A properly designed weathering testing program enables manufacturers
to achieve their product goals efficiently and productively.
The race to market is a lot shorter today as new products and better warranties drive the competition. Many manufacturers quickly put together a weathering program designed to help them understand their product’s durability and performance. However, they also test blindly, cut corners, or waste time, money, and resources on tests that may or may not be appropriate, leading to product failure and liability issues.
EMMAQUA (equatorial mount with mirrors for acceleration with water) is the most widely used outdoor accelerated weathering test method in the world today. All images: Atlas Material Testing
Before beginning any weathering testing program, it’s important to start with the bigger picture in mind. The service life of your product is directly related to the testing you perform upfront. Asking the appropriate questions can help you develop the right weathering process that will enable you to achieve your product goals more efficiently and productively.
Like a fine chef who needs to find the right balance of ingredients to create delicious cuisine, manufacturers need to find the perfect blend of ingredients, such as UV and heat stabilizers, to develop a quality product. When it comes to testing materials, you are basically creating a recipe for weathering–one that follows a complete testing program to give you a better idea of how your product will perform in its end-use environment. From packaging to coatings, all of your weathering tests should be set up to determine how various environmental conditions can change a product’s composition.
Two factors to consider are the ever-changing consumer lifestyles and expectations. How and when a product is used today may be different from how it was used five or ten years ago. For example, consider interior products. The increased use of natural light entering a home has implications for durability and appearance issues; therefore, it has become even more important to ensure your product will stand the test of time. The last thing a stainless steel appliance maker wants to hear is that the protective coating on their refrigerator has problems with light fastness and is beginning to yellow.
Typically, before manufacturing a product, you want to know if you have a good formula. Understanding the effects of light, temperature, and moisture on your formulation is where the real science of weathering comes into play.
Why test?
The tricky thing about interior performance or outdoor weathering is that it will likely cause undesirable changes in a product at some time. This point has to be taken into account from the way a product is formulated and manufactured to the way it is packaged and displayed on a store shelf. No matter how hard you try, there is just no escaping it. So right from the beginning you need to consider the impact of light, temperature, moisture and other environmental factors and accept that they will, somehow, affect your product.
Now, the main reason we test is to avoid product failure. Sure, you can develop a product, avoid thorough testing, launch it, and never look back, but is that a risk you want to take? Once your product is out in the market, so is your company’s reputation. The last thing you want is to destroy your brand image, lose customers, and spend considerable time and money doing damage control. Chances are, you want to catch performance problems with your product before you hear about it from your customers.
Undertaking a well-designed testing program allows you to see which environmental factors cause your product to break down in chemical, physical, or color and appearance properties. In addition, changes to your formulation and processing or even changes to the way a purchasing department orders materials, such as changes in grade or vendor, can all have an effect on product performance and durability. As you go through the testing process, you want to gain as much knowledge as possible about your product. This information can aid not only in quality and risk assessment, but also in product and processing improvements, competitive advantages, and cost reductions as well.
How good is the product?
Whether you’re making a protective coating for stainless steel or manufacturing a new plastic casing, it starts with a good formulation. A general rule of thumb is to always think about product stability ahead of time and put specific ingredients, such as heat or UV stabilizers, into your product to help make it more durable.
After putting together your formulation, create test panels before going into production. At this stage, you primarily want to validate the product’s material formulation with these test panels by exposing them to outdoor and accelerated weathering tests.
Creating a weathering test
Outdoor weathering testing is a process in which you mount your samples onto an exposure rack to learn how sunlight and other weathering elements affect your material. Often, exposure angles are near horizontal, usually 5º, 45º, 90º, and an angle equal to the test site’s latitude (26º in south Florida and 34º in Arizona, for example).
When considering outdoor testing, you need to ask, “How and where is my product intended to be used?” If you know its intended use is for a specific market, for example, high solar radiation or wet climates, you will want to send your test panels to a test site that is representative of those environments. However, there’s a good chance your product will be used in a variety of geographical locations, so you may need to expand the range of your outdoor testing environments.
Customers are notorious for using products in ways and locations manufacturers never thought of–or tested for.
This concept is fairly easy to understand, but there are two potential limiting factors to keep in mind. The first assumes you know exactly where your product is going to be used, but perhaps not every end-use environment is factored into your testing. The second, outdoor testing is a long-term test. It’s important to get your test panels out to exposure sites the moment they’re ready, because it takes time to acquire realistic data on the actual effects of weathering. But often we must make some product business decisions before we can wait for the outdoor testing to be completed in real time.
Today, there are more advanced natural accelerating weathering instruments that employ a “follow-the-sun” system to help speed up material degradation. One such test method uses ten flat mirrors to concentrate natural sunlight onto test samples mounted on the device. The mirrors uniformly focus sunlight onto the samples at a much greater intensity than that of global daylight and much stronger than the UV portion of the spectrum. Since this test method exposes samples to the full spectrum of natural concentrated sunlight, it is one of the most realistic accelerated weathering tests you can subject your materials to.
Now, let’s say you have a product you want to launch to market in six months. Obviously, you don’t have the luxury to wait 10 years for the results of your outdoor tests. Because there is a need for faster evaluations of material durability than can be obtained by outdoor exposure tests, instruments with artificial light sources are generally used to accelerate the degradation. Light sources such as filtered long arc xenon, fluorescent, metal halide lamps and carbon arc are used in weathering instruments to conduct accelerated laboratory weathering testing.
Accelerated laboratory testing allows you to design a test that will lead to faster answers. The primary benefit to conducting these tests is the repeatability and reproducibility over what is essentially an uncontrolled and variable phenomena—the actual weather. Of course, there is always the potential that the results from any kind of accelerated test may not actually reproduce what happens in the real world environment, but you can get close. After all, your goal is to understand what a particular material is likely to be sensitive to and why it may possibly fail.
Changing too many variables
One of the first things you learn in testing is that if you change too many variables at once, you’re risking failure in determining casual factors. Can you imagine all the possible test combinations? Also, sometimes the mixture of a formulation and an environmental stress factor can combine to produce a change that you normally wouldn’t see with just one or the other. It could be the concentration of ingredients, processing variables or environmental issues such as sunlight and moisture that all act together to produce a result that is greater than the sum contributions from the individual parts.
For example, what makes apple juice taste good to somebody is an optimum combination of sugar and pH balance. If you change the concentration of sugar or the acidity, the formulation changes, making the apple juice taste bad. There is a potential interaction between the degree of acidity and sweetness that work together to produce good apple juice.
The same is true with materials. There is an interaction between the environmental stress and the formulation that in some unique way you can’t detect by changing just one variable by itself. This is what we call an “interaction effect.” And the best way to test and measure for these potential interactions is to test through a design of experiment (DOE) plan.
Designing a DOE
Every experiment should follow a DOE testing plan. The purpose of the DOE is to ask specific questions about what you want the test to accomplish and what you want it to reveal about the product, or its manufacturing process. A good DOE analyzes the raw ingredients, processing parameters and every aspect that goes into making a formulation. It also examines how your product will be used and what is the intended range of possible environments where your product may be exposed.
With this information, you can now set the limits of how to design a quality test plan. Rather than putting samples in an incomplete number or type of test environments, you can instead look at creating a realistic mix of environmental variables and test them with a minimum number of experiments, or look at a range of worst-case environments and test to the maximum boundary range of conditions. If the product passes or fails at any of the predetermined levels, then you can go back and refine the experiment and fine-tune how and where a product is either passing or failing.
This is a much more efficient way of doing testing. It doesn’t rely on changing one variable at a time or pure luck because you’re testing with the fewest number of experiments. Setting experiments to these worst-case environment scenarios is typically faster and more likely to catch plausible product failures. Another advantage of a worst-case environment scenario is that it can help detect when a product may be at the low end of its specified performance range and fails when it sees environmental stresses at the high end of the expected “normal” range—a classic failure scenario.
Screening materials before production
Whether you’re developing a new coating or designing a newly formulated resin for patio chairs, your formulation should always begin with good science.
But how do you know your formulation will create a good product? A proper DOE should include a material screening process. Material screening allows you to quickly test material performance to outdoor weathering or indoor exposures. This helps validate your materials before you invest too much time and money turning it into a product that may not perform well.
There are two fundamental approaches to material screening. The first is to simulate the worst-case environments representative of where your product is intended to be used. In other words, if the product is a sun umbrella and it’s only going to be sold in North America, then the worst-case scenario will most likely be a high solar radiation and wet environment like Miami, or a high solar radiation, hot and dry environment like Phoenix. By testing to these two locations, you’re exposing your product to the two worst possible locations in North America where it is intended to be used. If you need to consider northern freeze/thaw or marine salt air conditions, you can test for that, too.
Another way to screen materials is by creating a forced degradation test. The purpose of this test is to deliberately cause your product to fail by picking the worst environmental stress factors that may impact your material. If you can make the product change or fail in some way, you can relate that change to the environmental stress whether, for example, it is temperature, moisture, or a combination of both. This helps determine what environmental conditions your product may be sensitive to. With this information, you can decide how to reformulate or process, change application or warranty information, or adjust marketing plans, for example.
You’re probably asking yourself “wouldn’t it be easier to just forget the traditional material exposure tests and go straight to the forced degradation test?” In some cases, a manufacturer may do just that. However, different testing approaches have different stages depending on your final objective. All testing requires time, money, and resources. The more you invest, the finer degree of resolution of product performance you’re going to be able to get in your weathering program. On the other hand, the more you shortcut the entire process, the risk that your product will not perform as expected.
Test, test, test
Static natural weathering exposure racks are used to test films, building materials, paints, plastics, sealants, elastomers, adhesives, and packaging.
Material screening, in combination with accelerated and outdoor testing, is an effective way to begin validating the quality of your material. Once the formulation goes through your weathering process and is turned into an actual product, you may need to go back and conduct similar testing to understand how the new manufactured product will perform once it is introduced to a variety of environmental stresses.
Why? Because sometimes you can’t tell if a failure may occur in your product until it is combined with other elements of the finished product, such as a coating on a particular substrate. For example, picture the inside of a car. You have an airbag that relies on a plastic cover to open instantaneously on impact. But what happens when you combine this plastic cover with dissimilar materials on the rest of the instrument panel? In order for the airbag to deploy, the plastic cover needs to work in combination with other parts of the airbag. Does your coating on the plastic door cover cause it to become brittle with time and shred the airbag when it deploys? In these types of complex products, you need to test the part as it works in combination with an entire physical structure as a final product. In other words, it’s very important to test everything in the manner it’s intended to be used in the field.
Why not just go right to this step? Well, this is very late in the cycle to catch problems or make changes. Also, if there is a problem, it is much harder to determine if it was due to a formulation problem, a processing problem, or related to the final structural details.
Independent validation
You’ve conducted all your tests; you’re satisfied with the results, so now it’s time to go to market, right? A safer methodology would be to obtain third party independent verification of your test results, especially one familiar with materials, environmental durability testing, and performance prediction. If the results agree, you have a much higher level of confidence, and so will the prospective customers of your product. If the results do not agree, you have the additional opportunity to review and modify the testing protocol before proceeding to the re-test and ultimately the marketplace. Relying on just one set of results carries some risk, just like relying on one doctor’s prognosis that you need surgery.
A good third party lab understands all the potential pitfalls about your product and tries to factor the most important ones into the testing program. Of course, if you can’t afford to do every test then you want to make sure you are conducting the right tests accurately. Based on their experience, a third party can direct you to the right testing processes that are designed to give you answers to key questions more efficiently.
Asking the right questions
Accurately predicting the lifetime of a product is not something you can just pick up by reading a book or taking a class. It takes determination and time to fully grasp the effects of weathering on a material. And even after that, you’ll still encounter new challenges.
One thing to remember as you develop a complete environmental durability or weathering test program is to follow a recipe, a formal well-designed test plan. A proper DOE is your fundamental blueprint that will take your product through the various stages of testing. Knowing your product and what goals you hope to achieve with it will help you ask the important questions, such as: Where are we starting? What is our final objective? Is it to understand the range of flexibility and process or to understand how and where the product may be sold or used?
Finding the answers to these key questions is what weathering testing is all about. Like most everything in life, there is a starting point and ending point. It’s the details of how to get to that end point that is determined through a good scientifically designed weathering testing program.
—Kerry Quilter,
Team Leader, Marketing Services
Atlas Material Testing Technology LLC
