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Fig. 7 Strain at break (%) versus 1D shrinkage (%) of handsheets sprayed with the different polysaccharide solutions. The paper properties were measured after restrained (R) and unrestrained (UR) drying. The average values with standard deviations are shown
shrinkage has previously been studied and reported (Strand et al. 2017). Alginate was the only tested polysaccharide that actively increased paper shrinkage during unrestrained drying, which lead to noticeably higher strain at break values of the handsheets. The air permeability of the handsheets was mea- sured after restrained and unrestrained drying. After restrained drying, the water spraying had increased the air permeability from 2868 to 4020 mL/min (Table 3). The large influence of the spraying procedure was, however, not visible after unrestrained drying (Table 4). After restrained drying, all of the polysac- charide additions resulted in decreased air
permeability values (Fig. 8). Alginate lowered the air permeability values of the handsheets significantly. Chitosan or cationic guar gum did not result in similar decreases. A drastic decrease in air permeability has previously been also reported after addition of agar onto wet sheets; the value decreased by approximately 84% (Vishtal and Retulainen 2014a). In the same study, it was reported that a surface film of agar could be useful in grease-barrier applications due to the hydrophilic nature of the polysaccharide and the dense structure of the surface. The sprayed top sides of the different handsheets were imaged using a scanning electron microscope
Fig. 8 The air permeability (mL/min) of handsheets sprayed with the different polysaccharide solutions. The permeability values were measured after restrained and unrestrained drying. The average values with standard deviations are shown. Alg alginate, C-gg cationic guar gum, Chit chitosan. The amount of added sorbitol is also shown in the x-axis legends
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