Daniel O Carlsson

Surface Modified Nanocellulose Fibers Yield Conducting Polymer-Based Flexible Supercapacitors with Enhanced Capacitances

We demonstrate that surface modified nanocellulose fibers (NCFs) can be used as substrates to synthesize supercapacitor electrodes with the highest full electrode-normalized gravimetric (127 F g(-1)) and volumetric (122 F cm(-3)) capacitances at high current densities (300 mA cm(-2) ≈ 33 A g(-1)) until date reported for conducting polymer-based electrodes with active mass loadings as high as 9 mg cm(-2). By introducing quaternary amine groups on the surface of NCFs prior to polypyrrole (PPy) polymerization, the macropore volume of the formed PPy-NCF composites can be minimized while maintaining the volume of the micro- and mesopores at the same level as when unmodified or carboxylate groups functionalized NCFs are employed as polymerization substrates. Symmetric, aqueous electrolyte-based, devices comprising these porosity-optimized electrodes exhibit device-specific volumetric energy and power densities of 3.1 mWh cm(-3) and 3 W cm(-3) respectively; which are among the highest values reported for conducting polymer electrodes in aqueous electrolytes. The functionality of the devices is verified by powering a red light-emitting diode with the device in different mechanically challenging states.

Electroactive nanofibrillated cellulose aerogel composites with tunable structural and electrochemical properties

This work presents conductive aerogel composites of nanofibrillated cellulose (NFC) and polypyrrole (PPy) with tunable structural and electrochemical properties. The conductive composites are prepared by chemically polymerizing pyrrole onto TEMPO-oxidized cellulose nanofibers dispersed in water and the various nanostructures are obtained employing different drying methods. Supercritical CO2 drying is shown to generate high porosity aerogel composites with the largest surface area (246 m2 g−1) reported so far for a conducting polymer–paper based material, whereas composites produced by ambient drying attain high density structures with mechanical properties significantly surpassing earlier reported values for cellulose–conducting polymer composites when normalized with respect to the content of reinforcing cellulose (Youngs modulus = 0.51 GPa, tensile strength = 10.93 MPa and strain to failure = 2.5%). Electrochemical measurements clearly show that differences in the porosity give rise to dramatic changes in the voltammetric and chronoamperometric behavior of the composites. This indicates that mass transport rate limitations also should be considered, in addition to the presence of a distribution of PPy redox potentials, as an explanation for the shapes of the voltammetric peaks. A specific charge capacity of ∼220 C g−1 is obtained for all composites in voltammetric experiments performed at a scan rate of 1 mV s−1 and this capacity is retained also at scan rates up to 50 mV s−1 for the high porosity composites. The composites should be applicable as electrodes in structural batteries and as membranes in ion exchange applications requiring exchange membranes of high mechanical integrity or high porosity.

Translational study between structure and biological response of nanocellulose from wood and green algae

The influence of nanostructure on the cytocompatibility of cellulose films is analyzed providing insight into how physicochemical properties of surface modified microfibrillated cellulose (MFC) and Cladophora nanocellulose (CC) affect the materials cytocompatibility. CC is modified through TEMPO-mediated oxidation and glycidyltrimethylammonium chloride (EPTMAC) condensation to obtain anionic and cationic nanocellulose samples respectively, while anionic and cationic MFC samples are obtained by carboxymethylation and EPTMAC condensation respectively. Films of unmodified, anionic and cationic MFC and CC are prepared by vacuum filtration and characterized in terms of specific surface area, pore size distribution, degree of crystallinity, surface charge and water content. Human dermal fibroblasts are exposed to culture medium extracts of the films in an indirect contact cytotoxicity test. Moreover, cell adhesion and viability are evaluated in a direct contact assay and the effects of the physicochemical properties on cell behavior are discussed. In the indirect cytotoxicity test no toxic leachables are detected, evidencing that the CC and MFC materials are non-cytotoxic, independently of the chemical treatment that they have been subjected to. The direct contact tests show that carboxymethylated-MFC presents a more cytocompatible profile than unmodified and trimethylammonium-MFC. TEMPO–CC promotes fibroblast adhesion and presents cell viability comparable to the results obtained with the tissue culture material Thermanox. We hypothesize that the distinct aligned nanofiber structure present in the TEMPO–CC films is responsible for the improved cell adhesion. Thus, by controlling the surface properties of cellulose nanofibers, such as chemistry, charge, and orientation, cell adhesion properties can be promoted.

Haemocompatibility and ion exchange capability of nanocellulose polypyrrole membranes intended for blood purification

Composites of nanocellulose and the conductive polymer polypyrrole (PPy) are presented as candidates for a new generation of haemodialysis membranes. The composites may combine active ion exchange with passive ultrafiltration, and the large surface area (about 80 m2 g−1) could potentially provide compact dialysers. Herein, the haemocompatibility of the novel membranes and the feasibility of effectively removing small uraemic toxins by potential-controlled ion exchange were studied. The thrombogenic properties of the composites were improved by applying a stable heparin coating. In terms of platelet adhesion and thrombin generation, the composites were comparable with haemocompatible polymer polysulphone, and regarding complement activation, the composites were more biocompatible than commercially available membranes. It was possible to extract phosphate and oxalate ions from solutions with physiological pH and the same tonicity as that of the blood. The exchange capacity of the materials was found to be 600 ± 26 and 706 ± 31 μmol g−1 in a 0.1 M solution (pH 7.4) and in an isotonic solution of phosphate, respectively. The corresponding values with oxalate were 523 ± 5 in a 0.1 M solution (pH 7.4) and 610 ± 1 μmol g−1 in an isotonic solution. The heparinized PPy–cellulose composite is consequently a promising haemodialysis material, with respect to both potential-controlled extraction of small uraemic toxins and haemocompatibility.

Cooxidant-free TEMPO-mediated oxidation of highly crystalline nanocellulose in water

Selective oxidation of C6 hydroxyls to carboxyls through 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, where the oxidizing species (TEMPO+) is generated by cooxidants, such as NaBrO, NaClO or NaClO2, has become a popular way to modify the surfaces of nanocellulose fibrils in aqueous solutions. Employing highly crystalline nanocellulose from Cladophora sp. algae we demonstrate that the same degree of oxidation (D.O.) can be achieved within approximately the same time by replacing the cooxidants with electrogeneration of TEMPO+ in a bulk electrolysis setup. The D.O. is controlled by the oxidation time and the maximum D.O. achieved (D.O. 9.8%, 0.60 mmol g−1 of carboxylic acids and 0 mmol g−1 aldehydes) corresponds to complete oxidation of the surface-confined C6. This shows that TEMPO+ is not sterically hindered from completely oxidizing the fibril surface of Cladophora nanocellulose, in contrast to earlier hypotheses that were based on results with wood-derived nanocellulose. The oxidation does not significantly affect the morphology, the specific surface area (>115 m2 g−1) or the pore characteristics of the water-insoluble fibrous particles that were obtained after drying, but depolymerization corresponding to ∼20% was observed. For extensive oxidation times, the product recovery of water-insoluble fibrils decreased significantly while significant amounts of charge passed through the system. This could indicate that the oxidation proceeds beyond the fibril surface, in contrast to the current view that TEMPO-mediated oxidation is confined only to the surface.

Convenient One-Pot Formation of 2,3-Dialdehyde Cellulose Beads via Periodate Oxidation of Cellulose in Water

Convenient One-Pot Formation of 2,3-Dialdehyde Cellulose Beads via Periodate Oxidation of Cellulose in Water

Susceptibility of Iα- and Iβ-Dominated Cellulose to TEMPO-Mediated Oxidation

The susceptibility of Iα- and Iβ-dominated cellulose to TEMPO-mediated oxidation was studied in this work since the cellulose Iα-allomorph is generally considered to be thermodynamically less stable and therefore more reactive than the cellulose Iβ-allomorph. Highly crystalline Cladophora nanocellulose, which is dominated by the Iα-allomorph, was oxidized to various degrees with TEMPO oxidant via bulk electrolysis in the absence of co-oxidants. Further, the Cladophora nanocellulose was thermally annealed in glycerol to produce its Iβ-dominated form and then oxidized. The produced materials were subsequently studied using FTIR, CP/MAS (13)C NMR, XRD, and SEM. The solid-state analyses confirmed that the annealed Cladophora cellulose was successfully transformed from an Iα- to an Iβ-dominated form. The results of the analyses of pristine and annealed TEMPO-oxidized samples suggest that Iα- and Iβ-dominated cellulose do not differ in susceptibility to TEMPO-oxidation. This work hence suggests that cellulose from different sources are not expected to differ in susceptibility to the oxidation due to differences in allomorph composition.

A Comparative Study of the Effects of Rinsing and Aging of Polypyrrole/Nanocellulose Composites on Their Electrochemical Properties

The effects of polymerization conditions, rinsing, and storage on composites composed of polypyrrole (PPy) and Cladophora nanocellulose in terms of purity, chemical composition, conductivity, and electroactivity were investigated using conductivity measurements, cyclic voltammetry, FTIR-ATR, XPS, and ICP-AES. A clear correlation between rinsing volume and PPy degradation was found using water- or NaCl-rinsing solutions as evidenced by conductivity and electroactivity losses. It was further found, through FTIR-ATR as well as XPS-measurements, that this degradation was caused by incorporation of hydroxyl groups in the PPy-layer. The extent of degradation correlated with a shift in the FTIR-ATR peak around 1300 cm(-1), showing that FTIR-ATR may be used as a quick diagnostic tool to evaluate the extent of degradation. By the use of acidic rinsing solution, this degradation effect was eliminated and resulted in superior samples in terms of both conductivity and electroactivity and also in a more efficient removal of reactants. Upon ambient storage, over a period of 200 days, a gradual decrease in conductivity was found for initially highly conductive samples. The electroactivity, on the other hand, was relatively unaffected by storage, showing that conductivity measurements alone are ineffective to determine the degree of polymer degradation if the water content is not controlled. Also, FTIR-ATR measurements indicated that the oxidation state did not change to any large extent upon storage and that only minor degradation of PPy occurred. The results presented herein thus offer valuable guidelines on how to develop simple and reliable postsynthesis treatments of conducting polymer-paper composites with performance fulfilling requirements on stability, electroactivity, and purity in applications such as environmentally friendly energy storage devices and biomedical applications.

Aspirin degradation in surface-charged TEMPO-oxidized mesoporous crystalline nanocellulose

TEMPO-mediated surface oxidation of mesoporous highly crystalline Cladophora cellulose was used to introduce negative surface charges onto cellulose nanofibrils without significantly altering other structural characteristics. This enabled the investigation of the influence of mesoporous nanocellulose surface charges on aspirin chemical stability to be conducted. The negative surface charges (carboxylate content 0.44±0.01 mmol/g) introduced on the mesoporous crystalline nanocellulose significantly accelerated aspirin degradation, compared to the starting material which had significantly less surface charge (0.06±0.01 mmol/g). This effect followed from an increased aspirin amorphisation ability in mesopores of the oxidized nanocellulose. These results highlight the importance of surface charges in formulating nanocellulose for drug delivery.

Tailoring porosities and electrochemical properties of composites composed of microfibrillated cellulose and polypyrrole

Composites of polypyrrole and nanocellulose (PPy/nanocellulose) have a high potential as electrodes in energy-storage devices and as membranes for electrochemically controlled ion-exchange systems. In the present work, it is demonstrated that such composites with 42–72% porosity can be produced by using microfibrillated cellulose (MFC) prepared through enzymatic pretreatment or carboxymethylation, or by using different amounts of MFC in the composite synthesis. Together with previous work, this shows that the porosity of PPy/nanocellulose composites can be tailored from 30 to 98% with increments of ∼10%. Employing the full porosity range of the composites, it is demonstrated that the electrochemical oxidation rate of the materials depends on their porosity due to limitations in the counter ion diffusion process. By tailoring the porosities of PPy/nanocellulose composites, the electrochemical properties can consequently be controlled. The latter provides new possibilities for the manufacturing of electrochemically controlled ion-extraction and energy storage devices with optimized volumetric energy and power densities.