A preliminary study of the spreading of AKD in the presence of capillary structures

There may be several mechanisms at work in the process of migration or redi stribution of alkyl ketene dimers (AKD) on cellulose fiber surfaces during paper sizing and curing. This work is the second part of a continuing inves tigation of the spreading behavior of AKD on the surfaces of hydrophilic su bstrates. Paper sheets, single cotton, and cotton lint fibers and smooth ce llulose film were used as substrates. These represent samples that have por es, V-shaped grooves, and no capillary structure at all. A very simple and effective testing method for studying the AKD migration behavior through th ese substrates was designed. AFM was used to study the surface capillary st ructures of cotton and cotton lint fibers. The results of this study provid e hard evidence supporting our finding that capillary structures in the for m of either interfiber pores in a paper sheet or V-shaped grooves on the su rface of single fibers are essential in order for the spreading of molten A KD on a cellulose substrate to occur. Some preliminary results on the exist ence and the surface diffusion of an autophobic precursor of AKD are also p resented. The results support the conclusion we reached in the first part o f this investigation; i.e., the molten AKD wets but does not spread on smoo th, capillary-free hydrophilic surfaces such as glass and cellulose. The dr iving force from interfacial energy alone does not cause spontaneous "flow- like" spreading of molten AKD on these surfaces. This is possibly associate d with the formation of an autophobic precursor in front of an AKD droplet. The results in this study do not support the perception that molten AKD fo rms a single molecular layer on the surface of cellulose fibers by spreadin g during heat treatment, although the autophobic precursor in front of an A KD droplet could theoretically be of a monolayer thickness and the surface diffusion of this precursor may contribute to the sizing development after heat treatment. (C) 2001 Academic Press.