Karl Fischer Determination of Trace Water in Polyethylene Terephthalate
Polyethylene terephthalate trace moisture determination relies on Karl Fischer coulometric oven extraction at 170 to 180 degrees Celsius to prevent chain scission.
Molecular Sieve Dry Column
Meaning
Filtration components filled with zeolites or desiccant beads remove moisture from instrument carrier gases. A molecular sieve dry column protects the titration cell from external water that would otherwise interfere with the resin moisture measurement. If the gas stream is not perfectly dry, the instrument records a high background drift that obscures the actual water content of the polymer sample.
The column uses materials with specific pore sizes to trap water molecules while allowing the carrier gas to pass through.
Physical Adsorption
Trapping of water vapor occurs as the gas flows through the bed of desiccant beads. A molecular sieve dry column captures moisture through a process of surface attraction within the microscopic pores of the zeolite. This mechanism is efficient at low concentrations, making it ideal for protecting sensitive analytical equipment.
The effectiveness of the adsorption determines the lower detection limit of the entire moisture measurement system.
Regular Maintenance
Replacement or regeneration of the desiccant material is required to maintain the protection of the instrument. A saturated molecular sieve dry column allows moisture to break through into the carrier gas stream, causing erratic readings. Technicians often use color indicating silica gel alongside the molecular sieve to provide a visual cue for when the column is exhausted.
Keeping the column fresh is a standard part of the preventative maintenance routine in a moulding facility.
Continuous Purity
Operation of the moisture analyzer depends on a steady supply of dry, clean gas. The molecular sieve dry column prevents contaminants and water from degrading the expensive reagents inside the titration cell. Clean gas flow ensures that the baseline current remains stable for several days of continuous testing.