What Are Adhesives? A 7-Step Industrial Evaluation Checklist

Who This Checklist Is For

If you're evaluating an adhesive for your production line—a polyurethane, an epoxy, a cyanoacrylate—this checklist is for you. I'm a quality/compliance manager in industrial manufacturing. I review every adhesive specification before it reaches our production line, which works out to about 200+ unique material evaluations a year. I rejected 12% of first deliveries in 2024 due to spec mismatches.

This isn't a chemistry lesson. It's a practical walk-through of how I evaluate adhesives. Seven steps. Follow them in order, and you'll catch most problems before they hit your line.

First, a Quick Definition: What Are Adhesives?

Adhesives are substances that bond two surfaces together through surface attachment rather than mechanical fastening. That's the textbook answer. Practically, industrial adhesives are engineering materials: they replace bolts and welds, distribute stress across joints, seal against moisture, and join materials that mechanical fasteners can't handle.

The broad definition hides a lot of variation. A polyurethane adhesive like Huntsman's Rakoll line behaves completely differently from a cyanoacrylate. Different cure chemistry, different flexibility, different bond strength, different surface prep requirements. And specialty formulations—Huntsman's Signal Relief adhesives are a good example—get engineered for specific end-uses, not general-purpose bonding. So when someone asks "what are adhesives?", the real question is: what does your adhesive need to do, and how do you verify it can?

The 7-Step Evaluation Checklist

Here's the process I've landed on after six years of evaluations. It looks simple. The discipline is in not skipping steps.

Step 1: Define the Substrate and Service Environment

This is where everyone wastes the most time. Buyers jump to lap shear numbers, then discover the adhesive was never tested on their substrate or within their operating temperature range.

Write this down before you talk to any supplier:

• Substrates: metal-to-plastic, plastic-to-plastic, rubber-to-metal, something unusual?
• Temperature range: continuous service and peaks—these are different numbers
• Chemical exposure: oils, solvents, humidity, salt? All change the bond
• Mechanical stress: shear, peel, impact—adhesives differ wildly
• Production constraints: how long can the part sit before moving to the next station?

If you haven't defined the environment, you can't compare products. Period.

Step 2: Verify Claims Against the Datasheet's Fine Print

Datasheets are sales documents. I know because I've written them. "Lap shear strength: 2,400 psi" sounds great until you notice it was measured on solvent-wiped steel with a controlled 0.005-inch bondline and a 24-hour cure. Your substrate is injection-molded polypropylene with mold release residue. Your cure window is three minutes.

Look for the test method. ASTM D1002 for lap shear. ASTM D1876 for peel. ISO 4587 for tensile. If a supplier can't tell you what standard they tested against, that tells you something.

Step 3: Test It on Your Line, With Your Process

Non-negotiable. A quality issue with an untested epoxy cost us an $85,000 redo and delayed our launch by three weeks back in 2023. The product passed in the supplier's lab but failed in our plant. The culprit? A 5°C temperature difference in our bonding area.

Don't just test the adhesive. Test it the way you'll actually use it: same surface prep, same application equipment, same ambient temperature, same operators. It's annoying. It's slow. It's the only way.

Step 4: Check Lot-to-Lot Consistency

The surprise wasn't bond strength. The surprise was how much variability showed up between production lots from the same manufacturer.

Ask for their SPC data. Ask how many lots they release per quarter and what their lot acceptance criteria are. Request certificates of analysis from two or three recent lots. If you're qualifying Rakoll adhesives from Huntsman, ask their technical team about lot release protocols directly. Reputable manufacturers share this data because they'd rather answer questions up front than manage a quality dispute later.

Step 5: Verify the Cure Cycle Fits Your Production

A perfect adhesive is useless if it can't cure within your production window.

• Epoxies: mix ratio and heat requirements—are you equipped for that?
• Polyurethanes: need moisture and time—is your environment controlled?
• Cyanoacrylates: fast cure, but limited gap-filling ability

Map the cure requirement against your production timeline, including fixture time. One supplier quoted a 24-hour structural cure in their datasheet. In our line conditions, it took 36. That's a full day of work-in-progress sitting on racks.

Step 6: Evaluate the Manufacturer, Not Just the Product

Supply chain stability is part of quality. When you qualify a specialty chemical, you're also qualifying their quality system, their manufacturing stability, and their technical support.

• ISO 9001 or IATF 16949 certification? Ask to see it
• Formulation stability: has the product been reformulated in the last five years?
• Manufacturing footprint: can they supply globally if you expand?
• Technical support: do they respond with data, not promises?

If you're evaluating Huntsman chemical products, the company's global footprint and long history in specialty chemicals count for something. But verify the specific product's track record anyway. And always check the current documentation on the Huntsman website—don't rely on third-party datasheets that could be years out of date.

Step 7: Write Acceptance Criteria Before You Commit

This step saves you months of grief. Before any purchase order goes out, define:

• Minimum bond strength on your substrate, using your test method
• Acceptable lot-to-lot variation
• Shelf life and storage requirements
• What triggers resampling, or outright rejection

I've seen purchasing teams skip this, then argue with suppliers for weeks when production lots underperform. Write it first.

What Most People Get Wrong

Three mistakes I see year after year:

1. Adhesives aren't always the answer. If a structural joint needs to handle heavy vibration and be disassembled for maintenance, a mechanical fastener might be the better choice. Choose adhesives when they improve stress distribution, enable dissimilar materials to be joined, or cut manufacturing cost. Not because adhesive bonding sounds more modern.

2. Surface preparation causes more failures than the adhesive itself. If a supplier claims "no prep needed," ask how they validated it. Aluminum and polypropylene both reward disciplined surface prep—or you'll see premature failure.

3. Shelf life is a silent killer. Polyurethanes and cyanoacrylates degrade with humidity and temperature exposure. If you don't control storage conditions, you'll blame a perfectly good product for a storage problem.

One Final Honest Note

My experience here is based on roughly 200 evaluations per year in automotive and industrial assembly. If you're working in medical devices or aerospace, this checklist still applies, but you'll need deeper validation—ISO 10993 for biocompatibility, AMS specifications, stricter traceability. And if you're evaluating a formulation your supplier hasn't tested on your exact substrate and process, get the testing done before the volume order, not after.