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Photoresponsive pulp fibers are prepared by self‐assembly of photoactive cationic cellulose derivatives with pulp fibers in aqueous environment. Photoactive groups of the derivatives undergo 2π + 2π cycloaddition reaction under UV‐light irradiation. Fast photocrosslinking leads to the formation of the covalent bonds between the photoactive groups on the fiber surfaces. This results in drastic enhancement of the mechanical properties of the fiber network. Tensile strength and Z‐directional tensile strength increase by 81 and 84% compared to the original fiber network. Stiffness of the individual fibers increases by 60%. Such concept of controlling mechanical properties of the fiber materials by the light gives a possibility to design smart bio‐based materials and to increase end value of the fiber products.

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The paper describes the synthesis of multifunctional cellulose derivatives (MCDs) containing a fluorescent and a cationic moiety and their application in the functionalization of pulp fibers. The cellulose derivatives, namely N-(3-propanoic acid)- and N-(4-butanoic acid)-1,8-naphthal­imide esters of cellulose, differed in the degree of substitution (DS) and by the aliphatic chain connecting naphthalimide photoactive groups to the polymer backbone. The derivatives were decorated with a cationic moiety, namely (3-carboxypropyl)­trimethyl­ammonium chloride. The fluorescent pulp fibers were prepared by direct self-assembly of the water-soluble fluorescent MCDs on the fibers in water at room temperature. The results indicated that the adsorption was mainly driven by an ion exchange mechanism. UV–vis and fluorescence spectroscopic studies showed that the adsorption yield of the fluorescent MCDs depended on the length of the aliphatic chain of the photoactive groups. Because of the adsorption, the modified pulp fibers gained fluorescence in the visible part of the spectrum. Under black light illumination, the modified fibers fluoresced, which made them visually distinguishable from the reference fibers. Thus, the fluorescent pulp fibers prepared in a simple way can be potentially used as an authenticity indicator in packaging materials.

Xylans are one of the most common hemicellulose polysaccharides and natural polymers in plants. The utilization of xylan as a polymer has great potential for functional materials in different applications. In this chapter, different processes for the extraction of xylans from biomass are evaluated, due to their influence on the final properties of the extracted polymers such as molar mass and purity. Pressured hot water extraction (PHWE), a very common but versatile method for extracting xylans from hard wood, is described in detail. Cold caustic extraction (CCE) of xylans from bleached hard wood pulps is discussed as an alternative route for obtaining extremely pure xylan polymers. Derivatisation of the extracted xylans by incorporation of functional groups such as ethers and esters to the xylan backbone is a toolbox that allows the incorporation of a huge range of tailor-made new features for the polymer. Fibre engineering with sorption of xylans and xylan derivatives through self-assembly gives the perfect opportunity for incorporation of brand new functionalities to fibre-based products, which results in improved performance and helps to broaden the application areas for these materials.