Depolymerization of guar gum solution using different approaches based on ultrasound and microwave irradiations Amrutlal L. Prajapat, Parag R. Gogate * Chemical Engineering Department, Institute of Chemical Technology, Matunga, Mumbai 400 019, India A R T I C L E I N F O Article history: Received 4 September 2014 Received in revised form 22 November 2014 Accepted 29 November 2014 Available online 2 December 2014 Keywords: Ultrasound Microwave Guar gum Sequential effect Potassium persulfate Free radicals A B S T R A C T The present work investigates the application of ultrasound and microwave operated individually or in combination for depolymerization of aqueous solution of guar gum. In addition, intensification aspects due to the use of an initiator, potassium persulfate (KPS), has been investigated. The extent of depolymerization has been analyzed in terms of the reduction in intrinsic viscosity. Also, the effectiveness of treatment approach has been analyzed on the basis of kinetic rate constant, limiting intrinsic viscosity and the time required for the desired extent of viscosity reduction. The kinetic rate constant has been found to increase with an increase in the temperature and KPS loading. For the individual operation involving irradiations, the rate was found to be higher in the case of ultrasound as compared to the microwave irradiations. In the case of sequential approach, microwave followed by ultrasound was more effective as compared to the approach of ultrasound followed by microwave. The obtained results clearly established that ultrasound in combination with KPS was the most effective approach for depolymerization. The work has also enabled to understand the effective role of KPS and operating temperature in intensifying the viscosity reduction of guar gum polysaccharides. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction Guar gum (GG) is a water-soluble and naturally occurring poly galactomannan derived from the seeds of Cyamopsis tetragonolobus (guar) plant [1]. It is mainly comprised of a linear backbone of b (1-4)-linked D-mannose units (M) with randomly attached side chains of a (1-6)-linked galactose units (G) [2]. Due to the low cost and capacity to impart high viscosities at relatively low concentrations, guar gum has been used in different industrial applications including food and pharmaceutical sectors. Guar gum is used as a food supplement [3] and also as additive in many food products such as sauces, syrups, ice cream, instant foods, beverages, confectionaries and baked goods. GG is also used as a thickening and gelling agent [4,5]. Considering the pharmaceutical sector applications, GG is used in tablet manufacturing as a binder and disintegrating agent and also for drug micro-encapsulation [6]. Furthermore, GG has been reported to be useful in the therapy of hypercholesterolemia and hyperglycemia as well as an indigest- ible sugar in obesity treatment [7]. Another important use of guar gum has been reported in the gas and oil sector as a hydraulic fracturing fluid [8,9]. All these industrial applications of guar gum are feasible because of the capability to form hydrogen bonding with water molecules. For all above applica- tions, guar gum needs to be depolymerized in a controlled manner giving lower molecular weight fractions as desired for the specific application. The important properties of polysaccharides depend on their molecular weight, which can be expressed as a function of the intrinsic viscosity. For obtaining the desired molecular weight of the polymers in an efficient manner, development of fast and inexpensive methods for depolymerization of native polysacchar- ides is very important. Depolymerization of polysaccharides has been studied using various methods though acid based [10] and enzymatic [11] methods have been most common. Even though the acidic and enzymatic methods are convenient, these methods suffer from important drawbacks as higher treatment time, higher treatment costs especially in the case of enzymatic methods and difficulty in achieving an uniform molecular weight distribu- tion after degradation [8,12]. Some of the newer methods for depolymerization include methods based on the use of ultrasound [13,14] and irradiation (treatment with ionizing radiation) [15] as well as free radical induced degradation [12]. Use of ethylene dibromide or ethylene oxide for degradation of polysaccharides is associated with the problems related to the handling of hazardous chemicals. Irradiation is a simple method for controlled * Corresponding author. Tel.: +91 22 33612024; fax: +91 22 33611020. E-mail address: pr.gogate@ictmumbai.edu.in (P.R. Gogate). http://dx.doi.org/10.1016/j.cep.2014.11.018 0255-2701/ ã 2014 Elsevier B.V. All rights reserved. Chemical Engineering and Processing 88 (2015) 1–9 Contents lists available at ScienceDirect Chemical Engineering and Processing: Process Intensification journal homepa ge: www.elsev ier.com/locate/cep