Ultrasonic degradation of polymers: Effect of operating parameters and intensification using additives for carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA)by Ashish V. Mohod, Parag R. Gogate

Ultrasonics Sonochemistry

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Article history:

Received 10 July 2010

Received in revised form 26 October 2010

Accepted 2 November 2010

Available online 13 November 2010

Keywords: weight (also the intrinsic viscosity) is simply by splitting the most susceptible chemical bond. Application of ultrasonic energy for polymer degradation dates back to the 1930s when natural polymers were subjected to sonication, which resulted in a reduction in viscosity [5]. Ultrasound has been used for degradation of a wide range of polymers. The ultrasonic degradation of polymers is of degraded species [8,16,17]. Akyuz et al. [17] investigated the degradation of PVP using ultrasound and compared the different theoretical and phenomenological models of evolution of the molecular weight during sonication with the obtained on-line data.

Typically, these models share the property of an initial rapid drop in molecular weight followed by a slowing down of the rate of molecular weight decrease. Different models are also proposed to explain the degradation based on cavitation induced by ultrasound [18]. In the first model, the degradation is interpreted in terms of the high temperature and pressure generated during the bubble collapse. The Jellinek model attributes chain scission to the ⇑ Corresponding author. Tel.: +91 22 33612024; fax: +91 22 33611020.

E-mail addresses: pr.gogate@ictmumbai.edu.in, paraggogate@yahoo.co.in (P.R.

Ultrasonics Sonochemistry 18 (2011) 727–734

Contents lists availab

Ultrasonics So elsGogate).1. Introduction

The past few decades have seen a dramatic rise in the applications of high-intensity, or power, ultrasound in chemistry, with a range of synthetic procedures and process methods having found to benefit from sonication [1–3]. One of the beneficial applications of ultrasound is for the polymer degradation [4]. Sonochemical degradation of polymers has proved to be an attractive process especially considering the fact that there are no changes in the chemical nature of the polymer and the reduction in molecular great interest [6,7], and the degradation of several polymers such as polystyrene [8], polyvinyl acetate [4], polypropylene [9], polybutadiene [9], poly(methylmethacrylate) [10], dextran [11], hydroxy propyl cellulose [12], carboxymethyl cellulose [13],

Polyacrylamide [14], and poly(e-caprolactone) [15], has been investigated. A variety of different theoretical models has been proposed to attempt to explain the way in which the factors such as frequency, intensity, solvent, temperature, nature of dissolved gas, external pressure and the molecular mass distribution influence the rate of degradation and final molecular mass of theUltrasonic degradation

Carboxymethyl cellulose

Polyvinyl alcohol

Intrinsic viscosity

Scale up aspects

Process intensification1350-4177/$ - see front matter  2010 Elsevier B.V. A doi:10.1016/j.ultsonch.2010.11.002Use 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.  2010 Elsevier B.V. All rights reserved.a r t i c l e i n f o a b s t r a c tUltrasonic degradation of polymers: Effe and intensification using additives for ca and polyvinyl alcohol (PVA)

Ashish V. Mohod, Parag R. Gogate ⇑

Chemical Engineering Department, Institute of Chemical Technology, Matunga, Mumbai journal homepage: www.ll rights reserved.of operating parameters oxymethyl cellulose (CMC) 019, India le at ScienceDirect nochemistry evier .com/ locate /ul tsonch cs Sincreased frictional force generated on cavitational collapse. In the final model, Doulah [19] suggests that the shock-wave energy released on bubble collapse gives rise to a series of eddies which interacts with the macromolecules in solution. The factors influencing polymer degradation rate and final molecular weight of degraded species have also been studied [8,20,21]. It is generally agreed that the hydrodynamic forces have the primary importance.

Hydrodynamic forces may originate as a result of increased frictional forces between the ultrasonically accelerated faster moving solvent molecules and the larger, less mobile, macromolecules.

Hydrodynamic forces may also be due to the high pressure associated with the collapse of cavitation bubbles [5,22]. It is believed, that ultrasonic degradation, unlike chemical or thermal decomposition, is a non-random process, with cleavage taking place roughly at the centre of the molecule and with larger molecules degrading the fastest.