Industrial environments rarely expose adhesive bonds to benign conditions. Acids, bases, solvents, fuels, hydraulic fluids, cleaning agents, and process chemicals all contact adhesive joints in manufacturing and operational settings. Chemical attack on adhesives degrades performance through mechanisms distinct from thermal aging or moisture damage, and the consequences — loss of cohesive strength, dissolution of the adhesive matrix, interfacial attack — can develop rapidly when the wrong adhesive contacts an aggressive chemical.
Mechanisms of Chemical Attack
Acid and Alkaline Attack
Strong acids and bases are among the most aggressive chemicals for adhesive bonds. Their effects depend on the adhesive chemistry:
Alkaline attack on epoxies — concentrated sodium hydroxide and potassium hydroxide solutions hydrolyze ester linkages in bisphenol-based epoxy systems and attack amine-cured networks, generating polar fragments that swell the adhesive and reduce modulus. Alkaline solutions also strip adhesive from many metal substrates by dissolving the metal oxide layer the adhesive bonds to, creating interfacial failure even in adhesives with good bulk chemical resistance.
Acid attack on polyurethanes — mineral acids cleave urethane linkages and dissolve polyurethane networks at elevated concentrations or temperatures. Even dilute acid exposure over extended time in industrial equipment — pickled metal parts, battery environments, acidic process streams — gradually reduces urethane adhesive strength.
General polymer degradation — extreme pH environments swell polar adhesives, extract plasticizers and low-molecular-weight components, and chemically modify the crosslink network. The resulting adhesive may appear intact but tests at a fraction of original strength.
Solvent Attack
Organic solvents interact with adhesives through two mechanisms: swelling and dissolution. Swelling occurs when solvent molecules diffuse into the adhesive matrix, separating polymer chains and reducing their entanglement and interaction. The adhesive expands, softens, and loses strength without chemical bond breaking. On solvent removal, the adhesive may recover partially, but repeated swelling and drying creates fatigue damage and leaves residual stress.
Dissolution occurs when the adhesive’s polymer backbone is chemically similar to the solvent — “like dissolves like” — and the solvent actively breaks apart the adhesive network or extracts uncrosslinked components. Thermoplastic adhesives are vulnerable to dissolution in appropriate solvents; even thermoset adhesives can be dissolved in sufficiently strong solvents if the crosslink density is low.
In industrial settings, solvent attack is common in adhesive bonds exposed to fuel, oil, paint thinner, cleaning solvents, and processing chemicals. Joints in fuel systems, paint booths, solvent degreasing lines, and chemical processing equipment all face this risk.
Oxidizing Chemical Attack
Strong oxidizing agents — hydrogen peroxide, concentrated nitric acid, hypochlorite bleach, ozone — attack adhesive polymers through a different mechanism from simple acid or base. Oxidizers generate radical species or directly oxidize carbon-hydrogen and other bonds, fragmenting polymer chains and degrading mechanical properties. Chlorine-based sanitizers used in food processing and water treatment, and peroxide-based disinfectants in pharmaceutical and medical device manufacturing, represent practical industrial sources of oxidizing chemical attack.
Silicone adhesives generally have better resistance to oxidizing chemicals than carbon-backbone polymers, though highly concentrated oxidizers attack even silicone. Fluoroelastomer and perfluoropolymer adhesive systems offer exceptional resistance to oxidizing media.
Email Us to discuss chemical resistance requirements for adhesive bonds in your industrial process environment.
Industrial Environments with High Chemical Attack Risk
Food and beverage processing — alkaline clean-in-place (CIP) systems with NaOH concentrations of 1–4% at 70–80°C, followed by acid CIP with nitric or phosphoric acid, subject adhesive bonds to cycling acid and alkali exposure. Joints in equipment housings, conveyor systems, and processing vessels must withstand these cleaning cycles without degrading over thousands of cycles per year.
Chemical processing plants — adhesives used in pipe flanges, equipment housings, and sensor mountings in chemical plants face process streams with specific aggressive chemicals. A joint that is highly durable in an epoxy-incompatible organic solvent may fail within weeks without appropriate chemical resistance assessment.
Automotive underhood and driveline — adhesive joints in engine compartments encounter fuel, engine oil, brake fluid, coolant, and battery electrolyte. Each chemical has a different attack mechanism and rate, and adhesives for this environment must survive contact with multiple chemicals simultaneously.
Offshore and marine — saltwater is not merely saline — it is slightly alkaline, contains dissolved oxygen that drives interfacial corrosion, and is accompanied by biological growth that produces localized acidic conditions. Adhesive bonds in marine structures face combined salt, pH, biological, and mechanical fatigue attack.
Assessing Chemical Resistance
Evaluating adhesive chemical resistance requires coupon immersion testing under representative conditions. The standard approach:
- Prepare adhesive film or lap shear specimens
- Immerse in the target chemical at the service temperature and concentration
- Remove specimens at timed intervals and measure residual mechanical properties
- Compare retained strength (typically expressed as a percentage of dry baseline) versus exposure time
The retained strength versus time curve reveals both the degradation rate and whether the adhesive reaches a plateau (indicating limited chemical attack) or continues declining (indicating progressive dissolution or degradation). For critical applications, testing should extend to the planned service interval and beyond.
Swelling measurement — weighing specimens before and after immersion — provides complementary data. High weight gain indicates significant chemical uptake; dimensional measurement confirms volume change. Adhesives with low swell in a target chemical typically also retain mechanical properties better.
Chemical Resistance Hierarchy
Generalizing adhesive chemical resistance from most to least durable in aggressive industrial chemical environments:
Highest resistance: Fluoroelastomers, perfluoropolymers, ceramic-based adhesives — resistant to acids, bases, solvents, and oxidizers, but limited by low strength or high processing demands
High resistance: High-Tg aromatic epoxies with dense crosslinking — good resistance to aqueous acids and bases at moderate concentration, limited solvent resistance
Moderate resistance: Standard epoxies, phenolics — acceptable resistance to dilute aqueous chemicals, poor resistance to strong solvents and oxidizers
Lower resistance: Polyurethanes, acrylics, polyesters — variable depending on specific formulation, generally more vulnerable to alkaline hydrolysis and solvent attack than epoxies
Incure’s Chemically Resistant Formulations
Incure develops adhesive systems for chemically demanding industrial environments, with formulations designed to maintain strength and adhesion integrity under sustained exposure to specific industrial chemicals. Products are validated through immersion testing protocols against relevant chemicals at service conditions.
Contact Our Team to discuss the specific chemicals your adhesive bonds encounter and identify Incure formulations with validated resistance.
Conclusion
Chemical attack on adhesives in harsh industrial conditions occurs through acid and base hydrolysis of polymer linkages, solvent swelling and dissolution of the adhesive matrix, and oxidative chain fragmentation. The dominant mechanism and severity depend on the specific chemical, concentration, temperature, and adhesive chemistry. Selecting chemically resistant adhesive formulations, validating performance through immersion testing, and designing joints to minimize chemical exposure of the bond edge are the core strategies for maintaining adhesive bond integrity in chemically aggressive industrial environments.
Visit www.incurelab.com for more information.