Cellulose (2021) 28:5775–5791
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Fig. 5 Examples of two frequently observed mechanisms ( a fiber failure and b fiber pull-out) during the failure of polymer-modified paper sheets during tensile straining in the wet state, captured with a self-made Zwick-videography setup
17.6 Nm g - 1 and 0.3 Nm g - 1 for the dry and wet state, respectively. If the same paper is now being treated with one of the solvents without any copolymer and a similar swelling/drying protocol in combination with UV-exposure is used as with the copolymer impregnation process, we observe a decrease of both, dry and wet tensile index, to 9.8 and 0.2 N m g - 1 (RefSwell—H 2 O), 12.1 and 0.2 N m g - 1 (RefSwell—IPA) and 12.2 and 0.2 N m g - 1 (RefSwell—BuOH), respectively. There are multiple factors which have to be taken into account, when analyzing the effect of such a swelling/drying treatment with UV-exposure. Gravi- metric experiments show, that drying under climate controlled conditions (23 C, 50% r.h.) leads to a significant increase in moisture content (for all three solvents—detailed information in table S4), which can weaken the forces described earlier, being responsible for the intrinsic strength of paper, and thus the tensile strength. Further on, it has been found that unre- strained drying, which is comparable to drying on a mesh, significantly lowers the tensile strength (Strand
quantitative macroscopic tensile behavior of the paper sheets, and in particular, of polymer-functionalized paper sheets, which allows for higher throughput of various samples.
Impact of swelling-drying-cycles combined with U V - treatment
In order to compare the tensile strength of paper samples treated with the copolymer, we first analyzed the influence of the solvent treatment without any copolymer. When comparing the tensile-straining behavior of the Ref - and RefSwell -samples in the dry state in Fig. 3, it is apparent, that the treatment without copolymer leads to a significantly lower maximum force at break, while the elongation (strain at break) is increased. In the wet state, however, differences in the elongation are not as significant. In Fig. 4 the dry and wet tensile index, as derived from the stress–strain curves for the different paper samples are shown. If a reference paper sheet (Ref) is analyzed with respect to the tensile index, we observe typical values of about
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