Poly lactic acid Starch Blends

Poly(lactic acid) (PLA) and starch are two promising candidates for biodegradable polymer blends since both materials are commercially available. PLA is a synthetic polymer produced from a natural monomer derived from starch, and of course starch is naturally abundant, which is derived from several plant forms [1-28], 

10 times larger than conventional synthetic polymers. Amylopectin, on the other hand, is a branched polymer. The molecular weight of amylopectin is much larger than amylose. Light scattering measurements indicate that the molecular weight is on the order of 10.  

Most native starches are semicrystalline with a crystallinity of about 20-45%. Amylose and the branching points of amylopectin form the amorphous regions. The short branching chains in the amylopectin are the main crystalline components in granular starch [30, 31]. 

Poly(lactic acid) Synthesis, Structures, Properties, Processing, and Applications, edited by R. Auras, L.-T. Lim, S. E. M. Selke, and H. Tsuji Copyright 2010 John Wiley Sons, Inc. 

Ke et al. [22] investigated the effect of amylose content in starches on the mechanical properties of PLA/starch composites. Four dry com starches with different amylose contents were blended at 185°C with PLA at various starch/ PLA ratios using a lab-scale twin-screw extmder. Starch with 

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Zhang IF, Sun X (2004b), Mechanical properties of poly (lactic acid)/starch blend compatibilized by maleic anhydride , Biomacromolecules 5, 1446-1451. 

Zhang J.F., Sun X., Physical characterization of coupled poly (lactic acid)/starch/maleic anhydride blends by triethyl citrate, Macromol. BioscL, 4, 2004,1053-1060. 

Ke T, Sun XS (2003) Thermal and mechanical properties of poly(lactic acid)/starch/methy-lenediphenyl diisocyanate blending with tiiethyl citrate. J Appl Polym Sci 88 2947-2955... 

Typical tensile curves of extruded and molded poly (lactic acid)/starch (60 40) blends containing 1 5% of various plasticizers as representatives (Ke and Sun, 2001 b). 

Other blends such as polyhydroxyalkanoates (PHA) with cellulose acetate (208), PHA with polycaprolactone (209), poly(lactic acid) with poly(ethylene glycol) (210), chitosan and cellulose (211), poly(lactic acid) with inorganic fillers (212), and PHA and aUphatic polyesters with inorganics (213) are receiving attention. The different blending compositions seem to be limited only by the number of polymers available and the compatibiUty of the components. The latter blends, with all natural or biodegradable components, appear to afford the best approach for future research as property balance and biodegradabihty is attempted. Starch and additives have been evaluated ia detail from the perspective of stmcture and compatibiUty with starch (214). 

SCH 08] ScHWACH E., Six J.L., Averous L., Biodegradable blends based on starch and poly(lactic acid) comparison of different strategies and estimate of compatibilization Journal of Polymers and the Environment, vol. 16, no. 4, pp. 286-297,2008. 

WAN 01] Wang H., Sun X.Z., See P., Strengthening blends of poly(lactic acid) and starch with methylenediphenyl diisocyanate , Journal of Applied Polymer Science, vol. 82, no. 7, pp. 1761-1767,2001. 

Ren, J., Fu, H., Ren, T., and Yuan, W. (2009]. Preparation, characterization and properties of binary and ternary blends with thermoplastic starch, poly(lactic acid] and poly(butylene adipate-co-terephthalate]. Carboh dnPoI m., 77, 576-582. 

Liao et al. [261] reported biodegradable nanocomposites prepared from poly(lactic acid) (PLA) or acrylic acid grafted poly(lactic acid) (PLA-g-AA), titanium tetraisopropylate, and starch. Arroyo et al. [262] reported that thermoplastic starch (TPS) and polylactic acid (PLA) were compounded with natural montmorillonite (MMT). The TPS can intercalate the clay structure and that the clay was preferentially located in the TPS phase or at the blend interface. This led to an improvement in tensile modulus and strength, but a reduction in fracture toughness. 

Shi, Q., Chen, C., Gao, L., Jiao, L., Xu, H., Guo, W. Physical and degradation properties of binary or ternary blends composed of poly (lactic acid), thermoplastic starch and GMA grafted POE. Polym. Degrad. Stab. 96, 175-182 (2011)... 

G. li, P. Sarazin, W.J. Orts, S.H. Imam, B.D. Favis, Biodegradation of thermoplastic starch and its blends with poly(lactic acid) and polyethylene Influence of morphology. Macromol. Chem. Phys. 212, 1147-1154 (2011)... 

H. Wang, X. Sun, and P. Seib, Properties of poly (lactic acid) blends with Vcuious starches is affected by physical aging. J. Appl. Polym. Sci. 90(13), 3683-3689 (2003). 

M.A. Paglicawan, B.A. Basilia, M.T.V. Navarro, C.S. Emolaga, Influence of nanoclay on the properties of thermoplastic starch/poly(lactic acid) blends. Journal of Biobased Materials and Bioenergy 7 (1) (2012) 102-107. 

Poly(lactic acid) (PLA) (Fig. 1.16) is an aliphatic polyester polymerised by lactic acid which is made by fermentation of natural raw materials, for example, com starch and sugarcanes. Due to the chiral nature of lactic acid and its effects on the polymer s characteristics, the biodegradability and mechanical properties of PLA can be tailored by varying the proportion of different forms. Meanwhile, PLA can also copolymerise with other monomers or blend with other polymers to improve some properties of the material, eg, flexibility. PLA and PLA-based copolymers are the most popular biodegradable materials for the production of absorbable sutures (Li, 1999) (Fig. 1.16). 

Another way of generating biopolymers is the fermentation of starch, sugar and other commodities by various microorganisms. Typical examples are poly(hydroxyalkanoates) (especially poly(hydroxybuty-rate) (PHB)) and poly(lactic acid) (PLA). Due to the chirality of lactic acid (D- L-form), two distinct forms of poly(lactic acid) exist (poly(L-lactic acid) and poly(D-lactic acid)). PLA is used, e.g. in biomedical application (sutures, stents, drug-delivery, preparation of bioplastic), in agriculture (mulch-film), packaging, and in blends with synthetic polymers. 

The interfacial interaction between poly(lactic acid) (PLA) and starch was improved and mechanical properties of PLA blends with starch were enhanced by an addition of methylene diisocyanate (MDI) [111-112]. 

Wang H., Sun X., Seib E Properties of poly(lactic acid) blends with various starches as affected by physical agmg,J.Appl. Polym. Sci. 90 (2003) 3683. 

One of the remarkable properties of PHAs is the ability to mix well with many other polymeris materials to produce highly compatible composites or so-called polymer alloys. Such blends often possess synergistic properties not obtainable by individual components. Of great interest is the compatible blend of Nodax with certain other classes of degradable polymers, especially those made from renewable resources, such as starch and poly(lactic acid) (PLA). For example, hard and somewhat brittle PLA and much more ductile PHA are excellent complementary materials, which can balance the shortcomings of each other when used together. We report here some newly discovered interesting properties of PLA/PHA blends. 

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