Ultrasonic Degradation Of Polymers Research Articles

Novel Approach to the Ultrasonic Degradation of Polymers: Development of a General Kinetic Equation

In order to develop a general kinetic equation for the ultrasonic degradation of polymers, the general applicability of the common kinetic equations is discussed. The common ultrasonic-kinetic equations for polymers are used to fit original data collected from all available literature (over 366 experimental data points). The fitting accuracy of the kinetic equation is evaluated by the residual standard deviation. The fitting results indicate that the first-order equation and second-order equations are the most accurate and can replace other kinetic equations. Based on this, a general kinetic equation for the ultrasonic degradation of polymers is proposed, [Formula: see text] where n = 1 or 2, i.e. when n = 1, it becomes a first-order dynamic equation; when n = 2, it is a second-order dynamic equation.

Chain Degradation under Low-Intensity Sonication of Polymer Solutions in the Presence of Filler: Mechanism of Ultrasonic Degradation of Flexible Chain Macromolecules

Routine dispersion of fillers in polymer solutions in a usual ultrasonic cleaning bath has been shown to lead to chain degradation. It is the filler presence, only, that has been demonstrated to provoke chain degradation under low-intensity sonication. A critical analysis of the literature concerned with the effects arising from propagation of acoustic waves in a liquid and an experimental study of ultrasonic degradation of polymers in solution were carried out. Based on these results, the mechanisms of chain degradation were discussed. Our previously proposed universal mechanism of chain degradation in inhomogeneous hydrodynamic fields has been shown to explain the basic facts repeatedly confirmed over the years of studying the ultrasonic degradation: (i) the existence of a limiting molecular weight such that macromolecules with lower molecular weights are not subject to degradation and (ii) the dependences of degradation rate on polymer molecular weight, polymer concentration, and temperature.

Ultrasonic degradation of polymers: Effect of operating parameters and intensification using additives for carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA)

Use of ultrasound can yield polymer degradation as reflected by a significant reduction in the intrinsic viscosity or the molecular weight. The ultrasonic degradation of two water soluble polymers viz. carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) has been studied in the present work. The effect of different operating parameters such as time of irradiation, immersion depth of horn and solution concentration has been investigated initially using laboratory scale operation followed by intensification studies using different additives such as air, sodium chloride and surfactant. Effect of scale of operation has been investigated with experiments in the available different capacity reactors with an objective of recommending a suitable type of configuration for large scale operation.The experimental results show that the viscosity of polymer solution decreased with an increase in the ultrasonic irradiation time and approached a limiting value. Use of additives such as air, sodium chloride and surfactant helps in increasing the extent of viscosity reduction. At higher frequency operation the viscosity reduction has been found to be negligible possibly attributed to less contribution of the physical effects. The viscosity reduction in the case of ultrasonic horn has been observed to be more as compared to other large capacity reactors. Kinetic analysis of the polymer degradation process has also been performed.The present work has enabled us to understand the role of the different operating parameters in deciding the extent of viscosity reduction in polymer systems and also the controlling effects of low frequency high power ultrasound with experiments on different scales of operation.

Mass Spectrometric Analysis for High Molecular Weight Synthetic Polymers Using Ultrasonic Degradation and the Mechanism of Degradation

We have investigated ultrasonic degradations of poly(ethylene oxide) (PEG) and poly(methyl methacrylate) (PMMA) in aqueous media by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The ultrasonic degradation of polymers was monitored as a function of ultrasonication duration to examine the structural details of ultrasonic degradation polymers. PEG solution ultrasonication produced five types of oligomers (M approximately 1000 Da) with different end groups, irrespective of the initial average molecular masses (M=2, 6, 20, and 2000 kDa). Several degradation pathways with free radical reactions have been suggested to explain these degradation products: the ultrasonic degradation of PEG is initiated by breaking of the C-O bond in the PEG chain, generating polymeric radicals with two terminal groups, i.e., X*( approximately CH2CH2*) and Y*( approximately CH2CH2O*), followed by termination with extraction or release of a hydrogen atom. However, PMMA (M=1630 Da) ultrasonication generated only one type of degradation oligomer, which has a hydrogen group at both ends, the same as that of the original oligomer. It has been suggested that the presence of the radical terminal groups X*( approximately CH2*) and Y*( approximately (CH3)CCOO(CH3)C*) is due to selective C-C bond breaking in the chain during the ultrasonic degradation of PMMA. The MALDI-TOFMS combined with the ultrasonic degradation technique (UD/MALDI-TOFMS) developed in this study could be extended to the analysis of synthetic polymer structures with high molecular weights.

Distributed midpoint chain scission in ultrasonic degradation of polymers

AbstractThe ultrasonic degradation of poly(bisphenol A carbonate), poly(ε‐caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observed for all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2258–2265, 2004

Molecular‐weight distribution kinetics for ultrasonic reactions of polymers

AbstractUltrasonic degradation of polymers is distinguished from thermal degradation by: midpoint rather than random chain scission; a lower limit of molecular weight (MW), xf, below which the polymer will not undergo midpoint scission; and possible biomodal distribution evolving with time. The molecular‐weight distribution (MWD) is governed by a population‐balance equation whose time dependence is deduced from MW moments. To examine if ultrasonically induced reactions have similarity solutions, the moment equations were considered in terms of the time evolution of generalized gamma distribution parameters. The rate coefficient for chain scission is assumed to depend on MW, x, as κ (x − xf), where xf is the limiting MW. The MWD approaches a similarity solution (with a polydispersity of 1.5) only when limiting MW xf is zero. This study also provides an exact analytical solution for the MWD, showing how the MWD can evolve, with reaction time, from an unimodal distribution to a bimodal distribution. Numerical solutions are presented for cases when a polymer undergoes a reversible chain‐end scission along with midpoint chain scission. The rate coefficients for chain‐end scission and polymerization are assumed independent of MW. The theory satisfactorily explains experimental observations.

Effect of solvent on ultrasonic degradation of polymers

The effect of the type of solvent and polymer on ultrasonic degradation was investigated. It was found that there is a correlation between the rate of degradation of the polymer and parameters characterizing the degree of coiling of the polymer sphere—intrinsic viscosity and the Huggins constant. The rate of degradation increases with an increase of dimensions of the polymer sphere.

The Effect of Ultrasonics On the Injectivity And Viscosity of Xanthan Gum For Enhanced Recovery Applications

Abstract This paper outlines preliminary studies which have indicated that the injectivities of xanthan gum solutions can be improved by ultrasonic treatment without adversely affecting formation viscosities in enhanced recovery methods. Introduction One of the major concerns in applying polymer flooding to reservoirs with relatively tight oil sands (less than 100 md) is to have good injectivity while maintaining high solution viscosities(l). If the solution is mixed well and the molecules are dispersed thoroughly without being mechanically degraded, then this optimum situation is reached. Ultrasonic waves have been used to disperse particles of the micrometre Size(2). The capability of ultrasonic waves to disperse particles or agglomerates stems from the cavitation caused by ultrasonics. Cavitation occurs in the regions of the liquid which are subjected to rapidly alternating pressures of high amplitude(3). Besides dispersion, ultrasonic waves have been utilized to break up polymer molecules. The ultrasonic degradation of polymers in solution is of a mechanical nature. The stresses set up in the polymer molecule are caused by the friction forces generated by the relative movement of the molecules of solvent and the polymer molecule as a result of the collapse of cavitation bubbles(4). The permanent degradation can be measured by determining viscosities and by chemical reactions. A recent review of the work in this area is presented by A. M. Basedow and K. H. Ebert(4). Ultrasonics were also found to be effective in liquefying gels(5). The polymer molecules that are used as- mobility control agents in enhanced oil recovery are between 0.1 µm and 0.5 µm in diameter(6). Xanthan gum molecules (Kelzan -XC) have been reported to be around 0.3-0.4 µm(7). These molecules have bonds between them that are weaker than the covalent bonds between the units of the chains. Morris suggests that these weak non-covalent associations between aligned molecules build up a tenuous gel-like network. He also proposes that this network is progressively broken down with increasing shear rate(8). These bonds lead to an increase of entanglements between the polymer chains. Moorhouse et al. characterize the bonds between the molecules as hydrogen bonds(9). If one can break the hydrogen bonds and decrease the degree of entanglement without destroying the covalent bonds, then he can increase the injectivity of the solution and still maintain the high viscosity level. It has been suggested that the larger polymer aggregates present more resistance to flow and accumulate greater shear stresses; hence they are more vulnerable to rupture than the smaller species or the dispersed molecules(4). The principle of utilizing ultrasonic waves to improve the flow properties of polymer solutions through porous media without decreasing the viscosities is examined in this investigation. Procedure In a previous study, the optimum blending of xanthan gum solutions was obtained by the shearing of the solution through several orifice plates, with 100 psi pressure drop each plate(7). Excessive pressure drops across the orifices leads to mechanical breakdown of the molecules. Some of these solutions prepared by optimum blending were subjected to ultrasonic radiation; their injectivities and viscosities were determined.

Ultrasonic degradation of polymers in mixed solvents

Ultrasonic degradation of polymers in mixed solvents

Ultrasonic degradation of polymers in solution and its computer simulation (author's transl)

Ultrasonic degradation of polymers in solution and its computer simulation (author's transl)

Studies in the mechano-chemistry of polymers—XIV. The importance of the concentration of acoustic energy in the ultrasonic degradation of polymers in solution

Studies in the mechano-chemistry of polymers—XIV. The importance of the concentration of acoustic energy in the ultrasonic degradation of polymers in solution