Structure, Dispersibility, and Crystallinity of Poly(hydroxybutyrate)/ Poly(L-lactic acid) Blends Studied by FT-IR Microspectroscopy and Differential Scanning Calorimetry Tsuyoshi Furukawa, †,‡ Harumi Sato, † Rumi Murakami, † Jianming Zhang, † Yong-Xin Duan, †,§ Isao Noda, ⊥ Shukichi Ochiai, ‡ and Yukihiro Ozaki* ,† School of Science and Technology and Research Center for Environment Friendly Polymers, Kwansei Gakuin University, Gakuen, Sanda, Hyogo 669-1337, Japan; S.T. Japan Inc. 1-16-27, Minaminakaburi, Hirakata, Osaka 573-0094, Japan; Institute of Chemistry, Chinese Academy of Sciences, Beijing, China; and The Procter & Gamble Company, 8611 Beckett Road, West Chester, Ohio 45069 Received March 5, 2005; Revised Manuscript Received May 22, 2005 ABSTRACT: The present study is aimed at investigating structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and poly(L-lactic acid) (PLLA) blends by using FT-IR microspectroscopy and differential scanning calorimetry (DSC). Four kinds of PHB/PLLA blends with a PLLA content of 20, 40, 60, and 80 wt % were prepared from chloroform solutions. Micro-IR spectra obtained at different positions of a PHB film are all very similar to each other, suggesting that there is no discernible segregated amorphous and crystalline parts on the PHB film at the resolution scale of micro-IR spectroscopy. On the other hand, the micro-IR spectra of two different positions of a PLLA film, where spherulite structures are observed and they are not observed, are significantly different from each other. PHB and PLLA have characteristic IR marker bands for their crystalline and amorphous components. Therefore, it is possible to explore the structure of each component in the PHB/PLLA blends by using micro-IR spectroscopy. The IR spectra of a position of blends except for the 20/80 blend are similar to that of pure PHB. On the other hand, the IR spectra of another position of the blend consist of the overlap of those of pure PHB and PLLA. For the 20/80 blend, it is difficult to find a position whose spectrum is similar to that of pure PHB. However, a crystalline peak due to the CdO stretching band is observed at 1718 cm -1 . This means that PHB crystallizes as very small spherulites or immature spherulites under such blend ratio. DSC curves of the blend show that the heat of crystallization of PHB varies with the blending ratio of PHB and PLLA. The recrystallization peak is detected for PLLA and the 20/80 blend respectively at 106.5 and 88.2 °C. The lowering of recrystallization temperature for the 20/80 blend compared with that of pure PLLA suggests that PHB forms small finely dispersed crystals that may act as nucleation sites of PLLA. The results for the PHB/PLLA blends obtained from IR microspectroscopy indicate that PHB crystallizes in any blends. However, crystalline structures of PHB in the 80/20, 60/40, and 40/60 blends are different from those of the 20/80 blend. Introduction Poly(3-hydroxyalkanoate)s (PHAs) are biologically synthesized polyesters produced by microorganisms and are consequently subjected to biodegradation by bacteria in the soil. 1-8 Among PHA polymers, poly(3-hydroxy- butyrate) (PHB) is one of the most well-studied bacterial polyesters. The chemical structure and physical proper- ties of PHB are fairly similar to those of certain petroleum-based synthetic polymers. Therefore, PHB has been a matter of extensive studies as an environ- ment-friendly polymeric material. However, the high crystallinity of PHB makes it rigid and stiff, and thus PHB is not necessarily well-suited for certain applica- tions as a commodity plastic. To reduce the excess crystallinity and improve the overall physical properties of PHB, copolymers and blends of PHB have also been investigated. 9-16 PHB has been blended with nonbio- degradable polymers as well as biodegradable polymers. For example, Marthscelli et al. 13,14 investigated thermal and crystallization behavior of PHB blended with poly- (ethylene oxide) (PEO), ethylene-propylene rubber (EPR), and poly(vinyl acetate) (PVAc). They also studied radial growth rate of PHB spherulites in the blend. PHB/PEO blends and PHB/PVAc blends are miscible because both blends show single glass transition tem- perature, a depression of the melting temperature, and the radial growth rate of PHB spherulite. PHB/EPR blends are deemed immiscible because the radial growth rate of PHB in the blend is independent of the EPR content. Azuma et al. 15 analyzed the thermal behavior and miscibility of PHB blends with biodegradable synthetic polymer, poly(vinyl alcohol) (PVA). Their results indicated that melting temperatures of PHB and PVA in the blend are lower than those found for pure PHB and PVA. The melt temperature remains almost unchanged as the PVA content increases, and the miscibility of the blend is enhanced with the increase in the PVA content. Gassner and Owen 16 explored the physical properties and morphologies of PHB blended with poly(ǫ-caprolactone) (PCL). 16 Melting points of both components in the blend shift to lower temperatures depending on the blending ratio, and their structures also have different layered appearances depending on the blending ratio. Poly(L-lactic acid) (PLLA) is one of the chemically synthesized polyesters. 8,17-19 It can be readily degraded by hydrolysis under mild conditions to lactic acid, which * Corresponding author: e-mail ozaki@kwansei.ac.jp. † Kwansei Gakuin University. ‡ S.T. Japan. § Chinese Academy of Sciences. ⊥ Procter & Gamble. 6445 Macromolecules 2005, 38, 6445-6454 10.1021/ma0504668 CCC: $30.25 © 2005 American Chemical Society Published on Web 06/29/2005