A data-driven comparison of POK and Nylon under humidity — and why the difference between them can mean the difference between a successful component and a costly field failure.
A high-tolerance gear or valve passes post-mold inspection perfectly. Yet, after weeks of field operation in a humid environment, the mechanism binds or seizes. This critical failure stems from unexpected engineering plastic dimensional change caused by material moisture absorption. For structural components operating in wet environments, unexpected size variation leads directly to system failure.
While polyamides (Nylon) are the traditional industry default, Polyketone (POK) represents a significant shift in dimensional control. This guide analyzes the data behind POK vs. Nylon under humidity to help you make data-driven selections.
For a complete property analysis, see our comprehensive Polyketone vs Nylon Guide →
The Chemistry: Polar Amide Groups vs. POK Barrier Structure
Nylon's vulnerability to water lies in its polar amide groups. These groups form strong hydrogen bonds, drawing water molecules directly into the polymer matrix. The absorbed water acts as a plasticizer—disrupting intermolecular bonds and decreasing tensile strength.
In typical environments (35% to 65% RH), unfilled nylon reaches an equilibrium moisture content of 1.5% to 2.0% by weight. When submerged, short-chain nylons like PA6 spike to 9.0% or higher. Conversely, Polyketone's highly crystalline structure results in exceptionally low water absorption profiles幕。
The Core Data: Head-to-Head Technical Comparison
| Material Grade | 24h Water Absorption (23°C) | Saturated (Immersed) | Max Dimensional Change |
|---|---|---|---|
| POK (Unfilled) | < 0.5% | ~1.0% | ~0.2% |
| POK GF30 | < 0.25% | — | < 0.1% |
| PA6 (Unfilled) | ~1.6% | 9.0%+ | ~2.0% |
| PA66 (Unfilled) | ~1.2% | 7.0%+ | ~3.5% |
Mechanical Property Retention in Wet States
Evaluating the wet-state behavior shows that Polyketone retains approximately 93% of its tensile yield strength, sustaining 56 / 60 MPa with virtually zero elongation impact. Conversely, standard Polyamides like PA66 undergo significant plasticization, suffering a 30% to 50% loss in elastic modulus and a severe reduction in structural rigidity when saturated.
Engineering Applications: Where POK Excels
Precision Drivetrains: Gears & worm drives maintain consistent tooth alignment in humidity without post-mold conditioning. No swelling-induced binding occurs.
Pump Housings & Valves: Continuous submersion causes PA6 to swell, leading to seal failures. POK safely maintains physical dimensions, effectively resisting water-induced softening.
Electrical Connectors: Humidity spikes warp standard nylon connector housings, causing pin misalignment. POK maintains exact geometry across the full operating range.
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Glass Fiber Reinforcement: Capabilities and Limits
Glass fiber-reinforced POK grades consistently outperform glass-filled PA6 and PA66 in dimensional control. The critical insight: fiber restrains movement, but does not alter the base resin's water chemistry.
Under long-term submersion, the nylon matrix within a PA66 GF30 part still picks up water, leading to internal micro-stresses and eventual creep. POK GF30 eliminates this risk because the base resin itself rejects moisture—the fiber and the matrix work together rather than in opposition.
Technical Selection Framework
When evaluating your application requirements, if the operating environment features less than 60% RH and is not submerged, standard or modified Nylons remain cost-effective options. However, when the environment exceeds 60% RH or involves direct submersion, and mating tolerances are tighter than ±0.1 mm, Polyketone is strongly recommended.
PROCESSING EFFICIENCY NOTE POK's low moisture affinity allows engineers to bypass complex pre-drying or post-mold moisture conditioning stages, directly streamlining production cycle times and reducing process complexity.
Conclusion
When precision cannot be compromised by ambient humidity, moisture absorption shifts from a datasheet footnote to a primary failure mode. While Nylon remains excellent for dry, low-tolerance components, Polyketone provides the dimensional stability and wet-state strength retention required by modern structural engineering。
The data is unambiguous: for tight-tolerance components operating above 60% RH or in submerged environments, POK's intrinsic moisture barrier chemistry eliminates an entire category of field failure risk — without the need for material modifications or complex processing controls.
