{"id":4202,"date":"2026-04-23T09:37:45","date_gmt":"2026-04-23T09:37:45","guid":{"rendered":"https:\/\/nylonplastic.com\/?p=4202"},"modified":"2026-06-10T06:03:23","modified_gmt":"2026-06-10T06:03:23","slug":"moisture-absorption-nylon-effects-measurement-control","status":"publish","type":"post","link":"https:\/\/nylonplastic.com\/fr\/moisture-absorption-nylon-effects-measurement-control\/","title":{"rendered":"Moisture Absorption in Nylon: Effects, Measurement, and Control"},"content":{"rendered":"

Understanding moisture absorption in nylon \u2014 how it affects mechanical properties, dimensional stability, processing, and design strategies to manage it.<\/p>\n

\"Absorption<\/p>\n

Nylon’s Moisture Sensitivity: A Critical Design Variable<\/h2>\n

\"Absorption<\/p>\n

Of all common engineering thermoplastics, nylon absorbs the most moisture. PA6 reaches 9.5% by weight at saturation, while PA66 reaches 8.5%. This is not a minor property \u2014 it fundamentally alters the material’s mechanical behavior, dimensions, electrical properties, and appearance.<\/p>\n

Designers and engineers who ignore moisture absorption face a common failure mode: parts that fit perfectly when molded (dry) but swell, distort, or change flexibility after exposure to normal humidity. A nylon gear that meshes perfectly in the factory may bind and wear prematurely in a humid warehouse. Understanding and controlling moisture effects is essential for reliable nylon part design.<\/p>\n

Mechanism: How Nylon Absorbs Water<\/h2>\n

Nylon’s molecular structure contains amide groups (-CONH-) that form hydrogen bonds with water molecules. This is the same hydrogen-bonding mechanism that makes nylon strong in the first place \u2014 but water molecules occupy hydrogen-bonding sites that were previously linking nylon chains together, reducing inter-chain forces.<\/p>\n

**Absorption Rate**:
\nThe rate of moisture absorption depends on thickness and humidity:<\/p>\n\n\n\n
1mm film<\/th>\n2 hours<\/th>\n8 hours<\/th>\n<\/tr>\n<\/thead>\n<\/table>\n\n\n\n\n\n
2mm sheet<\/th>\n8 hours<\/th>\n36 hours<\/th>\n<\/tr>\n<\/thead>\n
6mm plate<\/td>\n3 days<\/td>\n12 days<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

This is why thin-walled parts reach equilibrium faster \u2014 and why thick sections can retain dry conditions in the core while the surface is saturated.<\/p>\n

**Drying Reverses the Process**:
\nHeating nylon above 80\u00b0C drives off absorbed moisture. At 100\u00b0C for 4-6 hours, PA6 and PA66 reach dry-as-molded condition. However, the dimensional changes from drying are not fully reversed \u2014 the part does not shrink back to its dry-molded dimensions because the polymer chains have reorganized.<\/p>\n

Effects on Mechanical Properties<\/h2>\n\n\n\n\n\n\n
R\u00e9sistance \u00e0 la traction<\/th>\n95 MPa<\/th>\n75 MPa<\/th>\n-21%<\/th>\n<\/tr>\n<\/thead>\n
Tensile Modulus<\/td>\n3.2 GPa<\/td>\n2.0 GPa<\/td>\n-37%<\/td>\n<\/tr>\n
Module de flexion<\/td>\n3.0 GPa<\/td>\n1.8 GPa<\/td>\n-40%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n
Allongement \u00e0 la rupture<\/th>\n80%<\/th>\n180%<\/th>\n+125%<\/th>\n<\/tr>\n<\/thead>\n
Hardness (Shore D)<\/td>\n82<\/td>\n74<\/td>\n-10%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

**Key insight**: Moisture acts as a plasticizer for nylon. The material becomes softer, weaker in tension and flexure, but significantly tougher. Impact resistance nearly doubles in conditioned nylon vs. dry nylon.<\/p>\n

**Design Implication**: If you design to dry property values, your conditioned parts will be 20-40% weaker than calculated. Always design to the highest moisture condition the part will experience in service.<\/p>\n

**Glass fiber reinforcement mitigates moisture effects** \u2014 GF30 grades show only 10-15% strength reduction from dry to conditioned (vs. 20-25% for unfilled). The glass fiber network is unaffected by moisture; only the nylon matrix is plasticized.<\/p>\n

Dimensional Effects and Warpage<\/h2>\n

Moisture absorption causes linear expansion in nylon:<\/p>\n

**Dimensional Change from Dry to Saturated**:<\/p>\n\n\n\n\n\n\n
Grade<\/th>\nLinear Expansion per % Moisture<\/th>\n<\/tr>\n<\/thead>\n
PA6<\/td>\n0.25-0.30%<\/td>\n<\/tr>\n
PA66<\/td>\n0.22-0.28%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n
PA12<\/th>\n0.12%<\/th>\n<\/tr>\n<\/thead>\n
PA66-GF30<\/td>\n0.07%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

A PA6 bushing with 50mm OD, molded dry, will expand to approximately 50.35mm at 50% RH saturation (0.35% change \u00d7 50mm = 0.175mm). If the assembly requires 50.0-50.1mm fit, this is a critical tolerance issue.<\/p>\n

**Unequal Moisture Distribution Causes Warpage**:
\nIn thick sections, the outer surface absorbs moisture while the core remains dry. This creates differential swelling \u2014 the surface wants to expand while the core resists. The result is warpage (bowing, distortion) even in parts with symmetrical geometry.<\/p>\n

**Design Strategies**:
\n1. **Anneal before final dimensioning** \u2014 Heat treat parts at 120-130\u00b0C for 1-2 hours to crystallize and stabilize dimensions before machining or assembly
\n2. **Condition to equilibrium** \u2014 Allow parts to reach uniform moisture content before final assembly
\n3. **Use GF or CF reinforcement** \u2014 Fiber reinforcement reduces moisture-induced expansion by 70-80%
\n4. **Specify PA12** \u2014 At 1.5% saturation vs. 8-9% for PA6\/66, PA12’s dimensional change is negligible<\/p>\n

Processing: Drying Requirements<\/h2>\n

Excess moisture in nylon during injection molding causes catastrophic defects:<\/p>\n

**Moisture Defects**:
\n– **Bubbles and voids**: Steam formed during injection creates internal voids
\n– **Silver streaks**: Water vapor flashing off during injection creates surface streaks
\n– **Reduced molecular weight**: Hydrolysis during processing weakens the material
\n– **Reduced mechanical properties**: Even if surface looks good, the material is degraded<\/p>\n

**Required Drying Parameters**:<\/p>\n\n\n\n\n\n\n
Mat\u00e9riau<\/th>\nDrying Temperature<\/th>\nDrying Time<\/th>\nMax Moisture Content<\/th>\n<\/tr>\n<\/thead>\n
PA6<\/td>\n80\u00b0C<\/td>\n4-6 heures<\/td>\n0.20%<\/td>\n<\/tr>\n
PA66<\/td>\n80-85\u00b0C<\/td>\n4-6 heures<\/td>\n0.15%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n
PA12<\/th>\n80\u00b0C<\/th>\n3-4 hours<\/th>\n0.10%<\/th>\n<\/tr>\n<\/thead>\n
PA66-GF30<\/td>\n85\u00b0C<\/td>\n4-6 heures<\/td>\n0.12%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

**Drying Equipment**: Desiccant dryers are mandatory for nylon. Hot air dryers are insufficient because they cannot remove moisture below the surface. Desiccant dryers with dew point below -40\u00b0C are required.<\/p>\n

**Moisture Analyzers**: Use Karl Fischer titration or loss-on-drying to verify material moisture before processing critical parts. Most production facilities check every batch.<\/p>\n

PA12 vs. PA6\/PA66: When to Choose Low-Moisture Grades<\/h2>\n

For applications where moisture is unavoidable, PA12 is the logical choice:<\/p>\n

**Applications where PA12’s low absorption is essential**:
\n– **Underwater or marine components**: PA12 maintains properties in submerged conditions where PA6\/66 would absorb 5-8%
\n– **Outdoor exposed parts**: PA12’s 1.5% saturation vs. 8-9% means far less dimensional change through seasonal humidity cycles
\n– **Food processing (steam cleaning)**: PA12 resists steam exposure better than PA6\/66
\n– **Fluid metering components**: Dimensional stability in humid air is critical for precision metering
\n– **Cable conduits**: PA12 handles underground moisture without swelling<\/p>\n

**Cost vs. Benefit**:
\nPA12 costs approximately 2-3\u00d7 more than PA66. The premium is justified when:
\n1. Field failures from moisture-induced swelling are costly
\n2. Dimensional tolerances are tight (\u00b10.05mm or tighter)
\n3. The part is exposed to water, humidity, or steam
\n4. Assembly requires parts at equilibrium condition before fit testing<\/p>\n

**Hybrid Approach**:
\nFor many applications, PA66-GF30 achieves a practical balance: the glass fiber reinforcement reduces moisture absorption by ~70% (effective absorption drops from 8.5% to ~2.5%), and the GF network limits dimensional change. This is why PA66-GF30 is the automotive default \u2014 it handles under-hood humidity without the premium cost of PA12.<\/p>\n

\n

FAQ<\/h2>\n
\"Moisture
Moisture Absorption in Nylon: Effects, Measurement, and Control<\/figcaption><\/figure>\n
\nHow do you know whether Moisture Absorption in Nylon: Effects, Measurement, and Control fits a part?<\/summary>\n
\n

Moisture Absorption in Nylon: Effects, Measurement, and Control fits a part when its load capacity, temperature range, moisture exposure, wear behavior, and processing method match the real service conditions.<\/p>\n<\/div>\n<\/details>\n

\nWhat properties should be checked for Moisture Absorption in Nylon: Effects, Measurement, and Control?<\/summary>\n
\n

V\u00e9rifier la r\u00e9sistance, la rigidit\u00e9, la r\u00e9sistance aux chocs, la r\u00e9sistance \u00e0 la chaleur, l'absorption d'humidit\u00e9, la stabilit\u00e9 dimensionnelle, le frottement, l'usure et la compatibilit\u00e9 chimique.<\/p>\n<\/div>\n<\/details>\n

\nWhat is the biggest selection risk for Moisture Absorption in Nylon: Effects, Measurement, and Control?<\/summary>\n
\n

Le plus grand risque est de choisir \u00e0 partir d'une fiche technique sans tenir compte de l'environnement r\u00e9el, de la m\u00e9thode de traitement, de la g\u00e9om\u00e9trie de la pi\u00e8ce et de l'utilisation \u00e0 long terme.<\/p>\n<\/div>\n<\/details>\n

\nWhen should Moisture Absorption in Nylon: Effects, Measurement, and Control be tested before production?<\/summary>\n
\n

Les essais sont recommand\u00e9s lorsque la pi\u00e8ce est soumise \u00e0 une charge, \u00e0 la chaleur, \u00e0 des produits chimiques, \u00e0 l'humidit\u00e9, \u00e0 des tol\u00e9rances serr\u00e9es, \u00e0 des exigences r\u00e9glementaires ou \u00e0 un nouvel environnement de travail.<\/p>\n<\/div>\n<\/details>\n<\/div>\n\t\t\t

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