Naoko Yoshie

Thermal behaviour and miscibility of poly(3-hydroxybutyrate)/poly(vinyl alcohol) blends

Abstract Thermal behaviour and miscibility of poly(3-hydroxybutyrate) (P(3HB)/poly(vinyl alcohol) (PVA) blend films prepared by casting have been analysed by d.s.c., n.m.r. and density measurements. Blends containing glycerine were also analysed by d.s.c. Melting temperature (Tm) of the P(3HB) crystalline phases decreased as PVA content increased, whereas Tm of the PVA phase remained almost unchanged. The crystallinity of P(3HB) in the blends also decreased with increase of PVA content. These results indicated that the thermal behaviour of the P(3HB) phase was influenced by the existence of PVA. Glycerine had no effect on the thermal properties of the blend, except for depression of Tm of the PVA phase. Miscibility in the amorphous phase of the blend has been analysed by density measurement. If P(3HB) is completely immiscible with PVA, the crystallinity of PVA can be estimated from the crystallinity of P(3HB) and the density of the sample. However, the crystallinities of the PVA phase estimated for some blend samples were greater than unity. This behaviour can be accounted for when these blends are partially miscible in the amorphous phase. In order to investigate the miscibility in detail, we have determined the 1H spin-lattice relaxation times in the laboratory frame (T1) and in the rotating frame (T1ϱ). Both T1 and T1ϱ values for the P(3HB) and PVA phases tend to approach those of blend partners with increase of PVA content. That is to say, the increase of PVA content in a blend enhances the miscibility.

Synthesis of Readily Recyclable Biobased Plastics by Diels-Alder Reaction

Readily recyclable biobased plastics were designed and synthesized utilizing the thermally reversible DA reaction. Furyl-telechelic poly(butylene succinate) prepolymers (PBSF(2)) were extended with bis- and tris-maleimide linkers (M(2) and M(3)) by the DA reaction in the bulk state to produce linear and network polymers, respectively. The DA reaction was able to proceed at 25-80 degrees C, at which crystalline domains of PBSF(2) were present. In the linear polymer system, the molecular weight in the reaction equilibrium was dependent on the chain length of the prepolymer, but almost independent of the reaction temperature. The cycle of DA and retro-DA reactions was repeatable with no prepolymer deterioration.

A Simple Modification Creates a Great Difference: New Solid-Base Catalyst Using Methylated N-Substituted SBA-15

A simple modification, methylation of the nitrogen-substituted mesoporous silica SBA-15, enhances the basicity of a solid-base catalyst. The methyl group donates an electron to the nitrogen atom in the silica framework. This catalyst accelerates Knoevenagel condensation using benzaldehyde and diethyl malonate, which conventional solid-base catalysts reported to date cannot do. This report demonstrates a possible new type of base catalyst using nitrogen-substituted mesoporous silica materials.

Cocrystallization and phase segregation of blends of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Abstract The competition between cocrystallization and phase segregation in blends of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHB–HV) containing 9 and 15% HV has been studied by 13 C cross-polarization magic-angle sample spinning (CPMAS) NMR and DSC techniques. The PHB homopolyester samples with selectively 13 C-enriched methylene carbon (PHB ∗ ) were used. Assuming a simple two-phase model, the 13 C resonances were resolved into two peaks arising from the crystalline and amorphous phases. Owing to the 13 C-enrichment of PHB ∗ , the relative areas of the crystalline peaks for the methylene and the methine carbon resonances on 13 C CPMAS NMR spectra change depending on the PHB ∗ content in the crystalline phase. By comparing the ratio of these areas for the blends with those for pure PHB ∗ and PHB–HV, the composition in the crystalline phase of the blends was determined. For PHB ∗ /PHB–9%HV blends, the composition in the crystalline phase is very similar to that in the blend. This means that almost perfect cocrystallization of PHB and PHB–9%HV occurs in these blends. For PHB ∗ /PHB–15%HV blends, the PHB content in the crystalline phase is larger than that in the whole blend. The phase segregation precedes the crystallization in these blends. Therefore, the degree of phase segregation (or the percentage of PHB–HV that segregates from the growth front of crystals) changes depending on the HV content of PHB–HV. As the HV content increases, the copolymer content in the crystalline phase decreases.

Temperature dependence of cocrystallization and phase segregation in blends of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The phase structure of the miscible blends of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) has been analyzed through DSC measurements and the observations of spherulite growth. Melting temperature and spherulite growth rate of the blends changed depending on the blend composition, which indicates that the extent of phase segregation increases as the HV content of PHB-HV increases from 0 to ca. 30 mol% and as the crystalline temperature increases from 90 to 120°C. When the HV content of PHB-HV is very low, the PHB/PHB-HV blend shows complete cocrystallization. The PHB content in the crystalline phase is similar to the whole composition of the blend. As the HV content of PHB-HV or the crystallization temperature increases, the PHB-HV content in the cocrystalline phase decreases. As a result, a large amount of PHB-HV chains are remained in the miscible amorphous phase between the PHB lamella when the HV content of PHB-HV is over 20% and the PHB-HV content of the blend is large. These PHB-HV chains may form the second and third crystalline phases, which are the PHB-HV crystal and the cocrystals with the PHB chains remaining in the amorphous phase. These data suggest that the cocrystallization of PHB and PHB-HV is induced by the entrapment of the PHB-HV chains near the growing front of the crystals by the PHB chains being about to crystallize.

Influence of tacticity and molecular weight of poly(vinyl alcohol) on crystallization and biodegradation of poly(3-hydroxybutyric acid)/ poly(vinyl alcohol) blend films

The crystallinity and the profile of biodegradation by environmental microorganisms in river water were investigated for bacterial poly(3-hydroxybutyric acid) [PHB] blend films with stereoregular poly(vinyl alcohol)s [PVA] and low-molecular weight atactic PVAs. According to the DSC thermal analysis, the crystallization of PHB was found to be not suppressed by blending with highly isotactic PVA. This result is consistent with previous results obtained by using Fourier-transformed infrared spectroscopy, that is, PVA sample with higher syndiotacticity brings about higher suppression of crystallization of PHB. In the PHB/PVA blend system, the formation of small PHB crystals was found by wide angle X-ray scattering, even in the samples for which the melting endotherm of PHB was not detected by DSC. The biodegradation profile of these blend films depends strongly on the water solubility of the PVA component. The PHB blends with low-molecular weight atactic PVA, which shows higher water solubility than atactic PVA with higher molecular weight and stereoregular PVA, exhibited faster degradation compared to the PHB blends with high-molecular weight atactic PVA system. The biodegradability of the PHB blends with stereoregular PVA became extremely low, when the PVA composition in the blends became high.

Hydrolytic degradation of blends of poly(3-hydroxybutyrate) with poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Abstract The hydrolytic degradation behaviour and some other properties were analysed for blends of microbial poly(3-hydroxybutyrate) [P(3HB)] with microbial poly(3-hydroxybutyrate- co -3-hydroxyvalerate) [P(3HB- co -3HV); 3HV content, 22.3 mol%]. From the analysis of differential scanning calorimetry (d.s.c.) curves, the main component of the crystalline phase in the blend films was found to be P(3HB). The crystallinity of P(3HB) decreases on blending with P(3HB- co -3HV). The hydrolytic degradation of the blend films was carried out on the solution-cast films in phosphate buffer at 55°C and pH 7.4. The rate of hydrolytic degradation of the blend films was accelerated by blending with P(3HB- co -3HV), and showed linear correlation with crystallinity. Therefore, the degradation rate of P(3HB) can be controlled by blending with P(3HB- co -3HV). The lower the initial crystallinity of the blend films, the higher the rate of hydrolytic degradation is seen to be.

Seawater-Assisted Self-Healing of Catechol Polymers via Hydrogen Bonding and Coordination Interactions

It is highly desirable to prevent crack formation in polymeric materials at an early stage and to extend their lifespan, particularly when repairs to these materials would be difficult for humans. Here, we designed and synthesized catechol-functionalized polymers that can self-heal in seawater through hydrogen bonding and coordination. These bioinspired acrylate polymers are originally viscous materials, but after coordination with environmentally safe, common metal cations in seawater, namely, Ca(2+) and Mg(2+), the mechanical properties of the polymers were greatly enhanced from viscous to tough, hard materials. Reduced swelling in seawater compared with deionized water owing to the higher osmotic pressure resulted in greater toughness (∼5 MPa) and self-healing efficiencies (∼80%).

A structural study of the crystalline state of the bacterial copolyester poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s (P(3HB-co-4HB)s) with a wide range of 4HB contents were biosynthesized, and their crystalline states were studied by differential scanning calorimetry (d.s.c.) and compared with those of the cold-stretched copolyesters of poly(3HB-co-3-hydroxyvalerate) (P(3HB-co-3HV)). A structural study was also carried out by the use of molecular mechanics calculations. It was demonstrated that P(3HB-co-4HB) cannot form isomorphic crystals because of the extent of the structural difference between the 3HB and 4HB comonomer components.

Polymers with Multishape Memory Controlled by Local Glass Transition Temperature

A multishape memory polymer with flexible design capabilities is fabricated by a very simple method. Local glass transition temperatures of a loosely cross-linked polymer film are changed by immersing sections of the film in a cross-linker solution with a different concentration. Each section memorizes a temporary shape, which recovers its permanent shape at a different recovery temperature depending on the local glass transition temperature. As a base polymer, we chose a network polymer prepared by a Diels-Alder reaction between poly(2,5-furandimethylene succinate) (PFS) and 1,8-bis-maleimidotriethyleneglycol (M2). Quintuple shape memory behavior was demonstrated by a PFS/M film with four sections with distinct glass transition temperatures. The number of temporary shapes was determined by the number of different M2 solutions. Furthermore, owing to the reversibility of the Diels-Alder reaction, the permanent shape was rewritable.