Modern paper consists of a multitude of different components. Besides fibers, glue, impregnating agents and auxiliary materials paper contains, depending on the type, up to 30 % fillers. Typical filler materials are for instance calcium carbonate, talcum, kaolin, gypsum, and titanium dioxide. Thereby, material properties like printability, glare, or opacity can be optimized as required. In the finished product, the individual components are visually virtually indistinguishable. Also, defects often have only a low visual contrast and are therefore difficult to analyze.
FTIR spectroscopy is a measuring method by which the chemical identity of various organic and inorganic materials can be determined in a very rapid manner. Since many paper types have a very inhomogeneous composition and defects are often extremely small, the analysis with macroscopic measurement methods is usually not possible.
With the aid of an FTIR microscope, it is possible to measure an IR spectrum anywhere on the sample with a high lateral resolution and thereby to determine the chemical composition of the defect. A mapping measurement allows the qualitative analysis of the components and the determination of the distribution on the measured sample area.
This example shows the analysis of a contamination on the surface of a paper sample. Due to the low visual contrast, the contaminated area is only barely visible to the unaided eye. The analysis of the paper was done with an automated mapping measurement. The resulting chemical image shows the semi quantitative distribution of the contamination. The acquired spectral information allows to identify the contamination as a silicate making it much easier to find the cause of the impurity.
|Learn more in our Application Note AN M137 about identifying defects and inhomogeneity in paper.|