The potential of zwitterionic bonding in paper

This research examines the nature of bonding between cellulose fibers and the effects produced by introducing ionic functionalities on the surface of the fibers. The potential of utilizing ionic bonds besides the natural papermaking bonds, e.g., hydrogen bonds, lies on their inherent higher enthalpy (15-20 kcal/mol) and facility to be formed under the conditions prevailing in standard papermaking processes. A limitation in previous efforts to build an ionic bonding system on cellulose fibers was the difficulty of achieving balance of charges in order to avoid electrostatic interaction of fibers before paper formation. In the present work this was achieved by introducing zwitterions onto cellulose fibers via chemical modification. Among various possibilities, zwitterions, exemplified by trifunctional amino acids such as tyrosine, lysine and cysteine, were fixed to cellulose fiber surfaces by means of cyanuric chloride, which acted as a bridging molecule. The approach investigated consisted in first reacting cellulose fibers with cyanuric chloride and, in a second step, the partial modified fibers (triazinylated fibers) were treated with the amino acids. Samples from an alternate approach to the synthesis of zwitterionic fibers were prepared and also examined here.; The attachment of amino acids onto the fibers was verified by chemical analysis and examination of the fiber surface by ESCA. Handsheets made from zwitterionic pulps showed increased bulkiness, which was interpreted as being due to poor bonding between the fibers. When the density of the handsheets was restored by hot-pressing, the dry strength of the zwitterionic fibers matched that of untreated samples. Examination of the strength of re-wetted zwitterionic paper (wet strength) confirmed the positive effect previously reported for the ionic interactions of cellulose fibers.; Measurements of the strength of never-dried zwitterionic paper webs indicated that the introduction of zwitterions onto the fibers produced stronger webs at solid contents above 55%, imparting to them some ability to stretch. It seems possible that any positive effect propitiated by the zwitterionic moieties at low solids content is counteracted afterwards by morphological changes in the fibers and/or physical hindrance of hydrogen bonds by the bulky zwitterions when the web is practically fully dried.