Cellulose (2018) 25:3781–3795
3785
Table 2 Properties of the polyanions used in the experimental series
Charge density [ l eq/g]
Polyanion
Molar mass [kDa]
CMC, Aldrich, DS 0.80–0.95
- 4176
700
CMC, Acros Organics, DS 0.7
- 3351
250
CMC, Acros Organics, DS 0.9
- 3892
250
CMC, Acros Organics, DS 1.2
- 4513
250
Fig. 1 The measured turbidity values of polyelectrolyte complexes (PECs) of polyDADMACs or different cationic starches with CMCs (250 kDa) of DS 0.7, 0.9, and 1.2. The presented turbidity values were determined within 1 min of PEC formation
associative phase separation of the oppositely charged polyelectrolytes into colloidal particles (Piculell and Lindman 1992; Kekkonen et al. 2001). The turbidity increased up to cation/anion ratios close to the theoretical neutralization point of the polyelectrolytes, and decreased after this ratio was exceeded. The calculated theoretical neutralization points between the different polyelectrolytes are presented in Table 3. In order to illustrate that the turbidity maxima were connected to charge neutralization, the polycations were mixed together with CMCs of different charge density, or degree of substitution (DS). Using a CMC with higher charge density shifted theoretical point of
neutralization towards higher cation/anion ratios, since a larger amount of polycation was needed in order to neutralize the anionic charge. The turbidity curves in these experiments were similar to previously published results using other polyelectrolytes (Dragan and Cristea 2001; Hubbe et al. 2005; Lofton et al. 2005). It has been shown that PECs coexist with dissolved polyelectrolyte species at cation/anion ratios above and below the direct vicinity of the neutralization point (Kekkonen et al. 2001). However, PEC mixtures close to the neutralization point only contain low residual amounts of dissolved polyelectrolytes. Excess
Table 3 Theoretical cation/anion ratio for charge neutralization
CMC DS 0.7, 250 kDa CMC DS 0.9, 250 kDa CMC DS 1.2, 250 kDa CMC DS 0.8–0.95, 700 kDa
PolyDADMAC 200–350 0.7
0.8
0.9
0.8
PolyDADMAC 100–200 0.8
1.0
1.2
1.0
Raifix 25035
1.8
2.1
2.4
2.2
Raisabond 15
3.8
4.4
5.1
4.7
Raifix 01015 SW 4.2
4.7
5.4
5.0
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