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(SEM). It was seen that the handsheets had a much denser surface structure with alginate, compared to with cationic guar gum or chitosan (Fig. 9). The alginate seemed to fill out some of the roughness of the paper surface, which also lowered the air permeability of the fiber network significantly. This was similar to the previously reported effect of agar (Vishtal and Retulainen 2014a). The available results indicate that anionic additives may form a film on top of the sheet after spray addition, while cationic additives may migrate more freely throughout the fiber network, once saturated. This is also in agreement with previous findings that iminated amphiphilic galactoglucoman- nans formed a film on top of the paper after spray addition, while cationic galactoglucomannans were able to penetrate deeper into the fiber network during impregnation (Lindqvist et al. 2014). The formation of an alginate film on the top side of the paper resulted in
enhanced paper shrinkage, which significantly increased the strain at break and 2D formability strain after unrestrained drying. The shrinkage of the wet al- ginate film during drying was most likely transferred to the rest of the fiber network causing enhanced paper shrinkage, much like the reported effect of agar (Vishtal and Retulainen 2014a).
Conclusions
Model polysaccharide films were prepared from alginate, cationic guar gum, or chitosan. Alginate resulted in very strong and stiff films with low strain at break values, while cationic guar gum and chitosan resulted in significantly weaker and softer films with high strain at break values. The different polysaccha- ride solutions were sprayed onto wet handsheets, and
Fig. 9 SEM micrographs of the top surfaces of handsheets sprayed with alginate ( A , B ), cationic guar gum ( C ), and chitosan ( D ).Allof these handsheets were sprayed with 2% polysaccharide with addition of 20% sorbitol, and subjected to restrained drying
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