Low water absorption material testing measures the amount of moisture that plastics, composites, foams, and other polymeric materials absorb under controlled immersion and humidity conditions. This testing is critical for verifying dimensional stability, electrical insulation performance, and long-term durability in industries such as electronics, automotive, aerospace, and marine engineering. Using internationally recognized standards such as ASTM D570 and ISO 62, laboratories quantify water uptake gravimetrically to confirm that materials comply with strict low-absorption specifications.
Technical Overview
Water absorption refers to the uptake of water by a material when it is exposed to liquid water or a humid atmosphere, expressed as a percentage of the material's dry mass. For many engineering applications, excessive moisture absorption leads to plasticization, dimensional swelling, reduced mechanical strength, degraded dielectric properties, blistering, and accelerated aging. Materials classified as low water absorption typically exhibit a 24-hour immersion value below 0.5%, and premium engineering materials such as PTFE, PE, PP, and PPS can achieve values below 0.05%.
Low water absorption testing is a gravimetric evaluation in which conditioned specimens are dried to constant mass, immersed in water under specified temperature and duration conditions, and reweighed after surface moisture is removed. The percentage increase in mass quantifies water uptake. Time-dependent weighing also allows determination of diffusion behavior and saturation uptake, which are essential for predicting long-term performance in humid or submerged service environments.
- Typical 24-hour absorption values: PTFE 0.01%, HDPE 0.01%, PP 0.01–0.03%, PPS 0.01–0.03%, PEEK 0.1–0.5%, PC 0.15–0.2%, PA6 1.3–1.9% (nylons are high absorption).
- Absorption follows Fickian diffusion in most homogeneous polymers, where moisture content increases with the square root of exposure time until saturation.
- Specimen thickness, surface condition, and cut edges significantly influence measured absorption, so standardized geometry and conditioning are mandatory.
Testing Samples
Thermoplastics
Samples include polyolefins (PE, PP), fluoropolymers (PTFE, FEP, PFA), engineering plastics (PPS, PEEK, PEI, PSU, PPE), and commodity resins (PS, ABS, PMMA, PVC). Specimens are typically flat discs or plaques of 50 mm diameter or square by 3 mm thickness, or rods and tubes with dimensions defined by the applicable standard.
Thermosetting Resins
Epoxy, phenolic, unsaturated polyester, polyurethane, and silicone resins are tested in molded or cast form. Curing state must be fully documented, since incomplete cure artificially elevates moisture uptake.
Composites and Reinforced Materials
Carbon fiber and glass fiber laminates, SMC, BMC, and pultruded profiles are evaluated to assess matrix absorption and fiber-matrix interface durability. Saturation immersion testing is frequently required for marine and aerospace qualification programs.
Foams and Cellular Materials
Rigid polyurethane foams, polystyrene foams, and polyolefin foams are tested using dedicated buoyancy-based procedures because open-cell content and water penetration into cells require volumetric assessment rather than simple mass gain.
Elastomers, Sealants, Coatings, and Films
Rubber compounds, silicone sealants, potting compounds, conformal coatings, and barrier films are evaluated for fluid resistance, moisture uptake, and water vapor transmission behavior relevant to sealing and packaging performance.
Testing Items
Testing programs for low water absorption materials typically include the following evaluation items:
- Water absorption after 24-hour immersion at 23°C (percentage mass gain)
- Water absorption after 2-hour immersion in boiling water
- Water absorption at saturation (equilibrium) under long-term immersion
- Water absorption under humid atmosphere exposure at 50% RH
- Moisture diffusion coefficient and saturation content determination
- Dimensional change (swelling) due to water absorption
- Retention of mechanical properties after immersion (tensile, flexural, impact)
- Effect of immersion on electrical properties (dielectric constant, dissipation factor, insulation resistance)
- Surface wettability and contact angle as a supplementary hydrophobicity indicator
- Water vapor transmission rate for films and barrier layers
Testing Methods
Specimen Preparation and Conditioning
Specimens are machined or molded to the geometry required by the standard, with edges finished consistently to avoid uncontrolled edge effects. Prior to testing, specimens are dried in an oven (typically 50°C for 24 hours, or to constant mass) and cooled in a desiccator. The initial dry mass (W1) is measured with an analytical balance accurate to 0.1 mg.
Immersion Test at 23°C
Specimens are fully immersed in distilled or deionized water maintained at 23°C for 24 hours. After removal, surface water is quickly blotted with a dry lint-free cloth, and the specimen is weighed within one minute (W2). Water absorption is calculated as (W2 − W1) / W1 × 100%.
Boiling Water Immersion Test
Specimens are immersed in boiling water for 30 minutes (ISO 62 Method 2) or 2 hours (ASTM D570), then cooled in room-temperature water for a defined period, blotted, and weighed. This accelerated condition reveals absorption behavior under thermal stress and is used to screen materials for humid, elevated-temperature service.
Saturation and Long-Term Immersion
For saturation testing, specimens remain immersed and are reweighed at increasing intervals (e.g., 24 h, 48 h, 96 h, weekly) until the mass change between successive weighings falls below a specified threshold. The plateau value defines equilibrium water content, which is critical for hygrothermal aging studies and composite qualification.
Humidity Exposure Testing
Specimens are placed in a climate chamber at 23°C and 50% relative humidity (or accelerated conditions such as 85°C/85% RH) to determine moisture uptake from humid air, simulating storage and operating environments where direct liquid contact does not occur.
Applicable Standards
- ASTM D570 — Standard Test Method for Water Absorption of Plastics
- ISO 62 — Plastics: Determination of Water Absorption
- ASTM D2842 — Water Absorption of Rigid Cellular Plastics
- ISO 2896 — Cellular Plastics, Rigid: Determination of Water Absorption
- ASTM D5229/D5229M — Moisture Absorption Properties and Equilibrium Conditioning
- ASTM D471 — Rubber Property: Effect of Liquids
- ASTM D618 / ISO 291 — Conditioning of plastics for testing
Applications
Low water absorption testing supports material selection, incoming inspection, and product qualification across many industries:
- Electronics and electrical engineering: certification of connectors, PCB substrates, encapsulants, and insulating housings where moisture degrades dielectric performance and promotes corrosion.
- Automotive: validation of under-hood components, sensor housings, fuel system parts, and battery components exposed to humidity, wash fluids, and road splash.
- Aerospace: qualification of carbon fiber composites and structural adhesives, where absorbed moisture reduces glass transition temperature and matrix-dominated strength.
- Marine and offshore: assessment of hull laminates, buoys, pipe linings, and flotation foams subject to continuous water contact.
- Medical devices: evaluation of instrument housings, sterilization trays, and polymer components that must withstand repeated washing and autoclave cycles.
- Packaging: verification of moisture barrier performance for flexible films, containers, and desiccant-integrated structures.
- Construction and infrastructure: testing of pipe materials, cable insulation, geosynthetics, and protective coatings for damp-service durability.
FAQ
What is considered a low water absorption value? Generally, materials with a 24-hour immersion absorption below 0.5% are regarded as low absorption, while values below 0.05% are considered excellent. PTFE, PE, PP, and PPS are benchmark low-absorption materials with values near 0.01–0.03%.
Which standards govern low water absorption testing? ASTM D570 and ISO 62 are the primary standards for plastics. ASTM D2842 and ISO 2896 apply to rigid cellular plastics, while ASTM D5229 covers moisture diffusion characterization for composites.
What specimen size and quantity are required? For plastics, standard specimens are typically 50 mm diameter by 3 mm thick discs or equivalent square plaques; a minimum of three specimens per condition is recommended for statistical validity.
How long does the testing take? The standard 24-hour immersion test plus conditioning typically requires 3–4 working days. Saturation testing can take several weeks or months depending on specimen thickness and material diffusivity.
Why does specimen geometry affect results? Water enters primarily through surfaces and cut edges; thinner specimens saturate faster and show higher short-term percentage uptake. Comparisons are only valid between specimens of identical geometry and surface finish.
Can water absorption testing be combined with mechanical or electrical evaluation? Yes. Specimens are commonly tested for tensile, flexural, or dielectric properties before and after immersion to quantify property retention, which is essential for humid-environment product qualification.