Meaning
Chemical degradation through water cleavage defines hydrolysis PA66 PBT, a polymer resin property governing moisture resistance in compounded engineering thermoplastics. Polyamide 66 and polybutylene terephthalate degrade when elevated thermal energy drives water molecules to attack ester linkages and amide bonds during compounding or injection moulding. Polymer sourcing must restrict moisture content below designated thresholds prior to processing because residual humidity breaks polymer chains and drops molecular weight permanently.
Moulded parts suffer from reduced tensile strength and early mechanical failure when processing temperatures accelerate this degradation mechanism.
Moisture Threshold
Raw material specification sheets list maximum allowable water content percentages for virgin resin pellets before hopper entry. Processing parameters require drying operations to reduce moisture levels beneath specific ppm limits to prevent polymer chain scission inside the heated barrel. Regrind usage introduces variable moisture histories that complicate drying cycles and demand stricter testing protocols than virgin material.
Part specifications demand strict adherence to these drying limits because excessive moisture produces brittle mouldings with compromised impact resistance.
Thermal Degradation
Melt temperature variations during injection moulding influence the rate of moisture attack on polymer chains. Barrel residence time dictates the duration that molten polyamide 66 and polybutylene terephthalate remain exposed to thermal stress alongside trapped humidity. Processing drift occurs when heaters run outside controlled tolerances, causing localized overheating that triggers rapid polymer breakdown.
Moulded components exhibit surface blistering and silvery streaks when degraded material emerges from the nozzle, indicating severe molecular weight loss.
Economic Impact
Virgin resin economics rely on precise pellet preparation to avoid costly scrap rates during high volume production runs. Scrap generation increases when operators fail to maintain correct drying temperatures, forcing expensive material sorting and regrind processing. Part cost calculations incorporate dryer maintenance and moisture testing equipment as necessary investments to protect component structural integrity.
Component rejection rates rise sharply when hydrolytic degradation compromises the mechanical performance required by structural end use applications.
