As a supplier of POM plastic parts, I understand the critical importance of ensuring the chemical resistance of these components. Polyoxymethylene (POM), also known as acetal, is a high - performance engineering thermoplastic widely used in various industries due to its excellent mechanical properties, low friction coefficient, and good dimensional stability. However, its performance can be significantly affected when exposed to certain chemicals. In this blog, I will share some practical methods to test the chemical resistance of POM plastic parts.
Understanding the Chemical Environment
Before conducting any tests, it is essential to have a clear understanding of the chemical environment in which the POM plastic parts will be used. Different industries have different chemical exposure scenarios. For example, in the automotive industry, POM parts may be exposed to fuels, lubricants, and cleaning agents. In the food and beverage industry, they may come into contact with acids, alkalis, and various food additives.
By identifying the specific chemicals and their concentrations, temperatures, and exposure times, we can simulate the real - world conditions as accurately as possible during the testing process. This step is crucial because the chemical resistance of POM can vary depending on the type of chemical and the environmental conditions.
Visual Inspection Method
One of the simplest and most straightforward ways to test the chemical resistance of POM plastic parts is through visual inspection. This method involves immersing the POM samples in the target chemicals for a certain period and then observing any visible changes on the surface of the samples.
- Sample Preparation
- Cut the POM plastic parts into small, uniform samples. The size and shape of the samples should be consistent to ensure the accuracy of the test results. Usually, rectangular or square samples with a size of about 50mm x 50mm x 3mm are suitable.
- Clean the samples thoroughly with a mild detergent and distilled water to remove any contaminants on the surface. Then dry the samples in a clean environment.
- Immersion Test
- Place the prepared samples into separate containers filled with the target chemicals. Make sure the samples are completely submerged in the chemicals.
- Seal the containers to prevent the evaporation of the chemicals and keep them at a constant temperature according to the actual usage conditions. For example, if the POM parts are used at room temperature, the test can be carried out at around 23°C.
- Observe the samples at regular intervals, such as every 24 hours or 48 hours, depending on the expected exposure time in the real - world application. Look for any signs of discoloration, swelling, cracking, or blistering on the surface of the samples.
- Evaluation
- Based on the visual observations, we can evaluate the chemical resistance of the POM plastic parts. If there are no visible changes on the surface of the samples after a certain period of immersion, it indicates that the POM has good chemical resistance to the tested chemicals. However, if significant changes such as severe discoloration or cracking are observed, it means that the POM may not be suitable for use in the chemical environment.
Mass Change Measurement Method
In addition to visual inspection, measuring the mass change of the POM plastic parts before and after chemical exposure is another effective way to assess their chemical resistance. This method can provide more quantitative data about the interaction between the POM and the chemicals.
- Initial Mass Measurement
- Use a high - precision balance to measure the mass of the prepared POM samples before immersion in the chemicals. Record the mass values accurately.
- Immersion and Mass Measurement after Exposure
- Immerse the samples in the target chemicals for a specified period. After the exposure, take out the samples and gently wipe off the excess chemicals on the surface with a clean cloth.
- Allow the samples to dry in a desiccator for a certain time to remove any remaining moisture. Then measure the mass of the samples again using the same balance.
- Calculation and Evaluation
- Calculate the mass change of the samples using the following formula:
[ \text{Mass change}(%)=\frac{m_2 - m_1}{m_1}\times100% ]
where (m_1) is the initial mass of the sample and (m_2) is the mass of the sample after chemical exposure. - A small mass change indicates that the POM has good chemical resistance. Generally, if the mass change is within ± 1%, it can be considered that the POM has excellent chemical resistance to the tested chemicals. However, a large mass change may suggest that the POM is being attacked by the chemicals, resulting in swelling, dissolution, or other forms of degradation.
- Calculate the mass change of the samples using the following formula:
Mechanical Property Testing
The chemical exposure of POM plastic parts can also affect their mechanical properties, such as tensile strength, hardness, and impact resistance. Therefore, testing the mechanical properties of the POM samples before and after chemical exposure is an important part of evaluating their chemical resistance.
- Tensile Testing
- Prepare standard tensile test specimens according to relevant standards, such as ASTM D638 or ISO 527.
- Use a universal testing machine to measure the tensile strength and elongation at break of the specimens before chemical exposure.
- Immerse the specimens in the target chemicals for a certain period. After exposure, dry the specimens and repeat the tensile test.
- Compare the tensile strength and elongation at break values before and after chemical exposure. A significant decrease in these values indicates that the chemical exposure has degraded the mechanical properties of the POM.
- Hardness Testing
- Use a hardness tester, such as a Shore D hardness tester, to measure the hardness of the POM samples before and after chemical exposure.
- Press the indenter of the hardness tester onto the surface of the sample with a certain force and record the hardness value.
- A change in hardness can indicate the degree of chemical attack on the POM. For example, if the hardness decreases significantly after chemical exposure, it may suggest that the chemical has softened the POM.
Analytical Techniques
In some cases, more advanced analytical techniques may be required to fully understand the chemical resistance of POM plastic parts. These techniques can provide detailed information about the chemical structure and composition changes of the POM after chemical exposure.
- Fourier - Transform Infrared Spectroscopy (FTIR)
- FTIR can be used to identify the functional groups in the POM and detect any chemical changes caused by the exposure to chemicals.
- By comparing the FTIR spectra of the POM samples before and after chemical exposure, we can determine if there are any new chemical bonds formed or existing bonds broken, which can help us understand the mechanism of chemical attack.
- Scanning Electron Microscopy (SEM)
- SEM can provide high - resolution images of the surface morphology of the POM samples.
- After chemical exposure, SEM can be used to observe any surface damage, such as cracks, pits, or changes in the surface texture. This can help us understand the physical changes of the POM caused by the chemicals.
Conclusion
Testing the chemical resistance of POM plastic parts is a comprehensive process that requires a combination of different methods. By using visual inspection, mass change measurement, mechanical property testing, and analytical techniques, we can accurately evaluate the chemical resistance of POM and ensure that the parts meet the requirements of different applications.
As a POM plastic part supplier, we are committed to providing high - quality products with excellent chemical resistance. Our OEM Molded Injection Polyurethane Washer And Gasket and Injection Plastic Moulded Parts ABS/POM/PA66/PP/PC/PA are carefully tested to ensure their performance in various chemical environments. We also offer Small batch injection molding services to meet the different needs of our customers.
If you are interested in our POM plastic parts or have any questions about chemical resistance testing, please feel free to contact us for procurement negotiation. We look forward to working with you to provide the best solutions for your projects.
References
- ASTM D638 - Standard Test Method for Tensile Properties of Plastics.
- ISO 527 - Plastics - Determination of tensile properties.
- Various research papers on the chemical resistance of POM plastics in scientific journals.