The properties of coatings, adhesives, sealants, and elastomers are evaluated through a variety of analytical and diagnostic tests. Spectral characterization probes the interaction of a material with electromagnetic radiation, revealing details of chemical composition, surface profile, or refractive index. Physical characterization determines properties such as complex dynamic modulus, tensile strength and elongation, hardness, and flexibility. Rheological characterization determines properties such as viscosity, thixotropy, and stages of drying and cure. Listed here are some of the analytical capabilities that August Research Systems (ARS) employs to characterize materials and to quantify changes that occur as a result of service life or exposure to accelerated test environments.
Spectral Characterization
Color and Reflectance
Spectral reflectance and color is evaluated using a spectrophotometer. Color is quantified mathematically through coordinates defined by the International Commission on Illumination (CIE) according to ASTM E308. ARS utilizes a diffuse hemispherical measurement geometry (d/8°) for measuring color conforming to ASTM E1331.
UV-VIS-NIR
In some applications, the reflectance of a material beyond the visible spectrum is important. Ultraviolet (UV) and near-infrared (NIR) spectra can be measured at ARS from 250 to 1000 nm in a d/8° configuration.
FTIR Spectroscopy
Fourier Transform Infrared (FTIR) spectroscopy obtains the infrared molecular absorption spectrum of a material. This spectrum acts as a fingerprint which can be used to identify a material and its chemical makeup. It can also be used to assess the change in the chemical makeup of a material over time owing to chemical reactions or chemical changes from environmental exposure.
DRIFTS
Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) is a method for characterizing the diffuse reflectance of powders or opaque films. This property is closely related to the emissivity of opaque materials.
Specular Gloss
A glossmeter is used to measure the specular reflectance of light from a surface, providing a quantifiable way to differentiate between a glossy, semi-gloss or matte coating. This measurement conforms to ASTM D523.
Physical Characterization
Dynamic Mechanical Analysis (DMA)
DMA measures the mechanical properties of a material as a function of time, temperature, and frequency. A wealth of information can be obtained from the DMA measurement of a material, including, but not limited to its viscoelastic behavior, glass transition temperature (Tg), vibration and sound damping characteristics, and tendencies to creep and relax. ARS often employs DMA measurements to evaluate changes that result from various accelerated environmental exposures.
Adhesion
Several tests are used for evaluating the adhesion of coatings to substrates. The quick and easy way of evaluating adhesion is the tape adhesion test that is performed according to ASTM D3359. A quantitative evaluation of adhesion is provided by a pull-off tester conforming to ASTM D4541.
Tensile and Elongation Testing
Tensile and elongation of elastomeric materials are measured using a universal test machine according to ASTM D412. Samples held between two jaws are elongated as the jaws separate at a given rate. Tensile force and displacement are tracked, permitting the determination of yield stress, ultimate stress, percent elongation and modulus as a function of elongation.
Hardness
The hardness of a coating can be evaluated using a pendulum hardness tester conforming to ISO 1522. A well-characterized pendulum is suspended from a fulcrum that rests on a coating surface. The time required for the pendulum amplitude to decay to half its initial value is the hardness, expressed in seconds. For thicker materials, ARS employs a Shore M Durometer in accordance with ASTM D2240.
Flexibility
ARS evaluates the flexibility of coatings using the cylindrical mandrel bend, conical mandrel bend and the GE impact tester. The conical mandrel (pictured) provides a continuous range of flexibility values, rather than a binary pass/fail determination. Mandrel bend tests are performed according to ASTM D522. The GE impact test conforms to ASTM D6905. Each of these test can be conducted at ambient, sub-ambient or super-ambient temperatures.
Rheological Characterization
Dry Time
The dry time recorder tracks the drying history of paint in four stages in accordance with ASTM D5895.
Viscosity
The rheology profile of a material is evaluated using a viscometer. ARS utilizes a cone/plate viscometer to evaluate material viscosity as a function of shear rate and temperature. Pot life of two-component coatings, adhesives, or sealants can be assessed through change in viscosity using a viscometer or viscosity cups.
