Synthesis and characterization of grafted hydroxypropyl guar gum by ceric ion induced initiation B.R. Nayak, R.P. Singh * Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, India Received 26 May 2000; received in revised form 6 December 2000; accepted 15 February 2001 Abstract A study was made of the ceric-ammonium-nitrate-initiated graft copolymerization of polyacrylamide onto hy- droxypropyl guar gum by solution polymerization technique. Six grades of graft copolymers have been synthesized by varying catalyst and monomer concentrations. The synthesized products were then characterized by various instru- mental techniques like viscometry, elemental analysis, IR, thermal, XRD and SEM studies. The percentage of grafting increases with increasing catalyst concentration and decreases with monomer concentration taking other parameters constant. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hydroxypropyl guar gum; Polyacrylamide; Graft copolymers 1. Introduction Graft copolymerization is a technique for modifying the chemical and physical properties of synthetic and natural polymers. Applications of these modi®cation reactions are useful areas in polymer chemistry. Syn- thetic polymers are much more eective than natural ones due to their versatile tailorability. However, they are not shear resistant. Natural polymers mainly poly- saccharides are fairly shear stable, biodegradable and cause drag reduction and ¯occulation at relatively higher concentrations. The biodegradability of natural polymers reduces their shelf-life and needs to be suitably controlled. It is thus evident that all polymers whether synthetic or natural have one or other disadvantages. Several attempts have been made in the past to com- bine the best properties of both by grafting synthetic polymers onto natural ones [1,2]. One of the great advantages thus obtained is the consequent reduced biodegradability because of the drastic change of the original regular structure of the natural polymer as well as the increased synthetic polymer content within the product. In the authors' laboratory, many graft copolymers have been synthesized by grafting polyacrylamide PAM) onto starch [3], carboxymethyl cellulose CMC) [3], guar gum [4], xanthan gum [5,6], and sodium algi- nate [7]. It has been observed that the graft copolymers having fewer but longer PAM branches are fairly shear stable and exhibit better drag reduction and ¯occulation characteristics [8]. Among the graft copolymers of PAM with starch constituents amylose and amylopectin), it has been observed that PAM grafted amylopectin per- forms the best as a ¯occulating agent [8±10], particularly for industrial euents. This has been attributed to the fact that the dangling PAM branches onto the rigid polysaccharide backbone have better approachability to the colloidal particles in the euents [2,8,11]. It is therefore concluded that by grafting ¯exible PAM chains onto the polysaccharide backbone, it is possible to develop ecient, shear stable and controlled biode- gradation resistant polymers for treatment in industrial euents and mineral processing. Ceric ion has been used to initiate graft copolymer- ization of many monomers on various substrates [12±16]. European Polymer Journal 37 2001) 1655±1666 www.elsevier.nl/locate/europolj * Corresponding author. Tel.: +91-3222-55224; fax: +91- 3222-55303. E-mail address: rps@matsc.iitkgp.ernet.in R.P. Singh). 0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0014-305701)00035-0