Cross-Linking Cellulosic Fibers with Photoreactive Polymers: Visualization with Confocal Raman and Fluorescence Microscopy

Abstract

The properties of paper sheets can be tuned by adjusting the surface or bulk chemistry using functional polymers that are applied during (online) or after (offline) papermaking processes. In particular, polymers are widely used to enhance the mechanical strength of the wet state of paper sheets. However, the mechanical strength depends not only on the chemical nature of the polymeric additives but also on the distribution of the polymer on and in the lignocellulosic paper. Here, we analyze the photochemical attachment and distribution of hydrophilic polydimethylacrylamide-co-methacrylate-benzophenone P(DMAA-co-MABP) copolymers with defined amounts of photoreactive benzophenone moieties in model paper sheets. Raman microscopy was used for the unambiguous identification of P(DMAA-co-MABP) and cellulose specific bands and thus the copolymer distribution within the cellulose matrix. Two-dimensional Raman spectral maps at the intersections of overlapping cellulose fibers document that the macromolecules only partially surround the cellulose fibers, favor to attach to the fiber surface, and connect the cellulose fibers at crossings. Moreover, the copolymer appears to accumulate preferentially in holes, vacancies, and dips on the cellulose fiber surface. Correlative brightfield, Raman, and confocal laser scanning microscopy finally reveal a reticular three-dimensional distribution of the polymer and show that the polymer is predominately deposited in regions of high capillarity (i.e., in proximity to fine cellulose fibrils). These data provide deeper insights into the effects of paper functionalization with a copolymer and aid in understanding how these agents ultimately influence the local and overall properties of paper.

Covalent Attachment of Enzymes to Paper Fibers for Paper-Based Analytical Devices

“…Because the polymer is coupled by a photochemical strategy, the application of photolithographic masks enables controlled local immobilization of the polymer within defined areas (Böhm et al, 2013b ). As was shown in previous studies, the polymer coating homogenously binds to the fiber surface, and the open porous structure of the paper substrate is not significantly altered upon polymer binding (Bump et al, 2015 ; Janko et al, 2015 ). The attached macromolecule accumulates at the fiber-fiber contacts during drying of the polymeric solution, thus yielding additional wet-strengthening properties by the cross-linking of individual fibers (Jocher et al, 2015 ).…”

“…These studies were correlated with the results of confocal Raman microscopy and spectroscopy, showing that the copolymers even photocrosslinked between individual fibers. For details, see Janko et al ( 2015 ) or Bump et al ( 2015 ).…”

Simple One Pot Preparation of Chemical Hydrogels from Cellulose Dissolved in Cold LiOH/Urea

“…In the full Raman spectra of the cellulose samples without MBA (G600 and G230), the specific bands at 1092 cm −1 , 1362 cm −1 and 2887 cm −1 , which can be assigned to asymmetric and symmetric C-O-C stretching, C-H 2 bending and C-H stretching, respectively, could be identified (data not shown) [73,74]. The zoomed Raman spectra between 700 cm −1 and 1900 cm −1 are presented in Figure 4a.…”

“…The data suggest that the intensity of the -C=O band in FTIR is proportional to the amount of grafted functional groups in the cellulose hydrogel, and both the reaction temperature and time significantly influence the cross-linking degree. In the full Raman spectra of the cellulose samples without MBA (G600 and G230), the specific bands at 1092 cm −1 , 1362 cm −1 and 2887 cm −1 , which can be assigned to asymmetric and symmetric C-O-C stretching, C-H2 bending and C-H stretching, respectively, could be identified (data not shown) [73,74]. The zoomed Raman spectra between 700 cm −1 and 1900 cm −1 are presented in Figure 4a.…”

POSS-Containing Polymethacrylates on Cellulose-Based Substrates: Immobilization and Ceramic Formation

“…Therefore, the use of functional papers in the advanced technological fields of printed electronics, capacitors, and sensors are steadily growing [25][26][27][28][29]. Thus, functional papers that provide a direct and technologically straight-forward control over the wettability and functionality through polymer modification are desirable as platforms for microfluidics or sensing applications [30,31]. Paper-derived ceramics were used for the preparation of biotemplated functional and hierarchically ordered materials, which are technologically relevant as micro filters or catalyst platforms [32].…”