Meaning
Synthetic thermoplastic polymers characterized by repeating amide linkages along the molecular backbone exhibit high mechanical strength and wear resistance. These materials are heavily utilised in automotive, industrial, and electrical components where structural integrity is paramount. In processing, polyamides are highly hygroscopic, absorbing moisture from the surrounding atmosphere due to the polar nature of the amide groups.
Moisture Sensitivity
Water molecules act as plasticisers when absorbed into the polymer structure, disrupting the intermolecular hydrogen bonds between the polymer chains. This molecular disruption increases the free volume, which lowers the glass transition temperature and alters the mechanical properties of the moulded part. Moulders must dry these resins to less than zero point two percent moisture content before melt processing to avoid severe degradation.
Moulding Processibility
Processing undried resins leads to hydrolytic degradation in the injection moulding barrel, where high temperatures break the polymer chains. This degradation decreases the molecular weight, reduces the melt viscosity, and causes flashing or splay. Parts moulded from degraded material suffer from brittle failures, failing to meet the mechanical specifications defined on the resin datasheet.
Part Performance
The mechanical properties of finished nylon parts change over time as they equilibrate with ambient moisture. Freshly moulded parts are dry and brittle, but they gain toughness as they absorb moisture, though their dimensional stability and stiffness decrease.
