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responsible for any correspondence. All authors contributed to the writing of the manuscript.
tensile indices, by using the aforementioned copoly- mer yielding relative wet strengths of up to 25%. Because H 2 O has the ability to readily swell cellulose fibers inside the paper network, a homoge- neous distribution of the copolymer in and on the fibers can be observed. This reinforces both the fiber crossing points and the fibers themselves, which increases the tensile index, especially in the wet state. By using solvents which do not swell the cellulose fibers, e.g. IPA or BuOH, the copolymer can’t penetrate into the fibers, the distribution of the copolymer on the surface of the fibers is less homo- geneous and wet tensile (relative wet-) strength is much lower. Overall, we can thus conclude that impregnation with IPA and BuOH solutions of the copolymer is preferable for the dry tensile strength, while impreg- nation with H 2 O dissolved macromolecules followed by photocrosslinking allows for increased wet tensile strength of paper samples. To gain an even deeper understanding of the underlying mechanisms, in particular when using the photo-reactive wet-strength agents, in future, we will focus in more detail on the influence of paper-extrinsic parameters, such as the source of light, illumination conditions and solvent content during illumination, as well as paper/paper technology intrinsic parameters such as a comparison of the here reported impregnated papers vs. the use of (charged) copolymers in wet end processes. Acknowledgments The authors thank Heike Herbert and Martina Ewald for technical support. Funding by the DFG under Grants #405422473, and #406026418 is gratefully acknowledged. This study was in part also supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC- 2193/1–390951807 ( li v MatS). Authors’ contributions J-LS and SS have contributed equally to this work. SS contributed the expertise and synthesized and provided the materials for photochemically cross-linkable copolymers and performed the measurements of the hydrodynamic radii. J-LS contributed the expertise in cellulose (paper) modification and prepared the functionalized paper samples, carried-out all tensile tests as well as confocal laser scanning microscopy measurements. ARvS prepared sample paper sheets as well as he provided specifications of the used lab-paper. OP and TB planned and supervised the synthesis of the copolymers, and TM planned and supervised the measurements by various microscopy techniques. JR and MB planned and supervised the whole project and are equally
Funding Open Access funding enabled and organized by Projekt DEAL. Funding of this work is provided by the German Research Council, DFG under grants #405422473 and #406026418 is gratefully acknowledged. This study was in part also supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2193/1–390951807 ( li v MatS). The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. All data generated or analysed during this study are included in this published article (and its supplementary information files). Availability of data and material
Declarations
Conflict of interest competing interests.
There are no conflicts of interest nor
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