Causes and Solutions for PP Flame Retardant Exudation

Most PP flame retardants are inorganic salts with strong polarity, such as ammonium polyphosphate (APP), aluminum hypophosphite (AHP), and melamine polyphosphate (MPP). PP resin molecules have a non-polar crystalline linear structure with low surface activity and are non-polar. This leads to a problem: after the inorganic and organic components in the PP flame retardant are physically mixed uniformly, over time, the polar inorganic groups will repel the non-polar organic substances in the PP, resulting in flame retardant exudation after injection molding, causing phenomena such as white spots. This is the main cause of exudation. What are the solutions?

One solution is to modify the surface of the inorganic flame retardant, for example, by introducing non-polar organic groups. This forms a non-polar oily substance on the surface of the inorganic flame retardant. During mixing with the organic polypropylene, the principle of interfacial similarity and compatibility generates bonding forces, thereby reducing the repulsive forces between the inorganic and organic groups.

In addition, lowering the processing temperature slows down the migration rate, and adding certain additives increases the migration resistance between inorganic flame retardants and polypropylene, thereby reducing the migration rate of low molecular weight flame retardants.

Using coupling agents and grafting techniques to physically bond phosphate or metal salt flame retardants to polypropylene increases the resistance to the precipitation of halogen-free flame retardants in PP.

The causes of PP flame retardant precipitation are likely far more numerous than those mentioned above. For example, particle size, physicochemical properties, and formulation all affect flame retardant precipitation. Generally, these issues are addressed by modifying the flame retardant, adjusting the formulation, and adjusting the processing temperature as needed.