Biranchinarayan Tosh
Orissa Engineering College, India
Title : Grafting of Cellulose and Application of the Grafted Products
Abstract :

Cellulose is the most abundant natural polymer which is used as such or its derivatives in a number of applications, for instance in paper, packaging or lacquer technologies. Moreover, cellulose is biodegradable and obtainable from renewable sources, and, thus acceptable from the environmental point of view. However to reach the required application properties, cellulose has to be modified, mostly by a reaction of hydroxyl groups leading to cellulose esters and ethers. In addition, cellulose backbone can be grafted with synthetic polymers via ‘grafting from’ or ‘grafting – onto’ ways, using various polymerization techniques. Thus, various materials were obtained by grafting, with different properties such as elasticity, ion exchange ability, thermal stability and mechanical properties. The grafting is mostly realized via free radical polymerization initiated with redox systems, based prevailingly on ceric or ferrous salts or sodium hydrogen sulfite systems in combination with peroxides. Also, depending on the reaction medium, the grafting reaction may be divided into two types viz. heterogeneous and homogeneous grafting. Heterogeneous graft copolymerization of synthetic polymers onto cellulose and cellulose acetate has been studied extensively over the past decades. Grafting of cellulose fiber by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization after reacting the hydroxyl groups with suitable RAFT chain transfer agents has also been carried out. Using these methods, a wide spectrum of cellulose and cellulose acetate graft copolymers with acrylamide, methyl methacrylate, vinyl acetate and acrylonitrile etc have been prepared; however, in heterogeneous medium the number, density, length and molecular weight distribution of the grafts are virtually impossible to control. The derivatization and/or grafting reactions in homogeneous conditions assures important advantages over heterogeneous system like, a better control of the degree of substitution, a more uniform distribution of substituents along the polymer and a higher conversion yield.
 
CAN in presence of nitric acid is an efficient initiator for graft copolymerization of vinyl monomers onto cellulose in heterogeneous medium but in homogeneous conditions this will produce gel confirming the regeneration of cellulose and also CA from the solution. It is only reported that CAN in presence of dimethyl sulfoxide (DMSO) can produce Ce+4 ion and can be a suitable redox system to initiate graft copolymerization process, but no work has been carried out on this system. A few work on grafting reactions involving BPO and Sn(Oct)2 as initiator has been carried out in homogeneous conditions. It has also been reported that, presence of methylene blue in the reaction system reduces the formation of homopolymers in the graft copolymerization process. We have reported the homogeneous graft copolymerization of MMA onto cellulose and cellulose acetate by dissolving cellulose in DMAc/LiCl and dimethyl sulfoxide/paraformaldehyde (DMSO/PF) solvent system and cellulose acetate (CA) in various solvents like DMSO, DMAc, 1,4-dioxane and acetone using CAN, BPO and Sn(Oct)2 as initiators. Three initiators have been chosen as they follow different reaction mechanisms during grafting. CAN forms free radical in the cellulose ring by homolytic cleavage of the C-C bond and also the presence a metal ion in the reaction medium reduces homopolymer formation and thus enhances grafting efficiency. BPO follows free radical mechanism by homolytic cleavage of O-H bond of the hydroxyl group whereas Sn(Oct)2 follows heterolytic cleavage of the O-H bond. The effect of varying in reaction time, temperature, concentration of initiator and monomer were studied to optimize the conditions under which grafting would occur more effectively. The effect of methylene blue on the control of homopolymer formation in presence of CAN in all of the solvents was also studied. Formation of Ce3+ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue (MB) was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights (Mn) and polydispersity indices (PDI) of the grafted PMMA were found out by gel permeation chromatography (GPC). The products were characterized by FTIR and 1H-NMR analyses and possible reaction mechanisms were deduced. The degree of crystallinity of cellulose, CA and the grafted products were found out by X-ray diffraction studies. The thermal degradation of the grafted products was also studied by thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) analyses.
Biography :
Dr. Biranchinarayan Tosh obtained his M. Sc. degree in Industrial Chemistry and he is a Doctorate in Polymer Chemistry with special reference to Biopolymers. After his Ph. D. he has worked at National Chemical Laboratory, Pune, India as a Research Associate in the field of Polycarbonate Nanocomposites and as a Post-Doctoral Fellow at Kyoto Pharmaceutical University, Japan in the field of Controlled Drug Delivery. At Present he is serving as the Professor and Head, Department of Chemistry, Orissa Engineering College, Bhubaneswar, India.
 
Dr. Tosh has total 13 years of research and teaching experience and his present area of research includes, radiation curable coatings, chitosan based nanomaterials, composite materials from cellulose derivatives for various applications. His research work has been published in 20 national and international journals and presented in more than 30 national and International conferences. Aufau Periodicals, India has recognized Dr. Tosh with the “Aufau Science Legend Award” in the year 2013 for his contribution to the journal “Chemical Science Review and Letters”. 
 
Dr. Tosh is associated with American Chemical Society as a member since 2008 and many scientific associations in India as life member. At present two scholars are doing their research work under his guidance.
 

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