Ultrasonic depolymerization of aqueous polyvinyl alcohol

Abstract

Ultrasonication has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Most of the effects involved in controlling molecular weight can be attributed to the large shear gradients and shock waves generated around collapsing cavitation bubbles. In general, for any polymer degradation process to become acceptable to industry, it is necessary to be able to specify the sonication conditions which lead to a particular relative molar mass distribution. This necessitates the identification of the appropriate irradiation power, temperature, concentration and irradiation time. According to the results of this study the reactors constructed worked well in depolymerization and it was possible to degrade aqueous polyvinyl alcohol (PVA) polymer with ultrasound. The most extensive degradation took place at the lowest frequency used in this study, i.e. 23 kHz, when the input power was above the cavitation threshold and at the lowest test concentration of PVA, i.e. 1% (w/w). Thus this study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller.

Ultrasonic degradation of solutions of poly(vinyl acetate) in tetrahydrofuran

“…These findings are consistent with the results of other investigators. 8 Our results indicate that the extent of degradation is more pronounced at low temperatures. This might be be-cause, with increasing temperature, v p of the solvent increases, and so the vapor enters the cavitation bubbles during their growth.…”

“…[5][6][7] Ultrasonication has been proved to be a highly advantageous method for degrading macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond in the center of the chain without causing any changes in the chemical nature of the polymer. 8 The passage of a longitudinal sound wave through a liquid causes cavitation. 6 The formation, growth, and rapid collapse of microscopic bubbles generate high temperatures and pressures during bubble collapse in the region of several thousand Kelvins and several hundred atmospheres, according to the system.…”

Sonochemical Grafting of Poly(vinyl alcohol) onto Multiwall Carbon Nanotubes in Water

“…18 Gronroos et al, reported ultrasonic depolymerization of poly(vinyl alcohol) (PVA) as a functions of frequency, and sonication power. 19 Lately, Gogate et al, investigated the reduction of intrinsic viscosity of carboxymethyl cellulose and PVA solutions. 20 The ultrasonic degradation of the polymer is often expressed as the reduction in the molecular weight of polymers under ultrasound.…”

Sonophotocatalytic Degradation of Poly (Vinyl Pyrrolidone) in the Presence of Fe (III)/H2O2

“…Cavitation produces vibrational wave energy, shear stresses at the cavitation interphase, and local high pressure and temperature. These are the major factors causing the degradation of polymers [21][22][23].…”