use." The Modular CompactRheometer (MCR) from Anton Paarcan be used to measure the proper-ties of unmodified as well as modi-fied samples to identify the changes.The MCR characterizes a poly-mer's viscoelastic properties, infor-mation that can be used to under-stand how the material behavesunder application and in storageconditions as well as the inherentstructure of the material. Therheometer also allows the additionof environmental accessories for avariety of application-specific meas-urements. "Versatility is important;people want one instrument that cando multiple types of testing andhandle multiple types of samples,"says Cassell.With the MCR, a user can meas-ure the extensional and torsionalproperties of solid samples fordynamic mechanical thermal analy-sis. The addition of light-scatteringand optical viewing modules canallow study of microstructures andthe molecular or structural changesthat result from additives. Cassellsays that there continues to begrowth in application of plastics aslower-cost and lighter-weight alter-natives to metals. When plastic isused for moving parts in assemblies,measuring the friction factor for thepart is important. The company'stribology module allows the user toanalyze how a plastic part wouldwear over time.Weathering AnalysisDeveloping a new formulation orchanging an existing resin, additive,or color for a plastic part used out-doors requires assessing how wellthe plastic will weather over time.In the case of a change of manufac-turing location or a change in raw-material source, a company maywish to revalidate the UV enduranceof the product. In other cases, com-panies may use weathering testingto troubleshoot product failures. Asone example, when a seal on a partfailed, the customer speculated thatsunlight had changed the plastic'smaterial properties. Weathering test-ing showed thatalthough the color didnot change, the surfacechanged from glossy tomatte, and that there wasa strong possibility thatthe change in surfacetexture also affected theseal.Solar Light Companyis a U.S. manufacturerof precision UV lightsources, solar simula-tors, radiometers, sen-sors, and detectors forseveral industries. It alsooffers testing servicesand has seen increasingrequests for these servic-es over the past few years.Filters in the company's solar simu-lator tune the light source to simu-late only the UV portion of thespectrum, which has the advantageof minimizing the temperatureincrease of the sample to only a fewdegrees above ambient temperature.Because Solar Light's instrumentsends light through a lens, it canamplify irradiance by reducing thearea of the sample that is exposed."Using a 57-mm-diameter circle oflight, we can produce six years ofexposure in one year of acceleratedtesting time," explains Drew Hmiel,a physicist at the company."However, by reducing the circle toa 20-mm diameter we can furtheraccelerate six years of exposure toonly one month of testing."Solar Light is currently correlat-ing accelerated laboratory results tooutdoor exposure for a wide rangeof polymers. The company meas-ures color and appearance changesof weathered samples using col-orimetry as well as reflectance andtransmission spectrophotometry. UVtransmittance can be measured aswell. The company does not offertensile testing, although customerscan do this testing elsewhere if theydesire. Hmiel notes that simulationThe MCR from Anton Paar USA character-izes a polymer's viscoelastic properties.A plastic building product underwent anexposure test for 10 years. The lower-rightphoto illustrates the exposure arrangement.Solar Light.www.4spe.org | OCTOBER 2011 | PLASTICS ENGINEERING |13
of indoor exposure of plastics isincreasingly requested. For exam-ple, exposing a sample behind glasssimulates sunlight coming through awindow. Using specific fluorescentlamps to generate UVA light simu-lates exposure to indoor fluorescentlighting, such as in a retail displaycase. Solar Light is currently work-ing on accelerating this type ofexposure and correlating it to actual"shelf-time." Thin Film AnalysisPolymer thin films, typically lessthan ~500 nm thick, are used asprotective coatings on windshields,helmets, and other products. Theoptical and mechanical properties ofthese films play an important role inthe overall lifetime of the product,and these properties can change atlower temperatures than they wouldin the bulk material. Cyclical tem-perature changes that oscillate frombelow to above the glass transitiontemperature of the polymer cancause transparent films to become"fuzzy" and flexible films tobecome brittle, for example.Currently, most reliable analysismethods don't have the resolutionnecessary to accurately measure thetrue behavior of polymer thin filmsat the nanoscale.Researchers from the University ofSouthern California (USA) havedeveloped a method to characterizepolymer thin films using hybrid opti-cal microcavity resonators.1Thesesensors operate using evanescentfield whispering gallery mode reso-nant cavities. Under laser illumina-tion, the circulating optical fieldinteracts with the microcavity, andany changes in the material cause adetectable shift in the resonant wave-length of the device. By coating amicrocavity with a polymer film, theresearchers created a sensor thatcould detect the optical propertiesand mechanical behaviors of a poly-mer film. The method is nondestruc-tive, which is important for measur-ing the effect of cyclic temperaturechanges on a polymer thin film. The researchers tested the tech-nique with polystyrene. "We specif-ically chose this polymer because itis very commonly used in foams,food containers, and other commongoods, and it has a moderate glasstransition temperature," says Dr.Andrea M. Armani, who led theresearch team. "We performed themeasurement several times, verify-ing that it is nondestructive, andshowed that the sensitivity tochanges in the optical properties ofthe device was improved by nearlythree orders of magnitude overalternate methods."The technique is ideally suited forthin films and cannot be used onthick samples because the illuminat-ing light interacts with only the first~100 to 150 nm of the film depth.The method is currently useful onlyin a laboratory setting, but theresearchers are working on alter-ations that might make it more use-ful in industrial settings. Developing New MaterialsResearchers at the U.S. Oak RidgeNational Laboratory (ORNL) andthe Technische Universität14| PLASTICS ENGINEERING | OCTOBER 2011| www.4spe.orgA scanning electron microscope image (left) shows the sensor device, which is approximately 25 microns in diameter. An artist's ren-dering (right) shows the laser confined within the sensor device interacting with a polymer thin film. This interaction enables detectionof changes in the film's properties. University of Southern California.