Non-Coagulant Spinning of High-Strength Fibers from Homopolymer Polyacrylonitrile Synthesized via Anionic Polymerisation

The rheological properties, spinnability, and thermal-oxidative stabilization of high-molecular-weight linear polyacrylonitrile (PAN) homopolymers (molecular weights Mη = 90-500 kg/mol), synthesized via a novel metal-free anionic polymerization method, were investigated to reduce coagulant use, enable solvent recycling, and increase the carbon yield of the resulting carbon fibers. This approach enabled the application of the mechanotropic (non-coagulating) spinning method for homopolymer PAN solutions in a wide range of molecular weights and demonstrated the possibility of achieving a high degree of fiber orientation and reasonable mechanical properties. Rheological analysis revealed a significant increase in solution elasticity (G') with increasing molecular weight, facilitating the choice of optimal deformation rates for effective chain stretching prior to strain-induced phase separation during the eco-friendly spinning of concentrated solutions without using coagulation baths. The possibility of collecting ~80 wt% of the solvent at the first stage of spinning from the as-spun fibers was shown. Transparent, defect-free fibers with a tensile strength of up to 800 MPa and elongation at break of about 20% were spun. Thermal treatment up to 1500 °C yielded carbon fibers with a carbon residue of ~50 wt%, in contrast to ~35 wt% for industrial radically polymerized PAN carbonized under the same conditions.

Morphology and transport properties of membranes obtained by coagulation of cellulose solutions in isobutanol

The evolution of structural-morphological transformations of cellulose membranes obtained from solutions in N-methylmorpholine-N-oxide through various temperature isobutanol coagulation baths and subsequent treatment with water and their transport properties were studied. Using SEM, it was found that during coagulation in water and drying of the membranes, a uniform monolithic microheterogeneous texture was formed. The replacement of an aqueous precipitation bath with an isobutanol one leads to the formation of a porous structure with wide pore size and shape distributions. With an increase in precipitant temperature in the as-formed membrane, transverse tunnel cavities are formed with respect to the membrane-forming axis, which collapses when the membrane is washed with water, forming a dense texture with a non-uniform membrane volume. The mechanical properties of the obtained membranes were determined and a mechanism is proposed that allows their values to be correlated with structural-morphological and transport properties.

[Possibile application of X-ray and high resolution CT in pneumoconiosis management]

The article covers results of clinical and roentgenologic data analysis. The data were obtained in the study that covered 447 pneumoconiosis patients, 75 of which were subjected to high resolution CT. If compared to chest X-ray, high resolution CT helps more precise forecast of further course in pneumoconiosis.

[Ultrasonic method of study and puncture biopsy in diagnosing thyroid nodules]

Results of diagnosis of thyroid nodes in 404 patients are analyzed. Ultrasonic examination and US-assisted puncture biopsy were carried out before operations. Their results were compared with ones of morphologic study performed after surgery. Solitary nodes were diagnosed in 171 (42.3%) patients, multiple--in 233 (57.7%). The most specific ultrasonic symptoms of different forms of thyroid nodes were revealed. Thyroid cancer is imaged as hypoechogenic node with clear and unclear contour, heterogeneous structure, multiple zones of hyperechogenicity and calcification. Adenomas are presented as isoechogenic homogenic nodes with clear border and cystic cavities. Colloid nodes picture is the same. Rathen often different morphologic forms of nodes are similar, thus ultrasonic examination permits to detect morphologic structure of nodes hypothetically only. Sensitivity of puncture biopsy for goiter, adenomas and cancer was 87.1, 92.9 and 69.7% respectively. Cancer was not diagnosed before surgery in 30.3% cases when colloid goiter or adenomas were suspected. In these cases small cancer was located amidst colloid nodes and didn't differ by ultrasonic symptoms. Diagnosis of malignant tumor in nodular goiter was highly precise. Morphologic form of cancer was verified cytologically in majority of cases.

[Immunochemical study of Clostridium botulinum type B toxin]

Fractionation of type B. Cl. botulinum toxin, a protein complex, was carried out; as a result, 3 fractions, alpha, beta, and gamma, were isolated in a pure form, alpha-fraction, or neurotoxin, is highly toxic (5-10.10(7) LDm per 1 mg of protein), beta-fraction showed hemagglutinating activity (64-128 HAU per 1 mg of protein), gamma-fraction was not biologically active. The molecular weight of alpha and gamma-fractions was 150,000. All these fractions had antigenic properties. alpha-fraction was serologically specific. beta- and gamma-fractions showed incomplete serologic identity.

[Production of a homogeneous Cl. botulinum type B neurotoxin]

The method for obtaining the neurotoxin, or alpha-fraction of the toxin, of Cl. botulinum, type B, is described. In accordance with this method, the toxin was precipitated three times with hydrochloric acid in the isoelectric zone with subsequent extraction with phosphate (pH 6.8) and citrate-phosphate (pH 5.6) buffers, then fractionated in columns with DEAE cellulose (pH 5.6), DEAE Sephadex A-50 (pH 7.2) and Sephadex G-200 (pH 7.2). The homogeneous neurotoxin preparations with molecular weights ranging from 145,000 to 160,000 and having the isoelectric point at pH 5.5 and toxicity 5.0--10.0 x 10(7) Dlm per 1 mg protein were obtained.

[Isolation and immunochemical study of the toxic complex of Cl. botulinum type F]

The toxic comples of Cl. botulinum, type F, was separated into the toxic and nontoxic protein fractions by the methods of ion exchange chromatography and gel filtration in accordance with a specially devised purification scheme. Highly purified, electrophoretically and serologically homogeneous toxin with a molecular weight of 150,000 and potency equal to 10 X 10(6) DLM per 1 mg of protein was isolated from the toxic fraction. The nontoxic protein component had faintly pronounced hemagglutinating properties and was essentially different from type A and B hemagglutinins. The toxic complex of Cl. botulinum, type F, was shown to contain a proteolytically active fraction.

[Deaminase activity of Cl. botulinum type A, B, E and F cultures]

The authors present the results of a comparative study of desaminase activity in the suspensions of resting cells and in ultrasonic desintegrates of cells of Cl. botulinum types A, B, E and F against a number of amino acids and their amides. It was shown that types A, B, E and F possessed active desamination enzymes; this process, however coursed with a different degree of intensity depending on the substrate. Common for all the 4 types was the presence of desamidase L-asparaginase and L-glutaminase, and also of the desamination enzymes of the aspartic and glutamic acids. Strains of type B had the greatest set of enzymes, and of type A--the least; bacteria of types E and F occupied an intermediate position. None of the types studied contained tryptophandesaminase. Some of desaminases are bound to subcellular structures.