Rubber mass change testing quantifies the percentage change in the mass of vulcanized or thermoplastic rubber after exposure to liquids, heat, or other service environments, providing a direct measure of swelling, extraction, and chemical compatibility. Performed in accordance with recognized standards such as ISO 1817, ASTM D471, GB/T 1690, and ISO 188, this test is essential for qualifying sealing materials in automotive, aerospace, industrial, and chemical processing applications. Reliable mass change data enables engineers to select the right elastomer compound, validate formulations, and predict long-term durability under real-world exposure conditions.
Technical Overview
Rubber mass change testing, also referred to as mass variation or mass loss testing, measures how much weight a rubber specimen gains or loses after exposure to a defined environment. The most common exposure is immersion in a test liquid such as fuel, lubricating oil, hydraulic fluid, water, brake fluid, acid, or alkali solution, but mass change is also evaluated after hot air aging, ozone exposure, and other accelerated aging treatments.
The basic principle is straightforward. A conditioned specimen is weighed to determine its initial mass (m1) using an analytical balance, typically accurate to 1 mg. The specimen is then exposed under controlled temperature and time conditions, removed, surface liquid is blotted off, and the specimen is immediately reweighed to obtain the final mass (m2). The mass change percentage is calculated as: Δm = (m2 − m1) / m1 × 100.
A positive mass change indicates absorption of the test medium and swelling of the elastomer network, which can reduce sealing force and dimensional stability. A negative mass change indicates extraction of plasticizers, antidegradants, or other soluble formulation components, which can embrittle the rubber and shorten service life. Both directions of change are valuable indicators of fluid compatibility and compound quality.
- ISO 1817 — Rubber, vulcanized or thermoplastic — Determination of the effect of liquids
- ASTM D471 — Standard Test Method for Rubber Property — Effect of Liquids
- GB/T 1690 — Chinese national standard for the effect of liquids on vulcanized or thermoplastic rubber
- ISO 188 and ASTM D573 — Accelerated aging and heat resistance tests, including mass loss after hot air aging
- ISO 23529 — General procedures for preparing and conditioning test pieces for physical test methods
Testing Samples
Standard Laboratory Coupons
The preferred test piece per ISO 1817 and ASTM D471 is a rectangular strip of approximately 25 mm × 50 mm cut from a cured sheet with a thickness of 2 mm ± 0.2 mm. Where geometric constraints exist, smaller pieces may be used, but the total specimen mass should be at least 1 g whenever practical to minimize weighing error. Specimens should be free of surface defects, mold release residues, and fabric reinforcement.
Finished Components and Products
Mass change can also be determined directly on finished articles such as O-rings, gaskets, diaphragms, hose linings, and molded seals. Testing actual products reflects the real surface-to-volume ratio and cure state of the part, which often differs from laboratory sheets. Comparative testing should always use specimens of identical geometry, since absorption behavior scales with surface area exposed to the liquid.
Sample Preparation and Conditioning
Rubber should be fully cured and, where possible, aged at least 24 hours after vulcanization before specimens are cut. Unless otherwise specified, specimens are conditioned at 23 °C ± 2 °C and 50% ± 5% relative humidity for a minimum of 16 hours prior to initial weighing, in accordance with ISO 23529. Surface contamination is removed with a dry lint-free cloth; solvent cleaning is avoided unless explicitly required by the product specification.
Testing Items
A typical rubber mass change evaluation program may include the following measurements, depending on the specification and end-use requirements:
- Mass change after immersion in standard reference liquids or service fluids
- Volume change after immersion, often reported alongside mass change
- Dimensional change (length, width, thickness) after exposure
- Hardness change (Shore A or IRHD) before and after immersion
- Tensile strength and elongation at break retention after fluid exposure
- Mass loss after hot air oven aging at elevated temperature
- Dry mass change after post-immersion evaporation, to separate absorbed volatile matter from extracted solids
- Effect of immersion on compression set and sealing performance, where required
Testing Methods
Liquid Immersion Testing (ISO 1817 / ASTM D471)
Specimens are fully immersed in the test liquid, kept at least 15 mm below the liquid surface, with a liquid volume of no less than 15 mL per gram of rubber and typically refreshed for long-duration tests. Common test temperatures include 23 °C, 40 °C, 70 °C, 100 °C, 125 °C, and 150 °C, and standard durations include 22 h, 70 h, 168 h, and extended multi-week exposures. After removal, specimens are quickly blotted with filter paper to remove surface liquid and weighed within 30 seconds to prevent loss of volatile absorbed components. For extended testing, specimens are re-immersed between measurements.
Standard Reference Liquids
To ensure reproducibility between laboratories, testing is frequently performed using well-defined reference media rather than variable commercial fluids:
- ASTM reference fuels A, B, and C — defined mixtures of isooctane and toluene simulating low, medium, and high aromatic content fuels
- IRM 901, IRM 902, and IRM 903 reference oils — standard ASTM test oils of increasing aniline point, used to evaluate oil resistance across elastomer classes
- Service fluids — commercial gasoline, diesel, engine oil, hydraulic fluid, transmission fluid, and brake fluid for application-specific qualification
- Aqueous media — distilled water, standard acid and alkali solutions, and salt solutions for chemical resistance evaluation
Hot Air Aging Mass Loss (ISO 188 / ASTM D573)
Specimens are exposed in a forced-air aging oven at a specified elevated temperature, commonly 70 °C to 300 °C depending on the polymer, for periods ranging from 24 h to 1000 h or longer. The resulting mass loss reflects volatilization of plasticizers and processing additives and provides insight into thermal stability and long-term aging behavior.
Calculation and Reporting of Results
The mass change is calculated for each specimen and reported as the median of at least three specimens. A complete test report identifies the material and compound, specimen type and dimensions, test liquid, exposure temperature and duration, individual and median mass change values, and any observed surface conditions such as cracking, tackiness, or discoloration. Interpretation is made against the acceptance limits defined in the product or material specification.
Applications
Rubber mass change testing is a cornerstone of material qualification and quality control across every major elastomer application sector:
- Automotive fuel and emission systems — fuel hoses, filler necks, injector seals, tank seals, and canister components validated against reference fuels and oxygenated fuel blends
- Hydraulic and pneumatic sealing — O-rings, rod and piston seals, and gaskets qualified for compatibility with hydraulic oils, fire-resistant fluids, and brake fluids
- Oil, gas, and chemical processing — hose linings, expansion joints, tank linings, and diaphragms exposed to crude oil derivatives, solvents, acids, and alkalis
- Aerospace and military hardware — seals and gaskets qualified against stringent fluid resistance and aging specifications
- Medical, pharmaceutical, and food-contact products — elastomeric closures, tubing, and seals evaluated for extractables and water exposure
- Research and development — formulation screening, polymer selection, curative and plasticizer optimization, and batch-to-batch quality release testing
FAQ
What does a positive mass change result indicate?
A positive result means the rubber has absorbed the test medium and swelled. Moderate swelling may be acceptable for some applications, but excessive swelling reduces sealing force, increases friction, and signals poor fluid compatibility for that polymer class.
What does a negative mass change result indicate?
A negative result means the rubber has lost mass, typically through extraction of plasticizers, antidegradants, or other soluble ingredients. Mass loss often leads to hardening, shrinkage, and cracking, and is a key quality concern for heat-aged or oil-exposed components.
Which standards govern rubber mass change testing?
The primary standards are ISO 1817 and ASTM D471 for liquid immersion, GB/T 1690 as the corresponding Chinese national method, and ISO 188 together with ASTM D573 for mass change after hot air aging. Accredited third-party laboratories routinely conduct testing to all of these standards.
What sample size and quantity are required?
The preferred specimen is a 25 mm × 50 mm × 2 mm strip, with a minimum of three specimens per condition for statistically meaningful results. Finished parts such as O-rings can usually be tested whole; laboratories typically recommend submitting a few spare parts to cover repeat measurements.
How long does a mass change test take?
Standard immersion points of 22 h, 70 h, or 168 h can be completed within one to two weeks including conditioning and reporting. Extended aging or immersion programs of 1000 h or more may require several weeks to several months.
What mass change level is considered acceptable?
Acceptance limits depend entirely on the application specification. As a general industry practice, high-performance fuel-resistant compounds such as fluorocarbon elastomers are often qualified with mass change limits in the low single-digit to low double-digit percentage range in reference fuels, while general-purpose compounds may have wider limits. The governing product standard or customer specification always defines the pass/fail criteria.