Yu. G. Baklagina

Morphology, deformation and failure behaviour of homo- and copolyimide fibres ☆: 1. Fibres from 4,4′-oxybis(phthalic anhydride) (DPhO) and p-phenylenediamine (PPh) or/and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM)

Abstract The morphology, deformation and failure behaviour of new high-performance polyimide (PI) fibres were examined by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and tensile measurements. PI fibres were prepared from rigid aromatic diamines p -phenylenediamine (PPh) and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM) and semi-rigid 4,4′-oxybis(phthalic anhydride) (DPhO) by wet-spinning of the N , N -dimethylacetamide solutions of their precursor poly(amic acids) in coagulation bath followed by thermal imidization at 400°C. The tensile properties and drawability of copolyimide (coPI) fibres were better than those of homopolyimides (homoPI). The improvement in fibre modulus and tensile strength of the coPI fibres can be explained by the microblock structure on the X-ray level and composed morphology on the macro level. Moreover, changes in the supermolecular structure and apparent fibril sizes, character of morphology, quantity of interfibrillar links, which affect the fracture mode were observed with the different composition of coPI.

Morphology of melt crystallized polypropylene in the presence of polyimide fibres

Hot stage optical and scanning electron microscopy were used to study isothermal crystallization of isotactic polypropylene (iPP) in the presence of polyimide (Pl) fibres. Under the same crystallization conditions, the occurrence of transcrystallization depends on the type of fibre used. The transcrystalline interphase has a composed structure, with a characteristic layer adjacent to the fibre surface. The layer is about 1 μm thick and has a crosshatched lamellar morphology. At the interface between iPP and the Pl fibre which causes transcrystallization, the nuclei from which the transcrystalline zone grows is observed. The nuclei consist of sheaves of closely packed parallel needleshaped lamellae of uniform thickness. The transcrystallization phenomenon can be explained by the epitaxial crystallization of iPP matrix on the surface fragments (domains) formed by extended chains of Pl fibres. Different abilities of Pl fibres to induce transcrystallization are associated with the superficial morphology of the fibres.

Deep desalination of water by evaporation through polymeric membranes

Transport properties and structural features of a number of already known and new types of polymeric membranes in desalination of aqueous salt solutions by membrane distillation and pervaporation were studied. The possibility of obtaining distilled water in a single stage by pervaporation from dilute or concentrated aqueous salt solutions was examined for the example of membranes fabricated from celluloses of varied origin (wood, cotton, bacterial).

Structure of cellulose Acetobacter xylinum

The data are presented on optimization of cellulose synthesis by Acetobacter xylinum (strain VKM V-880) and the structural characteristics of A. xylinum cellulose gel film synthesized during static cultivation. The structural changes caused by the removal of water from gel films are established and the structural organization of macromolecular chains in cellulose A. xylinum is studied.

Study of polyelectrolyte complexes of chitosan and sulfoethyl cellulose

The complexing of polycation chitosan and polyanion sulphoethyl cellulose during the formation of polyelectrolyte simplex membranes using the layer-by-layer deposition of a solution of one polyion on a gel-like film of another one has been studied. The structural characteristics of the multilayer composites and their components have been analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray microanalysis. A technique is proposed for studying the structure of surface layers of thin polymer films (15–20 μm) using a portable DIFREI-401 diffractometer. It is shown that the sequence of layer deposition during the formation of membrane films does not affect their structural characteristics. The interaction between positively charged chitosan groups (-NH3+) and negatively charged sulfoethyl cellulose groups (-SO3−) during the growth of polyelectrolyte complexes results in a packing of chitosan chains in the multilayer film.

Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.

Formation of organic-inorganic composite materials based on cellulose Acetobacter xylinum and calcium phosphates for medical applications

The formation of composites based on the cellulose Acetobacter xylinum and calcium phosphates has been investigated using X-ray diffraction, electron diffraction, electron microscopy, energy-dispersive analysis, and differential scanning calorimetry. It has been demonstrated that the planar morphology of calcium phosphate nanoparticles capable of interacting with nanofibrils of the cellulose matrix is an important factor providing interfacial contacts in the formation of organic-inorganic composite materials. It has been established that magnesium-containing calcium phosphates represent two-phase systems consisting of calcium magnesium phosphate Ca2.6Mg0.4(PO4)2 (whitlockite) and hydroxyapatite Ca5(PO4)3(OH). The biocompatibility of the composite materials based on two-phase calcium phosphate systems and the temperature range of their stability (∼20–250°C) determined by the thermal stability of the organic component have been investigated.

Chemical and structural transformations in chitosan films in the course of storage

Changes in the functional composition of chitosan films in the course of storage under ambient conditions were examined by conductometric titration and IR spectroscopy. The deformation-strength and thermal properties of the films were studied, and their supramolecular structure was analyzed by X-ray diffraction.

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films was studied. The optimal sorption parameters at which the amorphous form of the selenium complex is preserved in the composite were suggested.

Interrelation between the structural and transport properties of pervaporation membranes with diffusion layers based on poly-γ-benzyl-L-glutamate

The interrelation between the transport properties of pervaporation membranes (used to separate toluene-n-heptane mixtures) and the structure of poly-γ-benzyl-L-glutamate diffusion layers has been studied. The decrease in the membrane selectivity while increasing the flux at the transition from 3 to 50 wt % toluene in the mixture under separation is accompanied by a change in the ordered structure of poly-γ-benzyl-L-glutamate structure without variation in the α-helical conformation of the polypeptide chain.