Starch reactive extrusion

While starch copolymers are typically prepared by batch polymerization methods, reactive extrusion of starch has been studied. Mixtures of starch, polystyrene, styrene, sodium hydrogen carbonate, citric acid and water were extruded at temperatures between 100°C and 200°C.118 It was reported that expanded graft copolymers... 

Carr et al.119 investigated grafting via reactive extrusion of starch with cationic methacrylate, acrylamide and acrylonitrile monomers. Starch, monomer and CAN initiator were metered into a twin-screw extruder at starch contents of approximately 35% solids. The cationic methacrylate monomer showed poor reactivity during extrusion, with essentially no add-on. Acrylamide-starch systems (1 1 w/w) gave conversions of approximately 20% and add-ons of 16% to 18%. Acrylonitrile displayed the greatest reactivity during extrusion, with conversions of 74% and 63% for 1 1 and 1 2 w/w acrylonitrile/starch ratios, respectively. The corresponding add-ons were 27% and 42%. 

Kalambur, S.B. Syed, SH.R. Starch-based nanocomposites by reactive extrusion processing. Polym. International 2004, 53 (10), 1413-1416. 

Starch is the major carbohydrate reserve in higher plants and has been a material of choice since the early days of human technology. Recently starch gained new importance as a raw material in the production of plastics, in particular, for the synthesis of monomers to produce polymers such as polydactic acid) and, after chemical modification (e.g. esterification) and thermomechanical processing, to produce thermoplastic starch. This chapter gives a general overview of the most recent research on the development of materials from starch, focusing on thermoplastic starch and the perspectives for future development in this field. A brief review on reactive extrusion of thermoplastic starch is also provided. 

Keywords Starch, thermoplastic starch, biodegradable polymers, reactive extrusion... 

Currently, materials derived directly from starch by physical processing or by continuous chemical modification, as in reactive extrusion, are considered the most promising options for bio-based plastic production, particularly on economic grounds. A brief historical view of such starch-based materials is offered in the next section. 

Miladinov et al. reported the preparation of starch-fatty acid esters by reactive extrusion of plasticized starch and acid anhydrides (acetic, propionic, heptanoic and palmitic anhydrides) in the presence of sodium hydroxide as a catalyst [87]. Starch esters have been prepared by REX using maleic anhydride (MA) as a cyclic dibasic acid anhydride in the presence of 20 wt% glycerol as plasticizer. This material was melt-blended with biodegradable polyester. 

Compatibilization by reactive extrusion of starch and other polymers such as PLA has also been carried out successfully with diisocyantes such as 4,4-diphenylene diisocyanate (MDI) as reagent [80,90]. 

The emergence of TPS with tunable properties, by using continuous reactive extrusion, can lead starch to a new position in the market of thermoplastic materials based on renewable resources with functional properties such as biodegradabitly. 

Murua-Pagola, B., Beristain-Guevara, C.I., Martmez-Bustos, R, 2009. Preparation of starch derivatives using reactive extrusion and evaluation of modified starches as shell materials for encapsulation of flavoring agents by spray drying. J. Food Eng. 91, 380-386. 

O Brien, S. Wang, Y.J. Vervaet, C. Remon, J.R Starch phosphates prepared by reactive extrusion as a sustained release agent. Carbohydr. Polym. 2009, 76 (4), 557-566. 

Various conventional processing technologies, such as casting, extrusion, injection and compression moulding, have been adapted for processing starch-based materials, as well as some new techniques, such as orientation and reactive extrusion. 

Maliger et al. [216] have reported on a compatible blend of starch and polyester through reactive extrusion using maleic anhydride (MA) and dicumyl peroxide (DCP) as compatilizer and initiator, respectively. It was found that distributing diisocyanate in the polyester phase prior to blending resulted in better mechanical properties than distribution in starch phase [194, 196]. 

R.B. Maliger, P.J. Halley, Reactive extrusion for thermoplastic starch-polymer blends (book chapter), in Starch Polymers From Genetic Engineering to Green Apphcations, 2014, pp. 291-317. 

Recently, Wang et al. [16] reported preparation of PLA/starch blends by one-step reactive extrusion. In the presence of dicumyl peroxide, the compatibility of thermoplastic dry starch (DTPS)/PLA blends, using MA as compa-... 

In the same way. Song et al. (2011), reported starch nanoparticles prepared by reactive extrusion method. Their results indicate that with the addition of an appropriate cross-linker, starch nanoparticles with an average size of 160 nm could be obtained. 

Moad G (2011) Chemical modification of starch by reactive extrusion. Progr Polym Sci 36 218-237... 

In a similar study, Kalambur and Rizvi [166, 167] employed reactive extrusion to develop biodegradable starch-polyester (PCL) nanocomposite blends with higher... 

Reactive extrusion processing has been used as a technique for converting starch to chemicals, derivatives, and copolymers [85-90]. By this technique cationic derivatives, alkyl glucosides, carboxylates and oxidized starches have been produced [91]. Cationic starch has been prepared from native corn-starch and 3-chloro-2-hydroxypropyltrimethyl-ammonium chloride in aqueous sodium hydroxide using a twin-screw extruder as the reactor [92]. 

Wing, R. E., and Willett, J.L. (1997) Water Soluble Oxidized Starches by Peroxide Reactive Extrusion, Ind. Crop. Prod. 1, 45-52. 

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