Determining Water Content in Plastic Pellets

The water content in plastics, also known as moisture content, is a crucial quality parameter that significantly influences both the properties and processability of certain plastics. Elevated water content can result in degradation through hydrolysis or lead to surface imperfections. Furthermore, it can adversely impact the physical properties of some plastics.

Determining Water Content in Plastic Pellets

Image Credit: Metrohm Middle East FZC

For the study presented in this article, the water content determination of polycarbonate pellets was determined using the 885 Compact Oven Sample Changer and 899 Coulometer.

The oven technique was employed as volatile compounds within the plastic interfered with the direct determination of water content via coulometric Karl Fischer titration.

Sample

  • Plastic pellets (polycarbonate)

Sample Preparation

Approximately 3 g of sample was weighed into a sample vial, tightly closed with a cap, and placed on the rack of the 885 Compact Oven Sample Changer.

Configuration

Source: Metrohm Middle East FZC

. .
885 Compact Oven Sample Changer 2.885.0010
899 Coulometer 2.899.0010
Remote cable 6.2141.390
Double Pt-wire electrode 6.0341.100
Generator electrode without diaphragm 6.0345.100

 

Analysis

All measurements reported in this study were carried out at the same temperature with the same parameters.

After starting the sample series, the Sample Changer was moved to the conditioning vial. The needle then pierced the septum, the gas flow was initiated, and the titration vessel was conditioned.

A determination using an empty sample vial was then carried out to prepare the system and rinse all tubing.

Following system preparation, three blank values (empty sample vials) were determined, and the mean value of the blank was saved as a common variable. This value was then subtracted from the EP of the sample determination.

Subsequently, the water content of the samples was determined, and the titration vessel was reconditioned between each sample measurement.

Parameters 899 Coulometer

Source: Metrohm Middle East FZC

. .
Conditioning on
Start drift 10 μg/min
Drift correction auto
Automatic start off
Stabilizing time 10 s
Cond. stop time off
Pause 0 s
Endpoint at 50 mV
Titration rate optimal
Stop criterion rel. drift
Relative stop drift 10 μg/min
Extraction time 120 s
Generator electrod without diaphragm
Generator current 400 mA
Stirring rate 15
I(pol) 10 μA
Temperature 25 °C
Stop time off

 

Parameters 885 Compact Oven Sample Changer

Source: Metrohm Middle East FZC

. .
Temperature 250 °C
Flow rate 50 mL/min
Gas supply valve
Gas type nitrogen
End of series conditioning

 

Results

Source: Metrohm Middle East FZC

. .
Mean (n = 10) [μg/g] RSD [%]
766.7 0.55

 

This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.

For more information on this source, please visit Metrohm Middle East FZC.

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