foam density. 

The manufacturer Dongjin SemiChem claims a 35% share of the global market for chemical blowing agents in plastics and rubber combined. It produces 30,000 tonnes of foaming agents and decomposition activators a year, including exothermic and endothermic types. 

Azodicarbonamide, sulfonyl hydrazides, sulfonyl semicarbazides, and dinitro-pentamethylene tetramine are examples of exothermic blowing agents. Sodium borohydride, sodium bicarbonate, and polycarbonic acid are examples of endothermic blowing agents. 

Endothermal blowing agents require energy for decomposition and gas release therefore stops quickly after the supply of heat is terminated. Shorter cooling periods are needed and moulding cycles are therefore shorter. The base materials are bicarbonate and citric acid - which are also used as food additives, and present no handling problems. 

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