Structure performance of UVA and UVB light irradiated poly-p-phenylene benzobisoxazole fiber (PBO)

By UVA and UVB irradiating, the performance of poly-p-phenylene benzobisoxazole (PBO) fiber is changed with an increase in irradiation time, and the surface morphology, chemical structure, mechanical performance and thermal properties of the fiber are poorer. After 320-h irradiation, the properties of the PBO fiber irradiated by UVB are stronger than those irradiated by UVA. The strength of PBO fiber irradiated by UVB and UVA declined by 40% and 20%, respectively, than that of non-irradiated fiber. The roughness of fiber surface improved, and there was corrosion on the surface of PBO fiber irradiated by UVB. After the UV irradiation, the degree of macromolecule crystallinity and orientation changed, the macromolecule chain is broken, new groups (-NO2) are produced in the PBO fiber, and the temperature (660°C) of the thermolysis is decreased by 100°C from that of fibril.

Modelling of Elastic Modulus and Molecular Structure Interrelationship of an Oriented Crystalline Polymer

A modeling method is suggested on the basis of measurable structural and deformation parameters to estimate the interrelation between the interconnecting chains over amorphous segments conformation structure distribution and the elastic modulus in tension experimental value for a loaded oriented linear amorphous- crystalline polymer. Macromolecule chain pulling out value of polymer crystallite was defined using the Frenkel-Kontorowa’s dislocation model .

Binding of calcium ions to 2,3-dicarboxy derivatives of starch and amylose

A series of 2,3-dicarboxy derivatives of oxidation degree DO(d.c.) 0.13 to 0.90 was prepared by a two-stage oxidation of corn starch and amylose. The activity coefficient γCa2+ of calcium counterions was estimated in solutions of calcium salts of these carboxy derivatives in a 3.00 mmol (COOCa0.5)l-1 concentration by a metallchromic indicator (tetramethylmurexide) method. A loss of electrostatic free enthalpy, Δ(Gel/N)KCa, due to the exchange of Ca2+ → 2K+ cations was determined by potentiometric titrations of the investigated polyacids and pectinic acids of various linear charge density of the macromolecule employing potassium and calcium hydroxides. 2,3-Dicarboxy derivatives of starch and amylose show a considerably strong binding of calcium ions even at low oxidation degree of the starting polysaccharides in contrast to solutions of the corresponding pectinates and carboxymethyl derivatives of cellulose and amylose. The strong bond of calcium ions to 2,3-dicarboxy derivatives of starch and amylose is ascribed to a favourable spatial arrangement of two neighbouring carboxyl groups at C(2) and C(3) of the oxidized D-glucose units due to a flexibility of the macromolecule chain at sites of the pyrane ring cleavage.

Intramolecular binding of calcium ions to L-guluronan and D-galacturonan

The values of activity coefficients γCa2+, determined earlier in solutions of calcium oligoguluronates and oligogalacturonates of various polymerization degree n, were interpreted. Values γCa2+ corresponding to an intramolecular Ca2+ bond to a polymeric chain of L-guluronan and D-galacturonan were obtained by extrapolation of functions γCa2+ = f(1/n) and γCa2+ = f((n-2)/n) to lim n → ##h. The γCa2+ values were compared with those determined in solutions of calcium salts of O-acetyl derivatives of pectic acid and D-mannuronan. In molecular disperse solutions the Ca2+ ions are bound to L-guluronan and D-galacturonan by an electrostatic bond. The course of the above-mentioned functions leads to the conclusion that both terminal uronic acid units in polyuronates under study bind Ca2+ ions less firmly than do the inner units in the macromolecule chain. The linear course of the function γCa2+ = f((n-2)/n) for L-guluronan proves the additivity of contribution of the terminal and inner uronic acid units to the total activity of Ca2+ counterions bound to L-guluronan.