Blends of bacterial poly(3-hydroxybutyrate) and a poly(epichlorohydrin- co-ethylene oxide) copolymer: thermal and CO 2 transport properties A. Gonzalez * ,1 , M. Iriarte, P.J. Iriondo 2 , J.J. Iruin Department of Polymer Science and Technology, Institute for Polymer Materials (POLYMAT), University of the Basque Country, P.O. Box 1072, 20080 San Sebastia ´n, Spain Received 19 March 2003; received in revised form 5 August 2003; accepted 10 September 2003 Abstract In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) and its blends with a copolymer of epichlorohydrin and ethylene oxide (ECH-co-EO) have been studied. Blends were prepared by solution/precipitation. The aim to obtain miscible blends of iPHB with a rubbery second component (such as the ECH-co-EO copolymer) is to have mixtures with glass transition temperatures below room temperature. In these conditions, the iPHB chains not involved in the crystalline regions retain its mobility. This mobility seems to be necessary for the attack of microorganisms and the corresponding biodegradability. Miscibility is the general rule of these mixtures, as shown by the existence of a single glass transition temperature for each blend and by the depression of the iPHB melting point. The interaction energy density stabilising the mixtures, calculated using the Nishi – Wang treatment, was similar to those of other polymer mixtures involving different polyesters and poly(epichlorohydrin) (PECH) and ECH-co-EO copolymers. The so-called binary interaction model has been used in order to simulate the evolution of the interaction energy density with the ECH-co-EO copolymer composition. Previously reported experimental data on blends of iPHB with PECH and poly(ethylene oxide) (PEO) have been used to quantify the required segmental interaction energy densities. In the determination of the CO 2 transport properties of the mixtures, only iPHB rich blends containing up to 40% of copolymer were considered. The effect of the ECH-co-EO copolymer is to increase the sorption and the diffusion of the penetrant (and, consequently, the permeability) with respect to the values of the pure iPHB. This is primarily due to the reduction of the global crystallinity of the blends and to the low barrier character of the ECH-co-EO copolymer. Sorption data can be reasonably reproduced using an extension of the Henry’s law to ternary systems. q 2003 Elsevier Ltd. All rights reserved. Keywords: Poly(3-hydroxybutyrate); Miscible blends; Transport properties 1. Introduction The most studied and easily produced member of the biodegradable family of polymers denoted as poly(hydrox- yalkanoate)s is poly(3-hydroxybutyrate), (iPHB), an iso- tactic high molecular weight polymer with a melting point around 430 – 450 K, and a glass transition temperature close to 278 K. iPHB is a naturally occurring, thermoplastic polyester, produced in the form of intracellular granules by several microorganisms as carbon and energy storage material. It is a truly biodegradable and excellent biocom- patible material, suitable for two promising applications. One is as a viable candidate for packaging applications relieving the environmental concern caused by the disposal of other non-biodegradable plastics. The other potential application is to provide new-type of biomedical products for drug release and sutures. In both cases, the transport properties of gases and vapours (water) through the material have to be taken into account. However, its prohibitive cost, the narrow difference between the temperatures of thermal degradation and processability and the high crystalline content, which gives rise to poor mechanical properties [1], have prevented an extended use of iPHB in the packaging industry. Different alternatives have been proposed in order to 0032-3861/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2003.09.022 Polymer 44 (2003) 7701–7708 www.elsevier.com/locate/polymer 1 On leave from the Chemical Engineering Faculty. Universidad de Oriente, Santiago de Cuba (Cuba). 2 Tuboplast Hispania. Vitoria/Gasteiz (Spain). * Corresponding author.