Meaning
Chemical degradation processes that break the main backbone of a polymer molecule reduce the overall molecular chain length. In chain scission, the covalent bonds within the polymer chain are severed by thermal energy, mechanical stress or hydrolysis. This reaction alters the melt flow behavior.
Degradation Mechanism
Hydrolytic action at elevated temperatures represents the primary driver of this polymer breakdown in condensation polymers. Water molecules attack the ester or amide linkages in the molten state, which divides the long chains into shorter fragments. This reaction progresses rapidly once the processing temperature exceeds the melting point of the resin.
The presence of trace acid catalysts or metal impurities accelerates the rate of this degradation.
Mechanical Effect
Materials that have undergone this molecular breakdown exhibit lower tensile strength, reduced impact resistance and increased brittleness. The shortened chains cannot form the entanglements needed to distribute mechanical stresses throughout the plastic structure. Cracking or sudden failure occurs under loads that a normal polymer part would easily withstand.
This loss of structural integrity becomes a major risk for safety-critical industrial components.
Operational Prevention
Processing parameters must be controlled to prevent the degradation from occurring during the molding cycle. Drying the raw polymer beads to moisture levels below the specified threshold protects the polymer backbones from hydrolytic cleaving. Operators should also avoid excessive melt temperatures and long residence times in the heated barrel of the machine.
These control measures maintain the structural integrity of the polymer during the molding process.
