KEY WORDSPoly(butylene succinate-co-butylene carbonate) / Poly(L-lactic acid) / Crystalline Polymer Blends / Interpenetrated Spherulites / The numbers of the studies on miscible pairs of crystalline polymers with different chemical structures are still restricted compared with those with similar chemical structures. 1-10 The differences of the melting temperatures T m of the components are usually 100 • C in the former systems. In these cases, the higher-T m component crystallizes first in the crystallization process and the other component then crystallizes in spatially constrained amorphous regions inside the spherulites.In contrast, when T m s of both components are close enough to each other, the blends exhibit simultaneous spherulitic growth. The spherulites in poly(butylene succinate)/poly(vinylidene chloride-co-vinyl chloride) (PBSU/PVDCVC) blends, whose T m difference is about 35 • C, grow simultaneously. These blends were found to show interpenetrated spherulites (IPS). 11,12 They are characterized by the penetration of PBSU lamellae into PVDCVC spherulites since the lamellar population density in a spherulite is larger for PBSU than for PVDCVC. 13,14 They are expected to have various unique physical characteristics.The reports on the blend systems that show IPS are very few. This is partly because miscible crystalline polymers rarely have close T m s. Our group has been searching polymer blends that show IPS.Poly(butylene succinate-co-butylene carbonate) (PEC) and poly(L-lactic acid) (PLLA) are polyesters whose T m s are close to each other (106 • C and 140 • C, respectively). If they are miscible, they possibly crystallize simultaneously and show IPS. Furthermore, since both PEC and PLLA are biodegradable, PEC/PLLA blends can be ecological crystalline polymer blends.The purposes of this paper are to show miscibility of PEC/PLLA by differential scanning calorimetry (DSC), to study the crystallization behavior by polarizing optical microscopy (POM), and to investigate the possibility of IPS. PEC/PLLA blends were prepared with mutual solvent chloroform at room temperature. The solution was cast on glass plates and then the solvent was removed at room temperature to make thin films for POM observation. For DSC, the solution was dried for a week and then in a vacuum for three days to remove the solvent from the bulky samples.The glass transition temperature T g was determined by DSC (TA Instruments DSC 2910). Samples were heated to 170 • C for 5 min, quenched to −100 • C using liquid nitrogen, kept for 5 min, and heated at 10 • C min −1 . The value of T g was determined as the temperature of the half-height of the step transition.To study the morphology of the blends and the radial spherulitic growth rates G of PEC and PLLA, we used POM (Olympus BHP-P) equipped with a first order retardation plate and a temperature controller (Linkam TH-600). Samples were premelted at 170 • C for 3 min and then quenched to the crystallization temperature T c . RESULTS AND DISCUSSIONTo confirm the miscibility of the PEC/PLL...
KEY WORDSInterpenetrated Spherulites / Confocal Laser Scanning Microscopy / Poly(butylene succinate) / Poly(vinylidene chloride-co-vinyl chloride)/ Morphology/ Poly(butylene succinate)/poly(vinylidene chloride-covinyl chloride) (PBSU/P(VDC-VC)) is a miscible semicrystalline/semicrystalline polymer blend system in the melt state. The small difference of melting temperature between the two components enables them to crystallize simultaneously over a wide range of compositions and isothermal crystallization temperatures. In general, when two spherulites collide with each other, they stop growing and a clear boarder is observed by polarizing optical microscopy (POM). 1 • 2 In PBSU/P(VDC-VC) blend systems, however, PBSU lamellae continue to grow along P(VDC-VC) lamellae after PBSU spherulites collide with P(VDC-VC) spherulites, and interpenetrated spherulites are observed by POM. POM also shows that the birefringent pattern of a PBSU spherulite in certain crystallization conditions is neither positive nor negative; it is rotated by about 45° from positive or negative spherulites.The investigations of these blends by atomic force microscopy (AFM) 3 showed the following results. The lamellar direction in PBSU spherulites with neither a positive nor negative pattern was not parallel to the radial direction but inclined by about 45°. This explains its birefringent pattern. In addition, the population-density of the lamellae in P(VDC-VC) spherulites was lower than that in PBSU spherulites. This enables PBSU lamellae to penetrate into P(VDC-VC) spherulites. The penetration was characterized by the change in the lamellar direction of PBSU and the absence of depression in the height profile on the spherulitic border between PBSU and P(VDC-VC).POM is one of the most common methods to observe the time evolution of spherulites. However, the spatial resolution of POM restricts detailed investigations on the microstructure down to the lamellar level. On the other hand, AFM has high resolution sufficient to observe individual lamellae though its narrow scan area ( -20 µm X 20 µm) and long scan time ( -min) are sometimes inconvenient.Confocal laser scanning microscopy (CLSM) needs no special treatment on samples. Its resolution is intermediate between AFM and POM, and its scan time is short ( -sec). Therefore CLSM is appropriate for both static and dynamic observations of spherulites though few have been reported. 4 In the present work, our purpose is to observe the interpenetrated spherulites in PBSU/P(VDC-VC) blends by CLSM and compare the results with those by POM and AFM. We also show the potential of CLSM in visualizing the morphology of polymer spherulites.EXPERIMENTAL PBSU (Mw=140000, Tm=387 K, Tg=241 K) was supplied by Showa High Polymer. P(VDC-VC) (Mw= 100000, Tm =421 K, Tg=279 K) supplied by Asahi Chemical is a random copolymer of vinylidene chloride: vinyl chloride=S0: 20. In this study, we used PBSU/P (VDC-VC)=60/40 (wt/wt) blend films. Blends were prepared by dissolving the two components in N,Ndimethylformamide at abo...
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