Graft Copolymerization Onto Tamarind Kernel Powder: Ceric(IV)-initiated Graft Copolymerization of Acrylonitrile Puja Goyal, Vineet Kumar, Pradeep Sharma Chemistry Division, Forest Research Institute (ICFRE), Dehradun 248006, India Received 17 January 2008; accepted 8 February 2009 DOI 10.1002/app.30232 Published online 8 June 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Tamarind Kernel Powder (TKP) is derived from the seeds of Tamarindus indica Linn., a common and most important tree of India. It is extensively used in cot- ton sizing, as a wet-end additive in the paper industry, as a thickening, stabilizing, and gelling agent in the food industry. However, because of its fast biodegradability there is a need to prepare graft copolymers of TKP. The graft copolymerization of acrylonitrile (AN) onto TKP with ceric ammonium nitrate as a redox initiator in an aqueous medium has been studied. The reaction condi- tions were optimized to afford maximum percent grafting and percentage grafting efficiency of AN onto TKP, which was found to be 86% and 64%, respectively. Fourier Trans- form Infrared Spectrum of the grafted products showed an additional sharp absorption band at 2244 cm 1 due to ACBN stretching, thereby confirming the grafting of AN onto TKP. Scanning electron microscopy studies indicated change in contour of the polysaccharide on grafting and the thick polymeric coating of AN on its surface alongwith grafting of AN such that all the gap between polysaccha- ride particles have been closed. Thermal studies using thermogravimetric and differential gravimetric analyses confirmed that TKP-g-AN has overall high thermal stabil- ity than pure TKP. Reaction mechanism of grafting of acrylnitrile onto TKP is also proposed. V V C 2009 Wiley Periodi- cals, Inc. J Appl Polym Sci 114: 377–386, 2009 Key words: tamarind kernel powder; graft copoly- merization; acrylonitrile; ceric ammonium nitrate; free- radical initiator; scanning electron microscopy INTRODUCTION Tamarind (Tamarindus indica) is an economically most important and common tree cultivated throughout India and is particularly abundant in Madhya Pradesh and South India especially in Tamil Nadu, Karnataka, and Andhra Pradesh. The timber from the tree is very valuable. The wood is used as fuel and for making agricultural implements. Almost every part of it finds some use, but the most useful is its fruit. Fruit in the form of large pods is com- posed of 55% pulp, 34% seeds, and 11% shell and fibers. The pulp is acidic in nature, which is widely used in India as a souring agent in culinary prepara- tions. The seed is a by-product of the tamarind pulp industry, which is an agricultural waste; it is cheaper indigenous product when compared with other gums or synthetic mucilagenous substances. 1 The seed is exalbuminous and has about 70% ker- nel or endosperm enclosed by about 30% testa, which is rich brown in color. Tamarind Kernel Pow- der (TKP) is obtained from the seed kernel after dehusking of the brown testa and pulverizing creamy white kernel. The analysis of the seed ker- nels gave the following range of values: protein 17.1–20.1%; fat 6.0–8.5%; carbohydrates 65.1–72.2%; crude fiber 0.7–4.3%; and ash 2.3–3.2%. 1 The dark brown fatty oil from the kernels is used in the prep- aration of paints, varnishes, and for burning lamps. TKP, a crude extract of tamarind seeds has been used as a replacement for starch in cotton sizing and as a wet-end additive in the paper industry, where it replaces starches and galactomannans. 2 It also finds application as a creaming agent for rubber la- tex, as a soil stabilizer, in medical and pharmaceuti- cal application and oil-field applications. 3 Refined tamarind seed polysaccharide is used as a thicken- ing, stabilizing, and gelling agent in the food indus- try, particularly in Japan where it is a permitted food additive. 2,4 The proposed structure of the polysaccharide is composed of (1!4)-b-linked D-glucan backbone, sub- stituted by single unit, (1!6)-linked a-D-xylopyrano- syl side chains, some of which are further substituted by D-galactopyranosyl residues linked (1!2)-b. 4 Exact composition of polysaccharide is not fully known till date. The ratio of glucose : xylose : galactose in the polysaccharide has been reported by number of workers as approximately 3 : 2 : 1, 3 : 2.25 : 1, 2.25 : 1.25 : 1, 4 : 2 : 1, and 2.8 : 2.25 : 1.0. 2,4,5 Arabinose residues are frequently reported for tama- rind seed polysaccharide but these probably arise from contaminating arabinans. 4 Journal of Applied Polymer Science, Vol. 114, 377–386 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: V. Kumar (drvineet@gmail.com).