Polyamides blowing agents

The reaction of NCO groups and carboxylic acid groups resulted in the formation of amide linkages and carbon dioxide as blowing agent. This reaction has led to the invention of urethane foam preparation, and the polyurethane industry has become one of the biggest plastic industries. A model reaction of a polyamide foam formation is shown below ... 

The catalyst or add source can consist of ammonium phosphate or polyphosphate salts, phosphoric add-derived amides or alkyl or halo-alkyl phosphates. Charring agents are based on molecular structures that can form cross-linked networks such as pentaerythritol, sorbitol, melamine, and phenol-formaldehyde resins. Other polymeric systems capable of intumescence are some polyamides and polyurethanes. Blowing agents help form a porous structure in the char and can fadlitate its formation. Common blowing agents are based on urea and urea-formaldehyde resins, melamines, and polyamides that can liberate moisture. 

A wide variety of polymers can be foamed, including the polymethanes, polyisocyanurates, PVC, polystyrene, ABS, polycarbonate, PET, PBT, polyamides, PPO, EVA and the polyolefins. Other additives required for the foaming process besides blowing agents may include foam nucleating agents, stabilisers, surfactants, plasticisers, colourants, flame retardants and particulate fillers. 

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. 

PAA polyaryl amide PAI polyamide-imide PAN polyacrylonitrile PB polybutylene PBA physical blowing agent PBI polybenzimidazole PBNA phenyl- -naphthylamine PBT polybutylene terephthalate PC permeability coefficient PC personal computer PC plastic composite PC plastic compKJunding PC plastic-concrete PC polycarbonate PC printed circuit PC process control PC programmable circuit PC programmable controller PCB polychlorinated biphenyl PCB printed circuit board PCE perchloroethene PCR post-consumer resin pcf pounds per cubic foot... 

Dinitrosoterephthalamide n (DNTA) A chemical blowing agent for vinyls, liquid polyamide resins, and silicone rubbers. It is especially noted for its low decomposition exotherm. 

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