Papers by Alexander Leykin
Bioresources
The paracrystallinity of cellulose samples was studied with a complex of investigation methods in... more The paracrystallinity of cellulose samples was studied with a complex of investigation methods including X-ray, NMR, sorption, calorimetry, and some others. It was found that the paracrystalline fraction of cellulose is located on the surface of crystallites as thin monomolecular layers having an average thickness of 0.4 nm. The paracrystalline surface layers have distorted and loose packing that is characterized by a high distortion parameter δ p = 0.18, increased specific volume V p =0.664 cm 3 /g, and decreased specific gravity ρ p = 1.51 g/cm 3 . The paracrystalline fraction of the crystallite can be quantified by the parameter (α), which has an expressed influence on some properties of cellulose. Increasing of the α-value causes expansion of inter-plane distances in the C1 unit cell, as well as promotes mercerization and dissolution of cellulose.
Novel hydroxyurethane modifiers (HUM) for "cold" cure epoxy composite materials were sy... more Novel hydroxyurethane modifiers (HUM) for "cold" cure epoxy composite materials were synthesized. Properties of modified epoxy materials were studied by physical-mechanical and physical-chemical methods. It is established that the compositions with HUM demonstrate a significant increase in speed of curing process, as well as non-trivial increase in abrasion resistance and a marked improvement in strength properties. Other characteristics, such as chemical resistance, are not worse. General concept of generating new multifunctional modifiers was created. The HUM, which possesses a wide range of hydrogen bonds, embedded in epoxy polymer network without a direct chemical interaction.
Composite Interfaces, 2008
Interaction on the solid–liquid surface in dispersions of microcrystalline cellulose (MCC)
with ... more Interaction on the solid–liquid surface in dispersions of microcrystalline cellulose (MCC)
with various particle sizes has been studied by means of rheological methods. It was shown that the MCC dispersions possess shear-thinning rheological properties. An inversely proportional relationship between the average particle size of the MCC particles and the viscosity of the dispersions was discovered. This phenomenon is explained by the decrease of water mobility with increase in the specific surface of the MCC particles. Irreversible closing of the MCC pores reduces the viscosity of water dispersions. Addition of some water-soluble polymers leads to a considerable increase in viscosity due to formation of macromolecular net composed of solid particles.
Cyclic carbonates (CC) are a comparatively new class of raw materials for preparation of high per... more Cyclic carbonates (CC) are a comparatively new class of raw materials for preparation of high performance “green” heterochain polymers. CC can be prepared using different synthetic methods. In particular, the cycloaddition of CO2 into epoxides to afford five-membered cyclic carbonate with versatile reactivity and the subsequent reaction between the cyclic carbonate and aliphatic primary amine forming urethane linkage have been the active subjects of investigations since they allow non-isocyanate polyurethanes (NIPUs) to be prepared. Polycarbonates may be prepared also by polymerization of mono cyclic carbonates containing C=C double bonds.
Cellulose Chemistry and Technology, 2006
Structural characteristics of the microcrystalline celluloses (MCC) obtained by heterogeneous aci... more Structural characteristics of the microcrystalline celluloses (MCC) obtained by heterogeneous acid hydrolysis of cotton cellulose, under various conditions, with subsequent mechanical disintegration of the non-dried samples in a high-pressure homogenizer, have been studied. To obtain nano-scale MCC with CI-structure, the narrow concentration interval of the mineral acids (7-9 M) alongwith with mechanical disintegration, should be used. The correlation between the dispersity degree of MCC particles and the acidity function was established. Structural transformations of cellulose fibers during hydrolysis and mechanical disintegration are discussed.
Bioresources, 2011
The sorption of vapors by cellulose samples and by some cellulose derivatives was studied at 25 o... more The sorption of vapors by cellulose samples and by some cellulose derivatives was studied at 25 oC. To describe sorption isotherms, a thermodynamic equation was proposed: A=Ao/[1-(RT/g)lnφ], where Ao is maximal sorption value, φ is relative pressure of vapors, and g is specific thermodynamic potential. Depending on the g-value, this equation can describe isotherms of various shapes that occur for cellulose and its derivatives. Application of the equation makes it possible to calculate such structural characteristics of the polymers as accessible specific surface and crystallinity, as well as the substitution degree of cellulose derivatives. Moreover, amounts of monomolecular and multimolecular fractions of the sorbate can be determined.
The accessibility of cellulose samples with various crystallinity degrees to molecules of water, ... more The accessibility of cellulose samples with various crystallinity degrees to molecules of water, lower primary alcohols and lower organic acids was studied. It was found out that small water molecules have full access to the non-crystalline domains of cellulose (accessibility coefficient α = 1). The molecules of the lowest polar organic liquids have partial access to these domains (α < 1), while, with an increasing diameter of the organic molecules, their access to the cellulose structure decreases. The accessibility of cellulose samples to molecules of various substances is a linear function of coefficient α and of the content of noncrystalline domains. The relationship between the crystallinity (X) and accessibility (A) of cellulose to the molecules of some liquids was established as A = α (1-X). The water molecules were found to have greater access to the cellulose samples than the molecules of the investigated organic liquids. The obtained results permit the use of accessibil...
Professor Oleg Figovsky is a leading world scientist in the field of novel materials technologies... more Professor Oleg Figovsky is a leading world scientist in the field of novel materials technologies, member of European Academy, foreign member of two Russian academies (RAACN & REA) and founder, Director R&D of Israeli Research Centre Polymate was established in 1997 and since has developed many advanced and novel environmentally friendly superior polymer and composite materials and technologies, specialized in environmental engineering and nano-technologies. Now prof. O. Figovsky is also Director R&D of two US companies: Nanotech Industries, Inc. и Hybrid Coatings Technologies, Inc. (Daly City, CA). The main areas of researches of company "Polymate" and its employees are corrosion resistant polymer, silicate and hybrid coverings for various substrates as well as new binders for the concretes operating in adverse environments. The special attention is given the use of renewable raw material and environmentally friendly technologies particularly nonisocyanate polyurethane systems. Search of the new organic-modified silicates is conducted in the field of inorganic coatings. Development of the advanced binders for concrete are conducted mainly with the use of liquid rubbers and new silicone additives. A new direction in the creation of coatings and binders is a hybrid nano-structured composition. Main inventions made by employees of "Polymate" were devoted to polymeric materials for coatings based on hybrid nonisocyanate urethane-epoxides. A promising method was introduced in the form of a nonisocyanate urethane-epoxy polymer network with lower permeability and increased chemical resistance properties to non-polar substances. Moreover, hybrid nonisocyanate networks are made by a synthesis process that uses far more environmentally benign materials than isocyanates and phosgene. US patent issued to O. Figovsky [1] relates to a hybrid nonisocyanate polyurethane network polymer formed by cross-linking at least one cyclocarbonate oligomer and at least one amine oligomer. The cyclocarbonate oligomer contains a plurality of terminal cyclocarbonate groups. At least one cyclocarbonate oligomer further comprises from about 4% to about 12% by weight of terminal epoxy groups. Because at least one cyclocarbonate oligomer contains both cyclocarbonate and epoxy reactive groups, the network formed therefrom is referred to as a hybrid nonisocyanate polyurethane network. The cyclocarbonate oligomer or oligomers have an average functionality towards primary amines of from about 2.0 to about 5.44. The amine oligomer comprises at least one primary amine-terminated oligomer terminated with primary amine groups and has an average functionality towards cyclocarbonate groups of from about 3.0 to about 3.8. The amine oligomer is present in an amount from about 0.93 to about 0.99 of the amount of the amine oligomer that would be required to achieve a stoichiometric ratio between the primary amine groups of the amine oligomer and the cyclocarbonate groups of the cyclocarbonate oligomer. The hybrid nonisocyanate polyurethane network polymer formed has a gel fraction of not less than about 0.96 by weight. These materials, in particular, are useful as nonporous monolithic coatings, coverings and linings, which can be used for the corrosion protection and wear protection of concrete, metallic and wood surfaces. In US patent [2] chemically resistant materials with high mechanical properties was provided by using polycyclocarbonates of special structure. The polycyclocarbonates were prepared by the reaction of oligocyclocarbonates containing ended epoxy groups with primary aromatic diamines. Such oligomers may be used by two waysby curing the oligomers with primary aliphatic amines and by preparing adducts which are used for curing epoxy resins or cyclocarbonate oligomers for preparing chemically resistant coatings, constructive glues, sealants, etc. US patent [3] describes a foamable photo-polymerized acrylic composition for use in variety of indoor or outdoor sealing and coating applications, where it is required to seal, to fill or to repair cracks, joints, gaps etc. in concrete, masonry, stone, wood or other constructional materials. The composition comprises acrylic based reactionable oligomers and it can be foamed and then polymerized while producing
Nano-technology comprising steps of the acid depolymerization of natural cellulose materials and ... more Nano-technology comprising steps of the acid depolymerization of natural cellulose materials and the mechanical disintegration of non-dried samples have been developed for obtaining nano-scale particles. Low-stress mechanical treatment of the hydrolyzed cellulose doesn’t permit separation of nano-particles. In order to obtain nano-cellulose having Cl crystalline structure the specified acid concentrations together with the high-stress mechanical disintegration should be used. The correlation between particle size and concentration of the acidic catalyst was established. Structural transformations of cellulose fibers at the hydrolysis and mechanical disintegration are discussed.
Macro- and crystalline structure, as well as chemical composition of fibers related to various ty... more Macro- and crystalline structure, as well as chemical composition of fibers related to various types and sorts of Israeli cottons, both white and naturally colored, were investigated. The differences in structural parameters and chemical compositions of the cotton fibers were evaluated. Samples of cotton of the “Pima”-type had long, thin and strong fibers with highly ordered supermolecular structure. Fibers of middle-long and hybrid cottons had some lower-ordered structural organization in comparison to long-length cotton, while fibers of naturally colored cotton were characterized with disordered supermolecular and crystalline structure. Dependence of tensile strength on orientation of nano-fibrils towards the fiber axis was found. Conditions of cellulose isolation from the different cotton fibers were studied. Structural characteristics of isolated cotton celluloses and obtained MCC are discussed.
Dispersions of microcrystalline cellulose (MCC) with various structural characteristics have been... more Dispersions of microcrystalline cellulose (MCC) with various structural characteristics have been studied. It was shown the MCC dispersions possess specific pseudoplastic rheological properties. An inversely proportional relationship between the average particle size of the MCC particles and the viscosity of the dispersions was discovered. This phenomenon is explained by the decrease of water mobility with increasing the specific surface of the MCC particles. Drying of MCC articles reduces the viscosity of water dispersions, as due to an irreversible hornification of the MCC porous structure.
MICROCRYSTALLINE CELLULOSE: NANO-STRUCTURE FORMATION, 2006
Structural characteristics of the microcrystalline celluloses (MCC) obtained by heterogeneous aci... more Structural characteristics of the microcrystalline celluloses (MCC) obtained by heterogeneous acid hydrolysis of cotton cellulose, under various conditions, with subsequent mechanical disintegration of the non-dried samples in a high-pressure homogenizer, have been studied. To obtain nano-scale MCC with CI-structure, the narrow concentration interval of the mineral acids (7-9 M) alongwith with mechanical disintegration, should be used. The correlation between the dispersity degree of MCC particles and the acidity function was established. Structural transformations of cellulose fibers during hydrolysis and mechanical disintegration are discussed.
Recent advances in chemistry and technology of non-isocyanate polyurethane (NIPU) materials based... more Recent advances in chemistry and technology of non-isocyanate polyurethane (NIPU) materials based on cyclic carbonate oligomers are reviewed in this paper. Reaction of the cyclic carbonate and amino groups results in β-hydroxyurethane fragments with specifi c properties. Primary attention is given to the hybrid materials that contain epoxy and acrylic compounds, especially materials based on renewable raw materials. Hybrid organicinorganic composites comprising of silanes are also considered. An overview of the recent publications in this fi eld is provided with a more detailed description of the Polymate Ltd. achievements. The use of NIPU materials as coatings, adhesives, and foams is described.
Recent advances in chemistry and technology of non-isocyanate polyurethane (NIPU) materials based... more Recent advances in chemistry and technology of non-isocyanate polyurethane (NIPU) materials based on cyclic carbonate oligomers are reviewed in this paper. Reaction of the cyclic carbonate and amino groups results in β-hydroxyurethane fragments with specifi c properties. Primary attention is given to the hybrid materials that contain epoxy and acrylic compounds, especially materials based on renewable raw materials. Hybrid organicinorganic composites comprising of silanes are also considered. An overview of the recent publications in this fi eld is provided with a more detailed description of the Polymate Ltd. achievements. The use of NIPU materials as coatings, adhesives, and foams is described.
SITA, 11, 3-4, 160-188, 2009
Cyclic carbonates (CC) are a comparatively new class of raw materials for preparation of high per... more Cyclic carbonates (CC) are a comparatively new class of raw materials for preparation of high performance “green” heterochain polymers. CC can be prepared using different synthetic methods. In particular, the cycloaddition of CO2 into epoxides to afford five-membered cyclic carbonate with versatile reactivity and the subsequent reaction between the cyclic carbonate and aliphatic primary amine forming urethane linkage have been the active subjects of investigations since they allow non-isocyanate polyurethanes (NIPUs) to be prepared. Polycarbonates may be prepared also by polymerization of mono cyclic carbonates containing C=C double bonds.
Chemistry & Chemical Technology
The article reviews production and application of the nonisocyanate polyurethanes based on cyclic... more The article reviews production and application of the nonisocyanate polyurethanes based on cyclic carbonate oligomers. Nonisocyanate polyurethane (NIPU) networks are obtained by the reaction between the polycyclic carbonate oligomers and aliphatic or cycloaliphatic polyamines with primary amino groups. The result is a crosslinked polymer with β-hydroxyurethane groups of different structure defined as a polyhydroxyurethane polymer. The article discusses NIPU and hybrid NIPU (HNIPU), which also contains epoxy and acrylic compounds. Significant attention was paid to the formation of the materials based on renewable raw materials. The authors provide an overview of the recent publications in this field with a more detailed description of the Polymate Ltd. achievements.
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Papers by Alexander Leykin
with various particle sizes has been studied by means of rheological methods. It was shown that the MCC dispersions possess shear-thinning rheological properties. An inversely proportional relationship between the average particle size of the MCC particles and the viscosity of the dispersions was discovered. This phenomenon is explained by the decrease of water mobility with increase in the specific surface of the MCC particles. Irreversible closing of the MCC pores reduces the viscosity of water dispersions. Addition of some water-soluble polymers leads to a considerable increase in viscosity due to formation of macromolecular net composed of solid particles.
with various particle sizes has been studied by means of rheological methods. It was shown that the MCC dispersions possess shear-thinning rheological properties. An inversely proportional relationship between the average particle size of the MCC particles and the viscosity of the dispersions was discovered. This phenomenon is explained by the decrease of water mobility with increase in the specific surface of the MCC particles. Irreversible closing of the MCC pores reduces the viscosity of water dispersions. Addition of some water-soluble polymers leads to a considerable increase in viscosity due to formation of macromolecular net composed of solid particles.