Supplier Reformulated Your Adhesive: Requalify, Accept or Switch?

This answer covers a supplier-initiated change to an adhesive that is already qualified in your production. It does not cover choosing a new adhesive, or joints whose material is fixed by an outside approval body, such as an aerospace or medical device approval, where that body's change rules decide.

Which conditions decide whether to accept or requalify a reformulated adhesive?

Three conditions decide whether to accept or requalify a reformulated adhesive: what changed in the formulation, whether the supplier's data was produced on a joint like yours, and whether your own customer approved the joint with the old material. A fourth condition, time, decides whether you need old stock while you wait.

What changed sets the size of the risk. A second source for a raw material with the same CAS number and specification leaves the chemistry nominally unchanged. A cut in a minor additive changes the chemistry slightly; in Henkel's 2022 notice, the reduced stabilizer "represents a small percentage of the products' overall formulations" (Henkel, 2022). A change to the resin, hardener, filler or cure profile can change strength, durability and how the adhesive handles on your line.

Your customer's approval can override your own judgment. One automotive supplier manual, restating Groupe PSA requirements under IATF 16949 section 8.5.6.1, requires the supplier to carry out an impact study of a product or process change on product performance, the ability to produce in conformity and production capacity (SMR, 2021). If a requirement like this covers your part, a reformulated adhesive is your change to report, even though your supplier made it.

What does an adhesive change notification have to tell you?

An adhesive change notification has to tell you what changed, why, from when, which products and ordering numbers are affected, what testing supports the claim of unchanged performance, and how old and new material will overlap in your deliveries. Without those six items, you cannot place the change in the decision table below.

Henkel's 2022 notice is a useful public example. It names the reason, an upcoming labelling change under the EU CLP Regulation; lists the affected products; gives an expected start "most likely Q2/Q3 2022"; says product names stay the same but ordering numbers may change; states that the Safety Data Sheet will be updated; and warns of "a period of overlap where you may receive packages of both the new and old formulations" (Henkel, 2022). On testing, it says only that the new formulations are being tested against Henkel's own quality specifications and that side-by-side data will be shared when available and on request (Henkel, 2022).

The table below checks a notification before you act on it.

The key row is the first: if the notification does not say which ingredient changed, you cannot tell a second source from a resin change. For how the supplier side should weigh such a change, see How do you assess supplier risk when changing a raw material?.

Does the supplier test data cover your bonded joint?

Supplier test data covers your bonded joint only when it was produced on your substrate, with your surface preparation, bondline, cure and service environment. Most reformulation data compares the new adhesive with the maker's own product specification, which is a different question from whether your joint still performs.

The standard lap-shear methods say so directly. ASTM D1002-10(2019), the active edition for metal-to-metal lap shear, states that "the apparent shear strength of an adhesive obtained from a given small single-lap specimen may differ from that obtained from a joint made with different adherends or by a different bonding process" (ASTM D1002-10(2019)). The same method describes itself as "primarily comparative" and useful as a discriminator for surface preparation and adhesive environmental durability (ASTM D1002-10(2019)). ISO 4587:2003, the current edition of the rigid-to-rigid lap-shear method, states that the test procedure "does not provide design information" (ISO 4587:2003).

Read the supplier's data against four questions. Was it measured on your substrate class, such as the same alloy, plastic or coating? Was the surface prepared as you prepare it? Were old and new formulations tested side by side in the same run? Did it include aging at the heat, humidity or chemicals your joint sees? A "no" to any of these leaves that part of your joint untested, and that part is what your own requalification has to cover.

Which reformulated adhesive changes call for acceptance, requalification or a switch?

A reformulated adhesive can be accepted when the chemistry is nominally unchanged and data on your substrate supports it, needs requalification when the resin, hardener, filler or cure profile changes, and calls for a second source when the supplier gives no data in time.

The table matches the situation to a choice.

The row that catches most buyers is the fourth: an approval your customer gave covers the material you used at the time, so a supplier's assurance that performance is unchanged does not replace your customer's own sign-off.

Switching suppliers is not free of risk either. An alternate adhesive needs the same requalification as a resin change, so a switch is a choice for when the current supplier withholds data or timing, not a shortcut around testing. Whatever the choice, record the decision, the data it rested on and the first lot of the new formulation, so a later joint failure can be traced to the formulation that was in it.

How much requalification does a reformulated adhesive need?

A reformulated adhesive needs enough requalification to show that strength, failure mode and durability on your joint match the old formulation, scaled to what changed. For a resin, hardener, filler or cure change, that means a side-by-side lap-shear comparison on your substrate and an aging test matched to your service environment.

Test old and new formulations in the same run, with your substrate, preparation and cure. Sika's structural bonding guideline says the first check normally determines strength and adhesion "on actual substrates at expected application conditions" (Sika, 2022). Compare more than the average: Sika states that failure mode evaluation is always accompanied by measurements of actual strength and relative standard deviation, which must be compared to application specifications (Sika, 2022). The same mean strength with a shift from cohesive to adhesive failure is still a change.

Add aging when your joint sees heat, moisture or chemicals. Sika's reference conditions include a cataplasma exposure at 70 °C and about 98 % relative humidity for 30 days and the DVS 1618 cycle of 22 days (Sika, 2022). Sika also cautions that "no accelerated aging cycle can guarantee comparable results to any years of service life" (Sika, 2022), so compare old and new under the same cycle rather than reading the result as a lifetime.

Finish with a line trial for handling: dispense, open time, fixture time and cure on your equipment. Read the updated SDS before that trial, because the supplier may have revised the hazard information along with the formulation.

Should you build stock of the old adhesive formulation?

Build stock of the old adhesive formulation only when your requalification results will arrive after the old material runs out, and only as much as you can use within its shelf life. Old stock buys time; it does not remove the need to qualify the new formulation.

Estimate the gap first. Count the weeks requalification needs, including aging and your customer's review, against the date the old formulation stops shipping. Customer reviews can be long: one automotive electronics guideline projects a through-put time of 12 weeks for a component-level change and 20 weeks for a board-level change, from delivery of the notice to closure (ZVEI, 2024). For example, a 30-day aging test followed by a 12-week customer review needs close to four months of supply before any retest (illustrative).

Shelf life sets the ceiling. Check the shelf life and storage conditions in the old formulation's technical data sheet, and do not buy more than you can use before the earliest expiry. In Henkel's example, the ingredient being reduced was a shelf-life stabilizer (Henkel, 2022), so check shelf life in the new material too.

Watch the overlap. When product names stay the same and ordering numbers may change (Henkel, 2022), the label alone may not tell you which formulation you received, so record the lot on every receipt. In Lubinpla, a feasibility review sets accept, requalify, switch supplier and keep old stock as fixed options and compares, scenario by scenario, the risk that qualification results arrive late.

What should you ask the adhesive supplier about the reformulation?

Ask the adhesive supplier the questions that let you place the reformulation in the decision table: what changed and why, what was tested and how, and when and how the new material will reach you. Ask in writing and keep the answers with your qualification record.

1. Which ingredient changed, what does it do in the formulation, and does its CAS number or specification change?

2. Which properties were tested on the new formulation, on which substrates, at which temperatures and after which aging?

3. Can you send side-by-side data for old and new formulations from the same test run? Henkel's notice, for example, offered such data "as soon as available and upon request" (Henkel, 2022).

4. From which lot or date does the new formulation ship, and how is it marked on the label and certificate of analysis?

5. How long will the old formulation stay available, and can you reserve a quantity within its shelf life?

6. When will the updated SDS and technical data sheet be issued, and do any approvals or listings you rely on change?

A supplier that cannot answer the first two questions has given you no basis to accept the change. Treat the reformulation as a requalification case and, if the timing does not allow it, start qualifying an alternate source.