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Layered metal phosphonate, zinc phenylphosphonate (PPZn), reinforced poly(L-lactide) (PLLA) composites were fabricated by a melt-mixing technique. The nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, crystalline structure, and static and dynamic mechanical properties of the PLLA/PPZn composites were investigated. PPZn shows excellent nucleating effects on PLLA crystallization. With incorporation of 0.02% PPZn, PLLA can finish crystallization under cooling at 10 degrees C/min. The crystallization rate of PLLA further increases with increasing PPZn concentration. Upon the addition of 15% PPZn, the crystallization half-times of a PLLA/PPZn composite decrease from 28.0 to 0.33 min at 130 degrees C, and from 60.2 to 1.4 min at 140 degrees C, compared to the neat PLLA. With the presence of PPZn, the nuclei number of PLLA increases and the spherulite size reduces significantly. Through analysis of the crystal structures of PLLA and PPZn, it was proposed that the nucleation mechanism of the PLLA/PPZn system is epitaxial nucleation. The incorporation of PPZn has no discernible effect on the crystalline structure of PLLA. Moreover, PPZn has good reinforcement effects on the PLLA matrix. The tensile strength of the composite is enhanced with the addition of a relatively small amount of PPZn (<5%). The tensile and storage moduli of composites increase with increasing PPZn loadings, and they respectively improve by 28% and 34% with the incorporation of a 15% PPZn filler, as compared to the neat PLLA.

Interactions between the anticancer drug quercetin and biodegradable polyesters within micelles were investigated by DSC, WAXD, and UV analyses. For micelles based on poly(ethylene glycol) methyl ether-block-poly(epsilon-caprolactone) (MPEG-PCL), DSC analysis indicated that the interactions were between the hydrophobic core and the drug within the micelle. For micelles based on poly(ethylene glycol) methyl ether-block-poly(L-lactide) (MPEG-PLLA), the interactions were between the hydrophobic core and the drug and between hydrophilic segments and the drug. WAXD results indicated that no crystalline phase of the drug was found in either of the micelle types. Based on the DSC and WAXD results, two probable micelle structures were proposed. The UV spectra revealed the presence of hydrogen bonding as the main interaction between the drug and the polyesters. In vitro studies demonstrated that quercetin release from micelles was sustained and was affected by the polymer-drug interaction.

The glass transition and physical aging processes of poly(L-lactide) (PLLA) were studied by variable-temperature Fourier transform infrared (FTIR) spectroscopy and (13)C solid-state NMR spectroscopy. The glass transition temperature (T(g)) of PLLA can be well determined from the temperature-dependent FTIR intensity. Nearby T(g), a distinct change in the slope of spectral intensity versus temperature plot is detected. FTIR results suggest that the energy-favorable gauche-trans (gt) conformers rearrange into the less energy-favorable gauche-gauche (gg) counterparts with heating over the glass transition region, which becomes more distinct at temperature above T(g). Besides, the 1267 cm(-1) band, which shows different trends of variation from the other bands upon heating, was assigned to be more sensitive to the nu(as)(C-O-C)+delta(CH) vibration mode of the less energy-favorable gg conformers in PLLA. By comparing the FTIR spectra of the aged and deaged PLLA, it was demonstrated that the rearrangement from the high- to low-energy conformers, i.e., gg to gt, occurs with physical aging. (13)C spin-lattice relaxation measurements indicate that the relaxation rate distribution broadens with aging, which agrees with the previous suggestion that the locally ordered domains are formed during physical aging. Because of the larger variation in the conformational state and microstructure, the FTIR intensities vary much more abruptly for the aged sample with heating to nearby T(g).

The mechanical properties, such as Young's modulus, yield strength, and the elongation at breakage, were investigated for several sulfur-containing biopolymers P(3HB-co-3MP). A series of P(3HB-co-3MP) samples with 3MP unit content ranging from 6.6 to 39.1 mol-% was biosynthesized by fermentation using the PHA-synthesizing bacteria Cupriavidus necator. For comparison, the bacterially synthesized P(3HB) and P(3HB-co-3HP) with the 3HP unit content ranging from 13.1 to 21.1 mol-% were also investigated. It was found that the sulfur-containing P(3HB-co-3MP) is much more durable to stretching. Notably, P(3HB-co-3MP) with the 3MP unit content of only 6.6 mol-% was found to show excellent mechanical properties.

Poly(epsilon-caprolactone) (PCL)/chitin and PCL/chitosan blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method; that is, repeatedly pouring the PCL/chitin (or PCL/chitosan) blend solutions, with variable composition, onto polysaccharide layers. The compositional gradient structure in the resulting films was characterized by polarized optic microscopy, ATR-FT-IR and trans-FT-IR microscopic spectroscopy. Enzymatic degradability of the PCL/chitin and PCL/chitosan blend films with compositional gradients in the presence of lysozyme was compared with those of homogeneous films and two-layer films. It was found that the degradation rate of PCL/chitin blend films with a compositional gradient was far lower than that of the neat chitin film, whereas the degradation rate of PCL/chitosan blend films with a compositional gradient was close to that of the neat chitosan film. The suppression of the chitosan crystallization, which accelerates the enzymatic degradation, at the surface of PCL/chitosan films with a compositional gradient was much more severe than that for PCL/chitin films with a compositional gradient.

Solid-state structures and enzymatic degradability have been investigated for cocrystallized blends between poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP]. From wide-angle X-ray diffraction patterns, small-angle X-ray scattering data, and the comparison of the enzymatic degradability of these blends, the solid-state structures of PHBV/PHBP blend samples, in which the PHBV component has higher isothermal crystal growth rate (G) value than the PHBP one, might be similar to those of the component PHBVs; while those of the PHBP/PHBV blend samples, in which PHBP component has higher G value, were similar to the component PHBPs. Normalized one-dimensional correlation functions gamma(x) of PHBV/PHBP binary blends crystallized at 90 degrees C.

Inclusion complexes (ICs) between alpha-cyclodextrin (alpha-CD) and three kinds of biodegradable aliphatic polyesters with different sequence lengths of the monomeric repeating units poly(3-hydroxypropionate) [P(3HP)], poly(4-hydroxybutyrate) [P(4HB)] and poly(epsilon-caprolactone)(PCL) were prepared by mixing a solution of alpha-CD with that of the polymer, followed by stirring. The ICs were obtained as insoluble precipitates and characterized by FT-IR, WAXD and DSC. All measurements showed that the polymer chains of all three kinds of polyester were included into the alpha-CD cavity and formed ICs with different stoichiometries. WAXD patterns and thermal analysis indicated that these ICs possessed a channel structure and the crystallization of the polyester chains was suppressed upon inclusion into the alpha-CD cavity.

Fully-biodegradable bacterial poly(3-hydroxybutyrate) (PHB)/chemosynthetic poly(vinyl alcohol) (PVA) blend films with compositional gradient from one surface to the other surface of the films were prepared by a dissolution-diffusion technique. Three kinds of PVA samples, high- and low-molecular weight atactic PVA and highly syndiotactic PVA (s-PVA), were used in order to investigate the effects of molecular weight and tactic structure on the generation of compositional gradient. The solution of PHB in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is also a good solvent for PVA, was cast on the PVA film and then the solvent HFIP was evaporated. By selecting the optimum volume of solvent and the evaporation rate, the PHB/PVA blend film with compositional gradient was obtained. The formation of compositional gradient was confirmed by FT-IR microscopy and ATR-FT-IR analysis. The 50%/50% PHB/s-PVA blend film with a nearly ideal compositional gradient, that is, the composition of PHB (or PVA) in the film changing gradually from 100% at one surface to 0% at the other surface of the film was obtained by casting PHB/HFIP solution on to the s-PVA film. Positional dependence of the absorbance of C==O and OH stretching bands along the film thickness direction for the PHB/S-PVA cast films.

The comonomer-unit compositions and their distribution of as-produced bacterial copolyesters, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxy-butyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are described in this paper. Each copolyester sample can be comonomer-unit compositionally fractionated into several fractions, indicating that the original copolymers are mixtures of copolymers with different comonomer-unit compositions. The effects of comonomer-unit compositional distribution on thermal properties, crystallization, biodegradability and solid-state phase behavior are investigated using comonomer compositionally fractionated copolymers.

The change in the surface structure of poly[(R)-3-hydroxybutyrate] [PHB] films upon the enzymatic hydrolysis was analyzed by attenuated total reflection infrared [ATR/IR] spectrometry. As enzymes, PHB depolymerases isolated from Ralstonia pickettii T1 and Pseudomonas stutzeri were used. By curve decomposition of the carbonyl stretching band of ATR/IR spectra, the change in the surface crystallinity of PHB films by exposure to buffer containing 0, 1, and 4 microg of PHB depolymerases was estimated. It has been widely believed that the enzymatic hydrolysis first occurs in the amorphous phase, followed by the degradation in the crystalline phase, and extracellular PHB depolymerase can degrade only polymer chains in the surface layer of the film. Therefore, the surface crystallinity had been expected to increase upon the enzymatic degradation. However, the results were contrary to this expectation. The surface crystallinity was decreased by the enzymatic attack. Because ATR/IR spectrometry is sensitive to a small change in molecular structure of the sample surface, the decrease in the crystallinity shown by ATR/IR experiments probably does not indicate the complete loss of regularity of the crystalline phase. Because the chains at crystalline surface are more mobile than those inside the crystals, the C=O band for crystalline surface may appear at a position similar to those of the amorphous or interfacial phase in ATR/IR spectra of PHB. Only the chains inside the crystals may contribute to the C=O band of the crystalline phase. Thus, we rather suppose that the decrease in the crystalline peak of the ATR/IR spectra reflects the change in chain mobility or the increase of crystalline surface area by cracking of lamellas at the surface layers of PHB films or both.

The miscibility and phase behavior of two stereoisomer forms of poly(lactide) (PLA: poly (L-lactide) (PLLA) and poly(DL-lactide) (PDLLA)) blends with poly(epsilon-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and PCL-b-monomethoxy-PEG (PCL-b-MPEG) block copolymers have been investigated by differential scanning calorimetry (DSC). The DSC thermal behavior of both the blend systems revealed that PLA is miscible with the PEG segment phase of PCL-b-(M)PEG but is still immiscible with its PCL segment phase although PCL was block-copolymerized with PEG. On the basis of these results, PCL-b-PEG was added as a compatibilizer to PLA/PCL binary blends. The improvement in mechanical properties of PLA/PCL blends was achieved as anticipated upon the addition of PCL-b-PEG. In addition, atomic force microscopy (AFM) measurements have been performed in order to study the compositional synergism to be observed in mechanical tests. AFM observations of the morphological dependency on blend composition indicate that PLA/PCL blends are immiscible but compatible to some extent and that synergism of compatibilizing may be maximized in the compositional blend ratio before apparent phase separation and coarsening.

The enzymatic degradability of chemosynthesized atactic poly([R,S]-3-hydroxybutyrate) [a-P(3HB)] by two types of extracellular poly(3-hydroxyalkanoate) (PHA) depolymerases purified from Ralstonia pickettii T1 (PhaZ(ral)) and Acidovorax Sp. TP4 (PhaZ(aci)), defined respectively as PHA depolymerase types I and II according to the position of the lipase box in the catalytic domain, were studied. The enzymatic degradation of a-P(3HB) by PhaZ(aci) depolymerase was confirmed from the results of weight loss and the scanning electron micrographs. The degradation products were characterized by one- and two-dimension (1)H NMR spectroscopy. It was found that a-P(3HB) could be degraded into monomer, dimer, and trimer by PhaZ(aci) depolymerase at temperatures ranging from 4 to 20 degrees C, while a-P(3HB) could hardly be hydrolyzed by PhaZ(ral) depolymerase in the same temperature range. These results suggested that the chemosynthesized a-P(3HB) could be degraded in the pure state by natural PHA depolymerase.

Enzymatic degradability has been investigated for a series of bacterial poly(3-hydroxybutyrate-co-3-hydroxypropionate)s (P(3HB-co-3HP)s) with 3-hydroxypropionate (3HP) unit contents from 11 to 86 mol % as well as poly(3-hydroxybutyrate) (P(3HB)) and chemosynthesized poly(3-hydroxypropionate) (P(3HP)). The behavior of degradation by two types of extracellular poly(3-hydroxyalkanoate) (PHA) depolymerases purified from Ralstonia pikettii T1 and Acidovorax Sp. TP4, defined respectively as PHA depolymerase types I and II according to the position of the lipase box in the catalytic domain, were compared in relation to the thermal properties and crystalline structures of the PHA samples elucidated by differential scanning calorimetry and wide-angle X-ray diffraction. The degradation products were characterized by high-performance liquid chromatography and one- (1D) and two-dimension (2D) (1)H NMR spectroscopy. It was found that the PHA depolymerase of Acidovorax Sp. TP4 showed degradation behavior different from that shown by depolymerase of R. pikettii T1. PHA depolymerase from Acidovorax Sp. TP4 degraded the P(3HB-co-3HP) films with lower crystallinity in higher rates than those with higher crystallinity, no matter what kinds of crystalline structures they formed. In contrast, PHA depolymerase from R. pikettii T1 degraded P(3HB-co-3HP) films forming P(3HB) crystalline structure in higher rates than those forming P(3HP)s. The increase in amorphous nature of the P(3HB-co-3HP) films with P(3HB)-homopolymer-like crystalline structure increases and then decreases the rate of degradation by depolymerase from R. pikettii T1. The 3-hydroxybutyrate (3HB) monomer was produced as a major product by the hydrolysis of P(3HB) film by PHA depolymerase from Acidovorax Sp. TP4. The P(3HB-co-3HP) films could be degraded into 3HB and 3-hydroxypropionate (3HP) monomer at last, indicating that the catalytic domain of the enzyme recognized at least two monomeric units as substrates. While the PHA depolymerase from R. pikettii T1 hydrolyzed P(3HB) film into 3HB dimer as a major product, and the catalytic domain recognized at least three monomeric units. The degradation behavior of P(3HB-co-3HP) films by the PHA depolymerase of Acidovorax Sp. TP4 could be distinguished from that by the depolymerase of R. pikettii T1.

Poly-3-hydroxybutyrate (PHB) granules of Zoogloea ramigera I-16-M contained two major PHB granule-associated proteins (PGA12 and PGA16) as revealed by sodium dodecyl sulfate-polyacrylamide gel elecrophoresis. N-terminal amino acid sequences of these proteins were determined. The genes encoding these proteins were cloned and sequenced. The structural genes of PGA12 and PGA16 were 351 and 447 bp long, which encode polypeptides with deduced molecular masses of 12.3 and 16.0 kDa, respectively. PGA12 and PGA16 were expressed in Escherichia coli. PHB granules were isolated from cells of recombinant strains of E. coli JM109, which harbored and expressed the PHB-synthetic genes of Ralstonia eutropha H16 and PGA12 or PGA16. These PHB granules contained PGA12 or PGA16 as a major protein. The presence of pga12 or pga16 did not affect the amount of PHB synthesized in E. coli. PGA12 and PGA16 bound to crystalline and amorphous PHB granules.

Poly(L-lactide) (PLLA) thin film with 100 nm thickness was crystallized at 160 degreesC for 20 min from the melt obtained at 220 degreesC. Hexagonal crystals with three types of growth (derivative growth lamellae, overgrowth multistacked lamellae, and undergrowth multistacked lamellae) were simultaneously observed by atomic force microscopy (AFM). These phenomena are due to the differences of the formative points of secondary crystal nuclei against the basal lamella. Enzymatic degradation of PLLA thin film revealed two types of amorphous regions. These regions were identified as the free amorphous region around the crystals and the restricted amorphous region between the crystal and glass substrate. In situ observation of thermal behavior of lamellar crystals was performed to understand the correlation between the chain folding and stability of the crystal by using temperature-controlled AFM. The morphology of the sectors with [100] growth plane had changed to a comblike morphology despite the fact that the [110] growth plane remained unchanged, suggesting that the stability of the chain folding and the chain-packing state affected the thermal behavior.

Abstract: Aliphatic polyesters, which can be obtained from bacterial or chemical synthesis, are emerging as an important class of biodegradable and biocompatible polymers for applications as biomedical and conventional materials. The last two decades have witnessed explosive growth in this subject. Most biodegradable polyesters are crystallizable. The crystallization and thermal behavior of biodegradable polyesters have been extensively studied in recent years. The physical properties, such as the mechanical, thermal properties, and biodegradability (of biodegradable polymers) of a semicrystalline polymer generally depend on the crystalline structure. The polymorphic crystallization of biodegradable polyesters, including poly(3-hydroxybutyrate) [P(3HB)], poly(lactide) (PLA), poly(3-hydroxypropionate) (PHP), and poly(butylene adipate) (PBA), as well as isomorphic crystallization in many kinds of random copolyesters, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)], have been drawing more and more attention from both academic and industrial viewpoints. This article aims to provide a comprehensive review of the current understanding on (i) polymorphic crystallization and phase transition of biodegradable polyesters, (ii) isomorphic crystallization of biodegradable random copolyesters, where the effects of comonomer composition and crystallization conditions are highlighted. The relationships between the solid-state structure and physical properties as well as the biodegradability of biodegradable polyesters are also addressed. [Copyright &y& Elsevier]

The article discusses a study which investigated the crystallization kinetics of poly(e-caprolactone)-graphite oxide (PCL-GO) composites and their influence as nucleating agents on the crystallization of pure PCL. Information is presented on the materials and experimental procedures used. It was found that the introduction of GO as PCL-GO composites reduced the crystallization half-time for both the isothermal crystallization and nonisothermal crystallization of PCL.

Abstract: We isolated 5 mesophilic microorganisms that form clear zones around the colony on an opaque medium containing the aliphatic–aromatic copolyester poly(60 mol% butylene adipate-co-40 mol% butylene terephthalate) (PBAT). Among all strains, the fungal strain NKCM1712 degraded PBAT at the fastest rate (3.5 ± 0.3 μg cm−2 h−1). Genetic and morphological analyses revealed that this strain was closely related to Isaria fumosorosea (phylum Ascomycota). Mass spectroscopic analysis revealed that the degradation products were T, AB, TB, BAB, and ABT (T, terephthalic acid unit; A, adipic acid unit; B, 1,4-butanediol unit)] in the culture of the strain that used PBAT as the sole carbon source. Furthermore, the PBAT degradation ability of this strain in terms of BOD suggested that it could utilize the PBAT degradation products as growth substrates. This is the first report of a mesophilic strain that can mineralize an aliphatic–aromatic polyester into carbon dioxide on its own. [Copyright &y& Elsevier]

Abstract: The isothermal crystallization of isomorphic Poly(hexamethylene adipate-co-butylene adipate) [P(HA-co-BA)], with the HA unit content ranged from 100 to 45 mol%, forming the Poly(hexamethylene adipate) [PHA] type crystal was investigated with DSC, FTIR and WAXD. The BA units were found adopting their all-trans conformation in the crystalline phase of PHA type crystal. The inclusion of the BA units into the PHA type crystal was highly preferred in the isothermal crystallization at 25 °C. The exclusion of the BA units from the crystalline phase of the PHA type crystal was enhanced by elevating the crystallization temperature (T c), depending on the content of comonomer units. Increasing the HA unit content enhances the formation of the all-trans conformation of the BA units in the PHA type crystal. At low T c, such an enhancement significantly helps in retarding the exclusion of the BA units from the PHA type crystalline lattice. On the other hand, at high T c, the difficulty for forming the stable all-trans conformation of the BA units in cocrystal increased and hence the exclusion of the BA units from the cocrystal was accelerated. In conclusion, the all-trans conformation of the BA units can also play a critical role in the isomorphic crystallization of the P(HA-co-BA)s forming the PHA type crystal. [Copyright &y& Elsevier]

Abstract: The crystallization behavior has been investigated for poly(hexamethylene sebacate-co-hexamethylene suberate)s [P(HSe-co-HSu)] and poly(hexamethylene suberate-co-hexamethylene adipate)s [P(HSu-co-HA)] copolyesters by differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectrometer. Cocrystallization of comonomer units was found in the crystalline phase of both P(HSe-co-HSu) and P(HSu-co-HA) copolymers. Moreover, both P(HSe-co-HSu) and P(HSu-co-HA) copolymers exhibit isodimorphism. The PHSe and the PHSu type crystals were respectively developed in P(HSe-co-HSu)s, while the PHSu and the PHA type crystals were developed in P(HSu-co-HA)s respectively. The inclusion of the comonomer units in the PHSu type crystalline lattice is more favored than that in the PHSe type crystal of the P(HSe-co-HSu)s. Meanwhile, it is easier for the comonomer units to be incorporated into the PHA type crystalline lattice than into the PHSu type crystal of P(HSu-co-HA)s. Moreover, comparison between the isomorphic crystallization of P(HSe-co-HSu), P(HSe-co-HA) and P(HSu-co-HA) series copolyesters indicates that minimization of the difference in chemical structure helps in increasing the extent of cocrystallization of comonomer units. [Copyright &y& Elsevier]

Abstract: The nucleation effect of inclusion complex (IC) between poly(3-hydroxybutyrate) (PHB) and alpha-cyclodextrin (α-CD) on the rapid crystallization of a series of bacterial copolyesters poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) with 3HH molar fraction ranging from 7 to 18mol% was investigated by differential scanning calorimetry (DSC) and a polarized optical microscopy (POM). The results were compared with the effectiveness of PHB particles as a nucleation agent. Both the PHB-IC and the PHB particles enhance the nucleation and crystallization of PHBH, whereas the PHB-IC particles show much more effective nucleation ability than the PHB particles for the crystallization of PHBH. With introduction of PHB-IC, PHBH with 18% 3HH unit can finish crystallization during cooling process from the melt at 10°C/min, and its crystallinity is greatly increased. The crystallization half-time (t 1/2) of PHBH with 7–18% 3HH units decreases significantly in the presence of PHB-IC. The PHB crystals in the PHB-IC are suggested to favorably nucleate PHBH crystallization with the same crystalline lattice. [Copyright &y& Elsevier]

This study describes in situ observation of crystallization in a spherulite of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP] by FTIR microscopy. In order to trace the crystallization processes of blend components separately, PHBV was deuterated. The C–D and C&z.dbnd6;O stretching bands in the IR spectra, respectively, show the crystallization behavior of PHBV and the whole blend. D-PHBV containing 6 and 8% HV [D-PHBV6 and D-PHBV8] are blended with PHBP containing 11% HP [PHBP11]. The crystallization rates of D-PHBV6, D-PHBV8 and PHBP11 decrease in this order. In case of the blend of D-PHBV8 and PHBP11 the crystalline peaks of C–D and C&z.dbnd6;O bands grows simultaneously during crystallization, and the growth rates are rather close to that of D-PHBV8. The results indicate that D-PHBV8, which is the component that shows higher crystallization rate in the pure state, leads the cocrystallization of the blend. For D-PHBV6/PHBP11, on the other hand, the crystalline peak of C–D band grows faster than that of C&z.dbnd6;O band, indicating that the crystallization of D-PHBV6 proceeds before the crystallization of PHBP11. During the crystallization of D-PHBV6, PHBP11 molecules get away from the growing front of the spherulite, i.e. the phase segregation precedes the crystallization. These results demonstrate that FTIR microscopy is a powerful tool to trace the formation of different crystalline phases, such as cocrystallization and phase segregation. [Copyright &y& Elsevier]