ISO 15512: Moisture Content Testing in Plastics — Methods & Standards
What Is Moisture Content Testing in Plastics?
Moisture content testing measures the amount of water absorbed by or adsorbed onto a plastic material. Even trace levels of moisture — as low as 0.01% by weight — can significantly degrade the mechanical performance, dimensional stability, and processability of hygroscopic polymers such as nylon (polyamide), polycarbonate, PET, PBT, and ABS. ISO 15512 and related standards govern moisture content measurement in the plastics, packaging, automotive, and electronics industries.
Why Moisture Control Matters in Plastics
Processing Issues
Moisture in hygroscopic polymers causes hydrolytic degradation during melt processing (injection molding, extrusion). Water molecules at processing temperatures (200–320°C) catalyze chain scission, reducing molecular weight, melt viscosity, and mechanical properties. This manifests as surface splay, voids, reduced gloss, and brittleness in molded parts.
In-Service Performance
Absorbed moisture acts as a plasticizer in polyamides, increasing impact toughness but reducing stiffness and dimensional stability. In polycarbonate and PET, moisture reduces hydrolysis resistance and promotes stress cracking. Electronic component housings with excessive moisture absorption can create current leakage paths and accelerate corrosion.
ISO 15512 — Determination of Water Content
Scope and Applicability
ISO 15512 specifies methods for determining the water content of plastics using:
- Method A: Oven drying (gravimetric) — the difference in mass before and after drying at a specified temperature
- Method B: Karl Fischer titration — chemical titration using Fischer reagent that reacts stoichiometrically with water
Method A: Gravimetric (Loss on Drying)
Specimens are weighed, dried in an oven (temperature specified by resin supplier — typically 80°C for PC, 120°C for nylon 6) until constant mass is achieved, and reweighed. The mass loss represents water content. Simple and inexpensive, but requires careful temperature control to avoid degradation of volatile additives.
Method B: Karl Fischer Titration
Karl Fischer (KF) titration is the most accurate and specific method for water content, immune to interference from volatiles that would be falsely counted as water loss in gravimetric methods. Two variants are used:
- Volumetric KF: For water contents above ~100 ppm
- Coulometric KF: For trace moisture at 1–1000 ppm levels in high-performance engineering resins
The headspace KF method — heating the sample in a sealed vessel and sweeping evolved moisture into the titration cell — is preferred for solid plastics as it avoids dissolution issues.
Additional Related Standards
- ASTM D6869: Karl Fischer coulometric titration for plastics
- ASTM E203: Water determination by Karl Fischer (volumetric)
- IEC 62631-3-1: Moisture content of solid insulating materials
Industry Applications
Injection molders of polyamide, PBT, and PET measure incoming resin moisture before processing to verify adequate predrying. Automotive Tier 1 suppliers test the moisture content of glass-fiber-reinforced nylon structural parts to confirm that post-molding conditioning has been achieved before mechanical property testing. Electronic connector manufacturers validate that housing materials meet moisture absorption specifications per IEC 60068-2-78. Packaging film producers measure moisture in the EVOH and nylon barrier layers to predict the stability of the oxygen transmission rate.
Conclusion
Moisture content testing as per ISO 15512 provides a reliable framework for accurately determining the water content in plastic materials. By using standardized methods such as Karl Fischer titration and loss-on-drying techniques, it ensures precise and repeatable results. This testing is crucial for maintaining material quality, preventing processing defects, and ensuring product performance, making it an essential part of quality control in polymer manufacturing and related industries.
Why Choose Infinita Lab for Moisture Content Testing?
Infinita Lab is a leading provider of plastics moisture-content testing services, with a network of 2,000+ accredited labs across the USA, offering Karl Fischer titration, gravimetric methods, and full project management with confidentiality assurance.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090. [Request a Quote]
Frequently Asked Questions
What is the maximum acceptable moisture content for injection molding nylon? Most nylon 6 and nylon 6/6 grades require a moisture content below 0.20% (2,000 ppm) before injection molding to prevent hydrolytic degradation. Some high-performance grades specify <0.10%. Resin suppliers provide material-specific drying recommendations.
What is the difference between moisture absorption and moisture adsorption? Moisture absorption refers to water uptake into the bulk of the material (diffusion-driven), while adsorption refers to surface-only water accumulation. Hygroscopic polymers like nylon absorb moisture throughout their volume; non-polar polymers like polyethylene only adsorb surface moisture.
Why is Karl Fischer titration preferred over gravimetric methods for some plastics? Karl Fischer titration is chemically specific for water — it does not respond to other volatile components (solvents, monomers, plasticizers) that would be counted as mass loss in gravimetric measurements. For materials with volatile additives, KF provides a more accurate true water content.
How quickly do hygroscopic polymers absorb moisture from the atmosphere? Absorption rate depends on material, temperature, humidity, and part thickness. Nylon 6/6 pellets at 23°C/50% RH can absorb 1% moisture in as little as 24–48 hours. Thin films equilibrate faster than thick molded parts. This is why predried materials must be processed quickly or kept in sealed moisture-barrier packaging.
What is the ISO standard for measuring moisture content in plastics? ISO 15512 (Plastics — Determination of Water Content) is the primary international standard, covering both gravimetric (oven drying) and Karl Fischer titration methods. ASTM D6869 and ASTM E203 are the corresponding US methods for Karl Fischer titration.
