A Systematic Study of Noncross-linking Wet Strength Agents

Cellulosic
fibers are inherently hydrophilic, and the modification of them to
withstand moisture is important both commercially and scientifically.
The usual methods are based on the cross-linking chemistry of reactive
groups such as epichlorohydrins. Here, we present that it is possible
to attain paper with wet strength from a combination of polymers that
lack cross-linking chemistry, namely, carboxymethyl cellulose (CMC)
and Polybrene. To accomplish this, we first altered the surface charge
of the fibers by adsorption of CMC. Subsequent adsorption of Polybrene,
forming the fibers as paper sheets, and drying yielded paper with
wet strength properties. The wet strengthening was further investigated
by (i) varying the molecular weight of the CMC, (ii) varying the cationic
polyelectrolyte, and (iii) synthesizing polymers called ionenes to
study the structural properties behind the wet strength of Polybrene.
The results showed that (i) drying was necessary to obtain wet strength,
(ii) wet strength seemed to be a surface effect, (iii) high Mw CMC played an important role in the development
of wet strength, and (iv) only asymmetric ionenes ([3,6] and [6,12]-ionenes)
could attain wet strength while symmetric [3,3] and [6,6]-ionenes
failed to show wet strength properties.