When a clear hot-melt adhesive starts turning yellow, it can look like a product-quality issue even if performance is still “fine.” Here’s how an adhesive extender oil change helped one adhesive maker keep their product clearer over time.
Processing problems in adhesives don’t always show up as a line stoppage. Sometimes it’s a “slow burn” issue, like color drift, haze, odor changes, or complaints that only appear after storage.
In this case study, we share a real-world example (with details generalized) that shows:
- What the customer noticed
- What we tested
- What changed
- The results
Adhesive & sealant makers represent a $22 billion industry employing over 28,000 people here in North America alone. We’re here to help them and other process oil buyers understand how the choice of extender oil can make a big difference in end-product quality.
Suzanne Kingsbury, Director of Quality
The Problem: Yellowing In a Clear Hot-Melt Adhesive
Our customer produced a clear hot-melt adhesive that includes mineral oil as an extender to modify viscosity. They were noticing their clear hot melt yellowing over time.
It wasn’t just a cosmetic nuisance. This was a product that needed to stay clear for appearance-driven applications.
A few common questions came up right away:
- Did anything change in storage time, temperature, or packaging?
- Was the base polymer the same lot-to-lot?
- Did any tackifier, antioxidant, or adhesive extender oil source change?
The customer’s goal was simple: keep the adhesive clearer, longer, without creating new processing issues.
The Most Common Root Cause: Aromatics and “Color Drift”
Before we jump into testing, it helps to understand what often drives yellowing in clear adhesive systems.
In many adhesive formulations, yellowing is linked to trace components that are more reactive over time, especially when exposed to oxygen, heat, or light. One category that frequently matters here is aromatic content.
Aromatics, which can include trace compounds that tend to oxidize easily, are more reactive than more stable components. Over time (and especially with exposure to oxygen), they can contribute to gradual color formation, or what many people experience as yellowing.
That’s why, when the problem is “my clear adhesive isn’t staying clear,” the potentially reactive components in the adhesive extender oil used in production is a smart place to look.
The Diagnostic Step: Measuring UV Absorption
Rather than guessing, we reviewed extender oil options and used a simple screen: ultraviolet (UV) absorption testing.
UV absorption is commonly used as an indicator related to aromatic content:
- Higher UV absorption indicates more aromatic character.
- Lower UV absorption generally suggests a more saturated, more stable oil profile, which is key when the goal is better color stability.
This doesn’t replace full performance testing, but it’s a practical way to narrow the field quickly when yellowing is the complaint.
The Solution: A Higher-Quality Group II Process Oil With Low UV Results
After reviewing options, we recommended moving to a higher-quality process oil with a low UV and low aromatic content test result.
Specifically, the customer selected an API (American Petroleum Institute) Group II process oil option that:
- Met the customer’s technical requirements.
- Targeted lower UV absorption (supporting improved color stability).
- Fit the application need for an adhesive extender oil in hot-melt formulation work.
In plain terms: we aimed to reduce the “reactive tendency” in the extender oil portion of the formula so the adhesive had a better chance of staying clear over time.
Validation: Samples Tested, Then the Switch
As always, the customer tested samples in their own process and formulation. After confirming the performance and the improvement direction on color stability, they switched to our oil for ongoing production.
That in-house testing on the customer’s own line matters. Color issues can be affected by more than one variable, so we always want the customer to validate the full system (polymer + tackifier + additives + process conditions) rather than relying on a single lab value.
A Practical Checklist If Your Clear Adhesive Is Yellowing
If you’re seeing yellowing in a clear hot-melt or other clear adhesive product, here’s a simple way to pressure-test the likely causes.
Start with the basics. Make sure you review:
- Any recent raw material changes (including your adhesive extender oil)
- Storage time and temperature history (both raw materials and finished goods)
- Exposure to air (headspace) and light during storage
- Additive package and treat rates (especially stabilizers and antioxidants)
Then, when the extender oil is a suspect, it can help to compare:
- UV absorption results across candidate oils
- Your current oil’s consistency (lot-to-lot) and documentation
- Oil quality level (for example, moving to a more saturated profile when clarity matters)
Adhesive Extender Oil: How Renkert Oil Can Help
When customers call us about processing problems like yellowing, we don’t just “quote a product.”
We help you narrow the variables, compare options that fit your specs, and move fast on sampling so you can protect your product quality without risking new headaches on the line.
If you’re troubleshooting a clear adhesive issue (or you want to prevent one), Renkert Oil can help you choose an adhesive extender oil that supports the performance and the stable appearance your customers expect.
Want to talk through your issue? Reach out to Renkert Oil to discuss your formulation needs, sampling options, and supply reliability for specialty oils.
FAQs: Adhesive Extender Oil
1) What is an adhesive extender oil?
An adhesive extender oil is a specialty oil blended into many adhesive formulas to help with processing and performance, such as flow, tack, and consistency.
2) Why would a clear hot-melt adhesive start turning yellow?
Yellowing is often linked to trace components that react over time, especially with exposure to oxygen, heat, or light, which can slowly create visible color.
3) Is yellowing always a sign the adhesive is failing?
Not always. Performance can still be “fine,” but the appearance change can still create quality concerns for clear or appearance-driven products.
4) What ingredients should we review first when troubleshooting yellowing?
Start by checking whether anything changed with the base polymer, tackifier, antioxidants, or the adhesive extender oil, plus storage time, temperature, and packaging.
5) What are “aromatics,” and why do they matter for color stability?
Aromatics are a type of unsaturated hydrocarbon that can include compounds more likely to oxidize, which can contribute to gradual color formation over time.
6) What is ultraviolet (UV) absorption testing, and what does it tell you?
UV absorption testing is a quick screen that can indicate aromatic character—higher UV absorption often suggests more aromatics, while lower values can suggest a more saturated (paraffinic) profile.
7) Does a low UV absorption result guarantee the adhesive won’t yellow?
No. It’s a helpful way to narrow options, but full in-house testing is still important because many variables can affect color.
8) Why might an API (American Petroleum Institute) Group II oil help reduce yellowing?
API Group II oils are typically much more saturated, making them more stable and can show lower UV absorption, which may support improved color stability in clear formulations.
9) What’s the right way to validate a new adhesive extender oil?
Run samples through your actual formulation and process conditions, then evaluate both performance and appearance over time before switching.
10) How can Renkert Oil help if we’re dealing with yellowing or color drift?
We can help you narrow the likely causes, compare extender oil options that fit your specs, and move quickly on sampling to reduce risk and protect product quality.