Inverse gas chromatography study on partially esterified paper fiber.

Paper fiber was treated in a heterogeneous esterification reaction with four different fatty acids. This fiber was used to strengthen polyethylene (PE) composites. Modified and unmodified cellulose fiber was characterized with inverse gas chromatography. In previous work, characterization was also carried with X-ray photoelectron spectroscopy (XPS), solid-state NMR, differential scanning calorimetry and thermogravimetry. Individual fibers were found to be covered with the corresponding esters (cellulose undecylenate, undecanoate, oleate, stearate) with partial degrees of substitution of the cellulose. Comparison of XPS and NMR results showed that the surface degree of substitution of the cellulose fiber was higher than for the bulk, showing that the esterification reaction was a surface phenomenon. The aim of this work was to acquire information on the surface characteristics of the fiber and to see whether it could be correlated to PE composite mechanical strength results. The conclusions are that polar probes seem to diffuse more into the fibers than the non-polar probes, as the non-polar component of the surface tension of the modified fiber is much lowered towards that of PE, while donor-acceptor characteristics are hardly changed by esterification. The ester with the lowest non-polar component of the surface energy, the oleate, also gives the composite with the best mechanical properties.