Accelerated Aging
Key Takeaways
- Elevated temperature compresses the timeline, letting months of testing stand for years of shelf life.
- The Arrhenius relationship underpins it — roughly, each 10°C rise doubles the rate of chemical ageing.
- It cannot accelerate every mechanism. Diffusion, creep and ultraviolet damage do not all scale the same way.
- Real-time ageing runs in parallel and remains the reference; accelerated data supports a claim until real-time data confirms it.
Accelerated Aging
Accelerated aging is the practice of exposing a component to elevated temperature, humidity, or other intensified conditions in order to reproduce in weeks or months the property changes that would occur over years of normal storage or service. In medical device and packaging work it is the standard route to establishing a shelf-life claim without waiting out the claimed period.
The premise is that the chemical processes causing degradation — oxidation,
hydrolysis, plasticiser loss, stress relaxation — proceed faster at higher temperature
in a predictable way. Raise the temperature by a known amount, hold the sample for a
calculated period, and the resulting condition approximates that of a part stored for far
longer at ambient.
The Arrhenius Basis
The calculation rests on the Arrhenius relationship between temperature and reaction rate.
In the simplified form used by ASTM F1980 for sterile barrier systems:
Accelerated ageing time = Desired real time ÷ Q10[(Taged − Tambient) ÷ 10]
Q10 is the factor by which the reaction rate changes per 10°C. A value of 2
— rate doubling every 10°C — is the conventional conservative assumption.
Working an example at Q10 = 2, ambient 22°C and an ageing temperature
of 55°C: the acceleration factor is 23.3, roughly 9.8, so about 37 days at
55°C stands for a year of shelf life.
| Ageing temperature | Acceleration factor (Q10 = 2, ambient 22°C) | Days to represent 1 year |
|---|---|---|
| 40°C | About 3.5 | About 104 |
| 50°C | About 7.0 | About 52 |
| 55°C | About 9.8 | About 37 |
| 60°C | About 14 | About 26 |
Where the Method Breaks Down
Accelerated ageing is a model, and the most expensive mistakes come from treating it as a
simulation. The assumptions that can fail:
- The temperature must not change the mechanism. If ageing temperature
approaches a glass transition or melting point, or crosses a crystallisation threshold, the
sample degrades by a route that would never occur at ambient — and the result is not
conservative, it is simply wrong. - Q10 = 2 is a convention, not a measurement. The real value
depends on the actual activation energy of the dominant mechanism. Where a claim is
critical, it should be determined rather than assumed. - Not every mechanism is thermally activated. Ultraviolet degradation,
mechanical fatigue, creep under sustained load and gas diffusion follow their own kinetics
and are not correctly accelerated by heat alone. - Multiple mechanisms accelerate at different rates, so their relative
contributions shift — a part may fail by one route in the oven and another in the
field. - Humidity has to be controlled deliberately. A hot dry oven dries
hygroscopic polymers and can mask the hydrolysis it should be revealing.
Designing a Defensible Protocol
- Define the failure criteria before starting — the specific
properties, their acceptance limits and the test methods. Deciding what counts as failure
after seeing the data is not a qualification. - Choose an ageing temperature with margin below any transition in the
material. Higher is faster and less trustworthy. - Include the whole system. Age the assembly as it will be supplied,
including packaging, adhesives, inks and printed labels, since interactions between
components are a common failure route that component-level testing misses. - Age after sterilisation, not before, where the product is sterilised,
and include the maximum validated cycle count. Sterilisation changes the material that then
has to survive storage. - Test at intervals, not only at the end. Intermediate points reveal the
degradation trend and show whether failure is approaching gradually or abruptly. - Run real-time ageing in parallel. Accelerated data supports the claim
initially; real-time data confirms it, and regulators generally expect both. - Include the marks and decoration. Where the part carries a
machine-readable code, re-grade it after ageing rather than assuming permanence —
contrast and code grade are properties that age like any other.
What Actually Gets Measured
Ageing itself proves nothing; the properties measured before and after are the study. Which
properties matter depends on how the part fails, so the selection should follow from a failure
mode analysis rather than from habit:
| Property | Why it is measured | Degradation it reveals |
|---|---|---|
| Tensile strength and elongation at break | Elongation usually falls long before strength does | Chain scission, plasticiser loss, embrittlement |
| Impact strength | Often the first property to degrade meaningfully | Embrittlement, and the practical loss of toughness in service |
| Seal or weld strength | The joint frequently ages faster than the parts it joins | Interface degradation, adhesive ageing |
| Dimensional stability | Fit and sealing depend on it | Stress relaxation, continued crystallisation, plasticiser loss |
| Colour and appearance | Frequently a customer-facing acceptance criterion in its own right | Oxidation, ultraviolet damage, additive migration |
| Mark contrast and code grade | A machine-readable identifier that becomes unreadable is a failed part | Contrast loss, substrate yellowing around the mark |
| Barrier and permeation performance | Governs the shelf life of what is inside the package | Microcracking, layer delamination |
Measure a baseline at time zero from the same lot. Comparing aged samples against datasheet
values rather than against their own unaged controls is a common way to produce a result that
cannot be defended.
Related Terms and Reading
- Environmental stress cracking
- Engineering services and validation support
- Pharmaceutical and medical manufacturing
- Measuring adhesion and abrasion durability of coatings and inks
Applying this in production
The Sabreen Group provides independent engineering support for accelerated aging protocol design, shelf-life qualification and materials validation. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
How is accelerated aging time calculated?
From the Arrhenius relationship, in the simplified form given in ASTM F1980: real time divided by Q10 raised to the power of the temperature difference over ten. With the conventional Q10 of 2, ambient of 22°C and ageing at 55°C, the acceleration factor is about 9.8, so roughly 37 days represents a year of shelf life. The convention is deliberately conservative rather than precise.
What can accelerated aging not predict?
Anything that is not thermally activated in the same way. Ultraviolet degradation, mechanical fatigue, creep under sustained load and gas diffusion each follow their own kinetics and are not correctly accelerated by heat alone. Where several mechanisms operate, they accelerate at different rates, so their relative contributions shift and a part can fail by one route in the oven and a different one in the field.
Why does the ageing temperature need margin below the glass transition?
Because above or near a transition the polymer degrades by a route that would never occur at ambient temperature, which makes the result invalid rather than merely conservative. Chain mobility, crystallisation behaviour and diffusion rates all change across a transition. Choosing a lower temperature and a longer exposure is the safer trade whenever the margin is uncertain.
Should parts be aged before or after sterilisation?
After, and at the maximum validated cycle count. Sterilisation — whether steam, gamma or ethylene oxide — changes the material, and it is the sterilised material that then has to survive storage. Ageing an unsterilised part answers a question nobody asked. The same logic applies to any process step that alters the material before it enters its shelf life.
Does accelerated aging replace real-time testing?
No. It supports a shelf-life claim while real-time data is being generated, and regulators generally expect both, with real-time ageing running in parallel from the outset. Accelerated results are a model-based prediction; real-time results are the observation the model was predicting. Where the two diverge, the real-time data governs.
