How temperature and viscoelasticity determine the performance of envelope sealing strips

When an envelope closes, we expect one simple outcome: it stays closed.

Yet what happens at the microscopic level is anything but simple. The adhesive layer in a sealing strip must be tacky enough to bond instantly, while also remaining strong and stable as temperature and mechanical load change.

In this study, three commercially applied envelope sealing strips were investigated to understand exactly how they behave.

Using Dynamic Mechanical Analysis (DMA) and rheological pull-off testing, their performance was evaluated between –10 °C and 30 °C, a temperature range commonly encountered during storage, transport and use.

The three materials — referred to here as Sample 1, Sample 2 and Sample 3 — were tested under identical conditions, allowing meaningful comparison of both their intrinsic material properties and their real-world adhesive performance.

Why DMA and pull-off testing?

Adhesives are not simple solids. They are viscoelastic materials, meaning they behave partly like elastic solids and partly like viscous liquids. Their performance therefore depends strongly on temperature and deformation rate.

DMA allows this transition from glassy (hard and brittle) to rubbery (soft and tacky) behavior to be quantified through:

• Storage modulus (stiffness),
• Loss modulus (energy dissipation),
• Tan delta (the ratio of the two, indicating viscoelastic balance).

Pull-off testing adds a practical dimension by measuring how much force is required to detach the adhesive and how the material deforms and fails during separation.

Together, these techniques provide a powerful link between material physics and functional adhesion.

What DMA reveals about the three adhesives

The first clear outcome is that Sample 2 is fundamentally different from Samples 1 and 3.

DMA shows that Sample 2:

• has higher and broader glass-transition (Tg)
• exhibits a higher stiffness (storage modulus) across the entire temperature range,
• and shows a smaller Tan-delta peak, indicating a weaker viscoelastic response.

Samples 1 and 3, by contrast, display similar Tg ranges and a more pronounced transition from glassy to rubbery behavior.

In practical terms this means:

• Sample 1 undergoes the strongest transition and becomes highly tacky above Tg,
• Sample 3 follows closely,
• Sample 2 remains relatively stiff even at elevated temperatures.

From DMA alone, adhesion above Tg would therefore be expected to rank as:

Sample 1 > Sample 3 > Sample 2.

This prediction is then tested directly using pull-off measurements.

What happens when the adhesive is pulled apart?

Using a controlled rheometer-based pull-off test, each adhesive was evaluated at 30 °C, 20 °C, 10 °C and –10 °C. The measurement captures not only peak force, but also how the adhesive stretches, strain-hardens and finally releases.

Sample 1 – Consistent and balanced

Sample 1 shows remarkably stable behavior across the full temperature range.

• At 30 °C and 20 °C it is clearly tacky and viscous, with strong strain-hardening and long pull-off distances.
• At 10 °C the same characteristics remain.
• Even at –10 °C the adhesive still exhibits viscoelastic deformation before release.

Crucially, no delamination of the cardboard substrate is observed. The adhesive remains strong while still able to dissipate energy through deformation.

Sample 2 – Strong but overly stiff

Sample 2 behaves very differently.

• At 30 °C it is already relatively stiff and releases sooner.
• At 20 °C this stiffness increases.
• At 10 °C and –10 °C, failure no longer occurs in the adhesive but in the cardboard itself, which begins to delaminate.

This indicates that the adhesive becomes so stiff that it can no longer accommodate strain through deformation. Instead, the stress is transferred directly to the substrate, causing it to fail.

Sample 3 – Stable until a critical temperature

Sample 3 performs consistently between 30 °C and 10 °C, showing similar strain-hardening and release behavior.

At –10 °C, however, strain-hardening disappears and substrate delamination is observed, signaling a transition to a more brittle, glass-like state.

Bringing DMA and pull-off together

When the two techniques are combined, a coherent picture emerges.

Sample 1

Its glass-transition temperature lies within an optimal range for the tested conditions.

This allows it to:

• generate strong initial tack,
• dissipate stress through viscoelastic deformation,
• and release cleanly without damaging the substrate.

Sample 2

Its higher Tg and higher stiffness make it less tacky at room temperature and excessively rigid at lower temperatures, leading to substrate failure rather than controlled adhesive release.

Sample 3

Performs well in moderate conditions but crosses a critical stiffness threshold at –10 °C, where its ability to dissipate stress is lost.

Why this matter

In real applications, adhesive performance is not just about bond strength. It is about the entire system:

• the adhesive,
• the substrate,
• and the operating temperature.

A formulation that is too stiff can be just as problematic as one that is too soft. In cold environments, excessive stiffness leads to brittle behavior and substrate failure. In warmer conditions, insufficient stiffness leads to premature release.

This study shows how DMA and rheological pull-off testing together provide a powerful predictive framework. DMA defines the material’s viscoelastic landscape, while pull-off testing reveals how that landscape translates into real-world adhesion.

Conclusion

Across the investigated temperature range:

• Sample 1 offers the most consistent and robust adhesive performance,
• Sample 3 performs well between 30 °C and 10 °C,
• Sample 2 is the most temperature-sensitive, with substrate failure at lower temperatures.

In envelope sealing — and in many other adhesive applications — success is not driven by maximum stiffness, but by the right balance between tack, elasticity and energy dissipation.

That balance is exactly what advanced materials testing is designed to reveal.