Water soluble graft copolymer (κ-carrageenan-g-N-vinyl formamide): Preparation, characterization and application
Introduction
Presently the industrial application of natural polymers and their derivatives is the most fascinating and vastly investigated field. For this purpose, biodegradable natural polymers such as polysaccharides and protein have been widely used (Jeong et al., 1997, Younes and Cohn, 1987). One is κ-carrageenans; it is sulfonated anionic polygalactans extracted from marine red algae (Rees et al., 1982, Smidsrød and Grasdalen, 1982) (Rhodophyceae) mostly of genus Chondrus, Eucheuma, Gigartina and Iridaea. κ-Carrageenan is well differentiated with respect to disaccharide repeating units of alternating (1 → 3)-α-d-galactose-4-sulphate and (1 → 4)-β-3,6-anhydro-d-galactose residues (Harding et al., 1997, Layahe, 2001, Thanh et al., 2002). Carrageenan and its derivatives form valuable ingredients for foods, cosmetics and pharmaceuticals (Ruiter and Rudolph, 1997, Uruakpa and Arntfield, 2006). In recent years, they have demonstrated to play significant role in antioxidant activities (Yuan et al., 2006, Zhang et al., 2003, Zhang et al., 2004) and have been explored as effective excipients in controlled release drug delivery systems (Lazzarini et al., 2006, Makino et al., 2001). Even though, κ-carrageenan enjoys a number of applications, however, like other biopolymers, it also suffers from drawback like easier susceptibility of microbial attack and grafting provides an efficient route for removing this drawback. To date many investigations have been carried out on graft copolymerization reactions in view of preparing biopolymers based advanced materials. Reports on grafting of κ-carrageenan are scantly available (Pourjavadi et al., 2004, Pourjavadi et al., 2005) so, in the light of versatile applications of carrageenan and its derivatives, this work has been carried out with an aim to tailor κ-carrageenan based hybrid materials by grafting N-vinyl formamide.
N-vinyl formamide is a cationic hydrophilic monomer. With the availability of improved processes for synthesis and purification of N-vinyl formamide, poly(N-vinyl formamide) and its derivatives are widely used industrially (Pinschmidt et al., 1997). Poly(N-vinyl-formamide) has also been found to be an effective drag reducing agent (Marhefka, Marascalco, Chapman, Russell, & Kameneva, 2006). Prompted by the applications of N-vinyl formamide, hitherto unreported graft copolymer viz. graft copolymer (κ-carrageenan-g-N-vinyl formamide) has prepared by employing peroxymonosulphate/malonic redox system and to study some of the properties like swelling behaviour, metal ion sorption, flocculation and resistance to biodegradability behaviour. The graft copolymer has been found to be thermally more stable than the parent backbone, i.e., κ-carrageenan.
Section snippets
Materials
N-vinyl formamide (Sigma Aldrich) has been used after distillation under reduced pressure of 14 mmHg at 55 °C in nitrogen atmosphere. Potassium peroxymonosulphate (Sigma) and malonic acid (Merck) have been used as such without further purification. κ-Carrageenan was purchased from Sigma Aldrich. For maintaining hydrogen ion concentration, sulphuric acid (Merck) has been used. Methanol has been used for precipitation. The other chemical reagents were of analytical grade. All the solutions were
Swelling test
Swelling studies have been carried out with different grafted samples synthesized by varying the concentration of N-vinyl formamide. Each grafted sample (0.02 g) has been taken and immersed in 20 ml of triple distilled water and kept undisturbed for 24 h. The surface water on the swollen graft copolymer has been removed by softly pressing it between the folds of filter paper. An increase in weight of graft copolymer has been recorded. Calculation of the percent swelling (PS) and swelling ratio (SR
Grafting properties
The graft copolymer has been characterized as reported in the literature (Fanta, 1973a, Fanta, 1973b).
Determination of optimum reaction conditions
The optimum reaction condition was obtained by varying the concentration of peroxymonosulphate (PMS), malonic acid (MA), sulphuric acid, N-vinyl formamide (NVF),
Conclusions
The spectroscopic data confirm that the grafting of vinyl formamide has occurred at hydroxyl group of κ-carrageenan molecule. The thermal analysis data show that the grafted polymer is more thermally stable than ungrafted polymer (considering both higher final decomposition temperature and integral procedural decomposition temperature of the grafted polymer as compared to substrate). Grafted polymer shows very good water swelling ability and resistance to biodegradability. Grafting is further
Acknowledgement
Authors thankfully acknowledge to UGC, New Delhi for providing financial support.
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