Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) ShuwenPeng,YuxianAn,ChengChen,BinFei,YugangZhuang,LisongDong * State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China Received 3 May 2002; received in revised form 11 December 2002; accepted 13 December 2002 Abstract Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfullytodescribetheisothermalcrystallizationkineticsofPHBV,whichindicatesthattheAvramiexponent n ¼ 3 isgoodforallthetemperaturesinvestigated.Thespheruliticgrowthrate, G,wasdeterminedbyPOM.Theresultshows thatthe G hasamaximumvalueatabout353K.Usingtheequilibriummeltingtemperature(448K)determinedbythe Flory equation for melting point depression together with U  ¼ 1500 calmol 1 , T 1 ¼ 30 K and T g ¼ 278 K, the nucleation parameter K g wasdetermined,whichwasfoundtobe3.14  0.07  10 5 (K 2 ),lowerthanthatforpurePHB. The surface-free energy r ¼ 2:55  10 2 Jm 2 and r e ¼ 2:70  0:06  10 2 Jm 2 were estimated and the work of chain-folding(q ¼ 12:5  0:2kJmol 1 )wasderivedfrom r e ,andfoundtobelowerthanthatforPHB.Thisimpliesthat the chains of PHBV are more flexible than that of PHB. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Isothermal crystallization; Poly(3-hydroxybutyrate-co-3-hydroxyvalerate); Kinetics 1. Introduction Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a biodegradable thermoplastic copolymer which can be produced from renewable resources [1]. PHBV was first manufactured by ICI in 1983 and was originally intended to be used as a biodegradable substitute for oil-based polyolefins in plastic containers, films and bottles [2]. Po- tential uses for it also include medical implants, such as sutures or drug delivery devices, which will gradually de- grade in the body. Its formula is as follows: CH CH 2 CH 3 C O O CH CH 2 CH 2 CH 3 C O O x y It possesses a wide range of properties depending on the HV content. However, PHBV is a semicrystalline polymer with high crystallinity at all compositions [3,4]. Itsfinalproperties,suchasimpactresistanceandstress– strain property, depend on the crystallization procedure and on its crystallinity. Therefore investigation of the kinetics of crystallization is of importance. The crystal- lizationbehaviorofPHBVinasolventhadbeenstudied in detail by Barham, and the structure and morphology of PHBV has also been given [5]. Solid-state 13 C NMR results given by Kamiya show that PHBV crystallize in * Corresponding author. Tel.: +86-431-5262076; fax: +86- 431-5685653. E-mail address: dongls@ciac.jl.cn (L. Dong). 0014-3057/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0014-3057(03)00014-4 European Polymer Journal 39 (2003) 1475–1480 www.elsevier.com/locate/europolj