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C.V.G. Esteves: Oxygen deligni fi ed fi bers as a greener alternative for tissue paper
Figure9: Strength properties for the reference and oxygen deligni fi ed pulps at di ff erent levels of re fi ning as a function of kappa number. A) Wet tensile index and B) relative strength. (20 g/m 2 laboratory tissue handsheets were used). The numbers on the top of the symbols in graph A) are the total fi ber charge of the samples. The values are in meq/kg.
similar behavior was seen for the dry strength – Figure 10C. The oxygen deligni fi ed pulps even showed slightly better softness at speci fi c tensile strength than commercially bleached pulp. Unfortunately, the softness measurements through the TSA equipment come with a signi fi cantly large standard deviation for some samples, which gives some uncertainty about the softness comparison between the samples. 4 Conclusions This work showed the potential of using oxygen deligni fi ed pulps as a replacement for fully bleached pulps. Compared to the commercial fully bleached pulp, similar absorption and much higher tensile strength were obtained for the oxygen deligni fi ed pulps, especially for unre fi ned pulps. Two of the oxygen deligni fi ed pulps (K61_O25 and K61_OO18) achieved similar absorption capacity and faster water rising with higher bulk when compared to commercial pulp. Signi fi cantly higher wet strength and higher strength ratio were obtained for the oxygen deligni fi ed pulps, especially for the pulps with the highest lignin content. The oxygen pulps showed similar softness levels for higher tensile strength. Lignin content was seen to have an impact on the WRV but no e ff ect on absorp- tion capacity or capillary rising, which only depended on bulk. As expected, when the oxygen deligni fi cation starts with a kraft cooked pulp with a low kappa number the increase in
individual sensibility, bulk, fl exibility, thickness, among others. Softness is considered one of the most essential properties of tissue products (de Assis et al. 2018). The studied samples were evaluated using the Tissue Softness Analyzer (TSA), which is claimed to give a perception of the sample ’ s softness (Figure 10). The soft- ness can be estimated by the TS7 parameter, where lower TS7 values are attributed to higher softness (de Assis et al. 2020). The unbleached pulps (K61_O25 and K61_OO18) pre- sented similar TS7 values for slightly higher bulk as the reference pulp when no re fi ning was applied. The highest and lowest kappa samples also obtained a similar TS7 value as the reference but for lower bulk values. The in- crease in TS7 with re fi ning was expected since the higher strength is usually associated with lower softness (Deb- nath et al. 2021; Scott et al. 1995). Thus, an increased strength results in impaired softness and vice versa (Figure 10B and C). An increase in the paper strength is generally followed by a decrease in softness (Salem et al. 2023). However, it can be seen that unbleached pulps presented similar softness levels with much higher wet and dry strength (Figure 10B and C). Figure 10B shows that oxygen deligni fi ed pulps, when not re fi ned, present higher wet strength for lower TS7 values (higher softness). When the pulps are re fi ned, the wet strength signi fi cantly increases without varying the TS7 factor signi fi cantly (K109_O47 and K109_OO35). Quite
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