Vaporization Coulometry Moisture Analysis in Industrial Polyesters
Coulometric vaporization titration under ISO 15512 Method B2 quantifies trace moisture in industrial polyesters to prevent hydrolytic degradation during melt extrusion.
Ester Chain Scission
Meaning
Chemical degradation occurs when polymer molecules experience a permanent break along the backbone of an ester linkage. Through ester chain scission, the molecular weight of the resin drops as long polymer units divide into shorter segments. Hydrolysis remains the primary driver of this reaction in susceptible materials like polyethylene terephthalate or polyesters when moisture reaches the melt.
Thermal Stability
Processing temperatures exceeding the degradation threshold accelerate the internal breakdown of the chain. Manufacturers select stabilizers to mitigate this reduction in chain length during residence time in the barrel. Injection moulding parameters must strictly control drying procedures because residual water molecules initiate the chemical cleavage inside the heated screw and nozzle.
Resin Degradation
Lowering the average molecular weight via scission reduces the mechanical toughness of the final moulded part. Fragility increases as these shortened chains fail to entangle, leading to brittle fracture under stress. Regrind usage requires additional monitoring because repeated heating cycles increase the statistical probability of these bond ruptures.
Production Penalty
Excess moisture in the feed material forces immediate rejection of parts due to a visible loss of viscosity and strength. Costs accrue from scrap accumulation and the potential for premature tooling failure caused by volatile gas buildup. Proper material preparation confirms the chemical integrity of the polymer before it enters the high pressure zone of the press.