About moisture testing of plastic resin

The moisture content of plastic particles greatly affects the quality of injection molded products. Whether it is the moisture in the plastic particles or the moisture attached to the surface of the material, it will cause molding quality problems in engineering plastic processing.

Moreover, most plastics will absorb moisture from the air to a certain extent, and the amount of moisture absorbed by the plastic is generally related to the type of resin.

The water absorption of plastics will have an adverse effect on the molding process, which can easily cause problems such as rough surface, bubbles or poor mechanical properties of the processed products.

It is difficult to detect whether there is moisture in plastic particles by naked eye observation. Therefore, it is necessary to use corresponding testing equipment or technical means to measure the moisture content of plastics to improve the problems caused by excessive moisture content during the molding process.

Purpose of plastic moisture test

In the process of engineering plastic molding, it is very important to control the moisture content of plastic granule raw materials. Excessive moisture content of plastic granules can easily lead to bubbles on the surface or inside of the molded product, or problems such as decreased mechanical properties, spray marks, and surface silver wires.

The moisture content of PP plastic granules should be controlled below 0.2 or 0.4%, while the moisture content of ABS plastic granules should be controlled below 0.1%.

The purpose of using a drying method moisture meter to determine the moisture content of PP granules and ABS granules is to accurately determine through instrument measurement that the moisture content of engineering plastic raw materials meets the indicator range of: PP granules moisture ≤ 0.2% or 0.4%, ABS plastic moisture ≤ 0.1%.

If the moisture content exceeds the standard, the corresponding drying treatment is carried out before injection molding and molding.

If the moisture content meets the specification, it is not necessary to dry it to avoid blind drying treatment, increase energy consumption, and cause losses.

Principle of moisture test for plastic particles

The moisture content of plastic particles is tested by placing the plastic particles at a specified temperature, drying them, and calculating the percentage of the mass difference before and after heating and the mass of the plastic particles before heating, that is, the moisture content.

Plastic moisture test experiment

1) Requirements for preparation of ABS plastic particle samples
ABS plastic particles have a strong water absorption capacity, and their water absorption rate can generally reach 0.25% to 0.45%. It can be seen that after drying and placing them in the air for a period of time, they will absorb water and become damp, and the moisture content is likely to be greater than 0.4%. Therefore, before the customer requires the ABS material to be placed in a constant temperature drying oven, dried at 82°C for 2 hours, cooled, and tested for moisture content.
2) ABS plastic particle test mode, heating temperature and sampling volume
Before starting the test, first create a sample library, enter the sample name: ABS particles, select the measurement mode as automatic, set the heating mode to standard, and enter the test temperature in the temperature column.
3) ABS plastic particle test process

Put about 20g of ABS plastic particles in the sample tray, cover the heating chamber cover, select the start button, and at the end of the test, the instrument will automatically lock and display the moisture content of the sample. Repeat the test 3 times and record the data.

4) Data calculation

The average moisture content of ABS plastic particles W1=(0.05%+0.03%+0.06%)/3≈0.047%, which meets the requirement of moisture content of ABS plastic particles ≤0.1%.

5) PP plastic particle sample preparation requirements

PP plastic particles have weak water absorption capacity, and their water absorption rate is less than 0.03%. It can be seen that after drying and placing them in the air for a period of time, they will basically not absorb water and moisture, and the moisture content will hardly be affected. Therefore, sampling can be directly tested.

6) PP plastic particle test mode, heating temperature and sampling volume
Before starting the test, first establish a sample library, enter the sample name: PP particles, select the measurement mode as automatic, set the heating mode to standard, and enter the test temperature in the temperature column.

7) PP plastic particle test process

Take about 20g of PP plastic particles and place them in the sample tray, cover the heating chamber cover, select the start button, and at the end of the test, the instrument will automatically lock and display the moisture content of the sample. Repeat the test 3 times and record the data.

If you need a plastic moisture tester, please view the instrument information and contact us：

https://www.chinatestequipments.com/tests-on-plastic-raw-materials/halogen-moisture-meter.html 

sales@chinatestequipment.com