Figure 1 shows the liquid sorption properties of papers treated in water (A), ethanol (anhydrous) (B), methanol (anhydrous) (C), 1 N sodium hydroxide (D), up to five repetitive drying and wetting steps. It can be revealed that the highest absorption occurred with sample D (230.5% in the 1st cycle and 179.8% in the 5th cycle), followed by sample A (182.3% in the 1st cycle and respectively 170.6% in the 5th cycle), sample B (109.4% in the 1st cycle and 97.6% in the 5th cycle), and sample C (101.5% in the 1st cycle and 84.3% in the 5th cycle), respectively. However, the repetition of drying and wetting generally affects the decrease of liquid absorption of the sheets. This is not surprising because several researchers have already reported a definitive correlation between chemical treatments and the sorption properties of cellulosic materials.
Absorption properties of paper treated with different chemicals.
These reductions can be attributed to a change in the fiber polymer structure such as hydrogen bond cross-linking or removal of H-bonding sites for liquids. Because, all the switzerland email list liquids used in this study have hydrogen bonding ability and can penetrate into the paper network structure, followed by substitution of -OH by cellulose-to-cellulose hydrogen bonds. Furthermore, closure of larger pores that do not reopen upon rewetting may be an effect of high surface tension forces. This mechanism and subsequent strain hardening forces may weld the pores together and resist liquid penetration to some extent. These are in good agreement with the results reported by Wistara (1999) that dry fibers with higher initial swelling ability have lower resealing ability.
However, 1 sample treated with sodium hydroxide (D) has considerably higher absorption value than others. After 5th repeated wetting and drying cycle, sample D shows about 6% higher absorption than sample A, 85% than sample B and 114% than sample C respectively (Figure 1). It can be attributed to the reorientation of microfibrils and better alignment of cellulose chains in the lamella network structure promoting additional H-bonding sites for liquids. Das and Chakraborty (2006) found that during alkaline treatment, a lattice transformation from cellulose-I to cellulose-II took place and sodium hydroxide introduces considerable changes in crystallinity and orientation angle within the cellulose structure. These may affect less crystalline region in cellulose hence additional H-bonding site for liquids.