The 860 Thermoprep in conjunction with an 831 coulometer from Metrohm can be used for the determination of the moisture content in plastics during processing.
This analysis can be performed on the resin, preform or bottle to determine if excessive moisture is present.
The effectiveness of dryers can also be checked.
PET, for example, must be dried to very low levels (40ppm) prior to processing.
Processing problems and defects such as haziness, voids and streaks coupled with a fall in IV (intrinsic viscosity) may result in undesirable mechanical properties of the bottle.
To maintain quality throughput PET is dried for four to six hours at 160C-180C with an air dew point of less than -40C.
Moisture content in PET is determined using the Karl Fischer Titration method, where a sample is heated in a specially designed oven at 190C.
Inert gas (nitrogen or argon) passes over the sample and any moisture evolved from the heating is carried over into a coulometeric KF cell where it is titrated.
The level of water is determined automatically.
The 860 Thermoprep and 831 coulometer from Metrohm are suitable for this application, as well as for moisture determination of other solids and difficult samples.
This method provides an accurate means of measuring the water content.
Other techniques for measuring moisture content involving weight-loss measurement may lead to false readings as other non-water-based compounds can be boiled off from the PET.
