Dielectric properties of lignin and glucomannan as determined by spectroscopic ellipsometry and Lifshitz estimates of non-retarded Hamaker constants

We present in this study a quantitative estimate of the dispersive interactions between lignin, hemicellulose and cellulose, which are the dominating components in wood and also extensively used to produce paper and packaging materials. The dielectric properties in the UV-visible region of spin-coated films of pure lignin and glucomannan were determined by spectroscopic ellipsometry. The non-retarded Hamaker constants were estimated from the determined spectral parameters using Lifshitz theory for lignin and glucomannan interacting with cellulose, titania and calcium carbonate in vacuum, water and hexane. The Hamaker constants for the different combinations of cellulose, lignin and glucomannan fall within a relatively narrow range of 35–58 and 8–17 zJ, for the values in vacuum (air) and water, respectively. The estimated Hamaker constants for the interactions of the wood components with TiO₂ and CaCO₃, common additives in paper, in water range from 3 to 19 zJ, thus being similar in magnitude as the interactions between the wood components themselves. In contrast, the Hamaker constant is essentially zero for glucomannan interacting with calcium carbonate in hexane. The Hamaker constants for lignin, hemicellulose and cellulose determined in this study can provide information regarding the surface interactions important for e.g. adhesion, friction, swelling and wetting in paper processing as well as for the resulting behavior of paper products.