The boiling water hydrolysis test is an accelerated aging method used to evaluate the resistance of polymers, adhesives, coatings, films, and composites to water-induced chemical degradation at 100°C. This article provides a comprehensive technical overview of the test principle, applicable sample types, evaluation items, test procedures, relevant standards, and typical industrial applications of boiling water immersion testing.
Technical Overview
Hydrolysis is a chemical degradation mechanism in which water molecules cleave hydrolyzable bonds along polymer chains, such as ester, urethane, carbonate, and amide linkages. The boiling water hydrolysis test accelerates this process by immersing material specimens in deionized water maintained at 100°C, subjecting them simultaneously to saturated moisture contact and elevated thermal energy. Under these conditions, chain scission proceeds rapidly, causing reductions in molecular weight, tensile strength, elongation at break, and other mechanical and physical properties.
Because the test applies a severe combination of heat and liquid water, it serves as a highly accelerated screening tool for estimating long-term hydrolytic durability in a relatively short time frame. Materials such as polyesters (PET, PBT), polyamides, polycarbonate, polyoxymethylene, thermoplastic polyurethanes (TPU), polyester-based adhesives, and protective coatings are commonly evaluated using this method. Test procedures are typically conducted in accordance with recognized frameworks such as ISO 175, ISO 62, ASTM D570, ASTM D543, ASTM D471, ASTM D870, UL 746A, JIS K 7114, and the corresponding GB standards, and are frequently performed by accredited third-party laboratories as part of material qualification programs.
- Purpose: to assess hydrolysis resistance and quantify property degradation after boiling water exposure
- Medium: deionized water at 100°C, maintained under reflux or controlled heating
- Typical duration: 24, 48, 72, 168 hours or longer, depending on material and specification
- Primary outputs: property retention rates, mass change, dimensional change, and visual defect assessment
Testing Samples
A wide range of material forms can be evaluated in a boiling water hydrolysis test. Specimens are usually prepared as standardized test pieces, for example tensile bars machined or molded to ISO 527-2 or ASTM D638 dimensions, so that mechanical properties can be measured before and after exposure.
Engineering Thermoplastics
Molded or extruded specimens of PET, PBT, PA6, PA66, PC, POM, and modified blends are tested to verify hydrolytic stability in hot and humid service environments. These materials contain ester or acetal linkages that are inherently vulnerable to chain scission in boiling water, making them prime candidates for this evaluation.
Polyurethane Materials
TPU films, elastomers, foams, and polyurethane adhesives are frequently tested because polyester-based polyurethanes degrade rapidly in hot water. Specimens may be supplied as plaques, films, or die-cut dumbbells, and the test is often used to compare polyester-type versus polyether-type formulations.
Adhesives, Sealants, and Coatings
Bonded lap-shear specimens, peel coupons, and coated metal or plastic panels are immersed to evaluate retention of bond strength and coating integrity. Reference practices include ASTM D896 for adhesive chemical resistance, ASTM D471 for rubber-like materials in liquids, and ASTM D870 for water immersion resistance of coatings.
Films and Optical Materials
Polyester films, polarizer films, protective films, and backsheet materials used in displays and photovoltaic modules are tested to assess whitening, haze development, shrinkage, and loss of mechanical toughness after prolonged boiling exposure.
Composites and Laminates
Glass-fiber or carbon-fiber reinforced laminates and multilayer structures are evaluated for interlaminar strength retention, edge delamination, and blistering, since water ingress along fiber-matrix interfaces can dramatically reduce performance.
Rubber and Elastomer Compounds
Vulcanized rubber specimens are boiled to measure changes in hardness, tensile properties, volume swell, and surface condition, following the immersion principles of ASTM D471 and ISO 1817.
Testing Items
The test program typically includes a set of measurements performed on specimens in the dry, unexposed state and repeated after defined boiling intervals, allowing degradation to be expressed as a percentage retention of each property.
- Mass change and water absorption rate, determined gravimetrically per ISO 62, ASTM D570, or GB/T 1034
- Tensile strength and elongation at break retention, per ISO 527 or ASTM D638
- Flexural strength and modulus retention, per ISO 178 or ASTM D790
- Impact strength retention, per ISO 179, ISO 180, or ASTM D256
- Hardness change, measured with Shore A or Shore D durometers per ISO 868 or ASTM D2240
- Dimensional and geometric stability, including linear swelling and warpage
- Visual appearance evaluation, covering whitening, blistering, cracking, chalking, delamination, and gloss loss
- Adhesion performance, including lap-shear strength and peel strength retention for bonded assemblies
- Molecular weight distribution analysis by gel permeation chromatography (GPC) to quantify chain scission
- Thermal property changes, such as glass transition temperature shift measured by DSC or DMA
- Electrical property retention, such as dielectric strength and insulation resistance, relevant to UL 746A and IEC-based assessments
Testing Methods
Specimen Preparation and Conditioning
Specimens are cleaned, dried to constant mass where required, and conditioned in a standard atmosphere of 23°C and 50% relative humidity in accordance with ISO 291 or ASTM D618. Baseline measurements of mass, dimensions, mechanical properties, and appearance are recorded before exposure. A sufficient number of replicate specimens, commonly at least five per time point, is prepared to support statistical evaluation.
Boiling Immersion Procedure
Specimens are fully immersed in a bath of deionized water held at a sustained boil of approximately 100°C. A reflux condenser or sealed boiling apparatus is recommended to prevent water loss and maintain a constant liquid volume and concentration throughout the test. Exposure periods are selected according to the material specification, with common checkpoints at 24, 48, 72, and 168 hours; longer durations or cyclic boiling-and-drying schedules may be applied for more severe qualification requirements. Consistent with the immersion frameworks of ISO 175, ASTM D543, JIS K 7114, and GB/T 11547, the water should be refreshed or verified periodically to avoid contamination by extracted substances.
- Water quality: deionized or distilled water to exclude ionic corrosion effects
- Temperature: 100°C at atmospheric pressure; pressurized vessels may be used to extend exposure above 100°C
- Positioning: specimens kept separated and fully submerged without contact with the vessel walls
- Documentation: bath temperature, water replacement schedule, and exposure duration recorded for traceability
Post-Exposure Evaluation and Data Reduction
After each exposure interval, specimens are removed, quickly surface-dried with lint-free cloth, and reweighed immediately to capture absorbed water content. Mechanical tests are performed either in the wet-as-received state or after a defined reconditioning period, depending on the specification. Property retention is calculated as the measured value after exposure divided by the original value, multiplied by 100, and results are reported together with visual observations and any anomalies such as cracking or delamination. For comparison purposes, boiling water immersion data are often plotted alongside damp-heat results from IEC 60068-2-78 or IEC 60068-2-30 conditioning to characterize the temperature dependence of hydrolytic degradation.
Related Reference Standards
- ISO 62 and GB/T 1034: determination of water absorption of plastics
- ISO 175, GB/T 11547, ASTM D543, and JIS K 7114: determination of the effects of immersion in liquid chemicals
- ASTM D570: water absorption of plastics
- ASTM D471 and ISO 1817: effect of aqueous liquids on rubber and elastomeric materials
- ASTM D870: water resistance of coatings by water immersion
- UL 746A: polymeric materials, short-term evaluations including water exposure
- IEC 60068-2-30 and IEC 60068-2-78: environmental testing, damp heat methods used for complementary evaluation
Applications
Boiling water hydrolysis testing supports material selection, formulation development, incoming quality control, and durability qualification across many industries. Its accelerated nature allows suppliers and buyers to compare candidate materials and validate long-term performance claims within practical project timelines.
- Automotive: validation of connectors, sensors, under-hood plastic components, coolant-contact parts, and TPU cable jackets exposed to hot water and humid conditions
- Electronics and electrical: evaluation of PCB laminates, potting compounds, capacitor materials, connector housings, and insulation systems requiring humidity endurance
- New energy: qualification of PET-based photovoltaic backsheets, EV battery module materials, fuel cell components, and cable accessories
- Consumer goods: durability confirmation for waterproof breathable membranes, laminated footwear components, outdoor gear films, and appliance parts
- Medical and food contact: assessment of materials subjected to repeated steam or hot water cleaning, sterilization-compatible polymers, and reusable device housings
- Textiles and films: hydrolysis resistance of TPU films, laminated fabrics, and functional coatings used in demanding wet environments
- Research and development: accelerated aging studies that support service-life modeling, formulation comparison, and stabilization additive screening
FAQ
What is the purpose of the boiling water hydrolysis test?
The test accelerates the natural hydrolytic degradation of polymers by exposing specimens to liquid water at 100°C, allowing engineers to quantify how quickly mechanical properties, mass, dimensions, and appearance deteriorate. It is used to screen materials, compare formulations, and demonstrate compliance with customer or industry specifications for humid, hot service environments.
How long should specimens be boiled?
Exposure duration depends on the material and acceptance criteria. Common checkpoints are 24, 48, 72, and 168 hours, while some qualification programs extend to 240 hours or more. A time-series approach, in which multiple specimens are withdrawn at successive intervals, provides a degradation curve that is far more informative than a single-point result.
How does boiling water immersion differ from damp heat testing?
Damp heat tests, such as those in the IEC 60068-2 series, expose specimens to hot humid air, for example 85°C and 85% relative humidity, and primarily drive moisture diffusion. Boiling water immersion places the material in direct contact with liquid water at 100°C, which is substantially more aggressive and drives both water uptake and hydrolytic chain scission at a much faster rate. The two methods are complementary, with boiling immersion often used as a worst-case screening condition.
Which materials are most susceptible to hydrolysis?
Materials containing ester, urethane, carbonate, acetal, or amide linkages are most vulnerable, including PET, PBT, PLA, polyester-based polyurethanes, polycarbonate, polyamides, and POM. Polyether-based polyurethanes, polyolefins, and fully fluorinated polymers generally show much better hydrolysis resistance and are often selected after comparative testing.
How are test results interpreted?
Results are typically expressed as retention percentages of key properties, such as tensile strength retention of at least 50% or 70% after a specified boiling time, together with allowable limits for mass change, dimensional change, and visual defects. Acceptance thresholds are defined by product specifications, industry standards, or contractual agreements between suppliers and end users.
Can the test be performed above 100°C?
Yes. When an even higher acceleration factor is required, specimens can be immersed in water inside pressurized vessels or autoclaves at temperatures of 110°C to 135°C. These pressurized hot water exposures must be clearly distinguished from standard atmospheric boiling tests in reports, since degradation kinetics and failure modes may differ.
Where can this test be performed?
The boiling water hydrolysis test can be carried out in manufacturers' internal laboratories for process control or by accredited third-party laboratories for independent material qualification, compliance verification, and dispute resolution. Reports should document the apparatus, water quality, exposure conditions, measured properties, retention calculations, and any visual observations to ensure full traceability and repeatability.