Our previous articles covered the use of four specialized instruments, including the Brookfield Cone-Plate Digital Rheometer, the Aquastar Titrator, the Differential Scanning Calorimeter, and the Dielectric Analyzer. The series concludes with two additional and essential instruments, the Infrared Spectrophotometer and the Brookfield Digital Viscometer. For professional quality control and technical analysis, the right instruments are an essential part of any serious laboratory.

The IR Spectrophotometer is often used to determine surface contamination problems. This process involves washing a surface with a solvent and running an IR spectrum of the wash. You would compare the IR spectrum with that of the pure solvent; a match would show that surface contamination isn't likely. A spectrum that shows different peaks indicates a surface with low surface energy, one that decreases adhesion.

Infrared spectroscopy is widely used in both qualitative and quantitative analysis. Its single most important use has been for the qualitative identification of organic compounds whose spectra are generally complex and provide numerous maxima and minimas that are useful for comparison purposes. In quantitative analysis, the high selectivity often makes estimation of an analyte possible in a complex mixture, with little or no prior separation steps.

The Brookfield Digital Viscometer measures the viscosity of fluid materials, which is the resistance of flow of a liquid. Viscosity of water at room temperature is Newtonian and is the reference point for determining viscosity points. The viscosity of pure water at 25°C is defined as one centipoise, or one dyn/cm2. For operation, the instrument uses a rotating rod or spindle in a material at a fixed speed, and makes a measurement of the dragging force on the spindle due to the viscosity of the material.

Some shear-dependent properties are easily noticed, such as thixotropic materials which show decreasing viscosity at increased shear rates. By changing the rotation rate on the spindle without altering the sample gives a range of viscosity values on the material which characterize this property clearly for relative comparisons and quality control. There are some specific limitations: temperature control of the sample material is critical to the proper use of the instrument, and is an item typically left to the operator in control. There are accessories available for more specialized temperature control.

We routinely use the instrument for quality control testing and the development of new products. Since viscosity is a property that is strongly dependent upon the characteristics of a material's constituents, it is a good indicator of product stability. Stability testing of Fielco products nearly always involves the use of a viscometer. When investigating a customer problem involving dispensing or pumping, the first test usually involves the viscometer. If a material is too thin, the equipment may not be able to control how much flow occurs during a dispensing operation, leading to excessive adhesive usage. When a material is too thick, the equipment may not be able to dispense or transport material at all.

If you have additional questions about adhesive usage and testing, please feel free to contact us directly at (800) 825-7156, or outside the US at (215) 674-8700, or by e-mail at techd@fielco.com. We'll be more than happy to assist.