Product category:
Liquid Analysis: Titration, HPLC, IC
News Release from: Metrohm UK | Subject: Moisture in plastics
Edited by the Processingtalk Editorial
Team on 22 June 2007
Moisture content measurement of plastics
The determination of the moisture content of plastics during processing is crucial: 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
This article was originally published on Processingtalk on 2 Jul 2008 at 8.00am (UK)
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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 4-6 hours at 160C - 180C with an air dew point of below -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 832 Thermoprep in conjunction with an 831 coulometer from Metrohm is perfect for this application, and for moisture determination of other solids and difficult samples.
This method gives a very 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. Request a free brochure from Metrohm UK ...
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