Modification of starch by graft copolymerization

Abstract

Research toward bio-based and biodegradable polymers has received a lot of attention these last years, due to environmental concerns and the need to replace fossil resources. Starch is in this frame an interesting starting material due to its abundance and low cost. Native starch displays however, poor mechanical properties and is highly hydrophilic. New starch-based thermoplastic materials can be prepared to overcome these drawbacks by chemical modification, and notably graft copolymerization. A large range of polymers can be grafted on starch by ring-opening and radical polymerizations of various monomers in order to modulate the properties of the final product. Polymers can also be directly grafted onto starch using coupling strategies. This review presents the state of the art in the field.

Free-Radical Graft Polymerization onto Starch as a Tool to Tune Properties in Relation to Potential Applications. A Review

“…In the first step, radicals are created on the starch backbone, with an initiator that directly reacts with starch such as Cerium Ammonium Nitrate (CAN) or via a radical generating initiator that transfers radicals to starch via hydrogen abstraction from one of the hydroxyl groups [1,2]. Vinyl monomers react with the activated starch to form side chains attached via strong covalent bonds.…”

“…Vinyl monomers react with the activated starch to form side chains attached via strong covalent bonds. This method is also characterized as 'grafting from' (a backbone) [2]. The polymerization proceeds by the conventional chain-growth mechanism.…”

“…Numerous methods have been reported to perform the first step, also known as the initiation, and many monomers have been grafted onto, or from, numerous starches. A recent summary is presented by Meimoun et al [2] and a wealth of information on initiation methods can be found in older reviews of Fanta et al [1,10]. Almost all native starches are produced from various botanical sources, yet are comprised of two main types of molecules.…”

“…Graft copolymers based on starch or other polysaccharides have been the subject of intense investigations for over half a century now [1][2][3]. Still, the number of publications reporting about the structural properties of the grafted products, molecular weights, and spacing of the grafts is limited.…”

“…The copolymers are grafted onto starch, by for instance free radical methods. Besides the usage of different monomers (discussed later), structural parameters such as the amount of newly formed grafted polymer (grafting percentage, GP) and the selectivity of the grafting process with respect to the total amount of new polymer formed (grafting efficiency, GE), as defined in Table 1, are of great importance [2,3]. Table 1.…”