Binary and ternary blends of polylactide, polycaprolactone and thermoplastic starch Pierre Sarazin a , Gang Li a , William J. Orts b , Basil D. Favis a, * a CREPEC, Department of Chemical Engineering, Ecole Polytechnique de Montre ´al, P.O. Box 6079, Station Centre-Ville, Montre ´al, Quebec, Canada H3C 3A7 b USDA, ARS, Western Regional Research Center, 800 Buchanan Street, Albany, CA 94710, USA Received 18 July 2007; received in revised form 6 November 2007; accepted 10 November 2007 Available online 19 November 2007 Abstract In this study binary and ternary blends of polylactide (PLA), polycaprolactone (PCL) and thermoplastic starch (TPS) are prepared using a one-step extrusion process and the morphology, rheology and physical properties are examined. The morphology and quantitative image anal- ysis of the 50/50 PLA/TPS blend transverse phase size demonstrate a bimodal distribution and the addition of PCL to form a ternary blend results in a substantial number of fine dispersed particles present in the system. Focused ion beam irradiation, followed by atomic force micros- copy (AFM) shows that dispersed PCL forms particles with a size of 370 nm in PLA. The TPS phase in the ternary blends shows some low level coalescence after a subsequent shaping operation. Dynamic mechanical analysis indicates that the temperature of the tan d peak for the PLA is independent of TPS blend composition and that the addition of PCL in the ternary blend has little influence on the blend transitions. Both the a and b transitions for the thermoplastic starch are highly sensitive to glycerol content. When TPS of high glycerol content is blended with PLA, an increase in the ductility of the samples is achieved and this effect increases with increasing volume fraction of TPS. The ternary blend results in an even greater ductility with an elongation at break of 55% as compared to 5% for the pure PLA. A substantial increase in the notched Izod impact energy is also observed with some blends demonstrating three times the impact energy of pure PLA. The mechanical properties for the ternary blend clearly indicate a synergistic effect that exceeds the results obtained for any of the binary pairs. Overall, the ternary blend approach with PLA/TPS/PCL is an interesting technique to expand the property range of PLA materials. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Thermoplastic starch; Polylactide; Polycaprolactone 1. Introduction Environmental concern over the use of traditional petro- leum-based polymers has stimulated the development of poly- mers from renewable resources as an alternative. Starch, as the main reserve polysaccharide of higher plants, is a naturally oc- curring biopolymer and is of low cost. Starch consists of two main polysaccharides, amylose and amylopectin, based on chains of 1 / 4 linked a-D-glucose [1]. Amylose is essentially linear, amylopectin, often the major part (about 72% in wheat and maize starches), is highly branched containing on average one branch point which is 1 / 4 / 6 linked for every 20e25 straight chain residues [1]. The starch granule is partially crys- talline, and various crystalline forms are reported, depending on the proportion of the two main polysaccharides and the re- gions in the starch granules. Since the melting temperature (T m ) of pure dry starch is close to 220e240  C and the onset temperature of starch degradation is around 220  C [2], native starch has to be modified in order to be melt-processed as a thermoplastic. The addition of water to starch is known to have a strong plasticizing effect, causing a large decrease in the glass transi- tion temperature (T g ) [3]. When starch is usually heated in the presence of water the native crystalline structure is disrupted, a phenomenon known as gelatinization. In an excess of water, above the gelatinization temperature, the starch granule loses * Corresponding author. Tel.: þ1 514 340 4711x4527; fax: þ1 514 340 4159. E-mail address: basil.favis@polymtl.ca (B.D. Favis). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.11.029 Available online at www.sciencedirect.com Polymer 49 (2008) 599e609 www.elsevier.com/locate/polymer