Avinash P. Manian

Copper inclusion in cellulose using sodium D-gluconate complexes.

Copper containing cellulose material is of growing interest, e.g. offering alternative in the field of antimicrobials. Solutions of copper d-gluconate complexes (Cu(2+)-DGL) were used to introduce copper ions into a swollen cellulosic matrix. A ligand exchange mechanism forms the chemical basis of the sorption process. Copper sorption in cellulose was studied in the range between pH 6 and 13. An estimate for the complex stabilities of the Cu-cellulose system could be derived from the calculated species distribution of the different Cu(2+)-DGL complexes present. Spectrophotometry and cyclic voltammetry of Cu(2+)-DGL complex solution were used to confirm the presence of different species participating in the ligand exchange reaction. The pH dependent uptake of Cu(2+) ions in the cellulose matrix can be explained on the basis of the relative stabilities of Cu(2+)-DGL complex vs. Cu(2+)-cellulose complexes. In comparison to pH 10, higher copper content was observed at pH 6 and 13. Copper content was limited by carboxyl content of cellulosic materials, thus in analogy to the structure of Cu(2+)-DGL complexes participation of the carboxyl group as complex forming site is proposed. At high Cu(2+)-concentration and longer time of immersion in the copper complex solutions formation of solid deposits was observed on the surface of the treated fibres.

Ion-interactions as driving force in polysaccharide assembly

The structure of cellulose is characterised by extensive non-covalent interactions. Recent discussions suggest that hydrophobic interactions between polymer chains also play a significant role in governing cellulose solubility. Surprisingly in almost all cellulose shaping processes, chemical systems or solvents are applied, which base on melts or solutions of charged molecules. Ionic interactions play a significant role in the shaping and modification of cellulose based materials. Dependent on the systems used different principles govern the processes and define the results, e.g. formation of associates with alkali hydroxides, ion-exchange reactions to selectively bind multivalent ions at carboxylic groups, adsorption of dissolved polymers through surface charge neutralisation or metal complex formation, where cellulose takes the role of a polymer ligand system. Presence of charged compounds takes a significant role in cellulose swelling and dissolution, but also directs reassembly of polysaccharide material to solid three-dimensional structures.

Influence of steam and dry heat pretreatment on fibre properties and cellulase degradation of cellulosic fibres

Cellulosic fabric samples of cotton, viscose, lyocell and modal were pretreated with steam and dry heat in the range of 100–190°C. The samples were then treated with a Trichoderma reesei cellulase preparation (total culture filtrate – TC), with mechanical agitation, at a high enzyme dosage of 75% by weight of fabric, for 8 hours. Generally, viscose proved to be easily degradable, followed by cotton and modal. The degree of hydrolysis was the least for Lyocell. Dry heat pretreatments exerted a lower influence on degradation rate than steam pretreatments which showed a distinct maximum at a steam temperature of 130°C. The hydrolysis rate varied strongly depending on treatment conditions and fibre type. Water retention values in treated substrates were changed by up to 20% of initial values.

Drying Rates in Resin Treatment of Lyocell Fabrics

Many properties of lyocell fibers are markedly different from those of other cellulosic fibers. Hence, it is necessary to study Lyocell wet processing to determine and characterize variables that have a significant influence on the properties of finished products. At the Christian-Doppler Laboratory, we are conducting an investigation to characterize resin finishing of Lyocell. As a part of this investigation, we are studying the influence of drying conditions in the pad-dry-cure process on the performance properties of the finished products. The influence of the drying rate on the distribution of crosslinking reagents in treated lyocell fabric samples is similar to that reported for other cellulosics, but the effect of reagent distribution on the performance properties of treated lyocell is different from that reported for other cellulosics. These differences may stem from changes that occur in lyocell fibers with moisture sorption.

Three-dimensional embroidered current collectors for ultra-thick electrodes in batteries

A major bottleneck in batteries arises from the limitations in charge transfer between the active mass and the current collector. A number of strategies to increase the surface of current collectors have been proposed, examples are foam electrodes, porous nano-structured surfaces, coatings with carbon nanotubes. A simple and cost efficient approach to increase the surface of current collectors, which utilizes three-dimensional embroidered metal structures, is presented in this paper. In particular, for ultra-thick electrodes benefits with regard to mass loading and impedance could improve overall performance. In this paper we compare the electrochemical performance of thick LiFePO4 cathodes prepared with 3D embroidered aluminium current collectors versus aluminium planar foils, over a range of mass loadings. The 3D cathodes exhibit lower impedances, higher specific capacities, and higher energy efficiencies (up to 8% gain) as compared to the planar cathodes. The 3D cathodes also exhibit greater mechanical stability. These results, which demonstrate the potential for the use of 3D embroidered current collectors in preparation of high-energy batteries, can also be extended to other chemistries.

Characterization and mechanical properties investigation of the cellulose/gypsum composite

We synthesized cellulose/gypsum composites in the presence and absence of sodium alginate and investigated the interaction between the composite components as well as the mechanical properties of the final composites. Four different types of cellulose fiber materials were used: cellulose UFC100, cellulose B400, nanofibrillated cellulose, and Lyocell fiber. For all investigated composites the total amount of admixed cellulose was between 1 and 2 wt%, the amount of admixed sodium alginate was 0.5 wt%. We determined the morphology of the composites and observed that the particle and fiber dimensions of the admixed cellulose affect the mode of gypsum–gypsum interlocking and the total porosity of the composites. This in turn had a substantial influence on the mechanical properties of the final composite materials. The addition of sodium alginate resulted in an increase of ultimate strain values. Composites with Lyocell fiber, a synthetic fiber, also had a high Young’s modulus.

Particle Release from Woven Cellulosic Substrates

The linting propensity of a woven cellulosic substrate is investigated as a function of substrate characteristics and of different parameters in the test environment. The results from the linting propensity tests parallel those observed in liquid—solid extraction processes, where solutes are extracted from a matrix of other insoluble solids by selective dissolution in a liquid. The equation quantifying solute extraction in such systems also proves to be a good fit for the linting propensities observed in this work. Hence, it maybe possible to regard linting phenomena as extraction processes and to use the equation quantifying solute extraction to predict substrate linting as a function of both substrate characteristics and the test environment.

Polyelectrolyte-Assisted Immobilization of Oil-Based Nanocapsules on Cotton Fabric

Poly(diallyldimethylammonium chloride)-encapsulated n-octadecane nanocapsules (PDDA-Oc-cap) were easily immobilized on cationized cotton at ambient temperature using poly(4-styrenesulfonic acid) (PSS) as a binder. The cationized cotton was first treated with 1–50 mM of PSS and then soaked in the PDDA-Oc-cap emulsion in order to obtain stepwise PSS/PDDA-Oc-cap coating layers on the cationized cotton (Cat-cot/PSS/PDDA-Oc-cap). The negative molecules of PSS binder spontaneously attached to the cationized cotton and then acted as negative sites for further immobilization of positively charged PDDA-Oc-cap via electrostatic interaction. Uniform globular particles of PDDA-Oc-cap were observed on the surfaces of Cat-cot/PSS/PDDA-Oc-cap samples in the field-emission scanning electron microscopy images. The positive zeta potential was obtained in the Cat-cot/PSS/PDDA-Oc-cap samples due to the deposition of the positively charged PDDA-Oc-cap on cotton fabric. In addition, the Cat-cot/PSS/PDDA-Oc-cap samples preferentially adsorbed anionic dye eosin B over cationic dye methylene blue. Higher PSS concentrations used in the treatment resulted in higher quantities of PDDA-Oc-cap immobilized on the fabrics, resulting in the concomitant increase of eosin B adsorption. These results suggested that the PSS-assisted immobilization was an efficient alternative method for textile finishing.

Salt sorption on regenerated cellulosic fibers: electrokinetic measurements

Streaming potential measurements were conducted on lyocell and viscose fibers, to determine the relative order in sorption extents of salt cations and anions. The sorption of K+ was greater than Na+ ions, and the sorption extents of the anions, Cl− and Br−, were similar. Previously, we had examined accessibility of the same ions in the fibers, and found them to follow the order: K+ < Na+ and Cl− < Br−. From these two contrasting results, we find that the mode of salt interaction with cellulose, from aqueous solutions, changes with the salt concentration. At low concentrations, the interaction is governed by ion-exchange processes with the cellulose carboxyl groups and the Donnan equilibrium; but at higher concentrations, the interaction is a function of the mobility (or diffusivity) of the ions. Thus, sorption and accessibility of cellulose fibers as measured with salts may not apply for other solutes, and conversely, similar studies with other probe molecules may not be relevant for salts.

Polysaccharide Fibres in Textiles

Besides naturally grown cellulose fibres like cotton, hemp or flax, interest in textile fibres made up from regenerated cellulose is growing. By sure the use of a polymer material, which is provided by nature in huge amounts, favours its use as more sustainable material compared to oil-based products. However, a much stronger argument is the high variability of the properties that can be achieved, which allows design an extremely wide range of products.