materials testing | PVC weatherability G90 Low Temp. EMMA Horizontal
G90 Low Temp. EMMA Horizontal
Figure 7. Exposure temperature comparison for insulated black standard
Figure 8. Exposure irradiance comparison
3) a simple unaccelerated horizontal backed exposure on 8 and 9 August 2013 in Phoenix, Arizona. The data show the BST of the Low Temperature
EMMA device signifi cantly lower than the BST of the standard G90 device by about 36%. Additionally, the BST on the Low Temperature EMMA exposure appears comparable to the BST observed on the horizontal (unaccelerated) exposure. Additionally, researchers exposed uninsulated, black
painted automotive steel panels with thermocouples welded to the unexposed surface (BPTs). Again, near identical BPTs were simultaneously exposed on the new Low Temperature EMMA device as well as the tradi- tional G90 device near summer solstice in Phoenix, Arizona. The data show the BPT of the Low Tempera- ture EMMA device signifi cantly lower than the BPT on the standard G90 device by about 38%. UV irradiance comparison: Figure 8 shows approxi-
mate UV irradiance data obtained using Xenosensive irradiance sensors with a narrow wavelength response centred at 340 nm UV. These detectors were used for
References 1) ASTM G90-05 “Practice for Performing Accelerated Outdoor Weathering of Non-Metallic Materials Using Concentrated Natural Sunlight,” 2005 Annual Book of ASTM Standards, vol. 14.02, West Conshohocken, PA, American Society for Testing and Materials, 2005.
2) Hardcastle, H.K. “Infl uence of Backing on Weathering Induced Color Change of Two Rigid Vinyl Building Materials”, Proceedings of The Annual Technical Conference of The Society of Plastics Engineers, San Francisco, CA, May (2002).
3) United States Patent No.: US 6,073,500, Ultra-Accelerated Natural Sunlight Exposure Testing, June 2000.
4) United States Patent No.: US 6,225,551, Multi-Facet Concentrator of Solar Setup for Irradiating the Objects Placed in a Target Plane With Solar Light, May 2001.
5) United States Patent No.: US 6,604,436, Ultra-Accelerated Natural Sunlight Exposure Testing Facilities, August 2003.
50 COMPOUNDING WORLD | June 2014
comparison purposes only. Three identical detectors were simultaneously exposed on: 1) a standard G90 device; 2) the new Low Temperature EMMA device; and, 3) a simple unaccelerated horizontal backed exposure on 8 and 9 August 2013 in Phoenix, Arizona.
The data show that the new Low Temperature EMMA
device maintains the approximate UV irradiance at 340 nm slightly higher than the traditional G90 device. The standard G90 device appeared about 5.4 times higher in irradiance than the direct horizontal UV irradiance at 340 nm while the Low Temperature EMMA device appeared about 6.4 times higher in irradiance than direct Horizontal UV in this simultaneous comparison.
Summary Accelerated weathering devices like ASTM G90 some- times present limitations for temperature sensitive materials under high irradiance because exposure temperature co-varies with irradiance. Inappropriately high material exposure temperatures may adversely affect weathering results for appearance and mechanical properties. Researchers undertook a project to reduce material exposure temperatures on G90 devices while maintaining fi delity to the natural UV solar spectrum and high UV-Vis irradiance for acceleration. Energy balance calculations indicated fi ltering out longer wavelength Vis and NIR with special refl ectors could reduce heat build in exposed materials. Researchers developed a new Low Temperature EMMA device using spectrally selective refl ectors. Results showed dramatic reduction in material exposure temperature, with slight increases of UV irradiance over traditional G90 devices.
About the author Henry Hardcastle is research and development director and intellectual property leader at Ametek - Atlas Material Testing Technology.
www.atlas-mts.com
www.compoundingworld.com
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