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Miscibility and Crystallization Behavior of Biodegradable Poly(butylene succinate)/Tannic Acid Blends Fang Yang and Zhaobin Qiu* State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China ABSTRACT: Miscibility, crystallization behavior, crystal structure, and microstructure of biodegradable poly(butylene succinate)/ tannic acid (PBSU/TA) blends were studied with differential scanning calorimetry, optical microscopy, wide-angle X-ray diffraction, and small-angle X-ray scattering in this work. PBSU and TA are miscible as evidenced by the single composition dependent glass transition temperature over the whole blend composition range and the depression of equilibrium melting point of PBSU in the blends. Nonisothermal melt crystallization of PBSU is retarded by the presence of TA. It is found that blending with TA affects the spherulitic morphology of PBSU apparently but does not modify the crystal structure of PBSU. The long period and thickness of the amorphous phase become larger with increasing the TA content in the blends, indicating that TA mainly resides in the interlamellar region of PBSU spherulites.
’ INTRODUCTION Biodegradable polymers have attracted considerable attention recently. In terms of the preparation methods, biodegradable polymers can mainly be classified into the following two types. One is biosynthetic polymers, such as bacterial polyhydroxyalkanoates (PHAs). The other is chemosynthetic polymers, such as the linear aliphatic polyesters. Poly(butylene succinate) (PBSU) is one of them. The crystal structure, crystallization, and melting behavior of PBSU have been reported in the literature.18 Polymer blending is a simple and economical way to modify the physical properties and extend the practical application fields of biodegradable polymers. PBSU based polymer blends have been studied extensively. On the one hand, PBSU was found to be miscible with poly(vinylidene fluoride) (PVDF), poly(vinylidene chloride-co-vinyl chloride) (PVDCVC), poly(ethylene oxide) (PEO), poly(vinyl phenol) (PVPh), and poly(ethylene adipate) (PEA).915 On the other hand, PBSU was found to be immiscible with poly(hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(εcaprolactone) (PCL), and poly(lactic acid) (PLA).1619 Biodegradable tannic acid (TA) is a high molecular weight polyphenolic compound, which is mostly extracted from plants and microorganisms. Woo et al. have recently studied the miscibility and specific interaction of a series of binary blends comprised of TA and some biodegradable polyesters, such as PCL, PEA, and poly(butylene adipate) (PBA).20 They found that TA was miscible with PCL, PBA, and PEA over the whole composition range, respectively, as evidenced by the single composition dependent glass transition temperature; moreover, they concluded that the miscibility may arise from the presence of specific intermolecular hydrogen bonding interactions between the carbonyl groups of polyesters and the phenolic hydroxyl groups of TA on the basis of the Fourier transform infrared spectroscopy (FTIR) study.20 Woo et al. found that TA was miscible with PEO and studied the effect of TA on the crystalline morphology of PEO in detail; moreover, they also r 2011 American Chemical Society
studied TA induced single crystalline morphology in poly(ethylene succinate).21,22 However, to our knowledge, PBSU/TA blends have not been reported so far in the literature. In this work, miscibility and crystallization behavior of PBSU/TA blends were studied with various techniques in detail. It is expected that the research reported herein will be of help and interest for a better understanding of the miscibility and crystallization behavior of biodegradable polymer blends from both academic and industrial viewpoints.
’ EXPERIMENTAL SECTION Materials. PBSU (Mw = 63 000 g/mol) and TA (Mw = 1721 g/mol) were purchased from Sigma-Aldrich Co. Both samples were used as received. Sample Preparation. PBSU/TA blends were prepared with 1,4-dioxane as mutual solvent at room temperature. The solution of both polymers (0.02 g/mL) was cast on a Petri dish at room temperature and held for 1 day to evaporate the solvent in a controlled air stream. The resulting films were further dried in vacuum at 40 °C for 3 days to remove the solvent completely. Thus, PBSU/TA blends were prepared with various compositions ranging from 100/0, 90/10, 80/20, 60/40, 40/60, 20/80, to 0/100 in weight ratio, with the first number referring to PBSU. Characterization. Glass transition temperature (Tg) and melting temperature (Tm) of the meltquenched PBSU/TA blends were measured with differential scanning calorimetry (DSC) with use of TA Instruments Q100 equipment with a Thermal Analyst 2000 at 20 °C/min. The sample was first annealed at 150 °C for 3 min to erase any thermal history and Received: July 10, 2011 Accepted: September 27, 2011 Revised: August 25, 2011 Published: September 27, 2011 11970
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Figure 1. DSC traces of neat PBSU, neat TA, and their blends from the melt-quenched samples at a heating rate of 20 °C/min.
then quenched to 50 °C quickly. Nonisothermal melt crystallization behavior of neat PBSU and the PBSU/TA blends was studied with DSC at 10 °C/min from the crystal-free melt. Isothermal melt crystallization behavior of PBSU/TA blends was also examined with DSC. The sample was melted at 150 °C for 3 min, cooled quickly to the crystallization temperature (Tc), and then maintained at Tc until the crystallization was completed. After complete crystallization, the sample was heated to 150 °C at 20 °C/min (if not otherwise specified) to measure Tm of PBSU for the estimation of equilibrium melting point. It should be noted that only neat PBSU, 90/10 and 80/20 were investigated for the crystallization studies because PBSU did not crystallize or crystallized too slowly when the TA content was above 20 wt %. A polarizing optical microscope (Olympus BX51) equipped with a temperature controller (Linkam THMS 600) was used to investigate the spherulitic morphology of PBSU/TA blends. The samples were first melted at 150 °C for 3 min to erase any thermal history and then quenched at 60 °C/min to the desired crystallization temperature. Wide-angle X-ray diffraction (WAXD) experiments were performed on a Rigaku D/Max 2500 VB2+/PC X-ray diffractometer at 40 kV and 200 mA. The samples for the WAXD experiments were prepared as follows. The samples were first pressed into films with thickness of around 1 mm on a hot stage at 150 °C and then transferred into a vacuum oven at 100 °C for 3 days. Small-angle X-ray scattering (SAXS) measurements were carried out at room temperature with a NanoStar X-ray diffractometer (Bruker AXS Inc.) using Cu Kα radiation at 40 kV and 650 μA.
’ RESULTS AND DISCUSSION Miscibility and Nonisothermal Melt Crystallization Behavior of PBSU/TA Blends. Miscibility of PBSU/TA blends was
first studied with DSC in this work. Figure 1 shows the DSC heating traces of the melt-quenched samples for neat PBSU, neat TA, and their blends at 20 °C/min. Neat PBSU is a semicrystalline polymer with a Tg of ca. 33.9 °C and a Tm of ca. 111.8 °C, while neat TA is an amorphous polymer with a Tg of ca. 41.8 °C. As shown in Figure 1, all of the PBSU/TA blends exhibit a single composition dependent Tg between those of the two neat polymers; moreover, the values of Tg increase with increasing the
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Figure 2. Variation of Tg and Tm of the PBSU/TA blends with weight fraction of TA (the solid line is based on the Fox equation).
TA content in the blends, suggesting that PBSU is miscible with TA over the entire composition range. Similar to the TA based blends with PCL, PBA, and PEA,20 the miscibility of PBSU/TA blends may also arise from the formation of hydrogen bonding between the carbonyl group of PBSU and the hydroxyl group of TA. The specific interaction involved in the PBSU/TA blends studied by Fourier transform infrared (FTIR) is still underway and will be reported in the forthcoming work. In addition, Tm of PBSU shifts from ca. 111.8 °C for neat PBSU to ca. 104.3 °C for the 80/20 blend. When the amorphous TA content is higher than 40 wt %, Tm of PBSU cannot be detected in the blends. Figure 2 summarizes the variations of Tg and Tm with the weight fraction of TA. It is clear from Figure 2 that blending with amorphous TA increases Tg but reduces Tm of PBSU in the PBSU/TA blends. The Fox equation is often used to predict the variation of glass transition temperature of a random copolymer or miscible blend with composition as follows: 1 W1 W2 ¼ þ Tg Tg1 Tg2
ð1Þ
where W1 and W2 are the weight fractions of components 1 and 2, respectively, and Tg1 and Tg2 are the respective Tgs of the pure components.23 It is clear from Figure 2 that the experimental Tg values can be well-fitted by the Fox equation when the weight fraction of TA is higher than 60%. However, when the weight fraction of TA is lower than 60%, the experimental Tg values are greater than those predicted by the Fox equation, which probably arises from the stronger interaction between PBSU and TA. Nonisothermal melt crystallization behavior of neat PBSU and its blends with 10 and 20 wt % TA was studied with DSC at 10 °C/min. Figure 3 shows the DSC cooling traces for both neat PBSU and the PBSU/TA blends during nonisothermal melt crystallization. As shown in Figure 3, neat PBSU has a nonisothermal melt crystallization peak temperature (Tp) of 85.5 °C with a crystallization enthalpy (ΔHc) of 69.9 J/g. In the PBSU/ TA blends, the crystallization exotherms of the PBSU/TA blends shift to a lower temperature range with the increasing of TA. In the case of the 90/10 blend, Tp shifts to 79.1 °C with a ΔHc = 61.3 J/g; moreover, in the case of 80/20 blend, Tp further decreases significantly to be 42.9 °C with a ΔHc = 25.1 J/g. Such results indicate that the nonisothermal melt crystallization of PBSU has been retarded significantly by the presence of amorphous TA in the PBSU/TA blends, especially at higher TA 11971
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Figure 3. Nonisothermal melt crystallization of neat PBSU and its blends at a cooling rate of 10 °C/min.
Figure 5. Effect of heating rate on the subsequent melting behavior of a PBSU/TA 90/10 crystallized at 92.5 °C.
Figure 4. Subsequent melting behavior of a PBSU/TA 90/10 blend after isothermally crystallization at different Tcs.
Figure 6. HoffmanWeeks plots of neat and blended PBSU for the estimation of equilibrium melting points.
content. Similar results are often found in the binary miscible crystalline/polymer blends.23,24 Depression of Equilibrium Melting Point of PBSU in the PBSU/TA Blends. In the binary miscible crystalline/amorphous polymer blends, the depression of melting point of crystalline polymer provides important information of its miscibility. In general, immiscible blends do not show the depression of melting point significantly. However, the melting point of a polymer is affected not only by the thermodynamic factors but also by the morphological factors such as crystalline lamellar thickness and the perfection of spherulites. Therefore, equilibrium melting point (Tom) is introduced to separate the morphological effect from the thermodynamic effect in discussing the melting point depression as described by the NishiWang equation.25 Tom can be derived from the HoffmannWeeks equation:26
peak with one shoulder is observed for the melting behavior of PBSU. With increasing Tc, the lower melting peak (P1) shifts to a high temperature range, while the higher one (P2) remains almost unchanged; moreover, the ratio of the area of P1 to that of P2 increases. At Tc higher than 90 °C, P1 becomes dominant, and especially at 95 °C, P2 becomes a shoulder. The double melting behavior of PBSU may be explained by the mechanism of melting, recrystallization, and remelting of PBSU crystals.27,28 P1 corresponds to the melting of the crystals formed at Tc which are present prior to the heating scan in DSC, and P2 corresponds to the melting of the crystals formed by the recrystallization during the heating process. Similar results are also found in our previous work on PBSU/PEO blends, which were explained by the melting and recrystallization model through conventional and modulated temperature DSC studies.28 The scanning rate dependence on the double melting behavior is usually regarded as the evidence of the melting, recrystallization, and remelting model. Figure 5 shows the heating rate dependence of the melting behavior of a 90/10 blend crystallized isothermally at 92.5 °C. It can be seen from Figure 5 that P1 shifts to a high temperature range while P2 shifts to a low temperature range with increasing heating rate. In addition, P1 increases significantly in area size relative to P2. The aforementioned results indicate that recrystallization is restricted with increasing heating rate because less time is available for the recrystallization
Tm ¼ ηTc þ ð1 ηÞTmo
ð2Þ
where Tm is the apparent melting point at Tc and η may be regarded as a measure of the stability. As introduced in the Experimental Section, the melting behavior of PBSU/TA blends was studied in this work. Figure 4 shows the subsequent melting behavior of a 90/10 blend after crystallizing at various Tcs ranging from 85 to 95 °C. It can be seen from Figure 4 that two melting peaks or one main melting
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Figure 7. Spherulitic morphology of neat PBSU and the PBSU/TA blends crystallized at 100 °C (same magnification bar = 100 μm): (a) 100/0, (b) 90/10, and (c) 80/20.
Figure 9. One-dimensional correlation functions curves of neat PBSU and the PBSU/TA blends.
Figure 8. WAXD patterns of neat PBSU and the PBSU/TA blends.
at fast heating rate. Therefore, in the present work, Tm1 is used for the analysis with the HoffmanWeeks equation. Figure 6 shows the HoffmanWeeks plots for neat PBSU and the PBSU/TA blends, from which the Tom values are determined to be around 135.2, 127.4, and 117.8 °C for neat PBSU, 90/10, and 80/20, respectively. It is clear that Tom of PBSU decreases with increasing TA content. The depression of Tom indicates again that PBSU and TA are miscible in the PBSU/TA blends. Spherulitic Morphology, Crystal Structure, and Microstructure Studies of PBSU/TA Blends. In the above sections, the miscibility of PBSU/TA blends has been evidenced by the single composition dependent glass transition temperature and the depression of equilibrium melting point of PBSU in the PBSU/TA blends. In this section, the effect of TA on the spherulitic morphology, crystal structure, and microstructure of PBSU in the PBSU/TA blends was further studied with POM, WAXD, and SAXS. Figure 7 shows the spherulitic morphology of the neat and blended PBSU crystallized at 100 °C. It is seen that the spherulites of PBSU become larger with the TA content, indicating a decrease in the nucleation density of PBSU spherulites in the blends. For 90/10 and 80/20, the bundles of lamellae are fewer but thicker than those for neat PBSU and assume a featherlike pattern finally. The fact that PBSU spherulites are space-filling indicates that TA was rejected in the crystallization process as a noncrystallizable component and resided primarily in the interlamellar and interfibrillar domains of the PBSU spherulites.29,30 It is of interest to study the effect of TA on the crystal structure of PBSU in the PBSU/TA blends. Figure 8 shows the WAXD patterns of neat and blended PBSU crystallized at 100 °C for 3 days. As shown in Figure 8, both neat and blended PBSU exhibit almost the same diffraction peaks at the same location. The three main diffraction peaks located at around 19.5, 21.9, and
22.7° are assigned to (020), (021), and (110) planes, respectively.35 However, the intensity of the diffraction peaks decreases with increasing TA content, indicating that blending with amorphous TA does not modify the crystal structure of PBSU but decreases the crystallinity of PBSU in the blends. The microstructure of PBSU/TA blends was further studied with SAXS. The morphological parameters in the lamellar level, such as long period (LP), crystal layer thickness (Lc), and amorphous layer thickness (La), are determined by one-dimensional correlation function,31 γðzÞ ¼
1 Z γð0Þ
∞ 0
IðqÞq2 cosðqzÞ dq
ð3Þ
where z is the correlation distance, γ(0) is the scattering invariant, q is the scattering vector, which was calculated from q = 4π sin θ/λ (λ = 0.154 nm), 2θ is the scattering angle, and I is the scattering intensity distributions. Figure 9 illustrates the curves of normalized one-dimensional correlation function γ(z) for both neat and blended PBSU. From Figure 9, the values of LP, Lc, and La are obtained. The values of LP, Lc, and La are 9.6, 4.0, and 5.7 nm, respectively, for neat PBSU. For a 90/10 blend, they become 10.0, 4.0, and 6.1 nm, respectively. With further increasing the TA content, they become 11.3, 4.0, and 7.4 nm, respectively, in the case of an 80/20 blend. It is obvious that all of the values of LP and La of PBSU increase with increasing TA content in the PBSU/TA blends. It should be noted that Lc remains unchanged. However, the increase in La is large. For example, the increase in La is around 0.4 nm after blending 10 wt % TA as compared with that of neat PBSU. The increase in La is around 1.3 nm with further increasing TA content up to 20 wt % in the blend as compared to that of neat PBSU. Such increase in La indicates that amorphous TA may reside in the interlamellar region of PBSU spherulites. Accordingly, the LP values increase from 9.6 for neat PBSA to 10.0 and 11.3 nm for 9010 and 80/20, respectively. The increase in LP mainly arises from the increase in La in the PBSU/TA blends.
’ CONCLUSIONS In this work, completely biodegradable PBSU/TA blends were prepared via a solution and casting method. PBSU is miscible with TA as evidenced by the single composition dependent glass transition temperature over the whole blend composition range. Double melting behavior is found for both neat PBSU and the PBSU/TA blends, which may be attributed to 11973
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Industrial & Engineering Chemistry Research the melting, recrystallization, and remelting model. The miscibility between PBSU and TA is further confirmed by the depression of equilibrium melting point of PBSU with increasing TA content in the PBSU/TA blends. The nonisothermal melt crystallization peak temperature of PBSU shifted to low temperature range with increasing TA content in the PBSU/TA blends, indicating that the nonisothermal melt crystallization behavior of PBSU has been retarded by the presence of amorphous TA. Blending with TA affects the spherulitic morphology of PBSU apparently but does not modify the crystal structure of PBSU. It is also found that both the long period and thickness of the amorphous phase become larger with increasing TA content in the blends, indicating that TA mainly resides in the interlamellar region of PBSU spherulites.
’ AUTHOR INFORMATION Corresponding Author
*Fax: +86-10-64413161. E-mail:
[email protected].
’ ACKNOWLEDGMENT Part of this work was financially supported by the National Natural Science Foundation, China (Grant 20774013). ’ REFERENCES (1) Papageorgiou, G. Z.; Bikiaris, D. N. Crystallization and Melting Behavior of Three Biodegradable Poly(alkylene succinates). A Comparative Study. Polymer 2005, 46, 12081–12092. (2) Papageorgiou, G. Z.; Achilias, D. S.; Bikiaris, D. N. Crystallization Kinetics of Biodegradable Poly(butylene succinate) under Isothermal and Non-isothermal Conditions. Macromol. Chem. Phys. 2007, 208, 1250–1264. (3) Ihn, K.; Yoo, E.; Im, S. Structure and Morphology of Poly(tetramethylene succinate) Crystals. Macromolecules 1995, 28, 2460–2464. (4) Ichikawa, Y.; Suzuki, J.; Washiyama, J.; Moteki, Y.; Noguchi, K.; Okuyama, K. Strain-Induced Crystal Modification in Poly(tetramethylene succinate). Polymer 1994, 35, 3338–3339. (5) Ichikawa, Y.; Kondo, H.; Igarashi, Y.; Noguchi, K.; Okuyama, K.; Washiyama, J. Crystal Structures of α and β Forms of Poly(tetramethylene succinate). Polymer 2000, 41, 4719–4727. (6) Miyata, T; Masuko, T. Crystallization Behaviour of Poly(tetramethylene succinate). Polymer 1998, 39, 1399–1404. (7) Gan, Z.; Abe, H.; Kurokawa, H; Doi, Y. Solid-State Microstructures, Thermal Properties, and Crystallization of Biodegradable Poly(butylene succinate) (PBS) and Its Copolyesters. Biomacromolecules 2001, 2, 605–613. (8) Qiu, Z.; Komura, M.; Ikehara, T.; Nishi, T. DSC and TMDSC Study of Melting Behaviour of Poly(butylene succinate) and Poly(ethylene succinate). Polymer 2003, 44, 7781–7785. (9) Lee, J.; Tazawa, H.; Ikehara, T.; Nishi, T. Miscibility and Crystallization Behavior of Poly(butylene succinate) and Poly(vinylidene fluoride) blends. Polym. J. 1998, 30, 327–339. (10) Lee, J.; Tazawa, H.; Ikehara, T.; Nishi, T. Crystallization Kinetics and Morphology in Miscible Blends of Two Crystalline Polymers. Polym. J. 1998, 30, 780–789. (11) Qiu, Z.; Ikehara, T.; Nishi, T. Miscibility and Crystallization in Crystalline/Crystalline Blends of Poly(butylene succinate)/Poly(ethylene oxide). Polymer 2003, 44, 2799–2806. (12) Ikehara, T.; Kurihara, H.; Qiu, Z.; Nishi, T. Study of Spherulitic Structures by Analyzing the Spherulitic Growth Rate of the Other Component in Binary Crystalline Polymer Blends. Macromolecules 2007, 40, 8726–8730.
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(13) Qiu, Z.; Komura, M.; Ikehara, T.; Nishi, T. Poly(butylene succinate)/Poly(vinyl phenol) Blends. Part 1. Miscibility and Crystallization. Polymer 2003, 44, 8111–8117. (14) Qiu, Z.; Yang, W. Crystallization Kinetics and Morphology of Poly(butylene succinate)/Poly(vinyl phenol) Blend. Polymer 2006, 47, 6429–6437. (15) Wang, T.; Wang, H.; Li, H.; Gan, Z.; Yan, S. Banded Spherulitic Structures of Poly(ethylene adipate), Poly(butylene succinate) and in Their Blends. Phys. Chem. Chem. Phys. 2009, 11, 1619–1627. (16) Qiu, Z.; Ikehara, T.; Nishi, T. Poly(hydroxybutyrate)/Poly(butylene succinate) Blends: Miscibility and Nonisothermal Crystallization. Polymer 2003, 44, 2503–2508. (17) Qiu, Z.; Ikehara, T.; Nishi, T. Miscibility and Crystallization Behaviour of Biodegradable Blends of Two Aliphatic Polyesters. Poly(3hydroxybutyrate-co-hydroxyvalerate) and Poly(butylene succinate) Blends. Polymer 2003, 44, 7519–7527. (18) Qiu, Z.; Komura, M.; Ikehara, T.; Nishi, T. Miscibility and Crystallization Behavior of Biodegradable Blends of Two Aliphatic Polyesters. Poly(butylene succinate) and Poly(ε-caprolactone). Polymer 2003, 44, 7749–7756. (19) Yokohara, T.; Yamaguchi, M. Structure and Properties for Biomass-Based Polyester Blends of PLA and PBS. Eur. Polym. J. 2008, 44, 677–685. (20) Yen, K. C.; Mandal, T. K.; Woo, E. M. Enhancement of Biocompatibility via Specific Interaction in Polyesters Modified with a Bioresourceful Macromolecular Ester Containing Polyphenol Groups. J. Biomed. Mater. Res., Part A 2008, 86, 701–712. (21) Yen, K. C.; Woo, E. M. Formation of Dendrite Crystals in Poly(ethylene oxide) Interacting with Bioresourceful Tannin. Polym. Bull. 2009, 62, 225–235. (22) Huang, I. H.; Chang, L.; Woo, E. M. Tannin Induced Single Crystalline Morphology in Poly(ethylene succinate). Macromol. Chem. Phys. 2011, 212, 1155–1164. (23) Fox, T. G. Influence of Diluent and of Copolymer Composition on the Glass Temperature of a Polymer System. Bull. Am. Phys. Soc. 1956, 1, 123–124. (24) Li, Z.; Yang, F.; Qiu, Z. Miscibility and Crystallization Behaviors of Biodegradable Poly(butylene succinate-co-butylene terephthalate)/ Phenoxy Blends. J. Appl. Polym. Sci. 2011, 121, 720–726. (25) Nishi, T.; Wang, T. Melting Point Depression and Kinetic Effects of Cooling on Crystallization in Poly(vinylidene fluoride)-Poly(methyl methacrylate) Mixtures. Macromolecules 1975, 8, 909–915. (26) Hoffman, J.; Weeks, J. X-Ray Study of Isothermal Thickening of Lamellae in Bulk Polyethylene at the Crystallization Temperature. J. Chem. Phys. 1965, 42, 4301–4302. (27) Liu, T.; Petermann, J. Multiple Melting Behavior in Isothermally Cold-Crystallized Isotactic Polystyrene. Polymer 2001, 42, 6453–6461. (28) Qiu, Z.; Ikehara, T.; Nishi, T. Melting Behaviour of Poly(butylene succinate) in Miscible Blends with Poly(ethylene oxide). Polymer 2003, 44, 3095–3099. (29) Keith, H. D.; Padden, F. J., Jr. Spherulitic Crystallization from the Melt. I. Fractionation and Impurity Segregation and Their Influence on Crystalline Morphology. J. Appl. Phys. 1964, 35, 1270–1285. (30) Keith, H. D.; Padden, F. J., Jr. Spherulitic Crystallization from the Melt. II. Influence of Fractionation and Impurity Segregation on the Kinetics of Crystallization. J. Appl. Phys. 1964, 35, 1286–1296. (31) Strobl, G.; Schneider, M. Direct Evaluation of the Electron Density Correlation Function of Partially Crystalline Polymers. J. Polym. Sci., Polym. Phys. Ed. 1980, 18, 1343–1359.
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