Fiber surface characteristics evaluated by principal component analysis

Principal component analysis (PCA) was used to evaluate the results of standard fiber analyses, determinations of charge, electron spectroscopy for chemical analysis (ESCA) measurements, and selective staining of kraft fibers prebleached with oxygen, followed by hydrogen peroxide or ozone. The majority of data variance is explained by the lignin content in fibers and by polarity (hydrophilicity vs hydrophobicity) of functional groups. The lignin determination methods (kappa number, C1 (ESCA), selective staining) gave similar but not equal results, because they measure different parts of lignin. The determination methods of the charged groups (total charge, surface charge, C4 (ESCA), and hexenuronic acids) also gave similar but not equal results. The results of staining by using cationic dyes do not correlate with the quantity of anionic (mainly carboxylic) groups in fibers, regardless of whether the dyes are selective for lignin or hemicellulose. Hydrogen bonding and hydrophobic interactions seem to overrule ionic interactions between dyes and fibers. Therefore, the majority of bonds formed between fibers themselves, as well as between fibers and paper additives, can to a great extent be expected to have the character of hydrogen bonds.