Dmitry M. Rein

A novel composite based on ultra-high-molecular-weight polyethylene

Abstract A novel composite material consisting of ultra-high-molecular-weight polyethylene (UHMWPE) fibers and matrix has been prepared, characterized and shown to possess unique properties, in particular an elongation of over 70% in the direction transverse to the fibers which induces transverse orientation of the matrix. This indicates that excellent adhesion between fibers and matrix has been achieved in this composite material which exhibits the unique properties of the UHMWPE matrix.

True molecular solutions of natural cellulose in the binary ionic liquid-containing solvent mixtures

Evidence is presented for the first time of true molecular dissolution of cellulose in binary mixtures of common polar organic solvents with ionic liquid. Cryogenic transmission electron microscopy, small-angle neutron-, X-ray- and static light scattering were used to investigate the structure of cellulose solutions in mixture of dimethyl formamide and 1-ethyl-3-methylimidazolium acetate. Structural information on the dissolved chains (average molecular weight ∼ 5 × 10(4)g/mol; gyration radius ∼ 36 nm, persistence length ∼ 4.5 nm), indicate the absence of significant aggregation of the dissolved chains and the calculated value of the second virial coefficient ∼ 2.45 × 10(-2)mol ml/g(2) indicates that this solvent system is a good solvent for cellulose. More facile dissolution of cellulose could be achieved in solvent mixtures that exhibit the highest electrical conductivity. Highly concentrated cellulose solution in pure ionic liquid (27 wt.%) prepared according to novel method, utilizing the rapid evaporation of a volatile co-solvent in binary solvent mixtures at superheated conditions, shows insignificant cellulose molecular aggregation.

Molecular dynamics simulation of cellulose-coated oil-in-water emulsions

The behaviors of cellulose chains and cellulose mini-crystal in oil-in-water emulsions were studied by molecular dynamics simulations to investigate the coating states and the structural features of cellulose in these emulsions. In oil-in-water emulsion, dispersed cellulose chains gradually assemble during the progress of the simulation, eventually surrounding the octane droplet. In case of a cellulose mini-crystal, the cellulose chain at the corner of the crystal first contacts with the octane droplet through its hydrophobic surface. The other cellulose chains along the crystal plane then gradually move toward the octane molecules. In both emulsions, the cellulose was found to interact with both water and octane surfaces with specific conformations that allow the CH groups of the glucose rings to contact with octane molecules, while the OH groups of these rings contact with water molecules to form hydrogen bonds. The cellulose chains on the octane droplet also contact with each other through lateral hydrogen bonding between chains. These interactions stabilize the emulsion formed by cellulose molecules as surfactants.

Structure of cellulose/direct dye complex regenerated from supercritical water

The regeneration of cellulose from supercritical water in the presence of direct dyes was studied by small- and wide-angle synchrotron X-ray scattering and cryo-transmission electron microscopy to understand the effects of dyes on the structure formation of cellulose. In addition, the interactions between cellulose and the direct dyes were characterized using molecular dynamics simulations. Peaks corresponding to cellulose II crystals were observed in the wide-angle X-ray diffraction pattern of cellulose regenerated from supercritical water without dyes, whereas these peaks were not observed in the diffraction patterns of samples with direct dye (Direct Red 28 or Direct Blue 1). This result indicated that the direct dyes prevented the crystallization of regenerated cellulose. The results of the molecular dynamics simulations indicated that the planes of glucose rings interacted with the aromatic moieties of the dyes and that the sulfonate groups of the dye molecules interacted with the hydroxyl groups of cellulose. In addition, the CH groups of the glucose rings and aromatic moieties of the dyes (e.g., naphthalene and biphenyl moieties) interacted weekly. When cellulose regenerates from solution, cellulose sheet structures formed via hydrophobic interactions appear as the initial structure. The direct dyes were found to affect the formation of this cellulose sheet structure because cellulose molecularly dissolved in supercritical water. In the Kratky plots for small-angle X-ray scattering, a peak was clearly observed for the cellulose and cellulose/DR28 samples in the region of smaller q (<0.5), indicating that the nanoscale assembly structures dispersed in these systems. Bundled sheet-like and twisted ribbon-like structures were observed in the supernatants of the cellulose and cellulose/DR28 samples. These dispersed structures were considered to be intermediates in the structural formation of cellulose.

Enhanced hydrolysis of cellulose hydrogels by morphological modification

Cellulose is one of the most abundant bio-renewable materials on earth, yet the potential of cellulosic bio-fuels is not fully exploited, primarily due to the high costs of conversion. Hydrogel particles of regenerated cellulose constitute a useful substrate for enzymatic hydrolysis, due to their porous and amorphous structure. This article describes the influence of several structural aspects of the cellulose hydrogel on its hydrolysis. The hydrogel density was shown to be directly proportional to the cellulose concentration in the initial solution, thus affecting its hydrolysis rate. Using high-resolution scanning electron microscopy, we show that the hydrogel particles in aqueous suspension exhibit a dense external surface layer and a more porous internal network. Elimination of the external surface layer accelerated the hydrolysis rate by up to sixfold and rendered the process nearly independent of cellulose concentration. These findings may be of practical relevance to saccharification processing costs, by reducing required solvent quantities and enzyme load.

Structural Analysis of Cellulose-Coated Oil-in-Water Emulsions Fabricated from Molecular Solution

Natural cellulose has been used as a coating to stabilize oil-in-water (o/w) emulsions by exploiting the amphiphilic character of the cellulose chains molecularly dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate. Its cellulose coating exhibits a continuous amorphous structure which differs significantly from the cellulose particle stabilization used in Pickering emulsions. The structure of these cellulose-coated o/w emulsion particles, in particular the cellulose coating shell characteristics (thickness, porosity, and composition), is studied by using a combination of direct imaging methods such as cryogenic electron microscopy and fluorescence microscopy with small-angle neutron scattering measurements. This work suggests a unique multicompartment structure of the emulsion particles: an oil core, surrounded by an inner shell composed of a porous cellulose gel, encapsulated by a dense outer cellulose shell, a few nanometers in thickness. The thickness of the inner cellulose shell varies significantly. The nanoscale emulsion droplets exhibit a thickness of 10 ± 3 nm, whereas the larger micron-sized droplets exhibit a thicker inner cellulose shell of 500-750 nm. It is also inferred that the cellulose shells contain water rather than oil.