Tools to Probe Nanoscale Surface Phenomena in Cellulose Thin Films: Applications in the Area of Adsorption and Friction - The Nanoscience and Technology of Renewable Biomaterials - page 94

1600

DS 0.33

1200

DS 0.06

DS 0.035

800

400

DS 0.023

0.00 0.04 0.08 0.12 0.16 0.20

Xanthate DS

Figure4.2 Wet strength(wetbreakinglength)ofpaper treatedwithxanthatedstarchamine
having various tertiary amine and xanthate degrees of substitution (DS). The paper samples
were prepared fromunbleached kraft furnish treatedwith 3%XSA, oven dry pulp basis, at
pH7.0.ReproducedwithpermissionfromCarr,Hofreiteretal.(1977).

tertiary amine, anionic monomer methylene butanedioic acid (or itaconic acid,
IA), and neutral acrylamide (AM) monomer. Some of the advantages of synthetic
polyampholytes include higher charge densities; simple control of the molecular weight
and charge ratio of cationic and anionic groups; uniform molecular weight distribution
(lower degree of polydispersity), etc. The superior dry strength of polyampholytes
over simple polyelectrolytes was reported in several publications (Sezaki, Hubbe et al .
2006a, 2006b; Song, Wang et al . 2006; Wang, Hubbe et al . 2006; Hubbe, Rojas et al .
2007a, 2007b; Wang, Hubbe et al . 2007). Under the experimental conditions used,
polyampholytes were applied at 1% addition level on bleached hardwood kraft fibers.
Paper's breaking length increased 20-50% compared with control experiments (see
Figure 4.3). An interesting observation was the fact that the strength of the paper
increased as the charge density increased, reaching a maximum for polyampholytes of
intermediate charge density. After reaching a maximum strength value, the strength
decreased as highly charged polyampholytes were employed. A near neutral pH was
found to be optimum condition to maximize strength performance. This interesting
behavior could be explained by the fact that close to the iso-electric point (IEP) of the
polyampholytes, a maximum efficiency for adsorption is achieved and bonding between
fibersispromoted.
Despite the fact that a number of theoretical and computational efforts have been
reported (Gutin and Shakhnovich 1994; Kantor, Kardar et al . 1994; Kantor and Kardar
1995; Bratko and Chakraborty 1996; Ertas and Kantor 1996; Schiessel and Blumen 1996;
Srivastava and Muthukumar 1996; Lee and Thirumalai 2000; Yamakov, Milchev et al .
2000), there is still a lack of experimental data regarding the dynamics of adsorption,
and interactions of polyampholytes at the nanoscale. Understanding such phenomena
will lead to new functional formulations and improved performance of fibers after sur-
face modification. In this chapter we will revisit the issue of polyampholyte adsorption