What chemical resistance do nylon bushings provide?

What chemical resistance do nylon bushings provide? 7 practical questions buyers actually need answered

If you specify, buy or test nylon bushings for machinery, vehicles or industrial equipment, the key risk is unexpected chemical exposure that shortens service life or ruins dimensional stability. Below are seven specific, practical long‑tail questions engineers and purchasing specialists ask but rarely find detailed, current answers to. Each answer cites accepted test methods, typical material behavior, and procurement or testing actions you can take before accepting parts.

1. How do common fuel additives (ethanol and other oxygenates) affect long‑term dimensional stability and mechanical strength of nylon bushings?

What happens: Ethanol and other polar oxygenates (ethanol, ETBE, MTBE) are more aggressive toward polyamides than pure aliphatic hydrocarbons. They increase sorption (uptake of liquid), causing swelling and plasticization of the nylon matrix and reduction of stiffness and yield strength. At elevated temperature the effect accelerates.

Typical behavior: Unfilled PA6/PA66 will absorb polar solvents faster and to a greater extent than non‑polar fuels. Short exposure (hours) to low concentrations often causes reversible swelling; long exposure at elevated temperatures produces permanent property loss and possible hydrolysis‑assisted chain scission.

Practical guidance for buyers:
- Prefer PA grades formulated for fuel exposure (e.g., PA12 or specially stabilized PA6/PA66) for sustained contact with ethanol blends.
- Use glass‑filled or chemically modified grades to reduce sorption and dimensional change.
- Require supplier chemical‑compatibility test data with the exact fuel blend (e.g., E10, E85) and at relevant temperatures (ambient and operating temperature).
- If in doubt, mandate an accelerated immersion test (see Q6) and define allowable dimensional change and tensile retention.

2. Can nylon bushings survive steam, autoclave cycles or high‑humidity/high‑temperature engine‑bay environments without significant hydrolysis?

What happens: Polyamides are vulnerable to hydrolysis (water‑catalyzed chain cleavage) when exposed to hot water or steam. Hydrolysis is both temperature‑ and time‑dependent; steam/autoclave conditions (e.g., 121°C, saturated steam) are particularly aggressive.

Typical behavior: At elevated temperatures (>80–100°C) in presence of water/steam, PA6 and PA66 show progressive loss of molecular weight, declining tensile strength and embrittlement. Even if short cycles produce only reversible moisture uptake, repeated cycles or constant high‑temperature moisture accelerate irreversible degradation.

Practical guidance for buyers:
- Avoid standard nylon (PA6/PA66) for continuous steam or repeated autoclave use unless the specific PA grade is formulated and tested for hydrothermal stability.
- Consider PA12 (lower water uptake), fluoropolymers, PEEK or PPS for high‑temperature steam/chemical environments.
- Require supplier hydrothermal aging data where service includes steam or continuous high humidity at elevated temperature; specify test conditions and acceptance criteria.

3. How do fillers (glass fiber, carbon, PTFE) change a nylon bushing’s chemical resistance profile?

What happens: Fillers modify mechanical and diffusion behavior. Glass fiber and carbon reduce bulk sorption and swelling by lowering the polymer fraction and providing dimensional restraint. PTFE or graphite fillers can improve wear and reduce surface energy, indirectly affecting chemical uptake. However, fillers introduce interfaces where chemical agents can penetrate or catalyze degradation.

Typical behavior:
- Glass‑filled nylon: lower water uptake, better modulus retention, improved dimensional stability in many liquids compared to unfilled nylon.
- PTFE/graphite‑filled nylon: better lubricity and sometimes better resistance to certain chemicals at the surface, but base polyamide remains chemically similar.
- Note: Compatibilizers and coupling agents (e.g., silanes) used with glass fiber affect chemical resistance at fiber/matrix interfaces.

Practical guidance for buyers:
- Specify filler type and % by weight when procuring bushings; ask for chemical‑exposure test data for the specific filled grade.
- Beware that increased stiffness from glass fill may reduce impact toughness; set mechanical acceptance criteria post‑conditioning.
- When chemical ingress at the surface is critical, ask for microscopic analysis (SEM) or interfacial testing results from the supplier.

4. Which common lubricants and hydraulic fluids are generally compatible with nylon bushings — and which require caution or testing?

General rule: Mineral‑based lubricating oils and many greases are compatible with nylon; many hydraulic fluids (some mineral oils, some synthetic esters) are acceptable at typical operating temperatures. Aggressive solvents (ketones, chlorinated hydrocarbons), strong oxidizers and certain polar solvents are problematic.

Specifics to watch for:
- Mineral oils and many petroleum greases: generally compatible with PA6/PA66 at service temperatures.
- Synthetic esters and some brake fluids (glycol‑ether based) may be compatible at ambient conditions but can cause greater swelling at higher temperatures and longer exposure—testing required.
- Phosphate‑ester (some fire‑resistant hydraulic fluids) and certain additive chemistries can accelerate polymer attack — consult the fluid and polymer supplier data.
Practical guidance for buyers:
- Provide the exact lubricant/hydraulic fluid (including additive package) and operating temperature when requesting compatibility data.
- Require immersion or dynamic compatibility tests (lubricant + heat + mechanical load) if the bushing is in constant contact or in a sealed environment.
- Specify acceptance metrics (dimensional change Y%, hardness change

5. At what pH extremes do nylon bushings begin to lose structural integrity, and how fast does that happen?

What happens: Both strongly acidic and strongly alkaline solutions can hydrolyze polyamides. Alkalis (strong bases) are often more aggressive in cleaving amide bonds, especially at elevated temperatures. Strong oxidizing acids accelerate surface attack and embrittlement.

Typical behavior:
- Mild acids/bases (near neutral pH 4–9) are usually tolerable for many PA grades at ambient temperature.
- Concentrated acids (e.g., sulfuric, nitric) and concentrated alkalis (e.g., sodium hydroxide) rapidly degrade nylon; damage rates increase with temperature.
Practical guidance for buyers:
- Avoid nylon in continuous exposure to pH extremes unless the grade and exposure are covered by supplier data.
- If transient exposure occurs (splashes), design drainage and protective coatings, and set inspection intervals.
- For any exposure to pH <3 or >11, require supplier testing and consider alternative materials if mechanical integrity is mission‑critical.

6. How should I specify an accelerated chemical compatibility test so results meaningfully predict field life of nylon bushings?

Don’t accept vague immersion statements. Use standard methods and define pass/fail metrics:

• Standard test method: ASTM D543 (Standard Practices for Evaluating Effect of Chemicals on Plastics) is the accepted baseline for immersion testing. It defines specimen prep, immersion conditions and post‑test evaluations (weight change, appearance, hardness, tensile properties).
• Design test parameters to match field stress: select chemical, concentration, temperature (use operating and worst‑case temperatures), static vs. dynamic contact, and immersion duration. Acceleration by temperature is valid but must be justified (Arrhenius considerations) — don’t simply blow up temperature without correlation.
• Define acceptance criteria up front: e.g., dimensional change <1.0% after 1,000 h at 60°C; tensile strength retention >75% after 500 h; or no cracking/softening visible at 10× magnification.
• Use both static immersion and mechanical fatigue tests under chemical exposure (dynamic testing) if bushings are load‑carrying components.

Practical guidance for buyers:
- Include the exact ASTM/ISO standard in purchase orders and test reports.
- Require supplier test certificates with raw data (weight change, tensile curves) and photographic evidence.
- If possible, run an in‑house or third‑party verification on production parts prior to full acceptance.

7. Which post‑processing or surface treatments measurably improve chemical resistance and reduce absorption of nylon bushings?

Options that help:
- Annealing: reduces internal stresses and can improve dimensional stability; it doesn’t change polymer chemistry but helps mechanical property retention after conditioning.
- Surface coatings: thin barrier coatings (PTFE, parylene, specialized fluoropolymer coatings) reduce direct liquid contact and surface sorption; durability of the coating under load must be validated.
- Impregnation/sealing: polymer impregnation or sealants can reduce surface porosity and slow diffusion; these are common for reducing moisture uptake in precision components.
- Chemical stabilization: some commercial nylon grades include hydrolysis or oxidation stabilizers built into the resin for improved longevity in aggressive environments.
Practical guidance for buyers:
- Require data on coating adhesion, wear resistance and chemical resistance for the coated finished part, not just the substrate.
- If coatings are specified, include peel/adherence and cyclic chemical exposure tests in the acceptance criteria.
- Ask suppliers whether additives or stabilizers are used and request comparative data against an unstabilized grade.

Procurement checklist: how to buy nylon bushings for chemically aggressive environments

• Specify the exact chemistry, concentration, temperature range, mechanical load and exposure duration in the RFQ.
• Specify the polyamide family (PA6, PA66, PA12), filler type and % (glass, carbon, PTFE), and any stabilizers/coatings required.
• Mandate ASTM D543 immersion test data with clear acceptance criteria (dimensional change, tensile retention, hardness change) and request summary and raw data.
• Require producer QC documentation: material batch traceability, melt index/viscosity where relevant, and certificates of conformity to specified resin grade.
• Consider a pilot run for field‑validation, and include end‑of‑life inspection criteria and periodic scheduled inspections in the maintenance plan.

Why choosing the right nylon grade and validating it matters

Nylon bushings are cost‑effective and wear‑resistant, but their performance is highly dependent on the exact chemical and thermal environment. Small differences — PA6 vs PA66 vs PA12, unfilled vs 30% glass fill, or presence of a hydrolysis stabilizer — can change long‑term field life from months to many years. The best practice is to define exposure, request standardized accelerated testing (ASTM D543 + dynamic tests where needed), and accept only parts meeting explicit, measurable criteria.

Bost — practical supplier advantages for engineering‑grade nylon bushings

Bost offers a combination of procurement advantages valuable to engineering buyers:
- Material expertise: engineering support to select the correct polyamide family and filler package for your chemical environment.
- Testing and validation: in‑house or partner lab capability to run ASTM D543 immersion tests, hydrothermal aging and mechanical retention testing on finished parts.
- Custom machining and coatings: options for dimensional tolerances, post‑annealing and application of barrier coatings to reduce surface sorption.
- Traceability and documentation: certificate of conformity, material lot traceability and production testing data provided with parts.
These capabilities reduce risk in the supply chain and shorten validation cycles when you need parts that survive specific chemical exposures.

References

1. ASTM International, ASTM D543 — Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents, ASTM. (Accessed 2024‑05‑20).
2. DuPont, Zytel® (Nylon) product information and typical properties (PA6/PA66); manufacturer technical bulletins on moisture uptake and hydrolysis. (Accessed 2024‑05‑15).
3. Ensinger GmbH, Chemical Resistance of Plastics technical guide — practical chemical compatibility summaries for polyamides and filled grades. (Accessed 2024‑05‑18).
4. McMaster‑Carr product and material pages for nylons (practical usage notes about lubricants and oils) — catalog compatibility notes. (Accessed 2024‑05‑12).
5. SpecialChem / Plastics portals: Nylon (polyamide) technical reference pages describing water absorption, hydrolysis behavior and filler effects. (Accessed 2024‑05‑16).
6. ISO 62, Plastics — Determination of water absorption (reference for water‑uptake test methods and typical reporting). (Accessed 2024‑05‑20).