MATERIALS | ACCELERATED TESTING
Above: Images showing an unaged sample of a transparent construction film (left) compared with the same film after 180hrs exposure in an Eye Optix Super UV system (centre) and to 24 months of Florida sunshine (right)
screening tests when compared to conventional xenon or fluorescent UV, he adds. In a recent project, a building products manufac-
turer wanted to test the long-term UV resistance of a transparent film intended for outdoor use. The manufacturer was concerned about mechanical performance of the film as well as its colour and gloss retention. Vermillion says the first step in the project was to evaluate a well-understood subject material in the Super UV chamber. “We do have benchmark test methods for a
variety of materials, but differences in test subject material formulations and properties will likely require several iterations to fully understand the interaction between high irradiance, and other con- trol variables such as temperature and time,” explains Vermillion. “It is important to fully under- stand your product failure modes from natural weathering and their root causes.”
Failure benchmark While the initial benchmark experiment repro- duced the failure mode (colour change) correctly, the researchers ran several further experiments to determine the optimal Super UV test conditions to best match the degradation observed in static outdoor weathering including surface cracking. It was known that water exposure can contribute to the cracking, so the time of wetness was increased in the second experiment by reducing the tem- perature and increasing the relative humidity during the dew cycle, says Vermillion. In outdoor exposure, colour change and surface
cracking occur simultaneously; in the final two test iterations, the researchers aimed to fine-tune the temperature settings to synchronise the failure modes. This was achieved by first adjusting the temperature during the dew cycle to increase the rate of reactions occurring during the dark phase and after that by evaluating the effect of tempera-
58 COMPOUNDING WORLD | December 2021
ture during UV irradiance of the sample. “The customer has found that the Super UV
results correlate to xenon and outdoor weathering, and confirmed that highly accelerated weathering tests can be used effectively for product qualifica- tion. Some upfront work is required to validate correlation with natural weathering, but this is true when using any type of laboratory weathering equipment,” says Vermillion.
UV disinfection A growing concern for plastics materials is the effects of ultraviolet UV germicidal irradiation (UVGI); this high-energy UV short wavelength light (generally 200-280nm) has been increasingly used as a disinfection method for surfaces during the Covid-19 pandemic. UVGI with UVC light has been used for many
years for disinfection in limited medical applica- tions, but in the past two years UVGI has been more widely used for commonly touched surfaces in a range of public places. UVC light, however, is very different from natural sunlight or the light that is normally simulated by accelerated weathering testers. Radiation from sunlight has wavelengths longer than 295nm, which is primarily in the UVA range (315-400nm) with a small amount in the UVB range (280-315nm). While the effect of UVA/UVB light on plastics
durability is well characterised, the effect of UVC exposure is largely unknown, according to Matt McGreer, Director at Atlas Weathering Services. He points out that a wide range of UVC sterilising devices are available for use in private homes, as well as by commercial cleaning services, and with this broad use it is difficult to know what dosage of UVC materials are being exposed to. There are two available test methods for UVC
exposure but neither were designed for the current use conditions, says McGreer. Groups at ASTM and
www.compoundingworld.com
IMAGE: EYE OPTIX
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74
