ABSTRACT The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and po... more ABSTRACT The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) blends are investigated by using Raman microspectroscopy. Four kinds of PHB/PLLA blends with a PLLA content of 20, 40, 60, and 80 wt% were prepared from chloroform solutions. Differences in the Raman microspectroscopic spectra between the spherulitic and nonspherulitic parts in the blends mainly lie in the CO stretching band and C–O–C and C–C skeletal stretching bands of PHB and PLLA. In addition to such bands, the Raman spectra of spherulitic structure in the blends show a band due to the CH3 asymmetric stretching mode at an unusually high frequency (3009 cm−1), suggesting the existence of a C–H⋯OC hydrogen bond of PHB in the spherulite. The existence of C–H⋯OC hydrogen bond is one of the unambiguous evidence for the crystallization of PHB component in the blends. Therefore, it is possible to distinguish Raman bands due to each component in the spectra of blends. Raman spectra of the spherulitic structure in the blends are similar to a Raman spectrum of pure crystalline PHB, while those of the nonspherulitic parts in the blends have each component peak of PHB and PLLA. The present study reveals that the PHB component is crystallized in the blends irrespective of the blend ratio, and that both components are mixed in the nonspherulite parts. The crystalline structure of PHB and the nonspherulitic parts of PLLA in the blends are characterized, respectively, by the unique band of C–H⋯OC hydrogen bond at 3009 cm−1 and CCO deformation bands near 400 cm−1.
ABSTRACT Comparison of miscibility and structure of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhe... more ABSTRACT Comparison of miscibility and structure of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) (P(HB-co-HHx)) (Mw = 638,000 g mol−1) and poly(l-lactic acid) (PLLA) (Mw = 150,000 g mol−1) with those of poly((R)-3-hydroxybutyrate) (PHB) (Mw = 600,000 g mol−1), and PLLA having the blending ratios was investigated by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) microspectroscopy techniques. WAXD reflection patterns show that the lattice parameters of a and b axes for PHB and P(HB-co-HHx) are unchanged in their blends with PLLA regardless of blending ratio. These WAXD results suggest that their crystalline structures are independent of the second component. The glass transition temperature (Tg) of blend components did not significantly change. The crystallization temperature (Tc) of PLLA reveal that both PHB/PLLA and P(HB-co-HHx)/PLLA blends form mixed semicrystalline systems. The Tc of PLLA in the PHB/PLLA blends and that in the P(HB-co-HHx)/PLLA blends shift to opposite directions indicating that both blends are immiscible but exhibit different levels of compatibilities. Micro IR spectra show that crystalline bands due to PHB appear even for the 20/80 blend but those due to PLLA are hardly observed for all the PHB/PLLA blends investigated. On the other hand, the crystalline bands of PLLA are observed in the micro IR spectra of some spots in the 20/80 P(HB-co-HHx)/PLLA blend. Micro IR spectra also show significant differences in the compatibility and crystalline structures between the P(HB-co-HHx)/PLLA and PHB/PLLA blends.
... Address correspondence to James E. Mark, Department of Chemistry, The University of Cincinnat... more ... Address correspondence to James E. Mark, Department of Chemistry, The University of Cincinnati, Cincinnati, Ohio, 45221-0172, USA. E-mail: markje@email.uc.edu Mol. Cryst. Liq. ... Macromolecules, 19, 2871. [6] Noda, I., Green, PR, Satkowski, MM, & Schechtman, LA (2005). ...
ABSTRACT The present study is aimed at investigating structure, dispersibility, and crystallinity... more 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 CO 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.
ABSTRACT Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (P... more ABSTRACT Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (PLLA) from the melt and glassy states, respectively [J. Phys. Chem. B 2004, 108, 11514; Macromolecules 2004, 37, 6433]. Surprisingly, the quite different infrared (IR) spectral evolutions occur in the two crystallization processes at different temperatures in which the same crystal modification is expected to be formed. To clarify this unusual phenomenon, the crystal modifications and thermal behavior of PLLA samples prepared under different crystallization temperatures are investigated in detail by TEM, WAXD, and FTIR techniques. On the basis of the WAXD and IR data, a new crystal modification named the α form is proposed for the crystal structure of PLLA samples annealed at temperature below 120 °C. Such crystal modification with loose 103 helical chain packing is less thermally stable than the standard α form of PLLA. This assignment can explain all the experiment observations well. Other possible mechanisms for the IR spectral difference of bulk PLLA samples annealed at different temperatures are also discussed.
ABSTRACT Temperature-dependent X-ray diffraction and infrared (IR) spectra were measured for poly... more ABSTRACT Temperature-dependent X-ray diffraction and infrared (IR) spectra were measured for poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) P(HB-co-HHx) (HHx = 2.5, 3.4, 10.5, and 12 mol %) to explore their crystal and lamella structure and the C−H···OC hydrogen bonding in them. The X-ray diffraction and IR measurements of PHB and P(HB-co-HHx) revealed that the smaller the a lattice parameter, the higher the frequency (3008 cm-1) of the C−H stretching band of the C−H···OC hydrogen bonding along the a axis between the CH3 group of one helix and the CO group of another helix. Therefore, it seems that the C−H···OC hydrogen bonding becomes strong with the decrease in the a lattice parameter. To investigate the relation between the C−H···OC hydrogen bonding and the lamella structure, we estimated the number of C−H···OC hydrogen bonding along the c axis (the direction of the lamella thickness) based on the reported lamella thickness. It is about 8 or 9 for PHB and about 3 for P(HB-co-HHx) (HHx = 10.5 and 12 mol %). It is very likely that the C−H···OC hydrogen bondings break much more easily in P(HB-co-HHx) than in PHB because of the bulkiness of large amounts of amorphous parts. However, the polymer chains still keep the lamella structure even in the copolymers with the HHx content of more than several percent. This is the reason why the P(HB-co-HHx) copolymers show high crystallinity and essentially have the same lattice spacing as the PHB homopolymer even if the HHx content is more than 10%. We have concluded that the C−H···OC hydrogen bonding stabilizes the chain folding in the lamella structure of PHB and P(HB-co-HHx) and the high crystallinity of PHB and P(HB-co-HHx) partly comes from the C−H···OC hydrogen bonding.
ABSTRACT The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxy... more ABSTRACT The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); P(HB-co-HHx) (HHx=2.5, 3.4, and 12 mol %) have been explored by means of wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) spectroscopy. The WAXD pattern of P(HB-co-HHx) (HHx=12 mol %) copolymer measured at room temperature has revealed that it has an orthorhombic system (α=β=γ=90°) with a=5.76Å, b=13.20Å, c=5.96Å (fiber repeat), which is identical to that of poly(3-hydroxybutyrate) (PHB). It has been found from the temperature-dependent variations of the WAXD pattern that only the a lattice parameter shows the thermal expansion, while the b lattice parameter changes little with temperature in the crystalline P(HB-co-HHx) (HHx=12 mol %). This observation suggests that there are inter and intramolecular interactions between C=O groups and alkyl groups along the a axis and that interactions are broken little by little with temperature. IR spectra were measured for the four kinds of polymers over a temperature range from 30°C to high temperatures (200°C; PHB, 180°C; P(HB-co-HHx) (HHx=2.5 mol %), 180°C; P(HB-co-HHx) (HHx=3.4 mol %), 150°C; P(HB-co-HHx) (HHx=12 mol %)). Temperature-dependent IR spectral variations were analyzed for the CH, C=O, and C-O-C stretching band regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It has been found from the IR study that the strength of interaction between the C=O group and the CH3 (or CH2) group is similar among the four polymers and that the population of C=O groups that are not involved in the interaction becomes higher with the increase in HHx. Both WAXD and IR studies have revealed that the crystallinity of P(HB-co-HHx) (HHx=12 mol %) decreases gradually starting from relatively low temperature (about 60°C) while that of PHB remains high up to 170°C.
The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to t... more The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm(-1) that sequentially disappear before a band at 1740 cm(-1) due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 micrometer of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.
ABSTRACT The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and po... more ABSTRACT The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) blends are investigated by using Raman microspectroscopy. Four kinds of PHB/PLLA blends with a PLLA content of 20, 40, 60, and 80 wt% were prepared from chloroform solutions. Differences in the Raman microspectroscopic spectra between the spherulitic and nonspherulitic parts in the blends mainly lie in the CO stretching band and C–O–C and C–C skeletal stretching bands of PHB and PLLA. In addition to such bands, the Raman spectra of spherulitic structure in the blends show a band due to the CH3 asymmetric stretching mode at an unusually high frequency (3009 cm−1), suggesting the existence of a C–H⋯OC hydrogen bond of PHB in the spherulite. The existence of C–H⋯OC hydrogen bond is one of the unambiguous evidence for the crystallization of PHB component in the blends. Therefore, it is possible to distinguish Raman bands due to each component in the spectra of blends. Raman spectra of the spherulitic structure in the blends are similar to a Raman spectrum of pure crystalline PHB, while those of the nonspherulitic parts in the blends have each component peak of PHB and PLLA. The present study reveals that the PHB component is crystallized in the blends irrespective of the blend ratio, and that both components are mixed in the nonspherulite parts. The crystalline structure of PHB and the nonspherulitic parts of PLLA in the blends are characterized, respectively, by the unique band of C–H⋯OC hydrogen bond at 3009 cm−1 and CCO deformation bands near 400 cm−1.
ABSTRACT Comparison of miscibility and structure of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhe... more ABSTRACT Comparison of miscibility and structure of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) (P(HB-co-HHx)) (Mw = 638,000 g mol−1) and poly(l-lactic acid) (PLLA) (Mw = 150,000 g mol−1) with those of poly((R)-3-hydroxybutyrate) (PHB) (Mw = 600,000 g mol−1), and PLLA having the blending ratios was investigated by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) microspectroscopy techniques. WAXD reflection patterns show that the lattice parameters of a and b axes for PHB and P(HB-co-HHx) are unchanged in their blends with PLLA regardless of blending ratio. These WAXD results suggest that their crystalline structures are independent of the second component. The glass transition temperature (Tg) of blend components did not significantly change. The crystallization temperature (Tc) of PLLA reveal that both PHB/PLLA and P(HB-co-HHx)/PLLA blends form mixed semicrystalline systems. The Tc of PLLA in the PHB/PLLA blends and that in the P(HB-co-HHx)/PLLA blends shift to opposite directions indicating that both blends are immiscible but exhibit different levels of compatibilities. Micro IR spectra show that crystalline bands due to PHB appear even for the 20/80 blend but those due to PLLA are hardly observed for all the PHB/PLLA blends investigated. On the other hand, the crystalline bands of PLLA are observed in the micro IR spectra of some spots in the 20/80 P(HB-co-HHx)/PLLA blend. Micro IR spectra also show significant differences in the compatibility and crystalline structures between the P(HB-co-HHx)/PLLA and PHB/PLLA blends.
... Address correspondence to James E. Mark, Department of Chemistry, The University of Cincinnat... more ... Address correspondence to James E. Mark, Department of Chemistry, The University of Cincinnati, Cincinnati, Ohio, 45221-0172, USA. E-mail: markje@email.uc.edu Mol. Cryst. Liq. ... Macromolecules, 19, 2871. [6] Noda, I., Green, PR, Satkowski, MM, & Schechtman, LA (2005). ...
ABSTRACT The present study is aimed at investigating structure, dispersibility, and crystallinity... more 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 CO 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.
ABSTRACT Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (P... more ABSTRACT Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (PLLA) from the melt and glassy states, respectively [J. Phys. Chem. B 2004, 108, 11514; Macromolecules 2004, 37, 6433]. Surprisingly, the quite different infrared (IR) spectral evolutions occur in the two crystallization processes at different temperatures in which the same crystal modification is expected to be formed. To clarify this unusual phenomenon, the crystal modifications and thermal behavior of PLLA samples prepared under different crystallization temperatures are investigated in detail by TEM, WAXD, and FTIR techniques. On the basis of the WAXD and IR data, a new crystal modification named the α form is proposed for the crystal structure of PLLA samples annealed at temperature below 120 °C. Such crystal modification with loose 103 helical chain packing is less thermally stable than the standard α form of PLLA. This assignment can explain all the experiment observations well. Other possible mechanisms for the IR spectral difference of bulk PLLA samples annealed at different temperatures are also discussed.
ABSTRACT Temperature-dependent X-ray diffraction and infrared (IR) spectra were measured for poly... more ABSTRACT Temperature-dependent X-ray diffraction and infrared (IR) spectra were measured for poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) P(HB-co-HHx) (HHx = 2.5, 3.4, 10.5, and 12 mol %) to explore their crystal and lamella structure and the C−H···OC hydrogen bonding in them. The X-ray diffraction and IR measurements of PHB and P(HB-co-HHx) revealed that the smaller the a lattice parameter, the higher the frequency (3008 cm-1) of the C−H stretching band of the C−H···OC hydrogen bonding along the a axis between the CH3 group of one helix and the CO group of another helix. Therefore, it seems that the C−H···OC hydrogen bonding becomes strong with the decrease in the a lattice parameter. To investigate the relation between the C−H···OC hydrogen bonding and the lamella structure, we estimated the number of C−H···OC hydrogen bonding along the c axis (the direction of the lamella thickness) based on the reported lamella thickness. It is about 8 or 9 for PHB and about 3 for P(HB-co-HHx) (HHx = 10.5 and 12 mol %). It is very likely that the C−H···OC hydrogen bondings break much more easily in P(HB-co-HHx) than in PHB because of the bulkiness of large amounts of amorphous parts. However, the polymer chains still keep the lamella structure even in the copolymers with the HHx content of more than several percent. This is the reason why the P(HB-co-HHx) copolymers show high crystallinity and essentially have the same lattice spacing as the PHB homopolymer even if the HHx content is more than 10%. We have concluded that the C−H···OC hydrogen bonding stabilizes the chain folding in the lamella structure of PHB and P(HB-co-HHx) and the high crystallinity of PHB and P(HB-co-HHx) partly comes from the C−H···OC hydrogen bonding.
ABSTRACT The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxy... more ABSTRACT The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); P(HB-co-HHx) (HHx=2.5, 3.4, and 12 mol %) have been explored by means of wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) spectroscopy. The WAXD pattern of P(HB-co-HHx) (HHx=12 mol %) copolymer measured at room temperature has revealed that it has an orthorhombic system (α=β=γ=90°) with a=5.76Å, b=13.20Å, c=5.96Å (fiber repeat), which is identical to that of poly(3-hydroxybutyrate) (PHB). It has been found from the temperature-dependent variations of the WAXD pattern that only the a lattice parameter shows the thermal expansion, while the b lattice parameter changes little with temperature in the crystalline P(HB-co-HHx) (HHx=12 mol %). This observation suggests that there are inter and intramolecular interactions between C=O groups and alkyl groups along the a axis and that interactions are broken little by little with temperature. IR spectra were measured for the four kinds of polymers over a temperature range from 30°C to high temperatures (200°C; PHB, 180°C; P(HB-co-HHx) (HHx=2.5 mol %), 180°C; P(HB-co-HHx) (HHx=3.4 mol %), 150°C; P(HB-co-HHx) (HHx=12 mol %)). Temperature-dependent IR spectral variations were analyzed for the CH, C=O, and C-O-C stretching band regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It has been found from the IR study that the strength of interaction between the C=O group and the CH3 (or CH2) group is similar among the four polymers and that the population of C=O groups that are not involved in the interaction becomes higher with the increase in HHx. Both WAXD and IR studies have revealed that the crystallinity of P(HB-co-HHx) (HHx=12 mol %) decreases gradually starting from relatively low temperature (about 60°C) while that of PHB remains high up to 170°C.
The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to t... more The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm(-1) that sequentially disappear before a band at 1740 cm(-1) due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 micrometer of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.
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