The lack of renewable resources and their inefficient use is a major challenge facing the society. Lignin is a natural biopolymer obtained mainly as a by-product from pulp-and paper-making industry, and is primarily burned to produce energy. However, the interest for using lignin in more advanced applications has increased rapidly. In particular, lignin based nanoparticles could find potential use in functional surface coatings, nanoglues, drug delivery, and microfluidic devices. In this work, a straightforward method to produce lignin nanoparticles from waste lignin obtained from kraft pulping is introduced.Spherical lignin nanoparticles were obtained by dissolving soft wood kraft lignin in tetrahydrofuran (THF) and subsequently introducing water into the system through dialysis. No chemical modification of the lignin was needed. Water acts as a nonsolvent reducing lignin's degrees of freedom causing the segregation of hydrophobic regions to compartments within the forming nanoparticles. The final size of the nanoparticles depended on the pre-dialysis concentration of dissolved lignin. The stability of the nanoparticle dispersion as a function of time, salt concentration and pH was studied. In pure water and room temperature the lignin nanoparticle dispersion was stable for over two months, but very low pH or high salt concentration induced aggregation. It was further demonstrated that the surface charge of the particles could be reversed and stable cationic lignin nanoparticles were produced by adsorption of poly(diallyldimethylammonium chloride) (PDADMAC).

This paper combines theoretical considerations with experimental evidence to explain the behavior of cellulose when exposed to different media. The observations are explained based on the amphiphilic character of the cellulose molecule and fundamental physicochemical phenomena. Nanofibrillated cellulose was chosen to demonstrate the phenomena since due to its high surface area the effects at issue are pronounced. X-Ray photoelectron spectroscopy and contact angle measurements were used to demonstrate the chemical and energetical changes taking place on the cellulose surface, and atomic force microscopy was used to follow nanoscale structural changes. Due to its hydrophilicity cellulose is well dispersed in water. However, when exposed to non-polar media like air or organic solvents cellulose undergoes partly irreversible reorganization like aggregation or surface passivation in order to find the energetically most favorable state. We show that when NFC is dried directly from water it aggregates strongly and accumulates a very high amount of non-cellulosic material on the surface. Very similar effects also occur when using non-polar media like toluene. Hence, both the reactivity and nanoscale structure are lost. In contrast, NFC retains its reactivity and nano-scaled structure in amphiphilic media like dimethyl acetamide as is confirmed with a simple silylation reaction. We conclude that the interfacial phenomenon is general for cellulosic material but has the most practical impact on applications of nanoscaled cellulose or ultrathin cellulose films.

In a number of different applications for enzymes and specific binding proteins a key technology is the immobilization of these proteins to different types of supports. In this work we describe a concept for protein immobilization that is based on nanofibrillated cellulose (NFC). NFC is a form of cellulose where fibers have been disintegrated into fibrils that are only a few nanometers in diameter and have a very large aspect ratio. Proteins were conjugated through three different strategies using amine, epoxy, and carboxylic acid functionalized NFC. The conjugation chemistries were chosen according to the reactive groups on the NFC derivatives; epoxy amination, heterobifunctional modification of amino groups, and EDC/s-NHS activation of carboxylic acid groups. The conjugation reactions were performed in solution and immobilization was performed by spin coating the protein-NCF conjugates. The structure of NFC was shown to be advantageous for both protein performance and stability. The use of NFC allows all covalent chemistry to be performed in solution, while the immobilization is achieved by a simple spin coating or spreading of the protein-NFC conjugates on a support. This allows more scalable methods and better control of conditions compared to the traditional methods that depend on surface reactions.

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Influence of the supramolecular structure of thin films of more crystalline cellulose (left) and highly amorphous cellulose (middle) on water vapour induced behaviour (right).

This letter proposes a strategy to construct tunable films combining the physical characteristics of cellulose nanofibrils and smart polymers for membrane applications. A functional membrane template was obtained by first fabricating a water stable film from cellulose nanofibrils and subsequently surface grafting it with a thermoresponsive polymer, poly(N-isopropylacrylamide). The behavior of the membrane template was dependent on temperature. The increment in slope of relative water permeance around the lower critical solution temperature of poly(N-isopropylacrylamide) increased from 18 to 100% upon polymer attachment. Although the membrane template essentially consisted of wood-based materials, the benefits of smart synthetic polymers were achieved.