Analysis of Paper Surface (FTIR)
Paper is made from cellulose fibers separated from wood material. A binder is added and the fibers compressed. To retain strength and hold ink, sizing agents, pigments, clays, and other materials are also applied.
Furthermore, for special applications, some papers have their surface coated with various substances, depending on the application. Examples include paper food containers, adhesive tapes, release papers, coated papers, etc. The best way to analyze the surface of such papers easily is by using an infrared spectrophotometer (FTIR) and the ATR method.
Results from measuring paper with a variety of surface treatments using the horizontal ATR method are shown below. An overlay of spectra from measuring the front and back surfaces of four types of paper – cardboard, coated paper, milk carton, and release paper, is shown.
Absorption closely resembling kaolin clay is observed near 1000 and 900 cm-1 in the cardboard spectra.
In the coated paper spectra, absorption is observed near 1064 and 800 cm-1 for what is presumably SiO2.
In contrast, absorption for polymers can be confirmed in the milk carton and release paper spectra. For the milk carton, cellulose could not be confirmed on either the front or back side. Instead, absorption for polyethylene is observed. In the release paper spectra, peaks characteristic of silicone polymer are observed near 1260, 1100-1000, and 800 cm-1.
The ATR method measures samples by pressing them tightly against the surface of a plate-shaped prism made of material with a high refractive index. The surface roughness of paper may vary somewhat depending on the type of paper, but surface spectra can be measured for most papers by pressing them harder and more tightly against the prism.