Views: 0 Author: Site Editor Publish Time: 2026-04-10 Origin: Site
EPDM (Ethylene Propylene Diene Monomer) rubber is a high-performance synthetic elastomer with excellent ozone resistance, weathering resistance, heat aging resistance, and chemical stability. EPDM granules, manufactured by mixing EPDM rubber with fillers, vulcanizing agents, plasticizers, pigments, and other additives, are extensively applied in plastic runways, playgrounds, athletic fields, roofing materials, and automotive components. The rubber content—defined as the mass percentage of pure EPDM polymer in the total granule mass—is the most critical parameter affecting product quality. High rubber content ensures superior elasticity, impact absorption, wear resistance, and service life; conversely, excessive fillers (such as calcium carbonate, talc) will severely degrade mechanical properties.
In the market, some manufacturers adulterate EPDM granules by adding large amounts of inorganic fillers to reduce costs, resulting in products failing to meet standard requirements. Therefore, accurate detection of rubber content is essential for quality control in production, procurement inspection, and market supervision. Currently, there are various detection methods ranging from rapid field tests to precise laboratory analyses. This paper compares and analyzes these methods to guide the selection of appropriate detection technologies for different scenarios.
Rubber content (also called rubber percentage) refers to the proportion of pure EPDM polymer in the total mass of granules, calculated as: Rubber Content (%) = (Mass of pure EPDM rubber / Total mass of sample) × 100%. This excludes fillers (calcium carbonate, carbon black, talc), plasticizers, vulcanizing agents, pigments, and other additives.
Major standards for EPDM granules and plastic runways stipulate clear rubber content requirements. China’s GB/T 14833-2020 specifies that qualified grade EPDM granules shall have a rubber content of no less than 20%, high-quality grade no less than 25%, and competition grade no less than 30%. The International Association of Athletics Federations (IAAF) requires a rubber content of no less than 30% for professional athletic surfaces. The American standard ASTM D297 provides standard test methods for rubber constituents in rubber products, while the international standard ISO 9924-3 specifies the determination of total hydrocarbon rubber, carbon black, and ash content in rubber products, which indirectly supports the calculation of rubber content.
The principle of the solvent extraction method is to use organic solvents (such as toluene, xylene, acetone) to selectively dissolve the EPDM rubber component, while fillers and insoluble additives remain undissolved. The rubber content is then calculated from the mass difference of the sample before and after extraction. The specific operational procedure includes four steps: first, weigh the sample (recorded as m₀) and dry it in an oven to a constant weight (recorded as m₁); second, place the dried sample in a Soxhlet apparatus and extract it with the selected solvent for 8 to 16 hours; third, remove the insoluble residue after extraction, dry it again to a constant weight (recorded as m₂); finally, calculate the rubber content using the formula: Rubber Content (%) = [(m₁ – m₂) / m₁] × 100%. This method has the advantage of high accuracy, with an error of less than 2%, and is recognized as the standard arbitration method for rubber content detection. However, it also has obvious disadvantages: it is time-consuming, usually taking 8 to 24 hours to complete, requires the use of toxic organic solvents, and involves complex operational steps. It is mainly applicable to quality arbitration, third-party certification, and accurate laboratory testing scenarios.
Thermogravimetric analysis (TGA) works by heating the sample in an inert atmosphere (usually nitrogen). EPDM rubber decomposes at a temperature range of 400–550°C, while inorganic fillers do not decompose at this temperature and remain as residue. The rubber content is derived from the mass loss curve recorded during the heating process. The operational procedure is relatively simple: first, place 5–10 mg of the sample in a TGA crucible; second, heat the crucible from room temperature to 800°C at a heating rate of 10–20°C per minute under a nitrogen atmosphere; third, record the relationship between mass loss and temperature; finally, calculate the rubber content based on the mass loss during the rubber decomposition stage. The advantages of TGA include fast detection speed, usually completing the test within 30 to 60 minutes, high precision with an error of less than 1%, automated operation, and the ability to distinguish between rubber, oil, and fillers. Its main disadvantage is the high cost of the equipment. It is suitable for laboratory research and development, production quality control, and rapid quantitative analysis.
Fourier transform infrared spectroscopy (FTIR) relies on the characteristic infrared absorption peaks of EPDM rubber. By comparing the infrared spectrum of the sample with standard spectra, the rubber content can be quantified through the intensity of the characteristic peaks. The operational steps are as follows: first, prepare the sample into powder or pellet form; second, collect the FTIR spectrum of the sample in the wave number range of 400–4000 cm⁻¹; third, analyze the characteristic absorption peaks of EPDM (for example, the peak in the range of 1650–1750 cm⁻¹ corresponds to the C=C bonds in EPDM); finally, establish a calibration curve using standard samples and quantify the rubber content of the tested sample. This method is non-destructive, fast, with the test time less than 10 minutes, and high sensitivity with an error of ±0.5%. However, it requires standard samples for calibration, which is a certain limitation. It is mainly used for qualitative identification and quantitative analysis of EPDM rubber content.
The elemental analysis method is based on the fact that EPDM rubber is rich in carbon and hydrogen elements. By measuring the total carbon content of the sample after combustion, the rubber content can be calculated using the ratio of carbon content in pure EPDM rubber. This method has the advantage of high accuracy and can perform simultaneous multi-element analysis, providing more comprehensive component information. However, it requires complex sample preparation steps and high equipment costs, making it suitable for industrial quality control and scientific research scenarios.
Rapid field testing methods are mainly used for preliminary screening of EPDM granules on site, without the need for complex equipment, and can quickly judge the approximate rubber content. Common methods include the density method, combustion method, and visual and hand feeling method.
The density method is based on the difference in density between pure EPDM rubber and inorganic fillers. The density of pure EPDM rubber is 1.15–1.25 g/cm³, while the density of common fillers such as calcium carbonate is about 2.7 g/cm³. The higher the filler content in EPDM granules, the higher the overall density of the sample. The specific method is to measure the density of the sample using the buoyancy method; if the density is greater than 1.35 g/cm³, it indicates that the sample contains a large amount of fillers and has a low rubber content.
The combustion method relies on the different combustion characteristics of rubber and fillers. EPDM rubber burns to produce elastic soot residue, while inorganic fillers leave hard ash after combustion. By observing the residue after combustion, the rubber content can be roughly judged: samples with high rubber content will leave soft, black, and elastic residue after burning, while samples with low rubber content will leave brittle, hard, gray or white residue.
The visual and hand feeling method is a more subjective semi-quantitative method. Samples with high rubber content usually have bright colors, smooth surfaces, good elasticity, and are not easily broken; on the contrary, samples with low rubber content have dull colors, rough surfaces, brittle texture, and are easily crushed.
These rapid field testing methods have the advantages of fast detection speed (less than 5 minutes), no need for professional equipment, and suitability for on-site use. However, their accuracy is low and the results are subjective, so they can only be used for preliminary screening and on-site acceptance, not for accurate quantitative detection.
Different detection methods have obvious differences in accuracy, detection time, cost, and applicable scenarios. The solvent extraction method has high accuracy (error ±1%) but is time-consuming (8–24 hours) and medium in cost, making it suitable for quality arbitration and third-party certification. Thermogravimetric analysis (TGA) also has high accuracy (error ±1%) but is faster (30–60 minutes) and higher in equipment cost, which is suitable for laboratory quality control and research and development. Fourier transform infrared spectroscopy (FTIR) has medium-high accuracy (error ±0.5%), fast detection speed (10 minutes), and high equipment cost, which is suitable for both qualitative identification and quantitative analysis. The rapid field methods such as density and combustion have low accuracy but are extremely fast (less than 5 minutes) and low in cost, which are suitable for on-site preliminary screening.
Based on the above characteristics, the following selection suggestions are put forward: for production quality control, TGA or FTIR is preferred due to their fast detection speed and high precision; for third-party testing and quality certification, the solvent extraction method should be adopted in accordance with relevant standards as the standard arbitration method; for on-site inspection and preliminary screening of samples, a combination of density method, combustion method, and visual and hand feeling method is recommended to quickly judge the rubber content level.
Rubber content is the core quality indicator of EPDM granules, which directly affects the performance and service life of EPDM products. This paper systematically reviews five main detection methods for rubber content in EPDM granules, including solvent extraction, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), elemental analysis, and rapid field testing methods. Among them, the solvent extraction method remains the standard arbitration method for rubber content detection due to its high accuracy; TGA and FTIR are more favored in modern laboratories because of their fast detection speed and high precision; rapid field methods are irreplaceable in on-site preliminary screening scenarios.
For comprehensive and efficient quality control of EPDM granules, it is recommended to combine laboratory precision detection methods with on-site rapid testing methods, which can not only ensure the accuracy of detection results but also improve the efficiency of quality inspection. With the continuous advancement of detection technology, intelligent, portable, and non-destructive detection technologies will become the future development trend, providing more efficient and convenient solutions for the quality management of EPDM granules.
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2. ASTM D297-2023, Standard Test Methods for Rubber Constituents [S]
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