How to Properly Test the Chemical Resistance of Plastics and Rubber: A Step-by-Step Practical Guide

Photo: Hans Reniers / Unsplash

The chemical resistance of plastics and rubber is crucial for the reliability of components in the automotive, engineering, or chemical industries. Incorrectly selected materials can lead to degradation, cracking, or loss of mechanical properties, resulting in high costs for complaints and repairs. This practical guide will show you how to test material resistance to aggressive substances such as oils, solvents, acids, or alkalis using standard methods, helping you prevent issues in real-world operation.

1. Sample Preparation: The Key to Accurate Results

Proper testing of plastics and rubber resistance to chemicals begins with careful sample preparation. Samples should be representative of the final product—ideally in shape and thickness corresponding to real-world use. For standard tests, flat samples measuring 50 × 50 mm or rod-shaped samples with a defined cross-section are often used. The surface must be smooth, without visible defects such as cracks, bubbles, or impurities that could distort the results.

Before testing, samples must be conditioned according to applicable standards, typically at a temperature of 23 ± 2 °C and relative humidity of 50 ± 5 % for at least 24 hours. This step ensures that the material reaches an equilibrium state, and the results are not influenced by previous storage conditions. For more accurate evaluation, it is recommended to prepare at least three to five samples for each combination of material and chemical to statistically assess deviations.

2. Selection of Testing Chemicals and Conditions

The choice of chemicals for testing depends on the intended use of the material. For industrial applications, aggressive substances such as acids (e.g., sulfuric acid, hydrochloric acid), alkalis (sodium hydroxide), organic solvents (acetone, toluene), or oils and fuels are often tested. It is important to consider the concentration, temperature, and exposure time that correspond to real operating conditions. For example, automotive components are tested for resistance to fuels at temperatures up to 80 °C for several weeks.

Test conditions should simulate the worst-case scenario to which the material will be exposed. This includes not only temperature and exposure time but also mechanical stress, such as a combination of chemical exposure with tension or pressure. For long-term tests, accelerated methods are used, where elevated temperature or chemical concentration speeds up degradation processes. However, it is always necessary to verify whether accelerated tests correlate with the real-world behavior of the material in operation.

Photo: Trnava University / Unsplash

3. Test Execution: Methods and Procedures

The most common method for testing chemical resistance is immersing samples in the test liquid for a specified period. The samples are placed in sealed containers to minimize evaporation of the chemical and maintained at a constant temperature, for example in a water bath or thermostat. After the exposure period, the samples are removed, rinsed with distilled water or a suitable solvent, and allowed to dry at room temperature.

After exposure, changes in mechanical properties (strength, elongation), weight, dimensions, and appearance are evaluated. Mechanical properties are tested using standard test methods, such as a tensile test, where tensile strength before and after exposure is compared. Changes in weight and dimensions are measured with an accuracy of 0.1% and documented for each sample. Visual inspection includes assessing changes in color, gloss, the occurrence of cracks, or swelling, which may indicate chemical degradation.

4. Evaluation of Results and Data Interpretation

Evaluating the results of chemical resistance tests requires a systematic approach. First, the measured values are compared with the initial properties of the material, and percentage changes are determined. For example, a decrease in tensile strength of more than 20% or an increase in weight of more than 5% may signal significant degradation. It is also important to assess whether the changes are uniform or whether local defects appear, which could lead to material failure in operation.

The results are documented in a report that includes a description of the tested materials, chemicals used, test conditions, and measured data. For industrial applications, it is often necessary to compare the results with the requirements of standards or customer specifications. If the material does not meet the required parameters, it may be advisable to adjust the formulation, for example by adding stabilizers or selecting a more resistant polymer. However, repeated tests must always be performed to confirm the effectiveness of the changes made.

Photo: RephiLe water / Unsplash

Documentation and Reporting: How to Ensure Repeatability and Reliability of Results

Proper testing of the chemical resistance of plastics and rubber requires not only careful execution but also thorough documentation. Every step of the process should be recorded in a test protocol, which includes the identification of samples (material, production batch, dimensions), test conditions (temperature, exposure time, chemical concentration), and the methods used. The protocol should also contain information about any deviations from the standard procedure, such as temperature fluctuations or unexpected material reactions. This data is crucial for test repeatability and enables comparison of results between different batches or suppliers.

An important part of the documentation is also the visual record of the samples' condition before, during, and after the test. Photo documentation helps detect changes that might escape mere description, such as microcracks, color changes, or deformations. The protocol should be supplemented with the signatures of responsible persons and the date of the test. In the event of complaints or the need for third-party verification of results, such documentation is essential to demonstrate transparency and professionalism.

Safety measures during testing: How to minimize risks for workers and the environment

Testing the chemical resistance of plastics and rubber often involves working with aggressive or toxic substances, so safety is a top priority. Before starting the tests, a risk assessment must be carried out in accordance with the REACH and CLP regulations, which set out obligations for handling chemical substances. Workers must be equipped with appropriate personal protective equipment (PPE), such as safety goggles, chemical-resistant gloves, a laboratory coat, and, if necessary, a respirator. All tests should be conducted in a well-ventilated area or under a fume hood to minimize inhalation of vapors.

Another key aspect is the proper disposal of used chemicals and contaminated samples. Chemical residues must not be poured into drains or regular waste but must be collected in labeled containers and handed over for professional disposal. In the event of a chemical spill, an emergency plan must be in place, including neutralizing agents and decontamination procedures. Compliance with these measures protects not only the health of employees but also the environment and ensures alignment with legislative requirements.

Practical Tips for Optimizing Testing: How to Save Time and Costs Without Compromising Quality

Testing material resistance can be time-consuming and costly, but there are ways to optimize the process. One effective approach is combining accelerated tests with long-term exposures. Accelerated tests, such as those conducted at elevated temperatures, can provide a quick indication of material resistance, while long-term tests confirm results under real-world conditions. This method reduces the number of necessary repetitions and speeds up the development of new materials.

Further savings can be achieved by using standardized chemical testing kits that cover the most common applications for a given material. Instead of testing against dozens of different substances, a representative sample of the most relevant chemicals for the material can be selected. Regular calibration of measuring instruments and staff training are also important to minimize errors and unnecessary test repetitions. Investing in high-quality equipment and training thus quickly pays off in the form of more reliable results and lower costs.

Need help selecting raw materials?

Every chemical raw material supplied by GCG Group is accompanied by detailed technical and safety data sheets. Our experts will be happy to advise you on material selection and testing their resistance for your specific applications. Contact us – or browse our catalogue of over 1,300 products right away.