Carbohydrate Polymers 87 (2012) 2614–2618 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers j ourna l ho me pag e: www.elsevier.com/locate/carbpol Citric acid and maleic anhydride as compatibilizers in starch/poly(butylene adipate-co-terephthalate) blends by one-step reactive extrusion J.B. Olivato a,∗ , M.V.E. Grossmann a , F. Yamashita a , D. Eiras b , L.A. Pessan b a Departamento de Ciência e Tecnologia de Alimentos, Centro de Ciências Agrárias, Universidade Estadual de Londrina, Cx. Postal 6001, 86051-980 Londrina, PR, Brazil b Laboratório de Permeac¸ ão e Sorc¸ ão, Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, CP 780, 13560-970 São Carlos, SP, Brazil a r t i c l e i n f o Article history: Received 14 June 2011 Received in revised form 30 July 2011 Accepted 11 November 2011 Available online 22 November 2011 Keywords: Reactive extrusion Compatibilizers Starch Citric acid Maleic anhydride a b s t r a c t Starch/poly(butylene adipate-co-terephthalate) films were obtained by one-step reactive extrusion using maleic anhydride (MA) and citric acid (CA) as compatibilizers. The mechanical, structural, optical and bar- rier properties of the films were analyzed when glycerol (GLY), CA and MA were added to the starch/PBAT (55:45, w/w) according to mixture design. FTIR analysis showed that CA and MA were able to promote esterification/transesterification reactions and that CA induced them more efficiently. When a greater proportion of compatibilizer (1.5 wt%) was used, the resulting films were more opaque and had a greater tensile strength. A greater proportion of GLY (10.0%, w/w) improved the elongation at the break of the films. The barrier properties to water vapor of the films were improved by high levels of CA (1.5 wt%) and intermediate levels of GLY (9.25 wt%). The inclusion of compatibilizers resulted in blends with improved properties, representing a potential replacement for non-biodegradable films. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The market needs biodegradable packaging materials that can be effectively and safely deposited in the soil, and showing the same mechanical performance of the petroleum-derived plastics. This requirement has stimulated new research into starch/polyesters blends, which represent a new class of materials in development (Nabar, Raquéz, Dubois, & Narayan, 2005; Yu, Dean, Yuan, Chen, & Zhang, 2007). Starch, an abundant and renewable polymer, has been widely used as a component of polymeric plastic blends in the form of thermoplastic starch (TPS). TPS is obtained from the disruption of the granules when these are submitted to mechanical/thermal treatment in the presence of a plasticizer, resulting in a homo- geneous and amorphous matrix (Raquéz, Nabar, Narayan, & Dubois, 2008; Zullo & Iannace, 2009). TPS has several favorable attributes that make it suitable for utilization in biodegradable film production; however, its applicability is limited by deficient mechanical properties and a high sensitivity to moisture (Avérous & Fringant, 2001; Yoon, Chough, & Park, 2006). Poly(butylene adipate co-terephthalate) (PBAT) is a biodegradable aliphatic–aromatic co- polyester with mechanical and barrier properties that is capable of overcoming the limitations of TPS. Biodegradable polyesters, ∗ Corresponding author. Tel.: +55 43 3371 4565; fax: +55 43 3371 4080. E-mail address: jubonametti@uel.br (J.B. Olivato). such as PBAT, have a higher cost than the polymers they are being developed to replace. The addition of starch into the formulation may enable the reduction of the cost of the final product (Mani & Bhattacharya, 2001; Ren, Fu, Ren, & Yuan, 2009). The greater difficulty in making starch/PBAT blends is the defi- cient interfacial adhesion between the hydrophilic starch and the hydrophobic polyester. To address this issue, multifunctional substances, such as maleic anhydride (MA) and citric acid (CA), are added to promote esterification/transesterification reactions (crosslinking) at the interface between polymeric chains to improve their compatibility. This fact, according to Zhang and Sun (2004) has been effective for the morphology control in several polymeric systems. Using reactive extrusion for the preparation of starch/polyester blends has the advantage of combining several chemical processes into the extruder without using solvents (Wang, Yu, & Ma, 2007). In previous studies, researchers functionalized the starch or polyester by grafting reactive groups, such as CA and MA, onto the backbone. These graft-copolymers were then used as compatibilizers in a sec- ond step (Kalambur & Rizvi, 2006; Raquéz, Nabar, Srinivasan, et al., 2008; Shi et al., 2008). To make the process faster and more effi- cient, this work aimed to evaluate the influence of CA and MA, added directly to the starch/PBAT mixtures, on the mechanical, optical and barrier properties of blown films produced by one-step reactive extrusion. An additional objective was to reduce the PBAT ratio as much as possible, while still obtaining films with acceptable properties, to increase the content of starch, a renewable polymer. 0144-8617/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.11.035