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 93

Colby et al . 2004). These polymers find application in several other fields including
colloid stabilization, wetting, lubrication and adhesion (Mazur, Silberberg et al . 1959;
Bratko and Chakraborty 1996; Jeon and Dobrynin 2005; Sezaki, Hubbe et al . 2006a,
2006b; Song, Wang et al . 2006; Wang, Hubbe et al . 2006, 2007; Hubbe, Rojas et al .
2007a, 2007b).
Under appropriate conditions the acidic and basic groups in polyampholytes disso-
ciate in aqueous solution producing ionic groups and their respective counterions. If
the ionic groups on the polymer chain are weak acids or bases, the net charge of the
polyampholytes can be changed by varying the pH of the aqueous medium. At the
isoelectric point (IEP), the number of positive and negative charges on the polyion is
the same, giving a net charge of zero. In the vicinity of the isoelectric pH, the polymers
are nearly charge-balanced and exhibit the unusual properties of amphoteric molecules.
At conditions of high charge asymmetry (far above or below the isoelectric pH),
these polymers exhibit a simple polyelectrolyte-like behavior (Gutin and Shakhnovich
1994; Kantor and Kardar 1995; Ertas and Kantor 1996; Hwang and Damodaran

1996; Long, Dobrynin et al . 1998; Lee and Thirumalai 2000; Yamakov, Milchev

et al . 2000; Dobrynin, Colby et al . 2004; Jeon and Dobrynin 2005; Lord, Stenzel

et al . 2006).
As fiber recycling increases more interesting and new polymer molecular architectures
have been proposed as means to improve product strength from loses (especially in tensile
and burst strengths) due to reuse (Nazhad and Paszner 1994; Nazhad 2005). After
extensive recycling fibers may not longer be useful without the addition of chemical
additives.
While several polymer chemistries are used in the applications explained above,
polyampholyte treatments may be less common. To our knowledge, the first report
on the application of polyampholytes to enhance strength of paper was published in
1977 by Carr, Hofreiter et al . (Carr, Hofreiter et al . 1977). In this seminal report,
starch-based polyampholytes were prepared using xanthating cationic cornstarch deriva-
tives, which had either tertiary amino [

− CH 2 CH 2 N(C 2 H5) 2 ] or quaternary ammonium

CH 2 CHOHCH 2 N + (CH 3 ) 3 ] groups attached to the macromolecule. Anionic xanthate
groups were then introduced into the cationic starch amines. The substitution degree of
the obtained derivatives ranged from 0.023 to 0.33 for the amine cation and 0.005 to
0.165 for the xanthate anion. This work demonstrated that wet-end additions of a starch
polyampholyte was effective in improving both wet and dry strengths, exceeding those
given by either cationic or anionic starch polyelectrolytes. For a given amine degree of
substitution (DS), there was a charge ratio of A (amine, positive)/ X (xanthate, negative)
at which point each polyampholyte gave a well-defined maximum value for wet strength.
This A/X ratio was about 1 for tertiary amine with a low DS (DS of 0.023, 0.035, and
0.06) but was about 2 to 3 for tertiary amines with a high DS of 0.33 (see Figure 4.2).
The authors also found that polyampholytes with quaternary amines substitution were
slightly more effective than those with tertiary amines.
Recently fully synthetic polyampholytes were systematically investigated in our lab-
oratories with the aim of enhancing paper strength (Sezaki, Hubbe et al . 2006a, 2006b;
Song, Wang et al . 2006; Wang, Hubbe et al . 2006, 2007; Hubbe, Rojas et al . 2007a,
2007b).

−

[

The employed polyampholytes were prepared by free-radical polymerization

N-[3-(N ,N -dimethylamino)propyl]acrylamide of cationic monomer (DMAPAA), a