Expandable microspheres, small thermoplastic spheres encapsulated with gas, consist of a thermoplastic polymer shell and an encapsulated liquid alkane gas. When the microspheres are heated, the shell softens and the internal air pressure increases dramatically, causing the microspheres to expand dramatically to 60 times their original volume, giving them the dual function of a lightweight filler and a blowing agent. As a lightweight filler, expandable microspheres can greatly reduce the weight of products with very low density, and their density measurement is very important.
Figure 1 Expandable microspheres
- Principle of EASY-G 1330 series true density tester
EASY-G 1330 series true density tester is based on Archimedes' principle, using small molecular diameter gas as the probe and the ideal gas equation of state PV=nRT to calculate the volume of gas discharged from the material under certain temperature and pressure conditions, so as to determine the true density of the material. The small molecular diameter gas can be used as nitrogen or helium, because helium has the smallest molecular diameter and is a stable inert gas, which is not easy to react with the sample by adsorption, so helium is generally recommended as the replacement gas.
- Advantages of EASY-G 1330 series true density tester
EASY-G 1330 series true density tester uses gas as the probe, which will not damage the test sample, and the sample can be recycled directly; and in the testing process, the gas will not react with the sample, and will not cause corrosion to the equipment, so the safety factor of the use process is high; furthermore, the gas has the characteristics of easy diffusion, good permeability and good stability, which can penetrate into the internal pores of the material more quickly and make the test results more accurate.
①Warm-up: Open the cylinder main valve and pressure-reducing table, turn on the power switch at least half an hour in advance, gas pressure-reducing table output pressure: 0.4 ± 0.02 MPa;
②Instrument Calibration: Before the experiment starts, calibrate the instrument with standard steel balls to ensure that the volume of steel balls tested in all pipelines of the equipment are within the standard value before starting the experiment;
③Sample Tube Volume Determination: Install the empty sample tube into the instrument cavity and tighten it, set up the software, determine the sample tube volume, and record the corresponding sample tube volume at the end of the experiment;
④Sample Weighing: In order to reduce the testing error, it is necessary to weigh as many samples as possible, each test shall weigh the sample to about 3/4 of the sample tube volume, weigh the empty tube mass M1, add the sample and weigh M2 to calculate the sample mass;
⑤Sample Processing: All samples were not pretreated in order to achieve consistency with the production quality control conditions;
⑥True Density Determination: Install the weighed sample tube into the instrument, set the true density determination parameters in the software, and view the true density results on the software after the experiment.
Experiment Results and Discussion
The replacement gas of EASY-G 1330 series true density tester can be chosen from nitrogen or helium, and the experiments were conducted with two replacement gases respectively. The results were stable and within the theoretical value. The details are as follows.
①Helium test results
The true density results of Expancel DE microspheres tested with helium as replacement gas are shown in Figure 2.
Sample name: 461DET40d25
Test mode: Non-vacuum pump mode for measurement
Displacement gas: Helium
Test method: Fixed pressure test
sample mass: sample volume of about 3/4 of the sample tube
Sample pretreatment: not treated
Figure 2 True density test report of helium as replacement gas
From the test results, it was found that the equilibrium pressure value increased with the increase of the experimental point and the single point true density value also increased, probably because the small molecules of helium destroyed the pores inside the sample, thus leading to an increase of the true density value, far beyond its theoretical value;
②Nitrogen test results
The same Expancel DE microsphere samples were tested for true density using nitrogen as a replacement gas, and the results are shown in Figure 3.
Sample Name: 461DET40d25
Test Mode: Non-vacuum pump mode for measurement
Displacement Gas: nitrogen
Test Method: fixed pressure test
Sample Quality: sample volume of about 3/4 of the sample tube
Sample Pretreatment: not treated
Figure 3 True density test report of Nitrogen as replacement gas
From the test results, it was found that the equilibrium pressure value was stable, and the single point true density value was stable and changed in the 4th decimal place, and the test results were consistent with the theoretical value of this sample. The test results are in accordance with the theoretical value of this sample. The reason for the large value of helium is to be further investigated.
Through the above experiments, it can be seen that the true density of expandable microspheres can be accurately measured by using nitrogen as replacement gas. The EASY-G 1330 series true density tester from CIQTEK can test the true density of three expandable microspheres in parallel or alternately, which greatly improves the testing efficiency of materials and can be widely used for rapid quality inspection of products in industrial production lines.