How to Test Chemical Resistance of Plastics and

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The chemical resistance of plastics and rubbers is crucial for their long-term functionality in demanding conditions – whether it involves machine components, packaging for aggressive substances, or seals in the chemical industry. Incorrect material selection can lead to degradation, loss of mechanical properties, or even safety risks. This practical guide will take you through the testing process, from sample preparation to result evaluation, so you can reliably verify the suitability of a material for a specific application. We will focus on proven methods that comply with current standards and safety regulations.

1. Sample Preparation: The Key to Accurate Results

Proper sample preparation is the foundation of any testing of plastics and rubber resistance to chemicals. Start by selecting representative material samples that correspond to the final product – ideally in the form of flat sheets, rods, or tubes with a defined thickness. It is important to maintain uniform sample size, typically a minimum area of 50 × 50 mm is recommended for easy evaluation. Before testing, thoroughly clean the samples of dirt, grease, or residues of molding agents that could affect the results. Use a neutral cleaning agent and distilled water, then dry the samples at room temperature.

For accurate comparison of results, it is essential to condition the samples – this means leaving them for at least 24 hours in an environment with controlled temperature (usually 23 ± 2 °C) and relative humidity (50 ± 5 %). This step eliminates the influence of previous processing or storage on the mechanical and chemical properties of the material. For rubber samples, also pay attention to aging – some types of rubber may be sensitive to oxidation or UV radiation, so store them in the dark and in a cool place.

2. Selection of Test Chemicals and Exposure Conditions

The choice of chemicals for testing depends on the specific use of the material. Focus on substances that the plastic or rubber will come into contact with in real-world operation – for example, acids, alkalis, organic solvents, oils, or fuels. For general resistance assessment, standard reference chemicals such as sulfuric acid, sodium hydroxide, acetone, or toluene are often used. It is also important to consider the concentration and temperature at which exposure will take place, as these factors significantly influence the degree of degradation.

Sample exposure can be carried out in several ways: immersion in liquid, exposure to vapors, or application of the chemical to the surface. The most common method is full immersion, where you place the samples in a sealed container with the chemical and maintain a constant temperature (e.g., 23 °C, 50 °C, or 70 °C according to requirements). Exposure time ranges from several hours to weeks—short-term tests (24–48 hours) reveal acute reactions, while long-term tests (1,000+ hours) simulate real operating conditions. For precise monitoring of changes, measure the mass, dimensions, and mechanical properties of the samples before and after exposure.

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3. Evaluation Methods: How to Measure Property Changes

After exposure to chemicals, it is necessary to comprehensively evaluate changes in the physical and mechanical properties of the samples. The basic step is a visual inspection – look for changes in color, surface cracks, swelling, or dissolution of the material. Subsequently, measure weight and volume changes: an increase in weight usually indicates absorption of the chemical, while a decrease may signify leaching of additives or polymer degradation. For precise measurement, use analytical balances and calipers with an accuracy of 0.01 mm.

Test mechanical properties using standard testing methods, such as tensile testing (to determine strength and elongation), hardness testing (e.g., Shore A for rubbers), or impact resistance. Comparing results before and after exposure will reveal whether the chemical caused embrittlement, softening, or other structural changes. For rubber materials, also pay attention to elastic recovery – loss of elasticity can be critical for sealing applications. For detailed analysis, also use spectroscopic methods (e.g., FTIR) to identify chemical changes in the polymer.

4. Interpretation of Results and Practical Recommendations for Production

Test results for chemical resistance must be interpreted in the context of the specific application. For example, a 5% increase in weight after oil exposure may be acceptable for some industrial components, whereas it would be unacceptable for medical devices. Establish acceptability criteria based on requirements for product lifespan, safety, and functionality. It is also important to consider synergistic effects – the combination of multiple chemicals or mechanical stress can lead to faster degradation than indicated by individual tests.

Based on the results, optimize the selection of material or its processing. If tests reveal insufficient resistance, consider using additives (e.g., stabilizers, fillers) or changing the processing technology (e.g., a higher degree of crosslinking for rubber). For critical applications, we recommend validation under real conditions—while laboratory tests provide valuable information, they cannot fully replace operational environment testing. Document all steps and results for future reference and certification purposes, especially if the material is subject to REACH or CLP regulations.

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Choosing the right type of exposure: Immersion, spraying, or vapor contact?

The choice of exposure method significantly affects the relevance of the results. The most common is full immersion of the sample in the test liquid, which simulates long-term contact with the chemical, such as in tanks or pipelines. For applications where surface exposure occurs (e.g., cleaning agents on automotive parts), the spraying or droplet application method is more suitable. The samples are placed at an angle, and the chemical is allowed to run down the surface, mimicking real-world use.

For materials exposed to aggressive vapors (e.g., in chemical processing plants), exposure in a closed chamber with controlled vapor concentration is used. Temperature and humidity are maintained at a constant level to ensure reproducibility. For all methods, it is crucial to adhere to standardized conditions—typically, testing is conducted at temperatures of 23 °C, 50 °C, or 70 °C based on the expected operating environment. Exposure duration ranges from several hours to thousands of hours, with shorter tests revealing acute reactions, while long-term tests uncover gradual degradation.

Critical Parameters for Evaluation: What to Measure and Why

After exposure, it is necessary to evaluate changes in mechanical, physical, and chemical properties. The fundamental parameter is weight change, which indicates absorption or leaching of substances. An increase in weight of more than 5% usually signals excessive absorption, while a decrease may indicate polymer degradation. Additionally, dimensional changes—swelling or shrinkage—are measured, as these can lead to functional failures in components.

Mechanical properties such as tensile strength, modulus of elasticity, or hardness are tested using standard test methods. A reduction in strength of more than 20% after exposure often indicates that the material is unsuitable for the given application. For rubbers, changes in elastic properties, such as permanent deformation after compression, are also critical. Visual inspection reveals surface changes like cracks, discoloration, or tackiness, which may be the first sign of degradation.

How to Translate Laboratory Results into Real-World Production: Practical Tips

Laboratory tests provide valuable data, but their interpretation requires consideration of real-world operating conditions. For example, a short-term test at elevated temperature can simulate long-term exposure at a lower temperature—so-called Arrhenius equation helps estimate the acceleration of degradation. However, it is important to verify the results in real time, especially for critical applications.

When selecting a material for a specific application, it is necessary to consider not only chemical resistance but also mechanical stress, temperature fluctuations, or UV radiation. For instance, polypropylene may be resistant to acids but brittle at low temperatures. It is also recommended to consult with the raw material supplier, who can provide data from long-term tests or recommend additives to improve resistance. It is always advisable to conduct verification tests on the final product under real-world conditions before starting mass production.

Need to choose the right raw material?

Every material requires an individual approach – GCG Group provides detailed technical data sheets and safety data sheets (SDS) for supplied raw materials, including recommendations for testing chemical resistance. Contact us for a consultation on the specific requirements of your production. Get in touch – or browse our catalogue of over 1,300 products.