L Yu et al Prog.Polym Sct31(2006)576-602 585 omd时me he min component.the difference in the solubility para meters 6 and 62 of the blend components in the by high-resolution solid-state C NMR spectro Flory-Huggins equation was estimated to be 0.34 scopy.As co-crystallizable blends,both the blends (Jcm). show complete co-crystallization i.e.the PHE Zhang et al.[7]reported that PHB/PLA blend ame prepared by casting a film from solven On the e over the range PHB-HV blends forr PHB-rich phase had a thicker am lave than that of ate The rystallization of the pHB-Hy conolymers with the same overall Hv PHB in the blends was affected by the level of PLA content.Saad [67]studied the miscibility,melting addition.The thermal history caused a depression and crystallization behavior of poly[(R)-3-hydro- of the melting point and a decrease in the crystal xybutyrate](PHB)and oligo[(RS)-3-hydroxybuty the blends Compared with plair ble sing a DS blend P prop 68s 1g0 HB s "eo 10 racteris the mi ly[(R.S)-3 tion don ndont T and a the hydr atel (atapHB) brium melting te mperature of PHB.The negative weights using DSC and optical micro DSC value of the interaction parameter.determined thermograms for the blends of PLA and ataPHB from the equilibrium melting depression,confirms with Mw=9400 in the range from 0 to 50 wt%of misc bility between blend components. In paralle ataPHB content showed a single glass transition studie transition of differen 20 C,an the valu 0 lig HR Polym temperature after from 59 aPHB the an th aled the iscible ( -relaxation process for blends,indicating ity between the amorphous fractions of PHB and of PLA with high molecular weight ataPHB oligo-HB (M=140.000)showed two glass transition tem- peratures indicating that the binary blend was 3.3.PLA/PHB blends immiscible in the melt.The radial growth rate of e accel PLA/PHB blends have ben stud ied wi weigh edbytheaddnionoi atap o prod -D ts showed th sical PLA of cry sibility【68.Oho5h ct al.1681 and ed hy the ount of Doi [69]studied the miscibility of binary blends of ataPHB component.sugs sting that the addition of bacterial poly[(R)-3-hydroxybutyric acid](P[(R)- ataPHB-3 component facilitated crystallization of 3HBD)with poly[(S)-lactic acid](P[(S)-LAJ)of PLA components in the binary blends.The lamellar various molecular weights using DSC analysis thickness of PLA crystals decreased slightly with an which revealed that the structure of P[(R)-3HB] increase in ataPHB content,suggesting that ataPHB MI(S-LA blen nde on th The PI(R-3HBI of PLA SP e re xation phenon M ses in the melt the dynamic ctra for PLA/ataPHB at 200C.while the blends of P[(R)-3HB]with P[(S) LAl of M values below 18.000 were miscible ir crystallized at 120C,indicating that the partial the melt over the whole composition range.On the phase separation of two components occurs in the basis of the relationship between the miscibility of amorphous phase during the isothermal crystal- blends and the molecular weight of the P[(S)-LA lization process. found that PHB and HV can co-crystallize, and the content in the co-crystalline phase was determined by high-resolution solid-state 13C NMR spectro￾scopy. As co-crystallizable blends, both the blends show complete co-crystallization, i.e. the PHB content in the crystalline phase is the same as that of the whole blends, and the blends form a PHB￾rich crystalline phase. On the other hand, the PHB/ PHB-HV blends forming a PHB-rich crystalline phase had a thicker amorphous layer than that of the PHB-HV copolymers with the same overall HV content. Saad [67] studied the miscibility, melting and crystallization behavior of poly[(R)-3-hydro￾xybutyrate] (PHB) and oligo[(R,S)-3-hydroxybuty￾rate]-diol (oligo-HB) blends using a DSC. It was found that the thermograms of blends containing up to 60 wt% oligo-HB showed behavior characteristic of single-phase amorphous glasses with a composi￾tion-dependent Tg and a depression in the equili￾brium melting temperature of PHB. The negative value of the interaction parameter, determined from the equilibrium melting depression, confirms miscibility between blend components. In parallel studies, glass transition relaxations of different melt-crystallized polymer blends containing 0–20 wt% oligo-HB were dielectrically investigated between –70 and 120 1C in the 100 Hz–50 kHz range. The results revealed the existence of a single a-relaxation process for blends, indicating miscibil￾ity between the amorphous fractions of PHB and oligo-HB. 3.3. PLA/PHB blends PLA/PHB blends have been studied with the aim of producing PLA-based materials with a wide range of physical properties and improved proces￾sibility [68]. Ohkoshi et al. [68] and Koyama and Doi [69] studied the miscibility of binary blends of bacterial poly[(R)-3-hydroxybutyric acid] (P[(R)- 3HB]) with poly[(S)-lactic acid] (P[(S)-LA]) of various molecular weights using DSC analysis, which revealed that the structure of P[(R)-3HB]/ P[(S)-LA] blends was strongly dependent on the molecular weight of the P[(S)-LA] component. The blends of P[(R)-3HB] with P[(S)-LA] of Mw values over 20,000 showed two phases in the melt at 200 1C, while the blends of P[(R)-3HB] with P[(S)- LA] of Mw values below 18,000 were miscible in the melt over the whole composition range. On the basis of the relationship between the miscibility of blends and the molecular weight of the P[(S)-LA] component, the difference in the solubility para￾meters d1 and d2 of the blend components in the Flory–Huggins equation was estimated to be 0.34 (J cm–3). Zhang et al. [70] reported that PHB/PLA blends prepared by casting a film from a common solvent at room temperature were immiscible over the range of compositions studied, while the melt-blended sample prepared at high temperature showed some evidence of greater miscibility. The crystallization of PHB in the blends was affected by the level of PLA addition. The thermal history caused a depression of the melting point and a decrease in the crystal￾linity of PHB in the blends. Compared with plain PHB, the blends exhibited an improvement in mechanical properties. Ohkoshi et al. [68] studied the miscibility and phase structure of binary blends of poly[(S)-lactide] (PLA) with atactic poly[(R,S)-3- hydroxybutyrate] (ataPHB) of different molecular weights using DSC and optical microscopy. DSC thermograms for the blends of PLA and ataPHB with Mw ¼ 9400 in the range from 0 to 50 wt% of ataPHB content showed a single glass transition temperature after melting at 200 1C, and the value decreased from 59 to 10 1C with an increase in ataPHB content, indicating that the PLA and low molecular weight ataPHB (Mw ¼ 9400) are miscible in the melt at 200 1C within the ataPHB content up to 50 wt%. In contrast, the binary blends of PLA with high molecular weight ataPHB (Mw ¼ 140,000) showed two glass transition tem￾peratures, indicating that the binary blend was immiscible in the melt. The radial growth rate of PLA spherulites were accelerated by the addition of low molecular weight ataPHB components. X-ray results showed that the level of crystallinity of the PLA components in the melt-crystallized films were increased by the addition of a small amount of ataPHB component, suggesting that the addition of ataPHB-3 component facilitated crystallization of PLA components in the binary blends. The lamellar thickness of PLA crystals decreased slightly with an increase in ataPHB content, suggesting that ataPHB component was incorporated into the interlamellar region of PLA spherulites. The relaxation phenom￾ena were detected at two different temperatures in the dynamic mechanical spectra for PLA/ataPHB blends (containing ataPHB contents over 15 wt%) crystallized at 120 1C, indicating that the partial phase separation of two components occurs in the amorphous phase during the isothermal crystal￾lization process. ARTICLE IN PRESS L. Yu et al. / Prog. Polym. Sci. 31 (2006) 576–602 585