1. The Essentials of Laboratory Weathering
Sean Fowler Weathering & Corrosion Technical Manager
Q-Lab Corporation
Welcome to today’s webinar on the Essentials of Laboratory Weathering.

2. What We Will Talk About Why Perform Natural Weathering Tests?
What Exactly IS Natural Weathering Testing?
Laboratory Weathering Testing
Xenon
Fluorescent UV
Elements of an Effective Testing Program
Here are the main topics we’re going to cover today. You may wonder why we’re discussing natural weathering in a webinar titled “The essentials of laboratory weathering.” The reason is that you can’t truly understand laboratory or accelerated weathering without some background in outdoor weathering. Think of it as a prerequisite.
After giving you a brief overview including the forces of weathering, we’ll go into detail about accelerated weathering. By the end of this webinar, you should have a good understanding of the two primary technologies used in accelerated weathering, how they differ and complement one another, and the elements of an affective testing program. We’ll also go over some tips on writing internal weathering test procedures.

3. Here are the answers! Natural weathering tests are critical
Natural weathering tests don’t delay anything!
Modern laboratory weathering -- two technologies: xenon & fluorescent UV
The technologies are complementary, not competitive
Weathering testing helps you make better decisions
Let’s jump ahead to the conclusions. Regarding natural weathering testing, it’s a critical element to any research into the weatherability of your products. Performing outdoor weathering testing is faster than you think, and it doesn’t actually delay product development at all. Modern laboratory weathering uses two technologies, xenon and fluorescent ultraviolet lamps. Each has its strengths and weaknesses, and complement one another rather than compete. Finally, weathering testing of all kinds helps you make better decisions.

4. Why Perform Natural Weathering Tests?
Mother Nature’s weathering chambers are the true state of the art
Laboratory test results can be wrong
Can’t improve laboratory tests unless you know the real world result
The weathering test chambers we make today are the best ever. As you’ll see later, we can do a really good job of simulating sunlight and UV, creating and controlling moisture, and measuring and controlling temperature. However, Mother Nature remains the state of the art. Nature creates complex cycling conditions that test chambers can’t replicate. Nature tends to find ways of degrading materials that are difficult to simulate in the laboratory.
It’s actually quite easy to develop a poor laboratory weathering test. The problem is, it’s really hard to KNOW you have a poor test unless you have natural weathering data to compare it to.
When you have natural weathering data, you can experiment and modify your laboratory test techniques to match the outdoor results. With a bit of work you can get accurate, useful data from your laboratory tests.
A couple times a year, we offer a full hour webinar on this this topic, titled Outdoor Weathering Must Verify Accelerated Testing. You can also download a paper of this same name from our website.

5. Did you know…?
You can often get useful data from natural weathering tests in a year or less
Industries with highly durable products ( years) often have 2-3 year outdoor test approval protocols
You can expose 50 test panels in Florida or Arizona for about $500 per year
Natural weathering tests are useful for indoor products
Outdoor weathering is faster than most people realize. You can often get useful data in a year or less, and even when you have very durable products, a 2-3 year test is often long enough to guide your decision making. Industries with highly durable product, from automotive coatings to building materials, often have 2-3 year outdoor test approval protocols.
There is also a perception that outdoor weathering tests are expensive, when the reality is that it’s one of the least expensive types of testing available. Finally, although natural weathering tests are more commonly called outdoor tests, we specifically are using the term natural because many materials intended for indoor use are tested under glass outdoors.

6. What We Will Talk About Why Perform Natural Weathering Tests?
What Exactly IS Natural Weathering Testing?
Laboratory Weathering Testing
Xenon
Fluorescent UV
Elements of an Effective Testing Program
Next on the agenda is a discussion on the science behind natural weathering testing.

7. What is Natural Weathering?
Forces of weathering
Sunlight
Moisture
Heat
Global benchmark weathering sites
South Florida, Arizona, Northern Industrial
In order to really understand laboratory weathering, you must know something about the forces in nature that will degrade your products. We will provide some information on the critical aspects of sunlight, moisture, and heat that you must keep in mind when choosing a laboratory test method. Then we’ll provide some brief information on global benchmark weathering sites and why these sites are the standard.

8. Summer Sunlight Spectrum
In weathering testing, we like to talk about the summer sunlight spectrum because of course it’s the most severe.

9. The rate at which light energy falls on a surface, per unit area; W/m2
Irradiance:
The rate at which light energy falls on a surface, per unit area; W/m2
I don’t have a lot of technical jargon to share with you today, but one term that you do need to know is irradiance. The technical definition is “the rate at which light energy falls on a surface, per unit area.” A more common way to look at irradiance is that it’s the intensity or brightness of light. In all the data we’ll share, the unit of measure is watts per square meter. In other sources, you may see milliwatts per square centimeter or other units of measure. Usually, converting from one to another is a matter of moving the decimal point.
These definitions and other weathering industry terms can be found in ASTM G 113.
ASTM G113 -Terminology

10. Sunlight Spectrum, Noon Summer
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
250
300
350
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Irradiance (W/m 2 )
Visible Light
UVA
UVB
UVC
There are many, many definitions of sunlight out there. For our purposes, we like to use noon summer sunlight, the most intense sunlight of the year. This graph is called a spectral power distribution, and it simply graphs the intensity, or irradiance, of light versus its wavelengths. You will be seeing a lot of these types of graphs during this presentation. Due to differences based on moisture in the atmosphere and the exact time of day and year sunlight is being measured, it is very difficult to get reproducible sunlight measurements. So this sunlight definition is actually based on a mathematical model which is applied to accurate measurements of sunlight taken in outer space. This spectrum is in good agreement with measurements we’ve taken in multiple locations over the years.
The sunlight spectrum is often divided into a few key components. Here we see that summer sunlight contains UVB and UVA radiation as well as visible light. If we extended the graph further to the right, we would see the infrared portion of the spectrum.

11. Wavelength Regions of UV
UV - C
100 – 280 nm
Found in outer space
UV – B
280 – 315 nm
Includes shortest wavelengths at earth’s surface: severe polymer damage; absorbed by window glass
UV – A
315 – 400 nm
Causes polymer damage
When we focus in on the UV portion of the spectrum, we see that the shortest wavelengths, UVC, are not found on the earth’s surface. We do receive UVB energy, which causes severe polymer degradation. It is completely absorbed by standard window glass. The earth receives a lot of UVA energy, which is defined between wavelengths of 315 and 400 nm. It also causes polymer degradation and may or may not be filtered by glass, depending on the type of glass.
Organic compound
Coating
Sealants
Adhesives

12. Short Wavelengths - Polymer Degradation Long Wavelengths - Fading & Color Change
A useful generalization is that shorter wavelengths of sunlight cause polymer degradation, while longer wavelengths are responsible for most fading and color change. But keep in mind that this is only a generalization.

13. Inherent Characteristics Affect Spectral Sensitivity
Chemistry
Color
Thickness
Stabilization
The relationship between a given material and the wavelengths of energy that cause degradation is called its spectral sensitivity. The spectral sensitivity of a material is affected by its chemistry, and even slight changes to its chemistry can impact spectral sensitivity. Nylon 6 and Nylon 66 have a very similar molecular structure, but they have different spectral sensitivities. Spectral sensitivity is also affected by its color, thickness, so the end use application often has a significant impact on the spectral sensitivity of a material. Finally, the presence of UV stabilizers clearly affects a material’s sensitivity.

14. Moisture
Next to light, the second most important element of weathering is moisture. It is often overlooked.

15. Q-Lab’s Time of Wetness (TOW) Research Things Are Wet Outdoors Longer Than You Think
You need to pay attention to moisture in your weathering tests because materials in use outdoors are generally wet several hours every day. We’ve done some “time of wetness” research to quantify this.

16. TOW vs. Rainfall - Miami, FL
This chart is based on data taken over a one month period near Miami, Florida. The data points represented by triangles show the number of hours a panel was wet outdoors. The circular data points represent rainfall in centimeters. Two things stand out. First, the panels were wet more than 12 hours a day on average. This was true even when it didn’t rain at all. In fact, there is an inverse relationship bewteen rainfall and time of wetness.
When it rained, TOW went down.
On days when it didn’t rain, TOW was higher.

17. Dew Not Rain is the Source of Most Outdoor Wetness

18. Designing for Outdoors Means Designing for an Aqueous Environment

19. Effect of Moisture
This chart shows the danger of neglecting moisture in your accelerated weathering test. This test was on polyurethane coated panels in a QUV. In one exposure, the cycle was 4 hours with the UVA-340 lamps on and four hours of dark condensation. The other exposure replaced the dark condensation with 4 hours of dark only, with no moisture. The irradiance and temperature were the same in both cycles.
Gloss stayed constant in the exposure with no condensation/moisture cycle.
But in the exposure with moisture, there was a remarkable loss of gloss.
Again, moisture is the only variable. Eliminating moisture from this test would have resulted in potentially choosing to go to market with this formulation, where it would have catastrophically failed outdoors.
(This data is from research we did in You can find it in a paper titled “errors caused by using joules to time laboratory and outdoor exposures” on our website.)

20. Don’t Underestimate the Effect of Moisture
Changes The Rate
Changes Mode Of Degradation
Difficult To Accelerate
Most people seem to prefer to discuss UV and light aspects of weathering, but
moisture could be an overshadowing factor for many materials.

21. Heat
The last force of weathering we’re going to discuss is heat and temperature.

22. Photo-Chemical Reactions Not Usually Simple One-Step Reactions
In other words, usually the forces of weathering synergistically combine to cause
more damage than any one factor alone.
(Continued on next slide)

23. Primary Photochemical Reactions Not Affected by Heat
(Continued on next slide)

24. Secondary Reactions Are Affected By Heat
Heat itself usually does not cause much weathering damage. But it does accelerate
the destructive effects of light and moisture.

25. “Rule of Thumb”
10°C Increase in Temperature Doubles Rate of Chemical Reaction
This rule of thumb is a reasonable first guess of the Arrhenius equation for many reactions.
Experimentation is required to determine relationship to be truly useful in weathering and light-stability testing. The main point is that, in general, at higher temperatures, light and moisture induced degradation occurs more quickly.

26. Effect of Temperature: Oxidation Rate of Polyethylene
Time In Hours Exposed to UV lamps
Here is an an example of how higher temperatures increase the rate of degradation caused by ultraviolet light.
When heat is used in combination with UV exposure, there is an increased
incidence of oxidation.
(This graph was taken from “Know Your Enemy;” it’s from research by Matreyek
and Trozzolo, from their paper “Weathering of Polymers.”)

27. Thermal Cycling Effects
Physical stress
Coatings on plastics
Assemblies
In addition to increasing the rate of degradation-related chemical reactions, heat causes another problem. Thermal cycling creates physical stress on materials as they expand and contract. Product composed of multiple materials are further stressed because of differences in the coefficient of expansion and contraction between the materials. Coatings on plastics and assembled parts are greatly affected by this.

28. What is Natural Weathering?
Forces of weathering
Sunlight
Moisture
Heat
Global benchmark weathering sites
South Florida, Arizona, Northern Industrial
Now that you know something about the critical forces of weathering, let’s talk about global benchmark weathering sites and they these particular locations have been historically important in the field of weathering testing.

29. Florida Site Review Slides
Point out 280 MJ Annual Solar Energy as “Standard Florida Year”

30. This is the most common type of outdoor weathering rack
This is the most common type of outdoor weathering rack. Specimens are mounted 45 degrees facing south, and there is no backing so that they get full air circulation on the back side.

31. Arizona Site Review Slide
Point out 334 MJ as “Standard Year” in Arizona, 20% greater than FL

32. Here are some wood coatings on exposure in Arizona
Here are some wood coatings on exposure in Arizona. You can see how the dry heat is warping some of the specimens.

33. Why Florida & Arizona? Reasonable “worst case” environments
Accelerate degradation seen in major global markets
Established test locations
Long history
Competition
Florida and Arizona are commonly used by companies around the world for their weathering testing. In particular, many European companies find that Florida exposures are significantly accelerated compared to exposures in their domestic markets. Florida has the same weather, just more of it!
From a practical standpoint, Florida and Arizona have a long history of exposure testing, so there is a competitive market and a great deal of expertise in these locations.

34. Northern Industrial
For some applications—many coatings for example, the freeze thaw conditions observed in northern environments must be replicated in some outdoor tests. For other materials, industrial air pollutants can be an important component of weathering degradation. PVC building materials usually suffer from more severe color degradation in Ohio than they do in Florida or Arizona.

35. I mentioned earlier that many products and materials intended for indoor use are tested in Florida and Arizona. Here is an example of an under glass exposure.
Minimum of 3” between cover glass and specimen surface.
Glass cover protects samples from direct rainfall.
Typically single strength glass.
Typically oriented at either 5° or 45° South.
Under Glass Exposures

36. What We Will Talk About Why Perform Natural Weathering Tests?
What Exactly IS Natural Weathering Testing?
Laboratory Weathering Testing
Xenon
Fluorescent UV
Elements of an Effective Testing Program
Let’s switch gears and talk about the main focus of today’s webinar, laboratory weathering testing. I’ll give you a brief historical viewpoint of accelerated weathering testing and detail today’s state of the art.

37. Laboratory Weathering Testing
Repeatable and Reproducible
Can be done in-house
Accelerated
Practical for QC and R&D

38. Xenon Arc Light Spectra & Irradiance Control Temperature Control
Moisture
Critical factors in writing a test method

39. Xenon Arc Developed in the 1950s ISO 4892-2 ASTM G155 SAE J2412, J2527
Reference one of these if writing a test method

40. Xenon Arc
Here are schematics of two common xenon arc chamber configurations. We’re not going to discuss the merits of one over the other. My company makes both kinds, and each has its own strengths and weaknesses. You can get the same results regardless of the chamber configuration, and the next several slides will detail the truly important elements of xenon arc testing. Today, nearly all global standards allow both kinds.

41. Spectra of Xenon with Daylight Filters
There are three families of xenon arc filters. The most common are Daylight filters. These are designed to simulate direct sunlight. This chart shows three common types of daylight filters. As you can see, the shape of the spectrum is very similar to natural sunlight.

42. Daylight Filters – UV Region
As we zoom in on the critical UV region of the spectrum, you can see that daylight filters do a good job of reproducing the sunlight spectrum in this region.

43. Spectra of Xenon with Window Filters
Next are window filters. These simulate sunlight through glass. There are many types. The main characteristic is that they filter out UVB energy and some of the UVA as well.

44. Window Filters – UV Region
This graph shows the filtering effect of window glass filters.

45. Spectra of Xenon with Extended UV Filters – UV Region
Use of these filters is not recommended for most applications because of the extra short wave energy. However, many standards historically used the Q/B type filter. For space applications, these may be a good choice.

46. Summary of Filters Daylight Filters Window Glass Extended UV
(exterior exposures)
Window Glass
(indoor exposures, textiles, inks, etc.)
Extended UV
(auto specs., fast results)

47. Irradiance Control

48. Effect of Irradiance - Xenon
Sunlight
0.68 W/m2
0.55 W/m2
0.35 W/m2
340nm
Think of irradiance control as a dimming circuit. You can turn the power up or down. The shape of the spectrum does not change.

49. Irradiance Control Feedback Loop Control Light sensor Control module
Xenon arc lamp
Now we are going to talk about modern system of irradiance control

50. Irradiance Control Points
340 nm (narrow band)
420 nm (narrow band)
nm or TUV (wide band)
Lux
Global ( nm)
With the feedback loop system, these are two typical control points
However, Europe has developed other systems - 1) TUV 2)
Most industries are favoring either 340 nm or 420 nm
You can choose a control point according to your standard or portion of spectrum
that you are most interested in

51. Xenon Arc Moisture Water Spray Relative Humidity Control
No Condensation

52. Xenon Arc Water Spray

53. Xenon Arc Water Spray
Extremely pure water required for optical measurements
Common test cycles may not deliver enough moisture
Less effective than condensation
Back spray does NOT produce condensation

54. Xenon Arc RH Control Changes in relative humidity can stress materials
RH control may improve lab-to-lab reproducibility

55. What Does RH Do To Your Materials?

56. Temperature Control Black panel Chamber air
Hotter than ambient in sunlight
Not necessarily same as specimen temperature
Exists for test repeatability and reproducibility
Chamber air
Controlled somewhat independently
More relevant for some applications

57. Black Panel Temperature
(uninsulated)
Insulated Black Panel
Black Standard
Two types of black panels!

58. Xenon Arc Summary Best simulation of long wave UV & visible
Full spectrum - UV, Visible, IR
Best simulation of long wave
UV & visible
Calibration
Water spray
Relative humidity control

59. Writing a Xenon Arc Test Method
Do specify:
Optical filter
By family (Daylight, Window)
Or specific spectrum desired
Irradiance
Control Point (ok to allow choices)
Irradiance level (consistent with control point)
Make sure your cycle actually works. A major automotive OEM… (Volkswagen spec that couldn’t be run)

60. Writing a Xenon Arc Test Method
Do specify (cont)
Temperature
Which temperature(s) must be controlled
Black panel type
If controlling both BP and CA, ensure appropriate set points (BP is higher when xenon lamp is on)
Relative Humidity (when necessary)
Reference ASTM G155 or ISO

61. Writing a Xenon Arc Test Method
Do NOT Specify:
Method of lamp cooling
Irrelevant to test conditions or results
Optical filters by trade name, unless you add “or alternative with a similar spectrum”
Number of lamps
Chamber configuration (flat or rotating)
BP temperature during water spray cycles

62. Fluorescent UV Weathering Tester Introduced 1970 model QUV/spray ASTM G154 ISO 4892-3

63. Fluorescent UV Light Spectra & Irradiance Control Temperature Control
Moisture
Critical factors in writing a test method

64. Fluorescent UV ISO 4892-3 ASTM G154
Reference one of these when writing a test method

65. Fluorescent UV Lamps and light spectra UVB-313 and FS-40 UVA-340
Cool White

66. UVB Lamps

67. UVA-340 Lamps

68. UV Fluorescent Lamp Aging
Irradiance decreases
Stable Spectrum
Irradiance control provides very long lamp life

69. UVB-313 Lamps QUV/se
5,600 hour lamps
2-hour lamps

70. Effect of Intensity UVA-340
Sunlight
Intensified 75%
Typical Intensity

71. increasing the stresses often decreases correlation
Speed vs. Realism
increasing the stresses often decreases correlation
There is an inherent conflict between speed & realism.

72. Fluorescent Lamp Advantages
Fast results
Very stable spectrum
Minimal maintenance
Simple calibration
Low cost

73. QUV Moisture
Condensing humidity
Water spray
RH not controlled

74. QUV Condensation

75. Condensation Long time of wetness
Elevated temperature accelerates absorption and effects of moisture
Evaporation creates distilled water
Simulates Dew

76. Water Spray

77. Water Spray
Thermal shock
Erosion
Simulates effects of rain

78. Specimen Holders

79. Specimen Mounting

80. Writing a Fluorescent UV Test Method
Do specify:
Lamp type by name
Irradiance set point
Black panel temperature set point for each portion of cycle
Cycle
Reference ASTM G154 or ISO

81. Fluorescent UV vs. Xenon
UVA-340 best simulation of shortwave UV
UVB-313 might be too severe
No visible light
Stable spectrum
Irradiance control
No RH control
Water spray or condensation
Full spectrum
Best simulation of long wave UV & visible light
Spectrum changes
Irradiance control
Relative humidity control
Water spray

82. Choose an accelerated test method that best simulates degradation incurred by natural exposures.

83. What We Will Talk About Why Perform Natural Weathering Tests?
What Exactly IS Natural Weathering Testing?
Laboratory Weathering Testing
Xenon
Fluorescent UV
Elements of an Effective Testing Program
Let’s switch gears and talk about the main focus of today’s webinar, laboratory weathering testing. I’ll give you a brief historical viewpoint of accelerated weathering testing and detail today’s state of the art.

84. Always Use Natural Exposures
Real world results
Florida & Arizona benchmarks
Worst case environments
Very inexpensive
Faster than you think

85. Whenever Possible… Use standard laboratory test methods
Helpful for lab to lab comparisons
Must verify their effectiveness
However…what worked 30 years ago may not work now
Experiment and improve lab methods

86. Define
Mode(s) of Degradation
Failure End-Point

87. This ball illustrates both points
This ball illustrates both points. What mode of degradation are you evaluating? If you are looking at only color change of the coating, you would miss the most important failure mode, which is delamination of the coating. What is the failure end point? Is it when 5% of the coating has delaminated, 50%?

88. Measure Degradation Understand the Variability of the Measurements
Use Multiple Evaluation Intervals (minimum of 4)

89. Ideal Test Program Outdoor weathering in FL, AZ, or both
Real world data
Correlation
Accelerated weathering in QUV, Q-Sun, or Q-Trac or a combination
Fast results
Formulation changes QC
An effective test program will include outdoor, natural weathering. This data will allow you to verify that your laboratory tests accurately reflect what happens in the real world. And if you find that they do not, you can modify your laboratory technique until you can replicate the outdoor environment.
Choose an accelerated weathering test that best replicates what happens in the real world. Many programs use both xenon and fluorescent UV devices because each has its unique strengths. Having both reduces the risk that your laboratory test will miss a critical failure mechanism that occurs in the natural environment.
I didn’t talk about Q-TRAC today, but this is an outdoor accelerated test we offer as a service in Arizona. Visit our website or contact us if you’d like to find out more about this.
Ultimately, a weathering testing program should give you useful data and help you make sound technical and managerial decisions. Which materials should you choose? Which additive suppliers are the most cost effective?
In today’s world, you must use accelerated weathering to make decisions. So I hope the information today will help you develop a useful and effective program. And I also hope that you realize the role that natural weathering testing plays in this fast paced world. You don’t have to wait years and years for answers, but the outdoor data helps you optimize your laboratory techniques and improve the quality of your data.

90. Questions ? info@q-lab.com
Well, thank you for attending. For questions we didn’t get to, we will receive a transcript and get back to you in the coming days. If you send an to the address on your screen, we will have one of our technical experts get back to you with an answer.
This presentation will be made available to you, either through or a link to our website.