# Bringing Shelf-life Testing to the Production Line

- Link: https://flexitest.in/blogs/bringing-shelf-life-testing-to-the-production-line/
- Published: 2025-05-07T12:57:12+05:30
- Author: flexitest

# Bringing Shelf-life Testing to the Production Line

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 3. Bringing Shelf-life Testing to the Production Line

Source: Agr International, Inc. — “Bringing Shelf-life Testing to the Production
Line” (© 2014).

As soon as the bottle is filled and capped, the countdown begins. Single layer PET
bottles, though they appear to be impermeable, are slightly porous, and over time
CO_(2) escapes and/or O_(2) permeates through the material. How fast this process
happens determines the “shelf-life”.

In today’s fast-paced environment, it can take less than an hour from preform to
case packer. Products show up on the grocer’s shelf within a few short days. Bottles
that under perform with regards to shelf-life can affect a consumer’s experience,
impact future sales and ultimately damage the brand image. With the trend for bottle
self-manufacture by brand owners and increased emphasis on light weighting, bottle
shelf-life properties are increasingly impacted by the production process. Faster
production processes with lighter bottles dictate a new approach towards shelf-life
management. One such approach is the M-RULE^(®) container performance model for 
analyzing shelf-life in PET beverage bottles. The M-RULE model is notable because
of the speed of the tests, and the reproducibility of the result, all at a significantly
lower cost than traditional methods.

## Are all PET Bottles of the Same Design Alike?

When a bottle is designed, considerable effort is put into optimizing the mechanical
and aesthetic properties of the container. For a given bottle design, the shelf-
life is primarily determined by the surface area and effective thickness of the 
package sidewall, which in turn determines the weight of that package. Because cost
is a key objective, the package weight is usually the minimum needed to achieve 
the targeted shelf-life. In theory, if you get everything right and every bottle
is produced by a uniform process, then every bottle should exhibit the same shelf-
life properties. In reality, this is not the case. Variations that affect the bottle
blowing process continually occur. Differences in preform moisture content and temperature,
material properties, blow molder anomalies, plant environmental changes, operator
experience… to name a few, all impact material distribution and affect sidewall 
thickness, the property that is so crucial to shelf-life performance.

Why is this so critical now? In the past, variations in the blowing process were
masked by heavy sidewalls and extra material. Bottles were over-engineered, and 
their shelf-life exceeded the minimum targets. As a result, minor variations in 
material distribution had no impact on product quality. Light weight bottles are
the game changer. The processing window on a light weight bottle is very narrow,
and the target shelf-life is achieved only in bottles with optimal material distribution.
Minor deviations in material distribution and wall thickness that normally would
have little impact in the past, now can result in significant production that does
not meet shelf-life specifications.

With the reality of variability in the process inputs, the only way to ensure consistency
in shelf-life is to tightly control, monitor and continually adjust the blowing 
process. And, by pro-actively managing variations in material distribution and thickness,
shelf-life performance can be managed as part of this process. However, even with
the various process monitoring techniques in practice today, shelf-life is one aspect
that is not typically incorporated into the routine process monitoring and response
programs. This is because, until recently, monitoring shelf-life properties on the
production floor has not been a simple matter.

Traditional shelf-life testing methods can take as long as 8–24 weeks, hardly practical
when timely and accurate data is necessary to make process related decisions. Furthermore,
these tests require intensive laboratory preparation prior to testing, continual
monitoring and attention during the test, and have limitations that can result in
testing inaccuracies. Variations in bottle to bottle dosing, fill level, temperature
control of the testing environment and so forth affect test results, making it difficult
to predict shelf-life with confidence using these methods. “There are a lot of things
you can do to compromise a CO2 test…. It is sometimes like throwing dice” claims
a bottle development engineer at a major beverage producer.

## An Alternative to Traditional Shelf-life Testing using the M-Rule Model

Container Science Inc, Atlanta GA, offers a very tangible solution to the shelf-
life dilemma with its M-RULE container performance model for analyzing shelf-life
in PET beverage bottles. Commercially available since 2002, the model has been validated
repeatedly by brand owners, converters and technology developers. This model overcomes
the variability of traditional testing by providing a means to evaluate bottles 
using standardized data, testing and environmental conditions, resulting in a very
repeatable method. And, with results available within seconds, it overcomes the 
critical issue of timeliness.

The M-RULE container performance model for beverages is a web based predictive tool.
It operates by integrating the fundamentals of permeation with critically evaluated
physical data for the materials in a given package (bottle and closure) and other
pertinent data affecting the permeability of a container, such as temperature and
pressure.

The M-RULE model takes into account a host of parameters and bottle attributes as
part of the shelf-life determination, such as surface area, material distribution(
wall thickness), base design, filling conditions, storage and distribution conditions,
etc. The impact of material properties such as construction of the sidewall, resin,
orientation of the material, crystallinity, the modulus of the resin and scavenging
activity can also be tested. The model simultaneously predicts CO_(2), O_(2), N_(
2), and H_(2)O permeation based on first-principles calculation of the diffusion
and solubility of these gasses, along with the impact of stress, temperature, crystallinity
and modulus on these parameters. For this reason, the model can accurately predict
bottle performance under a wide range of conditions. Package-specific performance
is determined by applying bottle parameters such as surface area, weight, base design,
finish, volume and filling conditions. All calculations include the impact of the
closure on package performance. Below are three examples of the model’s predictive
capability vs. two different traditional test methods.

When specific bottle/package details are entered into the model, a very accurate
determination of shelf-life can be made. This is accomplished without the influence
of many of the issues that compromise the results of traditional tests such as:

 * Precision of initial test carbonation
 * Test control parameters and precision over the specified time
 * Storage and transportation temperatures
 * Sample handling
 * Length of the test and timeliness of data

With the M-RULE model these items are non-issues. Every test is performed to the
exact same conditions and testing protocol. Any difference in test results is a 
direct reflection of the shelf-life performance of the container, not the test conditions
or testing procedures.

A major advantage of the model, is that it can be used to determine the performance
of a given bottle design under a myriad of conditions or scenarios. How will this
bottle perform at 30^(o)C vs. 22^(o)C? Would the performance change if a different
brand or type of material was used? How is shelf-life affected if the bottle was
light-weighted by 0.5 gram or 1 gram?

Scenarios like these can easily be evaluated, and shelf-life performance identified
well before any investment is made in bottle production.

The M-RULE model is currently relied upon by major brand owners all over the world
to critically analyze designs for proper shelf-life performance characteristic prior
to prototyping and manufacture. Because of its comprehensive nature, it allows designers
to test and optimize designs before committing to actual production. It is also 
a valuable tool for determining the effect of minor changes to a bottle due to light
weighting and how those changes will affect the shelf-life performance. Further,
it can be used for assessing whether a package is over or under engineered and how
it will perform for any defined set of filling, storage or distribution conditions.

## Accuracy of the Model

The M-RULE model has been tested in a number of scenarios and results are identical
to traditional real-time tests, within the inherent error limits of those tests.
Where the M-RULE model excels is in the speed of the test and reproducibility of
the results.

These validation tests confirm the accuracy of the M-RULE Model in predicting CO_(
2) Shelf-Life. Other validation results show similar performance for oxygen ingress,
nitrogen loss, and water loss.

## Bringing the M-RULE Model to the Plant Floor

The M-RULE model offers a viable alternative to traditional testing, for both research
and design laboratories and production quality testing. Realizing the potential 
for M-RULE on the plant floor, Agr International, through an exclusive agreement
with Container Science, Inc., has incorporated the M-RULE container performance 
model into the [PPT3000^(TM)](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/)
Packaging Pressure Tester, a device that is routinely used by PET bottle makers 
to verify quality and performance of bottles on a regular basis during production.
By incorporating the M-Rule model into this device, it is now possible to bring 
shelf-life testing to the plant floor and take advantage of the accuracy, reliability
and precision of the model, and most importantly the availability of immediate results.

With this capability in the [PPT3000](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/),
it is possible to get quick and accurate feedback on material utilization and shelf-
life performance of newly blown bottles at the time and point of production.

## How the PPT3000 M-RULE Works

The[ PPT3000](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/)
with M-RULE works on the premise that if every bottle were identical, the shelf-
life would equally be identical. However, if one parameter changes then the shelf-
life would also change. Given that the wall thickness is the most critical parameter
for shelf-life, the wall thickness parameter is used as the variable. Any change
in wall thickness is reflected in the shelf-life results.

During a test, the bottle is pressurized to a pre-defined level. The volume expansion
and corresponding material thickness is captured when pressurization reaches the
appropriate level. The average material thickness on a bottle under test is automatically
entered into an embedded version of M-RULE model created for that bottle. The model
is seamlessly run with every PPT3000 test. With all other parameters in the M-RULE
unchanged, variations in volume expansion and the related thickness values reflect
changes in shelf-life. If thickness distribution changes over the course of bottle
production, routine tests with the [PPT3000](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/)
will identify any corresponding changes in shelf-life.

Different bottle designs are handled by the creation of unique “jobs” created by
Agr using the M-RULE laboratory version. These contain information on bottle design,
material type, surface area, finish, closure and other input data required to determine
shelf-life in the M-RULE model. These are stored on board the PPT3000 and can be
quickly called upon to test different bottle types produced within a plant or as
production changes.

The PPT3000 with M-RULE offers a practical method for testing shelf-life that takes
less than 60 seconds per bottle, requires no special preparation and can be performed
in the laboratory or on the production floor. This makes it possible to routinely
sample and test production bottles on a regular basis for proper shelf-life. The
real advantage of this system is that it can be used as a production tool to verify
that bottles meet shelf-life standards, and most importantly, identify compromising
issues when they are happening, not days or weeks later. Test results are displayed
on the PPT3000 system’s user interface in the form of shelf-life and percent material
utilization. This information can also be exported to a laboratory or plant data
system. In the event that shelf-life targets are not per specification, intervention
can occur immediately to correct the problem and get the process back on track.

## The Value of Shelf-life Management on the Plant Floor

Changes in shelf-life performance can occur quickly on today’s high-speed production
lines. Whether process changes have a minimal or a major effect on shelf-life is
only a guessing game unless regular testing is performed. Having visibility of the
effect of these variables on shelf-life at the blow molder (point when bottles are
blown) gives you better ability to control shelf-life for your finished product.

There is real value of doing shelf-life analysis near the line or in the bottle 
production lab. By doing so, you get an immediate sampling of container (shelf-life)
performance which is the direct result of current plant conditions and process variations
at the time.

The feedback gained can be used in multiple ways including:

 1. Manage your process to maintain consistent shelf-life particularly during production
    startup and/or during any change in the process
 2. Light weight successfully while maintaining shelf-life targets
 3. Manage inventory and warehousing to make sure that bottle shelf-life performance
    matches the needs and conditions at the point of sale
 4. Manage customer perceptions of quality of the brand

With regular testing, and the continual monitoring of shelf-life performance of 
the ongoing production run, it is possible to pro-actively manage your blowmolder
to maintain optimal utilization and as a result, maximize shelf-life for your production
and ultimately maintain the high standards of your brand.

 [ ⌊Preform CSD Bottle Container Testing Systems⌉ ](https://flexitest.in/packaging-testing-equipments/permeability-testing-instruments/wvtr-gravimetric-method-c360h/)

## 󠀁[Preform / CSD / Bottle & Container Testing Systems](https://flexitest.in/packaging-testing-equipments/)󠁿

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