How to Measure Moisture in PET with a Halogen Moisture Analyzer | PET Moisture Measurement Method — VicoMeter | Jiangsu Victor Instrument Meter Co., Ltd.

VM-E01 Halogen Moisture Analyzer（0.1mg/0.0001g）

Background

Plastic part suppliers and their customers care about quality and fast production. Proper moisture in raw material ensures trouble-free compounding and molding, smooth surfaces, and ideal mechanical properties. The VicoMeter VM-E01 rapid halogen moisture analyzer is ideal for simple, accurate moisture measurement on the production floor.

Measuring moisture in plastics with a halogen moisture analyzer is a recognized ASTM method: D6980-12, "Standard Test Method for Determination of Moisture in Plastics by Loss in Weight".

A VicoMeter solution for typical PET (polyethylene terephthalate) samples: measuring their moisture with the VM-E01 rapid halogen moisture analyzer, including operating procedures.

Related Information

Before measuring PET samples with the VM-E01, you may also want to know:

Can a halogen moisture analyzer replace the oven method? Yes — seeCan Rapid Halogen Moisture Analyzers Replace the Oven Method?as discussed in that article.
How to choose a fast, accurate model? See"Rapid Halogen Moisture Analyzer Selection Guide"as discussed in that article.
Where to learn more about halogen moisture analyzers? See"Basic Knowledge of Rapid Halogen Moisture Analyzers"、"Explanation of Halogen Moisture Analyzer Technical Specifications"、《Halogen Moisture Analyzer》and other articles.
Other questions about measuring plastics? See the FAQ in"FAQ: Measuring Plastics with a Halogen Moisture Analyzer"as discussed in that article.

Common Questions About PET and Plastics

WKT-A9 Karl Fischer Trace Moisture Analyzer Coulometric

Reference Value Determination

The PET reference moisture value was determined with the VicoMeter WKT-A9 Karl Fischer moisture analyzer and WKT-V2 Karl Fischer oven; released moisture is carried by dry nitrogen into the electrolytic cell.

Recommended Settings for Plastics Industry Samples

If you have no reference method for plastics samples on the VM-E01, VicoMeter recommends these settings from experimental experience:

Heating mode: Standard
Shutoff mode: Automatic (1 mg/140 s)
Sample size: 30 g
Resolution: High (0.1 mg/0.0001 g)
Warm-up: standby, 100°C; at standby temperature, preheat the empty pan for 1 minute, then tare.

Selecting the Drying Temperature

Same Sample Heated at Two Different Temperatures

Figure 1: Same Sample Heated at Different Temperatures

(Click image to enlarge)

Choose a drying temperature matching the Karl Fischer reference value. Melting or marked color change means the temperature is too high. Some samples inevitably discolor when heated (polyamide unavoidably turns brown).

Figure 1 compares samples after two heating runs. Left: correct temperature — no melting or discoloration. Right: the sample browned, so the temperature was too high.

Plastic Sample Handling

Measure samples promptly. Otherwise, fill the container completely (use a smaller one if needed) and seal it to minimize air and prevent moisture uptake during storage.

Operating Steps for PET (Polyethylene Terephthalate) Samples

Place the VM-E01 in a suitable spot, warm up 30 min, level it (bubble centered), and perform weighing and temperature calibration. Then measure PET samples (installation, environment, warm-up, calibration: seePreparation Before Formal Measurement with a Halogen Moisture Analyzeras discussed in that article; click the link to learn more.).

Halogen Moisture Analyzer Measurement Step: Taring

Tare Sample Pan

1. Place the empty pan on the center holder, preheat 1 min at 160°C standby, press tare to zero.

Halogen Moisture Analyzer Measurement Step: Spreading the Sample

Add Sample

2. Quickly spread about 30 g of PET sample evenly on the pan; wait for a stable reading.

One-Touch Start

3. Press start; the PET moisture result appears within minutes.

Test Data

VM-E01 Halogen Moisture Analyzer（0.1mg/0.0001g）

VM-E01 Settings Reference

Heating mode: Standard
Heating temperature: 160°C
Shutoff mode: Automatic (1 mg/140 s)
Sample size: 30 g
Resolution: High (0.1 mg/0.0001 g)
Warm-up: standby, 100°C; at standby temperature, preheat the empty pan for 1 minute, then tare.

Sample Information

Sample Description: PET, colorless, copolymer, crystal-clear.
Typical Maximum Allowable Moisture Content [%]: 0.05
Hygroscopicity (23°C/50% rH) [%]: 0.19

Moisture Chart for PET Samples Before and After Drying

Chart Notes

Recommendation: measure 6 PET samples with different moisture contents (dry vs. moist).
Green line:Moisture content (average) measured with the WKT-A9 Karl Fischer moisture analyzer and WKT-V2 Karl Fischer oven.
Blue line:Moisture content (average) measured with the VM-E01 rapid halogen moisture analyzer.
Red line:Typical maximum allowable moisture for pellet processing; refer to the supplier's material-specific values.

Moisture Data for PET Samples Before and After Drying

Sample Information	PET Moisture Content Before Drying		PET Moisture Content After Drying
Test Method	Halogen Moisture Analyzer	Karl Fischer Moisture Analyzers	Halogen Moisture Analyzer	Karl Fischer Moisture Analyzers
Moisture %MC	0.281	0.296	0.045	0.030
Std Dev Δ	0.002	0.006	0.001	0.001
Test Time [min]	21	30	7	30

Sample-Specific Test Notes

Maximum allowable moisture for pellet processing must always follow supplier specifications. Values here are typical only and may not suit your material or process.

These drying parameters were obtained on common plastics and do not cover all grades or colors; optimizing them may be needed for best results on a specific material.

FAQ

Can the Loss-on-Drying Method Measure Plastics?

Yes. Measuring moisture in plastics with a halogen moisture analyzer is a recognized ASTM method: D6980-12, "Standard Test Method for Determination of Moisture in Plastics by Loss in Weight".

Can a Rapid Halogen Moisture Analyzer Replace the Oven Method for Plastics?

Yes — seeCan Rapid Halogen Moisture Analyzers Replace the Oven Method?).

Can the same method for unreinforced plastics be used on reinforced plastics?

Yes — reinforced plastics contain glass or other materials that do not affect moisture measurement.

Can colorless-resin parameters be applied to a colored resin?

Adjust drying temperature for heat absorption — e.g., black resin about 10°C lower than white.

How to measure moisture in plasticized plastics?

Take care: loss on drying counts volatilized plasticizer as moisture. Heat at a lower temperature where possible to prevent plasticizer loss.

Can I apply my Karl Fischer oven temperature to the VM-E01?

Not directly. As a rule of thumb, the VM-E01 drying temperature is about 30°C lower than the oven's.

Can a method developed for one supplier's polymer be used on the same polymer type from other suppliers?

It is a good reference, but should be adapted to the other suppliers' polymer compounds.

Dr. Wei's Classroom

Polyethylene terephthalate (PET), formula (C10H8O4)n, is made by transesterification of dimethyl terephthalate with ethylene glycol or esterification of terephthalic acid with ethylene glycol, followed by polycondensation. A crystalline saturated polyester — milky-white or pale-yellow, highly crystalline, smooth and glossy. A common resin, classified into APET, RPET, and PETG.

Excellent physical and mechanical properties over a wide temperature range; long-term service up to 120°C. Excellent electrical insulation, retained even at high temperature and frequency, though corona resistance is poor. Creep, fatigue, and friction resistance and dimensional stability are all very good.