Degreasing is the first and foundational step in adhesive surface preparation — it removes organic contamination so that subsequent cleaning steps can access and activate the substrate surface. When degreasing is performed incorrectly, organic contamination remains on the surface through all subsequent steps, contaminating the adhesive bond from the start. Improper degreasing is responsible for a large share of adhesive bond failures that are misattributed to inadequate adhesive selection or application errors.

The Purpose of Degreasing in Bonding Preparation

Metal, plastic, and composite substrates arriving at bonding operations carry organic contamination from manufacturing processes: cutting oils, stamping lubricants, drawing compounds, rust preventives, mold releases, handling oils, and storage coatings. These organic materials are predominantly hydrophobic — they repel water and polar adhesives, preventing wetting and chemical bonding.

Degreasing dissolves and removes these organic contaminants, restoring the substrate surface to a state where it can be wetted by adhesives and where subsequent activation steps (abrasion, chemical treatment, plasma, silane primer) can act on the actual substrate rather than on a contamination layer. Without effective degreasing:

• Surface roughening by abrasion cuts through contamination rather than exposing clean substrate
• Chemical conversion coatings fail to adhere uniformly (contamination blocks the conversion reaction)
• Plasma or flame activation oxidizes contamination on the surface rather than the substrate
• Adhesive applied to a degreased-but-still-contaminated surface bonds to the contamination layer

The degreasing step sets the foundation for everything that follows. If it fails, all subsequent steps fail to achieve their purpose even if they are performed correctly.

Common Degreasing Method Failures

Solvent Wiping Errors

Solvent wiping with an organic solvent (acetone, MEK, IPA, heptane) is the most commonly used degreasing method for small-scale and field applications. Several specific errors cause it to fail:

Insufficient solvent volume — using too little solvent results in the solvent becoming contaminated with dissolved oil before it can remove all the oil from the surface. The contaminated solvent then redeposits oil as it is wiped. Adequate solvent volume per part area must be used; this means using fresh solvent generously, not using just enough to barely wet the cloth.

Back-wiping — wiping in one direction, then wiping back over the same area, redistributes the oil that was partially removed in the first pass. Oil displaced from one area is dragged back across already-cleaned sections. Single-direction wiping with progression to clean sections of the cloth prevents back-contamination.

Failure to remove solvent — some solvents leave residues if they are not completely evaporated. IPA in particular leaves a residue on metal surfaces at concentrations below visible wetting but detectable by surface energy testing. Wipe-then-wait for complete evaporation before applying adhesive or proceeding to the next preparation step.

Using solvent to clean heavily contaminated surfaces — solvent wiping is effective for light organic contamination. Heavily contaminated surfaces — thick stamping die lubricant, heavy rust preventive, molding compound residue — are not adequately cleaned by solvent wiping alone. Aqueous cleaning or solvent immersion is needed.

Aqueous Cleaning Failures

Aqueous cleaning systems — alkaline wash, ultrasonic cleaning, spray washing — are effective for many organic contamination types but require attention to process parameters:

Inadequate bath temperature — most aqueous cleaning chemistries work better at elevated temperatures (50–70°C). Running cleaning baths at ambient temperature reduces cleaning effectiveness substantially for petroleum-based contamination.

Bath loading and contamination buildup — cleaning baths become contaminated over time as they remove oil from parts. Oil accumulates in the bath and eventually redeposits on cleaned parts rather than removing contamination. Bath chemistry, pH, and oil contamination level must be monitored and the bath replaced or renewed before it becomes counterproductive.

Insufficient rinsing — aqueous cleaning agents must be rinsed off completely. Insufficient rinsing leaves cleaning agent residues — surfactants, alkaline chemicals, chelating agents — on the surface. These residues are themselves contamination and can impair adhesion or interfere with subsequent adhesion promoter application.

Drying conditions — parts dried in contaminated ovens or with contaminated compressed air receive contamination during the drying step. Drying air must be oil-free; drying ovens must be clean. Hot air from compressed air lines without oil separators deposits compressor oil on cleaned parts during blow-off.

Email Us to discuss degreasing process development for your adhesive bonding application.

Vapor Degreasing Issues

Vapor degreasing with chlorinated solvents (trichloroethylene, perchloroethylene) has historically been highly effective for removing petroleum-based contamination from metal parts. Regulatory restrictions on chlorinated solvents have driven transition to alternative processes, sometimes with inadequate evaluation of whether the alternatives achieve equivalent cleaning:

Alternative solvent effectiveness — non-chlorinated solvents marketed as vapor degreasing alternatives do not all perform equivalently to traditional chlorinated solvents for all contamination types. Qualifying alternative cleaning processes against the standard contamination for the specific application is necessary before transition.

Carryover contamination from solvent decay products — some chlorinated solvents decompose during use, forming acidic species (hydrochloric acid) that etch metal surfaces and introduce corrosion that later causes adhesive failure at the etched sites. Stabilized solvents and regular monitoring of solvent pH prevent this failure mode.

Validation of Degreasing Effectiveness

Verification that degreasing has achieved adequate cleanliness must be built into the process:

Water break test — the simplest real-time check. Cleaned metal surfaces should show complete water wetting without breaks for 30 seconds minimum. Any beading or breaks indicate residual hydrophobic contamination.

Surface energy measurement — contact angle measurement or dyne pen testing provides quantitative cleanliness confirmation. A target surface energy appropriate to the adhesive being used should be specified and verified.

Lap shear control specimens — periodic preparation and testing of bonded specimens from production-cleaned parts provides direct adhesion measurement. Declining trends in control specimen strength indicate cleaning degradation before field failures occur.

Incure’s Cleaning Process Guidance

Incure provides degreasing recommendations for specific adhesive applications, including cleaning chemistry selection, process parameter guidance, and verification methods appropriate to the substrate and adhesive combination.

Contact Our Team to discuss degreasing process design for your adhesive bonding application and verify that your current cleaning approach meets the requirements for reliable bonding.

Conclusion

Improper degreasing leaves organic contamination on substrate surfaces, undermining all subsequent preparation steps and producing adhesive bonds that are weak, inconsistent, and prone to early failure. Common degreasing failures include back-wiping, insufficient solvent, inadequate bath maintenance, and poor rinsing. Preventing degreasing-related adhesive failures requires specific, documented cleaning procedures with correct technique, adequately controlled process parameters, and surface energy verification before bonding to confirm that degreasing has achieved the required cleanliness level.

Visit www.incurelab.com for more information.