Sergey Antonov

Cellulose composite membranes for nanofiltration of aprotic solvents

Cellulose composite membranes have been fabricated by casting a cellulose solution in N-methylmorpholine oxide on a nonwoven polyester support. The membranes have been tested for nanofiltration of aprotic solvents. The solvent permeability has changed from 0.11 ± 0.02 to 2.5 ± 0.4 kg/(m2 h bar) in the following order: DMSO > NMP > DMFA > THF > acetone, which can be attributed to a decrease in viscosity of the fluids. The rejection of the anionic dyes Orange II (MW 350) and Remazol Brilliant Blue R (MW 626) has been found to range within 15–85% and 42–94%, respectively, on the solvent nature. Sorption experiments have revealed a noticeable difference between certain solvents in interaction with the membrane material: a lower degree of cellulose swelling in THF (37%) and a higher degree in DMSO (230%). In addition, it has been found that the rejection of solutes by the composite membranes correlates with the degree of cellulose swelling. A rejection of ≥90% has been achieved for Remazol Brilliant Blue R, which has the larger molecule, at a cellulose swelling ratio of 100% or higher. Thus, it has been concluded that polymer swelling leads to narrowing the porous structure of the cellulose layer of the composite membrane and, hence, improvement in separation parameters.

Rheology and adhesive properties of filled PIB-based pressure-sensitive adhesives. I. Rheology and shear resistance

Two nanosized fillers (fumed silica Rosil-175 up to 20 wt% and halloysite nanotubes up to 40 wt%) were used to suppress cold flow of polyisobutylene (PIB)-based adhesives. Rheological measurements revealed the presence of the yield stress in the PIB-halloysite system which is indicative of the three-dimensional network formation in the bulk of the matrix. However, further rheology tests identified low strength of the network. In case of Rosil, no yield stress was detected, only gradual increase in the viscosity. Shear bank testing showed 4–5 times increase in the PIB-halloysite system time to failure when 40 wt% of halloysite was incorporated into the PIB matrix. Increase in the time to failure for PIB-Rosil systems was over two orders of magnitude – at the Rosil content up to 20 wt%. Such superior properties of the Rosil adhesion joints are considered to be the result of Rosil high specific area and low strength of the halloysite nanotubes network.

Switch multiplexer of fiber-optic channels Based on multibeam acousto-optic diffraction.

The peculiarities of the multibeam acousto-optic Bragg diffraction of light by a multifrequency acoustic signal are investigated. The investigation is related to design of fiber-optic space division switch multiplexer 1xN. It is proved that a specialized two-dimensional acousto-optic deflector can perform high efficiency multifunctional light switching of fiber-optic channels. The device has advanced characteristics--the number of channels is up to a few hundred, the switching time is about a few microseconds, and the cross talk is limited to -45 dB.

Fabrication of composite nanofiltration membranes from cellulose solutions in an [Emim]OAc–DMSO mixture

The dissolution of cellulose in the [Emim]OAc ionic liquid mixed with DMSO as a cosolvent has been studied, and the possibility of fabricating composite cellulose membranes for the nanofiltration of organic media has been explored. It has been shown that the addition of DMSO to [Emim]OAc leads to a decrease in the dissolution time, which has a minimal value at a solvent ratio of 1 : 1. Composite membranes on a poly(ethylene terephthalate) support have been synthesized. The cellulose content in the casting solution was 6, 8, 12, or 16 wt %. It has been found that the rejection factor of the Remazol Brilliant Blue R dye (626 g/mol) varies from 42 to 82% depending on the composition of the casting solution.

Adhesive properties of liquid crystalline hydroxypropyl cellulose–propylene glycol blends

Adhesion (tack) of the liquid crystalline hydroxypropyl cellulose–propylene glycol (HPC/PG) systems has been studied under various loading modes as well as their rheology and phase state. The system with the optimum tack according to the Dahlquist criterion (HPC/PG = 85/15 wt.%) was chosen based on its rheological properties (viscosity, storage and loss moduli at 20 and 50 °C). Tack measurements were carried out for this system. Rheological measurements revealed the presence of the critical stress detected by the abrupt drop of viscosity. The adhesive behavior of the system deviates significantly from one of the conventional pressure sensitive adhesives (PSAs): almost no tack is observed when using contact force and contact time typical for a PSA. To achieve good adhesion with this system one needs substantially higher pressure and contact time. At 20 °C, adhesive failure is observed in most cases and high contact forces (over 500–600 g) are required to overcome critical stress and obtain noticeable tack characteristics. At 50 °C, fibrillation and cohesive failure are usually observed with some residue of the system on the probe after debonding. Usage of high contact forces (600–1000 g) and contact times (up to 1000 s) allows us to reach significant values of the maximum debonding stress (up to 1.25 MPa) and energy (up to 420 J/m2). These values are on the same level or even higher than the corresponding values for standard PSAs.

Phase-equilibrium and cellulose-coagulation kinetics for cellulose solutions in N-methylmorpholine-N-oxide

The dissolution of cellulose in N-methylmorpholine-N-oxide monohydrate and the dissolution of N-methylmorpholine-N-oxide monohydrate in water have been studied via optical interferometry. A part of the phase diagram for the cellulose/N-methylmorpholine-N-oxide system has been constructed. The phase diagram is characterized by crystalline equilibrium, hysteresis of the melting temperatures of the solvents, and a region of anisotropy. Optical interferometry has been used for the first time to study the kinetics of cellulose coagulation during the interaction of cellulose solutions in N-methylmorpholine-N-oxide with water and water solutions of N-methylmorpholine-N-oxide. Information on the values of interdiffusion coefficients and the morphologies of the resulting cellulose films has been obtained. The possibility to use optical interferometry to analyze the interaction of a solution with the coagulating agent in the case of cellulose fiber and film formation has been demonstrated. The influences of temperature, the nature of the coagulating agent, and the cellulose content on the kinetics of the process and morphologies of the formed films have been shown. The use of N-methylmorpholine-N-oxide as a part of the coagulation system decreases the rate of interdiffusion of solutions, thereby resulting in a more uniform and dense morphology of cellulose films. Increased temperature causes diffusion acceleration, thereby leading to the formation of an anisotropic morphology of the cellulose films.

The influence of uniform deformation of Ultem-1000 polyetherimide films on their mechanical and gas transport characteristics

The influence of controlled biaxial uniform deformation of annealed and unannealed (with residual solvent) Ultem 1000 amorphous glassy polyetherimide films on their mechanical and gas separation characteristics have been studied. It has been shown that the transport and mechanical properties of strained Ultem-1000 film samples can be examined on reaching the quasi-steady state 48 hours after the beginning of their deformation. It has been shown that an increase in the strain of the unannealed Ultem 1000 films leads to an increase in mechanical strength of the films (increase in elastic modulus, tensile strength, and upper and lower yield stresses and decrease in elongation at break), an increase in chain packing density, and orientation of chains in the dense part of the polymer matrix, with these changes resulting in a drop of gas permeability and an enhancement of ideal selectivity. It has been demonstrated that the deformation of the annealed Ultem films leads to a dramatic change in mechanical properties even at small strains: from brittle fracture to the emergence of plastic deformation. As the strain increases, the gas diffusion coefficients decrease for all the samples, suggesting the ordering of chain packing. Thus, the combination of the methods used has made it possible to obtain information about the effects of deformation of polymer films and the residual solvent on their structural and transport properties useful for achieving the best permeability–selectivity ratio.

Coprocessing of polymeric materials and high-boiling petroleum components by catalytic cracking

A recent trend in the utilization of carbon-containing technogenic wastes via joint processing with petroleum fractions by catalytic cracking into motor fuels and petrochemical feedstock has been studied experimentally. The catalytic cracking of a vacuum distillate with dissolved polymers has been performed on a commercial microspheric catalyst. The qualitative and quantitative compositions of the polymers dissolved in the vacuum distillate for the conversion into motor fuels and valuable petrochemical feedstock have been determined.

Rheology and adhesive properties of filled PIB-based pressure-sensitive adhesives. II. Probe tack and 90° peel testing

Two nanosized fillers (fumed silica Rosil-175 and halloysite nanotubes) were used to eliminate the problem of the cold flow and to increase the adhesion strength for polyisobutylene-based formulations. Well-dispersed silica, having high specific area, allowed to obtain up to 2 orders of magnitude increase in PIB’s shear resistance at 20 wt% Rosil content. PIB–20 wt% Rosil formulations mostly demonstrated slightly increased tack characteristics – up to 20–50%. Adhesive peel of the PIB-Rosil systems was observed with the peel strength of the systems staying at the level of the pristine PIB matrices or slightly changing (depending on the film thickness and peeling rate). Transition to the mixed failure mode was observed for thin PIB-20 wt% Rosil films tested under increased peeling rate accompanied by up to 300% peel strength increase. Formation of the three-dimensional filler networks in PIB-halloysite formulations allowed notably lower increase in the shear resistance of the systems – only 4–5 times in the case of much higher filler content (40 wt%), which was connected with the low strength of the network. Incorporation of 40 wt% halloysite into the PIB matrix did not lead to notable changes in tack properties, except for the tack of 150-μm films – in this case, 30–60% decrease in the tack characteristics was obtained. Peel strength of PIB-halloysite systems stays at the level of the pristine PIB matrices or increases up to 300% when the failure mode shifts from adhesive for the thin films to cohesive for the thick films.

Adhesion of liquid-crystalline polymer systems to substrates of varied roughness

Evolution of the adhesion behavior of a liquid crystalline system under various conditions of the adhesion joint formation was studied. A blend of hydroxypropyl cellulose with propylene glycol was selected as a model liquid crystalline system. Influence of the substrate roughness on the adhesion of the liquid crystalline systems was studied for the first time. It was found out that the roughness influence on the adhesion characteristics of the systems studied was much more pronounced than in case of the common pressure-sensitive adhesives. High values of the debonding energies for the systems studied (up to 280–330 J/m2) were obtained. These values are similar or even exceed the values obtained for the common pressure-sensitive adhesives.